usn towing manual

U.S. NAVY

TOWING MANUAL

SL740-AA-MAN-010

1 JULY 2002

0910-LP-101-2029

Published by direction of Commander, Naval Sea Systems Command

THIS DOCUMENT SUPERSEDES NAVSEA SL 740-AA-MAN-010 DATED 1 SEPTEMBER 1988

THIS DOCUMENT HAS BEEN APPROVED FOR PUBLIC RELEASE AND SALE;

ITS DISTRIBUTION IS UNLIMITED

UNITED STATES NAVY

NAV

ALSEA SYSTEMS COM

M

AND

REVISION 3

U.S. Navy Towing Manual

A

SL740-AA-MAN-010

Page No. * Change No.

Title and A . . . . . . . . . . . . . . . . . . . . . . . . 0Certification Sheet . . . . . . . . . . . . . . . . . . 0blank . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0Flyleaf-1 (Flyleaf-2 blank) . . . . . . . . . . . . 0i Foreword . . . . . . . . . . . . . . . . . . . . . . . 0ii blank . . . . . . . . . . . . . . . . . . . . . . . . . . . 0iii through xix . . . . . . . . . . . . . . . . . . . . . . 0xx blank . . . . . . . . . . . . . . . . . . . . . . . . . . 0xxi through xxxvi . . . . . . . . . . . . . . . . . . . 01-1 through 1-5 . . . . . . . . . . . . . . . . . . . . 01-6 blank . . . . . . . . . . . . . . . . . . . . . . . . . 02-1 through 2-10 . . . . . . . . . . . . . . . . . . . 03-1 through 3-27 . . . . . . . . . . . . . . . . . . . 03-28 blank . . . . . . . . . . . . . . . . . . . . . . . . 04-1 through 4-46 . . . . . . . . . . . . . . . . . . . 05-1 through 5-29 . . . . . . . . . . . . . . . . . . . 05-30 blank . . . . . . . . . . . . . . . . . . . . . . . . 06-1 through 6-37 . . . . . . . . . . . . . . . . . . . 06-38 blank . . . . . . . . . . . . . . . . . . . . . . . . 07-1 through 7-15 . . . . . . . . . . . . . . . . . . . 07-16 blank . . . . . . . . . . . . . . . . . . . . . . . . 08-1 through 8-62 . . . . . . . . . . . . . . . . . . . 0A-1 through A-3. . . . . . . . . . . . . . . . . . . . 0A-4 blank . . . . . . . . . . . . . . . . . . . . . . . . . 0B-1 through B-15. . . . . . . . . . . . . . . . . . . 0B-16 blank . . . . . . . . . . . . . . . . . . . . . . . . 0C-1 through C-6. . . . . . . . . . . . . . . . . . . . 0D-1 through D-18. . . . . . . . . . . . . . . . . . . 0

Page No. * Change No.

E-1 through E-6 . . . . . . . . . . . . . . . . . . . 0F-1 through F-5 . . . . . . . . . . . . . . . . . . . 0F-6 blank . . . . . . . . . . . . . . . . . . . . . . . . 0G-1 through G-19 . . . . . . . . . . . . . . . . . . 0G-20 blank . . . . . . . . . . . . . . . . . . . . . . . 0H-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0H-2 blank . . . . . . . . . . . . . . . . . . . . . . . . 0H-3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0H-4 blank . . . . . . . . . . . . . . . . . . . . . . . . 0H-5 through H-19 . . . . . . . . . . . . . . . . . . 0H-20 blank . . . . . . . . . . . . . . . . . . . . . . . 0I-1 through I-22. . . . . . . . . . . . . . . . . . . . 0J-1 through J-9 . . . . . . . . . . . . . . . . . . . . 0J-10 blank. . . . . . . . . . . . . . . . . . . . . . . . 0K-1 through K-9 . . . . . . . . . . . . . . . . . . . 0K-10 blank . . . . . . . . . . . . . . . . . . . . . . . 0L-1 through L-11 . . . . . . . . . . . . . . . . . . . 0L-12 blank. . . . . . . . . . . . . . . . . . . . . . . . 0M-1 through M-23. . . . . . . . . . . . . . . . . . 0M-24 blank . . . . . . . . . . . . . . . . . . . . . . . 0 N-1 through N-2 . . . . . . . . . . . . . . . . . . . 0O-1 through O-13 . . . . . . . . . . . . . . . . . . 0O-14 blank . . . . . . . . . . . . . . . . . . . . . . . 0P-1 through P-12 . . . . . . . . . . . . . . . . . . 0Q-1 through Q-27 . . . . . . . . . . . . . . . . . . 0Q-28 blank . . . . . . . . . . . . . . . . . . . . . . . 0R-1 through R-12 . . . . . . . . . . . . . . . . . . 0S-1 through S-13 . . . . . . . . . . . . . . . . . . 0

LIST OF EFFECTIVE PAGES

* 0 in this column indicates an original page.

Date of Issue for original page is 1 July 2002

RECORD OF CHANGESACN/FORMAL

SL740-AA-MAN-010

*CHANGEACN NO.

DATEOF

CHANGE

ENTEREDBY

TITLE AND/OR BRIEF DESCRIPTION**

*When a formal change supersedes an ACN, draw a line through the ACN number**Only message or letter reference need be cited for ACNs

Flyleaf-1/(Flyleaf-2 blank)


Table of Contents

Paragraph Page

Chapter 1 - OPERATIONS OVERVIEW

1-1 Introduction to Navy Towing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1

1-2 Harbor Towing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2

1-3 Point-to-Point Towing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3

1-3.1 Inland Towing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3

1-3.2 Ocean Towing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3

1-3.3 Defueled Nuclear Powered Ships . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3

1-4 Rescue and Emergency Towing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3

1-4.1 Naval Task Force Standby Duty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4

1-5 Salvage Towing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4

1-5.1 Combat Salvage and Towing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4

1-6 Special Ocean Engineering Projects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4

1-7 Tow-and-Be-Towed By Naval Vessels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4

Chapter 2 - OVERVIEW OF TOWING SHIPS

2-1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1

2-2 Requirements Placed on Towing Ships. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1

2-3 Design Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1

2-3.1 Stern Arrangement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2

2-3.2 Tug Powering and Bollard Pull. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2

2-3.3 Fenders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3

2-3.3.1 Features and Characteristics of Fenders . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-32-3.3.2 Operating Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3

2-4 Yard or Harbor Tugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6

2-4.1 YTL Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6

2-4.2 YTB Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6

2-5 Ocean Tugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6

2-5.1 ARS 50 Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7

2-5.2 T-ATF 166 Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7

Chapter 3 - TOWING SYSTEM DESIGN

3-1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1

3-2 Designing a Towing System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1

3-2.1 Tug and Tow Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1

3-3 System Design Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1

iii


3-4 System Design Methodology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2

3-4.1 Calculating Total Towline Tension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2

3-4.1.1 Calculating Steady Resistance of the Towed Vessel . . . . . . . . . . . . . . . . . . 3-23-4.1.2 Calculating Steady Towline Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-43-4.1.3 Calculating Steady Towline Tension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-43-4.1.4 Dynamic Loads on the Towline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-53-4.1.5 Factors of Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-73-4.1.6 Predicting Dynamic Tensions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-7

3-4.2 Calculating Towline Catenary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-9

3-4.3 Reducing Anticipated Towline Peak Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-10

3-4.3.1 Using an Automatic Towing Machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-233-4.3.2 Using Synthetic Towlines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-23

3-4.4 Tug and Equipment Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-24

3-4.4.1 Tug Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-243-4.4.2 Towing Gear Selection Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-26

Chapter 4 - TOWLINE SYSTEM COMPONENTS

4-1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1

4-2 Towline System Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1

4-3 Main Towing Hawser . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2

4-3.1 Wire Rope Hawser . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2

4-3.2 Synthetic Hawser. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2

4-4 Secondary Towline. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3

4-5 Attachment Points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5

4-5.1 Winches and Towing Machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7

4-5.2 Bitts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-8

4-5.3 Padeyes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-8

4-5.4 Padeye Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-13

4-5.5 Deck Structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-15

4-5.6 Smit Towing Bracket . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-15

4-5.7 Towing Hooks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-17

4-5.8 Chocks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-17

4-5.9 Fairleads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-17

4-6 Connecting Hardware (Jewelry) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-17

4-6.1 Shackles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-18

4-6.2 Other Connecting Links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-21

4-6.3 Wire Rope Terminations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-21

4-6.4 Synthetic Line Terminations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-23

4-6.5 Synthetic Spring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-25

iv


4-6.6 Bridles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-25

4-6.7 Pendants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-29

4-6.8 Retrieval Pendant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-30

4-6.9 Chain Stoppers, Carpenter Stoppers, and Pelican Hooks. . . . . . . . . . . . . . . . . . . . 4-30

4-6.10 Chafing Gear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-33

4-7 Fuse or Safety Link Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-33

4-8 Line Handling Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-36

4-8.1 Caprails . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-36

4-8.2 Towing Bows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-36

4-8.3 Horizontal Stern Rollers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-36

4-8.4 Capstans and Gypsy Heads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-36

4-9 Sweep Limiting Devices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-39

4-9.1 Vertical Stern Rollers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-39

4-9.2 Norman Pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-42

4-9.3 Hogging Strap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-44

4-9.4 Lateral Control Wire. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-44

4-10 Cutting Gear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-44

Chapter 5 - TOW PLANNING AND PREPARATION

5-1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1

5-2 Lessons Learned . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1

5-3 Staff Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2

5-3.1 Towing Ship Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2

5-3.2 Operational Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2

5-3.2.1 Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-25-3.2.2 Manned Tows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-25-3.2.3 Tug Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-25-3.2.4 Unsuitable Tows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3

5-3.3 Selecting the Navigation Track . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3

5-4 Towing Responsibilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3

5-4.1 Sponsoring Command Responsibilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5

5-4.2 Towing Command Responsibilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5

5-4.3 Assisting Command Responsibilities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5

5-5 Review Instructions and Operational Orders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5

5-6 Riding Crew Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5

5-7 Preparing the Tow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6

5-7.1 Installing Flooding Alarms, Draft Indicators, and Other Alarms . . . . . . . . . . . . . . . . . 5-6

5-7.1.1 Flooding Alarm Sensor Mounting Requirements . . . . . . . . . . . . . . . . . . . . . 5-8

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5-7.1.2 Wiring and Power Supply Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-85-7.1.3 Alarm Lighting Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-95-7.1.4 Audible Alarm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-95-7.1.5 Requirements for Other Alarms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-95-7.1.6 Draft Indicator Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-95-7.1.7 Towed Vessel Propeller Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-95-7.1.8 Removing Propellers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-95-7.1.9 Locking Propellers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-105-7.1.10 Allowing Propellers to Free-Wheel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-105-7.1.11 Stern Tube . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-10

5-7.2 Ballasting or Loading for Proper Trim . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-10

5-7.3 Ballasting for Proper Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-10

5-7.4 Two Valve Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-13

5-7.5 Inspecting the Tow for Structural Damage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-14

5-7.5.1 Barge Hull Thickness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-14

5-7.6 Locking the Rudder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-14

5-7.7 Installing Navigational Lights . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-18

5-7.8 Selecting the Rig . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-18

5-7.9 Preparing Tank Vents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-21

5-8 Emergency Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-21

5-8.1 Electrical Power. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-22

5-8.2 Fire-fighting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-22

5-8.3 Dewatering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-23

5-8.3.1 Deciding to Use Dewatering Equipment. . . . . . . . . . . . . . . . . . . . . . . . . . . 5-235-8.3.2 Choosing Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-235-8.3.3 Pre-staging Hoses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-24

5-8.4 Marking Access Areas on Tow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-24

5-8.5 Preparing for Emergency Anchoring of the Tow . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-24

5-9 Completing the Checklist for Ocean Tows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-26

5-9.1 Determining Seaworthiness. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-26

5-9.2 Towing Machine/ Towing Winch Certification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-26

5-9.3 Tow Hawser Certification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-26

5-9.4 Commercial Vessels (U.S. Coast Guard Inspected) Master’s Towing Certificate . . 5-26

5-9.5 Preparing for a Riding Crew . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-26

5-10 Accepting the Tow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-28

5-10.1 Inspecting the Tow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-28

5-10.2 Unconditionally Accepting the Tow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-29

5-10.3 Accepting the Tow as a Calculated Risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-29

5-10.4 Rejecting the Tow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-29

vi


5-10.5 Preparing for Departure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-29

5-11 Completing the Delivery Letter or Message . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-29

Chapter 6 - TOWING PROCEDURES

6-1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1

6-2 Initiating the Tow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1

6-2.1 Accelerating with a Tow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1

6-2.2 Getting Underway from a Pier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1

6-2.3 Getting Underway in the Stream . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3

6-2.4 Getting Underway while at Anchor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3

6-2.5 Recovering a Lost Tow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-4

6-2.6 Emergency Connection to a Disabled Vessel or Derelict . . . . . . . . . . . . . . . . . . . . . 6-6

6-2.6.1 Using the Anchor Chain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-76-2.6.2 Using Installed Bitts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-86-2.6.3 Using a Gun Mount or Foundation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-96-2.6.4 Placing a Crew on Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-9

6-2.7 Approaching a Drifting Tow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-10

6-2.7.1 Establishing the Relative Drift. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-106-2.7.2 Similar Drift Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-106-2.7.3 Dissimilar Drift Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-10

6-2.8 Passing the Towline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-10

6-2.9 Communications between Ships . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-12

6-3 Ship Handling and Maneuvering with a Tow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-12

6-3.1 Tug Steering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-12

6-3.2 Keeping a Tug and Tow in Step . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-14

6-3.3 Controlling the Tow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-14

6-3.3.1 Active Control of the Tow's Rudder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-146-3.3.2 Yawing and Sheering of the Tow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-166-3.3.3 Trim . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-166-3.3.4 Speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-166-3.3.5 Use of Rudder or Skegs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-166-3.3.6 Location of the Attachment Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-166-3.3.7 Propellers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-166-3.3.8 Steering Tug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-176-3.3.9 Sea Anchor or Drogue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-176-3.3.10 Bridle vs. Single Lead Pendant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-17

6-3.4 Backing Down with a Tow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-17

6-4 Routine Procedures While at Sea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-17

6-4.1 Setting Course . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-17

6-4.2 Towing Speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-17

6-4.3 Towline Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-18

vii


6-4.4 Towing Watch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-18

6-4.5 Periodic Inspection of Tow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-18

6-4.5.1 Boarding the Tow for Inspection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-196-4.5.2 Inspection Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-19

6-4.6 Towing in Heavy Weather . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-19

6-4.7 Replenishment at Sea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-21

6-4.7.1 Transferring Personnel and Freight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-216-4.7.2 Emergency Replenishment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-216-4.7.3 Rigging and Use of Fueling Rigs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-216-4.7.4 Astern Refueling from Another Tug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-216-4.7.5 Replenishment Near a Port . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-21

6-5 Terminating the Tow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-22

6-5.1 Requesting Assistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-22

6-5.2 Shortening the Towline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-22

6-5.3 Disconnecting the Tow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-22

6-5.4 Towing Delivery Receipt and Reports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-23

6-5.5 Transferring the Tow at Sea. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-23

6-6 Tow and Be Towed by Naval Vessels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-23

6-6.1 Towing Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-24

6-6.2 Towing Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-24

6-6.2.1 Procedure for the Towing Ship. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-246-6.2.2 Procedure for the Towed Ship . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-276-6.2.3 Quick Release of Towed Ship . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-27

6-6.3 Getting Underway with Tow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-27

6-7 Emergency Towing Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-28

6-7.1 Fire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-28

6-7.2 Tug and Tow Collision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-28

6-7.3 Sinking Tow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-29

6-7.3.1 Beaching a Sinking Tow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-296-7.3.2 Slipping the Tow Hawser . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-30

6-7.4 Disabled Towing Machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-31

6-7.4.1 Disconnecting the Tow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-316-7.4.2 Recovering the Towline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-32

6-7.5 Anchoring with a Tow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-32

6-7.6 Quick Disconnect System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-33

6-7.7 Man Overboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-33

6-7.8 Using an Orville Hook to Recover a Lost Tow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-34

6-7.8.1 Origin of the Orville Hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-346-7.8.2 Use of an Orville Hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-34

viii


Chapter 7 - SPECIAL TOWS

7-1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1

7-2 Target Towing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1

7-2.1 Williams Target Sled . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1

7-2.2 Towing Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2

7-2.3 Routine Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2

7-2.3.1 Transporting the Target to the Exercise . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-27-2.3.2 Streaming the Target . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-27-2.3.3 Making Turns with the Target . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-27-2.3.4 Recovering the Target. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3

7-2.4 Special Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3

7-2.4.1 Passing the Target to a Combatant Ship . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-37-2.4.2 Recovering a Capsized Target . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3

7-2.5 Target Towing Precautions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-4

7-2.6 Other Targets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-4

7-3 Towing Through the Panama Canal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-4

7-4 Towing in Ice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-5

7-4.1 Short-Scope Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-5

7-4.2 Saddle Method. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6

7-4.3 Rigging for Tow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6

7-5 Submarine Towing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6

7-5.1 Towing Arrangements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-7

7-5.1.1 Retractable Deck Fittings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-77-5.1.2 Tow Attachment Points. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-7

7-5.2 Personnel Safety Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-8

7-5.2.1 Protection for Work on the Deck. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-87-5.2.2 Boarding the Submarine. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-87-5.2.3 Personnel Experience . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-87-5.2.4 Submarine Atmosphere Problems Resulting from Fire . . . . . . . . . . . . . . . . 7-8

7-5.3 Tendency to Yaw and Sheer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-8

7-5.4 Rigging for the Tow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-8

7-5.4.1 Hardware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-97-5.4.2 Underwater Projections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-97-5.4.3 Towing by the Stern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-97-5.4.4 Use of the Sail as a Tow Connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-107-5.4.5 Welding to the Hull . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-107-5.4.6 Passing a Messenger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-10

7-5.5 Towing Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-10

7-5.5.1 Towing on the Automatic Towing Machine . . . . . . . . . . . . . . . . . . . . . . . . . 7-107-5.5.2 Towline Tension and Towing Speeds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-11

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7-5.5.3 Drogue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-11

7-6 Towing Distressed Merchant Ships . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-11

7-6.1 Information Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-12

7-6.2 Attachment Points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-12

7-7 Ships with Bow Ramp/Door. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-12

7-8 Towing Distressed NATO Ships . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-13

7-8.1 Standardized Procedures (ATP-43). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-13

7-8.2 Making the Tow Connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-13

7-8.3 NATO Standard Towing Link . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-14

7-9 Unusual Tows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-14

7-9.1 Dry Dock (Careened). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-15

7-9.2 Damaged Ship (Stern First). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-15

7-9.3 Inland Barge Towing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-15

7-9.4 Other Tows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-15

7-9.5 Towing on the Hip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-15

Chapter 8 - HEAVY LIFT TRANSPORT

8-1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1

8-1.1 Repair Work. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1

8-2 Special Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1

8-2.1 Dry Docking Comparison. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1

8-2.2 Commercial Fleet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-2

8-2.3 Choosing a Vessel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-2

8-3 Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-2

8-3.1 Designating the Lift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-2

8-3.2 Request for Proposal (RFP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-9

8-3.3 Preparations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-9

8-3.3.1 Choosing a Heavy Lift Team . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-98-3.3.2 Contractor Preparations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-118-3.3.3 Transport (Load) Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-118-3.3.4 Choosing A Load Site. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-138-3.3.5 Preparing The Deck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-13

8-3.4 Pre-Load Conference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-13

8-3.5 Load Site . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-14

8-3.5.1 Visual Survey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-148-3.5.2 Support Tugs/Divers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-14

8-3.6 Preparing the Asset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-15

8-3.6.1 Arrival Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-158-3.6.2 Transport of Damaged Vessels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-16

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8-4 Loading Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-16

8-4.1 Positioning of the Asset(s) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-16

8-4.2 Fendering. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-18

8-4.3 Riding Crew Accommodations During Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-18

8-4.4 Deballasting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-18

8-4.5 Connection of Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-18

8-4.6 Blocking and Seafastening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-19

8-5 Seakeeping and Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-19

8-5.1 Ship Motions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-21

8-5.1.1 Wind Heel Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-21

8-5.2 Stability of the Asset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-21

8-5.2.1 Stability Afloat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-228-5.2.2 Stability During Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-228-5.2.3 Draft-at-Instability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-248-5.2.4 Draft-at-Landing Fore and Aft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-27

8-5.3 Stability of the Heavy Lift Ship . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-28

8-5.3.1 Intact Stability Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-288-5.3.2 Stability During Ballasting/Deballasting . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-28

8-5.4 Stability of the Heavy Lift Ship with the Asset Secured Aboard during Transit . . . . 8-29

8-5.4.1 Damage Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-30

8-6 Blocking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-30

8-6.1 Preparing the Docking Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-32

8-6.2 Docking Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-32

8-6.2.1 Dynamic Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-338-6.2.2 Loading of Keel Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-348-6.2.3 Keel Block Loading Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-348-6.2.4 Distribution of Asset’s Weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-358-6.2.5 Calculation of the Asset’s Loading on the Docking Blocks by the Trapezoidal Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-368-6.2.6 Knuckle Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-408-6.2.7 Safe Allowable Compressive Stress of Blocking . . . . . . . . . . . . . . . . . . . . 8-42

8-7 Seafastening Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-43

8-7.1 Side Blocking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-43

8-7.1.1 Stability of High Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-45

8-7.2 Loading on Side Blocking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-45

8-7.2.1 Assessing the Loading on Side . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-468-7.2.2 Loading on Side Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-468-7.2.3 Dynamic Loads During Transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-478-7.2.4 Dynamic Loads from Ship Motions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-478-7.2.5 Dynamic Loads from Winds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-49

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8-7.2.6 Determining the total amount of side blocking required . . . . . . . . . . . . . . . 8-49

8-7.3 Additional Side Block Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-49

8-7.4 Spur Shores. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-50

8-7.4.1 Loading on Spur Shores. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-518-7.4.2 Determining the Number of Spur Shores . . . . . . . . . . . . . . . . . . . . . . . . . . 8-528-7.4.3 Distribution of Spur Shores . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-53

8-7.5 Seafasteners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-54

8-7.5.1 Dynamic Force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-548-7.5.2 Assumed Friction Factors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-558-7.5.3 Sea Fasteners Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-55

8-8 Surveys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-57

8-8.1 Hydrographic Survey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-57

8-8.2 Acceptance Survey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-57

8-8.3 Structural Surveys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-57

8-8.4 Indicators and Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-57

8-8.5 Pre-loading Block Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-58

8-8.5.1 Wooden Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-598-8.5.2 Block Securing Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-59

8-8.6 Additional Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-59

8-8.7 Asset Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-60

8-8.8 Post Float-On Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-60

8-8.9 Examination of the Seafastening. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-60

8-8.9.1 Prior to Transit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-608-8.9.2 During Transit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-618-8.9.3 Upon Arrival . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-61

8-9 Offloading Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-61

8-9.1 Prior to Arrival at Destination. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-61

8-9.2 Arrival Activities at Off Loading Site . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-61

8-9.3 Off Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-61

Appendix A - SAFETY CONSIDERATIONS IN TOWING

A-1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .A-1

A-2 Scope and Applicability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .A-1

A-3 Basic Safety Philosophy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .A-1

A-4 Specific Safety Precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .A-2

A-4.1 Specific Approaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .A-2

A-4.1.1 General Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .A-2A-4.1.2 Non-Emergency Towing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .A-2A-4.1.3 Safety. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .A-2A-4.1.4 Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .A-3

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A-4.2 Contingency Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .A-3

Appendix B - WIRE ROPE TOWLINES

B-1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-1

B-2 Traceability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-1

B-3 Strength. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-1

B-3.1 Elongation (Stretch). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-1

B-4 Maintenance, Cleaning, and Lubrication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-3

B-5 New Hawsers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-3

B-5.1 Unreeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-3

B-5.2 Reeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-3

B-5.3 Installing New Wire Rope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-5

B-6 Stowing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-7

B-7 Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-7

B-7.1 General Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-7

B-7.2 Specific Steps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-7

B-8 Special Precautions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-10

B-9 Wire Rope Hawsers for Navy Tow Ships. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-10

B-10 Wire Rope Terminations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-10

B-11 Wire Rope Procurement Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-12

B-12 Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-12

B-12.1 Wire Rope Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-12

B-12.2 Wire Towing Hawsers for T-ATF 166 Class Ships . . . . . . . . . . . . . . . . . . . . . . . . .B-12

B-12.3 2-1/4-Inch Towing Hawsers for ARS-50 Class Ships . . . . . . . . . . . . . . . . . . . . . .B-13

B-13 Sockets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-13

B-14 Lubrication. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-15

Appendix C - SYNTHETIC FIBER LINE TOWLINE

C-1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-1

C-2 Traceability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-1

C-3 Strength and Lifetime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-1

C-3.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-1

C-3.2 Specific . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-1

C-4 Elongation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-2

C-5 Maintenance and Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-2

C-6 Stowing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-3

C-7 Uncoiling or Unreeling New Hawsers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-3

C-8 Breaking in New Hawsers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-4

xiii


C-9 Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .C-4

C-10 Types of Wear or Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .C-4

C-11 Special Precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .C-6

C-12 Fiber Rope Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .C-6

Appendix D - CHAINS AND SAFETY SHACKLES

D-1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D-1

D-2 Traceability and Marking. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D-1

D-2.1 Traceability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D-1

D-2.2 Marking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D-1

D-3 Strength and Lifetime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D-2

D-4 Elongation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D-2

D-5 Maintenance and Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D-2

D-6 New Chain and Links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D-3

D-7 Stowing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D-3

D-8 Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D-3

D-8.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D-3

D-8.2 Specific . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D-3

D-9 Types of Wear. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D-4

D-10 Special Precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D-4

D-11 Chain Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D-5

D-12 Connecting Links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D-5

D-13 Safety Shackles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D-5

D-14 Proof Load, Safe Working Load, and Safety Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D-6

D-15 Plate Shackles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D-6

Appendix E - STOPPERS

E-1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .E-1

E-2 Types of Stoppers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .E-1

E-3 Prevention of Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .E-1

E-4 Stopping Off a Wire Towing Hawser . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .E-1

E-5 Synthetic Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .E-2

E-6 Stopper Breaking Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .E-2

E-7 Fiber Stoppers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .E-5

E-8 Stopper Hitches. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .E-5

E-9 Securing the Passed Stopper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .E-6

E-10 Setting the Stopper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .E-6

E-11 Releasing the Stopper. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .E-6

xiv


Appendix F - TOWING HAWSER LOG

F-1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .F-1

F-2 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .F-1

F-3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .F-1

F-4 Log. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .F-1

F-5 Failures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .F-1

Appendix G - CALCULATING STEADY STATE TOWLINE TENSION G-1 Self-Propelled Surface Ships . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G-1

G-1.1 Hull Resistance Curves. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G-3

G-1.2 Additional Resistance Due to Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G-3

G-1.3 Wind Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G-16

G-1.4 Propeller Resistance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G-16

G-2 Floating Dry Docks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G-16

G-2.1 Frictional Resistance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G-16

G-2.2 Wave-Forming Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G-16


G-2.4 Total Tow Resistance for Dry Docks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G-18

G-2.5 Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G-18

G-3 Barges. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G-18

G-3.1 Frictional Resistance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G-18

G-3.2 Wave-Forming Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G-18


G-3.4 Total Barge Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G-18

G-3.5 Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G-18

G-3.5.1 Frictional Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G-19G-3.5.2 Wave Forming Resistance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G-19G-3.5.3 Wind Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G-19G-3.5.4 Total Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G-19

Appendix H - CHECKLIST FOR PREPARING AND RIGGING A TOW

Appendix I - TOWING RIGS

I-1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-1

I-2 Single Tug, Single Tow Configurations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-1

I-2.1 Pendant or Single Leg Rig . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-1

I-2.2 Bridle Rig . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-1

I-2.3 Towing Alongside . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-5

I-2.4 Liverpool Bridle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-7

I-3 Single Tug, Multiple Unit Tow Configurations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-7

xv


I-3.1 Christmas Tree Rig. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-7

I-3.2 Honolulu Rig . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-12

I-3.3 Tandem Rig . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-12

I-3.4 Nested Rig . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-12

I-4 Multiple Tug, Single Tow Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-12

I-4.1 Side-By-Side Towing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-13

I-4.2 Steering Assistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-13

Appendix J - EMERGENCY TOWING OF SUBMARINES

J-1 Submarines Prior to the 688 and 726 Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J-1

J-1.1 Tow Attachment Points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J-1

J-1.2 The Towing Rig . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J-1

J-1.3 Chafing Pendant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J-4

J-2 SSN 688 Class Submarines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J-4

J-3 SSBN 726 Class Submarines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J-4

J-4 SSN 21 Class Submarines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J-7

Appendix K - COMMERCIAL TUG CAPABILITIES

K-1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .K-1

K-2 Tug Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .K-1

K-2.1 Salvage Tug Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .K-1

K-2.1.1 Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .K-1K-2.1.2 Draft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .K-2K-2.1.3 Freeboard/Depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .K-2K-2.1.4 Beam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .K-2K-2.1.5 Crew. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .K-2K-2.1.6 Towing Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .K-2K-2.1.7 Power. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .K-2K-2.1.8 Bollard and Towline Pull . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .K-2

K-2.2 Power, Bollard Pull, and Towline Pull . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .K-2

K-2.2.1 Power. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .K-2K-2.2.2 Bollard Pull . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .K-3K-2.2.3 Towline Pull . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .K-3K-2.2.4 Maneuverability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .K-6

K-3 Ocean-Going Tugs for Hire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .K-6

K-3.1 Ocean-Going Tug Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .K-6

K-3.2 Decline in Salvage Tug Availability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .K-8

K-3.3 Availability of Ocean-Going Tugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .K-8

K-4 Obtaining Tug Assistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .K-8

K-4.1 Emergency Tug Assistance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .K-8

K-4.2 Restrictions in Contracting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .K-9

xvi


K-4.3 Contracting for Emergency Commercial Towing Assistance . . . . . . . . . . . . . . . . . . .K-9

K-4.4 Arranging for Routine (Non-Emergency) Tows by Commercial Tugs . . . . . . . . . . . .K-9

Appendix L - TOWING MACHINERY

L-1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L-1

L-2 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L-1

L-2.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L-1

L-2.2 Functions of Towing Machinery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L-1

L-2.2.1 Attachment of the Hawser to the Tug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L-1L-2.2.2 Hawser Scope Adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L-1L-2.2.3 Storage of Unused Hawser . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L-1L-2.2.4 Quick Release of the Hawser under Tension . . . . . . . . . . . . . . . . . . . . . . . . L-2L-2.2.5 Protection of the Hawser . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L-2

L-3 Automatic Tension Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L-3

L-3.1 Tow Hawsers Surge Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L-3

L-3.1.1 Early Automatic Towing Machinery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L-3L-3.1.2 Electric Towing Machinery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L-3L-3.1.3 Wire Surge Example. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L-3

L-3.2 Automatic Features on Towing Machines - General . . . . . . . . . . . . . . . . . . . . . . . . . L-4

L-3.3 Limitations in Quantitative Understanding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L-4

L-4 Types of Towing Machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L-4

L-4.1 Conventional Towing Winches and Machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L-4

L-4.1.1 Drum Arrangements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L-4L-4.1.2 Drum Securing Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L-5L-4.1.3 Drum Prime Movers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L-5L-4.1.4 Automatic Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L-5L-4.1.5 Instrumentation and Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L-5

L-4.2 Traction Winches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L-5

L-4.2.1 General Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L-5L-4.2.2 Hawser Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L-5L-4.2.3 Traction Winch Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L-5

L-5 U.S. Navy Towing Machinery Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L-7

L-5.1 ARS 50 Class Towing Machinery. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L-7

L-5.2 T-ATF 166 Class Towing Machinery. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L-8

Appendix M - ESTIMATING DYNAMIC TOWLINE TENSIONS

M-1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-1

M-1.1 Ship Motion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-1

M-1.2 Wire Towline Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-1

M-1.3 Synthetic Towline Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-1

M-2 Design of the Extreme Tension Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-2

xvii


M-2.1 Understanding Wire Towline Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-3

M-2.2 Motions of the Tug and Tow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-3

M-2.3 Description of Physical Variables and Influences on Extreme Tension . . . . . . . . . M-3

M-2.3.1 Size of Tug and Tow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-3M-2.3.2 Wave Size, Angle, and Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-4M-2.3.3 Average Towline Tension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-4M-2.3.4 Weight and Scope of Towline Used . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-5M-2.3.5 Tow Speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-5M-2.3.6 Yawing and Sheering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-5

M-2.4 Display of the Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-5

M-3 Use of the Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-6

M-3.1 Allowable Extreme Tension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-6

M-3.2 Interpolation Within the Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-6

M-3.2.1 Ship Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-6M-3.2.2 Tow Speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-6M-3.2.3 Towing Hawser Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-7M-3.2.4 Wave Angle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-7M-3.2.5 Wind Strength and Wave Height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-7M-3.2.6 Adjust Calculations for Sheering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-7

M-4 Response to Worsening Sea Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-7

M-4.1 Reduce Speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-7

M-4.2 Increase Towline Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-7

M-4.3 Change Course . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-8

M-5 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-8

M-5.1 ATS 1 Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-8

M-5.2 ARS 50 Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-9

M-5.3 T-ATF 166 Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-9

Appendix N - REFERENCES

Appendix O - GLOSSARY

Appendix P - USEFUL INFORMATION

P-1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .P-1

P-2 Weights and Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .P-1

Appendix Q - HEAVY LIFT SAMPLE CALCULATIONS

Q-1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Q-1

Q-2 Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Q-1

Q-3 Draft-at-Instability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Q-7

Q-4 Draft-at-Landing Fore and Aft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Q-10

Q-5 Keel Block Build and Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Q-13

Q-6 Side Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Q-18

xviii


Q-7 Positioning of Spur Shores . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Q-26

Appendix R - CHECKLIST FOR PREPARING AN ASSET FOR HEAVY LIFT

Appendix S - INDEX

xix


xx

This Page Intentionally Left Blank


List of Illustrations

Figure Page2-1. ARS 50 Bulwark Forward Limits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-22-2. Typical Rubber Fenders. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-42-3. Pneumatic and Foam Fenders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-52-4. ARS 50 Class Salvage Ship . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-82-5. T-ATF 166 Class Fleet Tug. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-93-1. Towline Forces at Stern of Tow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-53-2. Towline Tension vs. Time. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-63-3. Available Tension vs. Ship’s Speed for U.S. Navy Towing Ships. . . . . . . . . . . . . . . . . . . 3-113-4. Catenary vs. Tension; 1 5/8-Inch Wire, No Chain. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-123-5. Catenary vs. Tension; 1 5/8-Inch Wire, 90 Feet of 2 1/4-Inch Chain.. . . . . . . . . . . . . . . . 3-133-6. Catenary vs. Tension; 1 5/8-Inch Wire, 270 Feet of 2 1/4-Inch Chain. . . . . . . . . . . . . . . . 3-143-7. Catenary vs. Tension; 2-Inch Wire, No Chain. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-153-8. Catenary vs. Tension; 2-Inch Wire, 90 Feet of 2 1/4-Inch Chain. . . . . . . . . . . . . . . . . . . . 3-163-9. Catenary vs. Tension; 2-Inch Wire, 270 Feet of 2 1/4-Inch Chain. . . . . . . . . . . . . . . . . . . 3-173-10. Catenary vs. Tension; 2 1/4-Inch Wire, No Chain. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-183-11. Catenary vs. Tension; 2 1/4-Inch Wire, 90 Feet of 2 1/4-Inch Chain. . . . . . . . . . . . . . . . 3-193-12. Catenary vs. Tension; 2 1/4-Inch Wire, 270 Feet of 2 1/4-Inch Chain. . . . . . . . . . . . . . . 3-203-13. Distance Between Vessels vs. Hawser Tension for 1,000 and 1,800 Feet of 6x37 FC Wire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-254-1. Typical Towline Connection Components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-24-2. Secondary Towline System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-44-3. Secondary Towline System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-64-4. Aft End of ARS 50 Towing Machinery Room and Typical Towing Fairleads /Bitts. . . . . . . 4-94-5. Horizontal Padeyes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-104-6. Vertical Free-Standing Padeyes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-124-7. Minimum Padeye Design Requirements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-144-8. Smit Towing Bracket. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-164-9. Types of Chocks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-184-10. Shackles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-204-11. Types of Wire Rope Terminations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-224-12. Towline Termination. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-234-13. Pear-Shaped Detachable Links. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-244-14. Synthetic Line End Fittings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-264-15. Synthetic Line Grommet. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-274-16. Towing Rigs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-274-17. Chain Bridles Using Plate Shackles and Safety Shackles.. . . . . . . . . . . . . . . . . . . . . . . 4-284-18. Pelican Hook and Chain Stopper.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-344-19. Carpenter Stopper. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-354-20. Chafing Gear and Stern Rollers.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-374-21. Caprails. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-384-22. Towing Bows. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-384-23. Capstans and Gypsy Head. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-404-24. Stern of T-ATF 166 Class. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-414-25. Stern Rollers (ARS 50 Class). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-424-26. Norman Pins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-434-27. Norman Pin Use. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-45

xxi


4-28. Rigging of Hogging Strap on Ships without Horizontal Stern Rollers. . . . . . . . . . . . . . . 4-465-1. Example of a Flooding Alarm Schematic.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-75-2. Special Draft Markings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-115-3. Securing the Propeller Shaft. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-125-4. Reinforcing Bottom Plating in Barges. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-175-5. Securing the Rudder. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-195-6. Securing the Rudder. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-205-7. Sample Provisions for Emergency Boarding of Tow at Sea. . . . . . . . . . . . . . . . . . . . . . . 5-255-8. Billboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-276-1. Methods for Securing Messenger to Towline.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-26-2. Accepting a Tow in the Stream. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-56-3. Sharing Towing Load Between Bitts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-76-4. Across Sea/Wind Approach - Similar Drift Rate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-116-5. Downwind Approach Crossing the “T” to Ship Lying Broadside to Wind/Sea. . . . . . . . . . 6-136-6. Effect of Towpoint on Steering. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-156-7. Passing a Tow at Sea. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-256-8. Tow-and-Be-Towed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-266-9. Orville Hook Retrieval Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-356-10. Orville Hook Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-366-11. Deployment of the Orville Hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-377-1. Williams Target Sled Rigged for Tow with Righting Line Streamed. . . . . . . . . . . . . . . . . . 7-17-2. NATO Standard Towing Link.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-148-1. Heavy Lift Vessel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-48-2. Heavy Lift Vessel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-58-3. Heavy Lift Vessel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-68-4. Plan of Action and Milestones. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-88-5. Assets Being Loaded.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-178-6. Phases of Stability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-208-7. Draft at Instability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-238-8. Limit of Stablility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-258-9. Draft at Landing Fore and Aft. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-288-10. GZ Curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-318-11. Load Distribution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-398-12. Keel Blocks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-418-13. Heavy Lift Blocks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-428-14. Cribbed Blocks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-448-15. Spur Shores . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-458-16. Overturning Moment Due to Wind Forces. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-488-17. Sea Fasteners. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-56B-1. Bird Caging. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-2B-2. Popped Core. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-2B-3. Kinks and Hockles.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-4B-4. Re-reeling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-4B-5. Wallis Brake. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-6B-6. Nomenclature of Wire Rope. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-8B-7. Measuring Wire Rope. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-9B-8. Poured Sockets FED Spec. RR-S-550D Amendment 1. . . . . . . . . . . . . . . . . . . . . . . . . .B-14D-1. Types of Chains and Connecting Links. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D-16D-2. Detachable Link with Identifying Marks for Assembly. . . . . . . . . . . . . . . . . . . . . . . . . . . .D-17

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D-3. Typical Method for Modifying Detachable Chain Connecting Links for Hairpin Installation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D-18E-1. Crisscross Chain Stopper. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .E-2E-2. Typical Stopper. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .E-3E-3. Half Hitches. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .E-4E-4. Crisscross Fiber Stopper.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .E-4E-5. Double Half-Hitch Stopper.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .E-5G-1. Example 1 - Scenario. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G-5G-2. Example 1 - Worksheet.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G-6G-3. Example 2 - Scenario. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G-11G-4. Example 2 - Worksheet.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G-12G-5. Available Tension vs. Ship’s Speed for U.S. Navy Towing and Resistance Curve. . . . G-13G-6. Hull Resistance Curve, RH/∆ vs. Tow Speed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G-14G-7. Wave Resistance Curve RS vs. Wave Height and Wind Force.. . . . . . . . . . . . . . . . . . . G-15I-1. Towing Rigs (Plan View).. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-2I-2. Example of Chain Bridle with Chain Pendant. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-3I-3. Example of Wire Bridle with Wire Pendant. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-4I-4. Towing Alongside. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-5I-5. Liverpool Bridle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-6I-6. Use of Liverpool Bridle on Stranding Salvage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-8I-7. Christmas Tree Rig.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-9I-8. Example of a Christmas Tree Rig Configuration with Chain Bridle. . . . . . . . . . . . . . . . . . I-10I-9. Example of a Christmas Tree Rig Configuration with a Wire Bridle. . . . . . . . . . . . . . . . . . I-11I-10. Three-Barge Tow in Christmas Tree Rig Ready for Streaming. . . . . . . . . . . . . . . . . . . . I-14I-11. Honolulu Rig. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-15I-12. Tandem Rig. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-16I-13. Two-Tug Tows. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-17I-14. Example of Chain Bridle and Pendant. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-18I-15. Flounder Plate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-19I-16. Plate Shackle and Pin for 2-Inch Closed Socket. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-20I-17. Plate Shackle and Pin.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-21I-18. Plate Shackle and Pin.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-22J-1. SSN 637 Class Towing Gear (Harbor Towing Only). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J-3J-2. Hinged Cleat for SSN 688 Class. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J-5J-3. Towing Gear Arrangement for SSN 688 Class (Harbor Towing Only).. . . . . . . . . . . . . . . . J-6J-4. Towing Arrangement for SSBN 726 Class.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J-8J-5. Emergency Towing Pendant Assembly for SSN 21 Class.. . . . . . . . . . . . . . . . . . . . . . . . . J-9K-1. Towline Pull vs. Towing Speed for Tugs with Controllable-Pitch Propellers and Nozzles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .K-4K-2. Anchor-Handling/Supply Tug. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .K-5K-3. Point-to-Point Towing Tug. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .K-5K-4. Salvage Tug. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .K-6L-1. Multi-Sheave Traction Winch.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L-6L-2. ARS 50 Towing Machinery. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L-7L-3. T-ATF Towing Machinery (SMATCO Winch).. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L-9L-4. T-ATF Towing Machinery (Series 332 Automatic Towing Machine). . . . . . . . . . . . . . . . . L-11M-1. Types of Motion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-2M-2. Extreme Tensions (Curves 0 to 24). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-10M-3. Extreme Tensions (Curves 25 to 49). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-11M-4. Extreme Tensions (Curves 50 to 74). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-12

xxiii


M-5. Extreme Tensions (Curves 75 to 99). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-13Q-1. DDG 51 Draft Diagram and Functions of Form. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Q-5Q-2. Draft at Instability Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Q-9Q-3. Draft-at-Landing Fore and Aft. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Q-12Q-4. Load Distribution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Q-16Q-5. Overturning Moment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Q-27

xxiv


List of Tables

Table Page3-1. Hydrodynamic Resistance of the Towline. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-33-2. Safety Factors for Good Towing Practice. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-83-3. Section Modulus for Wire Rope. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-223-4. Elongation of 1,500 Feet of 6x37, 2 ¼-Inch IWRC EIPS Wire Rope. . . . . . . . . . . . . . . . . 3-223-5. Operating Range for Automatic Towing Machines of Various Types of Ships. . . . . . . . . 3-264-1. U-Bolt Clips. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-314-2. Applying U-Bolt Clips. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-325-1. U.S. Navy Craft Not Recommended for Open-Ocean Tows. . . . . . . . . . . . . . . . . . . . . . . . 5-45-2. Minimum Plate Thickness for Forward One-Fifth of Barge Bottom. . . . . . . . . . . . . . . . . . 5-155-3. Minimum Plate Thickness for Mid-Section.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-165-4. Battery Capacity Requirements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-216-1. Information on U.S. Navy Bitts.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-88-1. Commercial Submersible and Semi-Submersible Vessels. . . . . . . . . . . . . . . . . . . . . . . . . 8-38-2. Heavy Lift Ship vs. Submersible Barge. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-78-3. Sample Cc Values. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-278-4. Heave and Surge Motion Parameters for Calculation of Loading Factors for Conventional Surface Ships. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-358-5. Pitch Motion Parameters for Calculation of Loading Factors for Conventional Surface Ships.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-368-6. Roll Motion Parameters for Calculation of Loading Factors for Conventional Surface Ships.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-388-7. Allowable Block Stress (Assuming Douglas Fir). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-41B-1. Wire Hawsers Carried by U.S. Navy Towing Ships.. . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-10B-2. Nominal Breaking Strength of Wire Rope 6x37 Class, Hot-Dipped Galvanized. . . . . . . .B-11B-3. Efficiency of Wire Rope Terminations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .B-13C-1. Fiber Comparisons. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-2C-2. Synthetic and Natural Line Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-6D-1. Die Lock Chain Characteristics (MIL-C-19944).. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D-7D-2. Navy Stud Link Chain Characteristics (MIL-C-24633). . . . . . . . . . . . . . . . . . . . . . . . . . . D-8D-3. Commercial Stud Link Anchor Chain. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D-9D-4. Commercial Detachable Chain Connecting Link.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D-10D-5. Commercial Detachable Anchor Connecting Link.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . D-11D-6. Commercial End Link. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D-12D-7. Type I, Class 3 Safety Anchor Shackle (MIL-S-24214A (SHIPS)). . . . . . . . . . . . . . . . . D-13D-8. Type II, Class 3 Safety Chain Shackle (MIL-S-24214A(SHIPS)). . . . . . . . . . . . . . . . . . D-14D-9. Mechanical Properties of Shackles (FED SPEC RR-C-271D). . . . . . . . . . . . . . . . . . . . D-15G-1. Calculation of Steady State Towing Resistance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G-4G-2. Characteristics of Naval Vessels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G-7G-3. Beaufort Scale. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G-10G-4. Drydock Towing Coefficients. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G-17J-1. Towing Arrangement for Higher-Population Submarine Classes. . . . . . . . . . . . . . . . . . . . J-2K-1. Typical Commercial Salvage/Towing Vessels for Hire Compared with US Navy Salvage Ship. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .K-7M-1. T-ATF Towing YRBM Barge Displacing 650 Tons. . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-14M-2. T-ATF Towing FFG 1 Frigate Displacing 3,200 Tons. . . . . . . . . . . . . . . . . . . . . . . . . . . M-15M-3. T-ATF Towing DD 963 Destroyer Displacing 6,707 Tons.. . . . . . . . . . . . . . . . . . . . . . . M-16

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M-4. T-ATF Towing AE 26 Displacing 20,000 Tons. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-17M-5. T-ATF Towing LHA 1 Displacing 40,000 Tons. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M-18M-6. ARS 50 or ATS 1 Towing YRBM Barge Displacing 650 Tons. . . . . . . . . . . . . . . . . . . . M-19M-7. ARS 50 or ATS 1 Towing FFG 1 Frigate Displacing 3,200 Tons. . . . . . . . . . . . . . . . . . M-20M-8. ARS 50 or ATS 1 Towing DD 963 Destroyer Displacing 6,707 Tons. . . . . . . . . . . . . . . M-21M-9. ARS 50 or ATS 1 Towing AE 26 Displacing 20,000 Tons. . . . . . . . . . . . . . . . . . . . . . . M-22M-10. ARS 50 or ATS 1 Towing LHA 1 Displacing 40,000 Tons. . . . . . . . . . . . . . . . . . . . . . M-23P-1. System of Metric Measures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .P-1P-2. System of English Measures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .P-2P-3. Basic English/Metric Equivalents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .P-3P-4. Circular or Angular Measure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .P-4P-5. Common Pressure Conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .P-4P-6. Common Density Conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .P-4P-7. General Conversion Factors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .P-5P-8. Power Conversion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .P-11P-9. Temperature Conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .P-11P-10. Common Flow Rate Conversion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .P-12Q-1. DDG 67 Information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Q-6Q-2. Draft at Instability Information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Q-7Q-3. Draft at Instability Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Q-8Q-4. Draft-at-Landing Fore and Aft Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Q-11Q-5. Draft-at-Landing Fore and Aft Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Q-11Q-6. Heavy Lift Ship (HLS) Blue Marlin Characteristics and Motions . . . . . . . . . . . . . . . . . . Q-13

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Chapter 1

OPERATIONS OVERVIEW

1-1 Introduction to Navy Towing

Modern Navy towing, as we perceive it to-day, began at the beginning of World War II.Prior to WWII, the Navy owned few salvageships of its own and depended heavily oncontracted assets to perform the duties oftowing and salvage. Merritt-Chapman andScott was one of the premier towing and sal-vage contractors of the day and maintained aninventory of assets. They held a contract withthe Navy to perform ship salvage on an as-needed, no cure-no pay basis. As the USwatched the war in Europe develop, the needfor specialized vessels and a dedicated ser-vice became apparent. The Royal Navy ofGreat Britain was forced into performingthese tasks as German U-boats inflicted dam-age throughout the military and commercialfleet. Performing towing and salvage serviceson damaged vessels was most often a fasterand cheaper way of putting the necessary ton-nage back into service.

In October of 1941, Congress pressedthrough legislation that gave the Navy thecontracting authority to obtain the salvage re-sources, public or private, necessary to per-form operations that were deemed in the bestinterest of the country. On December 7, 1941,the Japanese bombed Pearl Harbor and fourdays later the Navy signed a contract withMerritt-Chapman and Scott establishing theNavy Salvage Service. This service was re-sponsible for performing offshore salvage oneast and west coasts, the Caribbean, Alaska,and Panama. To do this, it utilized leasedcommercial assets including tugs. The re-sponsibility for towing distressed or disabledships into port, however, did not lie with theNavy Salvage Service. This duty was the re-

sponsibility of the tugs attached to the navaldistricts.

This arrangement made it difficult to muster alarge quantity of tugs to respond to largegroups of casualties that often resulted fromGerman U-boat attacks. These casualties in-cluded not only fleet vessels but merchantships, which were logistically critical to thewar effort. The US knew the value of keepinga strong logistical force operating. To helprectify these shortfalls and to better utilize theavailable assets, the Navy formed the NavyRescue Towing Service. This service fell un-der the command of Commander, Eastern SeaFrontier, and operated exclusively on the At-lantic Coast. All available tugs were orga-nized under this service, which was headedby Edmond Moran of Moran Towing. Ed-mond Moran understood the towing industryand was enrolled in the Naval Reserve to per-form this duty. This organization for the mostpart alleviated the problems of asset alloca-tion and allowed the rescue of many tons ofships and cargo.

The Navy operated tugs in support of their lo-gistic requirements for many years, but as thewar in Europe wore on, the need became ap-parent for more capable, sea-going tugs. TheNavy designed a fleet tug (ATF) for the 1939shipbuilding program. The NAVAJO (ATF64) was the first of a fleet of 3,000 shafthorsepower, diesel-electric ocean-going tugsequipped with an automatic tensioning tow-ing engine. Almost seventy of these vesselswere constructed before the end of the war.These ships would serve the Navy well fornearly fifty years. Their towing winchesproved very successful in taking disabledships under tow. Their long range and sea-worthiness also made them very suitable forcombat operations.

The Navy also built many Auxiliary tugs(ATA) to be used in support of the fleet tugs.They were also diesel driven (relatively newtechnology for tugs) but carried about half the

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horsepower of the fleet tugs. They had con-siderable endurance and were well suited toperform operations just outside the combatzone. They would often relieve a fleet tug of adisabled vessel and continue the tow intoport. This allowed the fleet tugs to return tothe combat zone where they also performedsome fire-fighting and salvage assistance.Rescue tugs (ATR) were wooden-hulled, usedin submarine infested waters, and providedexcellent fire-fighting support. Their rangewas limited, and although they were not con-sidered the best vessels for long distance tow-ing, they were excellent in coastal areas.

The early designs of the salvage ships werenot particularly well suited for towing. Thischanged with the steel-hulled BOLSTERclass (ARS 38) which were built as salvageships but were of similar horsepower to thefleet tugs (ATF). They were originallyequipped with a powered reel for towing, butit was soon discovered that they performedtowing duties almost interchangeably withthe fleet tugs. Automatic towing wincheswere diverted from the ATA program and in-stalled on these six vessels. These ships wereof excellent design and operated until the lastone was decommissioned in the mid-1990's.

The primary mission of the Navy's towingand salvage ships today is not very differentfrom the early days of these vessels. Theyprovide support to distressed or disabledships in the combat zone. However, duringpeacetime, the daily operation of these shipsdiffers tremendously. The Navy now operatesonly a few open ocean towing ships. At thetime of this writing, the Navy had four ARS50 class salvage ships and the Military SealiftCommand (MSC) had five T-ATF class ves-sels operating for the Navy. T-ATFs aremanned by civilian crews and do not carry theextensive salvage equipment of the ARS classbut are extremely capable towing platforms.In recent years, efforts to reduce military ex-penditures have resulted in not only decreasesin the number of tow ships available but also

an increase in the number of all ships beingdecommissioned. This has placed a high de-mand on the Navy's few towing assets andhas increased the amount of work being sentto commercial firms.

U.S. Navy towing and salvage ships also pro-vide battle damage control as an adjunct dutyto their primary role as towing and salvageplatforms. Fleet battle damage control is ren-dered in the combat zone to a battle-damagedship casualty, often under direct enemy fire.The assistance can take the form of off-shipfire-fighting from a salvage tug’s fire-fightingmonitors or of a damage control team fromthe salvage ship boarding the casualty.

Towing can vary from routine, well-plannedactivities to time-critical emergencies such asrescue or salvage towing. Routine Navy tow-ing includes a wide variety of activities suchas harbor work and offshore or open oceantowing. Navy emergency towing consists al-most entirely of escort, rescue, and salvagemissions. The types of vessels that may re-quire towing include Navy ships rangingfrom small patrol boats to large aircraft carri-ers; non-combatant vessels, including tar-gets, large fleet oilers, and supply ships; andvessels such as barges and floating dry docks.

The Navy recognizes several distinct typesof towing:

• Harbor towing

• Point-to-point towing

• Rescue and emergency towing

• Salvage towing

• Special ocean engineering projects

• Tow-and-be-towed by Naval vessels

1-2 Harbor Towing

Harbor towing is limited to protected waters.Harbor towing and base support includesdocking/undocking, standby duty, and safetyescort duty. These services are the province of

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yard tugs. These vessels are incapable of sus-taining long-distance, open ocean towing dueto design limitations. Harbor tugs do not havethe range, crew size, berthing and messing ca-pacity, and, in some cases, the structural orhydrodynamic design needed to support openocean towing. Their moderate horsepower,limited seakeeping characteristics, and mini-mal towing machinery also makes these ves-sels unsuitable for the open sea. The U.S. Na-vy currently operates three classifications ofyard tugs: the YTL, the YTM, and the YTB.

1-3 Point-to-Point Towing

Point-to-point towing can be defined as tow-ing a vessel from one harbor to another.Point-to-point towing and “open ocean” tow-ing are largely synonymous. Open ocean tow-ing was a natural outgrowth of harbor towing.If vessels could be moved from one end of aharbor to the other end, the next step was tomove them from one harbor to another.

Until the 1960’s, Navy ATAs or similar ves-sels, were generally home-ported in each na-val district in the continental United States,Alaska, Hawaii, and at selected overseasbases. The tugs were used for coastwise tow-ing of floating equipment, such as barges,pile drivers, and dredges. Since the 1960’s,the Navy’s towing fleet has declined in num-bers, with whole classes of towing vesselsbeing decommissioned. The ATF 76, ARS 6,ATS 1, and all ATAs have been decommis-sioned, and, in FY94, the last WWII vintageARS 38 class salvage ships were also retired.Consequently, Navy point-to-point towing iscurrently performed by ARS 50 and theMSC-operated T-ATF class vessels, with anincreasingly large percentage of tows con-tracted to commercial firms.

1-3.1 Inland Towing

Inland towing is point-to-point towing per-formed on inland waterways such as rivers,bays, canals, or intercoastal waterways. In-

land towing in the United States largely origi-nated on the Mississippi and Ohio River sys-tems. This type of towing was also done onthe Erie Canal and other inland man-madenavigational systems managed by the ArmyCorps of Engineers, such as the St. LawrenceSeaway and East Coast Intercoastal Water-way. The Navy does very little inland towing.

1-3.2 Ocean Towing

Ocean towing is point-to-point towing wherethere are few, if any, places of refuge enroute.Open ocean towing was a natural evolution-ary step from harbor towing. The demand foropen ocean tows led to more advanced tugdesigns that could accommodate more diffi-cult towing missions.

After harbor towing, open ocean towing is themost widely practiced form of Navy towing.Because of the unforgiving conditions facedon the open ocean; it demands the most prep-aration; the most robustly designed and con-structed equipment; and a higher level of op-erator knowledge.

1-3.3 Defueled Nuclear Powered Ships

The Navy has devoted a considerable effort indeveloping guidelines for towing UnmannedDefueled Nuclear Powered Ships. The uniqueconsiderations of towing a nuclear vessel thatis unmanned have led to the development ofspecific instructions that deal with this specif-ic situation. NAVSEA has published a seriesof instructions to specifically deal with un-manned towing of nuclear vessels (includingsubmarines, cruisers, and moored trainingships). The information contained in thosedocuments will not be repeated in this manu-al.

1-4 Rescue and Emergency Towing

The mission of rescue towing encompassessaving a stricken ship at sea and towing to asafe refuge. The vessel may be adrift at sea,or near a shore or harbor. In the latter case, aconnection must be made quickly to prevent

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the disabled ship from going aground. Onhigh value tows, the Navy may assign a tug toescort duty, to provide emergency towing ser-vices without the delay of mobilization.

1-4.1 Naval Task Force Standby Duty

Navy salvage ships routinely deploy to theMediterranean and to the Western Pacific toprovide salvage and towing support to the5th, 6th, and 7th Fleets. Aside from partici-pating in salvage exercises with foreignnavies, the salvage ships perform any salvageor towing mission tasked by the Fleet Com-mander for the deployed Carrier BattleGroup, Surface Action Group, or any auxilia-ry ships requiring salvage or towing assis-tance.

1-5 Salvage Towing

Salvage towing generally follows immediate-ly after a salvage operation. Immediately af-ter salvage services are rendered, prepara-tions are made to tow the stricken vessel. Thevessel may be towed to a safe haven for tem-porary repairs, or to a port or facility wherecomplete industrial-level repairs are possi-ble. The vessel may also be towed to a dis-posal site for sinking. In either case, towpreparations usually entail more than the nor-mal tow system installation. The added mea-sures include reinforcing weakened sectionsof the ship, either through shoring or tempo-rary structural reinforcement, or possible spe-cial rigging to release the tow for sinking in asafe, controlled manner.

1-5.1 Combat Salvage and Towing

Ships involved in combat salvage and towingmissions often escort amphibious landingforces and battle groups in hostile areas.Their job is to provide towing and salvageservices to ships or landing craft that are dam-aged, afire, disabled, or stranded. They are al-so prepared to tow transport and supply shipslaying off the beachhead. During amphibious

landings, these rescue tugs and salvage shipscan be subject to enemy fire.

1-6 Special Ocean Engineering Projects

Navy tugs often become involved with un-usual projects, such as target services, sub-mersible towing, array movements, deepocean search and recovery, and classified op-erations.

Many of the attributes that make salvageships good salvage and towing platforms alsomake them good platforms for performingthese ocean engineering operations. Specifi-cally, tugs that can perform open ocean towsare often equipped with heavy lift cranes,have large expanses of deck area for tempo-rary installation of specialized equipment,and are designed to keep station or moor overa site of interest. Navy tugs can also serve asdiving platforms and perform a variety ofdeepwater tasks, including the support and re-covery of remotely operated vehicles.

1-7 Tow-and-Be-Towed By Naval Vessels

Although most towing is performed by shipsthat have been specifically designed and builtfor towing, emergency towing is sometimesaccomplished by ships other than tugs. Thisconcept is referred to as “tow-and-be-towed”or “emergency ship-to-ship towing.” In anemergency, any ship can tow another in itsown or similar class, with each ship providinghalf the towline. Ships not specificallyequipped for towing can fashion a temporarytowline from anchor chains, wire straps,mooring lines, or combinations of theseitems.

NAVSEA General Specifications require thatevery class of U.S. Navy ship (except aircraftcarriers and submarines) be able to tow-and-be-towed in an emergency. Definitive tech-nical instructions for U.S. Navy tow-and-be-

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towed operations can be found in NavalShip’s Technical Manual (NSTM) S9086-TW-STM-010, Chapter 582, Mooring andTowing (Ref. A). This topic is also covered inSection 6-6 of this manual. In the event of aconflict between NSTM Chapter 582 and thismanual regarding tow-and-be-towed opera-

tions, NSTM Chapter 582 shall take prece-dence. In all other towing matters, with theexception of nuclear tows, this manual is thegoverning document. Tow-and-be-towed op-erations for NATO navies are covered in Al-lied Tactical Publication (ATP)-43(A) (NA-VY), Ship-to-ship Towing (Ref. B).

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1-6


Chapter 2

OVERVIEW OF TOWING SHIPS

2-1 Introduction

This chapter contains a brief description ofsome typical design features found on ocean-going tugs. It also presents a good overviewof the latest generation of the US Navy’socean towing ships. Modern harbor tugs uti-lize recent advances in propulsion and syn-thetic line, but ocean going tugs remain large-ly unchanged from earlier versions.

2-2 Requirements Placed on Towing Ships

The degree of service that the tug may be re-quired to furnish to its tow depends upon thecircumstances and principal missions of theNavy at the particular time and can cover awide spectrum of needs. The primary require-ment placed on a tug is to provide power thatthe tow does not have due to its construction,its service condition (i.e., decommissioned), acasualty, or a failure of its main power plant.Secondary requirements include:

• Steering for maneuverability

• Navigation

• Communications

• Security

• Damage control

• Fire protection

For long ocean tows, the tug can be called up-on to provide complete logistic support forthe tow and the riding crew. The tug may alsobe required to serve as a supply base and shopfor repairs, rigging, and damage control dur-ing rescue salvage towing operations. Addi-tionally, the tug may have to supply all therigging for the towing system.

2-3 Design Characteristics

Most U.S. Navy ships can tow in an emergen-cy, but only properly designed and outfittedtugs make good towing ships. The specificitems to be considered in the design of anocean tug are dependent upon the missionsand services that it will be called upon to per-form. Characteristically, a tug’s superstruc-ture is set forward, allowing a clear fantail sothe towing point can be close to the ship’spivot point. The towline, secured well for-ward of the rudder and propellers, is allowedto sweep the rail without limiting the maneu-verability of the tug. In addition to a clearfantail area, characteristics of a good tug mayinclude the following:

• High horsepower• Slow speed maneuverability• Large diameter propellers• Large area rudders• Towing machinery• Power capstans• Towing points• Bow thrusters• Deck crane

In general, a Navy ocean tug is a very versa-tile ship, but its design involves many com-promises. Appendix K provides data on fea-tures of some commercial tugs. The design ofa Navy tug will differ from a commercial tugbecause a commercial tug must make a profit.This influences manpower, automation, sec-ondary missions, and a host of other charac-teristics.

NOTE

Although ocean-going tow ships are significantly different from harbor tugs, the term “tug” will be used to de-scribe all tow ships in this manual to avoid confusion between “tow ship” and “towed ship.”

2-1


2-3.1 Stern Arrangement

The stern of the tug is designed to minimizechafing and damage to both the tug structureand the hawser. Caprail radius is generousand free from unintended obstructions to thehawser’s sweep from side to side as the tugmaneuvers in restricted waters. Most tugshave a system to restrain the tow hawsersweep, such as vertical stern rollers or Nor-man pins, while towing under steady-stateconditions at sea. To reduce wear on boththe hawser and the tug’s structure, chafinggear is often used where the towline crossesthe stern.

On most Navy towing and salvage vessels,the bulwark and the caprail are gently curvedupward and faired into the deck above thetowing deck (see Figure 2-1.). This ship’sstructure restricts the tow wire from leadingforward of the beam at the tug’s tow pointjust aft of the tow winch.

2-3.2 Tug Powering and Bollard Pull

The design of the main propulsion plant is acompromise among wide-ranging require-ments. The tug must have high free-runningspeeds for reaching the scene of a casualtyquickly. It also needs good economy withhigh towline pull for long-distance tows atreasonable towing speeds. High bollard pullis required for holding a distressed ship toprevent it from grounding and for refloatingstranded ships. It is also required for along-side operations (docking, maneuvering) andother high power/near zero speed evolutions.

In the absence of a good automatic towingmac h ine o r o t he r ac cura te mea ns o fmeasuring the towline tension, a knowledgeof the tug’s available towline pull and bollardpull is required for controlling the tension.Appendix K presents the methodology forestimating towline pull and bollard pull.

Figure 2-1. ARS 50 Bulwark Forward Limits.

2-2 As of 7/23/02


2-3.3 Fenders

Fenders are energy absorbing materials ordevices that protect both the tug and the tow(see Figures 2-2 and 2-3). Modern fenderingis an important part of towing operations whenalongside evolutions are required. Tugs work-ing alongside submarines should have subsur-face fenders. Small tugs working with largeships should have fendering to protect thedeckhouse from being damaged during largerolls (see the wing fenders in Figure 2-2).

Three types of standard fenders are currentlyin use:

• Rubber

• Pneumatic

— High-pressure (5 to 7 psi)

— Low-pressure (1 psi)

• Closed-cell foam covered with urethaneelastomer

2-3.3.1 Features and Characteristics of Fenders

The most significant features of fenders are:

• Energy absorption• Durability• Handling characteristics• Ease of storage aboard ship• Ease of maintenance when not in use• Required support equipment

Other important characteristics include:

• Standoff distance• End fittings• Time required for deployment and

recovery• Capability of being used if damaged.

2-3.3.2 Operating Considerations

The following items should be consideredwhen using fenders:

• Energy Absorption vs. Deployment.Rubber fenders, as seen in Figure 2-2,are an integral part of a tug’s structure.

These take no time to deploy but pro-vide little energy absorption beyondsimply eliminating steel-to-steel con-tact. Foam and pneumatic fenders re-quire rigging and handling but are farsuperior in their absorbing capability.

Large truck tires are very effective fromthe standpoint of energy absorption andare inexpensive. They can be rapidlydeployed and are particularly usefulduring salvage where unusual condi-tions may exist. Some tires should bekept on board for emergency fendering.

• Size vs. Capacity. Low-pressure andhigh-pressure pneumatic fenders havesimilar characteristics. Because theyare filled with air, however, they mustbe larger than foam-filled fenders toabsorb the same amount of energy. Onthe other hand, equal capacity andquality foam-filled fenders will likelybe more expensive and heavier thanpneumatic fenders.

• Pneumatic Fender Maintenance. Inaddition to the larger size of pneumaticfenders, other attending disadvantagesare the extra equipment needed topressurize them and to check theinternal pressure. Patch kits and specials l i ng s t o s up p or t t he f en de r ’smidsection when being deployed andretrieved are also necessary for the lowpressure types.

• Pressure Loss. All pneumatic fendershave safety valves. When these valvesrelieve under high fender loads, thefenders lose nearly all their energy ab-sorption capability.

• Fender Displacement. A major oper-ating problem can arise when either thetug or the tow has a low freeboard rela-tive to the other ship. When the heav-ing or rolling motions of the two ships

2-3


Figure 2-2. Typical Rubber Fenders.

W/L W/L

W ingFoam -Filled Fenders (P /S)

BowFenders

Subsurface Fenders

Side Fenders

2-4 As of 7/23/02


Figure 2-3. Pneumatic and Foam Fenders.

2-5


get out of step, the fender can be rolledupward between the two ships and popout onto the deck of the one with thelower freeboard.

• Friction Damage. When the tug andthe tow have nearly equal freeboard,the out-of-step motions of the two shipscan create a great deal of frictionalheating on the surfaces of the fenders.Spraying seawater onto the rubbing sur-faces helps lubricate them and keepthem cool.

• Ship Shell Plating Damage. Care mustbe exercised in the fore and aft place-ment of the fenders to ensure that theydo not bear against relatively largeareas of side plating that are not wellsupported by internal framing and lon-gitudinal structural members. This isespecially important in quartering seaswhen swells will cause the two ships topivot about the bow or stern and thenslam the sides together at the other end.

2-4 Yard or Harbor Tugs

The design of harbor tugs and the equipmentthey employ varies. The typical Navy harbortug is a single-screw, deep-draft vesselequipped with a capstan aft, H-bitts forwardand aft, towing hawsers, and additional linesfor handling ships or barges in restricted wa-ters. Harbor tugs may also be equipped withfenders, limited fire-fighting equipment, anddeck equipment to support harbor operations.Twin-screw harbor tugs have greater maneu-verability and ship control.

Harbor tugs are classified by shaft horsepow-er (shp). The U.S. Navy operates three classesof harbor tugs that are used primarily in har-bors and sheltered waters. As these vesselsage, the Navy relies more and more on con-tracted vessels to perform harbor operations.This allows the Navy to take advantage of the

latest tug designs, but at the same time dimin-ishes its fleet.

2-4.1 YTL Class

Yard tugs having 400 shp and under belong tothe YTL class. The primary mission of theYTL class is moving small craft and unload-ed barges from one berth to another within aharbor. YTLs can also assist in moving largervessels because they are small enough tomaneuver in tight, confined areas betweenthe large vessel and obstructions. Characteris-tics of this class are small size, maneuverabil-ity, and less robust construction than largerharbor tugs. The term YTL is used to coveran entire spectrum of harbor “pusher boats.”Very few of the vessels are constructed to thesame class specifications, and a large numberare custom built by the naval base usingthem. The YTLs are still in service, but liter-ally hundreds have been retired as their use-ful life has ended (most were built duringWWII).

2-4.2 YTB Class

The largest tugs, with 1,000 to 2,000 shp, be-long to the YTB class. The larger YTBs cur-rently have as much as 2,000 shaft horsepow-er and are similar to commercial harbor tugs.YTBs can be used in open-ocean towing, butonly for short distances under the most opti-mal weather conditions. YTBs are mostlyconfined to harbor operations with occasionalpoint-to-point towing performed on inlandwaters or on coastwise towing routes. YTBsconfigured for servicing submarines have aspecially designed fender system. YTBs arewidely used in all Navy ports, especiallyoverseas bases, but may also face retirementin the near future.

2-5 Ocean Tugs

The Navy’s ocean tugs are far more versatilethan harbor tugs in terms of horsepower andrange capabilities, as well as in terms of the

2-6 As of 7/23/02


services they can provide to their tows. Oceantugs and salvage/rescue type ships are theonly U.S. Navy ocean-going ships whose pri-mary mission includes towing. Thus, they arethe only types considered to be specificallybuilt for towing and for which towing activi-ties have significantly influenced the design.

Most of the ocean tugs used by the Navy to-day are carryovers and replacements or suc-cessors to similar ships used or developedduring WWII. Some of the differences be-tween the WWII vintage and the more mod-ern ships lie in increased horsepower and bol-lard or towline pull, hawser size, provisionsfor use of synthetic fiber hawsers, and, ofmajor importance, vastly improved onboardequipment and accommodations.

In addition to their power, range, and endur-ance capabilities, the ocean tugs can workand survive in heavy weather independentlyof other auxiliary or support ships. They arealso used in stranding and other salvage oper-ations. Ocean tugs should have automatictowing machines and load sensing systems toreduce dynamic loads and, if necessary, rap-idly release the towline.

The following section contains a brief de-scription of modern U.S. Navy towing andsalvage ships. Due to shrinking budgets,some of these vessels are no longer in service.Their characteristics are presented here forboth historic and comparative purposes. Formore detailed information, refer to the opera-tions manual of each vessel.

2-5.1 ARS 50 Class

The four ships of the ARS 50 Class (see Fig-ure 2-4) are replacements for the ARS 38Class. Each ship carries a crew of over 100and equipment sufficient to handle oceantowing, independent salvage, diving, damagecontrol, and fire-fighting capabilities in timesof war.

The automatic towing machine (ATM) onboard the ARS 50 Class is a Series 322 winchbuilt by Almon A. Johnson, Inc. (see FigureL-2). This double-drum ATM stores two3,000-foot, 2¼-inch diameter towing haw-sers. The ARS 50 Class also has a Series 400traction winch for handling synthetic line upto 14 inches in circumference. The tractionwinch is also useful for mooring and oceanengineering operations. These vessels are ex-tremely versatile. They are capable of sup-porting a wide range of missions and are ex-cellent towing platforms as well as fullycapable salvage ships.

2-5.2 T-ATF 166 Class

The T-ATF Class is a multipurpose, long-range, high-horsepower, seaworthy tug (seeFigure 2-5). It can conduct long-distance towsand, when augmented with additional crewand equipment, operate in support of fire-fighting, diving, and salvage missions. Theseseven vessels were designed for and are oper-ated by the Military Sealift Command (MSC).They carry approximately 20 crew members,and 18 transients.

This ship was conceived and specified to re-place the Auxiliary Ocean Tugs (ATA) andFleet Tugs (ATF) for routine towing. Becauseit also was designed to serve as a salvage ten-der, it has a large afterdeck, similar to an off-shore supply vessel. Although not normallycarried, various suites of special equipmentcan be installed on board the T-ATF to sup-port air and mixed gas diving, beach-gear op-erations, off-ship fire-fighting, search and re-covery operations, and oil spill recovery. Thisclass is capable in rescue towing applications,but has limited salvage capabilities on itsown. With its large fantail area, it can be aug-mented to perform salvage, but carries littleof its own equipment.

This 7,200 horsepower tug class carries a2,500-foot, 2 1/4-inch wire rope tow hawser.The T-ATF is equipped with a traction winch

2-7


Figure 2-4. ARS 50 Class Salvage Ship.

Length (ft): 255

Beam (ft): 52

Draft (ft): 17.5

Displacement,Full Load (LT):

3282

Propulsion, Main: 4 diesel2 screws

Maximum Sustained Speed (kts):

15

Shaft Horsepower: 4200

Cruising Range (nm): 8,000 @ 8 kt

Fuel Consumption(Gal/day):

2 engine: 21004 engines: 4200

Complement: 94 crew16 transients

Towing Machine: Almon A. Johnson, Inc.Automatic towing ma-chine, Series 322 (double-drum) 2 1/4-wire, 3000 ft. (will accept 2 1/2-inch wire) and 14-inch traction winch, Series 400

Bow Thruster: 1 @ 500 HP

These ships replaced the ARS 6 and ARS 38 Class and have modernized salvage and towing capability. They are also equipped with off-ship fire-fighting improvements.

2-8 As of 7/23/02


Figure 2-5. T-ATF 166 Class Fleet Tug.

Length (ft): 240

Beam (ft): 42

Draft (ft): 15.5

Displacement,Full Load (LT):

2260

Propulsion, Main: 2 diesel, 2 screwsControllable,reversible pitch in Kort nozzles

Maximum Sustained Speed (kts):

15

Shaft Horsepower: 7200

Cruising Range (nm): 10,000 @ 13 kt

Fuel Consumption(Gal/day):

1 engine: 41492 engines: 8300

Complement: 16 crew4 Navy communicators18 transients

Towing Machine: SMATCO* 2500 ft.2 1/4-inch wire winch(15-inch Lake Shore,Inc. traction winch)

Bow Thruster: 1 @ 300 HP

This class of tug has replaced the ATF 76 Class. These ships have a large working space aft for VERTREP (replenishment by helicopter) and can be readily outfitted for specialized salvage and ocean engineering missions.

* Some vessels of this class have been refittedwith Almon A.Johnson automatic machines.

2-9


that can handle synthetic hawsers up to 15inches in circumference. The class was origi-nally equipped with a single-drum, dieseldriven, non-automatic SMATCO towingwinch relatively common to the offshore oil

industry (see Figure L-3). Some members ofthis class have been refitted with an (AlmonA. Johnson) electrohydraulic automatic tow-ing machine (see Figure L-4).

2-10 As of 7/23/02


Chapter 3

TOWING SYSTEM DESIGN

3-1 Introduction

This chapter provides guidance on the stepsto take when preparing to perform a tow. Itcontains information for the planner in choos-ing a tug and for predicting tow speed.

3-2 Designing a Towing System

Tow system design is often an iterative pro-cess. Each iteration has three core stages:

1. Calculate steady towline tension. Start-ing with the ship to be towed:

• Select the desired towing speed and cal-culate the steady state tension that thetowline will encounter at that speed(see Section 3-4 and (Ref. G)).

• Select representative tow speeds aboveand below the desired speed and calcu-late the corresponding steady towlinetensions. The calculated tensionsshould be either plotted or arranged in atable to allow interpolation later.

• Repeat this process for representativewind/sea combinations anticipated dur-ing the tow.

2. Select the tug and design a rig.

• Compare the predicted towline tensionto the capabilities of available tugs andselect the tug best suited for the task.

• Once a tug is selected, design an initialtowing rig. Select the towing connec-tion elements (such as bridles and chainpendants), determine a recommendedhawser length, and check the catenary.Account for the effects of weather, typeof towline, and dynamic load mitiga-

tion. Use the appropriate safety factorsfor the materials and equipmentinvolved, anticipated weather, andother conditions of the particular tow-ing mission (see Section 3-4.1 and (Ref.M).

3. Make necessary adjustments.

• Recheck the refined calculations againstthe tug’s capabilities.

• If calculated requirements for power ortowline strength exceed capacities ofavailable equipment, another iterationis required. Options may include:

— Selecting a slower towing speed

— Using additional or more powerfultugs

— Decreasing resistance by changingthe tow’s characteristics, routing,and/or schedule.

3-2.1 Tug and Tow Configuration

The design of a towing system is dependenton the type of towing performed, theconfiguration of the tow, and the number ofvessels being towed. For examples of thetypes of tow configurations used for openocean towing for single and multiple tows,see (Ref. I).

3-3 System Design Considerations

When planning a tow and designing the towsystem, important considerations are:

• Tow size, type, and condition

• Expected or required towing speed

• Capabilities of available tugs (bollardpull, range, equipment, and crew)

• Towing hawser system specifications(type, diameter, expected maximumtension, scope and configuration)

• Towline tension as determined by thetotal resistance of the tow and re-

3-1


spective seakeeping motions of the tugand tow

• Maximum practical towline length, asdetermined by navigational and hydro-graphic restrictions on towline catena-ry depth

• Operational considerations

• Proposed season and route

• Unique characteristics of the anticipat-ed tow

• Stability characteristics of the tug

These factors are interdependent. For exam-ple, in theory, the desired towing speed wouldlargely determine the required tow hawsersize. But, in practice, there is little choice oftow hawser for a given tug class. Hawserchoice is governed by the ship which is avail-able for the towing assignment. For largetows using the full propulsion power of thetug, the tug determines the potential speed ofthe tow. In other cases, tow speed may belimited by weather or by the condition of thetow. Given the tug and the resulting speed ofthe tow, the tow hawser size can be checkedand an initial towing rig designed.

All of these factors must be considered to de-termine which ones will dictate the design ofthe system. The system must then be exam-ined as a whole to ensure that the best config-uration has been achieved.

3-4 System Design Methodology

3-4.1 Calculating Total Towline Tension

Tota l towl ine tens ion has two majorcomponents: steady tension and dynamictension. Steady (or static) towline tension canbe predicted with a fairly high degree ofaccuracy. Static towline tension has threecomponents:

• Resistance of the ship to be towed (see3-4.1.1)

• Resistance of the tow hawser (see3-4.1.2)

• Vertical component of wire catenary(which contributes to the total tensionof the towline itself but not to tug pro-pulsion requirements) (see 3-4.1.3)

Dynamic towline tension, on the other hand,is caused by the random motions of the seaand the ships and is difficult to predict withabsolute precision over time. Statistics, how-ever, allow prediction of dynamic tension ex-tremes within probability limits set by the in-vestigating engineer (see (Ref. M)). Dynamictension has two components:

• Slow dynamic loads caused by thetow’s yawing, sheering, and surging(see 3-4.1.4)

• More rapid dynamic loads caused bythe effect of waves on the relativeseakeeping motions of tug and tow (see3-4.1.4)

3-4.1.1 Calculating Steady Resistance of the Towed Vessel

Steady resistance (RT) of the towed vesselmay be estimated using the followingapproximation:

where:

RH = Hydrodynamic hull resistance of the tow

RP = Hydrodynamic resistance of the tow’s locked propellers

RW = Wind resistance of the tow

RS = Additional tow resistance due tosea state

(Ref. G) provides methods and a convenientworksheet for predicting each of these com-ponents. Effort can be saved by computingthe resistance for two or three differentspeeds for later comparison to tug capabili-ties. (Refer to the towing speed limitations

RT RH RP RW RS+ + +=

3-2


Table 3-1. Hydrodynamic Resistance of the Towline.

USE OF TABLE: Towline resistance can be selected for the case closest to the actual towlineconfiguration. The figures can be interpolated as required if additional accuracy is desired.

• For towline scopes less than shown, make a proportional reduction from the scopeslisted.

• For tension greater than 60,000 pounds, extrapolate assuming a resistance curve be-tween 40,000 and 60,000 pounds in a straight line.

Wire Size(in)

Wire Scope

(ft)

Chain Size(in)

Chain Scope

(ft)

Added Resistance (lbs)10,000 lb. Tension


4 kts 8 kts 12 kts 4 kts 8 kts 12 kts

1 5/81 5/8

30002000

----

----

1000900

40003500

72004100

1000700

30002500

58003300

2222

2000200020002000

--2 1/42 1/44 3/4

-- 90270270

2000250031003700

22005100

1000012000

6000120001930024500

1500190020002700

2200390072008900

40007900

1500017600

2 1/42 1/42 1/4

200020002000

2 1/42 1/44 3/4

90270270

150030005000

52008000

14100

115001850025500

130016004500

38006500

12900

80001450023000

2 1/42 1/42 1/4

300030003000

2 1/42 1/44 3/4

90270270

190031005500

83001200014400

175002480027800

160025005000

57008700

13300

131002010026000

Wire Size(in)

Wire Scope

(ft)

Chain Size(in)

Chain Scope

(ft)



4 kts 8 kts 12 kts 4 kts 8 kts 12 kts

1 5/81 5/8

30002000

----

----

600500

22002000

50003300

500250

19001000

42002500

2222

2000200020002000

--2 1/42 1/44 3/4

-- 90270270

1000120015002500

1700320051006900

35006500

1090014600

300100013002000

1200250042006800

300051008800

13200

2 1/42 1/42 1/4

200020002000

2 1/42 1/44 3/4

90270270

120014003600

350051009300

65001150018100

110012002900

310037005700

50008500

13200

2 1/42 1/42 1/4

300030003000

2 1/42 1/44 3/4

90270270

140019003500

41006500

10500

95001550021500

120013002000

250042007700

59001090017000

3-3


cited in Section 6-4.2) Likewise, wind andsea state resistances should be computed forbest and worst expectations as well as for themost probable conditions of each assumedtow speed.

3-4.1.2 Calculating Steady Towline Resistance

In addition to the tensions calculated in Ap-pendix G, the hydrodynamic resistance of thetowline must be included, and this can be sig-nificant for a typical wire hawser tow rig. Theresistance is dependent upon the size, length,and catenary of the towline, which in turn aredependent upon characteristics of the selectedtug and towing speed. When using a synthetichawser, the added resistance of the towline isnegligible and can be ignored in these calcu-lations.

If a particular tug has not yet been selected,estimate the hawser resistance (Rwire) to be 10percent of the tow resistance (RT). Experi-ence has shown that when Rwire is significant-ly more than 10 percent of RT, the catenary isvery deep and tension is, therefore, out of therange of concern for towline strength. If aparticular towline configuration is being eval-uated, Table 3-1 provides a more refined esti-mate of the hydrodynamic resistance.

3-4.1.3 Calculating Steady Towline Tension

Normal wire rope towline arrangements willassume a sag or catenary, as depicted inFigure 3-1. The total towline stress at anypoint is the vector sum of the horizontal andvertical components of the stress at that point.Figure 3-1 includes a vector diagram of thetowline forces acting immediately astern ofthe tug. Maximum stress occurs near the sternbecause the hydrodynamic resistance of theentire towline is added to the resistance of thetow, whereas no hydrodynamic resistance isadded at the bow of the tow. Because stress ishighest near the stern of the tug, this is thepoint of interest to towing planners.Computing the total steady-state towline

tension at the tow, even with as much as 270feet of chain pendant, shows that the totaltension is less than at the tug.

The steady-state towline tension at the sternof the tug is expressed by the formula:

where:

RT = Tow resistance (Section 3-4.1.1 and (Ref. G))

Rwire = Towline resistance (3-4.1.2 and Table 3-1)

TV = Vertical component of the towline tension

TV is the weight of the towline forward of thecatenary low point, less the slight upwardcomponent of hydrodynamic drag on the for-ward half of the catenary. Location of thecatenary low point and the vertical compo-nent of the hydrodynamic drag are beyondthe scope of this manual. Errors will tend tocancel out, however, if TV is assumed to bethe weight (in water) of one-half the scope ofthe wire towline. (See Table B-2 in (Ref. B)for dry weights and methods for calculatingweights in water.) Do not include the weightof any chain pendant at the tow in thiscomputation.

For example, assume that an ARS 50 is tow-ing a ship that provides a steady towresistance of 60,000 pounds at 8 knots. Thetowline consists of 2,000 feet of 2 ¼-inchIWRC tow hawser and 270 feet of 2 ¼-inchchain pendant at the tow. Table 3-2 providesa towline resistance estimate of 3,700 pounds.According to Table B-2, 1,000 feet of wiretowline (one-half of the scope) weighs 8,143pounds in water. Therefore:

T = Total Towline Tension

RT = 60,000 lbs.

Rwire = 3,700 lbs.

T RT Rwire+( )2Tv

2+=

3-4


TV = 8,143 lbs.

Solving the vector diagram provides a maxi-mum steady-state tension:

This example supports a rule of thumb thattotal steady-state tension can be estimated byadding 10 percent to the predicted steady towresistance (RT). This method is reasonableand accounts for both the wire resistance andthe vertical component of the catenary. In theprevious example, adding 10 percent to pre-dicted steady tow resistance of 60,000 poundswould yield a total tension of 66,000 pounds,a conservative estimate when compared to the64,218 pounds seen above.

In Figure 3-1, the tug must supply excessthrust only equal to the horizontal componentof the tension, that is, RT + Rwire. While the

tug must support the weight of the towline, itdoes not require forward thrust to do this.

3-4.1.4 Dynamic Loads on the Towline

While towing at constant tug speed in a sea-way, the towline tension is not steady, butvaries over time (see Figure 3-2). In additionto steady horizontal resistance (T), the tow-line is also subject to stress from yawingmovements (Tyaw) and from the wave-in-duced motions of the tug and tow (Twave), al-so known as dynamic tensions.

Yawing, also referred to as sheering, is theslow swinging of the towed vessel from oneside of the course line to the other. Tyaw alsoincludes surge - the slow change of span be-tween the tug and towed vessel. Sheering ten-sion fluctuates in such a way that the averagevalue is zero. Because each swing takes sev-eral minutes, sheering tension also takes sev-eral minutes to vary from its maximum to itsminimum and is sometimes called a “quasi-steady” tension.

Figure 3-1. Towline Forces at Stern of Tow.

/L

R

R

R 2 2

R

w ire

Wire

T + +

T

T

T

T

T

W -

V

V

S

C

D Horizontal Distance

TugTow

Weight Per Unit Length

T 60 000, 3 700,+( )28 143,

2+=

T 64 218 lbs,=

3-5


Wave-induced tension is caused by the effectwaves have on both tug and tow and is a ran-dom process with typical half-periods (thetime taken to vary from maximum to mini-mum) of 1 to 8 seconds. Like sheering ten-sion, wave-induced tension has an averagevalue of zero. Dynamic tension is the accu-mulation of the complex dynamic responsesof tug, tow, and towline to time-varying forc-es. While both the components of dynamictension have an average value of zero, at anyinstant in time, dynamic tension can have asignificant, if not catastrophic, effect on thetowing system. Specifically, these damagingeffects occur when the cumulative tensionsfrom yawing and waves are additive to thesteady-state tension in the towing system.The effects manifest themselves in peak load-ing that can destroy the towing system bypure overload or by metallurgical fatigue in-

duced in the system components after repeat-ed cyclic loading.

Extreme towline tension occurs when yawingtension and wave induced tension are addi-tive. The total towline tension or extreme ten-sion (Te), can be expressed as:

where:

Te = Extreme Tension

T = Steady towline tension (RT + Rwire)

Tyaw = Time-varying tension due to yaw-ing of the towed vessel

Twave = Time-varying tension due to wave action on the ship and on the tow.

In Figure 3-2, for example, T is 20,000pounds. Tyaw varies between -3,000 and

Figure 3-2. Towline Tension vs. Time.

Extrem e Tension (Te)

Time (Minutes)

Ten

sio

n, K

ips

35.0

30.0

25.0

20.0

15.0

10.0

5.0

0.00.0 .50 1.0 1.5 2.0 2.5 3.0

Wave-Induced (Twave)

Steady orStatic (T)

Yawing andSurging (Tyaw)

Te T Tyaw Twave+ +=

3-6


+3,000 pounds. Twave varies between -5,000and +5,000 pounds. Te, in this example, is ap-proximately 28,000 pounds.

The example shown in Figure 3-2 assumesconstant speed and could apply to a tow thatis small compared to the size and power ofthe tug. For large tows, where slow swingscan take 10 minutes or more, and for the typi-cal situation where the tug’s power setting isconstant, the tug and tow both slow down toaccommodate the increased tow resistance.This is especially true when the tow sheers offto one side. A poorly behaved tow, therefore,cannot be expected to attain the speed predict-ed by (Ref. G) without a significant increasein tug power and hawser tension, neither ofwhich may be possible or wise.

A badly sheering tow can apply a significantadditional tension peak when it “fetches up”at the end of each excursion to the side. Thismay dictate a further, deliberate slowing toprotect the towing gear, especially if the tow-ing machine is not in its automatic mode.

Determination of maximum values for thethree components of towline tension is desir-able in the planning or design of a tow, aswell as in the actual towing operation. Duringa tow operation, precise determination oftowline tension requires precision instrumen-tation. Normally tugs are not equipped withinstrumentation sufficiently accurate to mea-sure Twave. Most tugs, however, are equippedwith towing machine tension meters suffi-ciently accurate for determining steady andquasi-steady tension. Twave must be treated asdiscussed in the following sections.

3-4.1.5 Factors of Safety

Tow planners and operators have traditionallydealt with unpredictable dynamic tensions byapplying large safety factors to steady ten-sions when sizing components. Recommend-ed factors of safety for various componentsare presented in Table 3-2. To use this ap-proach, multiply the calculated steady-statetension by the appropriate factor of safety and

compare this number to the new breakingstrength of the component. Safety factors alsoaccount for many other effects such as tow-line fatigue, corrosion, and wear.

This approach is suitable when the operatorshave a great deal of experience with the tow-ing system under consideration. Unless it isknown that dynamic loads will increase thesteady-state tensions by more than 100 per-cent, apply these safety factors to the calcu-lated steady-state tension to determine the re-quired hawser strength. The safety factorshall be increased appropriately if the tow isunfamiliar or there is significant uncertaintyabout the degree of dynamic loads or the con-dition of the hawser. Judgement is requiredwhen assessing the situation. If technical as-sistance is required, contact NAVSEA 00C.

3-4.1.6 Predicting Dynamic Tensions

Until recently, the use of safety factors wasthe only way to offset unpredictable dynamicloads. Difficulties occur with this approach,however, when using a new towing system ortowing a ship or structure with which there isno previous experience. Sometimes thishappens when the standard design or materialfor a towing system has been changed. Themore effects that are combined into one factorof safety, the greater the uncertainty.

A new statistical approach is emerging forpredicting the impact of ship motion on tow-line tension in a given sea condition. This ap-proach estimates the extreme dynamic ten-sion level that the towline is l ikely toencounter under certain conditions. This in-formation can be used by the tow planner ifsea conditions are known. More importantly,the data can be used to predict acceptablerisks of extreme dynamic towline loadings,rather than relying solely on traditional fac-tors of safety that are based on steady-statetensions. (Ref. M) describes this approach indetail.

When using these new statistical techniques,multiply the “extreme tension” that is calcu-

3-7


3-8

Table 3-2. Safety Factors for Good Towing Practice.

Minimum Factors of Safety*

Towing Mode for Tug Wire Rope

Hawser

**Wire Rope

Pendant

Chain Pendant or Bridle Polyester

Synthetic Line

(Other)

Shackles and

Detach-able

Links

Bitts, Padeyes

etc.

Note 1 1 1 2 2, 3 4 5

Long-Scope Wire Rope Hawser

On automatic tension control 3 (4)*** 4 4 - - 3 3

On the brake 5 6 6 - - 5 5

On the pawl (dog) 7 8 8 - - 7 7

On the hook (bitt, pad, etc.) 7 8 8 - - 7 7

On the hook or brake with chain pendant 4 5 6 - - 4 4

On the hook or brake with syn-thetic spring 4 5 5 6 - 4 4

Long-Scope Synthetic Hawser with Wire Rope Pendant

On automatic tension control - 4 4 4 10 3 3

On the brake - 6 6 6 12 4 4

On the pawl (dog) - 8 8 8 12 4 4

On the hook (bitt, pad, etc.) - 8 8 8 12 4 4

NOTES:

1. Based on Minimum Breaking Strength.2. Based on Minimum New Dry Breaking Strength. These figures are for 8” circumference and larger. For

smaller lines, increase safety factor by 2. (See 4-2.2)3. For Nylon: Breaking strength is reduced by 15% when wet.4. Based on minimum breaking strength for links and proof load for shackles.5. Based on Material Yield Strength.

* “Minimum” applies only to new components, good weather, short duration, or emergency conditions. Old components, possible heavy weather, long-duration use, etc., may impose uncertainties which require use of safety factors greater than the listed minimum safety factors.

** When pendant is used as a deliberate “fuse” (i.e., safety link), use the same factor of safety as for the haw-ser but applied to the breaking strength of the pendant.

*** See 4-3.1 For Details.


lated by a safety factor of 1.5. This does notsupersede the traditional safety factor ap-proach described in the previous section.Both should be checked, since either maycontrol for a specific set of circumstances.The more severe criterion shall be consideredthe limit until significant quantitative experi-ence is gained with the dynamic theory.

Removal of the uncertainty caused by the dy-namic effects may eventually permit reduc-tion in traditional towing system safety fac-tors. As confidence in the dynamic loadingapproach develops, the use of factors of safe-ty may no longer be required.

3-4.2 Calculating Towline Catenary

When wire rope is used as a towing hawser,the catenary is the primary means of relievingthe peak dynamic tensions. The weight of awire rope towing hawser, either alone or incombination with a short segment of chain atthe tow end of the towline, causes a catenary,or sag, in the towline between the tug and thetow. Variations in the towline tension tend tosmooth out in the catenary. Temporary de-crease of the distance between tug and tow, ora decrease in tension, is absorbed by a deep-ening catenary depth. An increase in the sepa-ration between tug and tow causes the catena-ry to decrease in depth and the hawser tensionto increase. Thus, the wire catenary tends toact as a spring, softening the tug-tow interac-tion.

Due to the hydrodynamic drag of the wireduring the rising of the catenary, the springeffect is not immediate. For load increases ofa sharp or sudden nature, the catenary cannotbe expected to absorb the accompanying in-creases in towline tension completely. Usingan automatic towing machine or a syntheticspring (see Section 4-6.5) in conjunction withthe catenary will help provide an effective re-lief of changing loads over the full range ofconditions.

To avoid dragging or fouling the towline onthe bottom, while maintaining a sufficientcatenary depth to absorb changes in tug-towseparation, it is necessary to estimate the cat-enary depth of the towline. A number ofmethods have been used for estimating tow-line catenary.

To estimate catenary depth, it is necessary tohave the following data available:

• Steady tension in the towline

• Lengths of the towline components

• The weight per unit length in water ofeach component

The steady tension in the towline may be esti-mated by using the tension meter on the tow-ing machine, by the estimating procedure in(Ref. G), or by using the chart in Figure 3-3,which presents the calculated tug pull avail-able versus speed through the water. Thecomposition and total length of the towlineshould be known. Table B-2 and Tables D-1through D-9 provide the weight per unitlength for various towline components. Whenweight in water of steel components is notgiven, multiply weight in air by 0.87 to obtainweight in salt water.

An initial estimate of the catenary depth ofthe towline may be determined using the fol-lowing formula:

where:

C = Catenary or sag (ft)

T = Steady tension (lbs force)

W = Weight in water per unit length (lbs/ft)

S = Total scope (ft) (total of all com-ponents)

Total weight in water per unit length (W) iscomputed as the sum of the weights of the in-

C T W⁄ T W⁄ 1 WS 2T⁄( )2––=

3-9


dividual towline components divided by thetotal towline scope.

This formula applies to single componentwires hanging under their own weight. Forcalculating, scope (S) and weight (W), whenthe towline includes a bridle, the total weightof the bridle should be used, but the scope isestimated as a single leg of the pendant. Thisformula provides an acceptable estimate oftowline catenary for towline configurationswhere the ratio of towline scope (S) to catena-ry (C) is greater than 8:1. When the ratio isless than 8:1, the catenary depth predicted bythis formula does not provide an accurate es-timate of the towline catenary.

Based on this formula, Figures 3-4 through3-12 show the calculated catenary for variouscommon compositions and lengths of tow-line. These curves may be used for towingspeeds up to 12 knots. To decrease catenary,towline scope may be shortened or the towingspeed increased.

These graphs assume the chain is attached atthe bullnose. If additional chain is used after awire pendant (i.e., closer to the middle of thetow configuration) a deeper catenary will re-sult. These figures provide estimates and careshould be taken when there is a risk of bottomcontact.

To quantify effects of changes in tension, aship can draw its own curve, representing thescope actually used, and proceed along thatcurve to different tensions to find the new cat-enary. For example, a ship using a 2-inchhawser and no chain would refer to Figure3-7. For a scope of 1,500 feet, a new curvecould be plotted in between the existingcurves for 1,000 and 2,000 feet. This newcurve would show that increasing tensionfrom 20,000 pounds to 30,000 pounds woulddecrease the catenary depth from about 100feet to about 65 feet. Slowing down to a ten-sion of 10,000 pounds will almost double thecatenary to about 190 feet.

Likewise, a ship could plot curves of catenaryversus tension for several tension figures toprovide a graphical representation of theeffect of change in hawser scope. When waterdepth is limited, the ship can start with therequired catenary depth and work backwardsto determine the required scope/tensioncombination. In addition, some towingmachine technical manuals include tables orcurves to assist in solving scope/catenary/tension questions.

It should be noted that catenary depth willchange with varying tensions. If catenarydepth is a concern (e.g., bottom contact), ex-pected minimum tensions should be used.

3-4.3 Reducing Anticipated Towline Peak Loads

Several aspects of the towline design can sig-nificantly affect the peak towline tensions.Some are adjustable during the tow; some arenot, but nonetheless should be consideredduring the tow planning phase. These mea-sures include:

• Increasing towline scope

• Increasing length of chain pendant orbridle

• Inserting a synthetic spring into thetowline system.

The towline scope used during a tow dependsprimarily on four factors:

• Type of towing rig employed

• Water depth

• Catenary required to absorb changes intowline tension

• Scope required to keep the tug and tow“in step”

To estimate the towline scope required, it isfirst necessary to estimate the steady towlinetension required to maintain the desired tow-ing speed. Calculating total tow resistance is

3-10


Figure 3-3. Available Tension vs. Ship’s Speed for U.S. Navy Towing Ships.

3-11


Figure 3-4. Catenary vs. Tension; 1 5/8-Inch Wire, No Chain.

Cat

enar

y (f

eet)

Tension (pounds)

S cope (ft)

3-12


Figure 3-5. Catenary vs. Tension; 1 5/8-Inch Wire, 90 Feet of 2 1/4-Inch Chain.

Cat

enar

y (f

eet)

Tension (pounds)

S cope (ft)

3-13



Cat

enar

y (f

eet)

Tension (pounds)

S cope (ft)

3-14


Figure 3-7. Catenary vs. Tension; 2-Inch Wire, No Chain.

Cat

enar

y (f

eet)

Tension (pounds)

S cope (ft)

3-15


3-16

Figure 3-8. Catenary vs. Tension; 2-Inch Wire, 90 Feet of 2 1/4-Inch Chain.

Cat

enar

y (f

eet)

Tension (pounds)

S cope (ft)


Figure 3-9. Catenary vs. Tension; 2-Inch Wire, 270 Feet of 2 1/4-Inch Chain.

Cat

enar

y (f

eet)

Te n s io n (po u nd s)

S co p e (ft)

3-17


Figure 3-10. Catenary vs. Tension; 2 1/4-Inch Wire, No Chain.

Cat

enar

y (f

eet)

Tension (pounds)

S cope (ft)

3-18



Cat

enar

y (f

eet)

Tension (pounds)

Scope (ft)

3-19


3-20


Cat

enar

y (f

eet)

Tension (pounds)

S cope (ft)


described in detail in Section 3-4 and (Ref.G).

Having an estimate of the total towline resis-tance, it is then possible to compute the cate-nary that will be associated with a chosentowline scope and towline rig. Section 3-4.2presents a simple formula for estimating thecatenary. For hawser scopes greater than orequal to 1000 feet, Figures 3-4 through 3-12will provide catenary depth directly, givenhawser tension.

The following explores the ability of a wirecatenary to absorb ship movements by includ-ing “stretch” of the wire.

If the effects of hydrodynamic drag are ig-nored, catenary theory estimates the separa-tion between tug and tow as:

where:

D = Horizontal distance between the tug stern and the bow of the tow (ft)

S = Total scope of the hawser (ft)

W = Weight in water per unit length of the hawser (lbs/ft)

C = Catenary or sag (ft)

T = Steady tension in the towline (lbs force)

See Figure 3-1 for a graphical representationof these values.

To quantify the effect on the hawser tensionfor a given change in distance between tug intow, it is necessary to develop a table orcurve of distance (D) vs. tension (T) forvarious hawser scopes. The computation isfairly direct if tension (T) is assumed for agiven scope (S) of hawser; catenary depth(C) is computed, then horizontal distance (D)of the catenary.

Figure 3-13 shows a comparison between an1800 foot hawser and a 1000 foot hawser. For

instance, from an initial tension of 20,000pounds, the 1,000-foot hawser can absorbabout 19 feet of additional separation be-tween the tug and tow before it reaches200,000 pounds tension; the 1,800-foot haw-ser will not reach that tension until separationis increased by almost 36 feet. Similarly, a 20foot stretch of the 1,800-foot hawser increas-es its tension to only about 75,000 pounds.The longer hawser significantly reduces thepeak tensions caused by the same ship move-ments. A similar trend would be seen withIWRC wire. Ships with different hawsers canprepare a family of curves showing thechange in tension as the separation betweenthe ships changes.

The quantitative data shown in Figure 3-13are based on slow changes in distance or ten-sion. Classic catenary is limited in its abilityto absorb tug and tow motions, even wherethere is a relatively modest average hawsertension. Effectiveness of the classic catenaryin reducing dynamic loads has limitations.This is because the hydrodynamic resistancenormal to the tow wire significantly impedesit’s rise and fall at typical frequencies of dy-namic seakeeping loads. Therefore, the wiretowline does not always have time to fully re-sume its former deep catenary when the nextsurge in tension occurs. So, Figure 3-13should be used for qualitative comparisons ofdifferent towline configurations acting underdynamic loading.

A similar analysis of the advantages of add-ing chain to the towline can be prepared usingthe methodology shown in Table 3-4. Plotcurves showing the effect of adding one ortwo shots of chain pendant to a given hawserlength. The calculation process is identical,except that the comparison will be betweenhawsers of the same length but with differenttotal length and unit weights, because theweight of the chain is distributed throughoutthe hawser length. The analysis will demon-strate that adding only one shot of 2¼-inchchain provides a considerably softer system

D S 1 WC 3T⁄–( )=

3-21


Table 3-3. Section Modulus for Wire Rope.

Table 3-4. Elongation of 1,500 Feet of 6x37, 2 ¼-Inch IWRC EIPS Wire Rope.

Wire Diameter

Wire Type Load Percentage 1 5/8 inches 2 inches 2 1/4 inches

6 x 37 IWRC0 - 20% 16.4 24.8 31.4

21 - 65% 18.2 27.6 34.9

multiply all values by 106

Note: Assume constructional stretch has been accomplished through previous loadings.

1. Section Modulus (Area x Modulus of Elasticity) for 2 1/4-inch IWRC hawser is 31.4 x 106 through 20% strength of the wire; 34.9 x 106 over 20% load.

2. Change in scope due to wire elasticity. (ft)3. Total scope of hawser after stretch. (ft)4. Catenary depth per formula:

5. Distance between tug and tow per formula: Source: Wire Rope Users Manual, 3rd Edition, Table 17

TensionSection

Modulus1 Se2 Scope3 Catenary (ft)4

Distance (ft)5

010,00025,00050,00075,00088,000

100,000125,000150,000175,000200,000250,000275,000288,000

31.4 x 106

31.4 x 106

31.4 x 106

31.4 x 106

31.4 x 106

31.4 x 106

34.9 x 106

34.9 x 106

34.9 x 106

34.9 x 106

34.9 x 106

34.9 x 106

34.9 x 106

34.9 x 106

00.51.22.43.64.24.35.46.47.58.6

10.711.812.4

15001500.51501.21502.41503.61504.21504.31505.41506.41507.51508.61510.71511.81512.4

--257.9184.3

43.131.326.322.018.515.513.211.69.38.58.1

--1395.51471.21498.81501.91503.01503.41504.81505.91507.21508.41510.51511.61512.3

C T W⁄ T W⁄ 1 WS 2T⁄( )2––=

D S 1 WC 3T⁄–( )=

3-22


that develops lower peak tensions for thesame change in separation between tug andtow.

Two components of wire “stretch” must alsobe included when determining the distancebetween tug and tow: constructional stretchand elastic stretch. The Wire Rope UsersManual (Ref. C) estimates constructionalstretch as 0.5 to 0.75 percent for 6-strand, fi-ber-core (FC) wire and 0.25 to 0.5 percent for6-strand, independent wire rope core (IWRC)wire. Constructional stretch is caused by avirgin rope’s helical strands constricting thecore during initial loading. The constrictedcore is compressed and lengthened by thepressure exerted by the helical strands. For fi-ber core ropes, constructional stretch is pro-nounced due to the high compressibility of fi-ber when compared to an IWRC. Construc-tional stretch properties fade from wire ropeearly in its life, especially for IWRC ropes.Shortly after a wire rope has been repeatedlyloaded, the constructional stretch characteris-tic is no longer exhibited. Fiber core ropes,however, will retain this property longer, es-pecially if subjected to only light loads.

The elastic stretch of hawsers likewise varieswith load. For convenience, elasticity is as-sumed to be constant through 20 percentloading, with a different figure applying be-yond 20 percent loading. For common Navyhawsers, the figures in Table 3-3 can be usedwhere Section Modulus (which incorporatescompactness factors and variance of elasticmodulus) is expressed as the effective area ofthe steel in the wire multiplied by the modu-lus of elasticity of the steel (Section Modulus(lb) = area (in2) x Elasticity (pounds persquare inch)).

For example, a 1,500-foot, 2 1/4-inch IWRCwire with a 25,000-pound load will elasticallystretch:

This formula assumes that constructionalstretch has already occurred. Table 3-4 hasbeen developed for a 1,500-foot, 2 1/4-inchIWRC extra improved plow steel (EIPS) wirehawser.

3-4.3.1 Using an Automatic Towing Machine

The automatic payout and reclaim feature ofthe towing machines installed in most tugs isa very effective means of reducing peak tow-line tensions. Table 3-5 provides the range ofautomatic settings available on various tugs.Generally used when water depth precludedan adequate catenary, the towing machinewas often taken off “automatic” after suffi-cient towline catenary had been established indeeper water. Now, however, with questionsconcerning real effectiveness of a wire cate-nary in reducing peak tensions, it appears thatthe automatic feature is equally as importantin deep water. Operation in the automaticmode is generally preferred; this, however, isnot intended to conflict with the manufac-turer’s approved operating procedures. Forexample, in calm seas, the manufacturer’srecommended standard operating mode willprobably be manual.

Additional information on towing machinesand winches appears in 4-5.1 and in (Ref. L).

3-4.3.2 Using Synthetic Towlines

Using synthetic towlines is one of the bestmeans of absorbing dynamic towing loads.The characteristic elasticity of synthetics hasmany advantages over the other means of re-ducing dynamic loads. Those advantages in-clude, but are not limited to, the following:

• Speed of response. When compared toan automatic towing machine (ATM),synthetic lines are capable of instanta-neous response. If the dynamic load hasa low acceleration, both the ATM and

Change in length (ft)load lb( ) length (ft)×Section Modulus (lb)----------------------------------------------------=

25000 1500×

31.4 106×

--------------------------------- 1.2 ft.=

3-23


synthetic line absorb the dynamic loadcomparably. If the load has a high ac-celeration, however, the ATM may notbe able to respond fast enough before atension spike impacts the towing sys-tem.

• Passive system. Once deployed, thesynthetic line requires no operator andis non-mechanical. Its shock-absorbingaction requires no active input or main-tenance by the operator.

• Maintenance. An ATM is a complexmachine and while it is not a commonoccurrence, is subject to mechanicalfailure. Proper care and diligent mainte-nance is necessary to ensure depend-able operation. Synthetic line is affect-ed by other factors including abrasion,heat, and UV light. By limiting expo-sure to these factors, a synthetic towhawser should have a long service life.

Synthetic towlines take two forms: a com-plete synthetic tow hawser and a “spring”synthetic line inserted in the towing system.The synthetic spring consists of a length ofsynthetic line placed in the towing system be-tween the steel towing hawser and the chafingchain extending from the tow. A spring worksin combination with the catenary produced bythe heavier steel components. It can assist inabsorbing rapid acceleration peak loads whilethe catenary adjusts to loads applied moreslowly. A synthetic spring should be sized toa comparable breaking strength of the re-mainder of the towing system. Important re-strictions on the use of synthetic tow hawsersand springs found in Section 4-3.2, Section4-6.5, and (Ref. C). Consult and incorporatethese restrictions in any towing system designthat involves synthetic line.

3-4.4 Tug and Equipment Selection

3-4.4.1 Tug Selection

Much too often tug assignments have beenbased almost completely on availability. A

tug must have many other special attributes.It must be staffed with competent personneland have adequate power for the tow, propertowing gear to connect the tow to the tug, andsufficient endurance to complete the tow.

The principal measure of a tug’s power is itsability to exert tensile force on the towline.The maximum force a tug can exert on thetowline is defined as the tug’s maximum pro-pulsion power delivered at zero tug speed. Inthe jargon of the towing industry, this maxi-mum tug power/zero tug speed condition de-livers a force referred to as “bollard pull.”The tug’s available propulsion power and hy-drodynamic properties of the tug and tow de-termine the speed of the tow and, therefore,steady forces on the towline. Generally, atug’s power plant and propeller are designedto deliver maximum power and optimum effi-ciency at a designated towing speed. Thegreatest thrust (bollard pull) is produced atzero speed, with the towline pulling force di-minishing as the towing speed increases.When the tug reaches its maximum free routespeed, all its horsepower is used in propellingit. At this point, the available towline pullingforce is essentially zero.

Each class of ship should have its ownunique set of available tow tension curvesthat depend upon engine power setting, shipspeed, propeller rpm, and propeller pitch (forships with controllable pitch propeller [CPP]systems). For tow planning, the maximumavailable tow speed is the figure of interest.Figure 3-3 shows the available tow tensionversus ship’s speed for U.S. Navy oceantugs. Comparing a curve to a horizontal re-sistance value (as calculated in 3-4.1.3)provides the approximate maximum towspeed for an assumed condition. If the maxi-mum speed available does not coincide withthe assumed tow speed conditions, additionalresistance computations should be performedto achieve a balance between tension re-quired and tension available. A more direct

3-24


Figure 3-13. Distance Between Vessels vs. Hawser Tension for 1,000 and 1,800 Feet of 6x37 FC Wire.

NOTE

These curves plot the hawser tension vs. tug/tow separation. They demonstrate the much“softer” nature of the longer scope for the samechange in separation.

100 K

200 K

300 K

300 K

200 K

100 K

01840+40

1830+30

1820+20

1810+10

18000*

1790-10

2” FC IPS W ire1800 ’ S cope

1780-20

Separation Of Tug And Tow (ft)*Note: Zero represents steady-state cond ition

01020+20

1010+10

10000*

990-10

980-20

2” FC IPS W ire1000 ’ S cope

1030+30

1040+40

Ten

sio

n(p

ou

nd

s)Te

nsi

on

(po

un

ds)

3-25


method is to plot a curve of horizontal resis-tance directly onto a copy of Figure 3-3. Thetug and tow curves will intersect at the maxi-mum speed attainable with each tug forassumed tow conditions.

If the available tow speed exceeds the amountneeded (usually for small or non-ship tows),the tug will require less than maximum con-tinuous engine power. In this situation, a lesspowerful tug can be considered. Conversely,if available tow speed is less than required, amore powerful tug or multiple tugs must beselected. In the latter case, there will be twoor more towlines, so towline hydrodynamicresistance must be calculated appropriately.Otherwise, the available towline tension ofthe tugs is additive.

When the available tug is underpowered forthe desired tow speed, the most importantconsideration is whether it has sufficientpower to keep the tow out of danger underthe most severe wind and sea conditions thatcan be reasonably expected. For instance, itmay be acceptable that a given tug is unableto make headway over the ground, whiletowing a large ship in a sudden gale in theopen sea. The same tug, however, may beconsidered inadequate for towing the sameship under the same conditions near a leeshore. In the case of a planned tow of a largeship, adjustment to tow dates and carefulweather routing are essential. For more se-vere cases, adjustment of the assignmentsand schedules of other tugs also may be re-

quired to provide the required towingcapability.

For emergency or unplanned towing require-ments, the tow will be initiated by the firstavailable tug. Procedures outlined herein areuseful in determining whether additional tow-ing assets should be diverted to escort or takeover the tow. (Ref. K) contains data useful inestimating the power of commercial tugs thatmay be needed in an emergency.

3-4.4.2 Towing Gear Selection Factors

Once the tow vessel has been optimally sizedto fit operational requirements, towinghardware, including the “jewelry” connectingsys tem components , shal l be s ized toaccommodate the anticipated forces for thoseoperational requirements. The mechanicalproperties of typical components of towingsystems are covered in the Appendices of thismanual. Examples include wire rope and wirerope terminations ((Ref. B)), synthetic fiberlines ((Ref. C)), chain, shackles and links((Ref. D)), and line stoppers ((Ref. E)).Engineering design factors of safety for allsystem components are dis-cussed in 3-4.1.5.Towing gear is discussed at length in (Ref. 4).

Hawser size is generally fixed for a given tug.If a specific size hawser is required by thetype of tow, that fact, rather than the avail-ability of tugs, may determine tug selection.

The calculated steady towline tension valuesare multiplied by the safety factor to obtainthe required minimum breaking strength ofthe wire rope hawser. With the minimum

Table 3-5. Operating Range for Automatic Towing Machines of Various Types of Ships.

Types of Ships Operating Range (lbs.)

Salvage Ship (ARS 50) 20,000 - 110,000

Fleet Ocean Tug (T-ATF) 30,000 - 110,000

3-26


breaking strength known, (Ref. B) may beused to evaluate the wire hawsers carried bycandidate tugs. If there is no good match, theassumed tow speed can be adjusted until amatch between required hawser strength andavailable tugs is achieved. For a particulartug, with a specific hawser, the problem may

be reversed to find the maximum allowablesteady tension.

3-27



3-28


Chapter 4

TOWLINE SYSTEM COMPONENTS

4-1 Introduction

This chapter presents guidance on the use ofthe wide variety of components available foruse in towing. Tow planners and tow shipsshould carefully consider relative advantagesand disadvantages of each component whendesigning a tow rig. Consideration should begiven to durability, availability, ease of han-dling, and other pertinent factors.

4-2 Towline System Components

The towline system is made up of many com-ponents. A tow hawser often called the tow-line or towline connection, is only one com-ponent of the towline system. Figure 4-1illustrates a complete towline system. A tow-line system includes attachment points, ropeterminations, and tension components such aschain pendants, wire rope pendants, andspring pendants. These elements are joinedby shackles, links, or other connecting hard-ware.

A towline system is the tension-carrying linkbetween tug and tow and must be able towithstand steady loads, as well as dynamicpeak loads, often called shock loads. The pri-mary materials used in tension members arewire rope, synthetic fiber lines, and chain.

All items must be sized for the towing loadswith an appropriate factor of safety (see Table3-2). Size and compatibility are key consider-ations.

The following is a list of factors that influ-ence selection of the components of a towingsystem:

• Strength (static loads, dynamic loads,fatigue)

• Ability to nondestructively inspect

• Elasticity (stretch vs. load over a fullrange of loads and over the lifetime ofmaterial, set or permanent stretch)

• Predictability (strength and compliance)

• External abrasion resistance

• Internal abrasion resistance (related tofatigue life)

• Weight and specific gravity

• Survivability in a specific environment(effects of corrosion, ultraviolet light,sea water, acids, temperature, moisture)

• Ease of handling (surface characteris-tics: slippery, sticky, pliable, minimumbend radius)

• Stowage (volume shrinkage upon dry-ing, flexibility)

• Adaptability to fittings and terminations

• Compatibility of fittings and terminations

In various towing applications, one or moreof these factors may have a predominant in-fluence on the choice of material. Chain, forexample, often is selected as a chafing pen-dant or bridle because of its abrasion resis-tance and survivability. When used as a lead-er chain (see Figure 4-1), provides elasticitythrough catenary action rather than throughmaterial stretching. Likewise, polyester maybe suitable for a tow hawser or spring, butwould not be selected as a chafing pendant.Wire rope is generally favored for use as atow hawser on ocean tugs because of itsstrength and reasonably high abrasion resis-tance, with its flexibility, stowability, andease of handling also being important.

4-1


4-3 Main Towing Hawser

The tow hawser is the primary tension ele-ment of the towline system. Tow hawsers arenormally wire rope or a synthetic line. Theend of the hawser that extends to the tow isusually equipped with an end fitting such as asocket, thimble, or spliced eye; if the tugdoesn’t have a towing machine or winch,both ends of the hawser may have fittings.When the tow hawser is part of a tug’s equip-ment, it is stowed on the drum of the towingmachine, or in the case of synthetic line, in abin below deck. When the tow hawser is partof the towed vessel’s equipment, it may bestowed on a storage drum, reel, or brackets,or faked down in a tub, ready for use.

4-3.1 Wire Rope Hawser

Before the development of wire rope in the19th century, the primary material used fortow hawsers was natural fiber line made frommanila, sisal, and hemp. As ships becamelarger, the diameter of natural fiber lines in-creased to the point where handling and stor-age became difficult. Because of its superiorabrasion resistance and strength-to-weightand strength-to-size ratios, wire rope rapidlyreplaced natural fiber lines for towing haw-sers. Wire rope was accepted for towing de-spite being far less elastic than natural fiber

lines. At first, elasticity loss was countered byusing long spans of hawser, where the weightof the wire rope formed a catenary in the wireand provided a measure of effective elastici-ty. Later, tow ships often used manila springpendants, or “springs,” in conjunction withwire rope to provide the needed elasticity.Today, synthetic fiber springs perform thisfunction and are common in commercialpractice.

For wire rope in new or very good conditionand used in conjunction with an automatictowing machine, a minimum safety factor of3 is appropriate for routine ocean tows in goodweather (see Table 3-2). To be on the conser-vative side and allow for unforeseen occur-rences, a safety factor of 4 is recommendedfor routine tows. Other conditions requirehigher factors, as noted in the table.

4-3.2 Synthetic Hawser

When synthetic fiber line was developed forcommercial applications, it began to replacemanila rope for towing springs and hawserson small tugs. Synthetics also gainedacceptance as open-ocean towing hawsers,often replacing wire rope. The elasticity ofsynthetic hawsers easily absorbs tensioncaused by motion.

Figure 4-1. Typical Towline Connection Components.

To TugAttachm ent

Point

ChafingGear

H-BittsStern Rollerand Caprail

Tug’s TowingHawser

Optional Synthetic

Spring

ConnectionJewelry

Lead Chainor W ire

Pendant

ChafingChain

or Bridle

TowAttachm ent

Point

Deck EdgeFairlead

4-2


One of the first synthetic materials to be usedin towing was nylon. The Navy began toexperience problems, however, when usingnylon line as the peak load mitigation system.Some of the problems were due to nylonbeing weaker when wet than when dry.Additionally, the safe working load (SWL)and factors of safety for nylon in the marineenvironment had not been adequatelydefined.

A better understanding of the strength, ser-vice life, degradation, and elasticity of syn-thetic line has led to limitations in nylon’s useas the main towing hawser. Nylon line is onlyapproved for:

• Open-ocean towing of craft with lessthan 600 long tons displacement or intow-and-be-towed or emergencytowing operations

• Unique or special tows approved byNAVSEA on a case-by-case basis.

A material that is better suited for towing ap-plications is polyester. NAVSEA’s continu-ing investigation into using improved andcomposite designs of synthetic hawsers hasled to the approval for general use of singleand double braided polyester lines in all rou-tine and emergency towing applications, ex-cept where otherwise dictated. Thespecifications of the approved polyester lines

are provided in (Ref. C). Existing nylon tow-ing hawsers shall be replaced with the ap-proved polyester lines on a size-for-size ba-sis. Synthetic springs are discussed in Section4-6.5.

Table 3-2 provides factors of safety for syn-thetic lines being used as a main towing haw-ser. The steady towline tension value calcu-lated in Section 3-4 shall therefore bemultiplied by the safety factor listed in this ta-ble to obtain a required minimum strength.Note that the safety factor depends on the tugattachment point and the degree of tensioncontrol. (Ref. C) provides data for use in eval-uating one or more candidate synthetic lines.

Smaller l ines ( less than 8 inches c i r-cumference), with a greater portion of theirfibers exposed to abrasion and the effects ofultraviolet light and other chemical attack,require higher factors of safety. Increase thefactors listed in Table 3-2 by adding a valueof 2.

4-4 Secondary Towline

A secondary towline shall be rigged on alltows. The secondary towline is intended foremergency, short-term use. It may be of less-er strength than the primary towline (althoughit does not need to be) and is often made upwith synthetic line. Rigging methods willvary, depending on whether the tow ismanned or unmanned. A secondary hawser isplaced on the tow and is generally led downone side of the deck edge, rigged with aheavy messenger led outboard of the ship’sstructure, and terminated by a lighter floatingpendant with a marker buoy trailing astern ofthe tow (see Figure 4-2). This system isrigged so that the tug merely recovers a trail-ing messenger and heaves aboard the second-ary towline for connection to the hawser. Asecondary tow system can be rigged to towfrom either the bow or stern.

NOTE

Appendix C provides the breakingstrength values for synthetic line.Manufacturer ’s tables usual lyquote values for dry nylon. Break-ing strength for wet nylon line isabout 15 percent less than for dryline and, thus, the manufacturer’sva lues genera l ly mus t be de-creased by 15 percent for towing orother “wet” uses. Wet strength re-ductions do not apply to syntheticsother than nylon.

4-3


Figure 4-2. Secondary Towline System.

4-4


For small tows a primary pendant is riggedusing the ship’s anchor chain a secondarypendant is rigged from a stern tow pad usingthe ship’s emergency towing hawser with a200-foot floating messenger and small trail-ing buoy. When rigging an emergency towhawser aft, chafing chain should be connect-ed to the tow pad with a safety shackle. Peli-can hooks should not be used. For largetows or ships that will not tow well from thestern, a secondary tow hawser should berigged from the bow and fairled down thesides, stopped off in bights, to the messenger.

Secondary wire can be secured with a pieceof 3/8-inch round bar. The round bar is tackwelded to the deck edge and bent up andaround the wire. This allows the wire to bepulled out easily if needed. These clipsshould be spaced about 5 feet apart. A similarmethod can be employed when securingchain. (see Figure 4-3) .

All stops should be strong enough to hold inheavy weather but accessible to allow cuttingand light enough to be broken without dam-age to the towing pendant or tow. It must berigged outboard of all existing structure, in-cluding bitts and handrails, and should fallfree without turns that will cause kinking asthey pull out.

In all cases, a secondary towline will alreadybe connected to an appropriate hard point onthe tow and provided with necessary chafingprotection. As a minimum for vessels above600 L-ton displacement, the secondarytowing pendant should be 1 5/8-inch wirerope with the necessary chafing gear.

4-5 Attachment Points

This section discusses various types of attach-ment points on tows and describes the loadingvarious types of attachments may be subject-ed to. Every possible effort should be made toensure that an attachment point is subjected toonly one type of load in a known direction.Horizontal and vertical padeyes, for example,should be subjected to a force only perpendic-ular to the axis of the pin. See Section 4-5.3for more information.

The attachment points on tugs and tows trans-mit the towing load from the towline to thevessel. Attaching the towline system is of vi-tal importance and must be given careful con-sideration with regard to seamanship, rigging,and basic engineering mechanics.

Towline attachment points on U.S. Navy tugsare the towing machine or traction winch.

Attachment to the tow may be at a hard pointspecifically intended for towing, such as adeck padeye, chain stopper, or specializedtowing bracket, although many ships do nothave an attachment point specifically de-signed and fitted for towing. Some commer-cial ships are not designed to be towed, or thetow attachment is located somewhere otherthan originally designed. Often attachmentsrequire use of fittings or gear intended forother purposes, such as single point mooring(SPM) fittings, bitts, anchor chain holding fit-tings, or the tow’s anchor chain. Sometimes,for planned tows, a new attachment point willbe installed. The attachment point shall be in-spected for planned tows. Non destinctivetesting (NDT) shall include visual inspectionof the attachment point and surrounding areaand a dye-penetrant test of the padeye or bittattachment points is recommended. If there isany doubt about the strength of the padeye orattachment point, further testing and repairsare required.

CAUTION

Bights of wire hanging can be dam-aged or loosened if the tow goesalongside a tug or a dock.

4-5


Figure 4-3. Secondary Towline System.

Typical Secondary Tow Pendant Chain Clip

NO TE

D im ensions o f cha in a ttachm entclips a re to be de term ined bya llow ing 1 /16” clearance a lla round the cha in (i.e ., W idth p lus 1 /8 ”)

C ha in attachm ent clips a re tobe spaced approx im ately 3fee t apart.

1 .

2 .

N OTE 1

3/16TYP

1 1/4” R AD (TYP)

Secondary TowPendant C hain L ink

3/8” D IA. R oundbar (O SS)A ttachment C lip

N OTE 1

Typical Secondary Tow Pendant Securem entTypical Secondary Tow Pendant M essenger Line Securement

3/8” D ia. R ound Bar (O SS)A ttachment C lip

Exist D eck / Bulw ark S tructure

ABT 60” (TYP)

Secondary Tow Pendant W ire Rope

Typical Secondary Tow Pendant W ire R ope Attachm ent Clip

Approx. 1” R adius

1/8” x 1 /8” (M ax) Tack W eld TogetherA fter Insta lla tion on Every Third C lip

1/4TYP

3/8” D ia. R ound Bar (O SS)A ttachment C lip

D iam eter Equals W ire D ia. P lus 1/8”

Secondary Tow Pendant W ire Rope

Existing Deck / Bulwark Structure

3 1 /2 ”

S ide Shell

D eck

Round Bar

Secondary W ire

S e e R ig h t fo r m ore de ta il

4-6


For an emergency tow, a makeshift connec-tion, such as a heavy chain wrapped around astrong foundation, may be used. In everycase, the material condition of the fittings andstructures should be carefully inspected.

For deck fittings designed specifically fortowing, operators may assume that the appro-priate engineering was performed, if these fit-tings pass the NDT inspection. If the attach-ment point is inadequate or does not exist, itmust be designed, fabricated, and installed.Activity preparing a tow must arrange for en-gineering analysis to ensure a safe connec-tion.

An important factor when locating and in-stalling an attachment point is the need for anintegrated attachment point and fairlead sys-tem. A fairlead ensures that the tow load isapplied in the designed direction, i.e., no sideloading. Therefore, attention should be paidto both the attachment point and the fairlead.A common failure of the attachment systeminvolves gross structural failure of either theattachment point or fairlead. This problem isespecially relevant when towing minecraft,non-oceangoing craft, and wooden, alumi-num, or fiberglass vessels. Fairleads on thesetypes of vessels may not be strong enough towithstand towing loads.

Safety factors for attachment points should bedesigned and built in accordance with theGeneral Specifications for Overhaul of Su-face (GSO) Ships, U.S. Navy, Sections 582and 077, Naval Sea Systems Command,S9AA0-AB-GOS-010/GSO (Ref. D). Thecri-terion generally applied is that the break-ing strength of the line should not exceed35% of the padeye’s bitt, or cleats yieldstrength.

4-5.1 Winches and Towing Machines

Although wire rope is somewhat easier tohandle than wet manila line of equal strength,it cannot be faked out on deck when hauledin. Powered winches and towing machines

were a natural evolution, providing the in-haul and storage features for wire rope haw-sers, while eliminating the use of bitts andhooks.

All U.S. Navy tugs have automatic towingmachines, except for the MSC-operatedT-ATFs, which use SMATCO winches. MSChas backfitted automatic towing machines onselected T-ATFs. Each T-ATF requires a shipcheck for applicability.

The principal functions of towing machinesare:

• Acts as a hard point or attachment pointfor securing the towline to the tug.

• Pays out and heaves in the towline dur-ing towing operations.

• Transports or stows the towline as it isheaved in.

• Acts as a quick-release device for dis-connecting a towline if necessary dur-ing an emergency.

• Acts as an automatic tension control de-vice to limit or relieve peak dynamicloads in a towline system, thereby en-hancing the life and utility of the equip-ment, increasing maximum speed, andincreasing safety.

• Monitors and displays tow hawser con-ditions such as tension and scope.

A towing machine has a power-driven drumthat serves as an attachment point and storesunused portions of the wire rope towing haw-ser. The powered drum is used to control thelength of wire towline. Most U.S. Navy tow-ing machines have an automatic control sys-tem that automatically pays out line whentension exceeds a set value. More sophisticat-ed machines also have an automatic reclaimcapacity, which hauls back the hawser whentension decreases. Towing machines have afree-spooling feature that serves as a quickdisconnect system for the towing hawser.

4-7


As synthetic fiber line towing hawsers werebeing introduced in Navy towing, the multi-sheave traction winch was developed (seeFigure L-1). In addition to providing a hardpoint for attachment, the winch has payoutand heave-in features for adjusting the tow-line scope. Because reel-type storage is notpractical for synthetic line, the hawser isfairled into a stowage bin located belowdecks as it comes off the traction winch.Some traction winches are now equippedwith automatic controls, that pay out hawserto relieve high towline tensions. This controlgenerally does not provide automatic reclaimon the traction winches. Periodic heave-in,under manual control, may be required tomaintain the desired towline scope. Tractionwinches for wire hawsers are often found onlarger commercial ships.

Most towing machines and winches have a“dog” system that positively holds the drumagainst towing loads. A dog is a pawl orratchet type system that cannot be releasedagainst tension. When towing “on the dog,” atowing machine must be started up, engagedand the hawser heaved in slightly to releasethe dog. Therefore, when towing on the dog,there is no quick-release capability.

Refer to (Ref. L) for a more complete discus-sion of U.S. Navy towing machines andwinches.

4-5.2 Bitts

A bitt is a strong post used for belaying, fas-tening, and working ropes, hawsers andmooring lines. Bitts usually appear in pairsand are named according to their use.

The term bollard is occasionally applied to abitt, but more commonly is applied to a de-vice on a pier for securing mooring lines.

Bitts on U.S. Navy ships are designed towithstand a load equal to at least three timesthe breaking strength of the line they weredesigned to hold. See Section 6-2.6.2 for thesafe working loads of specific designstrengths of U.S. Navy bitts.

Towing or H-bitts are heavy steel castings orweldments secured to the ship’s structure (seeFigure 4-4) . Generally located near the tug’spivot point, they provide the hard point thatsustains athwartship loads imposed by a tow-line when it sweeps the fantail. In tugs fittedwith towing machines, the H-bitts are used tofairlead the main tow hawser to the drum toprevent transverse strain on the level windmechanism and are used to stop off the towwire when necessary. On the ARS 50, thefunction of the H-bitts is integrated into thedeckhouse structure.

Under normal towing conditions, using theH-bitts for holding the hawser is not recom-mended; such use is usually restricted to de-beaching operations or other instances whenisolating the towing machinery from hawsertension is necessary.

4-5.3 Padeyes

The most frequent means of attaching a tow-line to the towed vessel is by means of a pad-eye. Three distinct types of devices collec-tively are referred to as padeyes. Personnelrigging the connection must understand de-sign features. The three types of padeyesfound in towing are:

• Horizontal padeye

• Vertical free-standing padeye

• Towing bracket

Figure 4-5 shows two different styles of hor-izontal padeyes. Their distinctive feature isthat the pin has a vertical axis. The towline,therefore, is free to sweep in the horizontalplane, while constrained in the vertical plane.

NOTE

Unless specifically designed, bittsare generally not suited as towingattachment points and are not inthe proper position to be used astowing fairleads.

4-8


Figure 4-4. Aft End of ARS 50 Towing Machinery Room and Typical Towing Fairleads /Bitts .

Tow W ire Passages

Synthetic Stopper Padeye

W ire Rope Plate Fairleads

Tow W ire CarpenterStopper Padeye

Synthetic L ineFairlead

Aft End of ARS 50 Tow ing M ach inery Room Looking Forward

ARS 38

ATS

T-ATF

4-9


Figure 4-5. Horizontal Padeyes.

Deck Plate

FullPenetration

Welds

Stiffener

Longitudinal

Longitudinal

FullPenetration

Welds

Deck Plate

Stiffener

Chain Stopper Padeye

CAUTION

Integral-Pin Padeye

Chain stoppers are designed to bear only 60% of the breaking strength of the chain. C hain stopper pad eyes should, therefore, not be used as a single attachm ent point for pendants or brid les. They should be used only as attachm ents for chain stoppers.

4-10


There are two types of horizontal padeyes inuse today.

• The integral-pin type comes with itsown pin, with the female threads locat-ed in the base plate of the padeye (seeFigure 4-5, upper sketch). A lockingdevice prevents pin rotation. This stylepadeye has a lower profile, so the mo-ment arm of the towing load is corre-spondingly lower to the deck. This al-lows for lower loading moments andeases the design of the structure. Addi-tionally, the integral-pin padeye allowsthe open or end link of a chafing chainto be pinned directly to the padeye, re-quiring no additional connecting jewel-ry.

• The shackle-style padeye is located onthe forecastle of most U.S. Navy ves-sels (see Figure 4-5, lower sketch). It isthe standard fitting for the attachmentof chain stoppers to the forecastle deck.When using horizontal padeyes, there isoften insufficient space to accommo-date the bolt of a safety shackle due tothe padeye’s low profile. Therefore,U.S. Navy chain stoppers are providedwith a specially forged, screw pinshackle that is appropriate for use in atowing rig. Chain stoppers and their as-sociated padeyes are nominally de-signed for only 60 percent of the anchorchain’s breaking strength. The strengthof chain stoppers and their associatedpadeyes must be considered when using

them as components in a towing sys-tem.

The vertical free-standing padeye comes intwo basic designs as shown in Figure 4-6 .The difference is in the shape of the eyehole.The eye of a shackle-pin type padeye is a cy-lindrical hole through the plate designed toaccept the pin of a connecting shackle. In thedipped-shackle type padeye, the hole is elon-gated and the bearing area of the hole isrounded so that the bow of the shackle canproperly bear against the end of the slot. Inthis case, the shackle’s pin is presented to thechafing pendant.

The vertical free-standing padeye is less resis-tant to lateral loads than the horizontal pad-eye. The free-standing padeye must be usedwith a towing fairlead strong enough to with-stand the lateral loads of the towline, to mini-mize the risk of tripping the padeye. Thewidth of the shackle-pin type padeye plateshould occupy 75 to 80 percent of the jawwidth of the shackle, to prevent it from rack-ing and creating loads that tend to open thejaw of the shackle.

CAUTION

Chain stoppers are designed tobear only 60% of the breakingstrength of the chain. Chain stop-per padeyes should, therefore, notbe used as a single attachmentpoint for pendants or bridles. Theyshould be used only as attach-ments for chain stoppers.

4-11


Figure 4-6. Vertical Free-Standing Padeyes.

Tension

Tension

G usset

G usset

S tiffener

S tiffener

D ipped-Shackle Type

Shackle-P in Type

D eck P la te

D eck P la te

Longitudin al

Longitudin al

Full Penetratio n W elds

Full Penetratio n W elds

4-12


The vertical free-standing padeye may have ahigher attachment point than the horizontalpadeye. This makes for larger loading mo-ments on the structure itself and on the attach-ment system to the ship deck or frame struc-ture. This in itself is not a disadvantage if thedesign is proper and those who rig the systemunderstand it.

4-5.4 Padeye Design

Figure 4-7 provides an acceptable padeye de-sign for situations where no suitable connec-tion point exists. Given the predicted towlinetension and a specific plate thickness, thechart provides the minimum hole diameterand the minimum distance from the hole tothe edge of the plate. Given the same predict-ed tension and a specific thickness for thecontinuous fillet weld, the chart also deter-mines how long the padeye must be.

To design a padeye using this chart, followthese steps:

a. Estimate the towline tension that the pad-eye will meet. In this case, use the ap-proximate towline tension as determinedfrom the results of the calculations in Ap-pendix G. In Figure 4-7, this number iscalled the load or force (F). Locate thislevel using the numbers on the far right-hand side of the chart.

b. Choose a particular plate thickness (t).Each thickness is represented by a soliddiagonal line. These lines are labeled inthe lower left-hand side of the chart. Findthe point where the plate thickness (t) in-tersects with the predicted load (F).

c. To find the minimum hole diameter (d),draw an imaginary line from the intersec-tion point straight up to the top of thechart. The diameter measurements aredisplayed across the very top of the chart.

d. To find the minimum length from the holeto the edge of the plate, find the pointwhere the diameter measurement (d) in-tersects with the broken diagonal line thatappears in the upper left-hand portion ofthe chart. Look on the right-hand side ofthe chart to find the minimum distance tothe edge (L). This minimum distance ap-plies in all directions around the hole, in-cluding above and below.

e. To determine the minimum length for thepadeye, choose a particular thickness forthe continuous fillet weld (T). Each thick-ness is represented by a dashed diagonalline. These four lines are labeled on thebottom of the chart on the right-hand side.Find the point where the thickness (T) in-tersects with the predicted load (F). Tofind the padeye length (l), draw an imagi-nary line from the intersection pointstraight up to the top of the chart. Thelength measurements are displayed acrossthe very top of the chart and are expressedin inches.

For example you are tasked with planning atow using an automatic tow machine with anew towing hawser. Per calculations you esti-mate the towline tension (F) to be 80,000pounds and the maximum plate thicknessavailable to fabricate a towing padeye is 1 1/2inches thick (t). Determine the diameter ofthe hole (d) required and the distance (L) thehole must be from the leading edge of theplate. By using Figure 4-7 we can determinethe diameter of the hole (d) required. Enteringthe left side of Figure 4-7 find the line corre-sponding to the plate thickness (t). Trace theline upward until it intersects with the esti-mated towline tension of 80,000 pounds fromthe right side of Figure 4-7. Draw a line verti-cally from this intersection to the top of Fig-

CAUTION

If time and the situation permit, adetailed analysis of the padeye andconnection should be made toavoid unexpected failure of either.

4-13


Figure 4-7. Minimum Padeye Design Requirements.

Weld Thickness, T (Inches)

Pla

te T

hic

knes

s, t

(In

ches

)

1/2

5 /8

3 /4

7 /8

1

1-1 /4

1-1 /2

1-3 /4

2

2-1/

42-

1/2

2-3/

4

5/8

1/2

3/8

1/4

Lo

ad, F

(10

00 P

ou

nd

s)

M in imum HoleDiameter,d (Inches)

Dis

tan

ce t

o E

dg

e, L

(In

ches

)

d = Diameter of Hole, in InchesF = Load, in 1000 PoundsL = M inimum Distance to Edge, in Inchest = Plate Thickness, in InchesT = Thickness of C ontinuous Fillet W eld, in Inches

= Length, in Inches l

Length, (Inches)l0 10 20 30 40 50 60 70 80 90

0

20

40

60

80

100

120

140

160

180

200

8

6

4

2

5 4 3 2 1 0

l

d

F

Lt

T

NOTE

Padeye material should be ASTM-36, ABS Grade A, or similar.

4-14


ure 4-7. Where this line intersects the top ofFigure 4-7 determines the minimum hole di-ameter (d). In this case, a minimum hole di-ameter (d) of 2 3/4 inches is required. We canalso determine the minimum distance fromthe leading edge of the hole to the edge of theplate (L) by using the vertical line previouslydrawn and determining where it intersectswith the dashed diagonal line crossing the topof Figure 4-7. Going right from this intersec-tion to the right of Figure 4-7 determines theminimum distance to the edge of the plate(L). In this case the minimum distance (L) tothe edge of the plate is 4 inches. Assumingthe fillet welds are 1/2 inch thick (T), whatlength (I) padeye is required? We can deter-mine the length of the padeye by finding theline on the bottom of Figure 4-7 that corre-sponds to the weld thickness (T). Trace thisline upward to the left until it intersects withthe estimated towline tension from the rightof the figure. Draw a vertical line from the in-tersection to the top of Figure 4-7. Where thisvertical line intersects the top of the figure de-termines the minimum distance to the edge ofthe plate (I). In this case the minimum dis-tance to the edge of the plate (I) is 16 inches.

The example is satisfactory for 80,000pounds of tension. To verify that the hole isof sufficient size, check the size of the shack-le required. If an automatic tow machine isused, Table 3-2 shows a factor of safety of 3is required or a 240,000-pound proof-loadshackle (2 1/4-inch Grade B shackle). The pinfor this shackle is 2 1/2-inches thick and willjust fit the hole in the padeye. If the tow wereto be performed without an automatic towingmachine, but with a chain pendant, Table 3-2would require a shackle factor of safety of 4.(Ref. D) and Tables D-7 through D-9 showthat the minimum required Grade B shacklesize is 3 inches, with a 3 1/4-inch pin. The 11/2-inch available plate can be used with alarger hole, taking care to maintain the mini-

mum distance to the edge of the padeye (L)required by the load and plate thickness.

4-5.5 Deck Structure

When designing and locating padeyes, it isextremely important to examine the below-deck structure. Towing padeyes producelarge local loads that cannot be supported bydeck plating alone. It is necessary to locatepadeyes atop both longitudinal and trans-verse members to adequately distribute load-ing to the surrounding structure, particularlyif the padeye is likely to be subject to sideloads. The longitudinal member should bealigned directly under the main plate of thepadeye. The transverse member location issomewhat less critical but should be locatedas close to the padeye as possible, preferablydirectly underneath.

4-5.6 Smit Towing Bracket

The Smit Towing Bracket consists of twovertical plates, similar to a pair of free-stand-ing padeyes, with an elliptical pin fitted be-tween them (see Figure 4-8) . The pin is fit-ted with a keeper key or locking pin and canbe released in an emergency. The principaladvantage of the Smit Towing Bracket is theease of breaking the tow connection, even un-der significant load. This is accomplished byremoving the locking pin and driving thestriking bar to port with a sledge, allowing the

CAUTION

This method yields a design with aminimum factor of safety of 3 for allfailure modes. For a stronger pad-eye, use a higher assumed load.For instance, if a padeye with a fail-ure load of 300,000 pounds is de-sired, use 100,000 pounds as thedesign load. The below-deck struc-ture must be checked or altered totransmit towing stresses to theship’s structural members. Simplywelding the padeye to the deckplating is not enough.

4-15


Figure 4-8. Smit Towing Bracket.

Pin

Connecting link,as appropriate

S IDE V IEW

Full Penetra tion W elds

FRO NT VIEW

StrikingBar

LockingPin

A

ASlot W elds

TO P V IEWA-A

CAUTION

Chain smaller than about 3 1/4” willrequire a pear-shaped link or ananchor shackle to connect to thestandard Smit bracket. Check di-mensions carefully.

4-16


main pin to slide out of the pear-shaped link.The design uses no shackle. This style of tow-ing attachment, like the vertical free-standingpadeye, is susceptible to tripping loads and isdependent upon the fairlead chock.

The standard Smit Bracket design is manu-factured in two sizes. The larger size will ac-cept the standard end link of a 3-inch chain.Smaller chains will require a large safety an-chor shackle or a pear-shape link. This linkmay possibly be found aboard the ship outfit-ted with such a towing bracket.

The smaller standard size Smit Bracket is de-signed to accept the end link of 2-inch chain,or the common link of 2 3/4-inch chain.

Sometimes the Smit Bracket design is adapt-ed to other dimensions. In all cases, the di-mensions must be checked carefully to ensurethat properly sized jewelry is available tomake the connection.

4-5.7 Towing Hooks

Towing hooks rarely are seen in the UnitedStates, but may be found on foreign tugs, es-pecially European tugs. They are heavy steelhooks mounted on vertical pins that allowthem to swing. Each hook is shock-mountedby using a heavy compression spring and fit-ted with a quick-release device that trips thehook, much like a chain stopper. The com-pression spring provides a small amount ofdynamic load relief for the towline system.

4-5.8 Chocks

Most tows make the towline connection ondeck. Whether using a bridle arrangement ora single point connection, the selection of thepoint where the towline (or bridle legs)crosses the deck edge is critical to protectboth the towline and the towed ship’sstructure. These robust points includebullnoses, closed chocks, and roller chockswith a generous radius (see Figure 4-9).Planned tows often will involve installationof a special fairlead, because the radii ofchocks and other f it t ings designed formooring are generally not sufficient fortowing. Emergency tows generally mustmake do wi th wha tever i s ava i l able ,remembering that towline chafing andstructural damage to the tow are probable. Inthis case, the towline component crossing thedeck edge will usually be a chain, heavier insize than otherwise would be required forstrength alone.

4-5.9 Fairleads

Fairleads are used to lead mooring linesaround obstructions and align them properlywith winches or capstans. Fairleads are locat-ed to accommodate lines from both sides ofthe ship. Fairleads usually have rollers to re-duce line wear.

4-6 Connecting Hardware (Jewelry)

Connecting hardware or towing jewelry usedto rig the tow system include a variety ofshackles, chain detachable links, special fit-tings such as flounder plates, splices and endterminations for wire and synthetic line. Thishardware is used to connect the various por-tions of the towline system to each other andto the tow (see Figures 4-10 through 4-14).Components of different sizes are connectedby using offset plate shackles and pear-shaped detachable links.

CAUTION

The large and small Smit Bracketsare designed to accept the stan-dard end link of 3-inch and 2-inchchains, respectively. They will di-rectly accept the common link ofconsiderably larger chains. Checkdimensions carefully in designingthe tow connection.

4-17


4-6.1 Shackles

General purpose Navy shackles are describedin detail in RR-C-271D, Amendment 1, Fed-eral Specification, Chain and Attachments,Welded and Weldless (Ref. E) and in (Ref.D). There are two types, two grades, andthree classes of shackles. Of these twelve cat-

egories, only four can be used as towline con-nectors. These are as follows:

• Type I Anchor ShacklesGrade A - RegularClass 3 - Safety Bolt and Nut

Figure 4-9. Types of Chocks.

Plain Closed Chock(Am erican M arine Standard)

Navy StandardClosed Chock

Plain Open ChockW ithout Keeper Bar

(Am erican M arine Standard)

Plain Open ChockW ith Keeper B ar

(Am erican M arine Standard)

4-18


• Type I Anchor ShacklesGrade B - High StrengthClass 3 - Safety Bolt and Nut

• Type II Chain ShacklesGrade A - RegularClass 3 - Safety Bolt and Nut

• Type II Chain ShacklesGrade B - High StrengthClass 3 - Safety Bolt and Nut

Examples of chain and anchor shackles areshown in Figure 4-10.

Navy shackles are permanently and legiblymarked in raised or indented lettering on theshackle’s body identifying the manufacturer’sn am e , t r a d em a rk , s h a ck le s i z e , a n drecommended Safe Working Load (SWL).SWL of both Grade A and Grade B Navysafety shackles is suitable for sizing hardwarefor lifting purposes. However, SWL cannotbe used in towing. Proof loads for a shacklemust be used vice SWL. Recommendedfactors of safety listed in Table 3-2 andSection D-14 describe appropriate methodsfor sizing shackles for towing.

Although screw-pin shackles are a commonlyused type of marine shackle and afford aquick and simple means of connecting anddisconnecting, the screw pin shackle shouldnot be used for connections in a towing rig.Due to the cyclic loading associated withtowing, it is possible that the pin could backout. Excessive vibration or alternate athwart-ship movement coupled with the surging ofthe towline may cause screw pin shackles tocome undone.

Navy shackles are made of forged steel;welding to forged steel shackles can reducethe strength of the shackle by as much as 30percent. Shackles should never be welded on,nor should pins be secured by welding. Thenuts on safety shackle pins are secured by asmall locking bolt, with two jam nuts to se-cure the pin nut. The locking bolt can bepeened over if desired. This belt shall be ap-propriately sized to ensure the head of thelocking bolt and the jam nuts are in contactwith the nut of the safety shackle. This beltshould not exhibit looseness of play. Ifchange out or breaking the shackle connec-

CAUTION

Special forged shackles, whenused with chain stoppers and car-penter stoppers, use carefully ma-chined screw pins and are permis-sible in towing. Such pins mustremain accessible for inspectionand service while in use.

CAUTION

Screw-pin shackles, other than thespecial forged shackles for stop-pers, must never be used for con-nections in towing rigs. The pincould back out due to the constantvibration set up by the hydrody-namic actions on the towline.

CAUTION

Shackles and other fittings fre-quently come with cotter keys orpins. Cotter keys are not used intowing. Replace cotter keys withlocking bolts with two jam nuts. Thehead of the locking bolt and the jamnuts shall be appropiately sized toensure the head of the lockingbolts and the Jam nuts are in con-tact with the nut of the safetyshackle.The locking bolt can bepeened over if desired.

CAUTION

Never weld on forged steel shack-les. The welding process canweaken the shackle.

4-19


Figure 4-10. Shackles.

4-20


tion are anticipated during the tow it is goodpractice to procure additional properly sizedlocking bolts prior to getting underway. Cot-ter keys should not be used in towing.

4-6.2 Other Connecting Links

It is often difficult to pass a safety shacklethrough the opening in a link of chain. Alter-native connecting devices when rigging chainand wire pendants, bridles, include:

• Plate shackles (see Figure 4-10)• Detachable links (Navy and Kenter

type)• Detachable anchor connecting links

(pear-shaped or detachable end link)

Plate shackles shown in (Ref. I) (Figure I-16through Figure I-18) are commonly used tomake connections to the flounder plate andto connect chain and wire pendants.

Detachable links are similar in shape to chainlinks, but can be disassembled into severalpieces (see Figures D-1 through D-3). Thisallows the link to be used as a connection be-tween chain and other components. Pear-shaped links have one end that is smaller thanthe other; they are used to attach componentsof different sizes.

The practice of welding detachable linksclosed to assure security of the towing rig isone that continually plagues towing com-mands. This practice should never bepermitted. It is much safer and more cost-ef-fective to use a hairpin to secure the taperedpin in the link. This ensures that the link willnot come apart and simplifies the eventualdisassembly and re-use of the link. Details formodifying detachable links for use with hair-pins are contained in (Ref. D).

Detachable links should not be used in in-stances where they might be subjected tobending or twisting.

4-6.3 Wire Rope Terminations

Three types of wire rope terminations arenormally used in Navy towing applications:swaged, spliced, and socketed (see Figure4-11)

The wire rope swaging process attaches fit-tings to wire rope by means of cold plasticflow of metal under extremely high pressures.The process uses hydraulic presses in con-

CAUTION

Never weld detachable links. Thewelding process can weaken thelinks.

NOTE

When inspecting chain, inspect thedetachable links to determinewhether they have been properlyassembled. The key slot must be inthe proper place and the matchmarks must be identical andmatched. This is necessary be-cause detachable links are hand-fitted to ensure proper assemblyand full strength. All assembledlinks should be visually inspectedand sounded.

4-21


junction with suitable dies. The swaged fit-tings are usually made of special alloy steels.An advantage of this process is low cost andhigh efficiency.

Swaged eyes are more common than splicedeyes. Existing swaging technology is so high-ly advanced that virtually all types of wirerope terminations can be made. Properlymade swaged eyes develop 85 percent of thestrength of the wire. Swaged terminations areapplied only to wire rope with wire ropecores. A fiber rope core wire can be swagedby replacing the fiber core at the terminationwith a strand of wire.

The second type of wire rope termination, thehand-spliced eye, has less strength than thebreaking strength of the wire. For instance, 15/8-inch to 2-inch hand-spliced eyes have 75percent of the breaking strength of the wire,while 2 1/4-inch and larger wires have an ef-ficiency of 70 percent. (See Table B-3 formore details.) Nonetheless, hand-splicing en-

joys continued popularity because of field re-pair capability.

A subset of a wire splice is the use of wireclips. This is the preferred over the hand-splice because it can withstand 80 percent ofthe wire’s breaking strength if completedproperly. Both the hand-splice and the wireclip termination have less strength than thebreaking strength of the wire and should beused only in an emergency (such as damageto or loss of the normal end fitting). See Table4-1 and Naval Ship’s Technical Manual(NSTM) S9086-UU-STM-010, Chapter 613,Wire and Fiber Rope and Rigging (Ref. F) forthe proper placement and number of wireclips.

The third type of termination, the poured zincor Spelter socket, is very common and is pre-pared in accordance with NSTM, Chapter613 (Ref. F). This termination will withstand100% of the rope’s breaking strength if pre-pared properly. The end of the rope is seizedand the strands are unlayed all the way to the

Figure 4-11. Types of Wire Rope Terminations.

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individual wires. This broomed end is insert-ed into the socket and secured in place withthe poured zinc. Epoxy-type poured socketsare not suitable for towing purposes.

Sockets are of two types, open and closed(see Figure B-8). The open socket is fittedwith a locking bolt and secured by a lockingbolt with two jam nuts. Frequently used. ontowing hawsers, the closed socket forms aneye with a solid bail (see Figure 4-12). Figure4-13 demonstrates using a safety shackle andthree standard pear-shaped detachables to

connect the standard hawser termination to awide range of chain sizes.

4-6.4 Synthetic Line Terminations

In general, the same methods are used forsplicing synthetic lines as for natural fiberline. When splicing a synthetic fiber line,however, exercise care to maintain the strand-ed form. If this is not done, the strand willcollapse and form a bundle of tangled yarns.Also, since the felting action (tendency to mattogether) of synthetic fiber is considerablyless than that of natural fibers, more tucks areneeded to produce a safe splice. This is gener-ally true for lines of plaited construction. Forguidance in splicing single or double braidedlines, consult the manufacturer’s recommen-dation or contact NAVSEA 00C.

The traditional standard end fitting for manilawas a tear drop wire rope thimble. With theadvent of high-strength synthetics, however,the eye of the line could stretch sufficiently toallow the thimble to capsize out of the eye. In

Figure 4-12. Towline Termination.

Lock With Machine BoltSecured With Two Jam Nuts

(Not Cotter Pins)

Open Socket Closed Socket

CAUTION

Whenever a poured socket is in-stalled on a wire rope, the conditionof the lubricant in the portion of therope near the socket should bechecked and new lubricant appliedto dry areas.

4-23


Figure 4-13. Pear-Shaped Detachable Links.

NOTE

Three different pear-shaped de-tachable links will satisfy all normalchain connection requirements.

4-24


addition, the higher strength of the syntheticline caused thimbles to crush and fail. To re-solve these problems, a variety of solid thim-bles have been developed and have becomethe standard end fittings used on syntheticline. Figure 4-14 shows the approved Navystandard thimbles.

4-6.5 Synthetic Spring

A spring is a line made of material exhibitingelastic behavior. In towing, a spring absorbsshocks due to dynamic loading of the towingsystem; this is one reason that the ocean tow-ing industry first became interested in nylonand other synthetic fiber lines. Nylon re-placed manila in hawsers and spring pendantsbecause of its superior elasticity and becauseit is smaller, lighter, and easier to handle thanmanila of similar strength. Polyester has re-placed nylon (see Section 4-3.2) in most syn-thetic line towing applications. (Ref. C) con-tains more information on synthetic springsand specifications for lines made of polyesterfiber that are approved for use as tow hawsersand springs.

A synthetic spring is sometimes inserted be-tween the towing pendant and the tug’s haw-ser for dynamic load mitigation. Seen mostfrequently in commercial towing, the springusually is a length of synthetic fiber rope,spliced together, arranged into a grommet(see Figure 4-15).

A grommet is fabricated by splicing a line toform one continuous loop. The two sides ofthe loop are pulled together around two thim-bles, and seized with small stuff to form thegrommet or strap shown in Figure 4-15. Theline used to make the grommet must be sizedso the assembled grommet will have a totalsafe working load that is equal to or greaterthan the design load for the towing system.

Although the line is doubled in the grommet,its strength is not twice that of a single line.There are losses in strength in the splices, sothat the assembled grommet is only 0.9 times

as strong as twice the original breakingstrength. For this reason, the line used for thegrommet must have a basic breaking strengthequal to at least 5/9 of a single line spring inorder to have the same total strength whenfabricated into a grommet.

An alternative to the grommet arrangementis the synthetic spring consisting of a lengthof line with a standard eye splice in each end.Each of these eyes will normally employ athimble. Since the spring is not doubled, theline diameter must be greater than that usedin the grommet, but should be easier to han-dle.

At present, there is no agreement on themethod to calculate the proper length of asynthetic towing spring. Commercial opera-tors generally use a spring of 200 to 400 feetin length. For additional guidance on sizing asynthetic spring, contact NAVSEA 00C.

For a 2-inch IPS fiber core hawser towing onthe brake a grommet made from 10-inchcircumference double-braided polyesterwould be required. This would be determinedby applying the required factor of safety forwire from table 3-2 which is 4, when usedwi th syn the t i c sp r ing . There fo re themaximum steady working load is 288,000 ÷ 4or 72,000 pounds. For a synthetic spring(polyester), the factor of safety is 6. Thus asingle polyester spring, capable of handling72,000 x 6 or 432,000 pounds is required.Use in a grommet configuration will require astrength of 432,000 x 5/9 or 240,000 pounds.So, a 10-inch circumference double-braidpolyester line, with a specified breakingstrength of 277,000 pounds, will be requiredfor this grommet. The grommet’s weight perfoot in air is approximately equal to that ofthe wire (6.74 vs. 6.72 lbs/ft), however, thegrommet will be far more bulky

4-6.6 Bridles

If the tow has a configurational, operational,or directional stability problem that makes a

4-25


Figure 4-14. Synthetic Line End Fittings.

Thim ble with End Link Closed Thim ble

Synthetic Rope Thim ble Nylite Thimble

Lock With Machine Bolt Secured With Two Jam Nuts (Not Cotter Pins)

4-26


single pendant inadequate, a bridle should berigged (see Figure 4-16 and Figure 4-18).Barges with square bows are rigged withbridles because of the stabilizing effectproduced by pulling from both legs of thebridle. Some barges have a hull form and/orappendages that increase the directionalstability of the barge; these barges may berigged with a pendant, rather than a bridle,attached on centerline. Chain is the preferredmaterial for bridles in deep ocean towing andoften complements or substitutes for the wirependant. Chain’s advantage over wire comesfrom its greater weight per foot, whichdeepens the catenary, and from its superiorresistance to chafing. As a rule of thumb, thesize of the chain to use for bridles andpendants should be at least equal to the size ofchain used to anchor the tow. An exception is

for larger ships, where the 2 1/4-inch beachgear chain carried by Navy towing/salvageships is appropriately sized for the power andhawser size of these tugs.

The flounder plate, or fish plate, is acomponent of a typical towing bridle. Aflounder plate is designed to distribute thetowing force of a tug’s hawser to the separatelegs of a bridle. The deployment of flounderplates on typical towing rigs is described indetail in (Ref. I). Flounder plate design isdetailed in Figures I-15.

For service craft up to 500 tons, the bridlemust be equal in size to the ship’s anchorchain, but not less than 1 1/4-inch. For craftgreater than 500 tons, a minimum of 1 5/8-inch chain shall be used. Ships do not needchain larger than 2 1/4 inches when towed by

Figure 4-15. Synthetic Line Grommet.

Figure 4-16. Towing Rigs.

4-27


Figure 4-17. Chain Bridles Using Plate Shackles and Safety Shackles.

B rid le Leg R etriev ing W ire

B rid le LegB rid le LegB rid le Leg

R etriev ing W ire

S afe tyS hack le

F lounder P la teP lateS hack le

D etachab le L ink

P endanto r

Lead C hain

P endanto r

Lead C hain

NOTE

See (Ref. A) for additional examples of bridle sizes of components.

4-28


U.S. Navy tugs. More powerful commercialtugs will require larger chain bridles. Non-magnetic chain and attaching hardware shallnot be used for towing bridles. The length ofeach leg of the bridle from the towingattachment point to the flounder plate afterrigging is completed must be equal to orgreater than the horizontal distance betweenthe attachment points. The bridle apex angle,defined as the angle between the two bridlelegs as measured from the flounder platevertex, shall be less than 100 degrees, with anoptimal angle between 30 and 60 degrees (seeFigures I-1, I-2, I-3 for an illustration).

All towing bridles, when rigged correctly,must have a backup securing system. This isnormally accomplished by using wire rope ofappropriate size (able to lace through chainlinks) and taking sufficient bights of wire froma second securing point (bitts, heavy cleats,etc.) and lacing the wire rope through the afterend of links in the chain bridle (no less thanfour bights). Size and number of bights of wireshould equal the strength of the chain used inthe bridle. If a towing pad is used to connectthe bridle to the tow, the backup wires must belaced through the portion of the chain that isforward of the towing pads. The securing pointshould be aft of the towing pad to preventsnap-loading. If a set of mooring bitts is usedas a securing point for the bridle on the tow,the wire should be laced thorough the chainlinks that remain astern of the bitts after thethree or more “figure eights” are secured onthe bitts. There must be a sufficient number ofwire clips (see Table 4-1) on each bitter end ofthe backup wire, aligned in the same direction(See (Ref. I) and (Ref. J) for tow rig designplans.)

It may not always be possible or practical torig a backup system (i.e., submarine towing).In these cases, additional analysis of the maintowing attachment may reduce the risk. Wherepossible, the attachment should be designed

to a breaking strength well in excess of theother components.

On some ships with large bows (e.g., CV, AD,AOR, or AFS) it may be necessary to rig aone- or two-shot chain pendant between thebridle flounder plate and the towing hawser.Both bridle legs should be the same size andlength and should be checked by counting thelinks when rigging is complete. All detachablelinks in the bridle legs and chain pendant mustbe locked with a hairpin (see Section 4-6.2).

Because chain and wire bridles and pendantsare often subjected to wear and abrasion dur-ing towing, it is recommended practice to“over design” to allow for wear, particularlyfor long tows. Tables in (Ref. B) and (Ref. D)provide the breaking strength and weight perfoot of various types of wire and chain. Thesetables can be used together with the calculat-ed towline tensions and factors of safety ob-tained from Table 3-2 to determine whetherthe available selected wire or chain is suffi-ciently strong.

Sometimes a heavy wire is used as a bridlefor short tows or emergency situations, butspecial care is required to minimize chafingof the wire and damage to the structure fromthe wire’s extremely hard material. If the hardpoint is a considerable distance from the fair-lead, a fairly short length of chain, sufficientto ride in the fairlead, may be used to saveweight and sometimes to simplify the finalconnection to the tow, such as when usingbitts as the hard point.

4-6.7 Pendants

A pendant is often used between the tow andtowing hawser to facilitate the rigging problemof connecting heavy components. This iscalled a “lead” or “reaching” pendant. Thelead pendant usually is wire rope and shouldhave the same breaking strength as the mainhawser unless it is intended to be the safetylink, in which case it will be of lower strength(see Section 4-7 for information on the “safety

4-29


link” concept). The pendant may be up to 300feet long to permit connection/disconnectionon board the tug, while maintaining a safestandoff under heavy weather conditions. Of-ten, the arrangement of the tension memberthat extends outboard of the bow of the tow issuch that chafing could occur. If a wire ropependant is used in this case, it must be care-fully protected from chafing, or a portion of itmust be replaced with chain to provide chafingprotection.

Chain pendants frequently are employedwhen using a single-leg attachment betweenthe hawser and tow. This attachment general-ly runs through a centerline bullnose, chock,or fairlead near the tow’s centerline. A chainextending forward from the apex of a towingbridle is also called a lead chain. The purposeof the lead chain is to add weight to the end ofthe towline system. This improves the springin the system by increasing the towline’s cat-enary. Sometimes the chafing/lead chain isthe tow’s anchor chain, which can be veeredto the desired total length. During emergencytows of merchant ships, the tow’s anchorchain is frequently used as a tow pendant.

A wire lead or reaching pendant is frequentlyused with a chain pendant to simplify con-necting up the tow.

4-6.8 Retrieval Pendant

A retrieval pendant is a wire rope leadingfrom the deck of the tow to the end of thetowing pendant or flounder plate. The retriev-al pendant facilitates bringing the tow gearback onto the foredeck of the tow so it willnot drag the seafloor or foul the ship’s ap-pendages when the tow is disconnected. Theretrieval pendant often is handled on the deckof the tow by a hand-powered winch or adeck capstan. It must be capable of beinghandled by the riding crew or by a boardingparty put aboard the tow. The wire must bestrong enough to lift the flounder plate, bri-dle, and/or pendant, but it is not intended to

be exposed to towing loads. Examples of re-trieval pendant rigging are shown in Figures4-16 and 4-18 and throughout (Ref. I).

To size a bridle retrieval pendant, use a 4:1safety factor for lifting bridle weight but noless than 5/8-inch wire rope.

4-6.9 Chain Stoppers, Carpenter Stop-pers, and Pelican Hooks

The term “stopper,” as used in seamanship,describes a device or rigging arrangementthat is used to temporarily hold a part of run-ning rigging or ground tackle that may comeunder tension. There are many types of stop-pers and methods of attaching them to thetension members. Most stoppers cannot be re-leased under load and require the held line tobe heaved in to slack the stopper and allow itsremoval. Some stoppers, however, such asthe pelican hook and carpenter stopper, canbe released when under load.

In towing applications, the stopper is usuallyconnected to the deck pad by means of chainshackles. It is used to hold a towing pendanton deck during the hookup and breaking of atow. A chain stopper is sometimes employedas a quick-release device (see Figure 4-18).Stoppers are nominally rated to hold a mini-mum of 60 percent of the breaking strength ofthe chain or wire for which they have beendesigned. This must be considered in theiruse. It is important not to confuse chain stop-pers with pelican hooks. Pelican hooks aresignificantly weaker than chain stoppers ofthe same nominal size and are unable to graspthe chain in the desired manner.

Pelican hooks can be used to grasp chainthrough a long link attached to the bitter endof a chain. They cannot grasp a chain in themiddle like a chain stopper can (see Figure4-18). They can be used as quick release de-vices, although they do not have the holdingstrength of chain stoppers.

Carpenter stoppers are used when it is neces-sary to develop a grip on a wire rope and hold

4-30


Table 4-1. U-Bolt Clips.

Recommended Method of Applying U-Bolt Clips to Get Maximum Holding Power of the Clip. The followingis based on the use of proper size U-Bolt clips on new rope.

1. Refer to the Table 4-1 (part 2) in following these instructions. Turn back specified amount of rope fromthimble or loop. Apply first clip one base width from dead end of rope. Apply U-Bolt over dead end ofwire rope with live end resting in saddle. Tighten nuts evenly, alternating form one nut to the other untilreaching the recommended torque.

2. When two clips are required, apply the second clip as near the loop or thimble as possible. Tighten nutsevenly, alternating until reaching the recommended torque. When more than two clips are required, applythe second clip as near the loop or thimble as possible, turn nuts on second clip firmly, but do not tighten.Proceed to Step 3.

3. When three or more clips are required, space additional clips equally between first two - take up ropeslack - tighten nuts on each U-Bolt evenly, alternating form one nut to the other until reaching recom-mended torque.

4. Prior to use, apply a load to test the assembly. This load should be of equal or greater weight than loadsexpected in use. Next, check and retighten nuts to recommended torque.

In accordance with good rigging and maintenance practices, the wire rope and termination should be inspectedperiodically for wear, abuse, and general adequacy.

Inspect periodically and retighten to recommended torque.

A termination made in accordance with the above instructions, and using the number of clips shown in part 2of this table, has an approximate 80% efficiency rating. This rating is based upon the nominal strength of wirerope. If a pulley is used in place of a thimble for turning back the rope, add one additional clip.

The number of clips shown in part 2 of this table is based upon using right regular or lang lay wire rope, 6 x 19classification or 6 x 37 classification, fiber core or IWRC, IPS or EIPS. If Seale construction or similar largeouter wire type construction in the 6 x 19 classification is to be used for sizes 1 inch and larger, add one addi-tional clip.

4-31


Table 4-2. Applying U-Bolt Clips.

Clip Size Minimum Number of

Clips

Amount of Rope to

Turn Back(Inches)

TorqueFt./Lbs.

Weight(Lbs. per

100)

1/83/161/45/16

2222

3 1/43 3/44 3/45 1/4

4.57.51530

6102030

3/87/161/29/16

2233

6 1/2711 1/212

45656595

477680104

5/83/47/81

3445

12181926

95130225225

106150212260

1 1/81 1/41 3/81 1/2

6778

34444454

225360360360

290430460540

1 5/81 3/422 1/4

8888

58617173

430590750750

70092513001600

2 1/22 3/433 1/2

9101012

84100106149

75075012001200

1900230031004000

If a pulley (sheave) is used for turning back the wire rope, add one additional clip.

If a greater number of clips are used than shown in the table, the amount of turnback should be increased proportionally.

The tightening torque values shown are based upon the threads being clean, dry, and free of lubrica-tion.

Above values do not apply to plastic coated wire rope.

4-32


it to the breaking strength of the wire (see Fig-ure 4-19). Advantages of the carpenter stopperinclude its quick application and release, abili-ty to develop full tension without damage tothe wire, and low maintenance requirements.

Three types of carpenter stoppers have beenused in the U.S. Navy:

• The “old WWII” style• The “improved 1948” style• The “modified-improved 1968” style

Only the last style listed is approved. It can beidentified by four heavy ribs on the hingedcover and will have a Boston Naval Shipyardtest date of 1968 to 1973 or be manufacturedby Baldt after 1973.

Refer to (Ref. E) for more information on theuse of stoppers.

4-6.10 Chafing Gear

Chafing gear is usually used to reduce wearon both the hawser and the tug’s structure.Chafing gear includes materials such as mats,battens, strips of leather, canvas, grease,

worming, parcelling, roundings, and serving(see Figure 4-20). Material specifically man-ufactured for chafing gear is also availableand works very well. These materials lessenor prevent towline chafing and are applied atthe point where the towline crosses the sternrail or other structure.

Another method to control chafing is to peri-odically adjust the scope of the wire to reducethe wear on any one point. The amount oftime between adjustments will depend on thebehavior of the tow and the sea state. This iscalled “nipping” the wire or “freshening thenip.”

4-7 Fuse or Safety Link Concept

A safety link, sometimes called a fuse pen-dant, is the point or component in every tow-ing rig most likely to fail at a predicted load.A safety link is analogous to a safety valve ora circuit breaker. The safety link’s primarycharacteristic is its predictability; it ensures aknown location and mode of towing systemfailure in event of an overload. The safetylink should not fail under the anticipated ten-sions of a planned tow. Tow preparing activi-ties should identify the safety link of the sys-tem and provide that information to theofficer responsible for the tow so that designlimits are not exceeded.

Since every rig will have a weakest point, it isoften prudent to intentionally incorporate asafety link to protect a critical portion of thetow system, usually the hawser, from a possi-ble overload. A wire rope pendant is usuallyselected as the safety link, and is sized tohave a 10 to 15 percent lower breakingstrength than the main tow hawser. If a tow-ing system overload occurs, the failure willnot damage the tow hawser and it can be re-connected.

The breaking strength considers the hydrody-namic resistance of the towline, which creates

WARNING

Old-style carpenter stopperswith smooth covers are con-demned and should not be used.These old models are made ofcast metal and are subject to ex-plosive brittle fracture upon im-pact. Serious injury to personnelmay result from flying frag-ments.

CAUTION

A carpenter stopper should not beused unless it is specially designedfo r th e lay, h e l ix , number o fstrands, and diameter of the specif-ic wire rope. The stopper and thewire should both be clean and freefrom sand or other abrasives.

4-33


Figure 4-18. Pelican Hook and Chain Stopper.

DetachableLink

Pelican Hook

Chain Stopper

WARNING

Do not confuse pelicanhook with chain stopper.

4-34


Figure 4-19. Carpenter Stopper.

4-35


a higher tension at the tug end of the hawser.Such pendants should never be subjected tochafing or other unusual service.

4-8 Line Handling Devices

Towing requires extensive manipulation ofline. Virtually all of the line used in towingoperations is far too heavy to be handled byanything other than machines and unique de-vices that have evolved in towing practice.The following sections detail the function ofline handling devices used in towing.

4-8.1 Caprails

The caprail is the riding surface on top of thebulwark (see Figure 4-21). The tow hawserbears on the stern caprail as it passes astern ofthe tug and enters the water. Caprails are in-

stalled in several configurations. They can befabricated from pipe or plate. On newer tugs,they have large radius surfaces contoured tothe tug’s deck layout. It is important to keepthe caprail smooth and free of nicks and burrsthat damage both synthetic and wire hawsers.In current design practice, the bearing surfaceof the caprail is hardened to a minimumRockwell C hardness of 40 to 50.

4-8.2 Towing Bows

Towing bows are transversely installedbeams or pipe that bridge the caprails on theafterdeck of the tug (see Figure 4-22). Theirfunction is to keep the towline clear of alldeck fittings and to furnish a protected areabelow the sweeping tow hawser where per-sonnel can pass safely.

4-8.3 Horizontal Stern Rollers

Horizontal stern rollers minimize chafingduring heave-in and payout (see Figure 4-20).A stern roller is a large-diameter roller, set inthe stern bulwarks on the centerline andfaired to the caprail. The roller rotates withthe movement of the wire, constantly chang-ing the contact point. This movement spreadsthe wear from the wire. Because it is alsohardened, it resists scoring and thus providesa smooth surface on which the wire rides. TheARS 50 Class is not equipped with horizontalstern rollers. Instead they have a large-radius,hardened steel transom that minimizes wearon the hawser.

Chafing gear should be used even if sternrollers are available. When towing with aconstant towing scope, chafing comes fromport/starboard movement of the wire. Hori-zontal stern rollers do not reduce chafing inthis manner.

4-8.4 Capstans and Gypsy Heads

Capstans rotate on vertical shafts and are usedfor line handling, but not as towing machines(see Figure 4-23). The prime mover of a cap-

CAUTION

Since the safely link is the weakestpoint in the tow system, this will de-termine the safe working load. Towplanners must ensure the safetylink is capable of withstanding allexpected loads.

WARNING

Motions of the tug and tow cancause the towline to change po-sitions rapidly and without warn-ing. Personnel must be aware ofthe potential danger of a sweep-ing towline and remain clear ofall areas that may be within thissweep.

CAUTION

Whenever the surface of a caprailbecomes rough, steps should betaken to repair or replace it to pro-tect the hawser. Caprails should bekept free of any nicks or burrs.

4-36


Figure 4-20. Chafing Gear and Stern Rollers.

H aw serC hafing

G ear

Vertica lR o llers

C apra il

H orizon ta lS ternR o ller

B ackstays

4-37


Figure 4-21. Caprails.

Figure 4-22. Towing Bows.

Large-Radius Caprail (Hardened)

Half-Pipe Caprail

Deck

Towing Bows

4-38


stan is often located below deck. This permitsthe capstan to be mounted so that the linetravels relatively close to deck level. A gypsyhead, which is similar to a capstan, rotates ona horizontal shaft and is usually powered asan auxiliary of a winch. Gypsy heads, likecapstans, are used for line handling, but notfor towing.

4-9 Sweep Limiting Devices

Sweep limiting devices restrict the horizontalsweeping of the wire across the fantail.

4-9.1 Vertical Stern Rollers

Vertical stern rollers tend the towline duringheave-in and payout, and during long-dis-tance straight towing by preventing the wirefrom sweeping across the deck and rail. Onnewer ships, the stern rollers or pins are nor-mally operated hydraulically from a remotelocation (see Figures 4-24 and 4-25). On-board the T-ATFs, the hook-shaped items oneither side (just outboard of each vertical roll-er) are hydraulically operated “capturehooks,” often used instead of the vertical roll-ers to provide lateral restraint for the towline.On the ARS 50 Class, the vertical stern roll-

ers drop when the side force at mid-barrelheight exceeds 50,000 pounds.

The presence of the towline in the stern roll-ers limits the maneuverability of the tug be-cause it moves the tow point from the H-bittsback to the caprail.

Vertical stern rollers act as a fairlead for thetowing machine. The long distance betweenthe stern rollers and the towing machine en-ables the tow hawser to naturally reel itself onto the drum and the level wind performs onlylight duty. The stern rollers are normally usedto capture the hawser and to assist when pick-ing up or disconnecting a tow. The verticalrollers may limit the amount of lateral move-ment that the tow hawser receives as the towyaws from port to starboard.

Vertical stern rollers are designed only as afairlead device and cannot structurally with-stand loads of the magnitude of which the H-bitts is capable. Strong side loads commonlyseen in towing situations could very easilycarry the assembly away. On the ARS Class,the rollers will fold down to their stowed po-sition at the lateral load of 50,000 pounds ap-

WARNING

The vertical stern rollers andNorman pins onboard the ARS50 Class ships will drop when aload of 50,000 pounds or more isapplied to mid-barrel height. Theresulting uncontrolled sweepingof the towline may injure person-nel or damage equipment.

CAUTION

Using vertical rollers may put thetug “in irons,” seriously limiting thetug’s maneuverability.

NOTE

Stern rollers should be properlymaintained and lubricated to en-sure rotation and smooth surfaceconditions. Rollers can become fro-zen and their surface areasgrooved and scored from towlinewear. Such conditions directly con-tribute to the abnormal wear of thetowline.

4-39


Figure 4-23. Capstans and Gypsy Head.

Capstan(With M achinery

Below Deck)

Winch

Gypsy Head

Capstan(With M achinery

Above Deck)

4-40


Figure 4-24. Stern of T-ATF 166 Class.

WireCapture Hook

Nylon LineCapture Hook

4-41


plied at mid-roller height. The towline is usu-ally restrained in a stern roller assembly onlyunder light sea conditions. The vertical sternrollers should always be dropped when ma-neuvering in restricted waters or rough seas.

When the towline rides against a verticalstern roller, it is being bent over a small radi-us. This causes towline fatigue and possiblefailure at a lower load. Chafing gear is re-quired on the towline when it is scheduled forlong periods in the stern roller. Slacking off afew inches, or “freshening the nip” regularly,is a good practice to reduce wear on the wire.Wire grease is often used to reduce chafing atthese hard points. This is especially true whenusing a capture hook (as on a T-ATF) becausethere is little room for chafing gear.

4-9.2 Norman Pins

The primary function of Norman pins is tolimit the arc of sweep across the stern (seeFigures 4-26 and 4-27). Norman pins alsohelp keep the hawser out of the propellersduring slack wire conditions. Ocean tugs gen-erally are provided with sockets along theiraft bulwarks into which Norman pins are fit-ted. Some tugs have two sets of Norman pins,with one set that may be inserted into thestern caprail.

Retractable or movable Norman pins havevarious designs, ranging from simple, remov-able round stock or pipe to remote controlled,hydraulically operated devices. On olderships, the round pins could be removed fromany socket and moved to another location.This necessitated personnel moving about onthe fantail and thus being subject to hazards;

Figure 4-25. Stern Rollers (ARS 50 Class).

Low ered Position of

Vertical Hydraulic

Pin

Vertical Hydraulic

Pins Raised

Davit Sockets

4-42


Figure 4-26. Norman Pins.

Forward Aft

Typical Norman Pin

Remotely Operated Norman Pin

4-43


with remote control, the procedures are nowsafer. Newer tugs and salvage ships, such asthe ARS 50 class, have remote controlled, hy-draulically operated Norman pins in fixed lo-cations. On board the ARS 50 class, the Nor-man pins are set to drop when the lateral forceat mid-barrel height exceeds 50,000 pounds.The hazard potential is formidable. When thepins start inclining toward the horizontal, thewire (with 25 tons force propelling it) canjump the pin and sweep forward.

Current design practice requires that the wirebearing surface of the Norman pins be hard-ened to a minimum Rockwell C hardness of40 to 50.

4-9.3 Hogging Strap

The hogging strap limits the relative move-ment between the towline and the stern inboth vertical and horizontal planes (see Fig-ure 4-28). Movement in the vertical plane iscaused by the stern of the tug dropping fasterthan the towline or by a tow ranging up. Ahogging strap can be attached to the towlinewith a shackle or a special saddle-like fitting.The limitation of the shackle is the high con-centration of load it imposes on the hawser towhich it is attached. Saddle-like fittings arepreferred because they have larger radii; thisincreases the area of contact and distributesthe load over a wider arc.

Because the hogging strap transfers the towpoint aft from the H-bitt, it can cause reducedmaneuverability.

4-9.4 Lateral Control Wire

A l a t e r a l c on t r o l wi r e i s s im i l a r i nconfiguration to the hogging strap, but it hasthe added feature of variable scope. Instead ofa fixed-length strap holding the towline to thedeck, a snatch block is secured to the deckand the lateral control wire is led through it toa deck winch, lateral control winch, orcapstan. In this manner, the line can be fullyslacked to let the towline sweep free or can betaken in to give either partial or full snugginglike a hogging strap. The lateral control wireis helpful in keeping the towline out of thepropellers during slack wire conditions.

A dedicated lateral control winch, limited toapproximately 2,000 pounds straight linepull, is available on the ARS 50 Class ships.

Like the hogging strap, the lateral controlwire moves the tow point aft and can limitmaneuverability.

4-10 Cutting Gear

Most Naval ships are equipped with oxy-acet-ylene cutting equipment. Additionally, sometugs and most salvage ships are equippedwith hydraulic cutters.

CAUTION

A hogging strap may be necessaryto prevent the towline from jumpingthe stern rollers when towing ahigh-bowed ship at short stay. Ahogging strap may be subject toexcessive vertical loads. Careshould be taken not to part thestrap. Failure of a hogging strapmay result in the loss of tug controlor ranging up by the tow.

WARNING

Wire rope stretches far less un-der load then most natural andsynthetic fiber lines. If it fails un-der high loads, wire rope has asmaller zone of danger to by-standers if loose ends “snapback.” The elongation underload is sufficient, nonetheless,to be dangerous. The recoil canbe extremely violent and all per-sonnel should stay well awayfrom any potential recoil path.

4-44


For cutting chain, the oxyacetylene or exo-thermic cutting equipment is most suitable;hydraulic cable cutters may be better for cut-ting wire. Personnel safety is paramountwhen cutting any member of the tow assem-bly; therefore, every effort should be made toreduce the tension. This is particularly truewhen cutting wire and synthetic lines. Thegreater the distance between the person doingthe cutting and the cutting point, the greater

the safety factor. Securing the cutting torch toa boat hook is a good practice. Seizing a wirehawser on both sides of the intended cut is al-so a prudent measure. Cutting a synthetic linewith an axe is hazardous and should not bedone under tension. The use of stoppers tocontrol snap-back decreases the hazards in-volved when cutting any chain, wire or syn-thetic line.

Figure 4-27. Norman Pin Use.

Norm an Pins

45 Pivot Po int

H -B itts

Tow Should Never BeA llowed to Pass Abeam

M axim um Lim itof Haw ser Angle with

Aft Norm an P ins Up

SternRollers Free Sw eep Area of Haw ser

4-45


4

Figure 4-28. Rigging of Hogging Strap on Ships without Horizontal Stern Rollers.

Shackle o r Sadd le-Type FittingTow Haw ser

Restrains tow haw ser up and dow n.

Lim ited Lateral Sw eepTie-dow n point needs to be w ell aft on the fantail to be effective in restra ining the hawser.

Tow Haw ser

Caprail

Safety Shackles

Hogging/Grom m et Strap

Yaw Position

-46


Chapter 5

TOW PLANNING AND PREPARATION

5-1 Introduction

Because each tow is unique, the planning,preparation, and execution have to be careful-ly worked out each time. Tow preparationsmust be meticulous, uncompromising, andfarsighted. Fleet Admiral Nimitz provided avaluable guide for any ship operation whenhe said:

“The time for taking all measures for a ship'ssafety is while still able to do so. Nothing ismore dangerous than for a seaman to begrudging in taking precautions lest they turnout to be unnecessary. Safety at sea for twothousand years has depended on exactly theopposite philosophy.”

Incidents involving loss of tows have demon-strated an absolute need for a thoroughlyprofessional approach to towing. Tows havebeen damaged and lost by inattention to thebasic principles of proper planning and prepa-ration. The plan must cover all aspects ofthe tow and anticipate worst case scenarios.Planning a tow includes training personnel,practicing basic procedures, and devising safeevolutions.

This chapter discusses tow planning and pre-paration in general terms.

5-2 Lessons Learned

As Naval towing has evolved, several obvi-ous lessons have been learned. A list of theselessons first appeared in the first Navy towingdocument, COMINCH P-03, and are as validand meaningful today as they were in 1944when the document was published. The docu-ment noted that in the planning and task

analysis for towing operations, avoid the fol-lowing situations when possible:

• Keeping tugs waiting while tows arebeing prepared or disposed of after themission has been accomplished. In thisconnection, when the draft of the tow-ing tug is too great for the depth of thewater at either terminal, advance ar-rangements should be made to deliveror to take over the tow before the arriv-al of the deep sea tug.

• Employing large tugs to do work thatavailable smaller and less powerful orless seaworthy tugs can do.

• Employing small tugs to undertakework beyond their capacity.

• Employing tugs designed or especiallysuited for combat zone duty in rear ar-eas. Large salvage tugs are well suitedfor combat towing and for emergencysalvage or fire fighting in combat areas.

• Employing tugs that cannot survivemoderate damage in forward combatareas. Survival factors include stability,reserve buoyancy, and subdivision, aswell as being armed to ward off attacksby enemy planes.

• Routing tugs with large tows over areaswhere the water is too shallow for thehawser ’s catenary. Arrangementsshould be provided for shortening thetowline where necessary. Tows are fre-quently lost or involved in difficultiesdue to the towline fouling on sub-merged objects.

• Unnecessarily employing tugs forstandby duty on salvage or rescue oper-ations. Tugs should not be ordered tostand by unless there is a definite possi-bility that their services may be neededand they are capable of rendering theservice likely to be required.

5-1


• Diverting rescue tugs from areas wheretugs equipped with rescue facilities,such as salvage or fire fighting, may berequired.

• Employing tugs for tows that could beundertaken by other craft scheduled tomake the same passage, or by a shipthat could be more easily made avail-able than a tug.

5-3 Staff Planning

The underlying issue of staff planning is se-quencing all the required aspects of preparingthe tow. Orchestrating preliminary, opera-tional, and post mission requirements is afleet or group staff planner’s mission. Caremust be taken in planning a tow to select theproper gear and deciding on a route and de-parture date. In doing so, a tug may avoid ad-verse weather conditions that might subjectthe towing systems to loads that exceed itssafe working load.

5-3.1 Towing Ship Selection

In an ideal world, the staff planner would beable to match tug characteristics to the type oftow to perform the tow in a cost effectivemanner. Because the fleet has been reducedin size, planning appears to be easier becausethe potential combinations of choices is fewerwith fewer towing assets. In reality, planningis more difficult because the staff planner of-ten cannot properly match the size and resis-tance properties of the towed vessel to thehorsepower and bollard pull of the towingvessel. Fleet planners are sometimes forced toimproperly size the ocean tug to the tow.Consequently, the only vessel available totow a small, low resistance hull may be thelargest and most powerful ocean going tug inthe fleet. In many cases, routine tows not re-quiring the capabilities and manning of a fleetsalvage tug can be contracted through MSC.

This reserves the fleet salvage tug for opera-tions for which it is best suited.

5-3.2 Operational Considerations

5-3.2.1 Support

The staff planner must determine what sup-port will be required for the tow at the pointof origin, en route, and at the point of debar-kation. Included in support considerations areindustrial support required for preparing thetowing rig, temporary berthing and messingfor riding crews, refueling, provisioning, re-turn of any special issue equipment, taskingorders, and the logistics of tug assist for get-ting underway and disconnecting. Many ofthese functions may be passed to the towingship Commanding Officer.

5-3.2.2 Manned Tows

The tow sponsor is responsible for providingriding crews for the towed vessel. While di-rect financial support for riding crew trans-portation, messing, and berthing also resideswith the tow sponsor, there are aspects of ariding crew that have to be integrated into theplanning process for the towing ship. Staffplanners will determine:

• If there is a need for joint training of theriding crew with the towing ship’s crewfor a special tow

• If the riding crew will be berthed on thetowing vessel

• How long before the tow departure theriding crew will have to be temporarilyassigned to the towing ship.

5-3.2.3 Tug Selection

When selecting a tow ship and support crew,consideration must be given to any anticipat-ed complications of the tow. For instance, ifdamage control or salvage may be required,(towing a rescued vessel) experienced sal-vage personnel are essential. A fleet salvagevessel should be selected or a similar vesselsupplemented with a salvage crew. Commer-

5-2


cial tow ships have limited manning, and al-though capable, may be insufficient in num-ber to perform all required tasks withoutadditional personnel.

5-3.2.4 Unsuitable Tows

Many ships are unsuitable to be towed in theopen ocean. Table 5-1 lists vessels that arenot recommended for open ocean towing,along with supporting rationale as to whythey do not qualify. Of course, any vessel canbe towed, but the vessels listed in Table 5-1cannot be towed without serious risk. Thesecraft can be made safer by correcting the dis-qualifying condition, but in their normal op-erational configuration, they should not betowed in the open ocean.

5-3.3 Selecting the Navigation Track

The transit course should be determined usingpilot charts as an aid. Locations along or nearthe track where a lee can be found should benoted. These can be utilized, when practica-ble, to effect inspection, repair the tow, ortake shelter in heavy weather. Routine navi-gational issues must be reviewed in the con-text of having a vessel in tow. Pilot charts,navigational charts and Fleet guides must beconsulted for any restrictions for towing ingeneral, as well as the particular tow. TheNavigator shall be familiar with charts of allareas to be crossed, including potential safehavens. He shall account for geographic fea-tures such as lees of headlands, effects of riv-er outflows, and tidal currents to determinethe relative safety of a particular haven.When entering a safe haven, the Navigatorshall be aware of water depths where the towwire may snag, and stand ready to recom-mend shortening the towline as required.

An early consideration in selecting thenavigation track is the predicted weather enroute. Frequent contact should be made withthe Naval Meteorogical and OceanographicalCenter (NMOC) to maintain an up-to-datew ea t he r p i c t u re , a nd a d j us t e d t r a c k

accordingly. Anticipated heavy weathercould require selecting a larger, morepowerful towing asset. The towing commandwill use the Optimum Track Ship RoutingSystem (OTSR) to predict the weather alongthe planned navigational track and make anychanges to the track that adverse weatherdictates. A longer course on a favorableweather track should be selected in favor of ashorter one with unfavorable weather. Littletime is gained by taking a shorter trackthrough bad weather.

Once the navigation track has been selected,calculate total distance and estimate fuel re-quired for the type of tow. If refueling is re-quired either at the tow termination or enroute, contingencies must be formulated earlyin the planning process.

It should be clearly understood in advance byany vessels taking the towed vessel into itsberth how close to shore the ocean tug ex-pects to remain connected. The towing vesselmust hand off the tow to harbor tugs and pi-lots and pilot’s vessels at some point beforemooring. If there is confusion, an accidentmay occur. Conversely, it should be under-stood how far from shore the harbor tugs areprepared to retain charge of the tow. Bothparties should advise of any weather and seacondition limitations on their abilities. If pos-sible, a meeting of all vessel captains in-volved (tow ships and harbor tugs) should beconducted prior to getting underway. Alltransfer procedures and special requirementscan be worked out at this time.

5-4 Towing Responsibilities

Primary commands involved in a towing op-eration are the tow sponsor and the towingcommand. Frequently the sponsor will taskand fund an assisting command to performsome of the tow preparations. This sectiondetails the definitions, interrelationships, and

5-3


Table 5-1. U.S. Navy Craft Not Recommended for Open-Ocean Tows.

CRAFT CLASSIFICATION

REASONS FOR NON-RECOMMENDATION

LCU, YCU Landing CraftLCM8, LCM6 Landing CraftYFU, UFB, LWT

Low freeboard. Light construction of bowdoor locking mechanism. Structure can bestrengthened to reduce risk.

YFNG, YFNX Lighter,YNG Gate Craft,YSR Sludge Removal Craft

All have deck-mounted equipment whichrequires installing special protection beforetowing.

YPD Pile Driver,YD CraneLSMR

All tend to be top-heavy (have high centerof gravity) and may also have poor water-tight integrity. Topside high weights mayrequire removal and stowage prior to open-ocean towing to attain adequate stability.All require special preparations.

YSD (formerlySeaplane Derrick),YM Dredge

Low freeboard and high weights reducesea-keeping ability. Weights may requireremoval and stowage to improve stability atsea.

YTL Small Harbor Tug PTF Patrol Boat

Hulls considered too small for open-oceantows. Should be transported as deck cargo.

Mini-ATC, LCPLMK2, MK3, MK4, MK5personnel boats

Low freeboard. Light construction withpoor watertight compartment and weak tono attachment points for towing.

MK1, MK2 65’ utilityboats, MK4 50’ utilityboat, MK3, MK4 40’utility boats

Low freeboard. Deck mounted equipment.

5-4


specific responsibilities of the parties in-volved in a towing operation.

5-4.1 Sponsoring Command Responsi-bilities

The sponsoring command is the commandrequiring a tow, and is responsible for prepar-ing the tow for sea. Basic responsibilities ofthe sponsoring command include:

• Reviewing applicable Type Command-er and Fleet CINC numbered instruc-tions and operational orders

• Preparing the tow

• Assembling towing rig

• Completing Certificate of Seaworthiness(see Appendix H)

• Determining when there is a ridingcrew requirement

• Designating a receiving activity

• Returning all towing equipment, in-cluding towing bridle, to preparing ac-tivity or tow originator once the tow hasbeen completed.

• Towing machine/towing winch certifi-cation

• Tow hawser certification

• Commercial vessels (U.S. Coast GuardInspected) - Master’s Towing Certifi-cate

5-4.2 Towing Command Responsibilities

The towing command is the command thatperforms the tow. The Commanding Officeror Master is responsible for:

• Determining sailing date and time

• Determining the transit route

• Selecting towing rig and determiningtrim conditions

• Inspecting and accepting the tow

• Maintaining and protecting the tow dur-ing transit

• Delivering the tow and obtaining a re-ceipt from a receiving activity

5-4.3 Assisting Command Responsibilities

An assisting command is often a naval ship-yard, private shipyard (through the cognizantSupervisor of Shipbuilding, Conversion &Repair, SUPSHIP) or Naval Station. Assist-ing command responsibilities may include:

• Designing a towing hawser system

• Installing temporary towing hard pointson the tow

• Installing temporary alarms or electri-cal systems on the tow

• Supplying a riding crew

• Providing temporary messing and ber-thing for a riding crew at ports of em-barkation and debarkation

5-5 Review Instructions and Operational Orders

An important preliminary step in any tow is areview of pertinent instructions that governthe type of towing to be performed. Fleet andType Commander instructions are providedfor general towing procedures and periodicreporting procedures to be followed duringthe tow. Specific guidance may also be pro-vided for a particular type of tow, such asNAVSEAINST 4740.9 (Series) for towingdefueled, nuclear powered submarines. Oper-ational tasking, such as a Letter of Instructionsent via naval message, will also be providedto any vessel performing a tow. All governinginstructions should be reviewed for applica-bility to the unique tow being performed.

5-6 Riding Crew Requirements

A riding crew can add immeasurably to thegeneral safety of the tow. The Navy com-

5-5


mand requesting a tow should make a recom-mendation after considering personnel safetyand the value of the tow. Safety consider-ations must be based on the crew’s influenceon tow safety rather than the tow’s influenceon crew convenience. Value of the tow can beeither its replacement cost; value of its safeand timely delivery; or cost of consequencesof loss from a tactical, strategic, or public re-lations standpoint.

Rescue tows should have personnel onboard, if possible, to make the tow connec-tion and to respond to changes in the tow’smaterial condition. A riding crew can also re-spond to emergencies such as fire, flooding,hawser or bridle chafing, and towline loss.The tow must be adequately supplied andequipped to support a riding crew. Crew ac-commodations should include berthing,messing, and sanitary facilities, all of whichmust be properly ventilated.

Under normal conditions, most plannedpoint-to-point tows are undertaken without ariding crew. All tows can be unmanned ifproperly planned.

Riding crews shall be limited to personnel re-quired for maintenance and security duringthe voyage.

Approval to assign a riding crew must comefrom the Fleet Commanders- in-Chief(CINCs) in accordance with existing direc-tives. Factors governing a decision to assign ariding crew include:

• Safety of the riding crew

• Reduction of risk of towed ship loss byassigning a riding crew

• Material condition of the tow

• Flooding alarms and other monitoringdevices installed on board

See section 5-7.1 for more considerations.

5-7 Preparing the Tow

A tow’s hull design may require taking nu-merous steps in preparing to tow. Examplesinclude cranes, pile drivers, dredges, dumpscows or other equipment designed for oper-ation in sheltered waters. Preparing the towmay include removing high weights, secur-ing booms, dredge ladders, and other deckstructures; adding or removing ballast or ad-justing trim; stiffening the hull and perform-ing other functions. Heavy welded bracketsmust be used to secure heavy movable ob-jects and a tow should always be secured forthe worst sea conditions. Expect large anglesof roll and pitch and secure all heavy objectsaccordingly.

Hulls not considered seaworthy for open-ocean tows should be transported as deck car-go or on board a floating dry dock, semi-sub-mersible vessel, or LSD type ships.

5-7.1 Installing Flooding Alarms, Draft Indicators, and Other Alarms

All unmanned tows shall be equipped withflooding alarms. Flooding alarms indicate tothe towing ship that there is a problem withthe tow, allowing corrective action to be tak-en before the tow sinks. The tow preparingactivity is responsible for installing floodingalarms. Unmanned tows must be equippedwith high and low alarms rigged with multi-ple bulbs, and independently wired floodingalarm lights in all major compartments clos-est to the keel.

A schematic diagram of an acceptable flood-ing alarm is shown in Figure 5-1. No attempthas been made to provide detailed specifica-tions or installation instructions because thesevary with the type and size of the tow. Thenumber and location of the electrode blocksor alarm switches to be installed in an un-manned tow are determined by the activitypreparing the tow and agreed to by the towingcommand. Installation should be sufficient to

5-6


Figure 5-1. Example of a Flooding Alarm Schematic.

NOTE

This sam p le diagram is no t intended to restric t o r lim it the num ber o f a larm sconsidered necessary to p rov ideadequate pro tection to a ll im portantw ate rtight spaces.

Flashing LightAssembly

Flasher LightsRoad Construction TypeVisible 360°

Smashproof WireSTK No. G-6145-191-1962

Flooding AlarmContact MarkerAssembly

3’ 1’

5-7


provide coverage of major hull subdivisions.Alarms should be securely rigged and proper-ly serviced to ensure performance and reli-ability.

5-7.1.1 Flooding Alarm Sensor Mounting Requirements

There are a variety of alarm types. An elec-trical contact alarm that closes its circuitwhen water makes contact is a workablealarm most of the time. If used in the engineroom, however, oil in the bilge may coat thewires as flooding progresses and render thealarm useless. Carefully consider the practi-cality of each proposed alarm location. Inno-vation is advisable.

Refer to the following guidelines when in-stalling flooding alarm sensors:

• Installing flooding alarms may requirepiercing watertight decks and bulk-heads. Penetrations should be as high aspossible. Every attempt should be madeto use watertight penetrations, or tominimize the size of the penetration.

• Low level alarm sensors shall be in-stalled one foot from the lowest pointin the compartment, assuming that theship is in a bow up position whilewaterborne.

• High level alarm sensors shall belocated three feet above the low levelalarm sensors.

• Float type switches are recommended.However, if using sensing probes forflooding alarm sensors, they shall besecurely mounted on a suitable noncon-ductive, nonporous material such asMelamine. Plywood is not a suitablematerial; C-clamps are not suitable se-curing devices.

• Areas where flooding alarms are to beinstalled shall be certified gas-free toprevent explosion and fire from electri-cal contact sparking.

• When placing alarms in a wide flat-bot-tomed compartment. It may be benefi-cial to place an alarm both port andstarboard.

5-7.1.2 Wiring and Power Supply Requirements

• Wire the flood alarms so that any lowlevel alarm will activate the low levellights and that any high level alarm willactivate the high level lights. Existingships wiring may be used to supportthis installation.

• Batteries should be sized to support allflood alarms for continuous 24-houroperation. Sufficient electrical powershall be provided for all lights andalarms for the duration of the tow sothere is no need to board the towed shipto change power supplies. Power forthe flooding alarm system should beseparate from the power source for thenavigation lights.

• Secure and protect all wiring from anychafing, and protect all topside wiringfrom weather damage.

• Where practical, install a wiring boardto act as a compartment indicator. Itmust be wired so that a low level alarmin a given compartment will activate anindicator that identifies the floodingcompartment.

• NAVSEA has developed a towingalarm system that utilizes a radio linkfrom the towed ship to a console on thetug. This system allows the tow ship todetermine the location of the floodingwithout boarding the tow. Indicationsof low battery power and ground faultsfrom alarm wires are also indicated.This system has been packaged for atsea use and includes all power sources,lights, alarms, and wiring. This systemis available for issue from the ESSMwarehouse.

5-8


5-7.1.3 Alarm Lighting Requirements

• At least two high alarm and two lowalarm lights shall be installed. The highlevel alarm lights shall be positionedfour feet above the low level alarmlights. The alarm lights shall be mount-ed topside to be visible from the shipsin company.

• The high level alarm strobe lights shallhave an amber lens.

• The low level alarm strobe lights shallhave a white lens.

• Flooding alarm lights should be checkedto ensure their visibility during daylighthours. The lights shall be visible from360° and at a minimum distance of2,000 yards during bright daylight.

5-7.1.4 Audible Alarm

An audible alarm can be used to provide noti-fication during fog or heavy rain. This alarmmust be loud enough to be heard by ship’spersonnel while underway. Items such as foghorns can be a considerable power drain. It isrecommended that these be rigged for inter-mittent operation (a few seconds of sound;every few minutes) to avoid needing exces-sive batteries.

5-7.1.5 Requirements for Other Alarms

Depending upon the tow, its equipment andcargo, other alarms such as fire, radiological,or combustible gas may also be required.Specifications will be provided to the activi-ty preparing the tow. Wiring and poweringrequirements should apply to all additionalalarms.

5-7.1.6 Draft Indicator Requirements

The tow should have large, special waterlinemarks to allow a towing ship to check trim ofthe tow visually by day and by searchlights atnight. Marks should be painted on the bow,stern, and midships on both sides, in highlyvisible paint. These marks need not be paint-

ed below the waterline, but they must give thetow ship a clear indication of a change in thetow’s trim. See Figure 5-2 for samples of wa-terline marks.

5-7.1.7 Towed Vessel Propeller Preparation

A towed vessel’s propellers can be a valuabletool or an unpleasant obstacle during a tow.In either case, they require special attention.Tow planners must decide whether to removepropellers, lock them in place, or allow themto free-wheel. The procedure of free-wheel-ing propellers is not recommended, but can-not always be avoided.

5-7.1.8 Removing Propellers

For long-distance tows, fixed-pitch propellersmay be removed to decrease towing resis-tance. For some hull forms, however, the add-ed drag of locked propellers may be desirablefor better directional stability. Tow plannersmust also consider the economic feasibility ofremoving the propellers.

It is helpful to consider the vessel’s futurewhen determining disposition of it’s propel-lers. If the vessel is being transferred, but notdecommissioned or drydocked, it will proba-bly be best not to remove the propellers, asthere would likely be considerable cost forre-installation. This high cost may offset anyfuel savings gained by the reduced resis-tance.

If the vessel is being prepared for tow at a sitethat may find use for a propeller destined forscrap (spares for sister vessels) it may be ben-eficial to remove propeller prior to towing.

A propeller creates considerable resistance ineither a locked or freewheel configuration.This resistance adds a large contribution tothe directional stability of the tow, particular-ly in the absence of rudder control. If the pro-peller is removed, the directional stability ofthe tow should be examined. A water brake orsimilar device may be added if stability is ex-pected to be a problem.

5-9


Controllable pitch propellers may be left in-stalled if set in “maximum forward” pitch,where they offer the least resistance to tow-ing. They may also be set in a “zero pitch”condition for added drag if desired.

5-7.1.9 Locking Propellers

When propellers remain in place and are notallowed to free-wheel, lock the shafts by aninstalled shaft-locking device or by anothersuitable method as illustrated in Figure 5-3.

5-7.1.10 Allowing Propellers to Free-Wheel

If any type of propeller must be allowed tofree-wheel due to the condition of the towedvessel’s propulsion train, propulsion machin-ery must be disconnected from the shafts oradequate lubrication provided.

A means for lubricating the shaft bearingsmust be provided. The stern gland on theshaft will normally be water-lubricated. Pro-vision for this must be made while at thesame time ensuring that the water does notflood the space.

5-7.1.11 Stern Tube

There should be no leakoff at the stern tube.Equip the tow with extra packing for thestern gland to allow emergency repair duringtransit. The gland should be tightened sothere is no leakage with at least two inches ofroom before its tightest position. Use lock-nuts to prevent backing off.

5-7.2 Ballasting or Loading for Proper Trim

Proper trim is important because it can affectstability, towing characteristics, and speed.

Shifting ballast, fuel, cargo, or equipment onboard can bring about desired trim.

Follow these guidelines when adjusting thetow’s trim:

• Trimming by the stern has proven to bea stable and directionally true towedship load condition. A trim of one footby the stern for each 100 feet of thetow’s length has proven a good trim-ming rule; deep draft tows use some-what less than one foot per 100 feet.

• Completely fill all tanks or leave themempty to ensure there is no adversefree-surface effect.

• Ensure all normally dry compartmentsare dry to avoid adverse stability effectsof free surface areas and to providegreater reserve buoyancy.

• Ensure bilges are free of oil and waterto ensure that bilge flooding alarms arenot tripped by sloshing water. Oil in thebilge is a fire hazard and could foulalarm electrical contacts.

• Close all sluice valves to preventliquids from flowing between ad-joining tanks.

• Ballast landing craft or craft with bluntor raked bows to prevent heavy pound-ing. Pounding can be very destructiveto the vessel’s bottom and other struc-tural members. Preventing or reducingpounding also reduces shock loads onthe towing rig.

• Ensure the tow has zero list.

5-7.3 Ballasting for Proper Stability

Stability of the tow, in the case of an unmodi-fied or undamaged Navy commissioned ship,can be determined by reviewing Chapter II(a)of the ship’s Damage Control Book. Similarinformation for commercial ships should be

CAUTION

Do not allow main reduction gearsto rotate unless they are properlylubricated. This requires full lube oilpressure.

5-10


Figure 5-2. Special Draft Markings.

6"

6"

3"

12"

36"

30”

20”

Bow & Stern

Midship

5-11


Figure 5-3. Securing the Propeller Shaft.

Fillet W eld

Flange

Shaft

Shaft

Shaft

Flange

Flange

Bolt

Steel Securing Strap

W elded or Bolted



Bolt

Bolt

W elded or Bolted

W elded or Bolted

A. Heavy plate, 3/4″ to 1″ cut toaccommodate two (2) of thecoupling bolts.

B. Intermediate, horizontal platecut to accommodate and weld-ed to "A" and "C" with full fillet.

C. Deep channel or angle beam,welded to the nearest hullframes with full penetration filletweld.

5-12


available in the ship’s Trim and StabilityBooklet, as well as in the Deadweight Survey.When formal documentation of the ship’s sta-bility is not available, stability may be ap-proximated by timing the ship’s roll period.This method is reasonably accurate and isused by the U.S. Navy, U.S. Coast Guard, andregulatory bodies to confirm the accuracy ofinclining experiments and other similar sta-bility determinations. For small craft, timingroll period is the approved method for deter-mining stability.

The roll period can be estimated accuratelyenough even in fairly calm water by watchingthe masthead. Time several successive rolls(from extreme port to starboard back to ex-treme port is one period), then divide the totaltime by the number of rolls observed to ob-tain a good estimate. To determine the ade-quacy of the roll stability, compare the timeperiod with the value calculated from the fol-lowing formula:

where:

T=Time in seconds.

For adequate stability, the time in seconds fora ship to roll from port to starboard and backto port must be equal to or less than the calcu-lated time (T) in seconds. For example, for aship with a beam of 100 feet, the time ob-served for the ship to complete a roll periodmust be less than the 20 seconds calculated. Ifthe observed time is longer than the calculat-ed value, stability generally is considered in-adequate. Equally important is frequentchecking for a change in the tow’s roll period.Even if overall criteria are satisfactory, inves-tigate promptly any significant increase in pe-riod, since this suggests flooding and/or addi-tional free surface.

Each commissioned ship in the U.S. Navy hasa Damage Control Book containing specificmeasures for improving a ship’s stability.

This book also contains stability characteris-tics for various loading conditions that meetthe Navy’s stability criteria.

For small craft and barges that do not have aDamage Control Book, follow a few generalguidelines when attempting to improvestability:

• Completely fill any slack tanks

• Lower and secure or off-load highweights

• Secure any large hanging weights andadd ballast.

In addition to improving stability, completelyfilling tanks or adding ballast will decreasefreeboard.

5-7.4 Two Valve Protection

Tows of inactivated Navy vessels imply thatthe preparing activity has met the require-ments of Naval Ship’s Technical Manual(NSTM) S9086-BS-STM-010, Chapter 50,Readiness and Care of Inactive Ships (Ref.G). This NSTM calls for installing hullblanks for all sea chests that don’t providetwo valve protection to the ship’s interior.However, tow inspectors should still be at-tuned to potential flooding conditions on in-activated vessels.

For unmanned tows of other vessels, a towingvessel’s tow inspection team should pay add-ed attention to machinery room or low lyingspaces for potential flooding conditions suchas single valve protection. Two valve protec-tion consists of either two valves wired shutor one valve and a blank flange. Sea valvesmust be wired shut with steel wire to protectall sea openings from the sea.

Attention should be paid to any loose connec-tions or badly deteriorated spots in the drainpiping which originates above the waterlineand terminates within 20-feet of the water-line. If this piping shows excessive rust orother damage, this may represent a potential

T 2 Beam ft( )=

5-13


flooding path in the case of severe weather.These pipes should be repaired to ensure anydrainage flows overboard.

5-7.5 Inspecting the Tow for Structural Damage

Every tow should be inspected to ensure thatits structure is capable of withstanding the ef-fects of towing. If there is any question aboutthe vessel’s structural integrity or if the struc-ture shows signs of extensive deterioration ordamage, a qualified structural engineershould be consulted.

In emergencies, such as salvage and rescuetowing, structural reinforcement and load dis-tribution may be accomplished with addition-al structure or shoring. See Figure 5-4 for typ-ical timber framing practice. Protectionagainst slamming damage may be effected bypressing up the bow section of the hull withwater. This action may require counter-flood-ing or shifting of cargo. If the tow is to berigged for towing by the stern (secondary oremergency rigging), these areas should re-ceive similar attention.

Inspection may reveal damage or deteriora-tion of frames, bottom or weld seams. Partic-ularly when this occurs in the forward one-fifth of the vessel’s length, the vessel shouldbe dry-docked or ultrasonically tested, andnecessary repairs made. While in dry dock,check bottom, side, decks and inner bottom.All defective welds and plating should be re-paired or replaced.

5-7.5.1 Barge Hull Thickness

Table 5-2 lists minimum thicknesses based onbarge length and frame spacing, for typical

barges. Bottom plate thickness in the forwardone-fifth of the vessel must meet these mini-mum values for safe towing.

These values are the minimum thicknesses re-quired to meet 1991 American Bureau ofShipbuilding (ABS) 10, Rules for Buildingand Classing Steel Barges (Ref. H). If actualthickness is less than 75% of these values,consider reinforcement. The values in Table5-2 are for the forward section; thicknesses inthe mid-section can be seen in Table 5-3.Again, a 75% criteria should be applied. Re-inforcement should be considered if there areany signs of serious corrosion or excessiveout of plane damage (buckling, frame trip-ping, etc.)

To avoid special dry docking before towing,barges, cranes and other service craft shouldbe thoroughly examined during routine main-tenance. Plate thickness and weld inspectionsshould be conducted regularly during sched-uled dry docking, or by ultrasonic inspectionin water.

5-7.6 Locking the Rudder

Because a drifting rudder will cause the towto behave erratically, the rudder should begenerally locked amidships. The method usedto secure a rudder depends upon the tow’ssteering gear.

• Yoke or tiller arm steering gear.Structural steel can be welded acrossthe tiller arm to suitable ship’s structureon either side. (An independent engi-neering evaluation is required to ensurethat both securing device and ship’sstructure are adequate). Figure 5-5 de-picts an example of such an arrange-ment.

CAUTION

Many barges and barge-like ves-sels tend to be more susceptible todamage and deterioration thanconventional ship type vessels.They should therefore be inspectedfor hull strength prior to towing.

CAUTION

Do not use temporary lashings orother makeshift measures to lockthe rudder of a towed ship. Lockthe rudder amidships for towing.

5-14


Table 5-2. Minimum Plate Thickness for Forward One-Fifth of Barge Bottom.

Frame Spacing (inches)

BargeLength

18 21 24 27 30 33 36

100 ft. 0.250 0.271 0.292 0.313 0.334 0.355 0.376

120 ft. 0.261 0.282 0.303 0.324 0.345 0.366 0.387

140 ft. 0.272 0.293 0.314 0.335 0.356 0.377 0.398

160 ft. 0.282 0.303 0.324 0.345 0.366 0.387 0.408

180 ft. 0.293 0.314 0.335 0.356 0.377 0.398 0.419

200 ft. 0.304 0.325 0.346 0.367 0.388 0.409 0.430

220 ft. 0.315 0.336 0.357 0.378 0.399 0.420 0.441

240 ft. 0.326 0.347 0.368 0.389 0.410 0.431 0.452

260 ft. 0.336 0.357 0.378 0.399 0.420 0.441 0.462

280 ft. 0.347 0.368 0.389 0.410 0.431 0.452 0.473

300 ft. 0.358 0.379 0.400 0.421 0.442 0.463 0.484

320 ft. 0.369 0.390 0.411 0.432 0.453 0.474 0.495

340 ft. 0.380 0.401 0.422 0.443 0.464 0.485 0.506

All thickness dimensions are given in inches.

5-15


Table 5-3. Minimum Plate Thickness for Mid-Section.

Frame Spacing (inches)

BargeLength

18 21 24 27 30 33 36

100 ft. 0.286 0.316 0.346 0.376 0.406 0.436 0.466

120 ft. 0.299 0.329 0.359 0.389 0.419 0.449 0.479

140 ft. 0.312 0.342 0.372 0.402 0.432 0.462 0.492

160 ft. 0.326 0.356 0.386 0.416 0.446 0.476 0.506

180 ft. 0.339 0.369 0.399 0.429 0.459 0.489 0.519

200 ft. 0.352 0.382 0.412 0.442 0.472 0.502 0.532

220 ft. 0.365 0.395 0.425 0.455 0.485 0.515 0.545

240 ft. 0.378 0.408 0.438 0.468 0.498 0.528 0.558

260 ft. 0.392 0.422 0.452 0.482 0.512 0.542 0.572

280 ft. 0.405 0.435 0.465 0.495 0.525 0.55 0.585

300 ft. 0.418 0.448 0.478 0.508 0.538 0.568 0.598

320 ft. 0.431 0.461 0.491 0.521 0.551 0.551 0.611

340 ft. 0.444 0.474 0.504 0.534 0.564 0.594 0.624

All thickness dimensions are given in inches.

5-16


Figure 5-4. Reinforcing Bottom Plating in Barges.

BottomLongitudinals

WedgeWedge

Bottom PlatingTim ber Packing

Angle Strongback

Truss

Truss

Strongback

Strongback

Strongback

Bottom Longitudinal

WatertightBulkhead

Longitudinal Spacing 22-24 InchesTruss Spacing 8-10 Feet

Wedge

Packing

Bottom Plating

Bottom Longitudinal

Strongback

NOTES

W eld strongback to longitud ina l flanges.

D o not se t w edges w ith a ham m er heavier than 2 lbs.

N ail w edges to packing so tha t wedges w ill no t w ork loose .

A lte rna te d irection o f w edges to secure pack ing tim bers.

1 .

2 .

3 .

4 .

5-17


• Vane type steering gear. Extend anemergency wrench (or wrenches) witha heavy channel or beam to reach astrong ship structure. Use full penetra-tion welds on both the wrench and theship structure (see Figure 5-6).

•Hydraulic steering gear. The rams canbe secured by positioning the rudderamidships and securing the hydraulicsystem in an attempt to maintain a hy-draulic lock. Sheet rubber is wrappedaround the piston and split pipe is cut tothe proper length so the ends bearagainst the cylinders and/or yoke. Thesplit pipe should be secured in placewith bands. Both rams should be se-cured in this fashion. Welding a plate orstructural member to the yoke and tothe foundation or ship’s structure addssecurity. Refer to Figure 5-6.

Regardless of the securing method, an inde-pendent check (by an industrial facility,structural engineer, or mechanical engineer)of the rudder securing method should be ac-complished to ensure they are strong enoughto withstand the forces generated by the rud-der. Forces on the rudder, even at low speedsthrough the water may be very large due towave impact and other sea action. Theseloads will be transmitted through the steer-ing gear and absorbed by the ship’s structure.

It may not be possible to use any of the illus-trated arrangements, as in the cases of rescueand towing at sea under unfavorable weatherconditions. A temporary means may then beemployed. Chain falls or come-alongs mayalso be used in conjunction with tiller arms orquadrants. Where practical, chain should beused instead of wire rope. Ram hydraulic sys-tems may be isolated in some installations toassist rudder locking. These methods are onlytemporary; a permanent locking arrangementshould be installed.

For a manned tow, if the steering machineryis operable and reliable, a decision may bemade to steer the tow.

5-7.7 Installing Navigational Lights

The preparing activity must ensure a tow isequipped with proper navigational lights.Specific requirements concerning the correctpositioning, number and color of lights arecontained in Code of Federal Regulations(CFR) Part 81-72 COLREGS, Implementingrules (Ref. I).

Navigational lights should have a solar switchbuilt in to increase battery life and meet COL-REG requirements. Alternately, a single solarswitch can be added to the system. Towinglights generally have a 10 foot leader wire forattachment to batteries. If that length is insuf-ficient, Navy type DHOF-4 cable is suitablefor connections. Ensure that all wiring is wellsecured and protected from damage by the el-ements.

Table 5-4 lists battery capacity requirementsfor one 60-watt, 12-volt DC sidelight or sternlight for tows of various durations. Individualbatteries for each light may be used to elimi-nate the power loss in long cables. StandardNavy 12-volt lead-acid batteries protected bysteel containers provide the necessary am-pere-hour capacity.

5-7.8 Selecting the Rig

Tow rig selection is best based on past perfor-mance and the unique needs of the upcomingtow. Although most Navy tows are simple,single-tug, single-unit operations, some towsare considerably more complex, consisting ofa single tug with multiple towed units. Occa-sionally the displacement of the towed unitrequires using more than one tug. The follow-ing factors should always be considered whenselecting a towing rig:

5-18


Figure 5-5. Securing the Rudder.

Structure Angleor Wide Flange Beam

Full Penetration Weld

Rudder Post

Tiller ArmShell

Fore & Aft Tiller Arm

Athwartship Tiller Arm

Shear Plate(s)

To m ax im ize lever a rm , it m ay be necessary to use shear p la te (s) to secure tille r a rm to deck. See F igure 5 -6 for typ ical shear p la te exam ple.

NOTE

5-19


Figure 5-6. Securing the Rudder.

5-20


• Identify the type of towing rig requiredfor all conditions anticipated during thetransit and at either end of the tow.

• Ensure that all rigging is adequate. Ifin doubt, use a higher safety factor. Payparticular attention to protection fromchafing.

• Ensure that multiple tows are config-ured for optimum seakeeping ability.

• Provide a secondary towing rig on thetow in case the primary system fails.

• Provide for anchoring the tow in case ofemergency.

• Provide for all contingencies as out-lined in the checklist (see Appendix H).

Before towing a new or unique configuration,ensure design of the rig conforms to appropri-ate engineering and design criteria. A numberof towing configurations and arrangementsare shown in Appendix I. Consult NAVSEA00C to resolve any technical matters regard-ing towing.

5-7.9 Preparing Tank Vents

Vents to tanks and other closed spaces shouldbe covered with canvas socks to prevent wa-ter entry, but not plugged so as to prevent theescape of air or gas. Plugged vents allowpressure to build up within the tank with an

increase of atmospheric temperature. Bargesides and decks have been known to bulge se-verely when vents are plugged. Ensure hatch-es, scuttles, doors, portholes and other water-tight closures are provided with pliablegaskets and that material condition ZEBRA isset throughout the tow.

If vents may be subject to heavy weatherflooding (such as vents near the waterline), itmay be necessary to weld a blank over theopening to minimize the risk of flooding.

5-8 Emergency Systems

Adequate fire fighting equipment and materi-als, as well as damage control equipment andassociated fuel, should be placed on boardprior to starting the tow. For long voyages,tows should have bilge pumping equipment.If permanent bilge pumps on the tow are in-operative portable lightweight pumps or edu-cator systems should be provided, that can behandled by the riding crew or inspection partyfrom the tug. Tests should demonstrate thatthe pumps have adequate suction lift and dis-charge head. For larger ships, installation ofportable fire-fighting systems should be con-sidered. A portable system could make use ofthe existing firemain system aboard the towedvessel for distribution of fire fighting water.

Table 5-4. Battery Capacity Requirements.

Length of Tow (Days)12 Hr/Day Operation

60 Watt Light (Amp-Hr.)

5 300 Amp-Hr.

10 600 Amp-Hr.

16 960 Amp-Hr.

21 1260 Amp-Hr.

30 1800 Amp-Hr.

5-21


5-8.1 Electrical Power

Electrical power is required on the tow for thefollowing systems:

• Fire alarms• Lights• Flooding alarms (audible and visual)• Pumps• Communications equipment• Crew accommodations• Winches and capstans• Radiological alarms

All electrical and other systems should be in-spected and tested periodically to ensure reli-able operation. If electrical power on the towis supplied by an installed or portable genera-tor, a sufficient amount of fuel for the towshould be provided. A simple rule of thumb isto allow two gallons of fuel per day, per gen-erator horsepower, or to allow 2.7 gallons offuel per day, per kilowatt.

Batteries in a battery powered system shouldbe checked for capacity and condition. Bat-teries exposed to the weather must be protect-ed in watertight containers that will not per-mit the batteries to leak to ground. It isessential that all exposed wires and connec-tions be adequately waterproofed. Wiresshould be secured to prevent chafing andgrounding. Provisions must be made to venthydrogen gas from all batteries.

5-8.2 Fire-fighting

The need for fire fighting equipment must beevaluated by the tow planner and will dependon several factors. The value of the tow, po-tential sources of ignition, the consequencesof fire, and the effectiveness of fire fightingequipment (including personnel), should allbe considered when deciding how to ap-proach this requirement. Potential for fire ona planned unmanned tow should be relativelysmall, but this may not be the case. For in-stance, ships involved in a rescue and salvage

towing scenario will likely have serious po-tential for fire.

Risk of fire can be greatly reduced by elimi-nating as much of the combustible materialon board as possible. It is virtually impossibleto remove all combustible material from atow as items like insulation and cabling aredifficult and expensive to eliminate complete-ly. But paper products, furniture and combus-tible liquids and paints are relatively easy toremove and greatly reduce risk of a fire. Afull walk through of all compartments shouldbe done to identify any areas that may be apotential ignition source. Maintaining water-tightness and sealing as many compartmentsas possible will reduce the chance of a firespreading.

Fire fighting equipment should be compatiblewith determined risk. The capacity and porta-bility of installed equipment will determinethe effectiveness of any fire fighting effort.Active Navy ships should have three or moreportable fire fighting pumps on board. TheNavy has replaced gasoline driven P-250swith newer self-priming, diesel-driven P-100s. These pumps produce about 100 gal-lons per minute at around 85 psi. The 3-inchsuction hose (same as the P-250) is used topull a maximum of about 20 feet of suction.The discharge connection is typically a 2 1/2-inch Y-gate that can be connected to two 1 1/2-inch standard fire hoses. Only one hoseshould be used at a time due to pressure andflow limitations. It is prudent to connect two,however, to allow quick response in the eventof a ruptured line. Pumps and associated gearare generally located on the weather decknear repair lockers.

It may also be possible to connect to theship's installed firemain. An assessment ofthe pressure and flow rate needed to meet thefire fighting capability should be made to en-sure that adequate pumps are installed. Navyships will typically use 1 1/2-inch fire hose(50-foot lengths) from a 6 to 8 inch header.

5-22


This header should be charged to approxi-mately 150 psi. Access to spaces deemed aspotential fire hazards should contain extin-guishers and fire hose. These items should bestaged in a place to allow the boarding crewto begin fire fighting without endangeringtheir safety.

5-8.3 Dewatering

It is common practice to outfit a tow withflooding alarms. These tell the ship that thereis some problem on board and allow the towship to assess the severity of flooding to somedegree (using high and low level alarms). De-watering equipment, such as pumps and hos-es, is used to control flooding or remove wa-ter. If the flooding can be stopped withpatches or other repair, water can be removedto restore the vessel to its stable condition. Ifthe flooding cannot be stopped, this equip-ment can be used to limit the effects of flood-ing. If the rate of flooding is slow, dewateringpumps may be able to keep the vessel in a sta-ble condition until port is reached or repairscan be made.

5-8.3.1 Deciding to Use Dewatering Equipment

The decision to install or use dewateringequipment should be made by both the towplanner and the tow ship Commanding Offic-er or Master. Not every tow will need to berigged with dewatering equipment. It may bedesirable to use dewatering equipment onhigh value tows or tows with little compart-mentation. Critical compartments or compart-ments with damage can be rigged for dewa-tering while leaving other areas alone. Manytows are decommissioned vessels and havebeen prepared for long term storage. Oftenthese hulls have a high degree of water-tight-ness with all hull openings having weldedblanks. Flooding is a very unlikely event inthese cases. But not every scenario can beforeseen and things break and accidents hap-pen and flooding is still a possibility.

A vessel prepared for tow may have been pre-pared with extensive compartmentation.Compartmentation will serve to limit theflooding to certain areas of the ship and limitthe amount of water taken on. When prepar-ing a tow, level of compartmentation shouldbe a major consideration when determiningthe need for dewatering equipment.

Operational ships should have a fairly largecapacity for dewatering. If one of these shipshas been picked up in a distress status, towship personnel should become familiar withit’s installed systems. Operational USN shipshave flooding effect diagrams as part of theirdamage control package. These diagrams willtell the effect of flooding of a particular com-partment. In the absence of these drawings, aflooding matrix can be developed to show theextent and effect of flooding certain compart-ments.

Effectiveness of the installed equipment mustalso be evaluated. Pumps operating on a shipwith a very high freeboard will have a diffi-cult time transferring the water from lowdown in the hold, over the side and into thesea. If large pumps are used, it will likely beimpossible for a boarding crew to move themaround. Sufficient lengths of hose must be in-cluded to reach all areas of the vessel thatmay require dewatering.

5-8.3.2 Choosing Equipment

When preparing a compartment for dewater-ing, it is wise to identify potential floodingsources. For example, a damaged ship mayhave some patching, or a ship may have had arudder casualty. The size and amount ofequipment chosen should be able to over-come any flooding from these sources. Leak-age from a large patch may produce a greateramount of flooding than leakage around arudder post. Pumps should be sized accord-ingly. P-250s, P-100s or equivalent pumpsare often readily available on Navy ships and

5-23


provide good pumping capability. Submers-ible pumps may also be used effectively.

Pumps may need to run continuously to over-come flooding until repairs have been made.Sufficient fuel should be carried on board tooperate the pumps for at least 24 hours, al-though more is desirable. Adequate fuel stor-age should also be included with the capacityto hold this amount of fuel. Provisions can bemade to refuel if the operation will last long-er. The tow planner should be aware of thecapabilities of the tow ship and boardingcrew. If refueling is not an option, additionalfuel storage will be required.

5-8.3.3 Pre-staging Hoses

Consideration must be given to the capabili-ties of a boarding crew to rig hoses and oper-ate the pumps. Hoses can be pre-staged to themaximum extent possible, but watertight in-tegrity should not be sacrificed to rig hoses inadvance. Locating suctions in the bilge andrunning hoses throughout a compartment willeliminate a lot of effort by the boarding crewand save valuable time in an emergency. Hos-es should be rigged as high up and as near tothe compartment access as possible. Finalconnections can be completed in the eventthat a decision to open the compartment andrun pumps is made.

5-8.4 Marking Access Areas on Tow

A riding crew or boarding party from the tugmay find itself in an unfamiliar setting on alarge tow. The preparing activity should es-tablish route markings to areas susceptible toeither flooding or fire. Painted route markingsfrom a central location and/or from the board-ing point would allow personnel to go by themost direct route to the scene of possibleemergency. Established route markings to aida security patrol in making his rounds alsowould eliminate missed areas, adding to theefficiency of the patrol. Whenever possible apotential boarding party should become fa-miliar with the tow prior to getting underway.

Sufficient means for personnel to board a towat sea should be provided. See Figure 5-7 forexamples.

Access markings should be as reflective aspossible to allow access in a low light orsmoky environment. They should be locatedin enough areas to ensure that personnel willhave no confusion when attempting to locatean exit in an emergency. A line painted downthe center of the passage provides a continu-ous route. Adding reflective arrows will assistin locating the access route.

5-8.5 Preparing for Emergency Anchor-ing of the Tow

Anchoring the tow in an emergency should beconsidered. The following provisions shouldbe made when preparing the tow:

• Provide sufficient ground tackle or oth-er anchor-handling equipment. The an-choring system should allow anchoringin a minimum of 60 feet of water with ascope to depth ratio of 3:1. If deepercapacity is required for the proposedroute, maintain a 3:1 ratio. The ship’sanchor and chain may be used if in ser-viceable condition. If other jewelry isbrought on board, it should be of simi-lar size to the ship’s normal anchor.

• It may be necessary to seal the chainhawse pipe to prevent water from enter-ing compartments or tanks through thisopening. The simplest method of seal-ing a chain hawse pipe is to pack it withcloth filler and plug with cement.

• Consideration should also be given topower requirements for raising the an-chor if the tow will be anchored at theport of delivery.

• The anchoring system should be riggedfor quick release, it can be rigged on aspecially made billboard (see Figure5-8). Chain and wire should be able torun over the side without risk of ob-

5-24


Figure 5-7. Sample Provisions for Emergency Boarding of Tow at Sea.

Cargo Netting

Welded Rungs

Jacob’s Ladder

5-25


struction. The bitter end of the groundtackle should be connected to a padeyeor other fixture capable of withstandinganchoring loads.

5-9 Completing the Checklist for Ocean Tows

Appendix H provides a simple checklist forpreparing a vessel for ocean tow. The check-list is to be used by the preparing activity toaid in preparing a tow for sea and acceptanceby the towing unit. It lists general require-ments, most of which must be completed be-fore a towing unit will accept it for sea. If thepreparing activity has questions concerningthis checklist or preparations required toready the tow, it should communicate viamessage or phone with the towing unit or itsImmediate Superior in Command (ISIC). Thepreparing activity must fully complete thischecklist. Items which are not applicable orcannot be accomplished must be clearedthrough the towing unit’s ISIC or the towingunit.

5-9.1 Determining Seaworthiness

To be considered seaworthy, a towed vesselmust have adequate watertight integrity,structural soundness, and intact stability.

A representative of the preparing commandshall complete a Certificate of Seaworthi-ness for ocean tows. The certificate includesgeneral characteristics, type of cargo, towinggear, lights, speed limitation, and similaritems. A sample Certificate of Seaworthi-ness and its endorsements can be found inAppendix H.

5-9.2 Towing Machine/ Towing Winch Certification

The towing machine/towing winch shall beinspected and tested prior to the tow by aNAVSEA designated representative. After alldiscrepancies are addressed, an annual certifi-

cate shall be issued to the Commanding Of-ficer or the Master of the vessel as well as thesponsoring command.

5-9.3 Tow Hawser Certification

The towing vessel shall provide a certifica-tion of the tow hawser with respect to its in-spection, construction, and type.

5-9.4 Commercial Vessels (U.S. Coast Guard Inspected) Master’s Towing Certifi-cate

The towing vessel shall provide a copy of theMaster’s Towing Certificate that became ef-fective by the USCG TASC of 21 May 2001.

5-9.5 Preparing for a Riding Crew

After receiving approval to use a riding crew,the Commanding Officer or the Officer-in-Charge of the riding crew must ensure that:

• Adequate training and drills are per-formed. These include fire fighting;flooding and other material conditiondrills; drills for abandoning ship, boatlaunching, communications with thetug and securing a secondary towline.

• Security watches of machinery, water-tight integrity, the towline, navigationallights, communications, and otherwatches as necessary shall be stationed.

• There is an adequate method of board-ing the tow at sea. When feasible, fixedladder rungs are preferred. Figure 5-7depicts several methods for boardingladders.

• Radios, pumps, hoses, tools, fire-fight-ing equipment, and handling gear arepositioned and ready for use by theriding crew or tug personnel who boardthe tow. The towing plan also considersrequirements for messing and berthingquarters for the riding crew, auxiliarypower, fuel, damage-control equip-ment, and life-saving gear.

5-26


Figure 5-8. Billboard

Line to Crown Buoy

5-27


• Communication between ships is pro-vided as stated in Section 6-2.9.

5-10 Accepting the Tow

5-10.1 Inspecting the Tow

Prior to accepting a tow, the CommandingOfficer or Master of the towing ship must in-spect the tow to confirm its seaworthiness andreadiness for tow. The inspection should in-clude, but not be limited to items listed inSection 5-7 and this section.

• Review the towing inspection checklist,shown in Appendix H, to ensure it isthorough, adequate, and properly com-pleted.

• Inspect tow rig, appendages, and at-tachment point to ensure that the tow isproperly rigged per, applicable instruc-tions, or guidance from the tow spon-sor.

• Inspect the towline, bridle, and associ-ated towing gear for wear and to ensurethat improper substitutions have notbeen made in fittings and materials.Typical items to look for include:

— Mild steel substituted for forgedsteel in safety shackle pins.

— Stainless steel substituted forother high strength alloys.

— Improperly sized components.

Note whether a retrieving wire isrigged and if proper mooring lines areavailable.

• Ensure cargo on the tow is properlysecured to prevent shifting in heavyweather.

• Ensure liquid cargo tanks are pressedfull or left empty.

• Check all accessible spaces to make surethey are completely dry and watertight.

• Check to ensure that vents to tanks andother closed spaces are properly cov-ered or sealed.

• Ensure hatches, scuttles, doors, port-holes, and other watertight closures areprovided with pliable gaskets and thatmaterial condition ZEBRA is set.

• Ensure that running lights and floodingalarms are operating properly, thatbatteries are fully charged and batterylife is computed to be sufficient for thetransit.

WARNING

Substituting materials can bedangerous as well as detrimen-tal to the tow. Substitutions shallnot be made unless there is acomplete knowledge of the ma-terial being substituted. Materialsubstitutes frequently introducea new and unpredictable weaklink. Substituting a stronger ma-terial may change the location ofthe potential failure point in therig to a position that is hazard-ous to personnel.

CAUTION

A screw-pin shackle shall not beused as a replacement for a safe-ty shackle in towing. A safetyshackle will deform under loadand still hold, while a screw-pinshackle's pin can work itself out ofthe shackle.

WARNING

Use the applicable safety pre-cautions for entering voids andunventilated spaces. Failure todo so may result in injury ordeath to personnel.

5-28


• Ensure any required salvage pumpsand associated equipment with fuel aresafely stowed on board the tow.

• Ensure that any required fire fightingequipment with fuel, hoses, chemicals,and overhaul gear, is safely stowed onbo a rd . R e q u i r e a n op e ra t i on a ldemonstration that fire pumps can takea suction.

• Ensure that all high-value items on thetow are locked up and inventoried onthe tow report form.

• Ensure that provisions have been madefor quickly releasing the towline in anemergency.

• Ensure a provision has been made forstreaming a pickup line for the second-ary towline.

5-10.2 Unconditionally Accepting the Tow

Upon satisfactory completion of the towpreparations and inspection, the Command-ing Officer or Master of the tug shall acceptthe tow, notify his operational commander,and proceed with the mission.

5-10.3 Accepting the Tow as a Calculated Risk

If unsatisfactory conditions of seaworthinessor readiness are found and the differencescannot be resolved at a local level, the Com-manding Officer or Master of the towing shipshould notify his operational commander stat-ing why the tow is unsatisfactory. The reportshould include recommendations for correct-ing each deficiency. If conditions or circum-stances are such that a calculated risk is in-volved, the Commanding Officer or Masterof the towing ship should state that he will ac-cept the tow only on a calculated risk basis.

5-10.4 Rejecting the Tow

If the tow is in such poor condition thattowing would potentially endanger the tow orthe tow ship, the towing unit may reject thetow. Every effort should be made to correctany unsatisfactory conditions prior to reach-ing the decision to reject a tow. But if theCommanding Officer or Master of the towingship feels that the tow poses a serious risk, heshould notify his operational commanderstating why the tow is unsatisfactory. Thereport should include recommendations forcorrecting the deficiencies.

5-10.5 Preparing for Departure

With all other prerequisites completed, thesuggested items to complete prior to depar-ture include:

• Reconfirm the date and time of depar-ture with tasking authorities

• Recheck the weather forecast and sug-gested track immediately prior to de-parture.

• Discuss harbor maneuvers with localtug operators. A final tow conference ofall parties involved with local chartswill provide a forum for clearing anyuncertainty about maneuvers. This isparticularly useful when accepting atow in an unfamiliar port.

5-11 Completing the Delivery Letter or Message

Once the tow has been completed, the Com-manding Officer of the receiving activity willcomplete a delivery letter confirming receiptof the tow. A sample delivery letter is includ-ed in Appendix H.

5-29


This Page is Intentionally Left Blank

5-30


Chapter 6

TOWING PROCEDURES

6-1 Introduction

This chapter will provide some guidelines foroperating while underway with a tow, pick-ing-up a tow, and releasing a tow. This infor-mation represents the cumulative knowledgeof many operators gained during years oftowing. Although this will provide guidancefor a number of situations, each tow is aunique event with its own unique hazards.Caution and adherence to safety guidelineswill help minimize risk to personnel duringthis dangerous evolution.

6-2 Initiating the Tow

A tow can be picked up at a pier, in thestream, or at anchorage. When rescuing a dis-abled vessel or recovering a lost tow, it maybe necessary to pick up a tow at sea. Ocean-going tugs should not be asked to maneuverunassisted in restricted waters. If possible, thetow should be delivered to the ocean-goingtug by harbor tugs. At the very least, harbortugs should be available to assist the tug andtow to navigable waters.

Positive communication between the towship, pilot, and assist tugs is essential andshould be established as early as practical.

6-2.1 Accelerating with a Tow

When getting a tow underway, always build upspeed slowly. Judicious acceleration and de-celeration prevent damage to the towing gear.Sudden speed increases will cause dramatic in-creases in towline tension and potentiallyplace the tow and crew in danger. An increasein towline scope should accompany speed in-creases. This will help maintain catenary depthand reduce towline tensions. Good communi-cation between the tow ship and any assist tugsis also necessary for a safe underway.

Frequently the tow begins in restricted watersor a narrow channel. Beam winds or wavesmay force the tow out of its channel or intothe path of other ship traffic. Even if the towhas operable steering machinery, the initialtowing speed is often insufficient for control.For these reasons, it is prudent to retain har-bor tugs alongside the tow, or at least closeby, until the towing ship’s Commanding Of-ficer has control of the tow within navigation-al constraints.

Tow resistance increases with speed, yetwater depth may not permit sufficient hawserpayout to establish a catenary. A towingmachine’s automatic features are especiallyuseful in this situation. Also, syntheticsprings can provide an excellent means oftension reduction while getting underway (seeSection 4-6.5).

6-2.2 Getting Underway from a Pier

Getting underway from a pier with a tow re-quires that the Conning Officer be particular-ly aware of tides, currents, and wind. In addi-tion, the Conning Officer should discussintended procedures with the harbor tug mas-ter and pilot before getting underway.

When determining tugs to be used for assis-tance, consideration must be given to expect-ed sea conditions. The size and number oftugs must be sufficient to control the tow until

CAUTION

When picking up a tow, increasespeed slowly and gradually andmaintain an even strain on the tow-ing gear. If a tow hawser tensionreadout is not available on thebridge, have this information pro-vided by the Towing Watch.

6-1


Figure 6-1. Methods for Securing Messenger to Towline.

Mes

sen

ger

Sto

pW

ire

Str

ap

Sh

ackl

eP

end

ant

8 -

10 F

eet

21 -

Th

read

Sto

ps

Ro

llin

g H

itch

Hal

f -

Hit

ch

Mes

sen

ger

Pen

dan

t

6-2


the tow ship can establish sufficient speed totake control.

Good communication between the tow shipand harbor tugs is critical at this phase. If thetow and tug are not kept in line, at a near con-stant distance, large strains and damaged towgear could result. If the tow gear breaks, theharbor tug should be large enough to keep thetow under control to avoid a catastrophe.

Once the towing ship and the tow are in thechannel, the towline should be set at shortstay in keeping with the depth of confinedwaters to be crossed. Keep the catenary shal-low to avoid snags.

6-2.3 Getting Underway in the Stream

At times it is necessary to accept a tow in thestream. In this case, use the following procedure.The approximate channel course should be takenby the tow ship with bare steerage and assistingtugs should bring the tow to the tug’s stern.

Heaving lines are used to send a messengerline to the tow which is then attached to theprimary pendant (see Figure 6-1). Dependingon the height of the tow’s bow or other con-figuration considerations, it may be desirableto send a heaving line from the tow to the tug.Either way, the tug should always have spareheaving lines on deck in case they are needed.Once a messenger is passed, the pendant isheaved in and the tow connection is made.

If the harbor tugs are limited in their controlof the tow or are not available (rescue towing)or if the tug desires to control the tow with itsown power, riding lines can be used (see Fig-ure 6-2). When the tow is brought close to atug’s stern, a riding slip line is rigged with itseye on the bitts and then passed to the tow,reeved through a suitable deck chock on thetow, and led back to bitts on the tug. A secondriding line may be rigged for increased con-trol. A messenger line is then sent to the towand attached to the primary pendant. The pri-mary tow pendant is heaved in and the towconnection is made.

Using two riding lines is also a good methodfor lateral control, especially when towing asmall vessel at very short scope in shallow re-stricted waters prior to final streaming of thetow.

Regardless of attachment method, it is best tohave all items to be used in passing the pen-dant rigged on the tow before leaving the pier.An evaluation of the capabilities of the assetsavailable should be made when deciding thecorrect method for hook-up.

6-2.4 Getting Underway while at Anchor

At times it is necessary for the tug to make upto a tow with either or both vessels at anchor.This may be due to limited pier space, shal-low harbors, or simply the master’s prefer-ence. Suggested procedures for getting under-way in several situations are listed below.

• Tug underway/tow anchored. In mod-erate seas, the tug should come along-side the anchored tow and tie up withher stern as close as possible to the bowof the tow. The tow then passes a line tothe tug, which is used to pull a messen-ger and then a portion of the tow’schain pendant to the tug. As the chaincomes down on the tug’s faintail, astopper is passed on it to restrain itwhile the tug’s crew rigs the remainingtowline connection. When the connec-tion is made, the chain stopper is re-

CAUTION

Care should be exercised whenalongside in a seaway. The mo-tions of the tug and tow may besufficient to part mooring lines, re-sulting in damage and causing thetug to lose control of the tow.

CAUTION

The tow should be steadied on theriding l ines prior to attemptinghookup. Surging can produce highloads on the riding lines very quickly.

6-3


leased and the tug maneuvers clear. As-sistance of a harbor tug is usuallyrequired. When headed fair, the towweighs anchor, once the anchor ishoused, the tug can start ahead slowlyaccelerating. Significant time is re-quired to establish sufficient catenary inthe tow hawser and come up to towingspeed. If the tow has no power to its an-chor windlass, the crew should rig anappropriate retrieval line and buoy sothat the anchor can be slipped and re-covered later.

If unfavorable conditions for goingalongside prevail, passing the hawsercan be difficult. Expert seamanship isrequired to prevent the tug from driftingout of range on a downwind approach.It may be preferable to anchor, as dis-cussed below.

• Tug anchored/tow anchored. Ratherthan passing the towline while under-way, it is often advantageous for the tugto anchor upwind or upcurrent from alarge ship. While at anchor, the tug canprepare the towline for passing. The tugveers its anchor chain until within ashort distance of the tow’s bow. Whenthe tug’s stern is close aboard the tow’sbow, the towline can be passed and theconnection made. With the towlineconnected, the tug can use its engines tocome ahead and weigh its anchor, veer-ing towline as necessary. With the tugfree to navigate, the tow weighs anchorand the tow commences. If the towdoes not have power, it may be neces-sary to slip the chain and anchor andmark the anchor’s position with a buoyfor later retrieval.

• Tug anchored/tow underway withsteering tugs. The tug anchors and set-tles out into the wind and current. Asteering tug brings the tow up to thestern into the current or wind. A pen-

dant or lead chain is passed to the sternof the tug. Using the tug’s stern cap-stan, a messenger is heaved on boarduntil a sufficient amount of chain isbrought on board to pass a chain stop-per. The connection is made, the chainstopper released, and wire paid out asappropriate. The tug weighs anchor andbegins accelerating at a very slow rateof speed. This method is safe, simple,and expeditious.

6-2.5 Recovering a Lost Tow

There are occasions when a tug must recovera lost tow at sea. Towline chafing, a mechani-cal break, or other circumstances may causethe tow to separate from the tug, making itnecessary to recover the tow. In other cases,the original tug may become disabled or evenabandon a tow. Procedures used to recoverthe lost tow will be affected by the presenceof personnel on the tow, sea and weather con-ditions, existing contingency plans, and assetsavailable. See Section 6-2.7 for a discussionof approaching a drifting tow.

• If the tow is unmanned and the weatherand seas favorable, a boarding partymay be put on board the tow, a messen-ger passed, and the tow reconnected byroutine procedures. The risks involvedin sending a boarding party and the dif-ficulty of passing a new towline justifyrigging a secondary, emergency tow-line. If the emergency towline has beenused, consider rigging another emer-gency towline.

• If the tow is unmanned and the weatherdoes not permit sending a boarding par-ty, the tow ship should attempt to re-trieve the secondary pendant by meansof the floating pendant or marker buoy.The tow ship can either recover this us-ing one of its small boats or by grap-

6-4


Figure 6-2. Accepting a Tow in the Stream.

Yard tug hold station so tow does not overrun tug.

Lead Chain or Wire

Pendant Bitts

Pad

Tug has slight w ay on.

Riding Line

Tow Hawser

Hogging Strap

Laying Lazy

Messenger hauls

towing pendant aboard.

Leave endfree up to tow hawser or pendant supplied by tug.

NOTE

Riding lines may not be necessary if there is sufficient tug power available to control the tow.

6-5


pling the floating pendant directly fromthe tow ship. The secondary tow pen-dant is rigged to deploy as the tow shiptakes a strain. (See Section 4-4.)

• If the tow is manned, it may still benecessary to send a boarding party onboard. If the riding crew is not suffi-ciently large or able to safely and ade-quately handle re-rigging of the tow,the tug should provide knowledgeableassistance.

• The tug may use one or more of itssmall boats to act as a warping tug on adrifting tow, if the tow is not too large.The small boat can keep way on the townear shoal water, or maintain a towshead into the seas, thereby facilitatingrecovery. The small boat may alsochange the heading of the tow as neces-sary.

6-2.6 Emergency Connection to a Dis-abled Vessel or Derelict

Devising a means of attachment is a criticalconcern when rescuing a disabled vessel orderelict. This is particularly important in thecase of rescue towing, when time and shore-side support may not be available for install-ing padeyes and fairleads. Suggested attach-ment points of sufficient strength to tow in anemergency include:

• Using the ship’s anchor chain• Using installed bitts or padeyes• Wrapping a chain around a foundation

structure such as a gun mount or winch• Welding a padeye to the deck

The preferred methods are to use the ship’sanchor chain or installed padeyes. The othermethods are to be used in emergency situa-tions and may be necessary due to damage tothe tow or other unusual operating con-straints.

For situations where a padeye must be weldedto the deck, refer to Section 4-5.4 and Figure4-7 for acceptable padeye design specifica-tions. These figures provide means for con-structing a well-designed padeye. In an emer-gency situation, however, when detailedcalculations cannot be performed, it is recom-mended that the largest available material beused. These calculations can be performed af-ter installation, when the tow is out of danger,as a check against proposed towing speeds. Ifthe installed padeye is too small, speedshould be limited until a more appropriatepadeye can be constructed.

All towing bridles, when rigged correctly,must have a backup securing system. This isnormally accomplished by using wire rope ofappropriate size (able to lace through chainlinks) and taking sufficient bights of wirefrom a second securing point (bitts, heavycleats, etc.) and lacing the wire rope throughthe after end of links in the chain bridle (noless than four bights). Size and number ofbights of wire should equal the strength of thechain used in the bridle. If a towing pad isused to connect the bridle to the tow, thebackup wires must be laced forward of thetowing pads. The securing point should be aftof the towing pad to prevent snap-loading. Ifa set of mooring bitts is used as a securingpoint for the bridle on the tow, the wireshould be laced thorough the chain links thatremain astern of the bitts after the three ormore “figure eights” are secured on the bitts.There must be a sufficient number of wireclips (see Table 4-1) on each bitter end of thebackup wire, aligned in the same direction(See Appendix I and Appendix J for tow rigdesign plans.)

It may not always be possible or practical torig a backup system (i.e., submarine towing).In these cases, additional analysis of the maintowing at tachment may provide somereduction in uncertainty. Where possible, theattachment should be designed to a breaking

6-6


strength well in excess of the other com-ponents.

However the attachment point is affected, itmay also be necessary to cut through the bul-wark or to remove other fittings from thedeck in order to provide a clean sweep for thetowing pendant. When rigging a special at-tachment for towing, twin problems of attach-ment point and fairlead must be resolved.

6-2.6.1 Using the Anchor Chain

Often the simplest, strongest, and most effi-cient connection method is to shackle thependant into the tow’s anchor chain with thecorrect connecting link.

The usual method is to stop off the anchorand break the chain. Make sure that the in-board section will not be pulled down into thechain locker due to its own weight after it iscut. This can be accomplished by rigging twostoppers and cutting between them. In anemergency situation, it may be easiest to cutthe chain and lose the anchor. However, it issafest and economical to rig stoppers andsave the anchor.

Next, connect the bitter end of the chain di-rectly to the towing pendant brought throughan appropriate deck edge chock. The anchorchain can then be veered to provide chafingprotection and any desired additional catena-ry to the towline system for improved dynam-ic load mitigation. In this case, the ship’schain stopper system may not align ideallywith the fleet angle of the chain, but in mostcases the alignment will be sufficient. If thealignment produces sharp bends or other po-

Figure 6-3. Sharing Towing Load Between Bitts.

Shack le

W ire Pendant

Tow ing

Backup B itts(See D etail B )F irst B itts

O ne Turn O nly(See D etail A )

Chain Pendant

W irePendants

To C hain Pendants Deta il A

Lead B itts

Note O ne Turn O nly

To Backup

B itts

O ne Round TurnThen ‘F igure Eights ’

Deta il BBackup B itts

WARNING

In no case should the stud of thecommon chain link be removedto provide a connecting point toa chain.

6-7


tential failure spots, this area should be in-spected periodically and appropriate opera-tional steps taken to reduce risk of a failure.

Another method involving a tow’s anchorchain is to suspend the anchor from a wirestrap, or cut it loose completely, and towthrough the hawsepipe. The rigging for thisprocedure is complex and sometimes hazard-ous. Furthermore, this method often results inthe chain bearing against a sharp forward orupper outer lip of the hawsepipe, which mayconsist of a much smaller radius than wouldbe ideal for chain.

6-2.6.2 Using Installed Bitts

Mooring bitts are a possible choice for secur-ing a tow hawser. U.S. Navy bitts are de-signed to withstand the breaking strength ofthe mooring line for which they are designed,with a factor of safety of 3 on ultimatestrength. Since different types of synthetic

lines will have different breaking strengths,Table 6-1 lists the capacities of Navy bitts.The chart also contains some typical dimen-sions that will help to identify existing bittsand shows how each of these dimensions aremeasured. The maximum pull can be appliedto either barrel (not both), in any direction.

The strength criterion for bitts in commercialships is similar, except older ships and Navysupport craft often have been designed formanila mooring lines. Consider this whenemploying bitts for towing of commercial orolder Navy ships. In all cases, the strength ofthe bitts must be discounted if obvious corro-sion or poor maintenance is evident.

Attaching a chain directly to the typical-sizedbitts found aboard ships is feasible, but re-moving slack is difficult. Such a connectionis susceptible to shock load from sudden ren-dering and has a higher possibility of failure.

TABLE 6-1. Information on U.S. Navy Bitts.

Nominal Bitt Size

ABarrel Size

(inches)

BTop

Plate (inches)

CBarrel Height

(inches)

Maximum Moment* (inch-lbs)

Maximum Pull at Upper Edge*

(pounds)

Maximum Pull at Mid-

Barrel* (pounds)

Maximum Size

Synthetic Line

4 4 1/2 6 10 134,000 13,400 26,800 3

8 8 5/8 11 1/2 13 475,000 36,500 73,000 5

10 10 3/4 13 3/4 17 1,046,000 61,500 123,000 6 1/2

12 12 3/4 15 3/4 21 1,901,000 90,500 181,000 8

14 14 17 26 3,601,000 138,500 277,000 10

18 18 21 32 6,672,000 208,500 417,000 12

*These numbers are safe working load with a factor of safety of 3 on Material Ultimate Strength.

6-8


An improved connection where slack can beminimized can be made using wire that is thesame size as the towing pendant. (See Figure6-3.)

In Figure 6-3, note that the chain provideschafing protection at the deck edge, but wireis used to make the final connection. As stat-ed earlier, when using mooring bitts as an at-tachment point, a backup securing systemshould be used. The reason for using backupbitts is to share the load. To accomplish this,the loaded part should make only one turnaround one barrel of the first bitts. The firstturn will absorb 50 to 75 percent of the totalload on the wire, depending on the coefficientof friction, and pass along 25 to 50 percent tothe backup bitts. The wire should be securedto the second bitts by making one turn on thefirst barrel and then making figure-eightswith the remaining line. Backing up to a thirdset of bitts is not necessary.

If two turns are taken around the first set ofbitts, only about 6 to 12 percent of the totalload is passed on to the second bitts. Thus, ef-fective load sharing is voided.

If the wire required is too large to fit on thebitts, synthetic line may be used. This syn-thetic line is subject to the same restrictionsas synthetic towing hawsers. Minimum bendradius for all components should be checked.The same principles are applicable to synthet-ic line load sharing.

When using mooring bitts as bridle attach-ment points, heavy channel iron must bewelded across the bitts to prevent the bridlefrom jumping out.

6-2.6.3 Using a Gun Mount or Foundation

Another way to make an attachment is to passa chain around a gun mount or foundation ofa deck machinery installation or to rig a wirerope strap with a large eye on one end aroundthe bitts (see Figure 4-11).

6-2.6.4 Placing a Crew on Board

In an emergency, the presence of a function-ing crew aboard a disabled ship is of consid-erable help when making the connection. Ifthe ship has auxiliary power and is able to op-erate its anchor windlass or other winches,passing the towline assembly is a relativelysimple task, complicated only by adverse seaand weather conditions.

Connecting to a derelict poses the immediateproblem of placing a boarding party on board.A derelict vessel can present many unknownhazards to personnel. The boarding crewshould consider personnel safety as para-mount. If any potentially dangerous condi-tions were found during the pre-tow inspec-tion, these should be briefed to the boardingparty prior to attempting to board the tow.

If there are no means of boarding, grapnelsmay be heaved on deck or fabricated pipeboarding ladders may be used to get a manaboard. This person can then lower more con-ventional means such as a Jacob’s ladder. Theboarding party may have to carry an assort-ment of tools and rigging devices to help haulthe messenger on board and hook up a tow.These tools may include:

• Welding and cutting equipment

• Various size shackles

• Wire straps

• Rigging lines

• Battle lanterns

• Personal safety gear

• Sheaves for rigging

• Hand-held radios

WARNING

Boarding a derelict vessel canpresent many unknown haz-ards. Safety is paramount duringthese operations.

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6-2.7 Approaching a Drifting Tow

There are as many variations of approachinga drifting tow as there are variables in windand sea. Good seamanship is required to ap-proach and safely take in a drifting tow of anysize. Absolute coordination between the Con-ning Officer and the fantail crew is essential.Direct communication with personnel on thetow and all parties is crucial.

6-2.7.1 Establishing the Relative Drift

The first step in approaching a tow to bepicked up at sea is to establish differentialdrift between the vessels involved. This iscritical for positioning the tow properly andavoiding a collision. Despite obvious differ-ences in size and configuration, vessels’ ratesof drift are also affected by a host of othervariables, including displacement, draft, sta-bility, trim, damage, seas, wind, sail area, lo-cation of the superstructure, and currents. Theabove water hull configuration determines thetow’s relative heading into the wind. Depend-ing on trim, ships having a greater portion oftheir superstructure aft tend to head into thewind; ships having a greater portion of super-structure forward tend to lie with the windfrom aft of the beam to astern. A midship su-perstructure will normally cause a ship to liewith the wind abeam. With relative drift be-tween tug and tow determined, and the stateof the seas and wind taken into consideration,the tug can make its approach.

6-2.7.2 Similar Drift Rate

Figure 6-4 describes a tug’s approach acrossthe wind and seas where similar drift rates ex-ist. The tug begins an approach leading topass close aboard on the weather bow; themessenger and towline can then be passed.The tug keeps station while passing messen-gers and making the connection.

6-2.7.3 Dissimilar Drift Rate

Where dissimilar drift rates exist, a down-wind approach may be executed, as seen in

Figure 6-5. When approaching a ship lyingbroadside to the wind, tug speed should beslow, but fast enough to offer good steerage-way. Because on-station time is short, a mes-senger must be passed quickly. The towlinecan be passed in the lee of the ship’s bow.This situation requires a special effort to keepall lines clear of the propellers. Once connect-ed, acceleration should be slow and maneu-vering sequences gradual.

6-2.8 Passing the Towline

A towline is passed by messenger to the tow.It is generally preferable to have the tug passthe messenger and towline. The messengermay be passed by a hand-thrown heavingline, rocket, line-throwing gun, small boat,buoyant float, helicopter, or any other expedi-ent means. The hand-thrown heaving line,backed up with a line-throwing gun, is a com-mon and practical way of passing a messen-ger. An experienced seaman, under favorablecircumstances, can accurately throw a heav-ing line over 100 feet. Backup heaving linesshould be coiled and ready on deck to mini-mize time between attempts, should the firstattempt fail. Time considerations and atten-dant dangers, however, make it prudent togive as much time as possible to pass themessenger. Use of a line-throwing gun, there-fore, is the preferable procedure.

• In some cases it may be imprudent tonavigate close to a distressed ship. Inthis event, a boat can be used to passthe messenger. Line, free for running,should be faked down in the boat and

CAUTION

Approaching at too small an anglein the lee of a larger vessel can bedangerous. When working in thelee of a larger ship, establish an at-titude that permits the tug to main-tain a safe distance from the morerapidly drifting tow.

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Figure 6-4. Across Sea/Wind Approach - Similar Drift Rate.

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on board the tug, with the maximumamount possible in the boat.

• Buoys, life jackets, salvage floats, foamfenders, or drums can be attached to themessenger’s bitter end and floated tothe distressed ship. This can be expedit-ed by the tug crossing the disableds h ip ’s bo w w i th th e m e s s en g erstreamed.

• Line-throwing guns can carry the bitterend of the messenger; an experiencedseaman can safely and accurately firethe gun a distance of over 300 feet. Aheaving line can also be used effective-ly for shorter passing distances.

After a sufficient length of the initial messen-ger is on board, it may be run through a blockand the bitter end passed back to the tugwhere the tug’s machinery can haul the heavymessenger and towing assembly on deck. Thetow pendant is then made up to an availablestrong point on the derelict.

6-2.9 Communications between Ships

In a towing situation, most communicationbetween ships is by radio. Loss of radio, radiosilence, weather, or foreign language barriersmay require an alternate means of communi-cating. The most commonly accepted meth-ods for communicating between ships at seaare identified in the International Code ofSignals, Communicating Ship-to-Ship NWP -14-1 (Ref. J). These are by no means the onlymeans of communicating. Prearranged sig-nals and codes, as well as standard Navy pro-cedures such as those in NWP 14, are valu-able and highly useful tools available forcommunicating during towing operations.

6-3 Ship Handling and Maneuvering with a Tow

When the tow is underway, the tug begins toaccelerate slowly to towing speed. Rudder or-ders should permit slow and orderly coursechanges. It is important not to subject a towor towline to excessive dynamic loading.Slow course and speed changes will preventexcessive strain. If an automatic towing ma-chine is installed, a low tension setting can beemployed and the tow streamed as speed isincreased. Once desired scope is achieved,the setting on the automatic towing machinemay be increased to the desired value.

6-3.1 Tug Steering

Maneuvering characteristics of the tug can bedramatically affected when towing anothervessel. The ability of the tug to maneuver it-self under all conditions is essential.

The position of the tow point (the point wheretowline tension is applied to the tug) and thetension on the towline can create a momentthat opposes the rudder moment and hence re-stricts the turning motion of the tug. The tug’sability to steer is increasingly hampered asthe tow point is located farther aft. The effectis aggravated at low or zero speed. The term

CAUTION

Small increments of rudder angleare recommended when changingcourse under tow. This will ensurethat the tug maintains control of thetow and prevents the tow fromranging up on the tug. Never permitthe tow to pass forward of the tug'sbeam, as the tug or tow hawsermay be severely damaged.

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Figure 6-5. Downwind Approach Crossing the “T” to Ship Lying Broadside to Wind/Sea.

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“in irons” describes a condition where the op-posing moment of the towline is the same asor greater than the turning moment created byrudder and other hydrodynamic forces. Thetug is then rendered incapable of steering (seeFigure 6-6). Being in irons can be catastroph-ic for a tug, especially when maneuvering inconfined waters or in a poor orientation withrespect to the sea. A tug also can be renderedin irons when it cannot make headway underits own power because of the towline makingcontact with the bottom. In this case, the tugis effectively anchored by the stern. The tow,however, is not anchored and may close rap-idly. To avoid being run down, the tug shouldshorten the wire and regain headway at once.

Ideally, the position of the tow point shouldbe located at the tug’s natural pivot point, toallow the tug maximum freedom of rotationin steering. The tug’s natural pivot point isdependent on hull and rudder design; it isusually located on the center line at aboutone-third of the tug’s length from the bow.This is why the towing winch is mounted asfar forward from the stern as possible, al-though it is doubtful that any towing winch islocated exactly at the pivot point itself. Froma practical standpoint, the towing point is des-ignated as the towing winch or towing bitts, ifinstalled.

There are times, however, when the towingpoint is located farther aft—for example, on aNorman pin, hogging strap, or stern roller.During long ocean tows, these configurationsmay be preferred since they will restrict linesweep and therefore chafing of the towline. Iflittle maneuvering is needed, moving the towpoint aft may be acceptable. In any configura-tion, it is imperative that the operator beaware of the possible maneuvering restric-tions imposed on the tug and take the neces-sary precautions to avoid being placed inirons.

6-3.2 Keeping a Tug and Tow in Step

When a tug is at sea with a tow, the two ves-sels move distinctly and separately in surge,sway, heave, roll, pitch, and yaw in responseto the surface waves. The degree and timingof motion that either vessel experiences de-pend on the individual vessel’s characteris-tics. No two vessels will respond to the sur-face waves in exactly the same pattern. Incases where the surface wave pattern is char-acterized by a single predominant wave-length, it may be possible to minimize the dif-ference in the timing of the tug and towmotions. This involves adjusting the towlinescope to place the tug and the tow on crests ofthe predominant waves at the same time. Byplacing both vessels on the crest at the samemoment, they will move in response to thewaves in the same direction at approximatelythe same time. Adjusting timing of a vesselmotions in this way will reduce dynamic ten-sion in the towline. This practice has been re-ferred to as keeping the tug and tow “in step.”In tandem tows, this is rarely possible.

As the tug approaches shallow water, such asa coastline or channel, the wave frequencywill change (increase). The length of the towshould be adjusted, in conjunction with a pos-sible change in speed.

Keeping “in step” applies equally to all tow-ing situations, whether towing on the dog,hook, brake, or on an automatic towing ma-chine. The benefit of being in step is lowerpeak tensions.

6-3.3 Controlling the Tow

6-3.3.1 Active Control of the Tow's Rudder

The tow’s rudder can be used to stabilize anunwieldy tow or to maneuver in close quar-ters. Improper or excessive use of the rudder,however, can cause the tow to become direc-tionally unstable. The decision to use activesteering of the tow will depend on the reli-ability of the tow’s steering machinery andqualifications of the riding crew. A decision

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Figure 6-6. Effect of Towpoint on Steering.

Towing Tension Force

Towing Tension Force

Rudder Force

Pivot PointWithout Tow

Rudder Force

Winch

Pivot PointWithout Tow

ApproximatePivot Point

with Tow w henHawser Captured

at H-Bitt

For heavy towline tension, the pivotpoint may coincide with the sternrollers, placing the tug in irons.

A

Pivot point m oves tow ardthe stern when hawser is

captured astern.

Condition A has a decreased turning moment compared to Condition B.Condition A can place a tug “in irons”, therefore,

recomm ended towpoint for maneuvering is at the towing winchor H-bitts as shown in Condition B

B

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whether to use active steering rests with thetug.

6-3.3.2 Yawing and Sheering of the Tow

Most tows will yaw somewhat—that is, oscil-late in heading about the base towing course,usually in response to wave action on thetow’s bow or stern. This is not a serious prob-lem in itself. Many tows, however, will alsosheer off to the side, where the tow’s track isoffset from the tug’s track. This may be espe-cially prevalent in beam winds for ships withlarge deck houses aft.

The vessel may remain at a nearly constantsheer angle or sheer from side to side, re-maining at each side for as much as 10 min-utes or more. Excessive sheering will causeexcessive chafing of the towing rig, addition-al strain on the towline, reduction in towspeed, and possible collision or stranding inrestricted waters. In extreme cases, the towcan range up to a position abeam or evenahead of the tug.

Sheering may be initiated by an external forceor disturbance such as wind or wave action.Tows with bulbous bows tend to sheer morethan those with “fine” bows. Improperlyrigged bridles can also cause sheering. Legsof unequal length can generate a sheer prob-lem with the tow.

Yaw can also lead to sheering. Depending onthe tow’s inherent maneuvering characteris-tics, the amount of yaw and sheer may rangefrom small to substantial. In general, a tow isconsidered directionally unstable if the sheerangle continues to increase from swing toswing, despite an absence in the force thatinitially caused the motion. The followingparagraphs discuss ways to control the factorsthat influence yawing and sheering.

6-3.3.3 Trim

Before undertaking the tow, the towed vesselshould be trimmed by the stern slightly as de-scribed in Section 5-7.2. Trimming by the

stern makes the towed vessel less susceptibleto yawing.

6-3.3.4 Speed

Yaw of the tow may be increased or de-creased with a change in speed; a range oftow speeds may be attempted in an effort toobtain a desired reduction in yaw.

6-3.3.5 Use of Rudder or Skegs

If the tow is tracking poorly but is steerable,the rudder can be used to reduce or eliminateyawing and sheering. Active use of the rud-der, however, increases drag and adds the riskof steering machinery failure at a permanentrudder angle. Hull damage may cause the towto take up a permanent sheer angle. In thiscase, permanent adjustment of the rudder cansignificantly improve the tow’s behavior.

If excessive yawing occurs on a movabletwin-skegged tow, each skeg can be splayedat an outboard angle. Although the drag willincrease, the directional stability should im-prove. Outboard splaying is commonly doneon barges and the technique has been success-fully applied to twin-ruddered ships and float-ing dry docks. All such rudder or skeg move-ments should be made in moderation toachieve optimum towing performance withminimum increase in drag.

6-3.3.6 Location of the Attachment Point

A point of bridle entry into the tow may beselected to offer an optimum angle, and thuseliminate or reduce excessive yaw or sheer.Steps must be taken to prevent towline chaf-ing and to ensure that a fairlead is sufficientlyrobust. As an example, the LST 1179 Classrequires either a bridle or an off-centerlinependant because of the bow doors. Towing isperformed through a mooring chock on theside. These ships tow quite steadily with avery slight sheer.

6-3.3.7 Propellers

A locked propeller will create a larger dragthan a free-wheeling propeller, thereby result-

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ing in reduced towing speed. The additionaldrag in the stern due to a locked propeller,however, may decrease the tendency of thevessel to sheer off from the intended track.Refer to Section 5-7.1.7 through 5-7.1.11 forinformation on preparing the propellers fortow.

6-3.3.8 Steering Tug

The addition of an operational ship astern ofthe tug can offer effective steering control ofa tow. The trailing ship can use its enginesand rudder to maintain a light tension on aline to the tow. Following steering ordersfrom the tow ship, it can assist in keeping atow from sheering off.

6-3.3.9 Sea Anchor or Drogue

An object towed from the stern of a tow willcreate a drag that acts to resist yawing mo-tions. Nets, anchor chain, line, wire, kite an-chors, mine-sweeping gear, and a wide vari-ety of other drogues have been used asstabilizing devices on small tonnage or shal-low draft ships, especially those with fine hullforms. Care should be taken to prevent snag-ging of the drogue in shallow water.

6-3.3.10 Bridle vs. Single Lead Pendant

Certain hull forms are more conducive to be-ing towed by a single lead pendant. Subma-rines and ships with bulbous bows or forwardsonar domes tow better on a single pendantthan on a bridle. In general, fine lined shipsshould be towed with a single leg and broadbeamed ships towed with a bridle.

6-3.4 Backing Down with a Tow

If backing down is necessary, take great carenot to foul the towline in the propeller. Tow

position and speed of advance must be con-sidered to avoid collision.

For information on anchoring with a tow, re-fer to Section 6-7.5.

6-4 Routine Procedures While at Sea

This section deals with procedures that areperformed at sea on a routine basis but dealspecifically with towing. Each tow is unique,of course, and will present unique problemsand challenges, but some general guidelinesapply.

6-4.1 Setting Course

When adequate sea room is achieved, maneu-ver to set course and begin streaming the tow.Do not stream to full scope until sufficientwater depth is available to keep the towlinefrom dragging.

6-4.2 Towing Speed

Safe towing speed is determined by manyfactors, including material condition of thetow, currents, sea states, towing direction rel-ative to the surface waves, wind velocity anddirection, hull type of the tow, tug horsepow-er, capacity of the towline system, and avail-able powering assistance from other tugs orthe tow’s power plant.

The towing speed should be chosen to mini-mize the probability of damage to the tow.When towing damaged vessels and flat-bot-tomed craft, try to avoid excessive seakeep-ing motions and pounding. When necessary,

CAUTION

Except in an emergency, backingdown with a tow is not recommend-ed. It may be attempted if a colli-sion with another ship is imminent.

WARNING

Motions of the tug and tow cancause the towline to change po-sitions rapidly and without warn-ing. Personnel must be aware ofthe potential danger of a sweep-ing towline and remain clear ofall areas that may be within thissweep.

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towing course and speed should be chosenrelative to the sea state and wind direction tokeep a towed vessel motions within safe lim-its.

Barges generally should not be towed fasterthan about 8 knots under mild sea conditions.Small service craft and some dry docksshould be limited to about 6 knots. Deteriora-tion of weather conditions requires appropri-ate speed reduction to ensure continued safetowline loading. When towing larger surfaceships, the speed limitation usually is a func-tion of the tug’s capabilities. Sometimes,however, the dynamic loads induced by theship motions of a tug and tow in a seawaywill be the controlling factor in determining asafe towing speed (as opposed to the safetowing speed of the towed vessel or the capa-bilities of the tug). Appendix M contains dataabout the way ship motion affects dynamictowline loads.

6-4.3 Towline Scope

To estimate the towline scope required, fol-low these steps:

1. Choose a candidate scope

2. Estimate steady towline tension (see Sec-tion 3-4.1.3)

3. Compute catenary (see Section 3-4.2)

4. Estimate maximum and minimum towlinetensions

5. Ensure that catenary will not exceed wa-ter depth at minimum tension (A maxi-mum scope for the water depths expectedshould also be calculated.)

6. Adjust the scope as necessary and repeatsteps 1 through 5.

The scope should be adjusted to provide anadequate catenary for absorbing changes intowline tension without exceeding waterdepth. Dragging a towline on the sea floorwill damage the hawser through abrasion andcould lead to fouling on a sea floor obstruc-

tion. Also, once the hawser is in contact withthe bottom, the tug no longer has control ofthe tow and is in danger of being overtaken.

If the surface wave pattern has a predominantwavelength, attempt to adjust the towlinescope so that tug and tow ride on crests of thepredominant wave components at the sametime. Adjusting the towline this way maykeep tug and tow “in step,” thus reducingchanges in towline tension caused byseakeeping motions (see Section 3-4.1.4).

6-4.4 Towing Watch

With the tow streamed, the towing watchmust be set to observe the tow, towing loads,towing machine, towline, and the tow’sseakeeping performance. The tow watch mustroutinely advise the Officer of the Deck ofconditions observed. On board newer tugs,much of the information is automatically dis-played in the pilot house and control stations.

6-4.5 Periodic Inspection of Tow

Elements of the tow’s material conditionshould be visually inspected and continuouslymonitored, even at night. They include:

• Flooding and fire alarms, navigationlights, draft marks, and trim

• Sheer angle and seakeeping

• Timing of roll period for stability.

To supplement the flooding alarms, tug watchpersonnel should be alert to signs of floodingsuch as list, excessive drag (increase in tow-line tension without a change in conditions),change in roll period, or unexpected trim inthe tow. The towline should also be inspectedfrequently for chafing and damage during atow.

It is common practice to “freshen the nip” or“nip the tow” to avoid chafing. This is thepractice of changing the scope of the towlineso no single point is continuously in contactwith the caprail.

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6-4.5.1 Boarding the Tow for Inspection

When carrying a riding crew, the crew per-forms most of the inspection functions. Longdistance and valuable tows without a ridingcrew should be periodically boarded and in-spected, preferably by the same personnel oneach inspection. Because this operation is of-ten difficult and hampered by weather and seaconditions, inspection preparations should bewell planned and promptly and efficiently ex-ecuted. The following suggestions may aidthis process:

• When possible, consider seeking the leeof a land mass to make the operationsafer, easier, and more controlled.

• Shorten up the tow, this provides an op-portunity to inspect the towline and anypart of the tow rig that can be broughtaboard safely.

6-4.5.2 Inspection Guidelines

A written account should be kept of each in-spection, to be used as a reference for follow-ing inspections. The tow inspection partyshould perform the following:

• Check the tow connections and bridlefor integrity and unusual wear.

• Check propeller shaft locking system.

• Check rudder locking system.

• Check navigational lights and batteries.

• Check flooding and fire alarm system.

• Visually check open habitable compart-ments and topside areas.

• Sound any suspicious or questionablevoids, double bottoms, and liquid tanks.

• If indicated, visually check structuralframing and hull plating in the bow.

• Operationally check fire fighting anddewatering equipment weekly, or moreoften if conditions warrant.

• Upon completing the inspection, closeand make watertight all hull accessopenings. Any additional checks appro-priate to the peculiarities of the towshould be incorporated as needed intothe inspection checklist.

6-4.6 Towing in Heavy Weather

Long ocean passages rarely offer the opportu-nity to plan for favorable weather during theentire tow. Seasonal storms and sudden, un-expected weather can cause difficulty forboth the tug and the tow. Hurricanes and ty-phoons are the most dangerous and destruc-tive of all storms. Advice on actions to take inthe event of such storms is contained in Chap-ter 18 of Knight's Modern Seamanship (Ref.L).

Upon receiving a hurricane warning, takethese steps:

• Determine the location and track of thehurricane to plan a course that avoidsthe dangerous semicircle.

WARNING

Carefully adhere to safety re-qu i re m ents wh en e n ter in gclosed spaces. See Naval Ship’sTechnical Manual (NSTM) S9086-CH-STM-030, Chapter 074, GasFree Engineering (Ref. K).

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• If necessary, change course to avoid orride out the storm. It is far better to de-part from the projected track, ride outthe storm, and accept delays than to en-danger the ship and tow by remainingon a dangerous course and speed.

Estimate size and direction of the waves. Re-view applicable data in Appendix M to estab-lish average hawser tension limits for differ-ent wave heights and directions. Determinewhether extreme tension predictions can beeased by slight changes in course away fromtowing directly into the wind.

• Recognize that the tug and tow likelywill make negative speed over theground. Sail for a position that willminimize navigational hazards on adownwind track.

• Rig the fantail for heavy weather. Sternrollers and Norman pins should bedown and other obstructions to the tow-line cleared.

• Increase hawser scope, if possible.

• Set the towing machine on automatic ifit has an automatic feature. Otherwise,tow on the brake, rather than on thedog, to ensure rapid reaction to chang-ing circumstances.

CAUTION

Running before the sea and windcan cause difficulty in steering andin keeping the tow in the desiredposition. The tow may becomeawash or start to overtake the tug.If the tow begins to close on thetug, the tension in the towline willbe reduced and cause an increasein the catenary, which may alsocause the towline to snag on thebottom or bring the tug and tow toco l l i s io n . Th e re com men de dcourse of action is to head into theweather and maintain steerage-way, increase hawser scope and,as long as there is enough searoom, tolerate a negative speedover the ground. There is no rea-son to slip the tow unless the tow-ing ship is in danger of grounding.

CAUTION

Under more strenuous sea condi-tions, dynamic hawser tensions canbe significantly higher when towingdownwind than when heading intowind and seas at the same speedand power. Turning into the windand seas and slowing to maintainsteerageway are appropriate ac-tions under such conditions.

NOTE

If water depth permits, increase thetowline scope and use the auto-matic feature of the towing ma-chine in heavy weather. This en-hances shock load reduction forthe towline system. Every vesselrides differently in severe storms.Tug captains should use good sea-manship to determine how theirtugs and tows ride best. Theyshould use the best combination oftowline scope, speed, and heading.Generally, heading into the weatherallows better control of the tow.

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• Arrange for quick disconnection of thetowline. Methods for slipping the tow-line are discussed in Section 6-7.3.2.

6-4.7 Replenishment at Sea

Long ocean tows or emergency circumstanc-es may require the tug to replenish at sea. Re-plenishment at sea is a well-established rou-tine, with procedures documented in NavalWarfare Publication (NWP) MSC Handbookfor Refueling at Sea, NWP 14-2 (Ref. M).The methods outlined there are suitable forpassing fuel, water, and other logistic necessi-ties to a tug with a tow. The method selectedis influenced mostly by sea and weather con-ditions, bearing in mind other factors that af-fect safe and efficient ship handling. Due toreduced maneuverability of a tug with a tow,consideration should be given to having thesupply ship maintain station on the tug, vicethe receiving ship maintaining station. It maybe advantageous to replenish from astern ofthe replenishment ship due to speed and ma-neuvering limitations. It is also possible to re-plenish from the tow.

6-4.7.1 Transferring Personnel and Freight

Simple light line procedures are used fortransferring small freight. During these trans-fers it may be advantageous, as in fueling, fora transferring ship to keep station on the tug.

Personnel and mail should be transferred byboat or helicopter. In unusual circumstances,personnel can be transferred by rigging a highline, or, if necessary, a Stokes stretcher. Con-ditions permitting, a rubber raft or boatshould be used to avoid the maneuvering re-strictions of underway replenishment.

6-4.7.2 Emergency Replenishment

Emergency conditions, wartime operations,or heavy weather may require great ingenuityto replenish the tug or tow. Water and fuelcan be received from the tow, if available, byshortening the towline and streaming hosesfrom the tug. In calm seas, the tug may go

alongside the tow to effect necessary replen-ishment. This requires disconnecting the tow,but in calm seas reconnecting should pose noproblem.

6-4.7.3 Rigging and Use of Fueling Rigs

Surging, often experienced in towing, may re-quire that the replenishment ship keep stationon the tug. The greater maneuverability of theoiler and the lack of complete control by thetug recommend this procedure. The tug des-ignates the fueling station, receives the hose,and proceeds to take on fuel while employingstandard precautions of proper stability, safe-ty on deck, adequate communication, andproper navigation. Astern refueling is alsorecommended.

6-4.7.4 Astern Refueling from Another Tug

Being refueled astern from another tug whiletowing has become a common procedure dueto the limited number of replenishment ships.This process is somewhat different than thatdescribed in NWP 14 and can be accom-plished with or without the sending ship tak-ing the receiving tug in tow. Due to the slowpumping rates available, however, taking thereceiving tug in tow does simplify stationkeeping in what is sometimes a 24 to 36 houroperation.

6-4.7.5 Replenishment Near a Port

The towing ship can arrange a temporarytransfer of the tow to a local tug or tugs (seeSection 6-5.5). Then the ocean tug enters portto replenish, while the tow is maintained off-shore by a temporary replacement tug, or off-shore mooring. When replenishment is fin-ished, the towing ship returns, the tow is re-transferred, and the journey resumes.

If a long replenishment is anticipated, it maybe more economical to seek temporary dock-ing for the tow.

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6-5 Terminating the Tow

Terminating the tow at its destination requiresas much planning as any other phase in tow-ing. If the schedule and the condition of thetow permit, it is generally best to adjust speedto arrive at destination during daylight hours.Darkness can easily magnify a routine evolu-tion into a more difficult and dangerous situa-tion. Based on the nature of the tow, pilot as-sistance and/or harbor tug assistance might berequired.

6-5.1 Requesting Assistance

The Commanding Officer decides when touse a pilot, unless an order from senior au-thority supersedes. Some pilots, however,may be unfamiliar with towing and with thecharacteristics of the tug. If a pilot is not fa-miliar with towing, it may be preferable toemploy him as an advisor to the Conning Of-ficer rather than giving him the conn. TheCommanding Officer should be alert to diffi-culty and relieve the pilot if he deems it nec-essary.

Harbor tug assistance may also be necessary.Sea conditions may not permit harbor tugs tomake up alongside. In this case, the only sig-nificant assistance that can be rendered is forthe harbor tug to put a head line to the tow’sstern to assist in steering the tow. Once withinsheltered waters, harbor tug assistance can beused as required. If an additional tug is avail-able, it and the original tug can be made up,each on a quarter, to effectively keep the towheading fair to the channel. If the tow is largeand unwieldy, additional tugs may provideboth steering assistance and propulsion pow-er. When using multiple tugs, it is advisableto have pilots on board both the tug and thetow to coordinate control of the assistingtugs.

6-5.2 Shortening the Towline

When approaching restricted waters, a shorterscope and slower speed will make the toweasier to handle. It may be necessary to bringa tow to short stay to prevent the towline fromfouling on the bottom. Bringing a tow to shortstay avoids being overtaken and fouling thetowline. A delicate balance must be main-tained between scope and speed. In this situa-tion, an automatic towing machine is invalu-able. Because there will be little or nocatenary, automatic control of the towline orthe use of a synthetic spring (see Section4-6.5) are the only means of surge controlavailable. An automatic towing machine canshorten the scope in either automatic or man-ual modes. Often where there is a long dis-tance from sea buoy to berth, the ocean tugmay continue to tow, at short stay, to a conve-nient and safe location well inside the harbor.

6-5.3 Disconnecting the Tow

Before actually disconnecting the tow, lay outnecessary equipment, energize potentially in-volved machinery, and brief all personnel onprocedures. A well-drilled, disciplined teamwill perform the routine smartly and will alsobe responsive to any unexpected occurrences.

Disconnecting procedures start by reducingspeed to bare steerageway and bringing thetow up short with the towing winch. With as-sistance from whatever harbor tugs are in at-tendance, the towline is shortened until theconnection fittings are on deck. A stopper ispassed onto the pendant, the connection isbroken and with all personnel clear, the stop-per is released.

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When a tow bridle is long enough, the pen-dant can be brought fully aboard the tug anddisconnected at the bridle apex. This maykeep the pendant from dragging the bottom.The bridle and pendant may also be retrievedon the tow by using a previously rigged re-trieving line at the bridles apex. (see Figure4-18).

When slowing, the towline scope may need tobe reduced to prevent dragging the bottom. Adecrease in speed will cause a decrease intowline tension when the tow closes on thetug. As the tug and tow separate again, an in-crease in tension will occur. Deceleration,like acceleration, must also be done in a con-trolled and judicious manner. (See Section6-7.5 for information on anchoring with atow.)

6-5.4 Towing Delivery Receipt and Reports

If a harbor tug master is authorized to receivethe tow formally, he should be asked to do so.This allows physical and legal transfer instream without having to dock or anchor. Ifthe harbor tug master is not authorized, it maybe necessary to send personnel ashore to ob-tain necessary signatures on the letter of ac-ceptance. Sample forms for receipt of towand towing reports can be found in AppendixH.

6-5.5 Transferring the Tow at Sea

Casualty, operational orders, weather, or oth-er unusual circumstances may require trans-ferring the tow to another tug. Preparing fortransfer and understanding the transfer proce-

dure will ensure success and minimize diffi-culty. If possible, personnel from both vesselsshould review and agree on a plan prior toany action. Emergency conditions may not al-low this.

The following procedure may be used for dis-connecting the towline and passing the tow(see Figure 6-7).

a. Set a course into the seas and reduce spe-ed.

b. Heave in until the pendant is on deck.

c. Signal the receiving tug to come closeaboard on the designated side on a paral-lel course.

d. Secure tow bridle or pendant on deck witha chain stopper; allow sufficient length tolay on deck to facilitate disconnectionfrom the hawser.

e. Break the tow hawser from the pendant.

f. Receiving tug passes a messenger con-nected to the bitter end of its hawser or toa messenger strong enough to control thetow.

g. Bring the receiving tug’s hawser or heavymessenger on deck and bend it onto thetow pendant.

h. With all lines and personnel clear, trip thestopper and transfer the tow to the receiv-ing tug.

i. If a messenger was used, the receiving tugmakes the final connection to the towpendant on its own stern.

j. All special equipment and personnel asso-ciated with the tow are then transferredand appropriate documentation completed.

6-6 Tow and Be Towed by Naval Vessels

All U.S. Navy ships (except submarines andaircraft carriers) are capable of towing, using

CAUTION

Do not permit the disconnectedpendant or bridle to drag on thebottom — it can cause consider-able additional resistance and seri-ously disrupt maneuvering.

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their own emergency towing hawsers. Whentwo Navy ships are involved in a “tow and betowed” operation, each provides its ownemergency towing hawser to form half of thetotal towing system (see Figure 6-8).

Some Navy ships may be equipped with old,little-used hawsers. These ships may not beaware of the recently understood problemswith deterioration of nylon rope over time.All should be alerted to current directivesconcerning replacement of emergency towinghawsers. Double-braided polyester hawsers(MIL-R-24677) are preferred.

6-6.1 Towing Systems

Navy combatant surface ships have a towingpad and stern chock aft and a chain stopperpad (towing pad) and bow chock forward.Sometimes, because of equipment interfer-ence, the stern chock and towing pad are lo-cated on the quarter.

In addition to these deck fittings, Navy sur-face ships carry a towing hawser, chafingchain, pelican hook, shackles and other ap-pendages needed for emergency towing oper-ations.

Each ship in the Navy is provided with a tow-ing drawing that shows how to rig the ship forbeing towed or for towing another ship. Thisdrawing also shows such details as towinghawser size, chafing chain, and other append-ages. For surface ships and some submarines,the Ship’s Information Book (SIB) has detailson their towing gear and also contains dia-grams that illustrate how to rig for beingtowed or for towing another ship.

Aircraft carriers are only equipped to betowed. They do not have a padeye or othertowing equipment located aft for towing an-other ship. Carriers are equipped with a 2-1/2inch diameter 6 x 37 galvanized wire rope,900-foot towing hawser. The towing hawseris stored in the anchor handling compartmenton a horizontal storage reel.

Some submarines carry a towing bridle onboard, but in some cases (SSBN 726 Class),the towing gear is stored ashore. In this case,this equipment shall be provided by the tow-ing ship. Submarines are built with the neces-sary towing pads, cleats and chocks for beingtowed. When not in use, the cleats and chocksare arranged to retract and are housed insidethe faired lines of the hull. See Appendix J formore detail concerning submarine towing.

6-6.2 Towing Procedures

The information presented here is taken fromNSTM CH-582 (Ref. A) which is the govern-ing document for emergency ship-to-shiptowing. Where this manual and NSTM CH-582 differ on this topic, NSTM CH-582 shalltake precedence. Consult this reference forgreater detail.

6-6.2.1 Procedure for the Towing Ship

1. Connect the pelican hook to the after-tow-ing pad with a shackle.

2. Connect the chafing chain with an endlink to the pelican hook. Lead the chafingchain through the stern chock.

3. Connect the towing hawser end fitting tothe chafing chain with a detachable link.

4. Fake down the towing hawser clear forrunning fore and aft. Stop off each bightof the towing hawser to a jack stay with21-thread. Place shoring under the stopsfor ease in cutting.

5. Connect the NATO towing link to the freeend of the towing hawser. If a NATOtowing link is not available use an appro-priate size long link or shackle. This fit-ting should be capable of being connectedto the hawser of the towed ship.

6. Connect a messenger, composed of ap-proximately 100 fathoms (600 feet) ofthree-inch circumference line and 50 fath-oms (300 feet) of 1-1/2 inch circumfer-ence line (For a 10-inch circumference or

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Figure 6-7. Passing a Tow at Sea.

6-25


Figure 6-8. Tow-and-Be-Towed.

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larger hawser, use four-inch line insteadof three-inch), to the outboard end of thetowing hawser. Lead the free end of themessenger through the stern chock.

7. Pass the messenger to the towed ship us-ing a heaving line. Preparing extra heav-ing lines prior to hook up will allow sev-eral attempts to complete this pass duringmaneuvering. Control the pay out of thetow line messenger and hawser by cuttingthe stops. The tow line messenger andhawser should be payed out gradually toease handling of the tow line by the towedship and to avoid fouling the towing shipspropellers.

6-6.2.2 Procedure for the Towed Ship

1. Stop off the anchor (port or starboard) ofthe anchor chain to be used. Set up on theanchor windlass brake. Pass a pinch barthrough the chain, letting the bar rest onthe lip of the chain pipe, or pass a preven-ter to prevent the chain from backingdown into the chain locker and a preven-ter on the anchor to back up the stopper.Break the anchor chain at the detachablelink inboard of the swivel. If power isavailable, haul out the desired length ofchain using the anchor windlass. If poweris not available, the chain will have to behauled out manually.

2. Shackle the towing chain stopper to thedesignated (towing) padeye on the fore-castle, for stopping off the anchor chainafter the tow is properly adjusted.

3. Fake out the towed ship’s hawser ondeck, fore and aft, on the forecastle forclear running, prior to connecting it to theanchor chain. Use the towing ship’s mes-senger to haul the towing hawser from thetowing sh ip on board through thebullnose. Connect it to the towed ship’shawser secured to the end of the anchorchain. If the towed ship’s hawser is not tobe used, connect it to the anchor chain.

4. Pay out sufficient anchor chain (5 to 45fathoms [30 to 270 feet]) to provide a sub-stantial towing catenary when the towinghawser has been payed out. Syntheticline, by itself, will provide very little cate-nary.

5. Set the brake on the wildcat and pass andequalize the chain stoppers one outboardand one inboard of a detachable link, totake the strain on the towed ship’s anchorchain. Disengage the wildcat.

6-6.2.3 Quick Release of Towed Ship

1. Pay out the anchor chain connected to thetow line on board the towed ship so that adetachable link is just forward of the an-chor windlass.

2. To prevent the chain from returning to thechain locker when detached, pass chainstoppers on the anchor chain and lash theanchor chain just abaft of the detachablelink or apply the chain compressor wherefitted.

3. Disconnect the anchor chain between theanchor windlass and the chain stoppers sothat only the chain stoppers are holdingboth the anchor chain and tow line. Thisarrangement allows quick release of thetowing hawser and chain.

6-6.3 Getting Underway with Tow

Implement the following steps when the tow-ing hawsers are connected and both ships areready to start the tow:

1. The towing ship should come ahead asslowly as possible as the hawser begins totake strain. Increase turns slowly until theinertia of the tow is overcome and both

CAUTION

In case of emergency, for quick re-lease, tripping the pelican hook onthe towing ship is faster than theabove procedure.

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ships are moving with a steady tension inthe hawser. Increase speed slowly untilthe desired speed is reached. At no timeshould the tow speed be such that the towhawser lifts completely out of the water.The course of the tow may be changedgradually, as necessary. Getting under-way with a tow will likely result in thelargest tensions and requires the mostcare.

2. Pay out or haul in (assuming power isavailable to the anchor windlass) anchorchain as desired to keep both ships in step(that is, taking wave crests at the sametime). When a comfortable distance isfound, the chain stoppers are passed onthe anchor chain and the strain is equal-ized between stopper and wildcat. Lock-ing plates are installed and set on both thechain stoppers.

6-7 Emergency Towing Procedures

This section presents general guidelines forhandling emergency situations unique to tow-ing. As in all emergencies, prudent seaman-ship and adherence to safety guidelines areprimary assets in bringing a situation safelyunder control.

6-7.1 Fire

Fire on board is a well-known hazard; fireprevention and methods of fighting firesshould be drilled with the riding crew. Thereshould be little danger of fire on board an un-manned tow. One exception is the possibilitythat a shaft locking device might fail andcause an engine room fire.

When a riding crew is on board, the fire po-tential should be evaluated. If equipment isbeing operated for propulsion, auxiliary pow-er, pumps, or allied systems, the danger offire can be significant. Prudent and adequateplacement of pumps, hoses, fire extinguish-ers, axes, foam, and fire fighting equipment isrequired to help the riding crew fight fires. Ifnecessary, personnel may be transferred fromtug to tow to perform fire fighting and dam-age control. The tug, if it can be broughtalongside, can deliver large quantities of wa-ter for use on board the tow; associated pow-er, foam, hoses, and personnel from the tugcan be of valuable assistance. A charged 2½-inch fire hose can be streamed aft on salvageballoons if alongside fire fighting is not prac-tical.

6-7.2 Tug and Tow Collision

The tug and tow may collide when maneuver-ing in restricted waters with the tow at shortstay, or under other operationally complexcircumstances. A collision may also occurwhen:

• There is a loss of propulsion power orsudden reduction of the tug’s speed.With sufficient way on, the tow mayoverride the tug, and in extreme cir-cumstances sink it. The possibility isgreater if a tow is at short stay. If pro-pulsion power is lost on the tug, put therudder hard over to the weather andslack the towline. With sufficient wayon, the tug may fall clear of the advanc-

CAUTION

Riding crews normally consist of aminimum crew and can be expect-ed to perform only limited emer-gency functions on board.

CAUTION

When towing under unfavorableconditions, inclement weather, orat short stay, danger exists of be-ing overridden. In such a situation,particular care is advised in settingan underway material condition sothat watertight doors, hatches, andother openings are secured.

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ing tow. If power loss is imminent butthe tug can still make turns, considergoing alongside or otherwise clearingthe tow.

• Tug and tow will experience differentset and drift from seas, currents, winds,or towline drag. To avoid collision, re-duce speed and increase the towlinescope. If possible, the tug should turninto the predominant set, if the tow hasa larger sail area. This will cause thetow to drift away from the tug. Followthe opposite course if the tow’s sail areais smaller than that of the tug, as in thecase of a submarine.

• A tug and tow are dead in the water, al-lowing towline cantenary to draw themtogether. The same situation can occurbetween two tandem tows. In an emer-gency in shallow waters, it may be pos-sible to anchor both tug and tow by let-ting the towline come into contact withthe bottom. (Routine use of this prac-tice is discouraged because of possibletowline damage.)

If a collision appears unavoidable, deployingfenders may serve to reduce or eliminatedamage to both vessels.

6-7.3 Sinking Tow

Planning to sink a tow also requires specialconsideration and preparation. Often, specialpermission must be obtained and adherenceto environmental regulation can be difficult.Caution should be used when accepting a towwith the intention of sinking. This may be thecase following a salvage operation.

Flooding, structural damage, shifting of ballastor cargo, or other events may degrade the tow’sstability. When stability decreases, the tow maybe in danger of sinking. Excessive force placedon the tug as the tow sinks can damage and se-riously endanger the tug before the towlineparts. Prompt action is necessary to save thetow and to ensure the safety of the tug.

It is vital to monitor the condition of the towduring transit. Trim, list, roll period, seakeep-ing, and draft are monitored from the tug orby a riding crew. Upon noting an irregularity,a boarding party should be dispatched, if pos-sible, to investigate and correct any deficien-cy on board the tow. If the material conditionof the tow is so deteriorated that sinking islikely, the tug should consider the followingcourses of action.

6-7.3.1 Beaching a Sinking Tow

When towing a casualty or a vessel that islikely to sink, beaching may be the best wayto save the tow. The decision to beach the towis operational and should be based on an as-sessment of conditions. Weather conditions,rate of deterioration of the tow, damage con-trol equipment available, and distance to safeport should all be considered when decidingwhether to beach a tow. Permission to beachshould be obtained from the cognizant au-thority when feasible. Authorization to beacha tow should be made by immediate messageor voice communications when feasible. Sig-nificant time may be required to steam to asuitable site. It may be impossible to locate asmooth beach in time. If pumps are on boardthe tow and damage control procedures areemployed, the tow may be kept afloat fordays before beaching, but indecision has re-sulted in tows sinking.

When beaching a tow, follow these guide-lines:

• When possible, select a beach with asmooth, gradually sloping bottom.Avoid rocky shores with breaking surf.

CAUTION

When combatting a sinking tow,conditions can deteriorate rapidly.The boarding party should havesufficient survival gear and shouldbe prepared to abandon at any giv-en moment.

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Potential loss of the tow and danger tothe tug exist in shallow, rocky waters.

• Ground the tow with the bow towardthe beach. The tug’s assistance may berequired to put the tow on the beachbow first. If water depth is sufficient,the tug can tie up alongside in the lee ofthe tow and take the tow in. The alter-native practice of allowing a tow todrift onto the beach should be avoided.This can increase the likelihood ofbroaching and cause increased damageto the tow as well as make recoverymore difficult. Assistance from a small,shallow draft harbor tug is very valu-able when beaching a tow.

• Disconnect the pendant and bridle be-fore beaching, when possible, to pre-vent the tow from stopping short of thebeach.

• Prevent the tow from broaching andsustaining additional structural damagedue to excessive hull loading. Floodingthe tow can prevent it from broachingor going further aground. The shipshould be set down hard enough so thatit will not be too light and, consequent-ly, broach at high tide. It should be as-sumed that in time the tow will bepulled off; however, this does not elim-inate the need for securing it properlyand preserving it until it is extractedfrom the beach. If the tow has a sternanchor, it should be deployed to helpprevent broaching.

• Ballast the tow as soon as possible aftergrounding to hold it securely in posi-tion. Even in completely sheltered wa-ters, the range of tides and consequentcurrents can be powerful enough to al-ter the position of a beached ship.

6-7.3.2 Slipping the Tow Hawser

In emergencies, wartime conditions, or heavyweather, it may be necessary to slip the towhawser to remove the tug from a hazardouscondition. This condition could be a sinkingtow, danger to the tug from weather, or agrounded tow.

Options for slipping the hawser include:

• Paying out the hawser and allowing itto run off the towing machine (free-wheeling).

• Cutting the hawser with a torch or ex-plosive cable cutter. Synthetic hawsersunder no tension can be cut with an axe.

• Rigging carpenter stoppers and cuttingthe cable inboard of the stopper.

• If a ship with power is being towed, itcan sometimes cast off the towing pen-dant on the tow’s bow.

If time allows, attach a buoy to the bitter endof the towline before slipping the hawser,otherwise, it will be difficult (if not impossi-ble) to recover. Use a messenger that is atleast 200 feet longer than the water depth andstrong enough to lift the hawser. One end ofthe messenger is connected to the hawser andthe other to a recovery buoy line. The buoyline must be long enough to reach the bottomand strong enough to lift the messenger, but itneed not be strong enough to lift the hawseritself. The buoy should be adequately markedwith a bright color, radar reflector, staff, orflag so it can be easily located.

CAUTION

Releasing the hawser under ten-sion, or even its own weight, canbe hazardous, due to retained en-ergy in the hawser.

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6-7.4 Disabled Towing Machine

The main resource for recovering and storinga towline is the tow machine. If this machinefails, the tow ship should reduce speed and at-tempt to make repairs. The machine's me-chanical brake should be set to prevent an ac-cidental spooling off of the tow wire. If themachine cannot be fixed, it will likely be nec-essary to disconnect the tow, transfer the towand recover the towline by a more difficultmethod. Since Navy tugs employ a 2 1/4-inchwire rope, these evolutions can be very diffi-cult.

6-7.4.1 Disconnecting the Tow

If the tow machine fails while the tow is stillconnected, it will be necessary to break thisconnection at some point along the towline. Ifa retrieving wire has been rigged, this maynot be so difficult. If there is power on thetow, it should haul on the retrieving wire untilthe connection point is on deck. A chain stop-per (or other appropriate stopper) should bepassed on the towline with sufficient slack tobreak the connection without tension on theline. It may be necessary to rig a stopperaround the tow ship's towline to allow a con-nection to be broken. It may be sufficient tohaul in slightly on the main chain pendant,and break the connection at the main towingpadeye. Only stoppers with quick release ca-pability should be used.

The exact disconnect method and stopper tobe used is an operational decision and de-pends on many factors. If the tow is at itspoint of destination, and the main tow rig canbe destroyed, explosive cutters or torchesmay be an appropriate method of disconnect-

ing. The use of divers may be possible but,because of the inherent danger, should beused when there is no other solution. Ship-handling and working with heavy gear in aseaway are complicated evolutions that aremade more so when there are people in thewater.

If a retrieving pendant has not been rigged,the procedure is far more complicated anddivers may be the only solution. Sliding aworking line down a chain pendant has beendone with varied success. The loop may snagon the way down or slide off during retrieval.It may be better to attempt to run a shacklealong the tow wire, but this may also meetwith varying success. Certainly, divers canmake these evolutions more successful byproviding assistance to keep the line un-fouled. A better solution may be to use diversto rig a retrieval line. Depending on thelength of the pendant divers may be able toattach a line at the bitter end of the chain; atthe connection point. This is unlikely, though,since there will probably be a pendant longerthan 90 feet. If divers are working in SCUBA,bottom times will limit the amount of workthat can be done. However, divers may beable to rig a retrieving line of sufficient lengthto haul the main pendant on deck. By lacingsmall wire through links of chain 40 or 50feet below the surface, the chain can bebrought on the deck of tow ship (or an assist-ing vessel), once it has maneuvered along-side. The tow ship's deck machinery can beused to haul the heavy gear on board oncedive operations are completed.

Dive Supervisors must be provided with anaccurate and detailed sketch of the entire towrig. This will enable them to develop a safeand efficient plan and ensure that they areprepared with the proper tools to accomplishthe mission.

WARNING

When stopping the tow line forbreaking, only stoppers withquick release capability shouldbe used.

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6-7.4.2 Recovering the Towline

Once a tow has been disconnected, it is stillnecessary to recover the towline without theassistance of the main towing engine. Thetow ship is faced with two problems. Thefirst, how to recover the wire and second, iswhere to put it once its on deck. The weightof a 2 1/4-inch IWRC wire is almost 10pounds per foot. A typical towline scope is1500 feet or more. This is a total weight of al-most 15,000 pounds. It cannot be handledeasily without machinery.

Recovering a towline can be accomplished inseveral ways. One way is to slip the hawseroff the drum and recover it when repairs havebeen made. A marker buoy and suitable mes-senger should be rigged to the bitter end so itcan be found later. A messenger should bestrong enough to be able to lift the hawser ondeck for the depth of water. It need not bestrong enough to lift the entire hawser, but ifit breaks, divers will be required to rig anoth-er messenger, and it is very likely that thehawser will not be found without the markerbuoy. Moderately deep water will make thisalternative impractical. Additionally, it isprobably unwise for the tow ship to try tobring the hawser to shallow water. Assumingthe hawser is at a scope of 1500 feet or more,the hawser will drag the bottom for some timebefore sufficiently shallow water is reached.This may damage the hawser or cause maneu-vering problems for the tow ship.

Another way to recover towline is to use deckmachinery and carpenter stoppers. This meth-od requires a great deal of time and a largeamount of manpower. Assistance from shorecrews may be advisable. This method doesnot solve the problem of stowage. A largedeck area will be needed to fake out (figure-eight) this amount and size of wire. It may bepossible to hang the wire from the side of thetow ship and stop it off in bights, similar tothe method used when preparing a main towpendant on a tow, or a leg of beach gear. This

process will also be laborious and time con-suming.

A third method that may be used is to turn thetowing drum manually. A wire can be se-cured to a point on the side of the towingdrum and looped around the drum in the di-rection of reeling. A crane can pick up the bit-ter end and be used to lift this line and conse-quently turn the drum. Careful coordinationbetween the crane operator and a crewmanmanning the drum brake is required to pre-vent accidental un-spooling of the wire. If acrane is unavailable, deck machinery can beused if sufficient blocks can be rigged toreeve the hauling wire in the right direction.

These are by no means the only methods ofretrieving a tow wire, but are a few examples.Any of these methods require substantialmanpower and large amounts of time. Thisprocess, like all towing procedures should beperformed with close attention to safety ofpersonnel.

6-7.5 Anchoring with a Tow

In general, anchoring should always be con-sidered less desirable than remaining under-way. Steaming with a tow may prevent manydifficulties encountered at anchor. Providedthat there are no limiting operational factorsand there is sufficient sea room, steaming isusually the better choice. When anchoringwith a tow is necessary, the following alterna-tives should be considered.

• Reduce speed to bare steerageway,head into the predominant set, allow thetow to remain well astern, and then re-duce speed and allow the tug and tow tocome dead in the water at the anchordrop point. Let the tug’s anchor go andpay out the necessary scope of chain.The tow will follow as affected by set.

• Reduce speed and approach severalhundred yards to port or starboard ofthe desired anchorage. With the anchor-

6-32


age position broad on the bow and ap-proaching abeam, put the tug’s rudderhard over and reduce speed; maneuverto hold at the anchoring point, lettingthe tow pass by. When the tow clearsthe tug, drop anchor.

• The tow can be taken alongside in fa-vorable sea and wind conditions. Withthe tow alongside, the tug can maneu-ver in restricted waters, back down asnecessary, and drop anchor.

In some circumstances, such as shallow wa-ter, the towline itself may be used for lightholding of the tow and tug when the towlinecomes in contact with the bottom. Routineuse of this practice is discouraged because ofpossible damage to the towline.

If there is little wind or current, the tug mustbe alert to the probability of the hawser’sweight pulling the tow toward the tug, untilthe hawser rests on the bottom.

6-7.6 Quick Disconnect System

Most routine point-to-point tows are securelyrigged with no provision for quick release,other than slipping the tow wire from the tow-ing ship. When towing damaged ships, how-ever, it may be desirable to provide for aquick release of the tow pendant or bridle tofacilitate breakup of the tow. Even if the towhawser has already been disconnected, theweight of the chafing pendant or bridle legs

will be significant, and must be considered inselecting the means of disconnecting.

In the case of a damaged ship, the tow pen-dant or bridle legs, if chain, should be secure-ly held by multiple chain stoppers, each bear-ing equal tension. If the pendant or bridle legsare wire, then provision should be made forcutting with an oxyacetylene torch, a cablecutter, or any similar device. As cutting is ex-tremely hazardous, precautions should be tak-en to prevent whipping, and the wire shouldbe seized on both sides of the intended cut.When an emergency quick disconnect is pro-vided, make sure that all jewelry will fitthrough all fairleads.

6-7.7 Man Overboard

Standard man overboard maneuvers may notbe feasible in towing situations, primarily be-cause of the time involved and the tug’s limit-ed maneuverability.

• If maneuvering is limited, the tug sho-uld stop, or at least reduce speed to baresteerageway, and recover the manoverboard using a boat. If the tug isstopped, take precautions to keep thetow from overriding the tug and to keepthe towline clear of the propellers.Communications should be available

CAUTION

The mooring loads of the tug andtow may be greater than the hold-ing power or strength of the tug'sground tackle. A dragging anchoror failure of the ground tackle ispossible, resulting in loss of controlof the tug and tow.

WARNING

The tow wire or bridle will likelybe under tension when released,creating an extremely hazardoussituation. All nonessential per-sonnel must evacuate the areato prevent serious injury.

CAUTION

The towing ship should reduce thetension on the towing assembly byeither slowing down or stopping pri-or to cutting or otherwise releasingthe tow rig.

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between the boat and the tug so that thetug can direct the boat to the man.

• If the recovery requires maneuveringthe ship back to the man, seamenshould be stationed with heaving lines.Swimmers should be outfitted with im-mersion or wet suits and safety linesready to swim out to the man.

6-7.8 Using an Orville Hook to Recover a Lost Tow

Using an Orville Hook to recover a lost towwith a chain bridle may be a viable option if asecondary towline is not available or it is notpossible to recover the secondary towline.

6-7.8.1 Origin of the Orville Hook

The Orville Hook was initially designed andpatented by SAUSE BROS TOWING, Inc torecover lost tows which had a chain bridle.While the patent for this device has expired itstill remains a useful tool for emergency re-covery of broken or lost tows. This devicewas successfully used to recover the dry dockSUSTAIN when recovery of the secondarytowline was not possible due to fouling.

6-7.8.2 Use of an Orville Hook

Orville hooks are only recommended for re-covering tows which have a chain bridle.They are not recommended for recovery ofwire or synthetic tow pendants.

Figure 6-9 and 6-10 depict the general config-uration of the Orville Hook and its variouscomponents. Figure 6-11 depicts deploymentof the Orville Hook.

The Orville Hook is suspended in the hori-zontal plane by a trailing buoy and is towedparallel to the tow by the recovery tug. Oncethe recovery tug has overtaken the tow by asufficient distance dictated by the length ofthe towline, the recovery tug swings acrossthe bow of the tow thereby snagging themouth of the Orville hook on the chain bridle.The Orville hook is sized to fit between theindividual links of the chain. In most casesthe Orville hook will remain in place as longas tension is kept on the synthetic pendant.The synthetic pendant can then be retrievedalong with the chain bridle so a more perma-nent connection can be made between the towwire and the chain bridle.

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Figure 6-9. Orville Hook Retrieval Assembly

6-35


Figure 6-10. Orville Hook Configuration

6-36


Figure 6-11. Deployment of the Orville Hook

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This Page is Intentionally Left Blank

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Chapter 7

SPECIAL TOWS

7-1 Introduction

This chapter addresses tows of unusual con-figuration that occur infrequently or are of ahighly specialized nature. Topics includetowing in ice and towing targets, submarines,merchant ships, and NATO ships in peril.Emphasis has been placed on rigging and pro-cedural differences between these types oftows and towing operations previously dis-cussed.

As their recurrence is unpredictable, thesetypes of tows are not treated in depth in thismanual. Instead, these topics are presented tomake planners and operators aware that suchoperations have been successfully completed

in the past. When faced with a similar situa-tions, they should refer to reports of actualoperations.

7-2 Target Towing

The primary functions of ships such as theT-ATF, and ARS classes are salvage andocean towing; target towing is a secondaryfunction routinely assigned to them. Mostcombatant ships can tow target sleds withtheir standard shipboard equipment.

7-2.1 Williams Target Sled

Currently the catamaran-hulled Williams Tar-get Sled is the target used most for gunneryexercises (see Figure 7-1). The Navy also us-es sonar buoys, arrays, drones, and remotelyoperated boats as targets. Targets are towed,escorted, or carried as deck cargo to the oper-ations area.

Figure 7-1. Williams Target Sled Rigged for Tow with Righting Line Streamed.

To Tow

Righting StrapShackle

Coil Excess Line in Harborand Deploy Prior to Stream ing Target

60-Foot Length of O ld1-Inch Circum ference Towline

Float

7-1


7-2.2 Towing Equipment

The Williams Target Sled is towed from asynthetic line bridle shackled to the inboardsides of the catamaran hulls. The two bridlelegs are joined by a triangular flounder plate;a 30-foot pendant of synthetic line is alsoshackled to the flounder plate. The pendant isshackled to the main synthetic towline.

The towline is generated might cause thetarget to list or a damaged sled to capsize.

7-2.3 Routine Procedures

7-2.3.1 Transporting the Target to the Exercise

The tug can either pick up the target at itsberth or have the target brought out of theharbor by a delivery ship, usually a workboat. If a delivery ship is used to bring the tar-get out of the harbor to the towing ship, slowdown and maintain steerageway so that thedelivery ship can easily approach the stern.

For tows that begin at the target’s berth, thetarget can be made up to the towing shipbow-to-stern alongside (with the towlineshackled to the target’s bridle pendant),bow-to-bow alongside, or bow-to-stern aft ofthe towing ship. The target can also be madeup on the fantail of the towing ship. (It maybe similarly made up on the fantail duringprotracted delays between exercises or in theevent of impending heavy weather.) If the tar-get is made up on the fantail, use the ship’scrane or boom to set the target overboard up-on arrival at the operations area.

If the tow is made up in the water, slip the tar-get mooring lines when clear of the pier. Towtarget at short stay until clearing congestedwaters. Steaming at short stay does not affectmaneuverability or speed. When clear of theharbor and congested waters, about 600 feetof towline is usually streamed. If the towlineis not on the drum of a winch, it may be paidout using a gypsy head or capstan to maintaincontrol. Ships with towing bitts can controlthe payout of towline by taking turns aroundthe bitts. When enough line has been paid out,the towline is stopped off to the towing bittswith the towline passing over the stern roller.Speed is then built up slowly until the targetis towing steadily. If towing at night, makesure that the target’s stern and side lights arelit.

7-2.3.2 Streaming the Target

The towing ship times its arrival at the firingrange long enough before the exercise beginsto allow time to stream the target. Slowing toabout 4 knots and paying line out at 150 feetper minute is a safe way to stream.

7-2.3.3 Making Turns with the Target

Depending on the weather, turns can be madein one increment by using a small amount ofrudder so as to have about a 1,000-yard diam-eter turning circle. When making turns, keepthe target aft of the towing ship’s beam, pref-erably broad on the quarter.

When proceeding on a circular course, thetarget’s tendency to capsize is determined bythe speed of the tow, length and depth of tow-line, and the sea state and heading relative tothe wind. Turns to windward are differentfrom turns to leeward. When turning into thewind, the target screen area acts as a mainsailand holds the target away from the turn, re-quiring an increased rudder angle and givinga smaller transfer with a slightly greater ad-vance. When turning leeward, the screen actsas a sail effect and propels the target towardthe inner part of the turn, requiring less rud-

CAUTION

If the target is made up bow-to-stern, it should reverse directionand swing into posi t ion whenslipped. Too much way on, howev-er, will cause the target to be towedstern first. In a stern-first position,the target has a tendency to streamaft without reversing itself and canend up straddling the towline.

7-2


der and performing a greater transfer withless advance.

In all turns the target acts as a sea anchor,making a small tactical diameter while theship turns around the target with a larger tac-tical diameter. Turns with the current increasetransfer; turns against the current reducetransfer. The advance in all turns is small.

To keep the towline tension low and to avoidcapsizing the tow, keep the rudder angle aslow as is practical. A mean rudder angle of 12or 13 degrees is satisfactory. A good practiceis to make the turn in small increments,steadying up until the target is directly asternbefore going to each new increment.

7-2.3.4 Recovering the Target

When the exercise is over, the towline isheaved in to a shorter stay for the tow homeor brought up short so the target can be liftedaboard. Combatant ships use their capstans toheave the towline, MSOs use one drum of thesweep-wire winch, and salvage ships usetheir capstans or traction winches. Significanttime must be allowed to bring the hawser in ateven maximum capstan speed. Hawser recov-ery typically proceeds at 40 to 60 feet perminute. As soon as the towline is on board, itshould be faked on deck or spooled on a reel.

Upon entering port, the tow can either bebrought alongside, brought to short stay, orlifted aboard. The use of riding lines that havebeen stopped off on the tow hawser duringstreaming contributes to the ease of bringingthe sled alongside (see Section 6-2.3). Forleaving and entering port, some ships prefertwo-blocking the bow of the sled against theirstern. When the sled is firmly snugged intoposition and riding lines are added, this meth-od allows good maneuvering.

7-2.4 Special Procedures

7-2.4.1 Passing the Target to a Combatant Ship

It is sometimes necessary to pass a targetfrom one ship to another on the open sea. Thetowing ship selects the side and speed forpassing and signals this information to the re-ceiving ship well in advance of passing thetow. Stop off the hawser along one side of thetowing ship. The receiving ship steams intothe wind alongside the towing ship.

The receiving ship signals and sends a mes-senger when it is ready to receive the tow.The towing ship receives the messenger andsecures it to the hawser. The receiving shiphauls the messenger through its towingchock. The towing ship frees the hawser andthe receiving ship hauls it away (see Figure6-7).

7-2.4.2 Recovering a Capsized Target

A capsized target must be righted immediate-ly because it cannot be towed at any speed.Safety precautions must be strictly observedbecause of the hazards of recovery work.

WARNING

When tows are passed, most ca-sualties occur because the shipsdo not maintain a steady courseor speed or because the towingship releases the tow before theother ship is ready to accept thestrain.

WARNING

Always remain with a target sleduntil it is recovered or rightedand towed to port; it will becomea navigational hazard if left todrift.

7-3


If the target capsizes, the towing ship shouldheave in slowly. The ship may be required toback slowly while heaving in, being carefulnot to foul the towline in the propellers orrudder. Another method is to reverse courseand place the ship alongside the target.Weather conditions will determine the bestmethod to use for approaching the target.

Before getting underway, the target shouldhave been prepared for righting. A recoverypendant can be made from 60 feet of line and afloat. Attach one end of the line to the middleof the pipe framework at the apex of the tar-get. Coil the remainder of the line and secure itwith small stuff to one of the pipe frames nearthe trailing edge of one of the catamaran floats(see Figure 7-1). Tie the bitter end of the linewith a bowline onto the float. Before stream-ing the target, release the line and float tostream aft of the tow. If the sled capsizes, ma-neuver the ship alongside the sled and bringthe float and recovery line aboard the ship. Byleading the recovery line over the caprail to acapstan and heaving in, the sled can be madeto rotate to an upright position in a motion thatcarries the target away from the hull of theship. Once upright, inspect the target to makesure that it is not damaged and is fit for tow.

7-2.5 Target Towing Precautions

Take the following precautions when towinga target:

• Avoid surges

• Maintain a steady course, avoiding tig-ht turns

• Ensure that the target’s stern and sidelights are lit at night

• Do not tow the Williams Target Sledat speeds in excess of those authorizedby Fleet directives

• Do not tow a capsized Williams TargetSled

• Alter course gradually with a targetunder tow in order not to capsize thesled

• Approach the target with caution. Theshallow draft of the target sled causesconsiderable pitching and rolling atslow speeds or when drifting.

7-2.6 Other Targets

SEPTARs (Seaborne-Propelled Targets) areremote controlled, high speed surface targetsthat are transported to the operating area bya tug and then operated from the tug. Simi-larly, tugs can carry drone-type targets forantiaircraft and antimissile training exercis-es. They can also carry transducers and ar-rays for submarine and antisubmarine train-ing exercises. Each of these services isunique and presents special problems notfound with standard target sled towing.Some of the information necessary to sup-port specialized target services is classified.Generally, range personnel will provide spe-cific information regarding these specialsystems.

7-3 Towing Through the Panama Canal

Tows of unmanned vessels through the Pana-ma Canal present some unique concerns andoften require additional preparations. A canaltow may be the result of an East Coast de-commissioning of a nuclear vessel that needsto go to the West Coast for final disposal. Itmay be the result of an asset being transferredfrom a West Coast activity to an East Coastactivity. Either way, as more and more ves-sels are decommissioned, and assets becomefewer in number, tows through the canal havebecome more frequent.

The Panama Canal is unique and has restric-tions on size and requirements for specialbitts and chocks to accommodate tow wires.While many vessels that are designed forservice through the canal have the necessary

7-4


installed fittings, other ships, particularlywarships, may not meet all the specific re-quirements.

It is essential for a tow planner to fully under-stand the requirements when towing throughthe Panama Canal. Code of Federal Regula-tions (CFR) 35, Panama Canal (Ref. N) con-tains this information and is an invaluable re-source when planning a canal tow. It has alsoproven to be well worth the investment to flya representative from the Panama CanalCommission to the preparing yard. A walkthrough of the vessel by knowledgeable per-sonnel can identify any changes that need tobe made while the ship is still in the preparingyard. If the tow arrives at the breakwater inPanama, and does not meet the requirementsto go through, arrangements must be made toeffect repairs and modifications. This can re-sult in both substantial costs and delays. Ad-vance preparation is essential.

7-4 Towing in Ice

Arctic operations may require towing throughice. Towing ships may also be required torecover ships with no steering or propulsioncapabilities that have been stranded in iceconditions.

An icebreaker may be required for breakingthrough heavy ice, but Navy ocean tugs cantow through thin ice or broken ice. The NavyARS 50 and T-ATF Classes were built tomodified ice strengthening rules, but thosewith Kort nozzles are less suitable for heavyice operations.

The major considerations when towing in iceare:

• Protecting the hawser from ice dam-age. Long periods of exposure to icewill chafe and wear the hawser. To pre-

vent the hawser from coming into con-tact with the ice, adjust the catenary sothe chain bridle, or chain pendant entersthe water at the towed vessel. It mayalso be desirable to rig additional chainto help make this easier. This is ad-dressed in Allied Tactical Publication(ATP) 15, Arctic Towing Operations(Ref. O).

• Selecting the appropriate towing me-thod. When towing in ice, a tow shouldbe close to the tug’s stern to keep an icepassage open ahead of the tow. The towmay not have an ice-strengthened bowand could sustain impact damage fromfloating ice. Two approved towingmethods for keeping the tow close arethe short-scope method and the saddlemethod. The method used dependsupon type of towing ship and the de-sign of the ship being towed. The sad-dle method will ensure that the tow willnot encounter ice, but, if not riggedproperly, could cause damage to boththe tug and the tow.

7-4.1 Short-Scope Method

Navy ocean tugs should use the short-scopemethod because they have no saddles. A haw-ser scope of 150 to 300 feet should be main-tained. The tow’s rudder can be used, if nec-essary, to keep the tow in the tug’s wake.Occasional kicks from the tow’s propellermay also be necessary to augment the rud-der’s force. The tug’s propeller wash shouldkeep the tow from riding up on the stern; if itdoes not, the propeller of the tow should bebacked, if possible. Riding lines may be usedfor increased lateral stability (See Section

7-5


6-2.3). These lines will be very susceptible tochafing.

7-4.2 Saddle Method

The saddle method can be used by icebreak-ers and tugs with reinforced sterns and towingmachines. The U.S. Coast Guard has operatedsome icebreakers equipped with towing ma-chines or strengthened saddles. Even when atowing ship has a saddle, the saddle methodmay not be practical for tows with sharpprows, bulbous bows, or any other protuber-ances that can interfere with the tug’s propel-lers and rudders. Normally, the tow can bebrought up and held firmly in the saddle bythe towing machine.

If the tug does not have a saddle and the shortscope method of towing in ice is not feasible,a variation of the saddle method formerlyused by icebreakers may be possible for towships having strong, broad sterns. The tow isbrought up snug against the tug’s stern, usingextensive chafing gear, and heavy fenders.The towline is attached in the normal fashion;the towing machine should be in automaticmode to prevent the towline from parting ifthe ships pitch or surge. Two mooring linescan also be passed from the tug’s quarter-bitts

to the tow’s forecastle bitts to help keep thetow following fair. The tow’s engines can beused. If the tow begins to jackknife or sheeror yaw badly, however, it should slow at onceuntil it is again under control. A fire hoseshould be kept ready at the saddle or stern be-cause friction may cause fires in the chafingmaterial.

7-4.3 Rigging for Tow

The recommended gear for towing in ice con-sists of:

• Wire rope towing hawser

• A 2 1/4-inch chain pendant and connec-tion jewelry, or

• A 2 1/4-inch chain bridle with flounderplate and connection jewelry.

This heavy gear will provide protectionagainst the increased potential for chafing andimpact damage. Synthetic lines are not rec-ommended as main towing gear.

In a convoy with no icebreaker, any ship maybe expected to tow and should be prepared toboth tow and be towed. Rigging the tow bri-dle in advance quickly lowers the chance ofbeing caught in the ice. Gear should be pre-pared in advance; the crew should know howto complete the rigging quickly and safely.

Before entering the ice, the bridle or anchorchains should be rigged to receive a towline.Even when using a bridle, it is necessary tosecure bow anchors to keep them from strik-ing hummocks in the ice. This is especiallyimportant on low bowed ships.

7-5 Submarine Towing

This section provides an overview of emer-gency (unplanned) towing of submarines.Appendix J provides specific data that will beuseful in rigging submarines for emergencytow. For planned tows and for tows of deacti-vated submarines, consult NAVSEAINST4740.9E Towing of Unmanned Defueled Nu-

CAUTION

The tug should follow these recom-mendations and guidelines whentowing at short scope:

• The pull on the towline will besevere if the towed ship sud-denly contacts heavy ice.

• Take special precautions toprevent the chain bridle, chainpendants, and hawser fromchafing. An automatic towingmachine makes this easier.

• Avoid towing on the bitts theymay be torn out by the suddenincreases in tension if ice isencountered when towing atshort scope.

7-6


clear Submarines (Ref. P). This instruction,which takes precedence over this manual,may be useful also in planning and executingan emergency submarine tow.

Submarines are challenging tows. Eventhough they may be equipped for towing, thetowing arrangements are not as strong as ontypical surface ships, their configurationspresent serious topside personnel hazards,and they can be very poor at tracking behindthe tow ship.

7-5.1 Towing Arrangements

7-5.1.1 Retractable Deck Fittings

Modern submarines are built with essentiallyno flat surfaces on the main deck. All subma-rine deck fittings are either retractable or re-cessed. They are normally constructed so thatthey can be retracted to form a flush deck,and rotated into position where they can beused. In most cases, deck fittings can be ex-pected to be safe for working up to the break-ing strength of the line with which they arenormally used.

Most submarines have small hydraulic cap-stans, fore and aft, that can be useful in han-dling lines. They typically have a limited ca-paci ty of 3 ,000 pounds l ine pul l a t amaximum 40 fpm and a maximum pull of4,500 pounds at creep speed. These capstansare severely limited in assisting with the con-nection of a towing hawser. The tug, accord-ingly, should plan its connecting procedure tominimize reliance on the submarine’s cap-stans.

The controls for the retractable capstan areusually designed so that the capstan can beoperated from topside. The machinery, how-ever, is activated from inside the submarineand is dependent on the submarine’s havinghydraulic power.

7-5.1.2 Tow Attachment Points

The design of submarines is such that consid-erable ingenuity may be required to find suit-able towing attachment points. See AppendixJ of this manual for details on towing arrange-ments for specific submarines.

On several classes of submarines, a tow padis installed on the forward portion of the sail,where it is faired into the main deck. This is ahard point with an SWL of about 47,000pounds, depending on submarine class. Onsome other classes, the tow pad is installedforward of the forward escape trunk and is al-so rated at 47,000 pounds. The latest subma-rines are intended to be towed using a bri-dle-flounder plate arrangement secured to apair of 70,000-pound (SWL) mooring cleats.

On some submarines, the intended tow pointmay have been removed. In such cases, anemergency tow may well involve use of someof the installed cleats or other deck fittingssuch as capstans.

As a last resort, towing by the stern planes,the propeller, or the sail may be the only al-

CAUTION

The submarine's designed towingrig was intended for intra-harbortowing and is not generally accept-able for open-ocean towing.

CAUTION

Few deck fittings on submarinesare designed for loads that arecommonly considered in the designof surface ships. Care must be ex-ercised to ensure that the safe loadcapacity of fittings, such as thebul lnose fa ir lead, c leats, andpadeyes, is not exceeded. Particu-lar attention must be paid to theloads that may develop when thesubmarine yaws.

7-7


ternatives. In such an event, all parties mustbe aware of the damage that will likely result.

7-5.2 Personnel Safety Issues

The main deck of a submarine is frequentlyinaccessible and dangerous to board in a sea-way. There is very little freeboard, and ifthere is any sea running, the decks will mostlikely be awash. Great care is required whenmoving about on the deck; a tether or safetyline should be used. A safety track is provid-ed for attachment of personnel-restrainingsafety lines. The necessary fittings and har-nesses are carried on the submarine for usewith this track.

7-5.2.1 Protection for Work on the Deck

When connecting to a submarine in the opensea, all personnel working on the deck shouldwear full wet suits, survival suits, or othersuch dress that will provide both thermal andphysical protection if they are washed over-board. No one should be permitted to workwithout proper life preservers or other appro-priate safety equipment.

7-5.2.2 Boarding the Submarine

An inflatable boat may be the only successfulmeans for boarding a submarine. It is helpfulif the submarine is able to rig a Jacob’s ladderalongside for boarding purposes.

7-5.2.3 Personnel Experience

Submarine deck hazards are frequently com-pounded by limited personnel experience.Because submarines normally conduct inde-pendent operations, their personnel have fewopportunities to become familiar with manyof the deck seamanship procedures that arecommon to personnel on surface ships. At thesame time, personnel on the tug may have lit-tle or no experience with submarines and maylack familiarity with the particular fittings,equipment, and limitations of the submarine.Good communications between the subma-rine and tug crews are especially important.

Guidance from the submarine crew is particu-larly valuable in the area of safety. They arefar more experienced in the problems ofworking topside on the submarine thannon-submarine personnel. The submarine canalso provide additional assistance if required.The submarine, however, should follow theguidance provided by the tug. The tug is re-sponsible after the tow connection is made.

7-5.2.4 Submarine Atmosphere Problems Re-sulting from Fire

If the submarine has had a fire or has dis-charged i ts extinguishing system, theatmosphere inside may not be of breathingquality. If entering the submarine is neces-sary, proper breathing equipment should beused. The atmosphere in the submarine isdifficult to clear unless it is possible to runsome of the equipment on the submarine.Running the low-pressure blower or theemergency diesel engine will quickly pro-vide a change of atmosphere.

7-5.3 Tendency to Yaw and Sheer

Some model tests of the towing characteristicsof the various classes of submarines have beenconducted. These tests confirm the observedtendency for submarines to yaw and sheer faroff the towing track. This can be improved ifthe submarine is trimmed by the stern. Thiscan be done by sealing ballast tanks and de-ballasting the sonar dome. These actions willalso provide more freeboard forward for rig-ging the tow wire, thus facilitating the tow op-eration. In deep water, deploying the stern an-chor of the submarine may also help(assuming that hydraulic power is available).If rudders and planes are not being used tocontrol the submarine, they should be secured.

7-5.4 Rigging for the Tow

Innovation is often required when rigging asubmarine for towing. Creative thinking isneeded both when making up a connectionand when selecting the hardware to use. In anemergency, it is better to rig something as

7-8


strong as possible the first time, acceptingsome possible damage, than to risk loss of thetow at a more inopportune time in the future.

See Appendix J for information on riggingspecific submarines.

7-5.4.1 Hardware

There is no assurance that towing hardwarewill be carried by the submarine. Occasional-ly the submarine will carry special shacklesor other hull fittings to connect the towline tothe tow point. In most cases, however, a Navytug should have sufficient gear to make up atowing connection superior to that included inthe submarine design.

The ship conducting a tow must determinewhat special jewelry is available or required,from either the submarine crew or the appro-priate Squadron or Type Commander. If re-quired jewelry is stored ashore, it may be pos-sible for the tug to pick it up before gettingunderway or to have it delivered to the sceneof the casualty. Modifications to submarine’sdesigned towing jewelry may be necessary ascircumstances warrant. When jewelry is notavailable, it may be necessary to manufactureit. The necessity of providing for both ade-quate strength and chafing capability forwhatever jewelry is employed must be kept inmind.

It is advisable to use a length of chain as achafing pendant where the tow connectionpasses through the fairlead chock. It may benecessary to include a wire between the con-nection point and a short length of chain to re-duce the length (and weight) of chain used.The chain needs to be just long enough to takethe chafing at the fairlead. Assistance may beavailable from the submarine’s hydraulicdeck capstan, if it can be rigged and operated.Keep in mind the limited capacity and speedof the capstan. For submarines using a bridleattached to a set of mooring cleats (chieflySSN 688 and SSBN Classes), no fairlead isused and a wire chafing pendant is sufficient.

7-5.4.2 Underwater Projections

The submarine crew can provide informationon the location of all underwater projections.These projections must be rigged in to avoidproblems. Submarine personnel may not ap-preciate the deep angle of the tow hawser re-sulting from an adequate catenary. In addi-tion, most submarines can take wide swingsfrom the direction of the tow, meaning thatany projections forward of its tow fairlead,including items on the keel, can damage or bedamaged by a tow hawser or pendant. If thereis any doubt, a diving survey should be madeto assure the hull exterior is clear.

All tugs must also be aware that U.S. subma-rines have keel anchors, often located aft. Ifsuch a submarine is anchored, it will headdownstream. See Appendix J for identifica-tion of anchor location by submarine class.

7-5.4.3 Towing by the Stern

A submarine that has been damaged by agrounding or collision may require a sterntow. For submarines whose anchor is locatedaft, the anchor chain is the first choice for astern tow. Careful coordination is critical. Byusing divers, the tow ship may be able to con-nect to the submarine’s anchor chain, with orwithout the anchor removed. It also may bepossible to dip a wire around the anchorchain. If the stern planes or the propeller must

CAUTION

Every retractable item forward ofthe tow fairlead (or flounder plate, ifused) must be retracted by thesubmarine crew to preclude dam-age to the submarine and the towhawser.

NOTE

Use of the submarine’s anchorchain for towing may be feasible ifits windlass is operable.

7-9


be used for a tow point, take great care to en-sure that the attachment chain, strap, and soforth, are wrapped close to the hull. When us-ing stern planes or rudder, the strong operat-ing shaft extends only a short distance into thecontrol surface. It is important that the attach-ment point be held against the hull and not atthe outboard side of the rudder or plane.

7-5.4.4 Use of the Sail as a Tow Connection

For connection to a sail, consider chain, wire,or a wide heavy strap that is fabricated fromplate or from a wide synthetic lifting strap.Chafing gear may be required to distribute theload because the sails after edge may bebrought to a relatively sharp edge. Suitablechafing gear can be fabricated from a shortsection of split pipe and plate. Rigging such adevice, however, is not a simple task at sea.

7-5.4.5 Welding to the Hull

If welding is required, make sure that towingpads are fastened to the pressure hull (as op-posed to the non-pressure hull) and that thewelding is done in accordance with the speci-fications for the material of the hull.

7-5.4.6 Passing a Messenger

In establishing the initial connection, it is eas-ier for the submarine to pass an initial line tothe tug than vice versa. Limited deck spaceon the submarine makes it difficult to catch aheaving line or the line from a line throwinggun. It may be easier to rig a double messen-ger around the tow connection and use thetug’s power to heave around on the hawser. Asufficiently long messenger should be pre-pared in this case.

7-5.5 Towing Operations

Once a suitable tow connection is achieved,come up to speed very carefully. A constantwatch should be kept on the position and atti-tude of the submarine. At night, it may benecessary to require the submarine to contin-ually report its relative position until a stablecondition is achieved. If they cannot besteered, many submarines will tend to sheeroff and hold a position as much as 70 degreesrelative to the tow ship’s stern. Sometimesthe submarine will hold this extreme positionfor hours, only to veer suddenly to the otherside without warning. The tug’s Conning Of-ficer must be advised immediately. In such acase, the Conning Officer may have to reducepower to prevent the tug from surging aheadand compounding transient stresses devel-oped when a submarine fetches up on the oth-er side. This sheering characteristic, coupledwith a lack of strong fittings, is a major rea-son for insisting upon relatively modest ten-sions in towing submarines.

7-5.5.1 Towing on the Automatic Towing Machine

Every effort should be made to tow with anautomatic towing machine. Controls shouldbe adjusted for a maximum tension settingnot to exceed the safe working loads of thecomponents used for the tow rigging and fit-tings on board the submarine. Deploying asynthetic spring will also help to reduce peaktensions. More information about the use ofsprings is contained in Section 4-6.5 andNAVSEAINST 4740.9E (Ref. P).

CAUTION

Contact NAVSEA to obtain techni-cal advice before any welding isdone to a submarine's pressurehull.

CAUTION

Due to their severe sheering ten-dencies, submarines should em-ploy active steering (if available) asdirected by the towing vessel.

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7-5.5.2 Towline Tension and Towing Speeds

Attainable towing speeds will be dependentupon weather, class of submarine, type ofconnection, equipment used, and the abilityof the submarine to use its rudder. In general,towline tension should be limited to 25,000pounds for all submarine classes built prior tothe SSN 688/SSN21/SSBN 726 Class subma-rines. This will provide about five knots tow-ing speed under favorable sea conditions. The688/21/726 Class submarines should be limit-ed to a maximum of 35,000 pounds tension,resulting in about four knots speed under fa-vorable conditions. Normally, increasing ten-sion/speed should not be attempted withoutfirst observing the tow’s behavior and con-sulting with appropriate operational and tech-nical authority.

As with all towing operations, it may be nec-essary to slow down and simply maintainsteerage when the weather is severe.

7-5.5.3 Drogue

If the submarine rudder is out of commission,a drogue rigged behind the submarine mayassist it to stay on course. In deep water, thestern anchor may be deployed. In narrow wa-terways or where interference from other traf-fic is anticipated, docking (harbor) tugsshould be used alongside to properly controlthe submarine’s movements.

7-6 Towing Distressed Merchant Ships

Occasionally, during routine operations andnational emergencies, the Navy is called uponto engage in towing merchant-type ships indistress. These may be MSC ships, charteredships, ships engaged in support of operations,or any other merchant ships requiring assis-tance. In emergencies and in remote areas,these services also may be required to savelives and valuable ships and cargo. If pollu-tion is a concern, towing the ship to sea willlikely reduce the impact of any spill. Be sure

the distressed vessel is capable of survivingany increased seas.

Information on the events and circumstancessurrounding the towing should be collectedand documented as soon as practical, if notimmediately. The following information mayhelp the Navy in subsequent claims for reim-bursement:

a. Note reasonable availability of adequateprivately-owned or commercial towingassets at the time that the Navy towed thedistressed merchant ship. Examples ofsuch information are:

• Location of the nearest privately-ownedor commercial towing vessels.

• How the existence of nearby towingcompanies or vessels was known. Arethey locals whose presence was knownfrom past incidents that resulted in theneed for towing or salvage? Were theydiscovered as a result of communica-tions at the time of the casualty that re-quired the tow?

b. Nature and extent of services rendered.

c. Location of the nearest safe haven. If amerchant ship was towed elsewhere, thereason for towing to that farther pointshould be documented.

d. The citation of funds, cash deposit,"promise to pay", or other agreements ar-ranged by the merchant ship prior to thecommencement of any operation.

Supervisory control of the effort will ordi-narily remain in the Navy. A situation mayarise, however, in which it may be advisableto relinquish supervisory control to an owneror underwriter’s designated representative,even though Navy facilities are required. Re-linquishment of supervisory control may beeffected upon authorization by the cognizantnaval commander or higher authority. Promptnotification should be made of such action toCNO; the cognizant Fleet Commander in

7-11


Chief; numbered Fleet Commanders; NavalSurface Force Commander; COMNAVSEA-SYSCOM; and other interested authorities,because this may well affect the status of theNavy’s claim. Relinquishment of superviso-ry control shall in no case be construed to af-fect the responsibility of commanding offic-ers for the safety of their ships.

NAVSEA 00C should be contacted (703 6072753; DSN 327 2753; 24 hours: 703 6027527; DSN 332 7527) to assist in assessingcommercially available assets. Informationcan also be provided regarding towing proce-dures.

7-6.1 Information Sources

Various companies and trade groups have as-sembled information intended primarily toprovide guidance to merchant tanker opera-tors in contingency planning. This same in-formation can be equally valuable to Navypersonnel who may become involved in res-cue responses to merchant ships in distress.Some particular publications are cited in In-ternational Maritime Organization (IMO)Resolution A.535(13), Recommendations onEmergency Towing Requirements for Tankers(Ref. Q) and International Chamber of Ship-ping Oil Companies International Marine Fo-rum, Peril at Sea and Salvage: A Guide forMasters (Ref. R).

7-6.2 Attachment Points

Ideally, a distressed ship would present aneasily reached connection to the rescuer. Thiswould be a complete system including thehawser, or at least everything necessary toconnect the hawser to the ship. The Oil Com-panies International Marine Forum (OCIMF)recommendations have been superseded bysimilar IMO standards, but these have notbeen formally adopted. Nonetheless, many ofthe larger tanker operators have compliedwith the IMO recommendations.

Many ships employ a prearranged attachmentpoint on the tow such as the Smit Towing

Bracket (see Figure 4-8). Alternative pointsfor attachment include the bitts, the anchorchain, and the foundations of deck machinery(see Section 4-5).

Many commercial vessels have an emergencytow hawser and connecting jewelry in a pack-aged arrangement on the bow or stern. Theseboxes usually require assistance from thecrew or a boarding party. Light weight mate-rial is usually used and a connection can bemade very quickly. This arrangement shouldbe sufficient until a more permanent arrange-ment can be made.

7-7 Ships with Bow Ramp/Door

LST type tows are required to have hydraulicrams connected with bow ramp operating in-structions posted in the hydraulic controlroom. Ensure that mud flaps at the bottom ofthe doors are secured and that all dogs, heavyweather shackles, ratchet-type turnbuckles,and strongbacks are tightly and securely inplace so that they cannot work free. YFU/LCUs are inherently unseaworthy due to theirwide beams and flat bottoms. A lift of oppor-tunity should be used whenever possible. If itis absolutely necessary to tow these crafts, thefollowing must be strictly adhered to:

• The bow ramp must be secured with aminimum of four angle straps on eachside, welded on the outside of the ramp.Straps should be at least 4 inches by 3/8inches and overlap the bow ramp andsides of the craft by a minimum of 10inches.

• All normal securing devices (such asramp chains, dogs, and turnbuckles)must be in place and in good mechani-cal condition.

• All hatches, scuttles, and doors musthave good gaskets and all securingdevices must be in proper operatingcondition.

7-12


7-8 Towing Distressed NATO Ships

The NATO navies are concerned with emer-gency towing as part of their military mis-sions as well as normal maritime concerns forsafety of life at sea and pollution preventionfor all ships.

7-8.1 Standardized Procedures (ATP-43)

Standardized NATO emergency towing pro-cedures are found in the unclassified ATP-43(Ref. B). It was written for the situationwhere one combatant tows another. In thistype of operation, each ship typically pro-vides its own towing hawser as half of an en-tire rig of reasonable length. As in the U.S.Navy, this activity is sometimes referred to as“tow and be towed.” ATP-43 includes sec-tions on:

• Principles of Operations

• Organization and Command (includingCommunications)

• General Consideration of Towing Op-erations

• Preparation, Approaching the Casual-ty, Passing and Connecting the TowingRig

• Conduct of the Tow

• Emergency Release or Parting of the Rig

• Transferring the Tow

The Annex to ATP-43 contains data on theemergency towing hawser carried by eachclass of NATO warship and auxiliary ship, aswell as the end fittings on the hawser. It alsoprovides hawser strengths and dimensionsand the static tests of the end fittings.

ATP-43 should be available on board everyNATO warship and auxiliary vessel. Theassigned tow ship might remind the dis-abled ship’s Commanding Officer of thepublication’s existence, so that the disabledship can better prepare for the arrival of thetow ship.

The operational data contained in ATP-43,while accurate, are quite elementary com-pared to the background of the experiencedtug crew. Nonetheless, knowledge of the con-tents of ATP-43 will be useful to the navaltug or salvage ship since it describes what thecrew of the casualty should know concerningbeing towed.

7-8.2 Making the Tow Connection

It may be prudent to use the casualty’s ownhawser and end fitting to expedite the remov-al of the casualty from immediate danger. Insuch a case, the casualty may have alreadyrigged its own hawser ready to pass to thetug. The tug need only heave the casualty’shawser on board the tug to make the finalconnection to its own hawser, thus beingready to commence towing shortly after arriv-ing at the scene. The towing system can be re-rigged with the tug’s more robust gear afterthe casualty is removed from immediate dan-ger.

This is not to suggest that the damaged ship’stowing gear is preferred over a tug or salvageship’s gear. On the contrary, the tug’s gearwill be more robust than that of all but thelargest warships, and will almost always belonger than the casualty’s hawser. Further-more, unless the emergency hawser is con-nected to the ship’s anchor chain, there willbe insufficient long-term chafing protectionfor the casualty’s own hawser, and possiblyinsufficient catenary as well. Use of the tug orsalvage ship’s towing gear is preferred fortowing a warship or naval auxiliary. Connect-ing to the casualty’s hawser as an expedientmeans should be based on a careful balancingof the tactical circumstances, rapidity of com-mencing the tow, distance to be towed, andexisting and forecast wind and sea conditions.If the tactical situation requires initial use ofthe casualty’s hawser, re-rigging to the moreconventional connection is recommended atthe earliest possible opportunity.

7-13


When connecting to the casualty’s own emer-gency towing hawser, the towing ship shouldconsider inserting a shot of chain between thetwo hawsers to assist in maintaining a healthycatenary, provided that the water is deepenough. This may complicate recovery if therig is to be changed at sea.

7-8.3 NATO Standard Towing Link

Change 1 to the publication (May 1987) alsospecifies a NATO Standard Towing Link,which should soon be found on NATO shipsof over 1,000 tons displacement (see Figure7-2).

The ATP-43 comments relevant to the NATOStandard Towing Link are:

a. The NATO Standard Towing link is to beused during ship-to-ship towing opera-tions as an interface between the towingequipment of the towing ship and that ofthe ship towed, whichever of the twoships provides the equipment, in order toimprove interoperability.

b. Ships of less than 1,000 metric tons dis-placement, other than tugs, are not obligedto have the Standard Towing Link.

c. The interface will be at the presented endof one or both ships’ towing hawsers.(One of the ships will have to provide ajoining shackle.)

d. The NATO Standard Towing Link shallconform to the dimensions shown.

e. The strength of the link is the responsibil-ity of the providing nation.

The link is quite large, so the largest conceiv-able tow shackle (4 inches) can be dippedthrough it. Note that the strength of the link isleft to the Providing Nation. In the absence ofinformation to the contrary, assume that thelink strength exceeds the breaking strength ofthe casualty’s emergency tow hawser. As-sume that the casualty’s attachment points al-so exceed the strength of its hawser.

7-9 Unusual Tows

Conditions may require towing floating struc-tures that are in unusual positions. Manysuch tows have been successfully completedin the past.

Figure 7-2. NATO Standard Towing Link.

2 / ”18

13 / ”1516

140

MM

55 M M

355 M M

7-14


7-9.1 Dry Dock (Careened)

One example of an unusual tow is the towingof an AFDM through the Panama Canal.These dry docks are approximately 124 feetwide. Because the canal is only 109 feet wide,these docks must be careened for transit. Thishas become an established practice. When thetransit operation has been completed, the ca-reening procedure is reversed to restore thedock to its even keel condition for towing toits destination. An attempt should be made toadjust the trim to improve the behavior.

7-9.2 Damaged Ship (Stern First)

If a ship cannot be prepared properly for towdue to bow damage, the feasibility of towingby the stern may be considered. Some shipswill tow fairly easily by the stern, but mostcan be expected to track very poorly.

7-9.3 Inland Barge Towing

Barge towing supports Navy logistic require-ments. The basic techniques for inland bargetowing are almost identical for harbor tugsand towing ships. The principles of alongsidetowing and handling become part of theopen-ocean tow in making up, streaming, andentering the harbor. Naval Education andTraining Command (NAVEDTRA) 10122-E,The Boatswain's Mate First Class and ChiefRate Training Manual (Ref. S) provides athorough discussion of inland barge towing inits most common configuration, alongside.Understanding the basic principles set forth inthat manual will enable personnel on boardthe ocean going tug or salvage ship to ap-

proach inland towing in a professional man-ner.

7-9.4 Other Tows

Contact NAVSEA 00C for information con-cerning advice on unusual and unique towsincluding:

• NR-1, submerged tow

• Towing of gravity structures

• Non-self-propelled floating structures

• Minesweeping devices

• Submerged and surface towing of sub-mersibles

• SINKEX

• Test bodies

• Platforms

• Pipe structures

• Cable-layers

• Acoustic arrays

• Semi-submersibles

• Ships of unusual hull forms (SWATHs,PHMs, and so forth).

7-9.5 Towing on the Hip

While it is common practice for harbor tugsto tow on the hip, it is somewhat unusual foran ocean tug to do so. However, if an oceantug is involved in a salvage it may be neces-sary to engage in this type of towing. Cautionshould be taken if there is any sea state. Beamwaves, may cause the vessels to roll out ofsync and alternately separate and collide.

7-15



7-16

U.S. Navy Towing Manual DRAFT

Chapter 8

HEAVY LIFT TRANSPORT

8-1 Introduction

This chapter describes the personnel, proce-dures, preparations, and safety precautions re-quired for float on/float off (FLO/FLO) heavylift transports of Naval ships and craft. Heavylift, as used in this chapter, is defined as thetransportation of a ship, craft, or other assetaboard a larger semi-submersible ship orbarge. FLO/FLO refers to the method of load-ing and unloading. This alternative to towingwas developed for the movement of largedrilling rigs and other offshore structures.The United States military has used thismethod to transport smaller vessels some ofwhich were not suited for ocean transit aswell as damaged vessels that could not transitsafely under their own power.

Heavy Lift was used to return the bomb dam-aged destroyer, USS COLE (DDG 67), mine-damaged frigate, SAMUEL B. ROBERTS(FFG 58), from the Persian Gulf and to trans-port smaller assets such as mine warfareships, landing craft (LCU) and service craftacross the ocean. Two separate lifts broughtminesweepers from the United States to thePersian Gulf and three lifts brought othersback. Since these were operational shipswhose mission required rapid safe transport,heavy lift was used. Tugs, barges, and float-ing cranes have also been moved using theFLO/FLO process.

The Navy does not currently own any heavylift FLO/FLO ships and therefore uses con-tracted vessels to perform these services. Thischapter assumes that the heavy lift ship is acontracted vessel.

This chapter does not apply to nuclear pow-ered ships with the core installed.

8-1.1 Repair Work

Conducting a commercially chartered lift isan expensive undertaking therefore, any re-pair work to the asset should be arranged so itdoes not interfere with the heavy lift contrac-tor. For example, on the USS COLE heavylift the Heavy Lift Project Team prepared adesign sketch for a hull patch. The patch wasnot installed prior to departure due to cost andoperational considerations. The cost of delay-ing the operation for repairs is usually fargreater than the cost of dry dock lay days andsuch costs should only be incurred in emer-gency situations after careful considerationby the Operational Commander. Having theasset completely out of the water does presenta unique opportunity for inspection of hull fit-tings and rudders/propellers and certainlyshould not go unrealized. For example, on theDesert Storm lift of minesweepers four pro-pellers were found to be damaged and wererepaired because the assets were going towar. Because this is a transport operation, theasset has to be ready for sea transit; in partic-ular the water-tight integrity of the hull mustbe maintained. The operational commandershould identify a ship repair officer for theteam to coordinate their work.

8-2 Special Considerations

8-2.1 Dry Docking Comparison

A float on/float off procedure may be consid-ered similar to operations involving a dry-dock. Both involve positioning a floating as-set over docking blocks and then reducing theamount of water or distance between the ves-sel and the blocks. In the case of a gravingdock, the water is pumped out of the dock andthe asset settles on the blocks. In the case of afloating drydock, the draft of the drydock isdecreased by removing water from tanks untilthe blocks “lift” the asset. Although theseprocedures are similar, the FLO/FLO portionof a heavy lift transport is much more in-

8-1

U.S. Navy Towing ManualDRAFT

volved. Take the following considerations in-to account:

• The transport may be of a single asset,multiple assets from the same squad-ron, or multiple assets from differentoperational commanders. Assets of oth-er services may also be transported.

• The asset(s) may be lifted in open waterareas.

• Seafastening must be installed to ensurethat the asset remains secured on thecargo deck of the heavy lift ship.

• The assets must be secured internallyfor the sea transit.

• The asset being lifted may be in finaldays of preparing for extended deploy-ment and therefore may be topped offwith provisions, fuel, and water.

• The contract under which a FLO/FLOtransport is accomplished is a vesselcharter and differs significantly from adry docking contract.

• Some of the asset’s systems may be op-erational during transit. Therefore allpower and support interface require-ments must be identified.

8-2.2 Commercial Fleet

Some basic characteristics of the larger, com-mercial heavy lift ships are presented in Table8-1. These semi-submersible vessels are self-powered and have large open decks to sup-port cargo. They contain enough internaltankage to allow them to ballast down farenough that their cargo decks are well belowthe water’s surface. This allows assets to befloated over the deck and lifted upon dewater-ing. This process is almost identical to float-ing drydocks except that it is often done inopen water. Figure 8-1 shows a typical heavylift ship where the assets can be loaded fromport, starboard, or astern. The vessel shown inFigure 8-2 is more similar to a typical dry-

dock. The large wing walls provide someadded protection to weather, but assets mustbe loaded from astern. Figure 8-3 shows avessel with a deckhouse fore and aft. In thiscase, assets must be floated on from port orstarboard.

Smaller ships of this type also exist but arenot used to perform lifts of larger vessels.Commercial submersible and semi-submers-ible barges may also meet the requirements ofsome heavy lifts. Barges have the added com-plexity of a tow arrangement and are alsoconsidered less desirable due to stability con-cerns.

8-2.3 Choosing a Vessel

When deciding on which type of vessel touse, several factors must be considered.These factors are similar to those used to de-cide on a towing asset and whose significancewill vary depending on the mission beingsupported. For instance, for a coastal or in-land lift, a barge may be suitable but for antrans-ocean voyage, the added seaworthinessof a specially designed vessel will likely beworth the extra cost. Some of the factors to beconsidered are shown in Table 8-2.

8-3 Procedures

This section will discuss planning a FLO/FLO operation. Few FLO/FLO operations areever duplicates of earlier operations as therewill always be differences in season (weath-er), route, personnel, and configuration of theassets. Each FLO/FLO transport is uniqueand requires careful planning, preparation,and execution to minimize error and maxi-mize safety. This section presents FLO/FLOtransport procedures in general terms.

8-3.1 Designating the Lift

The cost of a heavy lift may make this optionseem disadvantageous, but several situationsmay dictate that this method may be an ap-propriate way to relocate an asset. Moving

8-2


8-3

DRAFT

Tab

le 8

-1.

Com

mer

cial

Sub

mer

sibl

e an

d S

emi-S

ubm

ersi

ble

Ves

sels

.

Com

pany

Nam

eV

esse

l Nam

eLO

AB

eam

Dec

k D

imen

sion

sW

all H

eigh

tD

raft

Ful

l Loa

dD

WT

abt

Net

herla

nds

Fre

ight

A

genc

ies

DE

VE

LOP

ING

RO

AD

134.

2 m

34.2

m11

5.0

m

x29

.2 m

9.

2 m

5.15

m13

,230

tons

Net

herla

nds

Fre

ight

A

genc

ies

SH

A H

E K

OU

134.

2 m

34.2

m11

5.0

m

x29

.2 m

9.

2 m

5.15

m13

,230

tons

Sm

it M

ariti

me

SM

IT P

ION

EE

R16

0 m

29.0

m2,

880

sq. m

7.06

m4.

43 m

6,50

0 to

ns

Sm

it M

ariti

me

SM

IT E

NT

ER

PR

ISE

160

m29

.0 m

2,88

0 sq

. m6,

500

tons

Con

dock

CO

ND

OC

K I

92.4

m20

.13

m74

.6 m

x 1

5 m

6.35

m4.

83 m

3,60

3 to

ns

Con

dock

CO

ND

OC

K II

I10

6.4

m20

.4 m

87.5

m x

15

m7.

95 m

4.83

m4,

074

tons

Con

dock

CO

ND

OC

K IV

106

m20

.4 m

87.5

m x

15

m7.

95 m

4.95

m4,

500

tons

Con

dock

CO

ND

OC

K V

106

m20

.4 m

87.5

m x

15

m7.

95 m

4.95

m4,

600

tons

Con

dock

OS

TAR

A10

6 m

19.6

mN

/AN

/A4.

85 m

4,40

0 to

ns

Doc

kwis

e N

VD

OC

K E

XP

RE

SS

10

153.

8 m

24.2

m2,

130

sq. m

8 m

8.89

m (

max

. sai

ling)

13,2

09 to

ns

Doc

kwis

e N

VD

OC

K E

XP

RE

SS

11

159.

2 m

24.2

m2,

130

sq. m

8 m

8.89

m (

max

. sai

ling)

13,2

09 to

ns

Doc

kwis

e N

VD

OC

K E

XP

RE

SS

12

159.

2 m

24.2

m2,

130

sq. m

8 m

8.89

m (

max

. sai

ling)

13,2

09 to

ns

Doc

kwis

e N

VM

IGH

TY

SE

RV

AN

T 1

160

m

40 m

4,80

0 sq

. mN

/A22

m (

subm

erge

d)21

,500

tons

Doc

kwis

e N

VM

IGH

TY

SE

RV

AN

T 2

170

m

40 m

5,20

0 sq

. mN

/A22

m (

subm

erge

d)23

,300

tons

Doc

kwis

e N

VM

IGH

TY

SE

RV

AN

T 3

180

m

40 m

5,60

0 sq

. mN

/A22

m (

subm

erge

d)24

,800

tons

Doc

kwis

e N

VS

UP

ER

SE

RV

AN

T 3

139

m32

m3,

500

sq. m

N/A

6.26

m (

tran

sit)

14.5

m (

subm

erge

d)14

,112

tons

Doc

kwis

e N

VS

UP

ER

SE

RV

AN

T 4

169

m32

m4,

380

sq. m

N/A

6.02

m (

tran

sit)

14.5

5 m

(su

bmer

ged)

17,6

00 to

ns

Doc

kwis

e N

VS

WA

N18

0.5

m32

.26

m4,

007

sq. m

N/A

10 m

32,6

50 to

ns

Doc

kwis

e N

VS

WIF

T18

0.5

m32

.26

m4,

007

sq. m

N/A

10 m

32,1

01 to

ns

Doc

kwis

e N

VT

EA

L18

0.5

m32

.26

m4,

007

sq. m

N/A

10 m

32,1

01 to

ns

Doc

kwis

e N

VT

ER

N18

0.5

m32

.26

m4,

007

sq. m

N/A

10 m

32,6

50 to

ns

Doc

kwis

e N

VT

RA

NS

SH

ELF

173.

5 m

40 m

5,28

0 sq

. mN

/A8.

8 m

(tr

ansi

t)34

,242

tons

Hin

ode

Kis

en C

o. L

td.

SE

A B

AR

ON

150

m32

m3,

600

sq. m

4.9

m5.

025

m10

,377

tons

AM

ER

ICA

N C

OR

MO

RA

NT

223.

06 m

42.2

5 m

47,2

30 to

ns


Figure 8-1. Heavy Lift Vessel.

8-4



8-5



8-6


small coastal vessels across the ocean can beslow, costly and a significant risk to both per-sonnel and the vessel. A vessel designed tooperate in sheltered coastal waters is ill-suitedto survive the winter storms of the North At-lantic. The asset may not have been designedto have the endurance to make the trip. Tow-ing the assets is an option but a long oceantow of a small vessel is not without its ownrisks. In the case of a multiple asset transfer, aheavy lift is far safer than a multiple tow. Inthe case of a damaged vessel, a heavy lift maybe the only option as towing may not be feasi-ble.

Figure 8-4 depicts a notional schedule forpreparing a heavy lift. This schedule allowssufficient time to perform all necessary docu-ment reviews as well as completion of allblock and seafastening builds. Some portionsof this schedule are extremely flexible, suchas the market search and contract solicitation,

but other areas are more rigid. The heavy liftship will require a certain amount of time toperform the lift and construct the blockingand seafastening. This process can be helpedby providing the most up to date documenta-tion.

Once an organization decides that a heavy liftis the preferred method of transfer, theyshould begin the planning phase by determin-ing some basic details of the operation. Spe-cific information about the what, where, andwhen of the operation will be needed whendeveloping the request for proposal (see8-3.2). If the lift is a planned transfer, theMilitary Sealift Command has been used suc-cessfully to administer contracts with com-mercial firms who are experienced in thisfield. In the case of an emergency, NAVSEA00C (Supervisor of Salvage) should be con-tacted to expedite planning and execution ofthe lift. The remainder of this chapter as-

Table 8-2. Heavy Lift Ship vs. Submersible Barge.

Heavy Lift Ship Submersible Barge

Stability Stable in all operational modes,Sheltered in head seas

Relies on bottom contact forstability during lift, limitedshelter in head seas

Access to Asset Asset on deck of vessel, accessthrough brow or ladder

Access limited by weather andsmall boat capability

Support Designed to support lift ops,usually good hotel services

Tug may have limited addition-al hotel services

Cost Specialized craft, more expen-sive, but generally shorter tran-sit time

Tug/barge combo may havecheaper day rate, but longerrent time

Insurance/Risk Generally insurance is less dueto larger more controllable plat-form

Insurance rates can be a sub-stantial cost

Speed Open ocean design, good speed Tow will be slower

Risk One unit, minimal risk withgood seafastening plan

With two craft and towline, riskis inherently greater

8-7


Figure 8-4. Plan of Action and Milestones.

Co

nd

erat

ion

to H

eavy

Lif

tTr

ansp

ort

Mar

ket

Su

rve y

Dec

isio

nto

Hea

vyL

ift

Tran

spo

rt

Req

ues

tG

FI

Req

ues

tfo

rP

rop

osa

ls

Rec

eive

Pro

po

sals

Co

ntr

act

Aw

ard

Rec

eive

Tran

spo

rtM

anu

alfo

rA

pp

rova

l

Pre

-Lo

adin

gC

on

fere

nce

Ap

pro

veTr

ansp

ort

Man

ual

Co

mm

ence

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8-8


sumes that MSC has issued the charter, butNAVSEA 00C or any office issuing the con-tract would have the same responsibilities.

8-3.2 Request for Proposal (RFP)

Previous FLO/FLO operations have been ac-complished through the Military Sealift Com-mand (MSC) Headquarters Contracting Of-ficer. MSC issues a Request for Proposal(RFP) or modifies an existing time charter toinclude the details of the particular operation.When the need for a FLO/FLO operation isdetermined by an operational command, theymust specify certain requirements to be in-cluded in the RFP or contract modification.Information required may include:

• Assets to be lifted

• Dates and locations of load and dis-charge points

• Supporting activities

• Asset specifics - class/name, conditionof readiness, loading condition, value,date of last dry docking

• Additional cargo

• Asset’s plant service requirements -both during the FLO/FLO operationsand preparations and during sea trans-port

Upon receipt of the proposals, MSC (and oth-er technical authorities; the operational com-mand, a dry docking authority, NAVSEAtech codes, SUPSALV, etc.) review the pro-posals for technical correctness and cost com-parison. MSC will then award a contract orcontract modification.

8-3.3 Preparations

Once a contract has been awarded, severalthings need to be done to prepare for the lift.In this preparation phase, communication be-tween the various organizations is critical to a

successful and timely execution of the lift.The items listed below should be accom-plished in advance of the date that the vesselwill arrive at the loading site.

8-3.3.1 Choosing a Heavy Lift Team

The personnel chosen to be the MSC/Navycoordination team functions much like a Su-pervisor of Shipbuilding monitoring a drydocking availability. They review the con-tractor’s proposals and ensure that he is per-forming the work in accordance with the con-tract and the Transport Manual. It is a goodidea to choose people that can be presentthroughout the process (plan development,contract award, loading, off-loading), al-though it is not necessary. A list of personnelis shown here as an example of what has beenused successfully in the past. This list mayvary slightly depending on the assets to belifted, the personnel available, and location ofthe lift.

Operational Commander

Generally the owner of the asset, the Opera-tional Commander has cognizance of the op-eration. He designates the need for a FLO/FLO operation, identifies the services re-quired to support the asset during all phasesof the lift, and prepares the asset for transport.The Operational Commander is responsiblefor selecting all the members of the heavy liftteam.

Designated Docking Activity (DDA)

The DDA is the technical point of contactduring the planning and approval phases. TheDDA provides on-site technical personneland requests technical and coordination assis-tance from cognizant commands as required.The activity designated as the DDA shouldhave experience in docking and undockingevolutions and is often located in the vicinityof the loading area.

8-9


Heavy Lift Project Officer (HLPO)

The HLPO is a senior technical officer, pref-erably an Engineering Duty Officer. Oncedesignated, he or she will be responsible forcoordinating both technical and logistics sup-port for the asset to be lifted and developmentof lift requirements as well as review of theTransport Manual. The HLPO is the leader ofthe Navy heavy lift team.

Dry Docking Safety Officer (Docking Ob-server)

The Docking Observer is responsible for thefloat on and float off portions of the transportand for seafastening during transport. TheDocking Observer reviews and approves allcalculations required to conduct the FLO/FLO operation. The Docking Observer mustbe familiar with the local ship repair and ser-vice industry and the environmental condi-tions in the loading and off-loading sites. He/she is responsible to ensure that the asset issafely positioned, lifted and secured for trans-port, and discharged.

Blocking Expert

The blocking expert oversees the constructionand installation of all necessary blocking andseafastening. He should be familiar with Na-vy docking drawings and the construction ofvarious types of docking blocks. The block-ing expert verifies that all blocks, blocking,seafasteners, and roll bars (spur shores) areinstalled properly and in accordance with theapproved Transport Manual.

Stability Expert

The stability expert should monitor the opera-tion to ensure adequate stability of both theship and the asset at all stages of the lift pro-cess. He/she should be familiar with the oper-ation of a heavy lift ship or floating dry docksand can verify the ballast/deballast sequenceis sound and performed in accordance withthe Transport Manual. He/she should inspectthe ballast/deballast system (including the

tank and draft indicator system) to ensure thatit operates properly and should monitor thissystem during loading and off-loading opera-tions.

Services Coordinator

This individual coordinates the installation ofasset plant services such as electrical power,fire main, and potable water. He/she also co-ordinates general vessel support during theFLO/FLO operation such as line handling, se-curity watches, communications, access,scupper overboard discharges, etc. The ser-vices coordinator should be familiar with theasset in order to verify all support require-ments.

Ship Repair Officer

A Ship Repair Officer is assigned at both theloading and off-loading sites to coordinateany emergent/emergency repair work thatmay be necessary, using the lift as a dockingof opportunity. Because this is a transport op-eration, the asset must be ready for sea tran-sit; in particular, the watertight integrity ofthe hulls must be maintained. The Ship Re-pair Officer should be familiar with local shiprepair and other services that may be neces-sary to complete repair work.

Riding Crew

The riding crew should be familiar with orcome from the asset being lifted and includepersonnel of each of several rates. For multi-asset lifts, the riding crew should include atleast one representative from each asset. Thesize of the riding crew is determined by theasset or assets being lifted and the berthingand messing capabilities of the heavy liftship. The riding crew is responsible for secu-rity, damage control, maintenance, and otherduties required for assets in a secured or part-ly secured status.

Independent Marine Surveyor (IMS)

An Independent Marine Surveyor (IMS),qualified by experience and credentials in the

8-10


operation of FLO/FLO heavy lift ship opera-tions and transports, should be appointed andbe present at all FLO/FLO operations for Na-vy assets. The IMS will be responsible for in-dependently assessing the following items:

Transport Manual

Material condition of the heavy lift ship

Ship systems

Blocking arrangement

Seafastening

Loading/off-loading procedures

Voyage arrangements

Preparation of the asset

The IMS is an independent third party to actas a mediator between the Navy and the con-tractor to provide independent analysis of theoperation and to assist in settling disagree-ments. The IMS selected should be agreed toby both the Navy representative and theheavy lift contractor.

Loadmaster

The Loadmaster is the heavy lift contractor'sdesignated coordinator. The Loadmaster di-rects the heavy lift ship's crew and subcon-tractors during the blocking build, the posi-tioning of the asset over the submerged heavylift ship, ballasting/deballasting operations,and the installation of the seafastening. TheLoadmaster coordinates the off-loading pro-cedure as well. The Loadmaster also ap-proves the loading and securing of the deckcargo before departure.

Contract Coordinator

The Contract Coordinator works with themembers of the different parties representedduring a FLO/FLO operation to resolve anycontract disputes. He will often be a represen-tative from the Military Sealift Command, theorganization that has contracted most Navylifts in the past. Any modifications or other

contractual questions should be coordinatedthrough this individual.

8-3.3.2 Contractor Preparations

Once awarded the contract, the contractormust provide information about the opera-tion. He must choose loading and unloadingsites and develop drawings and proceduresfor the entire transfer including both loadingand unloading.

The primary document detailing the prepara-tions and procedures is the Transport or LoadManual. The contractor prepares and pro-vides this document in advance (exact dateswill be specified in the contract, but usuallyno less than four days) of the transport ship’sarrival at the load site or the blocking buildoperations begin, whichever occurs first. It isrecommended that the government loadingteam be in contact with the contractor duringthe development of the Transport Manual toavoid delays if corrections or adjustmentsneed to be made. The document should be re-viewed to:

• Ensure adherence to technical require-ments

• Ensure that proper information, includ-ing drawings, is provided

• Verify references and their use

• Verify all engineering calculation andassure appropriate technical topics areaddressed

Upon approval, this document will serve asthe technical guide for all further events.

8-3.3.3 Transport (Load) Manual

The contractor shall provide a Transport(Load) Manual that details the technical re-quirements of the lift. The manual includes,but is not limited to, the following:

• Description of the heavy lift ship.• Particulars of cargo from the heavy lift

contract used by the contractor in the

8-11


development of the Transport (Load)Manual.

• Proposed route and probable sea statesto be encountered.

• Motion analysis of the heavy lift ship asloaded with the cargo, for determina-tion of roll and pitch angles and periodsand accelerations for use in developingblocking and seafastening arrange-ments.

• Critical motion curve or table depictingthe motions (angle and periods of roll,pitch, heave, and surge) to which theblocking and seafastenings are de-signed and which must not be exceededin transport.

• If an asset overhangs the edge of theheavy lift ship’s deck (either over theside or over the stern), a slammingstudy must be prepared to determine thenumber of occurrences and accelera-tions to which the asset may be subject-ed. The study should ensure the assetcan be safely transported without sus-taining damage.

• Stability analysis of the heavy lift shipas loaded, including calculation ofloading conditions and intact stabilityassessment including righting momentcurves and wind heeling moment, asdefined in Paragraph 5.3.3.1(b) of MIL-STD-1625 as specified in 8-5.2.3.

• Stability analysis (GM curve) duringthe ballast/deballast sequence as de-fined in Paragraph 5.3.3.1(b)(1) ofMIL-STD-1625, except that the mini-mum GM must not be less than speci-fied in 8-5.2.2 unless specifically ap-proved by NAVSEA at the request ofthe DDA.

• Cargo deck arrangement plan/drawing.• Structural analysis of longitudinal ben-

ding stress imposed on the heavy liftship by the proposed loading. Include acargo deck load diagram, plating thick-ness, and arrangement and size of trans-verse and longitudinal stiffeners with

acceptable cargo deck load capacity ordrawing(s).

• Structural data for the heavy lift ship:- Maximum allowable bending mo-

ment calculation.- Transverse strength calculation sus-

taining the maximum allowable pon-toon deck loading in long tons perlinear foot.

- Longitudinal deflection calculation.- Maximum keel block, side block,

and hauling block loading calcula-tions.

- Maximum pontoon deck loading atother than keel block and side blocklocations, if different than that of theblocking area.

- Structural arrangement and scant-lings.

- Longitudinal and transverse water-tight bulkhead design calculations.

- Maximum allowable differentialhead between tanks.

- Maximum allowable differentialhead between tanks and exteriortank draft.

• Cribbing/blocking plan/drawings, in-cluding table of keel and side block off-sets as specified in the docking draw-ings and calculation of loads includinganalysis of worst-case block loadingwhen the heavy lift ship is at extremetrim angle during ballasting/deballast-ing.

NOTE

Experience with past heavy liftsdemonstrated that locating sideblocks in the locations as specifiedon the Navy docking drawing offersthe best chance to have proper off-set heights. The Navy standarddocking drawing is a SelectedRecord Drawing (SRD) and takesprecedence over all other drawingsin determining offsets for height ofside blocks.

8-12


• Descriptions of the docking blocksshowing the physical characteristics ofthe blocks, including material and di-mensions, and calculations to verifythat the blocks will be stable and struc-turally adequate to withstand the load-ing used in lifting capacity calculationsand that side blocks (and shores) are ad-equate in number to provide sufficientbearing area to resist overturning mo-ments specified herein.

• Seafastening plan/drawings, includingdesign forces.

• Loading/off-loading sequence plan/drawings.

• The amount of damage the heavy liftship can withstand and survive withoutdropping the asset off the blocking andseafastening.

8-3.3.4 Choosing A Load Site

While the points of departure and destinationfor the assets will be specified in the contract,the contractor will select the actual load site,subject to approval. Weather will be the ma-jor factor in determining if a choice of loadsites is good or bad. The location should be asprotected as possible, although open water lo-cations offshore have been used successfully.A poor choice of location for conductingFLO/FLO preparations can lead to majorproblems. If the operation is to be conductedoffshore, take into consideration that the pre-ferred anchoring/mooring method may be toswing on a single anchor.

The site must have enough water depth to ac-commodate the heavy lift ship’s requireddraft for loading or off-loading, plus at leastone meter clearance below the keel. Adequatewater depth depends upon the draft of the as-set to be loaded and the height of the blockinginstalled. Semi-submersible barges may re-quire that one end of the barge rest on the bot-tom (for stability reasons) during loading.

The contractor may choose to do his prepara-tions at a location other than the site of load-ing. The preparations can be made at any full-service, easily accessible location and thenmoved to a staging area when ready for sea.

The location should be mutually agreed uponby all parties involved in the loading processincluding the IMS.

8-3.3.5 Preparing The Deck

It is the contractor’s responsibility to preparethe deck of the lift ship in accordance with theapproved Transport Manual and he will needto arrange for any necessary subcontractors.To assist in deck preparations, the contractorshould be provided with the most up to datedocking drawings available for the asset to belifted. The Planning Yard, or NAVSEA,should ensure that information and drawingsprovided to MSC for use by the contractor areaccurate and current. Any activity reviewingthe Transport Manual should also ensure thatthe docking drawing is the latest markup fromthe last dry docking, and that blocking loca-tions and heights are correct. The minimumnumber of keel and sideblocks is discussed in8-6. These blocks should be installed and in-spected a minimum of 24 hours prior to com-mencement of the lifting operation to accom-modate any last minute corrections. Thebuilding drawings presented in the TransportManual should be reviewed and approved pri-or to the start of the build.

8-3.4 Pre-Load Conference

A conference should be held prior to loadingwhere all parties involved are represented.The pre-load conference covers all aspects ofthe procedure so that all parties are familiarwith their respective roles. Important topicsto cover at this meeting are personnel, sched-ules, procedures, and responsibilities. This isoften the first opportunity for some parties tohave contact with each other. If possible, theconference should be held near the load siteand/or the assets. This will allow site/asset in-

8-13


spection and may identify potential problemsearly.

This conference should be held far enough inadvance to ensure that any changes or adjust-ments to the plan can be completed withoutadversely impacting the schedule. It shouldalso be near enough to the date of the loadingto allow for as many details as possible to befinalized. Separate meetings should be heldas part of that conference to discuss specificoperational details with line handlers, divers,block builders, tug masters, pilots, etc. It willlikely be beneficial to have each team leaderattend the conference. A similar conferenceshould be held prior to discharge.

8-3.5 Load Site

Prior to the start of the float on operation, allassets and support craft must be on scene andall preparations must be completed. Theheavy lift ship must complete the blockingbuild (see 8-6) and any preparatory efforts.These may be completed at the actual loadsite or at another facility. All work must beinspected to ensure compliance with theTransport Manual.

8-3.5.1 Visual Survey

At the load site (or preparation site), theblocking placement, arrangement, and buildon the deck are inspected to ensure compli-ance with the drawings referenced or includ-ed in the Transport Manual. The materialsused to build the blocks should be in service-able condition. Any blocks with rotted woodshould be replaced. At a minimum, a visualsurvey of the heavy lift ship and its systems isconducted, including the ballast/deballastsystem. This survey must be completed satis-factorily before the heavy lift ship is accepted(described in 8-9.2).

A survey of the assets should also be conduct-ed. The survey should include an inspectionof the floating condition of the asset including

drafts, trim, and list. An internal survey todocument the asset’s loading and any onboard weights should also be completed.

A complete checklist for both the heavy liftship and the asset is included in Appendix R.

8-3.5.2 Support Tugs/Divers

To assist in the positioning of the assets overthe blocks, support tugs and divers may beused. It is important to keep in mind that thearea of loading will likely not be as well shel-tered as a dry dock. Therefore, when selectingthe number and size of tugs, assume the worstcase for the weather. Tugs should be of suffi-cient size to hold the assets in the greatest ex-pected wind and seas. If wind and seas are toostrong, the operation should be postponed oranother suitable location found. If multipletugs are used it is important to keep lines ofcommunication clear. One person, a harborpilot or the loadmaster, should direct the posi-tioning and operation of all the tugs.

Divers should be used to check the finalalignment of the assets on the blocks. There isincreased risk for divers since the operation istaking place in open water vice in a drydock.

WARNING

All sea suctions for the assetand the heavy lift vessel shouldbe secured during diver opera-tions.

WARNING

All parties must be informedwhen divers are being used. Ex-treme caution must be used toensure the safety of these indi-viduals. No deballasting or othership movements should occurwhile divers are working directlyunder the asset.

8-14


Blocking heights are generally minimized, al-lowing little clearance between the asset andthe cargo deck. Appropriate safety measuresmust be taken and only divers with experi-ence in checking docking blocks should beused.

Tug masters and divers should be briefedabout the operation and should be present atthe preload meeting. Divers should be thour-oughly briefed on the blocking arrangements,build and marking to include a walk aroundof the blocking build prior to submerging thecargo deck.

8-3.6 Preparing the Asset

An asset must be specially prepared to be lift-ed and transported. Many preparations aresimilar to preparations for a long deployment,docking, tow, or other special event. Appen-dix P provides a thorough list of all items thatshould be checked prior to arrival at the loadsite.

The preparing activity should ensure that theasset has complete watertight integrity. It isnot necessary to go through the rigors of pre-paring a vessel for tow (locking propellers,two-valve protection, etc.) but every effortshould be made to make the hull as tight aspossible. All of these items should be accom-plished as early as practicable, leaving onlythose that are essential until the loading day.

• Condition Zebra should be set through-out the ship.

• All compartments and bilges should befree from oil and water.

• All sea valves should be secured andtagged out in accordance with normaltag out procedures. This may need to bedone while the vessel is being lifted orshortly after float-on. If connectionsfrom the heavy lift ship are to be usedfor items like cooling water, thesevalves should not be secured until theconnection has been made. A list of sea

valves should be prepared and madeavailable to watchstanders.

• All sounding tubes should be capped. Alist of sounding tubes and there condi-tion should be prepared and made avail-able to watchstanders.

• All between tank sluice valves shouldbe closed.

• All watertight boundaries should besealed. Where gaskets show signs ofwear or deterioration, new gasketsshould be installed.

• Rudders should be secured against anyvessel motions. This may be accom-plished after the asset has landed firmlyon the blocks. It may be accomplishedprior to this if no steering is requiredfor docking.

• All loose equipment should be secured.

8-3.6.1 Arrival Conditions

When the asset is delivered to the load site, itshould be in the condition (loading, drafts,trim, list, etc.) in which it is to be transported.If multiple assets are being transported, theyshould be in a similar condition of draft, trimand list. The assets should arrive earlyenough to allow for inspection by the heavylift team, the IMS, and the Loadmaster.

The trim should be less than one foot and listshould be less than 0.25 degrees. The finalconfiguration and details of loading should becompleted and made available as early aspossible, preferably at the preload confer-ence. This will ensure adequate time to pre-pare the vessel and plan the lift. It may not bepossible to bring the asset into proper trimand list by simply adjusting tank levels. Alltanks should be topped off or emptied to min-imize free surface effect.

Weights may be added to help achieve theright configuration. If weights are placed onthe asset to adjust draft, trim, or list, the struc-tural adequacy of the asset to support theweights during the transport must be consid-

8-15


ered. It must also be considered that the facil-ities at the off-load site may preclude removalof the weights. The docking officer should benotified as added weights may effect theblocking build. Assets of the same design thatare positioned alongside one another and inthe same longitudinal orientation should be ata similar draft and trim.

8-3.6.2 Transport of Damaged Vessels

The transportation of a damaged asset re-quires careful assessment. Stability must beassured but draft, trim, and list in excess ofthose indicated above may be accommodatedby the heavy lift ship's draft, trim, list, or free-board. For example, USS COLE was liftedwith 4 feet of trim by the bow and 1 1/2

o list to

starboard. This condition was the maximumthat the heavy lift ship could accommodate bythe freeboard on the after starboard caisson.

8-4 Loading Operations

This section will discuss the operations at theload site. It should be understood that manyheavy lift vessels require deep water to oper-ate. This may preclude these vessels fromperforming FLO/FLO functions in protectedwaters. It is essential that all preparations becompleted prior to the day of the lift. Favor-able weather windows may be small and un-necessary delays may jeopardize the safety ofthe operation or cause immense cost increas-es. Furthermore, poor or incomplete prepara-tion is a leading cause of accidents and haz-ards.

8-4.1 Positioning of the Asset(s)

When the heavy lift ship is in position andballasted to the proper draft, the Loadmasterwill assume control of the assets for final po-sitioning. The exact point of turnover shouldbe decided and agreed upon by all parties pri-or to the event. Support tugs, riding crew, andthe heavy lift crew should have good commu-

nications to ensure that all operations proceedsmoothly and all needs are met. Often, align-ment columns will be constructed to assist inthe athwartships alignment of the asset (SeeFigure 8-5). Sufficient fendering or other sys-tem must be employed on the alignment col-umns to prevent damage to the asset. Thiswill depend on the number and size of the as-sets being lifted. Support tugs will positionthe asset over the blocks and against thealignment columns or other guiding mecha-nisms. The Loadmaster will verify fore andaft position. Divers may also be used to verifyposition. (See 8-3.5.2)

Care should also be taken to ensure that thereis sufficient clearance for all underwater pro-jections such as sonars, propellers, bilge keelsand pit swords. During positioning, a mini-mum of 1 foot of clearance should be main-tained between the blocks and the asset (in-cluding all underwater projections). Thislimit is to allow for ship motions, so, if theship is expected to pitch more than 1 foot,more clearance should be allowed. No part ofthe asset should be closer than 1 foot to theblocks. A one foot clearance should also bemaintained between the asset and other partsof the heavy lift ship structure, such as wingwalls.

Actual placement of the assets on the cargodeck is dependent on adequacy of working area between and around the cargo. This is al-so affected by installation technique and con-figuration of blocking and sea fastening.Forklift trucks can be used to move materialaround the assets on deck. Work space maybe limited and spacing may dictate the workflow. A minimum spacing between assets of2800 mm (9.2 ft) should be adequate for onedirectional work flow and walking space.However, twice the minimum spacing allowsfor two directional work flow and forklifttruck access between the thrust blocks of thespur shores. A minimum of 2500 mm (8.2 ft)

8-16


Figure 8-5. Assets Being Loaded.

Alig

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ine

8-17


clearance between the ship and the edge ofthe cargo deck should be adequate for block-ing, working and access requirements. If pos-sible, additional spacing should be allowed sothat forklifts can still pass between the shipsafter the sea fastening spur shores (roll bars)are installed.

8-4.2 Fendering

Support tugs and alignment columns may beused to assist in positioning the asset(s) overthe pre-built blocking arrangement. Theriding crew should be prepared to providefendering from the asset in the event that in-sufficient fendering exists elsewhere. Thesefenders should be tended during the deballast-ing operation until the vessel comes to its fi-nal resting position. 4’ x 4’ sheets of plywoodmay prove useful in preventing damage as theasset is moved into its final position.

8-4.3 Riding Crew Accommodations During Loading

The riding crew is required on board each as-set for handling lines and tending hand fend-ers during loading and off-loading. This oper-ation may extend for some time and crew sizeshould be kept to a minimum. Since the assetmay be in a reduced operating status and haveno power during the loading, sanitary facili-ties and/or box meals for all personnel aboardthe asset during the procedure must be ar-ranged.

8-4.4 Deballasting

Once the assets are satisfactorily positioned,the heavy lift ship should begin deballastingprocedures. The assets should be observedcarefully for any abnormal motion or any in-

dications of damage or stress. The ridingcrew should tend the fenders to ensure that nodamage occurs to the asset. See 8-5.2.2 formore information concerning stability duringthis critical phase.

8-4.5 Connection of Services

During the transit, the assets may depend onthe heavy lift vessel for all necessary servic-es. In planned operations, it is common forthe riding crew to live aboard the heavy liftvessel. However, even if no one lives aboardthe assets during the transfer, certain servicesshould be made available. Connection ofthese services should not begin until the assetis in position and the heavy lift ship starts de-ballasting.

Fire fighting and cooling water servicesshould be connected as soon as possible afterthe asset is secured in position. These connec-tions should be completed prior to these seasuctions emerging from the water. Carefulpreparations, including a ship check prior tothe event will ensure a quick and trouble freeprocess. Connection of critical services, such

CAUTION

Personnel must be restricted fromthe heavy lift ship deck and on thelifted assets during both ballastingoperations and work periods asso-ciated with seafastening.

CAUTION

Connection of critical services,such as fire-fighting, should be giv-en priority over other events. Fire-fighting services should be avail-able throughout the process.

CAUTION

Once the asset is lifted, overboarddischarge from the asset must beavoided, restricted, or scupperedover the side of the heavy lift ship.

CAUTION

When the asset is on board theheavy lift ship, a security watchshould be established at the gang-way of the heavy lift ship.

8-18


as fire fighting, should be given priority overother events. Fire fighting services must beavailable throughout the process. Power ca-bles and fire fighting hoses, can be pre-stagedfor ready use when required.

Additional services may be required if theriding crew is to remain aboard the asset dur-ing the transit. These extra services should beconsidered a secondary priority compared todeballasting. If a problem occurs with one ofthese connections, deballasting should con-tinue without delay. A temporary means ofaccess should be provided as soon as possibleafter the deck is dry. Primary, all-weather ac-cess may be provided later, but must be in-stalled prior to departure.

After deballasting, the asset quarter deckwatch should be moved to the cargo deck ofthe heavy lift ship near the gangway. The as-set may be expecting technical representa-tives or other visitors who must be directed tothe safest means of egress. Because these op-erations are unique and interesting, sightseersmay be present; safety considerations shouldbe made for them. Similar coordination is re-quired for loading and fastening of any "Lift-on/Lift-off" deck cargo.

8-4.6 Blocking and Seafastening

Once the ship is deballasted, the blocking andseafastening should begin. Depending upon

the number and size of assets and the com-plexity of blocking and seafastening requiredto accommodate the shape of each hull form,the seafastening may require several days ofround-the-clock operation. A qualified Navyrepresentative, normally the Docking Observ-er or Blocking Expert, should be present toinspect these operations in coordination withcontractor personnel at all times. Personnelshould traverse the area with caution andavoid the area as much as possible to preventaccidents and/or delays. Because of the ex-tensive amount of welding on the cargo deck,personnel access and overboard dischargefrom the lifted assets must be restricted. Des-ignated access routes should be created tominimize any interference from traffic. Anyoverboard discharges from the asset shouldbe secured during the seafastening proce-dures.

8-5 Seakeeping and Stability

This section discusses some of the concernsassociated with the stability of the asset, theheavy lift ship, and the combination of thetwo. Some calculations are presented here,but a qualified stability expert will be re-quired to ensure the safety of all vessels in-volved.

During a FLO/FLO operation, several distinctstability considerations must be addressed,namely:

• Stability of the asset

• Stability of the heavy lift ship

• Stability of the asset/heavy lift ship sys-tem during the ballast/deballast opera-tion

• Stability of the heavy lift ship with theasset secured aboard during transit

The various phases of stability are depicted inFigure 8-6.

CAUTION

Welding and industrial facility safe-ty precautions must be followedclosely during blocking and seafas-tening.

CAUTION

Personnel must be restricted fromthe heavy lift ship deck and on thelifted assets during both ballastingoperations and work periods asso-ciated with seafastening.

8-19


Figure 8-6. Phases of Stability.

Phase 1

B a llas te d dow n,asset a floa t

Phase 2

A sset kee lcontac t

Phase 3

A sset la nded .H eavy lift vesse ltrim m ing to b ring cargode ck ou t o f the w ate r.

Phase 4

F orw ard e nd o f carg ode ck ou t o f the w ate r,rem o vin g trim to b ringaft en d ou t o f th e w a te r.A sset o u t o f w a te r.

Phase 5

D eba llas te d w ith asse ton bo ard , read y fo r trans it.

8-20


8-5.1 Ship Motions

A FLO/FLO transport is a very dynamic op-eration. Each of several assets and the heavylift ship move independently when the assetsare being positioned on the deck of the heavylift ship. This difficult situation is furthercomplicated if the operation takes place inunprotected waters or even in the open ocean.Once the assets are on the cargo deck of theheavy lift ship, they act as one. This at firstwould sound similar to the case when the as-set is in a floating dry dock. The dry dock,however, is in protected waters and is notnormally moved. In a normal dry docking, lit-tle else is done to secure the asset, (internallyor within the dry dock) with the exception ofproviding blocking for earthquake or hurri-cane force winds. With a heavy lift transport,the assets must first be made fit for sea (se-cured internally) and then secured aboard thecargo deck of the heavy lift ship for transit us-ing blocking and seafastening. The intent is tohold the asset in position on the cargo deckand cradle the asset to keep it from sliding ei-ther transversely or longitudinally or rollingover.

As the heavy lift ship proceeds through thewaves, it will flex (hog and sag). If the assetis rigidly tied down on the heavy lift ship, thisflexing will be imparted to the asset and maycause structural damage. It is therefore neces-sary to design a structure that will be bothstrong enough to resist the motions of theship, yet flexible enough not to cause damageto the asset. An understanding of the dynam-ics of the heavy lift ship and the asset is nec-essary to create such a structure. How to ana-lyze the effects of ship motions is covered inSections 8-6 and 8-7.

8-5.1.1 Wind Heel Criteria

FLO/FLO operations are best conducted insheltered waters, however, currents or chan-nel depths may make this impossible. Wher-ever the operation is conducted, the dominantweather patterns should be studied. If theloading operation is to be conducted in pro-tected waters a minimum wind of 60 knotswith a gust factor of 1.21 should be used toevaluate stability. If the operation is to beconducted in an open ocean area, the histori-cal data for that area should be consulted forexpected conditions. A gust factor of 1.21should be applied to expected winds. In theevent that there is no data available, a com-mercial standard of 100 mph (86.8 knots)shall be used as the expected wind and thenmultiplied by the gust factor.

Weather routing during transit requires a sep-arate analysis. Information concerning ex-pected sea states and winds should be ac-quired for planning purposes. Transitsinclude both the transfer from the point of de-parture to the unloading site as well and thetransfer from the loading site to the buildingsite (if they are different). If no data is avail-able the commercial standard of 100 mph(86.8 knots) shall be used. In no case shall awind of less than 60 knots be used.

8-5.2 Stability of the Asset

Stability of the asset, in the case of an unmod-ified or undamaged Navy commissioned ship,can be determined by reviewing the data inChapter II(a) of the ship's Damage ControlBook and a recent Inclining Experiment Re-port. Similar information for commercialships should be available in the ship's Trim

CAUTION

All personnel must strictly adhereto the operational plan and safetyguidelines.

WARNING

Loading and unloading shall notbe conducted in winds above 20knots or in a sea condition ofsea state 3 or higher.

8-21


and Stability Booklet and the DeadweightSurvey. Ship's from other services (USCG,US Army, etc.) should also have a consolidat-ed source for this information. These docu-ments will provide a good source for informa-tion for planning purposes and containspecific measures to improve stability. Thesebooks also contain stability characteristics forvarious loading conditions that meet the Na-vy's stability criteria.

For small craft and barges that do not haveDamage Control Books, follow these generalguidelines when attempting to improve stabil-ity:

• Completely fill any slack tanks to re-duce the free surface effect

• Lower and secure or off-load highweights

• Secure any large hanging weights andadd ballast

• Ballast by completely filling low tanks

Completely filling tanks or adding ballast willdecrease freeboard but will generally improvestability.

Do not shift, add, or remove any weight fromthe asset once it is on the heavy lift ship un-less specifically authorized by the Loadmas-ter, including liquids such as fuel or water.When permission is given to shift weights, anaccurate record of the amount and location ofthe weight change must be kept. Always ac-count for weight changes to ensure that theasset lifts from the blocks without losing sta-bility or taking an undue list or trim.

The asset must meet stability requirementsfor all potential environments of the FLO/FLO evolution. Four different environmentsshould be examined; loading, unloading, tran-sit, and any transitional periods (i.e., fromloading site to building site).

8-5.2.1 Stability Afloat

A thorough assessment of the asset’s stabilityshould be performed prior to the start of theFLO/FLO process. It is essential to evaluatethe stability of the asset in its actual condi-tion. A good weight survey (see 8-6.2.4)should be conducted on the day of the asset’sarrival to the loading site to ensure that theactual condition is known. This includes draftreadings, tank soundings and determinationof displacement (weight) and centers of grav-ity. However, such a detailed analysis maynot be possible if wartime or emergency con-ditions mandate quick action. Still, some esti-mate of the asset's stability should be ob-tained. If documentation of the ship's stabilityis not available, the stability may be approxi-mated by timing the ship's roll period. Thismethod is reasonably accurate and is used bythe U.S. Navy, U.S. Coast Guard, and otherregulatory bodies to check the stability calcu-lations to confirm the accuracy of the inclin-ing experiments and other similar determina-tions. This method is explained in 8-5.2.3and Table 8-6.

This approximation method is not to be usedas a substitute for a thorough stability analy-sis and weight determination. It only providesa measure of a ship’s stability to be used tovalidate stability estimates in emergent condi-tions.

Equally important is frequent verification thatthe ship's roll period has not changed. Even ifoverall criteria are satisfactory, any signifi-cant time increase in the period of roll shouldbe promply investigated, since this suggestsflooding or additional free surface.

8-5.2.2 Stability During Loading

A detailed report of the condition of the assetas it arrives at the loading site should be madeavailable to all parties so it can be evaluatedand the heavy lift ship can make the finalpreparations. All assets of the same designthat are to be loaded in the same fore and aft

8-22


orientation should arrive in a similar condi-tion of list (no more than 0.25 degrees), trim(no more than 1 foot) and draft. It may not bepossible to meet these limits with damagedassets.

The heavy lift ship can trim and list to matchthat of the asset. Additional considerationsmay limit the trim and draft of the vessels.

• Since this operation is performed in aseaway, the trim may be limited by thestability considerations addressedabove.

• When deballasting the vessel, consider-ation must be given to knuckle loadingon forward or after most blocks.

• Channel drafts may preclude excessivetrim angles by the heavy lift vessel.

• Freeboard requirements and limitingsubmerged draft may preclude exces-sive trim angles.

• During the ballast/deballast operations,the trim of the heavy lift ship must belimited so that the asset does not floatoff or slide on the blocking.

The deballasting operation will put the assetin an unusual stability condition. The reactionof the docking blocks on the asset is equiva-lent to removing weight from the asset's keel.This weight removal will serve to effectivelyraise the asset's center of gravity and reduceits metacentric height (GM) and thus reduceits stability (see Figure 8-7). As more andmore water is removed from the heavy liftvessel, the asset will be raised more and moreout of the water, the reaction on the docking

Figure 8-7. Draft at Instability.

( - R )R es id ua l B uoya ncy

KN∆

∆

GV

GRKN

WL

WL1

WL

WL1

D eck

K e e l B lock

K

W L = in itia l w a te rlineW L = deba llas ted w ate rline1

8-23

blocks will increase and this effect will be in-creased. The amount of reaction from thedocking blocks is equal to the difference be-tween the asset's floating displacement andthe displacement at the waterline under con-sideration in the landed condition. Eventual-ly, the reaction on the blocks will be largeenough to cause the center of gravity to rise toa point where the GM, and thereby the stabil-ity, will be zero. This is an extremely danger-ous condition, and the asset will almost surelycapsize unless side blocks are in place. Theasset's draft at this condition is called the"draft-at-instability."
The asset must land firmly on the keel andside blocks before this point is reached. If theasset has trim, it must land fore and aft on thekeel blocks before the draft-at-instability isreached, or it will turn over. It is necessary tocalculate both the draft-at-instability and thedraft-at-landing fore and aft to ensure that thevessel will not capsize during deballasting. Agood analysis should be provided by the con-tractor in the Transport Manual. There shallbe a minimum of one foot of difference be-tween the draft-at-instability and the draft-at-landing fore and aft.

If the draft-at-instability is much lower thanthe draft-at-landing fore and aft, the asset willhave acceptable stability and dock safely. Forexample, if the asset has a draft-at-instabilityof 13 feet and a draft-at-landing of 15 feet,the asset should remain stable until it lands onthe side blocks in calm water. Additional con-sideration must be given to the local sea stateconditions. As an example, if the weather cri-teria to perform this operation allows for theasset to pitch such that it may lift off theblocks after initial landing, a difference be-tween draft-at-landing and draft-at-instabilityof 1 foot would not be adequate for the assetto safely dry dock. If these draft values can-not be changed, this difference may dictatethe operational weather criteria.

8-5.2.3 Draft-at-Instability

A good measure of a vessel's initial stabilityis the vessel's metacentric height (GM). Itmeasures the ship's ability to recover fromdisturbances that cause small angles of heel.If GM is positive, the ship will be stable andreturn to its original heel angle when the dis-turbing force (wind, waves, etc.) is removed.If GM is negative, the vessel will be unstable.This means that if the vessel is disturbed, itwill not be able to recover and will continueto roll in the direction that it moved at the on-set of the disturbing force. In other words itwill capsize.

GM can be determined from known or pre-dictable quantities, KM and KG. The heightof the metacenter (KM) for a ship is the theo-retical point around which a ship rolls andthrough which buoyancy acts for small anglesof heel. This point is based on a ship's geome-try and is generally plotted on a ship's draftdiagram or curves of form. A ship's verticalcenter of gravity (KG) is the point that repre-sents the centroid of all the weights of a ship.This value is derived from the asset’s currentcondition of loading. Both of these quantitiesare measured from the keel and can be deter-mined with some degree of certainty. GM issimply the distance between these two pointsor:

As stated previously, a positive value for GMis required to be stable. By looking at thisequation, it is easily seen that KM must begreater than KG to have a stable vessel. Asthe heavy lift ship deballasts, and the assetlands on the blocks, the draft of the asset willbegin to decrease. As this draft goes down,the buoyant force on the asset (or residualbuoyancy) will decrease and the height of themetacenter will change. Additionally, theamount of the vessel supported by the keelblocks (or reaction of the keel blocks) will in-crease.

The reaction of the keel blocks acts as weightremoval at the asset's keel. This negative

GM KM KG–=

8-24


weight at the keel causes the same effect as anadded weight high in the ship. Both willcause an increase in the height of the center ofgravity (KG). Since the asset's weight did notactually change, this rise in KG is called avirtual rise. This virtual increase will effec-tively cause a reduction in GM and reduce thestability of the asset. As draft continues todecrease, this effect will become more pro-nounced and the asset will become unstable.This point of instability occurs in every dock-ing. The asset must land on the keel and sideblocks before this point is reached or it maycapsize.

To determine the draft-at-instability, it is nec-essary to determine the virtual reduction inmetacentric height caused by the virtual risein KG. The draft at which this virtual meta-centric height (GMv) equals zero, will be thedraft where the asset is unstable. The virtualGM can be found by subtracting the virtualcenter of gravity (KGv) from the height of themetacenter (KM) at the draft in question.

The virtual center of gravity can be found bysumming the weight moments of the asset:

Figure 8-8. Limit of Stablility

K M (∆−R )K N

D ra ft a t Instab ility

(KG ) (∆)

DR

AF

T (

ft.)

M O M E N T S (ft - tons)

KGo ∆⋅( ) Rkn 0⋅( )– KGv ∆ Rkn–( )⋅=

8-25


or:

Where:

KGv = Virtual center of gravity (ft)

∆ = Ship’s displacement (tons)

KGo = Afloat center of gravity (ft)

Rkn = Reaction at the keel blocks (tons)

(∆ − Rkn) = Residual buoyancy at a reduceddraft (tons)

When the asset lands on the blocks and thedraft begins to decrease, the asset is support-ed by two forces, the reaction of the keelblocks (Rkn) and buoyancy. The total of thesetwo forces equals the displacement (weight)of the asset. In other words, the difference be-tween the displacement and the reaction ofthe keel blocks is equal to the buoyancy at thereduced draft. This quantity (∆ - Rkn) is alsocalled the residual buoyancy. The residualbuoyancy can be determined for a given draftfrom the asset's curves of form or draft dia-gram. Knowing these values, the equation forGMv can be solved.

Where:

GMv = Virtual metacentric height (ft)

KM = Height of the metacenter (ft) fromship’s curves of afloat draft

KGv = Height of the virtual center ofgravity (ft)

∆ = Ship’s displacement (tons) from ship’s curves of afloat draft

KGo = Afloat center of gravity (ft)

Rkn = Reaction at the keel blocks (tons)

Note: The term (∆ − Rkn) is the displacementat a reduced draft, i.e. the residual buoyancyafter keel contact. This equation can besolved for a number of drafts, until a draft isfound where GMv equals zero. A shorter wayto determine this value is to set the equationequal to zero and solve graphically. By set-ting GMv equal to zero we see that:

or:

Both KM and the residual buoyancy (∆ - Rkn)can be found on the asset's curves of form ordraft diagram. To solve this graphically:

• Determine a range of drafts, starting atthe floating draft and decreasing in in-crements of one foot.

• For each draft, determine the asset's re-sidual buoyancy and KM

• For each draft, calculate the residualbuoyancy moment

• Calculate the displacement moment

(Note: This quantity is determined atthe assets floating draft and is not af-fected by the change in draft)

• Plot the residual buoyancy moment andthe displacement moment for the rangeof drafts.(Note: The displacement momentshould be a vertical line)

• Where these two curves intersect willbe the draft-at-instability.

A sample of this graph is presented in Figure8-8. and in Appendix Q.

KGv ∆KGo

∆ Rkn–( )-----------------------⋅=

GMv KM KGv–=

GMv KM ∆–KGo

∆ Rkn–( )------------------------⋅=

0 KM∆ KGo⋅( )∆ Rkn–( )------------------------–=

KM ∆ Rkn–( )⋅ ∆ KGo⋅=

KM ∆ Rkn–( )⋅( )

∆ KGo⋅( )

8-26


If information is not known, such as duringan emergency or rescue docking, an estimateof the vessel’s condition can be made. Bymeasuring the asset’s roll period (see Table8-6), an estimate of the GM and hence KGcan be made. Using the formula:

where:

GM = metacentric height (ft)

Cc = a constant (sample values given inTable 8-3)

B = beam of ship (ft)

T = period of roll for complete cycle,from a maximum on one side to amaximum the other and back (sec)

Thus, from the value of GM, KG may be ob-tained from equation:

where:

KG = height of center of gravity of shipabove keel when waterborne (ft)

KM = height of metacenter above theship’s keel (ft)

GM = metacentric height (ft)

The value of KM is obtainable from thecurves of form.

8-5.2.4 Draft-at-Landing Fore and Aft

A similar method can be used to determinethe draft-at-landing fore and aft. Again, it willbe a balance of the residual buoyancy mo-ments and the moment created by the dis-placement and the keel blocks (see Figure8-9). If the asset lands on the aftermost block(method is similar for bow landings) it willbegin to pivot about this point as the draftchanges. The ship will land fore and aft whenthe moment created by the buoyancy equalsthe displacement moment (each acting aboutthe aftermost keel block). To determine thedraft when this occurs, follow this procedure:

• Determine the displacement, LCG,buoyancy, and LCB for the floating as-set.

• Determine buoyancy and LCB for se-lected drafts below the floating water-line.(If the asset or heavy lift ship has con-siderable trim at the time of landing,horizontal waterlines may not providean accurate estimate. In most cases,

NOTE

It is emphasized that the Cc valueis only an approximation and en-ters the equation as the square ofits value. The GM value thus ob-tained is, therefore, an approxima-tion. This approximation methodshould not be a substitute for athorough weight analysis.

GMCc

2 B2⋅

T2------------------=

KG KM GM–=

Table 8-3. Sample Cc Values.

SHIP TYPES Cc

Auxiliaries 0.44

Aircraft Carriers 0.58

Cruisers 0.43

DD692 (short hull) 0.42

Destroyers (other) 0.44

Destroyer Escorts 0.45

Landing Ships 0.46

Patrol Craft 0.47

Submarines Body of Revolution hull Other (fleet type)

0.410.36

Tugs 0.40

8-27


however, differences will be negligi-ble.)

• Determine the distance between theknuckle block and the LCG.

• Determine the distance between theknuckle block and the LCB

• Calculate moments of residual buoyan-cy and moments of displacement aboutthe aftermost keel block.(Differences caused by the reactionpoint moving due to compression of thekeel block can be ignored unless thestability is marginal and a more precisecalculation is needed.)

• Plot these moments versus draft. Thedisplacement moment will be a verticalline.

• Where the line of buoyancy momentcrosses with the line of displacementmoment, will be the draft at landingfore and aft.

A sample of this graph and these calculationsis provided in Appendix N.

8-5.3 Stability of the Heavy Lift Ship

Any heavy lift ship considered for use as atransport platform for US Navy assets shall

be classified by one of the commercial regu-latory bodies (ABS, DNV, Lloyd's, etc.). Thecontractor must provide documentationshowing current certification. The regulatorybody should be contacted to verify that thevessel has met the latest requirements. Whentransporting assets, heavy lift ships must be ator below specified load line drafts that are in-tended to ensure adequate freeboard.

8-5.3.1 Intact Stability Requirements

The calculated stability and buoyancy charac-teristics of the heavy lift vessel (includingdisplacements and centers of gravity with andwithout the asset on board) must be provided.

• The intact stability must be determinedfor all modes of operation, includingthe five phases shown in Figure 8-6.Longitudinal stability must be includedfor Phases 3 and 4 of Figure 8-6. Freesurface effects must be determined andincluded in the calculations.

8-5.3.2 Stability During Ballasting/Deballasting

The ballast/deballast operation presents someunique stability concerns and must be evalu-ated thoroughly. Stability is largely impactedby the amount of waterplane area of the ship.As the cargo deck of the heavy lift ship goes

Figure 8-9. Draft at Landing Fore and Aft.

8-28


into or out of the water, the stability of the liftship changes rapidly and substantially. If thedeck is completely submerged, only the wa-terplane of the raised hull structure, which ex-tends above the cargo deck, will provide sta-bility to the vessel. Additionally, during thisphase, the water level in the ballast tanks ischanging and may not be in either empty orpressed up condition. This may produce afree surface effect which will also reduce sta-bility. The result is that the heavy lift shippasses through a phase of minimum stability(minimum GM) while the cargo deck is underwater. To control the amount of this change,heavy lift ships generally go through thisphase with some list and trim.

A thorough study of the changing conditionsof the heavy lift vessel must be completed forthe entire loading and unloading process. Thepoint of minimum stability should be knownto compare to the minimum stability condi-tions already calculated for the asset. Reviewthe stability of the heavy lift ship to ensurethat it is not at the point of minimum stabilityat the same time that the asset assumes itsdraft-at-instability. If this happens, the asset

and the heavy lift ship may roll out of phase,causing landing problems, or, even worse,causing the asset or the lift ship to becomeunstable, assume a large list or capsize.

During operations involving lifting of U.S.Navy assets, the heavy lift ship shall maintaina GM (including free surface correction) ofno less than 3.28 feet (1 meter). Trim of theheavy lift ship of up to 3° may be included tomeet the minimum GM. More trim than thismay cause the asset to float off the blocks onone end or slide on the blocks. The effect ofthis trim should be investigated to be sure it issatisfactory. Normally, if this trim on theheavy lift ship's cargo deck does not cause theassets draft at one end to be zero while thedraft on the other end is less than 2 - 5 feet ofthe afloat draft, the asset should not slide orfloat off. See Figure 8-6, phase 3. To waivethe 1 meter minimum GM, the asset must behard on the blocking before the phase of min-imum stability and the minimum GM (not ac-counting for the list) must meet or exceedregulatory body requirements of 0.5 feet(0.15m) in all phases of the operation, includ-ing the free surface effect. This is the mini-mum GM required by regulatory agencies. Adetailed stability analysis for all operationsmust be included with the waiver request. Inno case should a GM below 0.5 feet be ac-cepted. Efforts should be made to meet theNavy requirements.

8-5.4 Stability of the Heavy Lift Ship with the Asset Secured Aboard during Transit

The heavy lift ship with the asset aboard,must be able to withstand beam winds as de-scribed in paragraph 8-5.1.1. The contractormust present a stability analysis (righting armcurve) meeting these criteria in the TransportManual.

The dynamic stability under the righting armcurve at a given angle of heel is a measure ofthe amount of energy that has to be put into

CAUTION

Submersible barges that are usedfor FLO/FLO lifts rely on bottomcontact of one end of the barge toensure sufficient stability until thecargo has landed on the blocksand stability can be increasedthrough added waterplane. Prob-lems with exact positioning andhigh knuckle block loading add toan already difficult procedure.When one end of the cargo haslanded, the barge must rely on thecargo staying in position and con-tributing to the stability of thebarge/cargo system until more ofthe barge's cargo deck comes outof the water.

8-29


the ship to give it that angle of heel. Thisheeling or overturning energy can be suppliedby wind, waves, or a combination of theseand other forces. This quantity can be mea-sured by making a plot of the righting arm(GZ). See Figure 8-10. The area under thisGZ curve from zero degrees (or where thecurve first crosses the x-axis) to the angle inquestion, multiplied by the displacement, isequal to the amount of energy that is availableto return the vessel to the original static heelangle (most likely zero degrees).

The righting arm curve should also displaythe wind lever curve (see Figure 8-10). Thiscurve represents the heeling energy devel-oped by the wind acting on the sail area of thevessel (with the asset aboard). The area willchange as the vessel heels which gives thiscurve a downward arc. This curve is depen-dent on wind velocity and represents only oneparticular speed. For the purposes of analysis,the maximum wind including gusts expectedduring transit should be used.

The American Bureau of Shipping (ABS) us-es this GZ curve to establish their require-ments for dynamic stability. The area underthese two curves are then compared to deter-mine adequate dynamic stability. The area forthe GZ curve is computed from the first inter-cept (where it first crosses the x-axis) to thesecond intercept or the downflooding anglewhichever is less (see ship’s stability book fordownflooding angle). If both the downflood-ing angle and the second intercept are greaterthan 50 degrees, then 50 degrees is used. Thearea under the wind lever curve is taken from0 degrees to the same limiting angle. Therange of dynamic stability, from the intersec-tion of the wind lever and righting arm curvesto the point of zero righting moment must notbe less than 36 degrees (see Figure 8-10). Ad-ditionally, the second intercept point must begreater than 36 degrees.

ABS requires that the area under the rightingarm curve at or before the second intercept or

downflooding angle (whichever is less) is notless than 40 percent in excess of the area un-der the wind lever curve to the same limitingangle. Figure 8-10 demonstrates this graphi-cally.

The angle of heel at which the cargo deckedge is submerged must also be indicated.

8-5.4.1 Damage Stability

The damage stability requirements of MIL-STD-1625C Safety Certification Program forDrydocking Facilities and Ship buildingWays for U.S. Navy Ships, (Ref. T) were de-veloped to ensure the safety of a vessel in adry dock. If a floating drydock is subjected todamage to two main watertight subdivisiongroups, adherence to these guidelines ensuresthe safety of the docked vessel. These re-quirements may not be stringent enough toensure survival and safety of an asset on theheavy lift ship if it is damaged in a seaway.

8-6 Blocking

Unlike normal dry-docking operations, heavylifted assets are subjected to significant mo-tions caused by exposure to an ocean environ-ment. This section will discuss the design ofthe blocking which will be the support systemfor the asset. This structure will carry the en-tire weight of the asset as well as protect theasset from potential damage from the motionsof the heavy lift ship. The proper design ofthis system will ensure a safe transit for theasset.

NOTE

The current commercial fleet ofheavy lift ships and barges doesnot meet these requirements. Thevessels should meet the damagedstability requirements of their clas-sification society. These require-ments should be studied to under-stand the limits and risks involvedin regard to damaged stability.

8-30


Figure 8-10. GZ Curve

AREA (A+B) 1.4 AREA (B+C)≥ ⋅

Levers (M )

0 1 0 2 0 3 0 4 0 6 0

N ot le ss th an 36°

Angle of Heel (degrees)

A Righting Arm (GZ)

If over 50°,use 50°

5 0

Second intercept(m ust be greater than 36°)

F irst In tercept

B

W ind LeverC

For Adequate Dynam ic Stability:

NOTE

Downflooding Angle not shown.See ship’s stability book for appro-priate downflooding angle.

8-31


8-6.1 Preparing the Docking Plan

Most vessels, and certainly all active Navyvessels, have a dry-docking plan. This plancontains information that shows the correctplacement of docking blocks to provide aproper fit to the hull and to eliminate damageof underwater projections as well as distributethe docking loads. This serves as a first esti-mate in preparing a docking plan for a FLO/FLO operation, but preparation of the dock-ing and seafastening plan requires consider-ation of factors other than what is normallyconsidered in a dry docking.

A FLO/FLO is not an ordinary dry docking interms of operations and loading. For a FLO/FLO operation, the keel block height must beminimized. The keel block height will affectthe stability of the lift ship by dictating the re-quired depth of water and depth of submer-gence of the heavy lift ship. This will proba-bly determine acceptable loading sites.Additionally, tall keel blocks will requireeven taller side blocks. These blocks may besubject to loads caused by currents, waves ormotions of the asset. Precaution must be tak-en to be sure that these blocks do not tip overduring loading. Transporting across the oceansubjects the docking blocks to higher dynam-ic loading and, at the same time, requires thedocking blocks to absorb the flexing of theheavy lift ship under the asset.

A docking plan should be prepared for everyoperation. Previous plans can be used as aguide, but each FLO/FLO presents uniqueconcerns. The asset's loading condition,weather, and expected sea conditions willlikely be different and must be accounted forin the plan. Careful preparation is essentialfor a successful operation. As a start, the as-

sets dry-docking plan should be used as a pre-liminary plan. This will be sufficient to sup-port the weight of the vessel with minimaldynamic loadings. The loading due to dynam-ic motions, the gravity component at the max-imum angle of inclination, and the effects ofwind loading must all be included in the anal-ysis.

Check with the planning yard to be sure thatthe latest revision of the docking plan is beingused. This plan, along with any previousFLO/FLO docking plans for the asset, shouldbe provided to the lift contractor early in theprocess and, if possible, in the RFP.

8-6.2 Docking Blocks

The contractor should provide a proposeddocking plan in the Transport Manual. Itshould contain descriptions of all the dockingblocks. It should provide the physical charac-teristics of the blocks, including material anddimensions. Keel block height should be keptto a minimum to reduce the required depth forfloat on and float off. As such, the use of con-crete base blocks, common in dry docking,should be avoided.

The Transport Manual also provides calcula-tions to verify that the blocks are stable andstructurally adequate to withstand the loadingused in lifting capacity calculations and thatthe number of side blocks (and shores) is ade-quate to provide sufficient bearing area to re-sist overturning. Due to the dynamic nature ofthe operation, all blocks and shores should besecured to the cargo deck of the heavy liftship. Prior to loading, these blocks should beinspected to be sure that they are the same di-mensions, in proper location and in the samematerial condition as that reported by theTransport Manual.

The keel blocks are subject to both the staticweight of the asset and the dynamic loads inthe vertical direction imposed by the action ofthe sea. The side blocks and sea fasteners willbear some of the assets weight and also be

NOTE

Check with the planning yard to besure that the latest revision of thedocking plan is being used.

8-32


subject to dynamic loading in both the verti-cal and transverse directions. To find the totalforce on the blocks it is necessary to calculatethe effects of dynamic motion.

8-6.2.1 Dynamic Loading

The commercial industry designs sea fasten-ers using load forces based on equations fromthe Principles of Naval Architecture (PNA)The Society of Naval Architects and MarineEngineers (Ref. U) for roll and pitch. The USNavy developed their own series of equationsfor determining these dynamic forces. An ex-planation of these equations is contained inDOD-STD-1399-301A, Interface Standardfor Shipboard Systems Section (Ref. V). Thetwo equations produce very similar results fora similar set of conditions. The equationsfrom PNA are used to calculate the forces dueto dynamic motions separately from the staticforce due to weight then they are combined.The Navy equations combine these effects in-to a load factor. Both sets of equations use as-sumed values for maximum roll and pitch. Ei-ther approach can be used but only the Navyapproach is demonstrated here. See Princi-ples of Naval Architecture (PNA) The Societyof Naval Architects and Marine Engineers(Ref. U) more information about the commer-cial approach.

The keel blocks will bear most of the weightof the asset with the side blocks and seafas-teners taking only a partial load. To be con-servative, the keel blocks will be designed tosupport the entire weight. The weight of theasset is equal to its displacement at the timeof loading. As discussed earlier, an account ofthe dynamic loading must also be includedfor accelerations in the vertical direction.

To determine the design loads (forces) thatmust be resisted to hold the asset on the cargodeck of the heavy lift ship, multiply theweight of the asset (w) by an acceleration fac-tor (a) determined from the motions of the

heavy lift ship, taking into account the loca-tion of the asset.

The formulas for computing the acceleration(a) in the vertical direction (z direction) are asfollows:

where:

az = vertical acceleration factor (g)

h = heave acceleration (g) (Table 8-4)

P = Maximum angle of pitch (degrees)(Table 8-5)

x = distance of center of gravity of assetforward or aft from center gravity ofheavy lift ship (ft)

R = Maximum angle of roll (degrees)(Table 8-6)

y = distance of asset off centerline ofheavy lift ship (ft)

Tp = Period of pitch (sec) (Table 8-5)

Tr = Period of roll in (sec) (Table 8-6)

The first term in this formula accounts for thestatic force due to the weight, gravity compo-nent. This factor represents the portion of theasset’s weight to be borne by the blocking. Avalue of 1.0 is used for keel blocking to beconservative.

Values for pitch and roll amplitudes and peri-ods are given in Table 8-5 and 8-6. The com-mercial industry typically uses the followingvalues as a first estimate to develop their loadfactors:

R = 20 degrees of roll, one direction

P = 15 degrees of pitch, one direction

Tr = roll period of 10 seconds, port tostarboard back to port

az 1 h0.0214Px

Tp2

-----------------------0.0214Ry

Tr2

------------------------+ + +=

8-33


Tp = pitch period of 10 seconds, bow tostern back to bow

The load factors which have proved effectiveon past lifts, are approximately equal whencompared to those developed in DOD-STD-1399 Section 301A, provided that the loadingis similar to those in the past. Namely, GM androll/pitch periods must be in the same range.The ship motions observed during actual op-erations indicate that both approaches arecomparable for a sea state 7 analysis.

Using these commercial standards or the USNavy approach is acceptable, however, theyshould not take the place of a detailed motionstudy. This commercial industry approachdoes not include an additional heave accelera-tion. If the results from the motion analysis in-dicate that the heavy lift ship with assetsaboard will roll or pitch at periods greater thanthis rule of thumb, further evaluation byNAVSEA is required. These values should becompared with the expected values fromroute planning. If larger angles of heel orpitch are expected, those values should beused.

Information concerning acceleration factorsalong with the angles or roll, pitch, heave, andsurge should be presented in the TransportManual.

8-6.2.2 Loading of Keel Blocks

To find the total force on the blocks, multiplythis acceleration factor by the weight of theasset.

where:

DLk = total dead load on the keel blocks(tons)

w = weight of the asset (tons)

az = vertical acceleration factor (g)

8-6.2.3 Keel Block Loading Distribution

Using the Navy docking drawing as a guidein placement of keel and side blocks will as-sure alignment with ship’s structure, omis-sions for hull penetrations and appendagesand a proper fit to the curvature of the hull.Specifics of the blocking must be providedfor the proposed blocking arrangement tomake sure that the asset’s hull is properlysupported. To ascertain that structural re-quirements are not violated, the loading dis-tribution of the asset on the blocking must becalculated. The distribution of the asset’sweight, as shown on the longitudinal strengthdrawing (20 station weight breakdown), indi-cates how the asset’s weight is distributed onthe asset’s hull structure and thereby onto theblocking as shown on the Navy dockingdrawing.

The weight of the asset and the location of theasset’s centers of gravity (vertical, transverse,and longitudinal) must be accurately predictedin order to avoid overloading the blocks. Keelbearing should be uniform and continuous. Ifkeel bearing is non-uniform, as in the case of aasset with a partial bar keel, long overhangs,highly concentrated weights or excessive hullprojections, special considerations must begiven to further spread the load over individualkeel blocks. For loadings that are not continu-ous and uniform, a more rigorous method maybe required to determine the load distribution.As an example, MSOs and MCMs require ad-ditional shores to be placed under the stern dueto long overhangs.

DLk waz=

NOTE

The vertical acceleration factor, az,represents an increase in thedownward force. It is essentially amultiplier to increase the effect ofgravitational acceleration and theunits used, g, reflect this.

8-34


8-6.2.4 Distribution of Asset’s Weight

Once the total force on the keel blocks isknown (DLk from 8-6.2.2), an assessment ofthe loading distribution should be conductedto ensure that the blocking is not overloaded.This loading distribution should be comparedto the docking drawing that was used as a firstestimate of required blocking. To conduct aloading distribution:

Examine ship data for the latest information.Sources include docking drawings, curves ofform, and full load weight distribution.

Survey the asset to find information on allvariable weight and abnormalities (trimweights added, hull damage, cargo, etc.)

• Record vessels drafts

• Calculate the asset’s expected drafts atthe time of docking

• Calculate the asset’s displacement andcenters of gravity

Compare the expected values with the record-ed values and resolve any discrepancies.

Table 8-4. Heave and Surge Motion Parameters for Calculation of Loading Factors for Conventional Surface Ships.

SeaState

LBPmeters (feet)

Heaveacceleration (g)

Surgeacceleration (g)

4 Less than 46 (150)46-76 (150-250)76-107 (250-350)107-152 (350-500)152-213 (500-700)Greater than 213 (700)

0.100.100.100.060.060.04

0.060.050.050.040.040.02


0.170.170.170.140.100.07

0.100.100.100.050.050.05


0.270.270.270.210.160.11

0.150.150.150.100.100.05


0.40.40.40.30.20.2

0.250.200.200.150.150.10

8-35


8-6.2.5 Calculation of the Asset’s Loading on the Docking Blocks by the Trapezoidal Method

It is important to get an estimate of the loadon the blocks to ensure that they are not over-stressed. To do this, start by examining the re-quired blocking of the docking drawing. Thiswill provide the first estimate of the longitu-dinal location of the asset with respect to theblocking and its center of gravity with respectto the center of blocking (see Figure 8-11).


0.60.60.60.50.40.2

0.350.300.300.250.250.10

Table 8-4. Heave and Surge Motion Parameters for Calculation of Loading Factors for Conventional Surface Ships.

SeaState

LBPmeters (feet)

Heaveacceleration (g)

Surgeacceleration (g)

NOTE

In the event of lifting a damagedasset the displacement at the timeof lift may differ from the displace-ment to be transported. This is dueto the entrained water in the dam-aged area that will run out duringand after the lifting operation.

Table 8-5. Pitch Motion Parameters for Calculation of Loading Factors for Conventional Surface Ships.

SeaState

Length between perpendiculars (LBP)

meters (feet)

Pitch angle*degrees

Pitch periodseconds


2.02.01.01.01.01.0

3.54.05.06.07.08.0

8-36


It is important to use the weight distributionof the asset at the time of its loading onto theheavy lift ship. For the current condition ofloading, the displacement and centers ofgravity are calculated using the current draftreadings and the weight distribution as de-scribed above. In the case where the blockingcan be assumed to be continuous and uniform

(see Figure 8-12), the loading distributionmay be approximated by using a trapezoidalapproximation.

If the asset’s longitudinal center of gravity(LCG) aligns vertically with the center ofblocking (Cb), the forward and after blockswill share the load fairly equally. In practice,this is rarely the case. When the asset’s LCG


3.03.02.02.02.01.0

3.54.05.06.07.08.0


5.04.04.03.03.02.0

3.54.05.06.07.08.0


7.06.06.05.04.03.0

3.54.05.06.07.08.0


11.010.09.07.06.05.0

3.54.05.06.07.08.0

*Note: Pitch angle is measured from horizontal to bow up or down.

Table 8-5. Pitch Motion Parameters for Calculation of Loading Factors for Conventional Surface Ships.

SeaState

Length between perpendiculars (LBP)

meters (feet)

Pitch angle*degrees

Pitch periodseconds

8-37


is forward or aft of the Cb, we can assume theload distribution is roughly trapezoidal.Again, this is assuming that there is no signif-icant anomalies in either the ship’s load dis-tribution or in the blocking build. If the LCG

is aft of Cb, the after blocking will carry moreof the load.

The amount of load supported by the afterblocks will depend on the distance that LCG

Table 8-6. Roll Motion Parameters for Calculation of Loading Factors for Conventional

Surface Ships.1

SeaState

Beammeters (feet)

Roll angle 2

degreesRoll period

4 Less than 15 (50)15-23 (50-75)23-32 (75-105)Greater than 32 (105)

7665

See note3 for determination of rollperiod


1210109



19161513



28242220



42373431


1 Excludes multi-hulls, surface effect ships, and all craft supported principally by hydrodynamic lift.2 Roll angle is measured from vertical to starboard or port3 Full roll period is to be calculated from:

Where: Tr - is the full roll period (seconds) Cc - is a roll constant based upon experimental results from similar ships - usual rate 0.38 to 0.49 (sec/√ft) (0.69 to 0.89 (sec/√m)). For Heavy lift ships use Cc-0.40 unless a better estimate is provided. It may be as high as 0.44. See Table 8-3 for examples of other surface ships. B - is the maximum beam at or below the water line (m or ft). GM - is the maximum metacentric height (m or ft).

Tr Cc B×( ) GM( )1 2⁄

⁄=

8-38


Figure 8-11. Load Distribution.

Load M in

O H A

SRPAP

LBP

FP

A

LoadM ax

LBP = Length betw een perpendiculars of asset

SRP = D istance from AP to point from w hich d istance to keel b locks is m easured

LCG = Asset’s longitudinal center of gravity

O H A = D istance from SRP to keel b lock

6B = = A pproxim ate C enter of Trapezoid

A = D istance from asset’s LC G (center of G ravity) to C (center of B locking) = C -[LBP+SR P-LCG -O HA] (Note that if A is a negative num ber the trapezoid is reversed in the above d iagram so the Load m ax is greatest at the forw ard end of the asset

b

B

AP = After Perpendicular

= Length of keel b lock ingL k

L k

2= = C enter of b lockingC b

L k

LCG

B

L k

C b

Deck of Heavy L ift Ship

8-39


is from Cb. The further away from LCG thatCb is, the more uneven will be the distributionof loading. In fact, if the LCG is outside ofthe center third of the blocking arrangement,the load distribution will be triangular and thedifference between maximum load and mini-mum load may be significant. See Figure8-11 for an illustration of the relationship be-tween LCG and the center of the assumedtrapezoid, B. For a trapezoidal load distribu-tion, B will be approximately 1/3 of thelength of the keel blocking (Lk) from the afterend or 1/6 of Lk from the center of blocking(based purely on geometry). This is a goodinitial estimate to determine the maximumand minimum load.

To determine the maximum and minimumloads, use the following equations:

If A < B, load distribution is trapezoidal:

If A > B, load distribution is triangular:

where:

Load Max = Maximum expected blockingload (tons)

Load Min = Minimum expected blockingload (tons)

DLk = Loading due to weight and dynamiceffects (see ) (tons)

A = Distance from center of gravity ofasset to center of blocking (ft)

B = Distance from center of trapezoid tocenter of blocking (Lk/6) (ft)

Lk = Length of keel blocking (ft)

Le = Length of effective keel blocking(ft) = 1.5 Lk - 3 A

The load distribution, as defined by LoadMax and Load Min, is used to determine ifthe blocking (and in some cases the cargodeck) is adequate to support the asset. Checkthe maximum loading against the loading as-sumed for the ship’s docking drawing. Thekeel blocks should be checked to ensure thatthey are not overstressed. Assume that thelast block in the line will see Load Max. Tofind the stress on this block use:

where:

S = Stress on block (psi)

Load Max = Maximum expected blockingload (tons)

Ae = Effective area of keel block(in2)

This stress should be lower than the propor-tional limit for the material used. See Table8-7 and paragraph 8-6.2.7 for the allowablestress on blocks. If it is not, consider usingmore keel blocks, keel blocks with better con-tact area, or redistributing the asset’s loadmore evenly.

8-6.2.6 Knuckle Loading

Special consideration must be given to theend of the blocking arrangement as an asset

Load MaxDLk

Lk---------- 1

AB----+

=

Load MinDLk

Lk---------- 1

AB----–

=

Load Max4DLk

3 Lk 2A–( )---------------------------=

Load Min Load MaxLe

------------------------=

CAUTION

These calculations assume a con-tinuous row of keel blocks. If this isnot the case, increases in loadingshould be made accordingly.

SLoad Max

Ae------------------------

2240 lb1 ton

------------------ ×=

8-40


makes initial contact with the blocking. Theindividual block at each end of the keel blockrow is referred to as the knuckle block andmay be subject to high compressive stress asthe asset first lands. Initial contact will behighly localized and may cause high stressesand deformation of the block. For an assetwith trim by the stern, the reactions at the af-termost block should be analyzed. Even when

an asset is at an even keel condition, theheavy lift ship will likely deballast in a way toexpose deck area as quickly as possible. Thistrimmed condition may also cause localizedloading on the knuckle block.

As the heavy lift ship continues to rise, theknuckle block will deform and the asset willreduce trim. Additional support will be pro-

Figure 8-12. Keel Blocks.

Table 8-7. Allowable Block Stress (Assuming Douglas Fir).

Keel Width, ftAllowable Unit Stress

for Blocking(S), lb/in2

≥3.00 370

2.50 323

2.00 277

1.75 254

1.50 230

1.25 207

1.00 184

8-41


vided by blocks forward of the knuckle blockand contact with the asset will increase. Atthe same time, more and more of the asset’sweight will be supported by the blocking. Thestress seen at the knuckle block will likelyrise at first and then decrease, reaching amaximum somewhere between initial and fullcontact. This maximum stress should be ana-lyzed to ensure the strength limits of the ma-terial is not exceeded. Naval Ship’s TechnicalManual (NSTM) S9086-7F-STM-010, Chap-ter 997, Docking Instructions and RoutineWork in Drydock (Ref. W) provides a soundmethodology for computing the knuckleblock stress and much of the material present-ed here is borrowed from that source.

8-6.2.7 Safe Allowable Compressive Stress of Blocking

The allowable timber compressive stress fordistributed loading on keel blocks, taken asthe fiber stress at the proportional limit forDouglas fir, is 370 psi. This assumes a uni-form pressure on a 42 by 48 inch dockingblock resulting in a total load of approximate-ly 330 tons. When computing the stress forthe actual condition, the weight of the assetand the area in contact with the blocks shouldbe used to determine loading. Note that thislimit applies only to keel blocks. Side blockcriteria are discussed in 8-7.1.

Figure 8-13. Heavy Lift Blocks.

8-42


Table 8-7 lists allowable timber compressivestresses for the blocking based on the propor-tional limit for Douglas fir. The computedstress is dependent upon the area of the keelin contact with the knuckle. For vessels withkeels that are narrower than 3 feet, the allow-able stress has been reduced. This is neces-sary because of the compression of the blockduring loading. For narrower keels, there willbe less area in contact with the blocks con-centrating the load so that less load can besupported. Appendix D of NSTM, CH-997(Ref. W) presents a detailed explanation oftotal load as a function of compressive stress.

When docking ships with keels that are nar-row, it is advisable to use hard wood cappingat the knuckle block. The hard wood cappingwill be able to carry stress concentrations thatwould cause severe crushing of soft capping.Hard caps should be used in conjunction witha soft wood stratum below to give the sameoverall compressive characteristics to theblock. For certain vessels with bar keels (e.g.,tugs), using caps bound with steel angles willprevent the keel from cutting into the cap.

8-7 Seafastening Plan

The seafastening plan is a composite arrange-ment of side blocks, spur shores and seafas-teners (Figure 8-13). Side blocks will supplysome of the necessary support associated withthe vertical loading for the initial dockingphase. They provide resistance of any over-turning moment resulting from ship's motionsand heel angles. Spur shores, or roll bars, areinstalled to provide further resistance to thedynamic overturning moments in a seaway.Seafasteners (stopper blocks) are installed toprevent fore and aft and athwartships slidingaction as the heavy lift ship pitches and rolls.Each of these will be addressed separately inthis section.

Normal dry-docking plans contain calcula-tions to analyze the block’s resistance to thedynamic forces associated with both hurri-cane and seismic (earthquake) loading. In thecase of FLO/FLO, the dynamic loading mustbe based on ship motions and wind forces.This will result in greater angles of inclina-tion and significant overturning moments.

8-7.1 Side Blocking

Side blocking must be able to withstand someportion of the asset's deadweight as well asdynamic loading. As the heavy lift ship rollsor pitches, the contribution of the side block-ing in supporting the deadweight will in-crease. There is also an increase in dynamicloading due to the effect of rolling and pitch-ing. The static and dynamic effects will beexamined separately.

Side blocks are used for handling the loadingup to the angle to which the heavy lift shipwill heel over or a heel of 15°, whichever isgreater. Roll bars or spur shores (see Figure8-13) should be used for angles from 15° -45°.

To be effective, side blocks should have rela-tively planar surfaces (minimum curvature).Blocks will form to the shape of the hull un-der significant compressive loading. Attempt-ing to shape the blocks to exactly fit the sur-face of the hull will add considerable effortand may not significantly improve their con-tact area or overall performance. It will bedifficult to land the ship precisely in the in-tended location and small variations mayprove to make the shaping of the blocks awasted effort. Contact can be improved byusing wedging material. This will likely beeasier to accomplish if the block surfaces areplanar.

The blocks should be placed under the asset'smajor structural members such as main trans-verse bulkheads and secondary frames. Theyshould also have enough effective surface

8-43


area (width) to span two frames. The asset'sdocking drawing will provide recommendedlocations.

The transverse stability of individual sideblocks is essential and depends on overallblock height and hull shape. These sideblocks must be of a construction and locatedsuch that the resultant force (normal to theshell at point of tangency) falls within themiddle one-third of all horizontal layers ofblocking. Using a two-tiered block with adouble wide base will help ensure this stabili-

ty in both the transverse and longitudinal di-rection (see Figure 8-14). The side block capsshould be of a soft material such as DouglasFir or Southern Yellow Pine. The discussionconcerning the use of hard woods as cappingmaterial for keel blocks does not apply to sideblocking. Side blocks will compress and formto the curvature of the hull and are not subjectto the high knuckle loading associated withinitial landings. Side blocks must be securelyfastened to the deck of the heavy lift ship toresist overturning and sliding.

Figure 8-14. Cribbed Blocks.

C ribb ingM id 1 /3

M id 1/3

P rofile V iew

NOTE

Cribbed blocks should be arrangedsuch that the force at loading actsthrough the middle one-third of alltiers.

8-44


8-7.1.1 Stability of High Blocks

Heavy lifting Navy ships with large sonardomes or other underwater projection may re-quire the use of excessively tall blocks. Inthese cases, the stability of the blocks are aconcern and special precautions must be tak-en. These blocks may require additional crib-bing to ensure that they do not tip over. Usethe following guidelines when consideringthe stability of the blocks.

• All keel blocks over 8.5 feet in heightrequire cribbing

• Keel blocks over 6 feet but less than 8.5feet should be cribbed when located inthe after one-third or forward one-thirdof the block line

• Side blocks over 6 feet in height (mea-sured from the deck to the highest cor-ner of the soft cap) shall be tied togeth-er longitudinally (steel tie rods,cribbing, etc.)

• Loading force should act in the middleone-third of all tiers of blocks (see Fig-ure 8-14)

8-7.2 Loading on Side Blocking

The side blocking will support both static anddynamic loads. The side blocking supportssome of the weight of the asset in the zeroheel condition. This support increases as thevessel heels. Side blocking is also needed toresist dynamic loads that may be caused byship motions and wind which are dependenton environmental conditions during loadingand transit.

Figure 8-15. Spur Shores

8-45


8-7.2.1 Assessing the Loading on Side Blocking

There are several conditions that need to beexamined in determining when to install andthe amount of side blocking required for atransport. The most strenuous condition iswhen the asset is loaded on the heavy lift ves-sel and the vessel is in an open seaway. Inthis condition, the most extreme wind andmotions will be experienced. A reduced con-dition of loading exists during Float On. Thecondition of the loading associated with thefloat on operation should be evaluated. It maybe advantageous to not complete the contruc-tion of the side blocking until after the asset isloaded. This is normally to reduce the heightof the side blocking so that less submergenceof the cargo deck is required during the load-ing operation. If it is proposed to use fewerside blocks for the float-on operation, thiscondition must be analyzed separately (seeSection 8-7.3). As this is conducted in a rela-tively sheltered place, the expected loads areless. A third potential condition arises whenthe load site and the build site are not thesame. That is to say that there is some transitafter the loading but prior to the completionof the seafastening plan. If the location of thebuild site requires moving the vessel with theasset loaded, the environmental conditionsassociated with the transit should also be ana-lyzed as a separate evolution. This may occurif an asset is in extremis or the port of loadingdoes not have deepwater and adequate indus-trial services located in the same area. There-fore calculating the side loading of the block-ing is a multi-step process.

The approach outlined here breaks down theloading into static (deadweight) and dynamic(rolling and wind). Each of these compo-nents can be considered separately and thencombined to determine a suitable blocking ar-rangement. As a minimum, an analysis of the

open ocean seafastening plan should be con-ducted. Winds and ship motions associatedwith this transit should be evaluated to deter-mine the total number of side blocks and spurshores.

8-7.2.2 Loading on Side Blocks

The side blocks will support a portion of thedeadweight of the asset, both in a heeled con-dition as well as an upright condition. For thezero heel condition, assume that side blockswill take 15 percent of the assets displace-ment (w) and that this load is evenly distribut-ed between port and starboard. Therefore, theload on the side blocking for port or starboardis calculated by:

where:

DLs = Vertical load on side blocks for oneside (tons)

w = Displacement of asset at time ofloading (tons)

The number of side blocks required on oneside for supporting displacement (Nd) withoutconsidering dynamic and wind effects can becalculated by:

where:

Nd = Minimum number of side blocks onone side to support displacement

DLs0.15( )w

2-------------------- 0.075w= =

Nd

DLs

SpAe------------=

0.075w

SpAe1 ton

2240 lbs--------------------

---------------------------------------=

1086.4wSpAe

------------------=

8-46


DLs = Vertical load on side blocks for oneside (tons)

Sp = Strength at the proportional limit ofthe block material (lb/in2)

= 800 psi for Douglas fir

Ae = Effective surface area of side blockin contact with asset (in2)

w = Displacement of asset at time ofloading (tons)

8-7.2.3 Dynamic Loads During Transport

Side blocks and spur shores are also neededto resist dynamic loading due to wind andship motions. The method for calculating themoments associated with these forces are pre-sented. In performing an analysis, it is impor-tant to examine all likely conditions the ves-sel will experience. The predicted sea stateduring transit may be as high as sea state 7while the conditions during loading may belimited to sea state 4. Each of these scenariosshould be evaluated to ensure that the block-ing arrangement is sufficient. These dynamicloads will be dependent on the environmentalconditions encountered during the transport.

8-7.2.4 Dynamic Loads from Ship Motions

Calculating overturning moments caused bysea state dynamic forces is similar to calculat-ing seismic overturning moments for a nor-mal dry-docking operation (see NSTM 997).These calculations are modified to include theacceleration loads associated with rolling andpitching of the heavy lift ship. The maximumship motion and roll angle is found by exam-ining the expected weather during transit. Forexample, if the routing indicates that the max-imum condition is sea state 7, use roll andpitch angles from Tables 8-5 and 8-6. This isthe limit to which the heavy lift ship is as-sumed to heel during the transit. Note thatthis load is supported by only one side ofblocks.

For example, typical ship motions for oceantransport are:

R = 20 degrees of roll, one direction

P = 4 degrees of pitch, one direction

Tr = roll period of 10 seconds, port to stbdback to port

Tp = pitch period of 7 seconds, bow tostern back to bow

This estimate should not be used as a substi-tute for an actual route analysis.

The acceleration factor is calculated by:

where:

ay = athwartships acceleration factor in (g)

R = Maximum angle of roll (deg)

P = Maximum angle of pitch (deg)

x = Distance of center of gravity of assetforward or aft from center of gravityof heavy lift ship (ft)

y = distance of asset’s centerline off cen-terline of heavy lift ship (ft)

z = distance of center of gravity of assetabove center of gravity of heavy liftship (ft)

Tp = Period of pitch (sec)

Tr = Period of roll in (sec)

NOTE

These values should be comparedwith the expected values fromroute planning. If larger angles ofheel or pitch are expected, thosevalues should be used.

ay sin R0.0107Px

Tp2

----------------------- .0002R2y

Tr2

-----------------------0.0214Rz

Tr2

-----------------------+ + +=

8-47


To calculate the overturning moment (Mr) associated with athwartships motion, theweight of the asset is multiplied by the heightof the center of gravity above the asset’s keel.This is then multiplied by an acceleration fac-tor similar to that calculated for keel blocks.

where:

Mr = Overturning moment due to rolling(ft-lbs)

w = displacement of vessel at time ofloading (tons)

ay = acceleration factor for athwartshipsmotion (g)

KG = The center of gravity of the assetabove its keel (ft)

The effort to resist this overturning momentcan be provided by the side blocks, but thenumber of side blocks needed is dependent onthe size of the blocks and their distance fromthe centerline (see Figure 8-13) and availablespace on the cargo deck around the asset.Therefore, the number of additional side

blocks on one side required to resist the dy-namic loads due to rolling is:

where:

Nr = Number of additional blocks for roll-ing

Mr = Overturning moment due to rolling(ft-lbs)



= (800 psi for Douglas fir)

L2 = Average moment arm of side blockreaction force (ft)

But a better solution is to resist this momentwith a combination of side blocks and spurshores.

Figure 8-16. Overturning Moment Due to Wind Forces.

Mr w ay⋅( ) KG( ) 2240 lbs/ton( )=

Nr

Mr

AeSpL2------------------=

8-48


8-7.2.5 Dynamic Loads from Winds

Additional side blocking is necessary to resistthe overturning moment associated with thewind forces that will be encountered duringtransport. Calculating overturning momentscaused by wind is similar to calculating hurri-cane loading in a normal dry docking situa-tion. This is also a 2 step process, once for thewind force during loading (< 25 Knots) andonce for the wind loading during the transit.To determine the expected wind during tran-sit, use the guidelines listed in paragraph8-5.1.1.

The overturning moment associated with thewind forces can be estimated by the followingequations:

where:

Mw = Overturning moment due to windforces (ft-lbs)

As = Projected sail area of the asset (ft2)(See Figure 8-16)

L3 = Lever arm from the cargo deck tothe center of the sail area of the as-set (ft) (See Figure 8-16)

V = wind speed (knots)

Note: The factor in this equation provides forunit conversion.

The number of additional side blocks re-quired on one side to resist the forces due towind is:

where :

Nw = Number of additional blocks forwind

Mw = Overturning moment due to windforces (ft-lbs)



= 800 psi for Douglas fir

L2 = Average moment arm of side blockreaction force (ft)

8-7.2.6 Determining the total amount of side blocking required

The total amount of side blocking required isa combination of the amount calculated inparagraph 8-7.2.3 for dead weight loading inparagraph 8-7.2.4 for dynamic loading and inparagraph 8-7.2.5 for wind loading. That is

But a better solution may be a combination ofside blocks and spur shores. Side blocks pro-vide better support to static type loading be-cause of their higher compressive strength.Spur shores may be better placed farther outand higher against the hull of the asset to re-sist dynamic loading.

8-7.3 Additional Side Block Consider-ations

In some cases, the heavy lift contractor maydesire to install a minimum number of blocksduring float on and build the remainder of theblocks after the asset is loaded. This is nor-mally done to reduce the required depth ofsubmergence during loading. This is accept-able given that the environmental conditionsduring loading and transit to the build site areevaluated. The above calculations shouldtherefore be repeated using the maximum ex-pected weather conditions during loading andbuilding. Generally, using a sea state 4 condi-tion is acceptable. In no case should the mini-mum number of side blocks be less than the

Mw 0.004 As L3V2=

Nw

Mw

AeSpL2------------------=

NT Nd N+ r Nw+=

8-49


number necessary to support the static loadand the expected roll angle. A minimum offive degrees of roll should be used. If the as-set has an initial list, e.g., USS COLE had a2.5o list on loading, that value should be add-ed to the 5 degrees to determine the numberof initial side blocks for loading. The staticload is calculated using the equations in para-graph 8-7.2 and adjusting the roll angle. In nocase should the minimum number of sideblocks be less than four (two port and twostarboard).

In the past, obtaining an accurate fit of sideblocks has been a recurring problem. Contrib-uting factors include inadequate drawings,bad offsets, damage to the hull of the asset, orlanding the asset slightly out of position dueto the dynamic environment in which theselifts were done. Placing side blocks in posi-tions shown on the Navy Docking Drawingoffers the best possibility of a correct fit, butwedging material, may still be needed. Airbags have been used on top of the side blocksand inflated by divers after the asset waslanded. This has been effective in stabilizingthe asset for the lift. With wedging or airbags, however, the blocks have an unknowncompressive flexibility due to dynamic load-ing. If a significant change in the contact areaor the compressive flexibility is observed, thenumber of side blocks required should be re-calculated after the asset is loaded, taking intoaccount the dynamic loading, maximum rollangles, and actual location and effective areaof the side blocks. Additional side blocks orshores may be necessary.

The side blocks should be positioned asshown on the Navy docking drawing. Thiswill ensure the best possible fit since the sideblock build has been based on hull offsets inthese locations. This will also help to ensurestable blocks up to angles of 15°. This ap-proach is somewhat conservative as the spurshores will share some of the deadweight.

Considering the above, and bearing in mindthat side blocks work better in direct loadingand spur shores are better to resist dynamicover turning loads, we can again look at theequation for the acceleration factor, in para-graph 8-7.2.4 to determine the number of sideblocks to be used in combination with spurshores. The static, direct, loading for sideblocks can be determined from the first term(sinR) in the equation

while the remainder of the equation can beused as a first estimate of the number of spurshores required.

8-7.4 Spur Shores

The number of side blocks needed to resist allof the loads experienced during a transportwill likely be too large to fit the given space.In almost all cases, the number of side blocksthat can be placed in a given area will be lessthan what is needed. They simply may not fiton the cargo deck of the heavy lift ship, par-ticularly if more than one asset is transported.To make up for this difference and to resistdynamic forces associated with roll anglesgreater than 15 degrees, spur shores are used.A combination of spur shores and side blockswill be used to resist the total load.

Spur shores (roll bars) can be used in combi-nation with side blocks to resist overturningmoments due to dynamic motions of theheavy lift ship and high winds (Mr + Mw).Spur shores are tall, column like structuresthat are placed further outboard on the hullthan side blocks (See Figure 8-15). They donot contribute significantly to supporting theweight of the vessel, but they can make a sig-nificant contribution to resisting overturning.The number of side blocks can be reduced ifspur shores are used to help resist the dynam-ic moments associated with transit. Consider

ay Rsin0.0107Px

Tp2

-----------------------0.0002R

2y

·

Tr2

--------------------------0.0214Rz

Tr2

-----------------------+ + +=

8-50


the following points when deciding to usespur shores:

• Spur shores are generally easy to installand take up less deck space.

• Roll angles in excess of 24 degreeshave been observed during this type oflift/transport. Therefore, supportsshould be placed at various angles toencompass the total range of stability ofthe heavy lift ship. Spur shores aremore suitable than side blocks for thisduty.

• Spur shores are easily angled to resistthe highest roll the ship is likely to en-counter.

• Thrust blocks (base plates) must be pro-vided at the base of all spur shores andbe firmly secured to the cargo deck ofthe heavy lift ship.

• The shores must be suitably secured toprevent the shores on one side fromfalling out when those on the other sideare compressed. This limits the bearingload per shore to the compressive loadof the soft cap.

• A higher number of shores will likelybe required to resist the same momentas fewer side blocks.

• Sufficient space will be required be-tween multiple assets to install spurshores.

• Shores must be secured in the fore andaft, as well as the athwartships direc-tion.

• Because of their point loading on thehull of the asset, the local structurallimit must be evaluated in determiningthe number of spur shores to be usedand designed with a top spreader tospread the load to the asset's hull struc-ture.

8-7.4.1 Loading on Spur Shores

The number of shores required is dependenton several factors. Because the shores areslender, they will fail as columns before theywill fail in direct compression. This is the op-posite of the failure mode for side blocks. It isnecessary to determine the maximum columnstress that the shore can withstand to ensurethat the shores do not buckle under a com-pressive load. The actual load that each spurshore will see will be dependent on the num-ber of side blocks that are used and the localstructural load limit on the side of the asset. Ifspace limitations require only a few sideblocks, than a larger number of spur shoreswill be needed.

The equations will be based on the actualnumber of side blocks used. This number willlikely be less than the number calculatedabove and is largely dependent on deck spaceand the hull of the asset. The docking draw-ing and structural details should be checkedto determine suitable locations and placeswhere spur shores are more appropriate. Thefollowing series of equations determine themaximum column stress for the shore basedon its geometry and material. The maximumstress for each shore is found by:

where:

Sc = Maximum column stress (lb/in2)

C = Proportional limit

= 3,000 psi for Douglas fir parallel tograin

NOTE

In no case shall the number of sideblocks be reduced below the mini-mum number required for loading.

Sc C 113---

Ls

d K⋅---------

4

– =

8-51


Ls = Length of shore (ft)

d = Minimum dimension of shore crosssection (ft)

K = Relationship between elasticity andproportional limit

This constant (K) is calculated by:

where:

K = Relationship between elasticity andproportional limit

E = Modulus of elasticity of shore (lb/in2)

= 1.6 x 106 psi for Douglas fir

C = Proportional limit (lb/in2)

= 3,000 psi for Douglas fir parallel tograin

To prevent the shore from buckling, the shorereaction (Rs) must be equal to or less than:

where:

Rs = Maximum shore reaction (lb)

Sc = Maximum column stress (lb/in2)

As = Cross sectional area of the shore (in2)

8-7.4.2 Determining the Number of Spur Shores

To determine the number of shores required,for a given number of side blocks, it is neces-sary to evaluate the entire build. Informationabout the spring constants of both the blocksand the shores is required as well their loca-tions. To calculate the spring constant of theshore use:

where:

Ks = Spring constant of spur shores (lb/in)

As = Cross sectional area of shore (in2)

E = Modulus of elasticity of shore (lb/in2)

= (1.6 x 106 psi for Douglas fir)

Ls = Length of the shore (ft)

To test the suitability of a build (column sta-bility of the shore and compression of the sideblock) one would use the following series ofequations to determine the average reactions.

But since we know the maximum reactionthat a particular shore can handle, we can re-work the equation to find the minimum num-

NOTE

The Rs of a shore must be lessthan the local structural limit of theasset’s hull structure.

K 1.11 EC----=

Rs ScAs≤

Ks

AsE12Ls-----------=

Rs

Mw Mr+( ) KsL1( )

L12NsKs L2

2NbKb+-------------------------------------------------=

Rb

Mw Mr+( ) KbL2( )

L12NsKs L2

2NbKb+-------------------------------------------------=

8-52


ber of shores required. The equation then be-comes:

where:

Ns = Number of shores required on oneside

Mw = Moment caused by wind for transit(ft-lbs)

Mr = Moment caused by rolling for tran-sit (ft-lbs)

Ks = Spring constant of spur shores (lb/in)

L1 = Average lever arm of the spurshore's reaction forces (ft) (see Fig-ure 8-13)

Rs = Max allowable reaction of shores(lb)

L2 = Average lever arm of the side block-ing reaction forces (ft) (See Figure8-13)

Nb = Number of side blocks required onone side of the ship

Kb = Spring constant of side blocks (as-sume 200,000 lb/in)

8-7.4.3 Distribution of Spur Shores

The above procedure determines the mini-mum number of spur shores to be used. Thisprocedure assumes the number of side blocksused is determined by available spacing andfor the direct support up to the maximum ex-pected angle of roll. These sideblocks willgenerally be placed to resist rolls up to at least15 degrees but preferrably to the maximumangle of roll. The spur shores must resist rollsbeyond this angle. To help resist these rolls,the shores should be distributed throughoutthe range of angles.

Since spur shores need to support the loaddown the axis of the shore and tend to tripout, positioning the spur shores in incrementsof about 5 degrees should provide acceptableload sharing. They should be set up in pairs,fore and aft, to resist twisting. They need tobe positioned perpendicular to the hull on lo-cal structure and high enough on the hull toresist the overturning moment yet be shortenough or supported not to fail under buck-ling. While effective length dictates a higherangle, angles of 45 degrees or less should bechosen unless compensating for the overturn-ing moment dictates placing the shores higheron the hull.

This method may produce a different numberof spur shores than previously determined. Tobe conservative, the larger number should beused and a minimum of two shores (one foreand one aft) should be installed at each angle.The shores should be secured to the deck atthe foot of the shore to ensure that they do notslide when loaded. They should also be

NOTE

For larger assets or to reduce thenumber of shores required, consid-er using steel shores.

Ns

Mw Mr+( ) KsL1( ) RsL22NbKb–

RsL12Ks

------------------------------------------------------------------------------=

NOTE

The locations for spur shores areestimated by hull shape and struc-tural drawing. The actual position-ing of each shore is dependent ondetermining local structure on theship.

8-53


placed normal (perpendicular) to the curva-ture of the hull.

Final verification of the compensation of theoverturning moment (Mo) is accomplished bychecking to see that the overturning momentabout the attachment point of the spur shoresis less than the righting moment (Mr) pro-duced by the spur shores, that is

Mo < Mr

Mo is created by the transverse dynamic forceworking through the ship's center of gravityand its separation from the attachment pointof the spur shore.

Mo = (displacement) (ay)(Lo)

where Lo = distance between the line of ac-tion of the dynamic force working transverse-ly through the ship's center of gravity and theposition of the shores on the hull in the verti-cal direction.

Mr is created by the resultant force that thespur shores can create in the transverse direc-tion against the hull and its separation fromthe line of action of the weight of the vesselpassing through the ship's center of gravity.

Mr = (displacement)( 2- az) Lr cos R(R = maximum angle of roll)

where (az) is the dynamic load factor in thevertical direction which increased the load onthe blocking when the heavy lift ship pitchesup and decreases the loading on the blockswhen the heavy lift ship pitches down, (2-az).

Lr is the distance between the line of action ofthe downward force through the ship's centerof gravity and the position of the shore on thehull in the transverse direction. The cos Rfactor is to adjust the line of action of theweight from the vertical to account for themaximum angle of roll.

In practice, the Transport Manual will recom-mend a seafastening plan that will include,among other things, a plan for positioningspur shores. It is likely that the contractor willperform a detailed analysis to determine max-

imum loading for each spur shore through avariety of roll angles. This distribution shouldbe similar to the distribution determined bythe above method.

8-7.5 Seafasteners

Seafasteners must be designed to restrain theasset from movement at the high angles ofpitch and roll anticipated during transits.Some resistance to these forces is provided bythe friction between the keel and the blocks.Seafasteners must be installed at the forwardand aft ends of the keel or some other reason-ably accessible location of the asset to resistlongitudinal movements due to the maximumangle of pitch of the heavy lift. They shouldalso be installed on the port and starboardsides of the keel to help resist athwartshipsmovement of the asset during rolling. It isprudent to install seafasteners at both the foreand aft ends of the keel to prevent twisting. Aminimum of two seafasteners should be in-stalled at each end (one port and one star-board) (see Figure 8-17). However, eachseafastener should be capable of resisting theentire sliding force.

8-7.5.1 Dynamic Force

The dynamic force that must be restrained ineach direction is equal to the weight of the as-set times the dynamic load factor. This is sim-ilar to the procedure that was used to calcu-late the dynamic loading on the blocking (see8-7.2.4). Here, the main concern is the assetsliding off the blocking. However, for thetransverse direction, the dynamic load factor,ay, will be the same. Therefore, the dynamicload in the transverse direction will be

DLt = Dynamic load in the transverse di-rection determined by the maxi-mum angle of roll to be expected inroute. (tons)

∆ = Displacement (tons)

DLt ∆ay=

8-54


ay = Athwartship acceleration factor (g)(see 8-7.2.4)

Similarly, the dynamic load in the longitudi-nal direction will be:

DLl = ∆ax

DL1= Dynamic load in the longitudinal di-rection determined by the maximumangle of pitch to be expected in route.(tons)


ax = longitudinal acceleration factor (g),

where:

P = Maximum angle of pitch (degrees)(Table 8-5)

S = Surge acceleration (g) (Table 8-4)

x = Distance of center of gravity of assetforward or aft from center gravity ofheavy lift ship (ft)

z = Distance of center of gravity of assetabove center of gravity of heavy liftship

Tp = Period of pitch (sec) (Table 8-5)

Note that the commercial industry assumed apitch of 15o at a period of 10 seconds whichis considerably higher than the value for pitchin Table 8-5.

8-7.5.2 Assumed Friction Factors

In practice, it has been observed that a shipslides transversely when heel exceeds rough-ly 15 degrees and longitudinally when pitchexceeds roughly 3 degrees. The dynamic fric-tional resistance of steel on wet or greasedwood is approximately 22 percent. Depend-ing on the weight and center of gravity of aship on docking blocks, this equates to an an-gle of approximately 12 degrees before slid-ing will occur. These numbers work well for

relatively flat bottom vessels as long as thevessel doesn’t lift off the blocking due to be-ing submerged.

The friction factor used for longitudinal slid-ing is less because there is a greater possibili-ty of the vessel lifting off the blocks due tosubmergence. When a 500 foot heavy lift shippitches 3 degrees, the trim increases by 26feet. Other factors contributing to these con-clusions include variations in materials, vari-ations in hull shape, column stability of theblocks, and possible overhang of the asset.These approximations should be provide rea-sonable estimates for sizing seafasteners. Todetermine the amount of this load that is re-sisted by friction, multiply the weight of theasset by the frictional factor. For the trans-verse direction, assume a frictional factor of0.15. Therefore, the frictional resistance (FRt)can be found by

and

8-7.5.3 Sea Fasteners Resistance

The seafasteners must resist the force that isnot carried by friction. Therefore, the forcecarried by the seafastener is equivalent to:

In the transverse direction

Where:

SFt = Transverse Seafastener force (tons)

DLt = Dynamic load in the transverse direc-tion (tons)

sin P S0.0004Px

Tp2

----------------------0.0214Pz

Tp2

----------------------+ + +=

FRt 0.15∆=

FRl 0.05∆=

SF DL FR–=

SFt DLt FRt–=

8-55


FRt = Frictional resistance (tons)

In the longitudinal direction, assume a fric-tion factor of 0.05. Therefore,

Or,

Where:

SFl = longitudinal seafastener force (tons)

DLl = Dynamic load in the longitudinal di-rection (tons)

FRl = Longitudinal frictional resistance(tons)


ax = longitudinal acceleration factor (g)

Figure 8-17. Sea Fasteners.

SFl DLl FRl–=

SFl ∆ax 0.05∆–=

8-56


8-8 Surveys

Several surveys must be conducted to ensurethat the vessel and its systems can adequatelyperform the FLO/FLO operation. These sur-veys will determine that all material and pro-cedures are in accordance with the TransportManual and conform to the requirements ofthis manual.

8-8.1 Hydrographic Survey

The hydrographic survey must be conductedat the proposed loading and unloading sitesand in the approach channel by an adequatenumber of soundings referenced to MeanLow Water. These surveys are part of the de-cision making on choosing the loading andunloading sites and dictate the operating pro-cedures for each. A sounding chart must beincluded in the survey results. Complete tidalranges, approach channel width and depthconfiguration, dredging frequency, and anyregularities must be also noted. Where a his-tory of hydrographic data is available, rates ofsiltation must be noted.

8-8.2 Acceptance Survey

An acceptance survey should be conductedby the contracting officer (generally the MSCarea representative). This is a general surveythat shows that the vessel and its systems arethe same as those described in the TransportManual. If possible, the Contracting Officershould observe a ballast/deballast sequence.

If not, he should, as a minimum, review thetime required for a complete sequence (thisinformation should come from an actual oper-ation and not just from published capabili-ties). The inspection should also include ageneral walk through of the vessel to verifysea worthiness and proper adherence to classsociety regulations. First and foremost, theheavy lift ship must be in class and mustpresent the latest certificate of class and mate-rial condition survey. It is often prudent tohave the Docking Observer, IMS and Load-master participate in these surveys as well.

After the vessel has been accepted, severaldetailed surveys should be completed to en-sure all systems are in good working order.The surveys of the heavy lift ship, assets andblocking described below are conducted bythe Docking Observer, the IMS, and theLoadmaster.

8-8.3 Structural Surveys

A thorough inspection of the heavy lift ves-sels primary structure should be completed.The plating, strength members, joints, foun-dations, seachests, entire cargo deck whereblocking may be installed, and structure asso-ciated with mooring must be checked. Indica-tions of excessive corrosion or local failureshould be analyzed accordingly. In additionto this general walk around inspection, thelatest material condition survey, records ofrepair, and design data should also be exam-ined. These may alert the inspectors to any ar-eas that might warrant a more thorough in-spection. The information collected by thevisual inspection should be analyzed andcompared with the information contained inthe past surveys to determine whether detailsurveys and/or repairs are required in any ar-ea.

8-8.4 Indicators and Controls

An inspection of the heavy lift vessel’s bal-last/deballast control system shall be accom-plished. This system is critical to completing

NOTE

Heavy lift ships in general, are notdesignated to make contact withthe bottom. Adequate depth of wa-ter must be provided so that theheavy lift ship does not contact thebottom. Contact with the bottommay require dry docking or inspec-tion of the heavy lift ship by diversin order to maintain its class certifi-cation.

8-57


a safe operation and should be in good work-ing order prior to the start of the FLO/FLOprocedure. In general:

• Draft indicators must be providedshowing the draft of the heavy lift shipat all four corners of the ship and cargodeck. Backup systems such as visualobservation should be addressed.

• Indicators must be provided to continu-ously display trim and heel of the heavylift ship during docking and undockingballast/deballast operations.

• Ballast tank level indicators must pro-vide for controlling ballasting/debal-last. The accuracy of these indicatorsmust be adequate to prevent accidentaloverstressing of tank bulkheads by ex-cessive differential heads and acciden-tal overstressing of the overall shipstructure in shear and bending.

• Ballasting system valve indicators mustbe provided that show the position ofthe valves.

The surveyor should observe at least onecomplete ballasting and deballasting cycleand provide a report on the below systems. Ifpossible, this survey should take place at thesame time that the Contracting Officer per-forms the acceptance survey to avoid duplica-tion of effort.

Ballasting/Deballasting Systems andGauges

• Actual ballasting and deballastingtimes. If these times are different fromballasting and deballasting times forwhich the system was originally de-signed, reasons for this variation mustbe explained in the survey results.

• Adequacy of the power supply, deter-mined by operating all applicablepumps (and the fire pump, if installedon dock) at the same time.

• Effectiveness of the operation of allpumps, motors, valves, and generatorsby remote control and local control.

• The accuracy and reliability of waterlevel indicators when compared withactual sounding of the water level ineach tank.

• Tightness of air-cushioned boundaries,if they are required, in the tanks.

Controls

• Control panel: Check wiring, relays,bulbs and lenses for dust collection andabrasion of wires.

• Motor controls: Check contractors, re-lays electrical and mechanical inter-locks and manual overhauls.

• Limit switches: Check panel limitswitches and switch activator mecha-nisms.

8-8.5 Pre-loading Block Check

Before submerging the heavy lift ship, block-ing should be inspected to ensure it is in ac-cordance with the arrangements in the ap-proved Transport Manual. As a minimum, theinspection should concentrate on the follow-ing areas:

• Location of first keel block (after moston the asset)

• Location of the alignment marks or col-umns for port and starboard alignmentto the center of keel blocking

• Location of fore-and-aft centeringmarkers

• Side clearance of the asset

• Rudder, propeller, and other hull pro-jections clearances above the cargodeck and blocking

• Offsets from center line or from set keelblocks and side blocks

8-58


• Keel blocks levels for the length of theship’s keel (checked visually) to ensurethere are no excessively high blocks

• Heights of side blocks and keel blocks,if not flat

• Special blocking arrangements for hullprojections, hull openings, or specialsupport blocks

• Removal of unnecessary blocks

8-8.5.1 Wooden Blocks

Inspect wooden blocks for deterioration re-sulting from excessive crushing, warping,cracking, checking, rotting, or damage fromdogging. Check for loss of contact at edgesresulting from checking and unequal shrink-age.

8-8.5.2 Block Securing Method

All blocks must be secured in place. Secur-ings, supports, nuts, boltheads, and other fas-teners should be sounded. If the blockingdoes not land on transverse strength membersof the cargo deck, conduct an investigation tomake sure that adequate grillage is being usedto distribute loading to adjacent strengthmembers. Inspect the securing and bolt con-nections through the wood where blocks arebolted to clip angles or plates that are weldedto the cargo deck. When blocks are set onsteel frame supports, inspect the bolts andsupports as well.

8-8.6 Additional Systems

The two systems described above, structureand ballasting, are the two systems that makeFLO/FLO vessels different from other ships.In addition to these systems, the surveyorshould also conduct an inspection of the moretraditional ship’s systems. The survey shouldinclude a review of the following:

Communication Systems and Alarms

The communication systems and alarms mustbe checked thoroughly and tested for proper

operation so that communications can bemaintained between all operating stations.

Fire Protection Systems

The fire protection systems intended forfighting fire on the cargo deck or asset mustbe thoroughly checked and tested for con-formance to all requirements of paragraph5.3.14 of MIL-STD-1625. The capacity avail-able to serve the asset’s firemain (either per-manent or temporary) shall also serve the firestations on the cargo deck, but in no caseshall be less than 1,000 gallons per minute.The supply pressure shall be capable of pro-viding a minimum mozzle pressure of 60 psiwhen supplying fire nozzles at the specificcapacities at the most remote and highest ele-vation hose connections.

Block Handling Systems

The block handling system must be observedin operation and must be inspected.

Mooring and Anchoring Systems

The mooring and anchoring systems must beinspected thoroughly for adequacy and forsigns of local buckling and excessive loading.

Electric Power Systems

Both the primary and alternate electric powersystems must be inspected. Power switches,converting panels, and cables for providingpower to the asset must be inspected for ma-terial condition and proper fit and size.

Ship Positioning Gear

Bitts, bollards, winches and cleats must be in-spected for fatigue, looseness, or other signsof excessive loading.

Ship Services

Compatibility of all connections (firemain,electrical, cooling water, etc.) should be veri-fied as specified in the Transport Manual andidentified at the Pre-Loading conference.

Safety Equipment

8-59


All safety equipment necessary to complywith the governing regulatory agency shouldbe inspected. While some safety equipmentfrom the asset can be used, most will not besuited for this purpose. To avoid delays, besure that it is clear who is responsible for pro-viding safety equipment for the riding crew.

8-8.7 Asset Inspection

It should be ensured that the assets are riggedfor sea by completing a walkthrough of allcompartments and soundings of all tanks.This survey should include an inspection ofthe watertight integrity of the hull and ensur-ing that Condition Zebra is set. The final con-dition of the asset’s loading should be in-spected and recorded just prior to itsdeparture and copies made available to allparties. All tanks and voids must be accurate-ly sounded and photographs should be takenof the topsides of all assets. These photos willaccurately identify the nature and position ofany items that may be have been added top-side. They will be used to verify that the as-sets condition has not changed when it is timefor off-loading. No weights, including liquidssuch as fuel or water, should be shifted, add-ed, or removed from the asset unless autho-rized by the heavy lift ship's master and theOIC. A checklist is provided in Appendix H.

8-8.8 Post Float-On Inspection

When the asset lands on the blocks as debal-lasting begins, the condition of this landingshould be examined. Divers should be used toensure that no blocks have tipped, that the as-set is in the predicted location, and that thereare no interferences. Divers from the localdrydock facility should be proficient in thistype of inspection. Appropriate safety precau-tions must be taken as these operations will

be taking place in open water instead of with-in a drydock.

When the divers have reported that assetshave landed satisfactorily on the blocks, thedeballasting operation should continue untilthe cargo deck emerges from the water. Athorough examination of the condition of thelanding should be completed by the Load-master, Docking Officer and the IMS. A deci-sion whether to continue deballasting or to re-float the assets should be made. Anyirregularities found should be noted and cor-rected, and any necessary wedging and/orshoring must be placed.

If the decision is made to continue with thedeballast procedure, this effort should becompleted immediately and the remainder ofthe build should commence.

8-8.9 Examination of the Seafastening

8-8.9.1 Prior to Transit

Following the completion of the build, allcomponents, keel blocks, side blocks, andspur shores should be surveyed by the Load-master, Docking Officer, and IMS. Theyshould inspect the spur shores and seafasten-ing before departure to make sure that they

WARNING

All sea suctions for the assetand the heavy lift vessel shouldbe secured during diver opera-tions.

WARNING

All parties must be informedwhen divers are being used. Ex-treme caution must be used toensure the safety of these indi-viduals. No deballasting or othership movements should occurwhile divers are working underthe asset.

8-60


are satisfactorily installed and in accordancewith the Transport Manual. Any agreed tochanges should be noted.

8-8.9.2 During Transit

The seafastening and blocking should be in-spected daily by the OIC of the asset and theheavy lift ship’s Master, or more frequently ifrough weather is encountered during transit.

8-8.9.3 Upon Arrival

Upon arrival, the Heavy Lift Project Teamshould inspect blocking, spur shores, andseafastening and note any movement and/ordamage that may have occured.

8-9 Offloading Operations

The final phase of the operation is the offloadof the vessels. While this is less complicatedthan the loading procedures, it is still a criti-cal phase of the operation and demands care-ful planning. Selection of an appropriate off-loading site will allow the operation toproceed without incident.

8-9.1 Prior to Arrival at Destination

All parties involved in the offload proceduresshould be available at the discharge locationat least two days prior to the arrival of theheavy lift ship. A pre-arrival conference withall parties represented should be held to re-view off-loading details. This meeting is inadvance of the conference held after the arriv-al of the heavy lift ship. Many of the off-load-ing details, including the off-loading site,number of assist tugs, and a rough time linecan be determined or confirmed at this time.

Arrangements should be made for pier spacefor the assets after they are unloaded. Thesearrangements should be in place prior to thearrival of the lift ship. If the assets are to tran-sit under their own power, sufficient manningneeds to be arranged. If the assets are to betowed, sufficient tug assets need to be provid-ed.

8-9.2 Arrival Activities at Off Loading Site

When the heavy lift ship is safely at anchor,each asset and all cargo should be inspectedby Navy and contractor personnel as well asthe Independent Marine Surveyor. Any voy-age related damage should be recorded in apost transit report and made available to allparties. The assets should be returned to thefloat on conditions of loading prior to floatoff. All tanks and cargos should be in thesame condition as prior to float on. The OICof the riding crew should prepare an updatedloading condition report. If this is not possi-ble, as in the case of a damaged asset, e.g.,USS COLE, a deadweight survey of the assetshould be conducted.

The heavy lift contractor should prepare to re-move the seafasteners and any "Lift-On/Lift-Off" deck cargo and prepare the ship and as-sets for off loading. The seafasteners shouldnot be removed until the lift ship is at the finaloff load site.

An off loading conference should be held assoon as practicable before or immediately fol-lowing arrival of the heavy lift ship. Again,any unnecessary delays in releasing the heavylift ship can be very costly. All parties in-volved in the off loading operation, includingany local tug captains and pilots, should at-tend this meeting. A detailed review of the offloading procedure should be made and agreedto by all parties.

8-9.3 Off Loading

The off loading operation proceeds in essen-tially the reverse order of loading, with all theindividuals performing the same tasks as atloading. Any deviation from the approvedTransport Manual should be agreed on byrepresentatives from all parties.

If the assets are to be towed to their final des-tination, sufficient tugs to complete the un-loading and transport the vessels need to be

8-61


provided. Having an excess of tugs may be acheaper alternative to delaying the off-load-ing procedure.

8-62


Appendix A

SAFETY CONSIDERATIONS IN TOWING

A-1 Introduction

The purpose of this appendix is to supplementthe specific safety precautions for towing op-erations discussed in this manual with thegeneral safety precautions published inOPNAVINST 5100.19C, N45, 0579LD0571210, Navy Occupational Safety and Health(NAVOSH) Program Manual for ForcesAfloat (Ref. X).

A-2 Scope and Applicability

The safety information contained in this man-ual shall apply to all afloat Naval Commandsthat are involved in towing operations. It shallalso apply to United States Naval Ships(USNS) of the Military Sealift Command(MSC) and its activities and the MarineCorps, when embarked in the aforementionedvessels and to the extent otherwise deter-mined by the Commandant of the MarineCorps. This information, in combination withthe OPNAVINST 5100.19 series, comprisesthe Navy Occupational Safety and Health(NAVOSH) standards for towing operationsas required by the OPNAVINST 5100.23C,Navy Occupational Safety and Health (NA-VOSH) Program (Ref. Y). For additional sal-vage safety information, consult the US NavySalvage Safety Manual 0910-LP-107-7600(Ref. Z).

A-3 Basic Safety Philosophy

Many safety studies have indicated that hu-man error is a common cause of mishaps.Even though the failure of some item ofequipment may be listed as the “cause” of a

mishap, the equipment often has failed be-cause of an earlier human error or oversightin design, manufacture, maintenance, or useof the equipment.

Therefore, all personnel must be trained inthe use of, and have ready access to, appropri-ate Navy technical manuals and other publi-cations to guide them in their operations.Consequently, the approach to achievingsafety in towing operations is to:

• Comply with existing Navy parent doc-uments, such as the OPNAVINST5100.19 series for general policy andprocedural guidelines, and refer to thepertinent technical manuals and PlannedMaintenance System (PMS) cards forspecific information on operation andmaintenance of commonly used gearand equipment.

• Comply with Navy technical manuals,such as this volume on towing, andmanufacturers’ operating manuals formore detailed information on special-ized operations. Use PMS cards anddata for information on gear and equip-ment that are primarily or peculiarly as-sociated with such specialized opera-tions.

• Encourage the use of systems safetyanalyses, in which the overall system oractivity of concern is planned and re-viewed from the standpoint of safety.Factors such as the specific environ-ment in which an operation is to beconducted should be considered and ac-counted for in planning. Consequently,fewer omissions should occur and safe-ty awareness among all personnel whomay be involved should increase. SeeSection 3-4.1.5 and Table 3-2 for a dis-cussion of factors of safety in the selec-tion of towing components.

No list of safety precautions in towing can becomprehensive without the principles of good

A-1


seamanship. The precautions stated here andin the OPNAVINST 5100.19 series are basicand must be followed.

Personnel involved in towing operations mustbe thoroughly trained, disciplined, andequipped not only to perform routine duties,but also to react appropriately to unusual ornonroutine situations. The officers and crewof vessels involved in towing operationsshould continuously conduct safety indoctri-nation lectures and exercises aimed at reduc-ing unsafe conditions or practices and at re-acting appropriately to unusual circumstancesthrough professional knowledge of their du-ties and towing procedures.

A-4 Specific Safety Precautions

In addition to the safety precautions in theOPNAVINST 5100.19 series, many para-graphs within this manual also contain specif-ic notes of safety-related information. Ratherthan repeating notes from these two sources,the following paragraphs discuss only the ap-proaches that are recommended specificallyfor towing operations.

A-4.1 Specific Approaches

A-4.1.1 General Specifications

The General Specifications for Ships of theUnited States Navy (Ref. D) mandates thatany ship that is likely to require towing, espe-cially emergency towing, should be equippedto “tow or be towed.” The equipment inven-tory should be such that in an emergencynothing is required to be brought on board thetow or fabricated on the tow. Each ship mustbe capable of receiving or rigging an emer-gency towing rig designed so that the ship cantow or be towed.

A-4.1.2 Non-Emergency Towing

For non-emergency situations (and for emer-gencies, to the extent that time permits) thepreparation procedures outlined in this manu-al and in appropriate Type Command Direc-

tives or Instructions must be completed. Evenfor missions that are repetitions of previoustows, the preparation phase must be repeatedto ensure that nothing is overlooked. In boththe preparation and operational phases of anytow, it is essential that full and open commu-nication exists between the preparing activityand the towing vessel.

A-4.1.3 Safety

Safety is paramount in the preparation of in-dividual Command Instructions and TowingBills, as well as in the preparations for indi-vidual towing tasks.

Appendix H includes checklists to help in theoperational planning and preparations fortows. All hands must fully understand thatgood planning and preparation for emergencysituations are just as important for safe tow-ing as correct ship handling and good sea-manship. Planning is not a simple paperworkdrill. The preparation phase of a towing oper-ation demands the same knowledge and sea-manship skill as the actual at-sea phase.

Past experience has amply demonstrated that,from the very onset of the tow tasking, it isimperative that the plan for preparing the towfor the transit be thoroughly conducted andreviewed before implementation. In some in-stances, such as ocean tows of complex unitslike dry docks, the plans and the tow may beprepared by a civilian marine contractor andsupervised by the Supervisor of Shipbuildingand Repair at an appropriate Navy facility.

In a peacetime Navy (or in the early stages ofwar) the availability and quality of “in-house”expertise in the field of towing and tow prep-arations can vary widely. The towing unitmust therefore monitor the efforts of the ac-tivity preparing the tow. The towing unitmust make continuous inspections and takepositive action immediately to correct identi-fied deficiencies. The towing unit Command-ing Officer or a representative should attendany meeting held by the cognizant activity for

A-2


the tow and the preparing activity and shouldmake any comments or recommendationsnecessary.

A-4.1.4 Planning

Although this manual presents planning pro-cedures in considerable detail, extreme careand judgment must be exercised. Blind de-pendence upon the results of routine calcula-tion methods, especially computerized pro-cedures, without careful cross-checking canlead to major errors and possibly extreme op-erational difficulties.

Even a poor choice of location for conductingpre-tow preparations can lead to major prob-lems. If available, the tow should be preparedat a full-service, easily accessible locationand then moved to a staging area once fullyprepared and made ready for sea.

Few Navy tows will be exact duplicates ofearlier tows. Even though some tows may ap-pear to be duplicates, there will be differencesin weather, route, and configuration of thetowed vessel. Thus, the pre-tow planning andpreparations must be conducted each time atowing task is undertaken to ensure a mini-mum of oversights and mishaps.

A-4.2 Contingency Planning

Contingency planning is very similar to oper-ational planning, except that it concentrateson the aspects of being prepared to respondto emergency conditions. Being prepared in-cludes both knowing what to do and havingthe appropriate supplies and equipment avail-able to do it. The Navy “tow-and-be-towed”instructions, including individual ships’ billsand equipment, are one example of contin-gency planning.

A-3



A-4


Appendix B

WIRE ROPE TOWLINES

B-1 Introduction

The towing hawser is the key element in thetug-tow connection. For Navy towing ships,the hawser is usually wire rope. It is especial-ly important to keep a wire rope hawser in ex-cellent condition, to protect it against exces-sive wear, and to inspect and lubricate itregularly.

To maintain a written reference of a wire ropetowline’s history, the Naval Sea SystemsCommand requires that all U.S. Navy andMSC vessels regularly engaged in towing op-erations keep a Towing Hawser Log. Appen-dix F includes instructions for keeping thislog.

B-2 Traceability

The ability to trace a rope’s history is an im-portant element in accident investigation, aswell as in general product improvement ef-forts. Some of this information is maintainedin the Towing Hawser Log (see Appendix F).American made wire rope and some brands offoreign made rope can be identified by spe-cial core marker materials used as a part of, orlayered around, the core of the wire rope, aswell as by the metal tags and other informa-tion on the reel upon which the rope is deliv-ered. Identification of manufacturing sourcethrough core markers is particularly useful incases where the color coding has not been ap-plied to a strand. Additional information on aspecific domestic wire rope producer’s corecolor marking practices is available on re-quest from the manufacturer.

B-3 Strength

Steel wire rope currently provides the stron-gest towing hawser for a given diameter andis usually specified by the Navy as the pre-ferred hawser for towing.

Target sleds are virtually the only tows forwhich a synthetic fiber line hawser is current-ly specified.

Wire rope strength varies with the type ofconstruction and material as well as with size.Consequently, it is important to be certainthat all wire ropes used in towing are of theproper construction, core, and required mate-rial.

B-3.1 Elongation (Stretch)

In addition to the above noted danger, thesudden release of tension can sometimescause a popped core or a “birdcage” in the

CAUTION

Aramid fiber lines (Kevlar, Spectra)have a similar strength to diameterratio as wire rope and offer a con-siderable weight savings, but thislight line provides no catenary andaramid fibers do not possess thestretch characteristics of polyester.Therefore, these lines are not wellsuited for ocean towing.

WARNING

Wire rope stretches under loadfar less than most natural andsynthetic fiber lines and thuspresents less danger to bystand-ers from loose ends “snappingback” if it fails under high loads.The elongation under load is suf-ficient, nonetheless, to be dan-gerous. The recoil can be ex-tremely violent and all personnelshould stay well away from anypotential recoil path.

B-1


Figure B-1. Bird Caging.

Figure B-2. Popped Core.

B-2


rope when a failure in the towline or its con-nections allows the rope to rebound from anoverload. These conditions also can resultfrom operating a wire rope through an under-sized sheave groove (see Figures B-1 andB-2).

B-4 Maintenance, Cleaning, and Lubrication

Wire rope, like a machine, is made up ofmany moving parts. The individual steelwires slide independently and must be keptclean and protected against the effects ofmovement and pressure by adequate lubrica-tion.

Corrosion damage is also a danger. The exactloss of strength resulting from corrosion ofwire rope cannot be estimated. Washing thetow hawser down with fresh water and lubri-cating it during retrieval after each use canhelp retard corrosion. This, however, is not a“cure-all” since the core remains saturatedwith salt water.

Properly specified and procured wire rope islubricated during manufacture. Since the timein storage may not be known, the towing shipshould clean and relubricate a new towinghawser upon receipt. Relubrication will be re-quired, based on frequent inspection, and maybe required as often as after each use of thehawser. Procedures for inspecting and lubri-cating wires are detailed in NSTM CH-613(Ref. F).

A pressure lubricator has been developed forwire rope and is the preferred method of lu-brication. Grease (MIL-G-18458) is currentlyspecified. This product contains a corrosionpreventive and can be thinned with solventssuch as JP5 or turbine oil 2190 (MIL-L-17331) for cold application.

Take care that all sections, including deadlayers on the drum, are kept lubricated. These

inner layers can be lubricated at such oppor-tune times as:

• Overhauls

• When the hawser is reversed, end-for-end, on the drum

• When towing in good weather, at whichtime extra line may be run out to ex-pose the inner layers for lubrication.

The Navy procedures for wire rope lubrica-tion are currently being modified. The mostrecent guidance is contained in NAVSEA In-terim MRC for ARS 50 Class Running Rig-ging (Ref. AA).

B-5 New Hawsers

Wire rope for towing hawser is shipped in cutlengths on reels.

B-5.1 Unreeling

Unreeling wire rope requires careful andproper procedures. Mount the reel on a hori-zontal shaft supported high enough for thereel to clear the deck so the reel is free to ro-tate. To begin the unreeling process, hold therope end and walk away from the reel as itunwinds. Use a braking device to keep therope taut and prevent the reel from overrun-ning the rope. This is particularly necessarywith powered reeling equipment.

B-5.2 Reeling

When reeling a wire rope hawser from a reelto a towing machine drum, it is best for therope to travel from the top of the reel to thetop of the drum, (see Figure B-4). This meth-od avoids putting a reverse bend into the rope

CAUTION

Remove rope from the shippingpackage very carefully. Improper un-reeling can cause permanent dam-age, such as kinks and hockles (seeFigure B-3).

B-3


Figure B-3. Kinks and Hockles.

Figure B-4. Re-reeling.

B-4


as it is being installed. A reverse bend canmake a rope less stable and, consequently,more difficult to handle.

B-5.3 Installing New Wire Rope

Wire rope should be installed on a towingmachine drum under a tension of at least fivepercent of its breaking strength. Each wrapmust be positioned tightly against the neigh-boring wrap. A tight fit will help prevent thewire rope from becoming buried betweenwraps when used under heavy loading. Bury-ing the wire between wraps is likely to resultin serious damage. Loose or poorly spacedwires may cause movement in underlyinglayers during towing. In practice, the wirerope is initially installed on the towing ma-chine drum under as high a tension as practi-cal.

Using stoppers to load the wire bight by bightis one way to maintain tension, but it is cum-bersome and time consuming. During theconstruction of the first four ARS-50 Classships, a cable brake called a Wallis Brake wasused to help install the wire rope towing haw-sers (see Figure B-5). This cable brake is de-signed for the continuous loading of the wirerope under tension.

NAVSEA 00C has detailed plans for con-struction of a Wallis Brake. The Wallis Brake

is first tied down to a strong point aft of thedrum. In the case of a towing machine orwinch, there is usually a strong point on thefantail such as an H-bitt or a heavylift roller.These devices are not intended to be pulledon in the forward direction, but they are builtfor much heavier loads than they will be re-quired to withstand while supporting a cablebrake.

To install the wire, pass the bitter end throughthe brake and onto the winch or open thebrake by removing the spring assemblies andthe top plate. Place the wire to be loaded onthe bottom plate of the brake and reinstall thetop plate and spring assemblies. Next, tightenthe spring assemblies with the clamp nuts un-til the proper tension is reached. Once the ca-ble brake has been properly adjusted, windthe rope onto the winch in a continuous man-ner until all the wire is on the winch drum.

Take care to keep the wraps tightly together.Wind the first layer slowly, using a heavymaul or hammer to obtain a tight fit. Protectthe wire as necessary during any hammeringby using soft-faced hammers or woodenblocks. Once the first layer is installed itshould be retained as the foundation for sub-sequent layers and not disturbed during tow-ing operations.

If a Wallis Brake is not available, or if thewire rope could not be initially installed un-der sufficient tension even with the brake, itcan be shackled to a bollard or a mooringbuoy, payed off the drum, and then hauled inunder the correct tension.

When new wire ropes are put in service astowing hawsers or pendants, record theiridentification (see Section B-2 for Identifica-tion Markings) in the Towing Hawser Log(See Appendix F).

CAUTION

Rap id a cc e le ra t io n c a n c au sesignificant stress on a wire rope.Avoid such stress on the rope byaccelerating gradually.

NOTE

For both smooth and grooved drums,the towing hawser must be wound onthe drum under fairly high tension,approximate ly 5 percen t o f t hebreaking strength.

B-5


Figure B-5. Wallis Brake.

NOTE

Wallis Brake sized for a family of wirerope sizes. The approximate dimensionsfor a 2-inch Wallis Brake are shown.NAVSEA 00C has details for construction.

B-6


B-6 Stowing

When the towing hawser is removed from thedrum, wind it neatly on a reel and store it inan acid free, dry, protected location. Whenev-er a wire rope towing hawser is to be stored,lubricate it first with MIL-G-18458 grease(preferably with a pressure lubricator) andthen keep the outer layer lubricated with thesame grease throughout the storage period.

B-7 Inspection

B-7.1 General Criteria

Inspect the rope thoroughly as it is beingwound after each use. Refer to Figure B-6 fornomenclature of wire rope and Figure B-7 formeasuring guidelines.

The inspection criteria for general usage run-ning rope are as follows:

• Reduction of nominal rope diameterdue to loss of core support, internal orexternal corrosion, or wear of individu-al outside wires

• Number of broken outside wires anddegree of distribution or concentrationof broken wires

• Corroded, pitted, or broken wires at endconnection

• Corroded, cracked, bent, worn, or im-properly applied end connections

• Severe kinking, crushing, or distortionof rope structure

• Evidence of heat.

B-7.2 Specific Steps

Detailed steps for inspection and maintenanceof wire rope are specified in NSTM 613. Theprincipal steps in wire rope inspection are:

a) Clean the rope by wire brushing andwiping with rags.

b) Inspect wire rope for rust, deteriora-tion, corrosion, wear or flattening, bro-ken strands, and weakened splices.

c) Count number of broken or protrudingwires in each wire rope lay length.

d) Measure wire rope diameter with ver-nier calipers.

Replace wire rope when one or more of thefollowing conditions exists:

• The nominal rope diameter is reducedby more than the amount shown in Fig-ure B-7 for the applicable size rope formeasuring rope diameter

• Six wires are broken in one rope laylength or three wires are broken in onestrand lay length

• One wire is broken within one rope laylength of any end fitting (cut wire andreplace with new fitting)

• The original diameter of outside indi-vidual wires is reduced by one-third

• Pitting due to corrosion is evident

• Heat damage is evident

• Kinking, crushing, or any other damageresulting in distortion of the rope struc-ture is evident.

CAUTION

In general, wear gloves when han-dling wire rope, except when it ismoving under load. In this case,the gloves can get snagged andcan drag the hands into danger.Wire rope should not be handledwhen it is moving under load.

B-7


Figure B-6. Nomenclature of Wire Rope.

B-8


Figure B-7. Measuring Wire Rope.

ActualDiam eter

Correct Incorrect

Rope Diameter(Inches)

Maximum Allowable Nominal Diameter Reduction

(Inches)

5/16 and smaller 1/64

3/8 to 1/2 1/32

9/16 to 3/4 3/64

7/8 to 11/8 1/16

11/4 to 11/2 3/32

19/16 to 2 1/8

2 to 2-1/2 5/32

B-9


B-8 Special Precautions

Wire rope must be properly maintained whenused in critical or potentially dangerous situa-tions. It should not be subjected to any of thefollowing common abuses:

• Chafing

• Impact loads or rapidly changing loads

• Incorrect size of groove on drum orsheave

• Drum or sheave grooves that have be-come rough or corrugated through wear

• Inadequate diameter of drum or sheave

• Improper winding on drum

• Improper or insufficient lubrication

• Exposure to corrosive fluids

• Exposure to excess heat or electric arc-ing

• Lack of protection against moisture andsalt water

• Kinks or hockles.

If wire rope is struck by lightning, inspect itand consider replacing it

It is important to maintain minimum and even-ly distributed wear. Pay special attention topossible chafing points where the wire ropepasses over chocks, bitts, stern rollers, and soforth. Even though no particular wear may benoticed, it is advisable to freshen the nip atleast once per watch to change the location ofpossible wear.

B-9 Wire Rope Hawsers for Navy Tow Ships

Navy towing hawsers are of two types:

• 21/4-inch diameter, fiber core

• 21/4-inch diameter, Independent WireRope Core (IWRC).

Table B-1 lists the wire hawsers carried byeach Navy towing ship class. T-ATF-166 classvessels are replacing fiber core wire withIWRC wire during normal replacement cycles.Table B-2 provides the strength and weightper foot of 6 x 37 class IPS marine ropes.

B-10 Wire Rope Terminations

Wire rope towing hawsers are terminatedwith a closed, poured socket. The dimensionsand weights of four common sizes of openand closed Spelter sockets are shown in Fig-ure B-8. The strength of these sockets, whenproperly made, exceeds the strength of thewire rope for which they are designed. Thedimensions are given in detail to assist in se-lecting the appropriate mating jewelry.

Table B-1. Wire Hawsers Carried by U.S. Navy Towing Ships.

Ship ClassWire Rope

Hawser Diameterby Length

T-ATF 166* 2¼″ x 2500′ 6 x 37

ARS 50 2¼″ x 3000′ 6 X 37

* T-ATFs are being refitted with wire core rope when hawsers are due for replacement.

WARNING

Proper maintenance is extremely im-portant for wire rope used in critical orpotentially dangerous applicationssuch as towing.

B-10


Table B-2. Nominal Breaking Strength of Wire Rope 6x37 Class, Hot-Dipped Galvanized.

Fiber Core2

Nominal Diameter (inches)

Independent Wire Rope Core3

Weight in Air (lbs/ft)*

Improved Plow Steel (lbs)**

Weight in Air (lbs/ft)

Improved Plow Steel (lbs)**

Extra Improved Plow Steel (lbs)**

0.110.160.240.32

4,9327,668

10,98014,886

1/45/163/87/16

0.120.180.260.35

5,2928,240

11,80016,000

6,1009,500

13,60018,400

0.420.530.660.95

19,26024,30030,06042,840

1/29/165/83/4

0.460.590.721.04

20,70026,10032,20048,100

24,00030,25037,10053,000

1.291.682.132.63

57,96075,24094,680

116,280

7/811 1/81 1/4

1.421.852.342.89

62,30080,800

101,700125,000

71,10093,000

117,000144,000

3.183.784.445.15

139,860165,600192,600223,200

1 3/81 1/21 5/81 3/4

3.504.164.865.67

150,300178,000207,000239,400

172,800205,200237,600275,400

5.916.727.598.51

253,800288,000322,000360,000

1 7/822 1/82 1/4

6.507.398.359.36

273,600309,600345,600387,000

313,200356,400397,800444,600

9.4810.511.612.7

339,600439,200482,400525,600

2 3/82 1/22 5/82 3/4

10.411.612.814.0

430,200471,600518,400565,200

493,200543,600595,800649,800

13.915.116.417.7

570,600619,200687,800718,200

2 7/833 1/83 1/4

15.316.618.019.5

613,800666,000718,200772,200

705,600765,000824,400885,600

3 1/83 1/23 5/83 3/4

21.022.724.326.0

826,200883,200941,400

1,002,600

952,2001,015,2061,083,6001,153,800

* Weights are given in air. To obtain net weight in water, multiply air weights by 0.87.** Nominal breaking strength in pounds.

NOTES:

1. All data shown is for hot-dipped galvanized wire. Bright (uncoated) wire strengths are 10% higher and are listed in the same tables in Notes (2) and (3). Drawn galvanized wire rope has the same strength as bright wire.

2. Data for fiber core wire rope is taken from RR-W-410D, Table X.3. Data for Improved Plow Steel IWRC wire rope is taken from RR-W-410D, Table XI. Data for Extra Improved

Plow Steel IWRC galvanized wire rope is taken from RR-W-410D, Table XII.

B-11


See Table B-3 and NSTM 613 for efficiencyof wire rope terminations.

Poured socket wire terminations are not testedbecause they are presumed to be stronger thanthe safe working strength of the wire. Instead,reliance is placed on the skill of the operator,who is initially qualified and maintains thatqualification as described in NSTM 613. Fac-tors of safety listed in Table 3-2 and discussedin Appendix M are applicable to the nominalbreaking strength of new wire. If, under anemergency towing situation, a termination oth-er than a poured socket is used, the reduced ef-ficiency of the termination must be included inthe allowable load calculations. Furthermore,if the reason for alternate termination is to re-place a failed termination or a parted wire, itmust be assumed that the balance of the haw-ser has been overstressed as well. If it is neces-sary to continue using the questionable hawser,doubling the factor of safety against the low-ered system strength would be appropriate.

B-11 Wire Rope Procurement Requirements

This section discusses the applicable specifi-cations for the purposes of procuring wirehawsers for ARS 50 and T-ATF 166 classvessels. For detailed information, consult thebelow list of documents.

Federal Specifications

RRW410 Wire Rope and Strand

RS550 Sockets, Wire Rope

Manuals

Naval Ship’s Technical Manual S9086-UU-STM-010, Chapter 613, “Wire andFiber Rope and Rigging,” S9086-UU-STM-010/CH613, Second Revision, 1May 1995.(Ref. F)

Copies of Military and Federal Specificationsand Standards may be obtained from the fol-lowing facility:

Commanding OfficerNaval Publications and Forms Center(NPFC)5801 Tabor AvenuePhiladelphia, PA 19120

Tel: (215) 697-2179

B-12 Requirements

B-12.1 Wire Rope Characteristics

Independent wire rope core may be substitut-ed for fiber core and Extra Improved PlowSteel (EIPS) for Improved Plow Steel (IPS) inany of the cases below if deemed prudent bythe purchasing activity. The information be-low may reflect the original configuration,but availability at the time of replacementmay dictate an IWRC.

B-12.2 Wire Towing Hawsers for T-ATF 166 Class Ships

Wire rope shall be 2 1/4-inch diameter cut to2500-foot lengths (see 3-4.1.3 for tolerancesin lengths), IPS (or EIPS), drawn galvanized,preformed, regular (R.H.) lay, polypropylenefiber core (or Independent Wire Rope Core(IWRC)), Type I, Class 3, Construction 6, 6 x37 (Warrington Seale) IAW SpecificationRRW410. Documentation of all test results(as required by RRW410) from each MasterReel used in fabrication of wire lengths shallbe submitted for the production assemblies(one data set included with the report in Sec-tion 4-2.2)

WARNING

When using a termination of lessthan 100 percent efficiency, thebase strength to which the factorsof safety are applied must be ad-justed accordingly.

B-12


Each of the 2500-foot lengths of 2-1/4-inchwire rope shall have a closed zinc-pouredsocket on one end and a permanent seizing onthe other end (See Section B-13).

Wire rope shall be wound on reels, closedsocket first. Reel drums shall be modified asrequired to allow the closed socket to be in-serted into the drum and held so wire can beuniformly wound and tightly secured. Pres-ence of the closed socket must be verifiableby visual examination without disturbing thestowage of wire on the reel. Marking for ship-ment and storage shall be in accordance withbest commercial practices. Each reel shall beclearly marked on each side with the diameterand length of wire in a three-inch size lettersas follows: “2 1/4-in x 2500-ft w/closed sock-et termination.”

B-12.3 2-1/4-Inch Towing Hawsers for ARS-50 Class Ships

Wire rope shall be 2 1/4-inch diameter cut in-to a 3000-foot length, EIPS, drawn galva-nized, preformed, regular (R.H.) lay, IWRC,Type I, Class 3, Construction 6, 6 x 37 (War-rington Seale) procured IAW SpecificationRRW410. Documentation of all test results(as required by RRW410) from each MasterReel used in fabrication of wire lengths shall

be submitted for the production assemblies(one data set included with the report in Sec-tion 4-2.2)

Each of the 3000-foot lengths of 2 1/4-inchwire rope shall have a closed zinc-pouredsocket on one end and a permanent seizing onthe other end (See Section B-13).

Wire rope shall be wound on reels, closedsocket first. Reel drums shall be modified asrequired to allow the closed socket to be in-serted into the drum and held so wire can beuniformly wound and tightly secured. Pres-ence of the closed socket must be verifiableby visual examination without disturbing thestowage of wire on the reel. Marking for ship-ment and storage shall be in accordance withbest commercial practices. Each reel shall beclearly marked on each side with the diameterand length of wire in three-inch size letters asfollows: “2 1/4-in x 3000-ft w/closed sockettermination.”

B-13 Sockets

Each towing hawser shall have a closed zinc-poured socket on one end and a permanentseizing on the other end. Closed sockets shallbe Type B, procured IAW Specification

Table B-3. Efficiency of Wire Rope Terminations.

Type Terminations Efficiency*

Poured Spelter Socket 100 percent

Wire Rope Clips (See Table 4-1 for number) 80 percent

Swaged Socket** 100 percent

Eye splice (hand-spliced)2 1/4″ and larger wire1 5/8″ to 2″ wire1 1/8″ to 1½″ wire7/8″ to 1″ wire

70 percent75 percent80 percent80 percent

Flemish Eye (“Molly Hogan”) (with sleeve and thimble) 90 percent

* Efficiency is the strength of the termination divided by the nominal breaking strength of the wire.** Not recommended for fiber core ropes.

B-13


Figure B-8. Poured Sockets FED Spec. RR-S-550D Amendment 1.

WIREROPEDIAM

INCHES

DIMENSION IN INCHESWEIGHT

POUNDS

EACHA B C D F J K L

1 5/8 15/1/8 2 1/8 5 3/4 3 1/4 1 3/4 6 1/2 2 3/4 6 1/2 36

2 - 2 1/8 19 1/2 2 7/18 7 5/8 3 25/32 2 1/4 8 1/2 3 1/4 8 9/16 80

2 1/4 - 2 3/8 21 1/8 2 5/8 8 1/2 4 9/32 2 1/2 9 3 5/8 9 1/2 105

2 1/2 - 2 5/8 23 1/2 3 1/8 9 1/2 5 1/2 2 7/8 9 3/4 4 10 5/8 140

WIREROPEDIAM

INCHES

DIMENSION IN INCHESWEIGHT POUNDS

EACHA C D L M N O P

1 5/8 16 1/4 3 3 6 1/2 5 3/4 1 5/16 6 5/8 1/2 55

2 - 2 1/8 21 1/2 4 3 3/4 9 7 1 13/16 8 3/4 1/2 125

2 1/4 - 2 3/8 23 1/2 4 1/2 4 1/4 10 7 3/4 2 1/8 10 1/2 165

2 1/2 - 2 5/8 25 1/2 5 4 3/4 10 3/4 8 1/2 2 3/8 11 1/2 252

B-14


RRS550. Documentation of results of testsrequired by RRS550 shall be delivered witheach wire rope assembly. Closed zinc-pouredsockets shall be attached to the wire in accor-dance with the NSTM, CH-613 (Ref. F).Testing and proof of personnel qualificationsshall be as required by the Naval Ships Tech-nical Manual. A report of tests and personnelqualification documents shall be providedwith the wire rope assembly.

Tolerances on 2 1/4-inch wire rope lengthsafter sockets have been attached shall be plus

or minus five feet from the center of socketeye to the bare end of the wire rope.

B-14 Lubrication

All wire towing hawsers shall be lubricatedwith MIL-G-18458 grease in accordance withthe NSTM CH-613 (Ref. F) prior to beingplaced on the towing machine drum. The useof a pressure lubricator is preferable whenone is available.

B-15



B-16


Appendix C

SYNTHETIC FIBER LINE TOWLINES

C-1 Introduction

The material presented in this appendix doesnot supersede any Fleet or NAVSEA direc-tives on the operational use or care of synthet-ic towlines. The use of single- and double-braided polyester is approved for all routineand emergency towing applications. Nylonline is only approved for operations with craftof less than 600 tons displacements, or otherunique or special tows as approved byNAVSEA on a case-by-case basis.

Existing nylon line should be replaced on asize for size basis with double or single-braid-ed polyester. This includes emergency towand be towed hawsers.

Fiber lines, either natural or synthetic, can befound serving two functions in towline sys-tems. In some systems the main towing haw-ser is made of fiber line. In other systems thehawser is wire rope and fiber lines are used assprings to provide relief from dynamic ten-sion loads. In both uses, the fiber line shouldbe kept in excellent condition, protectedagainst wear, and inspected regularly.

When fiber line is used as the main towinghawser or as a spring, a written record of itshistory is required by the Naval Sea SystemsCommand in the form of the Towing HawserLog (see Appendix F).

C-2 Traceability

The ability to trace a line’s history is an im-portant element in accident investigation aswell as in general product-improvement ef-forts. Some of this information is maintained

in the Towing Hawser Log. American-madefiber line and some brands of foreign-maderope can be identified by special marker tapesinserted into the fiber lines, special-coloredmonofilaments and metal tags, and other dataon the reel upon which the line is delivered.Identification of manufacturing sourcethrough the marker coding is particularly use-ful in cases where the reel markings havebeen lost. Additional information on a specif-ic domestic rope producer’s identificationmarking practices is available on requestfrom the Cordage Institute, Suite 115, 350Lincoln Street, Hingham, MA 02043. Tele-phone (617) 749-1016.

C-3 Strength and Lifetime

C-3.1 General

Most synthetic fiber lines are stronger thannatural fiber (manila) lines, and they usuallyhave longer lifetimes because of their resis-tance to rot and other forms of environmentaldeterioration.

C-3.2 Specific

The primary type of fiber line currently usedby the Navy for towing is polyester. The useof nylon in towing is currently restricted intowing applications. Polypropylene is used insome applications but does not have the supe-rior characteristics of polyester or nylon. Ta-ble C-1 presents a qualitative summary of

WARNING

The failure of synthetic fiberlines under high tension loadscan be extremely dangerous.Synthetic lines, particularly poly-ester and nylon, retain highamounts of energy when undertension. These lines will have se-vere snapback if they fail underload. Personnel should stayclear of areas through which theend of a failed line may whip.

C-1


pertinent characteristics of the three types offiber lines.

As one may note from Table C-1, nylon’s wa-ter-absorption characteristic changes its com-parative rating from best to intermediate innearly every category. Consequently, the Na-vy has phased out the use of nylon in favor ofpolyester. Where springs are required in tow-line systems, polyester fiber will be used.Polypropylene will also continue to be usedfor certain purposes because it is the only oneof the three fiber lines that floats.

The Navy also employs synthetic lines insome of its lifting operations. These applica-tions demand lightweight, high strength,small diameter lines in very long lengths. Ar-amid fibers such as Kevlar, Spectra, and Vec-tran are well suited for this need. These typesof fiber are not approved for Navy towing,however. They have extremely low elonga-tion and, because of their light weight, do notprovide the catenary of wire rope. These fi-bers, therefore, do not provide the same ex-treme tension mitigation as the other hawsertypes.

C-4 Elongation

The elongation or stretch of fiber line undertension has both advantages and disadvantag-es. Elongation tends to greatly reduce dynam-ic loads in the towline such as shock loadsand wave-induced loads. Unfortunately, elon-gation also stores a great deal of energy inropes under tension and the release of this en-ergy when a rope fails causes a very danger-ous whipping or “snap back” of the line. Thestored energy, and potential danger, is muchgreater in the case of synthetic lines than forwire rope under the same load. For this rea-son, extreme caution is required when work-ing near fiber lines that are under load. Underheavy tension loads, nylon line can snap backat speeds up to 700 feet per second (500m.p.h.). Braided fiber lines tend to stretchabout one-half to two-thirds as much as plait-ed or stranded ropes of the same size.

C-5 Maintenance and Cleaning

Although fiber lines are not subject to corro-sion as wire ropes are, they still require care-

Table C-1. Fiber Comparisons.

Fiber Type Strength1 Cyclic2 Fatigues

Bending2 Fatigue

Abrasion Resistance

Heat Resistance

Creep

Nylon (dry) VG VG G E G G

Nylon (wet) G F F F — G

Polyester (dry) VG VG VG VG G VG

Polyester (wet) VG VG G G — VG

Polypropylene (dry) F F P P P F

Polypropylene (wet) F F P F — F

E = Excellent, VG = Very Good, G = Good, F = Fair, P = Poor

NOTES:1. Tensioned between two limits without bending.2. Usually running over pulleys. Some line wears out before failing from fatigue because of abra-

sion.

C-2


ful maintenance and cleaning. If the line be-comes oily or greasy, scrub it with freshwater and a paste-like mixture of granulatedsoap. For heavy accumulations of oil andgrease, scrub the line with a solvent such asmineral spirits, then rinse it with a solution ofsoap and fresh water.

The three different synthetic fibers show dif-ferent responses to various chemicals. Inbrief:

• Nylon weakens if exposed to acids, par-ticularly mineral acids. Its resistance toalkalis is good at normal temperatures.

• Polyester line will deteriorate with ex-posure to hot, strong alkali solutions. Itis particularly vulnerable to very strongacid solutions; therefore, even dilutedacid solutions should not be allowed todry on the rope.

• Polypropylene is resistant to both acidsand alkalis at normal temperatures, butis affected by some organic solventssuch as xylene and metacresol and bycoal tar and paint-stripping compounds.These types of chemicals are most like-ly to be found in the paint locker inthinners and cleaning compounds.

All synthetics are weakened by exposure tostrong sunlight and should therefore be storedout of the sun. Polyester has the best resis-tance to ultraviolet rays.

To extend the life of synthetic line, maintainminimum and evenly distributed wear. Payspecial attention to possible chafing pointswhere the line passes over chocks, bitts, sternrollers, and so forth. Even though no particu-lar wear may be noticed, it is advisable tofreshen the nip at least once per watch tochange the location of possible internal wear.

Do not subject fiber lines to any of these othercommon abuses:

• Incorrect size of groove on drum orsheave

• Drum or sheave grooves that have be-come rough or corrugated through wear

• Inadequate radius on fairlead or sternroller

• Rough or abrasive surfaces on fairleador stern roller

• Improper winding on drum

• Exposure to excessive heat

• Kinks or hockles.

C-6 Stowing

Stow synthetic line away from strong sun-light, heat, and strong chemicals, and cover itwith tarpaulins. If the line becomes iced over,thaw it carefully and drain it before stowing.If feasible, store the line on appropriatelytreated wooden dunnage. Nylon is susceptibleto a rapid reduction in strength when exposedto rust; make sure that it is not exposed torust-prone bare steel surfaces.

C-7 Uncoiling or Unreeling New Hawsers

Synthetic line is shipped in cut lengths, eitherin coils or on wooden reels. It must be uncoiledor unreeled very carefully to avoid abrasionand permanent damage to the fibers. Loopingthe line over the head of the reel or pulling theline off a coil while it is lying on the deck maycreate kinks or hockles in the line. Never allowsynthetic line to drag over rough surfaces sincethis will tend to abrade and cut the outer fibers.

CAUTION

A common method of uncoilingwire rope by rolling the coil alongthe deck is not recommended for fi-ber lines because of the potentialfor abrading or cutting the outer fi-bers, and also because the coil willcollapse when the bands are re-moved.

C-3


Synthetic lines are unreeled the same waythat wire ropes are unreeled (see SectionB-5).

C-8 Breaking in New Hawsers

NSTM CH-613 (Ref. F) suggests that a syn-thetic hawser is adequately “broken in” afterfive cycles of loading/unloading up to itsworking load or to within 20 percent ofbreaking strength, whichever is less. Thisworks the construction stiffness out of theline. When new lines are strained, they some-times produce a sharp crackling sound. Thisis the result of readjustment of the line’sstrands to stretching and should not be causefor alarm.

It is not always possible to get new line to layflat due to turns set into the line during stor-age on a reel. Never tow with a synthetichawser just to get the hockles or kinks out.Stream the line, controlling its payout with acapstan, until the bitter end is reached. Re-trieve it with the aid of the capstan and it willthen lay flat as the excess turns will run out ofthe line as it is being hauled in. The shipshould be stopped during retrieval of the line.

When a new line is put into service as a tow-ing hawser or spring, its identification infor-mation (see Section C-2) should be recordedin the Towing Hawser Log (see Appendix F).

C-9 Inspection

Regular inspection is essential to ensure thatsynthetic lines remain serviceable and safe.

Keep in mind that no matter what has weak-ened the line, the effect of the same injurywill be more serious on a small line than alarge line. Therefore, always consider the re-lationship of the surface area of the line to itscross section.

Examining the line about one foot at a time isusually practical. Turn the line to reveal allsides before continuing. At the same inter-vals, untwist the rope slightly to examine be-tween the strands of three-strand and plaitedrope.

Synthetic lines should be inspected after eachuse. Look for broken fibers in the outer layerand for discoloration or appearances of melt-ing. When examining between the strands,look for these same evidences of wear andlook also for any appearance of a powderysubstance between the strands. Broken outerfibers may indicate that the line has beendragged over sharp or rough surfaces. Discol-oration or melting may indicate excessivefrictional heat from either dynamic loads orfrom rubbing over smooth surfaces. Internalwear, sometimes indicated as a fuzzed orfused condition between strands, may indi-cate fatigue damage from repeated or cyclicloads and overloading.

If the examination raises any doubts about thesafety of the line, discard it. Again, keep inmind that the effects of wear and mechanicaldamage are relatively greater on smaller lineswhich, therefore, require more stringent stan-dards of acceptance.

The following section on types of wearshould be helpful during the inspection ofsynthetic lines.

C-10 Types of Wear or Damage

The usual types of wear exhibited by synthet-ic lines are as follows:

• General external wear. External wear dueto dragging over rough surfaces causes sur-

CAUTION

New synthetic hawsers should notbe subjected to heavy strain priorto breaking them in. Limit the tow-ing loads applied to a new hawseruntil it has been cycled up to itsworking load.

C-4


face chafing. In the extreme, the strands be-come so worn that their outer faces are flat-tened and the outer yarns are severed. Inordinary use some disarrangement orbreakage of the fibers on the outside of theline is unavoidable and harmless if not ex-tensive. Generally, nylon and polyester fil-ament lines have very good abrasion resis-tance.

• Local abrasion. Local abrasion, as distinctfrom general wear, is caused by the passageof the line over sharp edges while undertension and may cause serious loss ofstrength, especially if accompanied byfused areas signifying high heat generatedby rope surges under heavy load. Slightdamage to the outer fibers and an occasion-al torn yarn may be considered harmless,but serious reduction in the cross-sectionalarea of one strand or somewhat less seriousdamage to more than one strand shouldwarrant rejection. When such damage isnoticed, preventive measures should betaken. Typical protective steps are tosmooth and round off all rough or sharp ar-eas on the surface that are chafing the lineand apply chafing gear such as rubber orplastic sleeves or cloth material secured bysmall stuff around the line.

• Cuts and contusions. Cuts and contusionsare caused by rough or sharp surfaces. Suchcareless use may cause internal as well asexternal damage. This may be indicated bylocal rupturing or loosening of the yarns orstrands.

• Internal wear. Internal wear may be indi-cated by excessive looseness of the strandsand yarns or the presence of fuzzed orfused internal areas. It is caused by repeat-ed flexing of the line and by particles ofgrit that have been picked up. Ice crystalscan also cause internal wear. This conditionresults from towing in very cold weatherand will most likely occur at the stern ofthe tug and at the tow where the hawser is

occasionally wetted, but generally exposedto the cold air.

• Repeated loading. Although polyester fila-ment line resists damage from repeatedloading, permanent elongation will occurover time in heavily loaded ropes. If theoriginal length of the rope is known exact-ly, remeasuring under exactly the sameconditions indicates the total extension ofthe rope. This method, however, may notreveal severe local permanent elongationthat may cause breaking on subsequentloading. Measuring the distance betweenregularly spaced indelible markers on therope can help reveal this problem.

• Heat. Heat may, in extreme cases, causemelting. Any signs of melting should obvi-ously warrant rejection, but a line may bedamaged by heat without any such obviouswarning. The best safeguard is proper careand storage. A synthetic line should neverbe dried in front of a fire or stored near astove or other source of heat.

• Strong sunlight. Strong sunlight causesweakening of synthetic fibers, but is un-likely to penetrate beneath the surface. Un-necessary exposure should be avoided,however. Solar degradation should bechecked by rubbing the surface of the linewith the thumb nail. If degradation has tak-

WARNING

Surging of synthetic line undertension can cause sufficient fric-tional heat at the contact surfac-es to melt the surface of the line.The melting point of polypropy-lene line, for instance, is 320°Fto 340°F, while the softeningpoint is around 300°F. Compara-ble temperatures for polyesterare only moderately higher.These temperatures are quitequickly produced when a line issurged on a winch or capstan.

C-5


en place, the surface material will come offas a powder. In addition, the surface of theline will feel dry, harsh and resinous.

C-11 Special Precautions

• When using heavily loaded syntheticlines, the major precaution to be takenis to be constantly alert to the potentialdanger of line “snap back” during fail-ure. Personnel must remain clear of theareas through which the ends of a failedline may whip or snap.

• To avoid damage from rough surfaces,synthetic line should not be used in ar-eas where chafing potential is high. Useof a wire rope or chain pendant is pre-

ferred. This is particularly important onthe tow, as the conditions of the tow’schocks, bitts, etc. may be unknown andcontact with these may cause extensivechafing. Barges usually have veryrough chocks caused by previous repet-itive use of wire rope or chain. Specialattention should be paid to where thehawser crosses the stern of the tug.

• Since their coefficient of friction is be-low that of manila, synthetic lines mayslip when eased out under heavy loads,causing personal injury. Make sure thatpersonnel are thoroughly instructed inthese lines’ peculiarities. Take two orthree turns on a bitt before you “figure8” the line; this provides closer control.Stand well clear of the bitts.

C-12 Fiber Rope Characteristics

• Table C-2 provides the strength and weightof several sizes and types of fiber ropes.See NTSM CH-613 (Ref. F) for additionaldata on fiber lines.

WARNING

Listed below are three precau-tions to be considered when us-ing synthetic tow hawsers. Theyshould be taken as warnings asthey are critical to safety of per-sonnel.

Table C-2. Synthetic and Natural Line Characteristics.

Size (Inches)

Dry Nylon Double-Braid(MIL-R-24050 D)

Polyester Double-Braid(MIL-R-24667 A)

Polyester Single Braided 12-Strand (MIL-R-24750)

BS (lbs) WT/100 ft BS (lbs) WT/100 ft BS (lbs) WT/100 ft

356789

1011121314

27,82578,110

109,675149,800192,600243,000284,840351,000415,800475,200548,640

24.367.697.1132173219270327389450524

29,48074,000

105,000133,600180,000232,000277,000335,000396,150446,500500,650

31.984

128161220287337419510576646

25,60067,20096,000

131,200172,000215,200264,800319,200376,800440,800508,800

3078

112153200253312378449527612

BS = Breaking Strength WT = Weight

Strength shown for nylon is for new dry nylon. Nylon wet strength is about 15% less. Multiply figures listed by 0.85 to obtain the new breaking strength of wet nylon.

C-6


Appendix D

CHAINS AND SAFETY SHACKLES

D-1 Introduction

Chain is an important component in the con-nection between the towed vessel and the tug.It usually appears in the form of pendants orbridles at the towed-vessel end of the towline.The chain components serve one or more ofthe following purposes:

• A chafing-resistant strong terminal con-nection to the towed vessel

• An equalizing device (bridle) to sharethe towing load between two strongpoints located port and starboard of thetowed vessel’s bow (or stern)

• A means of absorbing dynamic loads inthe towline, by virtue of its weight,which increases catenary in the towline.

Chain, like other marine tension members,has evolved over the years. The Boston NavalShipyard led U.S. Navy chain developmentand manufacture for many years. Two majordevelopments and manufacturing responsibil-ities at the Shipyard were die lock chain andthe Navy detachable link. With the deactiva-tion of the Boston Naval Shipyard in 1972,this capability was lost to the Navy, althoughsimilar products were commercially manu-factured until the mid-1980s. Nonetheless,large amounts of die lock chain remainthroughout the Fleet and this type chain isperfectly acceptable for all uses for which itwas designed. The Navy now purchases“flash butt welded stud link” chain that issimilar in appearance to high quality, com-mercial anchor chain, usually referred to as“welded” or “stud link” chain. In this appen-dix, this new Navy chain will be called “stud

link” chain for the sake of simplicity. Navystud link chain is slightly stronger than stan-dard Type 1 die lock chain; they may be usedinterchangeably.

Until recently, commercial “DiLok” chainwas made by one manufacturer, Baldt. It isslightly stronger and heavier than Type 1standard Navy die lock chain. Section D-11discusses the strengths of the various chainsthat may be used in towing.

D-2 Traceability and Marking

D-2.1 Traceability

The ability to trace a chain’s history is an im-portant element in accident investigation aswell as in general product-improvement ef-forts. For identification, a corrosion-resistantmetal tag is attached to the end link at eachend of each shot or length of Navy chain. In-cluded among data plainly marked on the tagis a manufacturer’s serial number, which per-mits tracing the chain back to its manufactur-ing source. The manufacturers also provideinformation with new chain regarding size,type, material, proof tests, certification, andso forth. This information should be main-tained in the Towing Hawser Log (see Ap-pendix F) and updated as necessary for chainthat is used as an integral part of the towlineconnection.

D-2.2 Marking

Navy chain, whether die lock or stud link, ismarked in accordance with MIL-C-24633ANotice 1, Chain, Stud Link, Anchor, Low Al-loy Steel, Flash Bolt Welded (Ref. AB).

Commercial chain used in marine service, in-cluding DiLok, is controlled and certified byvarious marine classification societies such asthe American Bureau of Shipping (ABS),which certifies all U.S. flag vessels and manyforeign ships. Marine stud link chain is madein three grades. Grade 2 is most prevalent.ABS requires chain to be marked on the end

D-1


link of each shot, or every 15 fathoms if thechain is continuous (without connectinglinks). The markings include:

• Certificate number

• Chain size

• Classification society stamp (such as aMaltese Cross for ABS)

• Designation of the grade of chain, forexample: AB/1, AB/2, or AB/3. Theother classification societies havemarking requirements and grading sys-tems that are similar to those of ABS.

When towing a commercial ship, if it is in-tended to use the ship’s anchor chain for abridle or pendant, the chain should be careful-ly inspected in accordance with the require-ments of Section D-8. If the classification so-ciety grade marking cannot be determined,the chain should be assumed to be Grade 1,which is roughly one-half as strong as stan-dard Navy chain.

Chain from unknown or non-marine sourcesthat is unmarked or cannot otherwise be iden-tified should not be used in towing.

D-3 Strength and Lifetime

Chain, properly used, should be the strongestand longest-lived element in the towing sys-tem. Because of its construction and general-ly rugged configuration, chain is considerablystronger than wire or fiber rope of the samenominal size.

D-4 Elongation

The rugged, large-diameter, individualstrength members of chain give it the leastelongation, or stretch, under load of any tow-line component. This characteristic of chainis one of the prime reasons it is used as an el-ement in the towline system. Because it doesnot stretch, working at chafing points, under

constantly changing tension, is minimized.Additionally, the weight and flexibility of thechain promotes the towline catenary and miti-gates the effects of dynamic loading on therest of the towing system.

D-5 Maintenance and Cleaning

As with other elements of the towline, chainmust be properly maintained and cleaned.Perhaps the most important element of chainmaintenance is corrosion prevention. Corro-sion leads directly to loss of chain strength byreducing the diameter of the load-carryingrods that form the links. In stud link chains,corrosion can also loosen the studs and even-tually lead to their loss.

Corrosion prevention is best achieved by afresh-water washdown of the chain after eachuse, coupled with visual inspection for initialsigns of corrosion. During the required annu-al inspection, the chain should be carefullycleaned, inspected, and re-preserved as neces-sary; see Naval Ship’s Technical Manual(NSTM) S9086-TV-STM-010, Chapter 581,Anchoring (Ref. AC).

Cleaning should be done by scaling, sand-blasting, or wire brushing. Penetrating oilshould not be used to loosen the rust becauseit is difficult to remove and may reduce theeffectiveness of corrosion prevention coat-ings. After cleaning, a careful inspectionshould be made in accordance with SectionD-8. All suspected links should be checkedby non-destructive test methods, careful mea-surement, sounding, and so forth.

Preservation after cleaning and any necessaryrepairs should be performed in accordancewith Section D-8 and with NSTM CH-074(Ref. K). For most chain, the use of TT-V-51paint (asphalt varnish) or MIL-P-24380 paint(anchor chain gloss black solvent type paint)is satisfactory.

D-2


D-6 New Chain and Links

New or reissued chain or links that will beused as components of towline connectionsshould be treated in the same manner as newtowing hawsers. The chain and links shouldbe inspected and pertinent data entered in theTowing Hawser Log (see Appendix F).

D-7 Stowing

No special stowing precautions are neededbeyond attempts to prevent corrosion, such astrying to avoid moisture and salt. Again, oiland grease should be avoided.

D-8 Inspection

D-8.1 General

Annual inspection of chain components of atowline system should follow the Navy prac-tices for anchor chain detailed in NSTM 581.After cleaning by scaling, wire-brushing, orsandblasting, each link should be checked bysounding with a hammer. Give particular at-tention to locating possible loose studs, bentlinks, excessive corrosion, and sharp gouges.

D-8.2 Specific

Proper reactions to various conditions notedin the inspection are indicated in the follow-ing notes, most of which apply to stud linkchain:

• Missing stud: discard link.

• Out-of-plane bending of more thanthree degrees: discard link.

• Average of the two measured diametersat any point less than 95 percent ofnominal diameter, or a diameter in anydirection less than 90 percent of nomi-nal diameter: discard link.

• Crack at the toe of the stud weld ex-tending into the base material: discardlink.

• Surface cracks or sharp gouges: attemptto eliminate by light grinding. If thechain diameter is reduced to less than90 percent of the nominal diameter af-ter grinding: discard link.

• Excessively loose stud: since it is diffi-cult to quantify excessive looseness ofchain studs, the decision to reject or ac-cept a link with a loose stud depends onthe experience and judgment of the in-spector. Consider discarding a link if:

— The stud can move more than 1/8inch (3 mm) axially or more than3/16 inch (5 mm) laterally in anydirection, or

— A gap of more than 1/8 inch existsbetween the stud end in a link witha stud welded only on one end.

• Cracks detected by magnetic particleinspection in the internal locking areaof detachable link: discard link. Exter-nal surface defects in detachable linksare not cause for rejection if they can beeliminated by grinding to a depth of nomore than 8 percent of the nominal di-ameter of the chain.

• Length over six links exceeding 26.65times nominal chain diameter or lengthof individual link exceeding 6.15 timesnominal chain diameter: discard links.

• Excessive wear or deep surface crackon shackles, open links, or swivels: At-tempt to eliminate by light grinding. Ifthe cross-section area, diameter or criti-cal thickness in any direction is reducedmore than 10 percent by wear andgrinding: discard the chain.

If a substantial number of adjacent links in achain section meet the criteria for discarding,the chain section should be removed and thechain joined again by detachable links thathave been examined and found to be in ac-ceptable condition.

D-3


If a large number of links meet the criteria fordiscarding and these links are distributedthroughout the chain’s whole length, replacethe chain with a new one.

Rewelding of loose studs in the field is unde-sirable for the following reasons:

• Welding in the field may produce hardheat-affected zones that are susceptibleto cold cracking.

• Hydrogen brittleness may occur fromabsorption of moisture from the atmo-sphere or welding electrodes.

Weld repairs on loose studs should be de-layed as long as possible. Where a few linksare found with loose studs in a short sectionof a chain, it is recommended that this portionof the chain be cut out and a detachable linkinserted. If the major portion of the chain hasloose studs, the chain should be scrapped.

Any grinding to eliminate shallow surface de-fects should be done parallel to the longitudi-nal direction of the chain, and the grooveshould be well rounded and should form asmooth transition to the surface. The groundsurface should be examined by magnetic-par-ticle or dye-penetrant inspection techniques.

D-9 Types of Wear

The rough treatment to which chain items oftowing gear are exposed can lead to variouschain problems. Eight common problems forwhich towing personnel should be alert aredescribed below:

• Missing studs. The stud contributesabout 15 percent of the chain’sstrength. A chain link without a studmay significantly increase the possibili-ty of link failure. High bending stressesand low fatigue life in links are predict-able consequences of missing studs.

• Bent links. A bent link is the result ofchain handling abuse. The link may

have been excessively torqued whentraversing a sharp, curved surface or thechain may have jumped over the wild-cat, making point contacts between thelink and the wildcat.

• Corrosion. Excessive corrosion reduc-es the cross sectional area of the link,increasing the possibility of chain fail-ure from corrosion fatigue or overload-ing.

• Sharp gouges. Physical damage to thechain surface, such as cuts and gouges,raises stress and promotes fatigue fail-ure.

• Loose studs. Loose studs, caused byabusive handling or by excessivestretching of chain, result in lowerbending strength of the chain.

• Cracks. Surface cracks, flash weld cra-cks, and stud weld cracks propagate un-der cyclic loading and result in prema-ture chain failure.

• Wear. Wear between links in the griparea and between links and the wildcatreduces the chain diameter. The diame-ter reduction decreases the load-carry-ing capacity of the chain and invitesfailure.

• Elongation. Excessive permanent elon-gation may cause the chain to functionimproperly in the wildcat, resulting inbending and wear of the links. Wear inthe grip area of the chain as well asworking loads in excess of the originalproof load will result in a permanentelongation of chain.

D-10 Special Precautions

Because chain is generally the most ruggedcomponent of the towline system, there is atendency to become overconfident in its capa-bility and somewhat less rigorous in inspec-

D-4


tion. Avoid overconfidence when usingchain.

Personnel tend not to check carefully enoughon such items as:

• Adequate radius of curvature on surfac-es of fairleads, chocks, and so forth. Aratio of 7:1 is generally accepted as theminimum D:d ratio of bearing surfaceto chain size for heavy loads when thechain direction is changed significantlyover the surface.

• Wear in the grip (partially hidden con-tact) area between chain links.

• Looseness from excessive wear in shackles, swivels, and detachable links.

• Presence of detachable links that arenot equipped with safety-lock hairpins.

D-11 Chain Specifications

Navy die lock chain characteristics are in-cluded in Table D-1. The similar Baldt“DiLok” chain is 11 percent stronger and 1percent heavier. Table D-2 provides the char-acteristics of Navy stud link chain. Navy studlink chain is equivalent to commercial Grade3 as shown in Table D-3. Commercial Grade3 chain is about 3 percent stronger than Navystandard die lock. Grade 2 is only about 70percent as strong as Navy standard die lockand Grade 1 is only about 50 percent asstrong.

D-12 Connecting Links

Detachable chain connecting links are fre-quently used in lieu of more traditional shack-les, because they will pass through a smallerspace and are less likely to “hang up” duringthe rigging process. Pear-shaped detachablelinks fit two chain sizes. The strength of thislink is identical to the breaking strength of thelarger chain size that it is designed to accom-modate. Figures D-4 through D-5 and Tables

D-4 and D-5 describe detachable links and animproved locking system for use with the ta-pered link pins. End links (see Table D-6) arespecial studless links 1/8 inch to 1/4 inchlarger than the chain size. They are largerthan the chain size to compensate for the lackof a stud. They have the same strength as theparent chain system.

D-13 Safety Shackles

A safety shackle is characterized by a pin thatis secured by a bolt on the outside of theshackle. For towing use, the bolt itself is se-cured by a small machine bolt with two nutsjammed together to prevent rotation of thelarge nut. Screw-pin shackles, which use athreaded pin that screws into the body of theshackle, are not approved for Navy towing.Some deck layouts present no alternative dueto location and size of attachment padeye.Contact NAVSEA 00C for further guidance.

Navy shackles are manufactured in two types,two grades, and three classes of shackles. Me-chanical properties can be obtained from FedSpec RR-C-271D (Ref. E). Tables D-7through D-9 provide the physical dimensionsand strengths of safety shackles. Note the sig-nificant difference in strength between GradeA and Grade B shackles. The shackle size andsafe working load will be shown in raised orstamped letters on the shackle. The pins andbolts of Grade A - Regular Strength shacklesare unmarked, but Grade B pins and bolts aremarked “HS.”

CAUTION

Screw-pin shackles, other than thespecial forged shackles for stop-pers, must never be used for con-nections in towing rigs. The pincould back out due to the constantvibration on the towline.

D-5


D-14 Proof Load, Safe Working Load, and Safety Factor

Calculated or predicted design loads are com-pared to a baseline strength in computing thesafety factor. Conversely, the baselinestrength is divided by the recommended safe-ty factor to determine the allowable designload. Table 3-2 provides the recommendedfactors of safety for use in designing towingsystems. Note that safety factors, for a giventype design and service, are referenced to dif-ferent baselines such as breaking strength,yield strength, or proof load.

For chain, safety factors are referred to as“proof load,” a load demonstrated as part ofthe manufacturing process, which intentional-ly introduces a permanent stretch that im-proves the strength of the chain. Proof loadfor chain is 66 percent of minimum breakstrength.

For other forged-type hardware, such asshackles, proof load is a load at which no per-manent deformation is observed after the loadis released. This is important where the com-ponent must mate with other components orwhere the component has parts that must fittogether. In the case of shackles, it is impor-tant to be able to remove the pin after use.Unlike chain, however, there is no consistentrelationship between proof load and breakingload. The relationship depends upon the met-allurgical properties of the material.

Safe Working Load (SWL) is frequently usedfor rigging components and systems includ-ing such material. The concept of SWL issimilar to the use of a “safety factor” and isappropriate where the load is fairly wellknown and dynamic loads are limited. Thetypical use of SWL is for lifting purposes.The safety factor inherent in SWL for Navysafety shackles, compared to proof load, is 2for Grade A and 2.5 for Grade B shackles.This is insufficient for use in towing systems,where the dynamic loads are more difficult to

predict, than for simple rigging purposes. Ap-plying the safety factors from Table 3-2 in ad-dition to SWL, however, is overly conserva-tive and will result in unacceptably largecomponents. Therefore, when designing tow-ing systems for strenuous conditions, thesafety factors listed in Table 3-2 for shacklesshould be applied to proof loads listed in Ta-ble D-9.

Consider, for example, a predicted steadystate tow resistance of 80,000 pounds. This isappropriate for a 2-inch fiber core towinghawser under automatic towing machine con-trol. Table 3-2 requires a safety factor of 3 forshackles. If this factor is applied to SWL, 31/2-inch Grade B safety shackles, weighing310 pounds, would be required in the rig. Ap-plying the required factor of safety to proofload requires more reasonable 2 1/4-inchGrade B shackles.

D-15 Plate Shackles

Plate shackles are frequently used in salvageand towing operations because they are sim-ple, efficient, and easily fabricated from com-monly available materials. Plate shackles areefficient because many connections of chainto wire and chain to chain would require twosafety shackles, back-to-back, whereas oneplate shackle will accomplish the task. Thecheeks of towing plate shackles are fabricatedfrom “medium” (ABS Grade A or ASTMA-36) steel, the most readily available classi-fication, and the pins are fabricated from150,000 psi minimum yield strength barstock, also readily available. Appendix I in-cludes drawings of plate shackles for use intowing. Certain salvage ships can be outfittedfor heavy-lifting operations. In this case,stronger plate shackles than shown in Appen-dix I may be required. Check the specific rig-ging plans for the specified shackles forheavy lifting.

D-6


Table D-1. Die Lock Chain Characteristics (MIL-C-19944).

CHAIN SIZELink

Length(Inches)

A

LinkWidth

(Inches)B

Length Over Six

Links(Inches)

C

Number of LinksPer 15- Fathom

Shot

Approx.WeightPer 15- Fathom

Shot (Pounds)

Approx. Weight

Per Link(Pounds)

ProofTest

(Pounds)Break Test (Pounds)Inches mm

TYPE I: STANDARD

3/47/811–1/81–1/41–3/81–1/21–5/81–3/41–7/822–1/82–1/42–3/82–1/22–5/82–3/42–7/833–1/83–1/43–3/83–1/23–3/44–3/4

192225293234384244485154586064677073767983869095

121

4–1/2 5–1/4 6 6–3/4 7–1/2 8–1/4 9 9–3/410–1/211–3/41212–3/413–1/214–1/41515–3/416–1/217–1/41818–3/419–1/220–1/42122–1/228–1/2

2–5/83–1/83–3/1644–1/24–13/165–3/85–7/86–3/166–3/47–3/167–5/88–1/88–3/1699–3/169–7/810–3/810–13/1611–1/411–11/1612–1/812–5/813–3/817–1/8

19–1/222–3/42629–1/432–1/235–3/43942–1/445–1/248–3/45255–1/458–1/261–3/46568–1/471–1/274–3/47881–1/484–1/287–3/49197–1/2122–1/2

359305267237213193177165153143135125119113107101

979389878379777157

490680890

1,1301,4001,6902,0102,3252,6953,0953,4903,9354,4154,9155,4756,0506,6607,2957,9558,7009,410

10,11210,90012,50020,500

1.42.23.34.86.68.8

11.414.117.621.625.931.537.143.551.259.968.778.489.4

100.0113.4128.0141.6176.1359.7

48,00064,00084,000

106,000130,000157,000185,000216,000249,000285,000289,800325,800362,700402,300442,800486,000531,000576,000623,700673,200723,700776,000829,800

1,008,0001,700,000

75,00098,000

129,000161,000198,000235,000280,000325,000380,000432,000439,200493,200549,000607,500669,600731,700796,500868,500940,500

1,015,2001,089,0001,166,4001,244,8001,575,0002,550,000

TYPE II: HEAVY DUTY

2–3/433–1/2

707690

16–1/21821

9–7/810–13/1612–5/8

71–1/27891

978977

7,0008,100

12,000

72.291.0

155.8

584,100685,800972,000

882,9001,035,0001,530,000

TYPE III: HIGH STRENGTH

3/411–1/81–3/81–1/21–5/8

192629343842

4–1/266–3/48–1/499–3/4

2–5/83–3/1644–15/165–3/85–7/8

19–1/22629–1/435–3/43942–1/4

359267237193177165

5501,0001,2701,9002,2602,620

1.53.85.49.9

12.815.9

67,500116,100145,000211,500252,000292,500

91,100156,700195,000285,500340,200395,000

D-7


Table D-2. Navy Stud Link Chain Characteristics (MIL-C-24633).

* Not mandatory, for information only.

ChainSize

(Inches)

Link Length (Inches)

(A)

LinkWidth

(Inches)(B)

Length Over 6 Links (C)(Inches)

Number of Links per

15-Fathom Shot

ProofTest Load(Pounds)

BreakTest Load(Pounds)

NominalWeight per15-FathomShot (lb.)*Minimum Nominal Maximum

3/47/811-1/81-1/41-3/81-1/21-5/81-3/41-7/822-1/82-1/42-3/82-1/22-5/82-3/42-7/833-1/83-1/43-3/83-1/23-5/83-3/43-7/84

4-1/25-1/466-3/47-1/28-1/499-3/410-1/211-1/41212-3/413-1/214-1/41515-3/416-1/217-1/41818-3/419-1/220-1/42121-3/422-1/223-1/424

2-5/83-1/83-9/1644-1/24-15/165-3/85-7/86-5/166-3/47-3/167-5/88-1/88-9/1699-7/169-7/810-3/810-13/1611-1/411-11/1612-1/812-5/812-15/1613-3/81414-3/8

19-3/822-5/825-7/829-1/1632-5/1635-9/1638-13/164245-1/448-1/251-11/1654-15/1658-3/1661-7/1664-11/1667-7/871-1/874-3/877-5/880-13/1684-1/1687-5/1690-9/1693-13/1697-1/16100-1/4103-1/2

19-1/222-3/42629-1/432-1/235-3/43942-1/445-1/248-3/45255-1/458-1/261-3/46568-1/471-1/274-3/47881-1/484-1/287-3/49194-1/497-1/2100-3/4104

19-13/1623-1/1626-3/829-5/832-15/1636-1/439-1/242-7/846-1/849-1/252-3/456-1/859-3/862-3/46669-1/472-9/1675-7/879-3/1682-1/285-3/48992-5/1695-5/898-7/8102-3/16105-1/2

359305267237213193177165153143135125119113107101

9793898783797773716967

48,00064,40084,000

106,000130,000157,000185,000216,000249,000285,000318,800357,000396,000440,000484,000530,000578,000628,000679,000732,000787,000843,000900,000958,000

1,019,0001,080,0001,143,000

75,00098,000

129,000161,000198,000235,000280,000325,000380,000432,000454,000510,000570,000628,000692,000758,000826,000897,000970,000

1,046,0001,124,0001,204,0001,285,0001,369,0001,455,0001,543,0001,632,000

480660860

1,0801,3501,6301,9402,2402,5902,9803,3603,7904,2504,7305,2705,8206,4107,0207,6508,3209,0109,730

10,50011,30012,00012,90013,700

D-8


Table D-3. Commercial Stud Link Anchor Chain.

Chain Size LinkLength(Inches)

(A)

LinkWidth

(Inches)(B)

LengthOverFiveLinks

(Inches) (C)

GripRadius

(Inches)(D)

Approx.Weightper 15-Fathom

Shot (lbs)

No. ofLinks

per 15-Fathom

Shot

ABS Grade 1 ABS Grade 2 ABS Grade 3

ProofTest (lb)

BreakTest (lb)

ProofTest (lb)

BreakTest (lb)

ProofTest (lb)

BreakTest (lb)Inches mm

3/413/167/815/1611-1/161-1/81-3/161-1/41-5/161-3/81-7/161-1/21-9/161-5/81-11/161-3/41-13/161-7/81-15/1622-1/162-1/82-3/162-1/42-5/162-3/82-7/162-1/22-9/162-5/82-11/162-3/42-13/162-7/82-15/1633-1/163-1/83-3/163-1/43-5/163-3/83-7/163-1/23-5/83-3/43-7/844-1/84-1/44-3/84-1/2

192022242527283032333436384042434446485051525456585960626466676870717375767879818384868790929598102105108111114

4-1/24-7/85-1/45-5/866-3/86-3/47-1/87-1/27-7/88-1/48-5/899-3/89-3/410-1/810-1/210-7/811-1/411-5/81212-3/812-3/413-1/813-1/213-7/814-1/414-5/81515-3/815-3/416-1/816-1/216-7/817-1/417-5/81818-3/818-3/419-1/819-1/219-7/820-1/420-5/82121-3/422-1/223-1/42424-3/425-1/226-1/427

2-5/82-7/83-1/83-5/163-9/163-3/444-1/44-1/24-3/44-15/165-3/165-3/85-5/85-7/86-1/166-5/166-1/26-3/477-3/167-7/167-5/87-7/88-1/88-5/168-9/168-3/499-1/49-7/169-11/169-7/810-1/810-3/810-9/1610-13/161111-1/411-1/211-11/1611-15/1612-1/812-3/812-5/812-15/1613-3/81414-3/814-7/815-5/1615-3/416-3/16

16-1/217-7/819-1/420-5/82223-3/824-3/426-1/827-1/228-7/830-1/431-5/83334-3/835-3/437-1/838-1/239-7/841-1/442-5/84445-3/846-3/448-1/849-1/250-7/852-1/453-5/85556-3/857-3/459-1/860-1/261-7/863-1/464-5/86667-3/868-3/470-1/871-1/272-7/874-1/475-5/87779-3/482-1/285-1/48890-3/493-1/296-1/499

1/217/3237/645/821/3211/1625/3225/3225/327/87/815/1663/641-1/321-1/161-3/321-5/321-3/161-1/41-9/321-5/161-3/81-27/641-15/321-1/21-17/321-9/161-5/81-5/81-11/161-11/161-3/41-13/161-27/321-7/81-7/8222-1/162-1/162-1/82-1/82-3/162-3/162-5/162-5/162-15/322-15/322-5/82-11/162-3/42-7/82-15/16

480570660760860970

1,0801,2201,3501,4901,6301,7801,9402,0902,2402,4102,5902,7902,9803,1803,3603,5703,7904,0204,2504,4904,7304,9605,2705,5405,8206,1106,4106,7107,0207,3307,6507,9808,3208,6609,0109,3609,730

10,10010,50011,30012,00012,90013,70014,60015,40016,20017,100

357329305285267251237225213203195187179171165159153147143139133129125123119117113111107105103

99979593918987858583817977777371696765636159

23,80027,80032,20036,80041,80047,00052,60058,40064,50070,90077,50084,50091,70099,200

108,000115,000123,500132,000140,500149,500159,000168,500178,500188,500198,500209,000212,000231,000242,000254,000265,000277,000289,000301,000314,000327,000340,000353,000366,000380,000393,000407,000421,000435,000450,000479,000509,000540,000571,000603,000636,000669,000703,000

34,00039,80046,00052,60059,70067,20075,00083,40092,200

101,500111,000120,500131,000142,000153,000166,500176,000188,500201,000214,000227,000241,000255,000269,000284,000299,000314,000330,000346,000363,000379,000396,000413,000431,000449,000467,000485,000504,000523,000542,000562,000582,000602,000622,000643,000685,000728,000772,000816,000862,000908,000956,000

1,000,400

34,00039,80046,00052,60059,70067,20075,00083,40092,200

101,500111,000120,500131,000142,000153,000166,500176,000188,500201,000214,000227,000241,000255,000269,000284,000299,000314,000330,000346,000363,000379,000396,000413,000431,000449,000467,000485,000504,000523,000542,000562,000582,000602,000622,000643,000685,000728,000772,000816,000862,000908,000956,000

1,000,400

47,60055,70064,40073,70083,60094,100

105,000116,500129,000142,000155,000169,000183,500198,500214,000229,000247,000264,000281,000299,000318,000337,000357,000377,000396,000418,000440,000462,000484,000507,000530,000554,000578,000603,000628,000654,000679,000705,000732,000759,000787,000814,000843,000871,000900,000958,000

1,019,0001,080,0001,143,0001,207,0001,272,0001,338,0001,405,000

47,60055,70064,40073,70083,60094,100

105,000116,500129,000142,000155,000169,000183,500198,500214,000229,000247,000264,000281,000299,000318,000337,000357,000377,000396,000418,000440,000462,000484,000507,000530,000554,000578,000603,000628,000654,000679,000705,000732,000759,000787,000814,000843,000871,000900,000958,000

1,019,0001,080,0001,143,0001,207,0001,272,0001,338,0001,405,000

68,00079,50091,800

105,000119,500135,000150,000167,000184,000203,000222,000241,000262,000284,000306,000327,000352,000377,000402,000427,000454,000482,000510,000538,000570,000598,000628,000660,000692,000726,000758,000792,000826,000861,000897,000934,000970,000

1,008,0001,046,0001,084,0001,124,0001,163,0001,204,0001,244,0001,285,0001,369,0001,455,0001,543,0001,632,0001,724,0001,817,0001,911,0002,008,000

D-9


Table D-4. Commercial Detachable Chain Connecting Link.

Chain Size

A B C D E FProofTest

Break Test

Weightper Link

(lbs.)Inches mm

3/4 13/16 - 7/815/16 - 1

1-1/16 - 1-1/81-3/16 - 1-1/41-5/16 - 1-3/81-7/16 - 1-1/21-9/16 - 1-5/8

1-11/16 - 1-3/41-13/16 - 1-7/81-15/16 - 22-1/16 - 2-1/82-3/16 - 2-1/42-5/16 - 2-3/82-9/16 - 2-5/8

2-11/16 - 2-3/42-13/16 - 2-7/82-15/16 - 33-1/16 - 3-1/83-3/16 - 3-1/43-5/16 - 3-3/83-7/16 - 3-1/23-9/16 - 3-5/8

3-11/16 - 3-3/43-11/16 - 3-7/83-17/16 - 4

4-1/84-1/44-3/84-1/2

1921-2224-2527-2830-3233-3436-3840-4243-4446-4850-5152-5456-5859-6066-6768-7071-7375-7678-7981-8384-8687-8990-9294-9597-98100-102105108111114

4-1/2 5-1/4 5 6-3/4 7-1/2 8-1/4 9 9-3/410-1/211-1/41212-3/413-1/214-1/415-3/416-1/217-1/41818-3/419-1/220-1/421-1/821-3/422-1/223-1/42424-3/425-1/226-1/427

3 3-1/2 4 4-1/2 5 5-1/2 6 6-1/2 7-1/2 7-1/4 7-3/4 8-1/4 8-23/32 9-7/3210-3/1610-13/1611-1/811-5/812-1/812-5/813-3/3213-25/321414-1/21515-1/216-1/217-3/818-3/819-3/8

1-3/641-7/321-25/641-9/161-47/641-29/322-5/642-1/42-7/162-1/22-1/2

2-21/322-13/163-1/163-1/4

3-11/163-19/323-3/4

44-1/164-7/324-13/164-9/164-11/16

55-3/165-7/86-1/27-1/4

8

3/47/811-1/81-1/41-3/81-1/21-5/81-3/41-7/822-1/82-1/42-3/82-5/82-7/82-7/833-1/83-1/43-3/83-3/43-5/83-3/43-7/844-1/84-3/84-1/24-5/8

27/3263/641-1/81-17/641-13/321-35/641-11/161-63/6422-5/322-5/162-1/22-5/82-3/43-1/163-1/43-11/323-17/723-5/83-5/83-15/164-1/84-3/164-11/164-1/24-5/855-1/45-5/86

1/219/3221/3247/6413/1629/3283/841-1/161-3/161-1/41-5/161-13/321-1/21-9/161-3/41-13/161-29/321-31/322-3/642-5/322-1/42-13/322-5/162-7/162-5/82-11/162-25/322-7/82-15/163

67,50088,200

116,110145,000178,200211,500252,000292,500352,000285,000322,000362,000403,000447,000540,000649,000640,000693,000748,000804,100862,200

1,080,0001,021,1001,120,0001,205,0001,298,0001,347,0001,393,7001,569,7001,672,000

91,100119,000156,700195,000240,600285,500340,200395,000476,000432,000488,000548,000610,000675,000813,000981,000965,000

1,045,0001,128,0001,210,0001,296,0001,700,0001,566,0001,750,0001,863,4001,966,0002,062,5002,134,0002,398,0002,508,000

2.1 3.45.17.29.9

13.317.322.027.5323644526182

100107120138161177205215256271288384422460500

All specifications in pounds and inches, unless otherwise stated.See Figures D-2 and D-3 for hairpin locking details.

D-10


Table D-5. Commercial Detachable Anchor Connecting Link.

All specifications in pounds and inches, unless otherwise stated.See Figures D-2 and D-3 for hairpin locking details.

Small End Chain Size

A B C D E F GNo. Inches mm

234567891011

3/4 - 15/161 - 1-3/161-1/4 - 1-9/161-5/8 - 22-1/16 - 2-3/82-7/16 - 3-1/83-3/16 - 3-5/83-11/16 - 3-3/43-13/16 - 44-1/16 - 4-1/4

19-2425-3032-4042-5152-6062-7981-9294-9597-102103-108

7-5/8 9-3/811-3/414-7/817-7/822-1/825-3/427-1/43537

5-3/16 6-9/16 8-1/810-1/412-5/1614-13/1616-1/217-1/822-1/224

1-1/21-13/162-5/1633-5/84-5/85-1/45-3/47-1/28

15/161-3/161-9/1622-3/83-1/83-5/83-7/84-3/45

1-1/41-1/21-7/82-1/233-3/44-7/85-1/86-1/26-7/8

2-1/42-19/323-1/43-15/164-3/45-7/85-7/86-1/47-1/28

15/161-5/161-9/16 x 1-3/42-15/16 x 2-3/82-7/16 x 2-7/83-3/8 x 3-1/84-3/8 x 44-7/8 x 5-3/85-1/86-1/8

Small End Chain Size

H J KProofTest

BreakTest

Weightper Link

(lbs)No. Inches mm

234567891011

3/4 - 15/161 - 1-3/161-1/4 - 1-9/161-5/8 - 22-1/16 - 2-3/82-7/16 - 3-1/83-3/16 - 3-5/83-11/16 - 3-3/43-13/16 - 44-1/16 - 4-1/4

19-2425-3032-4042-5152-6062-7981-9294-9597-102103-108

1-3/81-3/42-7/322-29/323-15/324-3/85-1/8 x 5-1/45-9/167-1/87-7/8

21/323/41-1/321-1/41-15/321-29/322-1/82-1/42-7/83

1-3/161-3/81-11/162-1/162-17/3233-1/83-1/44-1/44-3/8

74,000118,000200,500322,000447,000748,0001,021,0001,120,0001,298,0001,440,000

113,500179,500302,500488,000675,0001,128,0001,566,0001,750,0001,996,5002,220,000

7142860107208328520850920

D-11


Table D-6. Commercial End Link.

Chain Size LinkDiameter(Inches)

A

LinkLength(Inches)

B

LinkWidth

(inches)C

Weightper Link

(lbs)

ProofTest(lbs)Inches mm

11/16 - 3/413/16 - 11-1/16 - 1-1/41-5/16 - 1-1/21-9/16 - 1-3/41-13/16 - 22-1/16 - 2-1/42-5/16 - 2-1/22-9/16 - 2-3/42-13/16 - 33-1/16 - 3-3/83-7/16 - 3-3/43-13/16 - 4

17-1921-2527-3233-3840-4446-5152-5859-6466-7071-7678-8687-95

97-102

13/161-1/161-3/81-5/81-7/82-1/82-1/22-3/433-1/43-5/844-1/4

5-5/87-1/29-3/811-1/4131516-7/818-3/420-1/222-1/225-1/42830

2-7/83-3/44-7/85-3/46-5/87-5/88-3/49-3/410-3/411-5/81314-1/215-1/4

1.84.08.0

14.221.634.245.462.081.0

105.0148.0202.0258.0

48,00084,000

130,000185,000249,000322,000403,000492,000590,000693,000862,000

1,120,0001,298,000

D-12


Table D-7. Type I, Class 3 Safety Anchor Shackle (MIL-S-24214A (SHIPS)).

Size

(D)Minimum

Diameter

Bolt

(P)Minimum

Diameter

Inside

Eye (E)Maximum

Width between eyes (W) Length inside (L)

Width

Minimum(B)

Diameter

Outside

Eye (R)Maximum

Approx.

Weight

per 100ShacklesNominal

Tolerance (+) Nominal

Tolerance (+)

Inches Inches Inches Inches Inches Inches Inches Inches Inches Pounds

1/2

5/8

3/47/8

1

1-1/81-1/4

1-3/8

1-1/21-5/8

1-3/4

22-1/4

2-1/2

33-1/2

4

5/8

3/4

7/81

1-1/8

1-1/41-3/8

1-1/2

1-5/81-3/4

2

2-1/42-1/2

2-3/4

3-1/43-3/4

4-1/4

23/32

27/32

31/321-3/32

1-7/32

1-11/321-15/32

1-5/8

1-3/41-7/8

2-5/32

2-13/322-21/32

2-29/32

3-13/323-29/32

4-13/32

13/16

1-1/16

1-1/41-7/16

1-11/16

1-13/162-1/32

2-1/4

2-3/82-5/8

2-7/8

3-1/43-7/8

4-1/8

55-3/4

6-1/2

1/16

1/16

1/161/16

1/16

1/161/16

1/8

1/81/8

1/8

1/81/8

1/8

1/81/4

1/4

1-7/8

2-13/32

2-27/323-5/16

3-3/4

4-1/44-11/16

5-1/4

5-3/46-1/4

7

7-3/49-1/4

10-1/2

1315

17

1/8

1/8

1/41/4

1/4

1/41/4

1/4

1/41/4

1/4

1/21/2

1/2

3/43/4

3/4

1-3/16

1-1/2

1-3/42

2-5/16

2-5/82-7/8

3-1/4

3-3/84

4-1/2

5-1/45-1/2

6-3/4

7-3/89

10-1/2

1-3/8

1-7/8

2-1/82-3/8

2-5/8

2-7/83-1/4

3-1/2

3-3/44-1/8

4-1/2

5-1/45-3/4

6-1/4

6-3/48-1/2

9-1/2

82

158

280395

560

7851,120

1,520

1,9502,410

3,130

4,6305,650

9,400

14,50025,000

35,800

D-13


Table D-8. Type II, Class 3 Safety Chain Shackle (MIL-S-24214A(SHIPS)).

See Table D-9 for shackle strengths.

Size(D)

Minimum

Diameter

Bolt(P)

Minimum

Diameter

InsideEye (E)

Maximum

Width between eyes (W) Length inside (L)Diameter

OutsideEye (R)

Maximum

Approx.

Weightper 100

ShacklesNominalTolerance

(+) NominalTolerance

(+)

Inches Inches Inches Inches Inches Inches Inches Inches Pounds

1/2

5/8

3/47/8

1

1-1/81-1/4

1-3/81-1/2

1-5/8

1-3/42

2-1/2

33-1/2

4

5/8

3/4

7/81

1-1/8

1-1/41-3/8

1-1/21-5/8

1-3/4

22-1/4

2-3/4

3-1/43-3/4

4-1/4

23/32

27/32

31/321-3/32

1-7/32

1-11/321-15/32

1-5/81-3/4

1-7/8

2-5/322-13/32

2-29/32

3-13/323-29/32

4-13/32

13/16

1-1/16

1-1/41-7/16

1-11/16

1-13/162-1/32

2-1/42-3/8

2-5/8

2-7/83-1/4

4-1/8

55-3/4

6-1/2

1/16

1/16

1/161/16

1/16

1/161/16

1/81/8

1/8

1/81/8

1/8

1/81/4

1/4

1-5/8

2

2-3/82-13/16

3-3/16

3-9/163-15/16

4-7/164-7/8

5-1/4

5-3/46-3/4

8

910-1/2

12

1/8

1/8

1/41/4

1/4

1/41/4

1/41/4

1/4

1/41/2

1/2

3/43/4

3/4

1-3/8

1-7/8

2-1/82-3/8

2-5/8

2-7/83-1/4

3-1/23-3/4

4-1/8

4-1/25-1/4

6-1/4

6-3/48-1/2

9-1/2

76

156

262365

535

7271,020

1,3351,850

2,310

2,8504,110

8,450

12,30021,800

31,000

D-14


Table D-9. Mechanical Properties of Shackles (FED SPEC RR-C-271D).

Size (D) Working Load LimitProof Load(Minimum)

Breaking Load(Minimum)

Inches

Pounds Pounds Pounds

Grade A Grade B Grade A Grade B Grade A Grade B

3/161/45/163/87/161/29/165/83/47/811-1/81-1/41-3/81-1/21-5/81-3/422-1/42-1/22-3/433-1/24

6501,0001,5002,0003,0004,0005,0006,5009,50013,00017,00019,00024,00027,00034,00040,00050,00070,00080,000110,000120,000170,000240,000300,000

1,0001,5002,5004,0005,2006,6008,000

10,00014,00019,00025,00030,00036,00042,00060,00070,00080,000

100,000120,000160,000180,000220,000280,000350,000

1,4302,2003,3004,4006,6008,800

11,00014,30020,90028,60037,40041,80052,80059,40074,80088,000

110,000154,000176,000242,000264,000374,000528,000660,000

2,2003,3005,5008,800

11,44014,52017,60022,00030,800

41,0055,00066,00079,20092,400

132,000154,000176,000220,000264,000352,000396,000484,000616,000770,000

3,2505,0007,500

10,00015,00020,00025,00032,50047,50065,00085,00095,000

120,000135,000170,000200,000250,000350,000400,000550,000600,000850,000

1,200,0001,500,000

5,0007,500

12,50020,00026,00033,00040,00050,00070,00095,000

125,000150,000180,000210,000300,000350,000400,000500,000600,000800,000900,000

1,100,0001,400,0001,750,000

D-15


Figure D-1. Types of Chains and Connecting Links.

NOTE

See F igures D -2 and D -3 for N avydetachable locking ha irp in deta ils .

Lok-a-Loy Kenter

Pear-Shaped Detachable Link

NavyDetachable Link

Cast Stud Link

Welded Stud Link

Die Lock Link

Detachable LinkHairpin

D-16


Figure D-2. Detachable Link with Identifying Marks for Assembly.

NO

TE

S

1. I

NS

TR

UC

TIO

NS

FO

R G

RO

OV

ING

A

. R

EP

LAC

EM

EN

T T

AP

ER

PIN

:

A.

AF

TE

R IN

SP

EC

TIN

G A

ND

CLE

AN

ING

DE

TAC

HA

BLE

LIN

K,

IN

STA

LL T

AP

ER

PIN

WH

ICH

HA

S B

EE

N W

IPE

D W

ITH

OIL

.

B.

DR

IVE

TA

PE

R P

IN D

OW

N T

IGH

T U

SIN

G A

HA

MM

ER

&

AS

SE

MB

LIN

G P

UN

CH

.

C.

US

ING

A D

RIL

L 1/

32-I

NC

H L

ES

S IN

SIZ

E T

HA

N T

HE

HA

IR-

P

IN D

IAM

ET

ER

, DR

ILL

MA

RK

TH

E T

AP

ER

PIN

TH

RO

UG

H

ON

E O

F T

HE

HA

IRP

IN H

OLE

S IN

TH

E D

ETA

CH

AB

LE L

INK

.

D. D

RIV

E O

UT

TA

PE

R P

IN U

SIN

G H

AM

ME

R &

DIS

AS

SE

MB

LNG

P

UN

CH

. M

AC

HIN

E T

HE

GR

OO

VE

AT

DR

ILL

MA

RK

TO

TH

E D

IME

NS

ION

S S

PE

CIF

IED

IN C

HA

RT

BE

LOW

.

GR

OO

VE

FO

R H

AIR

PIN

TO

BE

LOC

AT

ED

AF

TE

R A

SS

EM

BLI

NG

LIN

K W

ITH

RIG

HT

-HA

ND

CO

UP

LIN

G &

LE

FT

-HA

ND

C

OU

PLI

NG

, AN

D D

RIV

ING

T

HE

TA

PE

R P

IN D

OW

N T

IGH

T.

D

TAP

ER

PIN

C2

A

DE

TAC

HA

BLE

LIN

K

CE

B

SE

CT

ION

C-2

SE

CT

ION

VIE

W S

HO

WN

WIT

H

LIN

K F

ULL

Y A

SS

EM

BLE

D

LIN

K S

IZE

3/4

HS

7/8

HR

S

1 H

S 1

1/8

HS

1 1/

4 H

S 1

1/2

HS

1 5/

8 H

S 1

3/4

HS

2

2 1/

8 -

2 2

3/8

2 1/

2 -

3 1/

8 2

3/4

HD

3H

D

3 1/

4 -

3 1/

2 3

1/2

HD

“A”

.12

.15

.18

.28

.28

.34

.34

“ØB

”

.09

.12

.15

.25

.25

.31

.31

“C”

.366

.438

.630

.768

1.08

2

1.07

6

1.34

6

“D”

.109

.140

.171

.265

.265

.327

.327

“E”

.12

.15

.18

.28

.28

.34

.34

D-17


Figure D-3. Typical Method for Modifying Detachable Chain Connecting Links for Hairpin Installation.

FG

E

SE

CT

ION

C-2

SE

CT

ION

VIE

W S

HO

WN

WIT

H

LIN

K F

ULL

Y A

SS

EM

BLE

D

D

TAP

ER

PIN

GR

OO

VE

FO

R H

AIR

PIN

TO

BE

LOC

AT

ED

AF

TE

R A

SS

EM

BLI

NG

LIN

K W

ITH

RIG

HT

-HA

ND

CO

UP

LIN

G &

LE

FT

-HA

ND

C

OU

PLI

NG

, AN

D D

RIV

ING

T

HE

TA

PE

R P

IN D

OW

N T

IGH

T.

B

AC

C2

DE

TAC

HA

BLE

LIN

KL

INK

SIZ

E“A

”“B

”“C

”“D

”“Ø

E”

“F”

“G”

3/4

1/4

19/

649/

323/

321/

1615

/64

3/32

7/8

19/6

45

/16

5/16

1/8

3/32

7/32

1/8

111

/32

3/8

3/8

1/8

3/32

9/32

1/8

1 1/

83/

87

/16

11/3

21/

83/

3211

/32

1/8

1 1/

427

/64

15/

3215

/32

5/32

1/8

11/3

25/

321

3/8

15/3

23

3/64

33/6

45/

321/

825

/64

5/32

1 1/

21/

23

7/64

9/16

5/32

1/8

29/6

45/

321

5/8

35/6

43

9/64

39/6

45/

321/

831

/64

5/32

1 3/

419

/32

41/

645/

87/

323/

1629

/64

7/32

1 7/

811

/16

45/

6411

/16

3/16

5/32

35/6

43/

162

3/4

49/

643/

47/

323/

1637

/64

7/32

2 1/

813

/16

13/

1613

/16

1/4

7/32

19/3

21/

42

1/4

7/8

7/8

7/8

1/4

7/32

21/3

21/

42

3/8

29/3

27

/87/

89/

321/

45/

89/

322

1/2

15/1

67

/87/

89/

321/

45/

89/

322

5/8

11

15/

169/

3223

/32

5/16

2 3/

427

/32

1 1

/16

1 1/

3211

/32

5/16

3/4

11/3

22

3/4

HD

11

3/6

41

3/32

11/3

25/

1647

/64

11/3

22

7/8

1 1/

161

3/3

21

3/32

11/3

25/

1625

/32

11/3

23

1 1/

81

9/6

41

1/8

11/3

25/

1653

/64

11/3

23

HD

1 1/

81

1/8

1 1/

811

/32

5/16

13/1

611

/32

3 1/

81

5/32

1 1

1/64

1 3/

163/

811

/32

53/6

43/

83

1/4

1 7/

321

7/3

21

7/32

13/3

23/

827

/32

13/3

23

3/8

1 5/

161

11/

321

5/16

13/3

23/

8 31

/32

13/3

23

1/2

1 11

/32

1 1

3/32

1 5/

1613

/32

3/8

1 1/

3213

/32

3 1/

2 H

D1

1/2

1 1

3/32

1 3/

813

/32

3/8

1 1/

3213

/32

3 5/

83

3/4

1 13

/32

1 1

5/32

1 3/

813

/32

3/8

1 3/

3213

/32

3 7/

8 4 4

3/4

1 13

/16

1 7

/81

13/1

617

/32

1/2

1 3/

817

/32

NO

TE

S

1.

INS

TR

UC

TIO

NS

FO

R G

RO

OV

ING

A

. R

EP

LAC

EM

EN

T T

AP

ER

PIN

:

A.

AFT

ER

INS

PE

CT

ING

AN

D C

LEA

NIN

G D

ETA

CH

AB

LE L

INK

,

IN

STA

LL T

AP

ER

PIN

WH

ICH

HA

S B

EE

N W

IPE

D W

ITH

OIL

.

B.

DR

IVE

TA

PE

R P

IN D

OW

N T

IGH

T U

SIN

G A

HA

MM

ER

&

AS

SE

MB

LIN

G P

UN

CH

.

C.

US

ING

A D

RIL

L 1/

32-

INC

H L

ES

S IN

SIZ

E T

HA

N T

HE

HA

IR-

P

IN D

IAM

ET

ER

, DR

ILL

MA

RK

TH

E T

AP

ER

PIN

TH

RO

UG

H

ON

E O

F T

HE

HA

IRP

IN H

OLE

S IN

TH

E D

ETA

CH

AB

LE L

INK

.

D. D

RIV

E O

UT

TA

PE

R P

IN U

SIN

G H

AM

ME

R &

DIS

AS

SE

MB

LNG

P

UN

CH

. M

AC

HIN

E T

HE

GR

OO

VE

AT

DR

ILL

MA

RK

T

O T

HE

DIM

EN

SIO

NS

SP

EC

IFIE

D IN

CH

AR

T B

ELO

W.

D-18


Appendix E

STOPPERS

E-1 Introduction

The term “stopper,” as used in seamanship,describes a device or rigging arrangementthat is used to temporarily hold a part of run-ning rigging or ground tackle that may comeunder tension. The stopper is an indispens-able tool in a towing operation.

E-2 Types of Stoppers

There are many types of stoppers and meth-ods of attaching them to the tension mem-bers. There is no single “best” type of stop-per for all situations. For the three basictypes of tension members—chain, fiber line,and wire rope—the following stoppers arerecommended:

• Chain. The attachment to the tensionmember should be made by means of asuitably sized, jaw-type chain stopper(see Figure 4-18).

• Fiber Line. Fiber line always should bestopped off with fiber stoppers.

• Wire Rope. Wire rope should bestopped off with a carpenter stopperSee Figure 4-19), Klein grip, chain, orfiber stopper using Kevlar.

Most stoppers cannot be released under loadand require the held line to be heaved in toslack the stopper and allow its removal. Somestoppers, however, such as the pelican hookand carpenter stopper, can be released whenunder load. In some cases, it may be possibleto use a combination of two stoppers toachieve this capability, for example, attachinga pelican hook to a fiber stopper (the fiberstopper holds the line and the pelican hookholds the stopper, allowing a quick release.)

E-3 Prevention of Damage

When passing a stopper, prevention of dam-age to the tension member is a major consid-eration, second only to safety of personnel. Ifthe hawser is damaged, the towing ship is es-sentially out of action. Properly using a stop-per on a towing hawser entails considerablymore than merely passing the stopper. It re-quires very close coordination between theConning Officer on the bridge and the Boat-swain’s Mate in charge of passing the stopperon the fantail.

During the period when the stopper is in useon the towing hawser or pendant, the Con-ning Officer should not increase speed or rad-ically change course without first notifyingthe afterdeck and reaching concurrence withthe Afterdeck Supervisor that it is safe to doso. Direct communication between the deckwork area and the bridge is mandatory. TheConning Officer should also be well versed inthe use of stoppers, especially concerningtheir applications and limitations.

E-4 Stopping Off a Wire Towing Hawser

If possible, a properly fitted carpenter stoppershould always be used when stopping off awire rope towing hawser. See NAVSHIPS0994-004-8010 Carpenter Stopper, Opera-tion and Maintenance Instruction (Ref. AD).

WARNING

Never pass a stopper on a ten-sion member that is under astrain greater than the safeworking load of the stopper, oron a tension member that mightbe subjected to a heavier load-ing condition while the stopperis in place.

E-1


In a situation where a carpenter stopper is notreadily available, the hawser can be stoppedoff with a chain. If using a chain stopper, bevery careful not to damage the hawser (seeFigure E-1).

E-5 Synthetic Line

In recent years, synthetic fiber line has re-placed virtually all large natural fiber line inthe Navy. Synthetic fiber has many goodqualities, such as its superior strength andelasticity. Its prime weakness, however, is itssusceptibility to physical damage. It is veryeasily cut by sharp objects, melted by friction,and abraded by rough surfaces. All threetypes of damage can occur from the action ofa poorly passed stopper.

When stopping off a synthetic towing hawser,a synthetic fiber stopper should always beused.

E-6 Stopper Breaking Strength

Ideally, the strength of the passed stopperwould be equal to or greater than the strengthof the tension member, thus eliminating thestopper as the weak

link in the system. This condition is easy toachieve when stopping off relatively smalllines such as fiber boat falls.

The prime factor limiting breaking strength ofa large stopper is the physical size that can behandled manually by the deck seaman. Astopper of ½-inch chain can be passed fairlyeasily and one of ¾-inch chain can be passedwith some difficulty. If, however, one were totry to match the breaking strength of a largetowing hawser of 2- to 2½-inch wire, a stop-per of 1½-inch or 2-inch chain would be re-quired. From an engineering point of view thenumbers would match up, but the seamanwould be faced with an impossible task.

In cases of heavy rigging, the stopper oftenbecomes the weak link. Thus, all personnel

Figure E-1. Crisscross Chain Stopper.

E-2


Figure E-2. Typical Stopper.

E-3


Figure E-3. Half Hitches.

Figure E-4. Crisscross Fiber Stopper.

E-4


who are involved in the towing hawser/stop-per passing procedure must be aware of in-herent dangers.

E-7 Fiber Stoppers

Fiber stoppers are the simplest and most com-monly used type of stopper (see Figures E-2through E-5). One version, called a rat tailstopper, is merely a length of fiber line withan eye in one end and the section of the stop-per that makes contact with the tension mem-ber flattened. When using a three-strand line,a section is flattened by passing a seizing, un-laying the line, and then weaving the lineback together in a three-strand braid. In thecase of double-braided line, slip the coverback and remove a section of the core to flat-ten the stopper.

Stoppers made of Kevlar are now availableand are acceptable for use on fiber line.

E-8 Stopper Hitches

A number of methods can be used to attachthe stopper to the tension member:

• A rolling hitch backed up with halfhitches (see Figure E-2)

• A long series of half hitches, known asa crossover or Chinese stopper (see Fig-ure E-3)

• A series of crisscrosses formed byweaving the stoppers over and underthe tension member—this is the mostpreferred method (see Figures E-1 andE-4)

• Two long series of half hitches formedby half hitching a double stopper to thehawser (see Figure E-5)

• Any desired number or combination ofthe above.

Again, there is no universal “best” stopperhitch. The decision about which hitch ar-rangement to use depends on the size andcomposition of the line to be stopped, thesize and composition of the stoppers avail-able, and the judgment of the Boatswain’sMate in charge.

Figure E-5. Double Half-Hitch Stopper.

E-5


E-9 Securing the Passed Stopper

When securing a passed stopper to a part ofrelatively small, low-tension rigging, such asa boat fall, the end of the stopper is usuallyheld in place by hand. To secure a passedstopper to a large tension member, such as atowing hawser, the ends of the stoppershould be securely seized to the hawser withsmall stuff.

E-10 Setting the Stopper

Once the stopper is in place and all personnelare safely out of the way, the tension membershould be very slowly and carefully eased out.

This should continue until a determinationcan be made as to whether the stopper is hold-ing or not. This critical determination is nor-mally made by the Boatswain’s Mate.

If the stopper is slipping, or shows any indi-cation that it might slip, the stopper should beremoved and reattached.

• The Conning Officer must be madeaware of any overloading of a towinghawser stopper so that corrective ac-tion is taken, such as easing the ten-sion by slowing or stopping the ship.

E-11 Releasing the Stopper

Some stoppers, such as the carpenter stopper,chain stopper, and pelican hook, are designedto be released under tension. These devicesall have hinge-type grabs that can be releasedby striking a pin with a sledge. This pin doesnot see full line tension and can be removedunder load.

Fiber stoppers and stopper hitches cannot bereleased under load except by cutting. This isnot recommended except in an emergency. (Itmay be prudent to rig a block of wood as astriking surface so the stopper may be cutwith a fire axe instead of a knife. This shouldbe done prior to setting the stopper.)

• Normal release of stoppers should beunder no tension. The stopped lineshould be heaved in to allow the stop-per to be slacked. The stopper can thenbe removed safely by personnel. Thismethod is recommended for all stop-pers, including quick release types.

WARNING

Releasing a stopper under loadcan cause shock loading in thestopped line. Personnel shouldbe kept clear of any potentialsnapback.

WARNING

Carpenter stoppers, once set,may retain tension even afterwire is slacked. These stoppersshould always be opened care-fully.

E-6


Appendix F

TOWING HAWSER LOG

F-1 Introduction

The purpose of this appendix is to establishthe requirement for towing ships to keep aTowing Hawser Log. Entries in this log arecritical when evaluating past hawser usage,evaluating the present condition of the haw-ser, and making decisions concerning re-placement. The log provides the Command-ing Officer with a documented reference touse when determining the readiness of thehawser. Since the condition of the hawsermay not be apparent, even to the experiencedoperator, the record of usage can be a deci-sive factor in evaluating operational readinessand overall system safety. This appendix re-places the NAVSEAINST 4740 series regard-ing hawser logs.

F-2 Background

Historically, fewer towline component fail-ures have occurred on ships where close at-tention has been paid to the condition and his-to ry o f the hawser and o the r t ens i lecomponents of the towline. Life of towlinecomponents depends less on age than on careand use. Fiber lines of all types, includingnatural and synthetic fiber, deteriorate withage, exposure, and usage. The fiber core inwire ropes, particularly if it is natural fiber,also deteriorates with age. Old wires with nodocumentation should be treated with suspi-cion.

F-3 Discussion

In some instances when hawsers and othercomponents have failed, it was impossible toascertain usage, manufacture, and installation

data because a log had not been kept. Thislack of data precluded a meaningful analysisof the failure.

NSTM CH-613 (Ref. F) describes the fabri-cation, conditions of use, care, and preserva-tion of wire rope, fiber rope, and cordage. Inaddition, the Wire Rope Users' Manual (Ref.C) and handbooks and catalogs published bymajor wire and rope manufacturers are use-ful.

Keeping a hawser log is mandatory for alltowing ships. Selection and identification ofother components that should be similarlylogged and administered is left to the discre-tion of the Commanding Officer. Ships mayalso find it beneficial to keep a similar log onmooring lines. Salvage ships may also find itprudent to keep logs on beach gear compo-nents, chain, and connecting hardware.

F-4 Log

Salvage ships, fleet tugs, and surface shipscarrying emergency towing hawsers and en-gaging in tow-and-betowed operations shallmaintain a Towing Hawser Log in the formatof Attachment A to this appendix. Ships mayalso keep similar logs on other towline com-ponents.

The log shall record a comprehensive historyof all towing hawsers on the ship, includingthe main wire rope hawser, all synthetic haw-sers, and target towing hawsers.

It is the responsibility of the command tomaintain the log. Periodic review is mandato-ry. Type Commanders should include the re-quirement for keeping hawser logs as acheck-off item in their Operational Readinessand Administrative Inspection Lists.

F-5 Failures

Ships experiencing failure of hawsers andother logged towline components should

F-1


advise NAVSEA (Attention SEA 00C andSEA 03P8) and provide details that can beused for technical evaluation.

Whenever a hawser or other logged compo-nent breaks under suspicious conditions, savethe broken ends and at least twelve feet ofgood rope (or three links in the case of chain)on each side of the break. Serve the broken

ends to prevent unlaying of fiber line or oilthem to prevent corrosion of wire rope. Logand describe details of the break. Save frag-ments and pieces for analysis. Also recordnames of any witnesses to the failure. If thebreak occurs in the vicinity of an end fitting,the end fitting also should be sent for test andevaluation, with the broken end wrapped inplastic.

F-2


Attachment A to Appendix F

Towing Hawser Log

1. The Towing Hawser Log is used to record data about both wire rope and fiber line hawsers. Itmay be used to record data about other towline components as well. The Towing Hawser Logshould be kept in a standard record book. A separate book or separate section of the samebook should be kept for each component.

2. The log for any towing hawser or other component consists of three parts: New Rope Entry,Operations Entry, and Post-Operations Entry.

PART A: New Rope (Hawser or Component) Entry

Record data as follows:

1. Date and place of installation.

2. Identification of installer (ship’s force, yard, etc.).

3. Method of installation. For example, was the line put on drum under back tension? If so, whatwas tension? How was tension applied? If not applied, what was done to ensure a tight spool?

4. Comprehensive description of new item. For wire rope and fiber line, include material (suchas IPS, EIPS, or stainless for wire; nylon or polyester for fiber); size (rope diameter for wire;circumference for fiber line), and breaking strength. Ensure that the Federal Stock Numberand any other specifications are included.

5. Details of line construction as found on tag attached or tacked onto shipping reel. Include theactual tag in log if possible, or attach a photocopy.

6. Manufacturer of rope or line (obtain from tag or shipping reel).

7. Date of manufacture of basic rope/line/chain. Also include dates of any rigging loft work.

8. Source of rope (such as NSC or private supplier).

NOTE

When measuring any rope length and identifying (mapping) a spot alongthe hawser, always measure back from the original outboard end. Do thesame if hawser is end-for-ended, but carefully measure the entire lengthwhen end-for-ending and precisely log the conversion technique to be usedin subsequent mapping. If the hawser is shortened to install a new end fit-ting, use the original measuring system; that is, measure as if it were still allthere, but make a note in the comments section that the hawser has beenshortened for installation of a new end fitting.

F-3


9. Details of end fittings at both ends. Provide details of splices and servings for synthetic haw-sers and springs. Include photos.

10. Record any other observations of the hawser or component, such as degree of lubrication, lev-el of rust, discoloration, or other damage. Include observations from internal inspection ofrope or line.

PART B: Operations Entry

Record for every employment of the hawser or component:

1. Description of the basic employment, for example, towing an FFG or hauling on a wreck.

2. Duration of use (days/hours).

3. Scope of tow hawser used (if varied, cite maximum and minimum scopes).

4. Maximum strains experienced by hawser or component. This may come from towing machineor other strain measuring instrumentation. Include notations of weather on trip.

5. A map and complete description of all chafe, bearing or nip points and any chafing gear used.Include photos when practical.

6. Description of use of carpenter stopper, chain stopper or other hardware on rope. For example,where was stopper placed on rope (lengthwise)?

7. For fiber line hawsers, include a description of how it was secured on towing vessel: for ex-ample, wrapped around main traction sheave/drum, stopped on the H-bitts, etc.

8. Minimum depth of water traversed. For example, did hawser drag bottom?

9. If hawser was passed to a wreck, include a description of how it was passed. Was the hawserfloated or dragged across the bottom? If the hawser was dragged, how far was it dragged, andacross what type of bottom was it dragged?

10. Other experiences of note, for example surging against hawser/components or fouling onrocks or ship’s appendages.

11. Between-use maintenance: type of lubricant applied, how applied, and by whom applied.

12. Respooling method (as listed in Part A-3).

PART C: Post-Operations Entry

Record after every use:

1. Specific inspection of hawser for wear points such as carpenter or chain stopper wear points,caprail/nipping chafe area, shock bearing points, sheaves and fairleads, and so forth. Includephotographs.

2. Quantification of wear:

a. General and wire rope. Include count of “fish hooks” and record and identify (map) spots.Count fish hooks per strand lay. Count all broken wires, not just those that protrude from

F-4


the rope. Record maximum number of broken wires per lay (total) and maximum num-ber of broken wires per strand lay. Include information on any “birdcaging,” kinking,broken surface wires, and surface wire flattening. Indicate surface corrosion. Includephotographs. Record and map any instance of burying. Periodic inspection/maintenanceof hawser or components, which includes opening the lays and internal inspection, neednot be performed after every employment, but when undertaken, it should be logged.When lubrication is performed, carefully log stock number and manufacturer’s data onlubricant as well as who performed the maintenance and inspection.

b. Fiber line. Include information on surface chafing and abrasion wear, kinking, or anyother visible damage. Include photographs.

c. Chain. Pay particular attention to the link bearing points (the “grip” area). Pay specialattention to places along the chain where it passed through or bore against chocks orfairleads. In these latter places a straight edge should be laid against the flat face of thelink to ensure that the link is not bent in this plane. Any bending is to be reported as fail-ure and requires replacement.

d. Joining links and shackles of all kinds. Inspect the mechanical joints and screw threads.In the case of safety shackles, measure the mortise to ensure that the bow is not sprung.If sprung, dispose of the shackle. Ensure that all detachable link pieces have serial num-bers and are matched in sets. Ensure also that the hairpins fit snugly.

3. General comments. Include as a minimum a general post-f observation of hawser, compo-nent, and end fitting.

F-5



F-6


Appendix G

CALCULATING STEADY STATE TOWLINE TENSION

This appendix provides a method for calculat-ing the towing resistance of various ships andcraft. The data required to calculate resistancefor self-propelled ships, dry docks, and barg-es come from different sources; therefore,each category is discussed separately.

Calculating tow resistance is often an itera-tive process. Starting with the ship or craft tobe towed, resistance is usually computed forseveral assumed towing speeds and for differ-ent wind and sea conditions. The resultingvalues are then compared to the capabilitiesof available tugs.

Next, the towing connection elements (bri-dles, chain pendants, etc.) are selected, tow-ing hawser length determined, catenarychecked, and towline hydrodynamic resis-tance estimated. This process may result in atowing ship pull requirement or total hawsertension that will require an adjustment to theassumed tow speed.

G-1 Self-Propelled Surface Ships

The following method combines hull, propel-ler, wind, and sea state resistances into onecalculation for determination of the total towresistance of a ship. Methods for calculatingthe resistance of the towline are discussed inChapter 3 (see Section 3-4.1.2 and Table3-1). Use Table G-1 as a worksheet for deter-

mining tow resistance, following the step-by-step procedures below.

Use Table G-2 for Items 4 Through 9

Item 1

Identify the ship class under consideration, orselect a class as close as possible.

Item 2

Select tow speed (VTOW), in knots.

Item 3

Select tow course, in degrees.

Item 4

List the displacement in long tons (∆). If theship is known to be lighter than full load, ad-just the full load figures from the table ac-cordingly.

Item 5

List frontal windage area (AT) in square feet.Estimate this number for ships not listed.Ships at lighter than full load condition willhave increased windage area than that listedin Table G-2.

Item 6

List wind drag coefficient (CW).

Item 7

List projected area of all propellers (AP) insquare feet. This value assumes that propel-lers are locked. If propellers are trailing, re-duce this value by one-half. If propellers havebeen removed, use a value of zero.

NOTE

The coefficients used to calculateresistance account for unit conver-sion. If recommended units areused, these equations will yield re-sistance in pounds.

G-1


Item 8

List the curve number for hull resistance.(See Section G-1.1.)

Item 9

List curve number for sea state resistance.(See Section G-1.2.)

Item 10

The expected sustained wind speed should beused when calculating towline tensions. Theestimate should be conservative and shouldaccount for anticipated changes in weather.

Item 11

With the aid of Table , determine the Beau-fort wind force number. This number is basedon expected or measured wind velocity or ob-servation of the sea state (Item 10).

Item 12

List relative wind speed (VR) in knots. (If un-known, assume worst condition, that is, towspeed plus true wind speed.)

Item 13

Select a heading coefficient (K). If the rela-tive wind is dead ahead, use 1.0. If the rela-tive wind is 15 to 45 degrees off the bow, use1.2. For 45 to 90 degrees relative wind, use0.4. There is higher wind resistance to aheadmovement when the wind is slightly off thebow than when directly ahead, because of thelarger ship area presented to the wind. As thewind veers farther aft, however, the wind ef-fect on the ahead direction falls off faster thanthe increase of the area presented to the wind.(See Section G-1.3 for additional guidance.)

Item 14

Calculate the wind resistance (RW) by multi-plying 0.00506 by the frontal windage area(item 5) by the wind drag coefficient (item 6)by the relative wind speed (item 12) squared

by the heading coefficient (item 13). (SeeSection G-1.3).

RW = 0.00506 x (AT) x (CW) x (VR)2 x (K)

Item 15

In Figure G-6, locate the curve identified initem 8 and compare it to the tow speed (item2). The point where these two values intersectis the value for RH/∆. (See Section G-1.1.)

Item 16

Calculate the hull resistance (RH) by multi-plying 1.25 by RH/∆ (item 15) by the displace-ment (item 4). (The factor 1.25 accounts forhull roughness and other variables).

RH = 1.25 x (RH/∆) x (∆)

Item 17

In Figure G-7, locate the curve identified initem 9 and compare it to the Beaufort windforce number identified in item 11. The pointwhere these two values intersect is the seastate resistance (RS). (See Section G-1.2.)

Item 18

Calculate the propeller resistance (RP) bymultiplying 3.737 by the projected area of thepropellers (item 7) by the tow speed (item 2)squared. (See Section G-1.4.)

RP = 3.737 x (AP) x (VTOW)2

Item 19

Calculate the total steady-state tow resistance(RT) by adding the four resistance values(items 14, 16, 17, and 18).

RT = RW + RH + RS + RP

Item 20

Using Table 3-1, estimate the hydrodynamicresistance of the towline (RWIRE). If the sizeof the tow hawser is not yet determined, esti-mate the towline resistance to be 10 percentof the tow resistance (item 19).

G-2


Item 21

To calculate horizontal tow hawser tension,add the tow resistance (item 19) to the towhawser resistance (item 20).

R = RT + RWIRE

Figures G-1 through G-4 contain sample cal-culations.

G-1.1 Hull Resistance Curves

Hull resistance curves are plotted on a per-ton-displacement basis. Thus they are appli-cable to similar hull shapes. Hull shapes arelargely influenced by speed/length ratio:

Assume that it is necessary to estimate thetowing resistance of a large tanker with thefollowing design characteristics:

Displacement: 110,000 long tons

Length: 850 feet

Speed: 15 knots

Speed/length ratio 0.51

NAVSEA 00C can provide assistance in lo-cating a hull of similar dimensions. In thiscase, the T-AGM 20 is similar; with a speedof 14 knots, a length of 595 feet and, there-fore, a speed/length ratio of 0.57. This isclose enough for the purpose intended. InFigure G-6, use curve 5 (from Table G-2) forthe T-AGM 20 at the assumed tow speed andread resistance per ton. For instance, at 6knots, read 0.75 lbs. resistance per ton. If thetanker is at full load, its hull resistance is 1.25x 0.75 x 110,000 = 103,125 lbs. Even withoutestimating propeller, wind, or sea state resis-tance, it is apparent from Figure 6-1 that tow-ing this ship at this speed is impractical forNavy tow ships except the T-ATF. Whileworking on curve 5, it will save time to alsocompute the smooth hull resistances for 5, 4,and 3 knots as well, for future use. The result-ing smooth hull resistance values are 66,000,42,600 and 20,600 pounds, respectively.

G-1.2 Additional Resistance Due to Waves

Note that there is no method provided for es-timating the effect of other than head seas.Under the more usual sea conditions wherethe tug has total freedom in course-setting,the effect of the waves on the tow and tug ismodest. Under the more strenuous cases, thetug will have to set a course into the seas tomaintain stability as well as to relieve dynam-ic effects on the hawser. It is unlikely that thetug will be able to take advantage of follow-ing seas under the more strenuous cases.

For the larger ships (represented by curves 2and 3 in Figure G-6), the added resistance issignificant at the higher sea states. Underthese conditions, however, the tug itself mayexperience difficulty and may simply have toreduce power to maintain steerageway. Speedover the ground of the tug and tow may wellbe sternward in this case, and is perfectly ap-propriate.

Note 1: The method of estimating the addedresistance from waves at certain tow speeds isnot well developed. The data presented hereare developed from stationary (anchored) the-ory and include no correction for tow courseor speed. From the shape of the curves, it canbe seen that there is little effect in seas up toState 4 or 5. The added resistance increasesrapidly in heavier seas, which usually requirethe tow to head into the seas. Furthermore,the effect of the additional speed of the tow issmall compared to the speed of the seas inthis case and can be ignored. Therefore, theamount of error introduced by assuming headseas and neglecting tow speed is small, and,in any event, provides a conservative answerfor most tow courses.

Following wind and seas will reduce the towresistance. However, the dynamic effects ofship motions on the tow hawser may precludetowing downwind under strenuous sea condi-tions (see Appendix M). Likewise, stability of

V

L-------

G-3


Table G-1. Calculation of Steady State Towing Resistance.

SH

IP: _

____

____

____

____

____

____

____

____

____

____

____

____

CA

LCS

BY

: ___

____

____

____

____

____

____

____

____

____

____

____

____

___

Item

Des

crip

tion

Sym

bol

Uni

tsS

ourc

e

1S

hip

Cla

ss (

AE

, CV,

etc

.)

2To

w S

peed

VT

OW

Kno

ts

3To

w C

ours

eγ

Deg

rees

4To

w D

ispl

acem

ent

∆Lo

ng to

nsTa

ble

G-2

5F

ront

al W

inda

ge A

rea

AT

Sq.

feet

Tabl

e G

-2

6W

ind

Dra

g C

oeffi

cien

tC

WTa

ble

G-2

7To

tal P

roje

cted

Are

a of

Pro

pelle

rsA

PS

q. fe

etTa

ble

G-2

8C

urve

Num

ber

for

Hul

l Res

ista

nce

Tabl

e G

-2

9C

urve

Num

ber

for

Sea

Sta

te R

esis

tanc

eTa

ble

G-2

10Tr

ue W

ind

Spe

edV

win

dK

nots

11B

eauf

ort N

umbe

rTa

ble

G-3

12R

elat

ive

Win

d S

peed

VR

Kno

ts

13H

eadi

ng C

oeffi

cien

tK

Sect

ion

G-1

14W

ind

Res

ista

nce

RW

Pou

nds

RW

= 0

.005

06(A

T)(

CW

)(V

R)2 (

K)

15R

esis

tanc

e F

acto

rR

H/ ∆

Figu

re G

-6

16H

ull R

esis

tanc

eR

HP

ound

sR

H =

1.2

5(R

H/ ∆

)(∆ )

17S

ea S

tate

Res

ista

nce

RS

Pou

nds

Figu

re G

-7

18P

rope

ller

Res

ista

nce

RP

Pou

nds

RP =

3.7

37(A

P)(

VT

OW

)2

19To

tal S

tead

y S

tate

Tow

Res

ista

nce

RT

Pou

nds

RT =

RW

+ R

H +

RS +

RP

20To

w H

awse

r R

esis

tanc

eR

WIR

EP

ound

sTa

ble

3-1

or 1

0% o

f RT

21To

tal T

ow H

awse

r Te

nsio

nR

Pou

nds

R =

RT +

RW

IRE

G-4


G-5

Figure G-1. Example 1 - Scenario.

Towed ship: FFG 7

Wind @ 20 knots

The predicted tow resistance is 74486 lbs. Assuming an 2000-ft 2 1/4-inchhawser w ith 90 feet of 2 1/4-inch chain pendant, the tow hawser resistancewill be approxim ately 2700 lbs. The total tug requirement is 77186 lbs.Inspection of Figure 3-3 shows that the T-ATF 166, and ARS 50Classes can perform this tow. The other tugs can tow at a slow er speed.

Full load displacem ent - 3585 LTDesired speed - 8 ktsCourse - 000 TRelative w ind: 28 kts @ 000 R

F F G 7

Example 1. Scenario


Figure G-2. Example 1 - Worksheet.

SH

IP:

C

ALC

S B

Y:

LT. M

AR

K F

IVE

Item

Des

crip

tion

Sym

bol

Uni

tsS

ourc

e

1S

hip

Cla

ss (

AE

, CV,

etc

.)F

FG-7

2To

w S

peed

VT

OW

Kno

ts8

64

3To

w C

ours

eγ

Deg

rees

4To

w D

ispl

acem

ent

∆Lo

ng to

nsTa

ble

G-2

3585

3585

3585

5F

ront

al W

inda

ge A

rea

A TS

q. fe

etTa

ble

G-2

2200

2200

2200

6W

ind

Dra

g C

oeffi

cien

tC

WTa

ble

G-2

0.7

0.7

0.7

7To

tal P

roje

cted

Are

a of

P

rope

llers

AP

Sq.

feet

Tabl

e G

-217

017

017

0

8C

urve

Num

ber

for

Hul

l R

esis

tanc

eTa

ble

G-2

22

2

9C

urve

Num

ber

for

Sea

Sta

teR

esis

tanc

eTa

ble

G-2

11

1

10Tr

ue W

ind

Spe

edV

win

dK

nots

2020

20

11B

eauf

ort N

umbe

rTa

ble

G-3

55

5

12R

elat

ive

Win

d S

peed

VR

Kno

ts28

2624

13H

eadi

ng C

oeffi

cien

tK

Sect

ion

G-1

1.0

1.0

1.0

14W

ind

Res

ista

nce

RW

Pou

nds

RW

=0.

0050

6(A

T)(

CW

)(V

R)2 (K

)61

0952

6844

88

15R

esis

tanc

e F

acto

rR

H/ ∆

Figu

re G

-64.

42.

91.

7

16H

ull R

esis

tanc

eR

HP

ound

sR

H=1

.25(

RH

/ ∆)(

∆ )19

718

1299

676

18

17S

ea S

tate

Res

ista

nce

RS

Pou

nds

Figu

re G

-780

0080

0080

00

18P

rope

ller

Res

ista

nce

RP

Pou

nds

RP=

3.73

7(A

P)(

VT

OW

)240

659

2287

010

165

19To

tal S

tead

y S

tate

Tow

R

esis

tanc

eR

TP

ound

sR

T=

RW

+ R

H +

RS +

RP

7448

649

134

3027

1

20To

w H

awse

r R

esis

tanc

eR

WIR

EP

ound

sTa

ble

3-1

or 1

0% o

f RT

2700

2200

1250

21To

tal T

ow H

awse

r Te

nsio

nR

Pou

nds

R=

RT +

RW

IRE

7718

651

334

3152

1

G-6


Table G-2. Characteristics of Naval Vessels (sheet 1 of 3).

“e” represents best estimate

∆ AT CW AP

CLASS DESCRIPTION FUL

L L

OA

D

DIS

PL

AC

EM

EN

T

(L. T

ON

S)

LIG

HT

SH

IP F

RO

NT

AL

WIN

DA

GE

AR

EA

(Ft

)

WIN

D C

OE

FFIC

IEN

T

TO

TA

L P

RO

JEC

TE

D

AR

EA

OF

AL

L

PRO

PE

LL

ER

S (

Ft)

CU

RV

E F

OR

HU

LL

RE

SIST

AN

CE

SEE

FIG

UR

E G

-6

CU

RV

E F

OR

WA

VE

RE

SIST

AN

CE

SEE

FIG

UR

E G

-7

BB 61-64

CVN 74-77

CVN 68-73,65

CVN 59-64, 66, 67

CV 41-43

CV 14-34

CVS 9-39

CA 68-124

CA 134-148

CGN 38-41 (DLGN)

CGN 36-37 (DLGN)

CGN 35 (DLGN)

CGN 25 (DLGN)

CGN 9

CG 47-56

CG 26-34 (DLG)

CG 16-24 (DLG)

CG 10-12

DDG 51-53

DDG 993-996

DDG 37-46 (EX-DLG 6/9)

DDG 2-24

DDG 31-34

DD 963-992, 997

DD 931-951

DD 445 CLASS

DD 692 CLASS

DD 710 CLASS

DE 1006 CLASS

FFG 7-61

FFG 1-6 (DEG)

FF 1052-1097 (DE)

FF 1040-FF 1051 (DE)

LCC 19-20

LHA 1-5

LPH 2-12

LPD 4-15

LPD 1-2

LSD 41-48

LSD 36-40

LSD 28-35

LST 1179-1194

LST 1171-1178

LST 47-1088

LKA 113-117

MCM 1-14

MHC 51

MSO 427-511

T-ACS 1-12

BATTLESHIPS

AIRCRAFT CARRIERS

AIRCRAFT CARRIERS

AIRCRAFT CARRIERS

AIRCRAFT CARRIERS

AIRCRAFT CARRIERS

ASW AIRCRAFT CARRIERS

GUN CRUISERS

GUN CRUISERS

GUIDED MISSILE CRUISERS


GUIDED MISSILE CRUISER







GUIDED MISSILE DESTROYERS





DESTROYERS

DESTROYERS

DESTROYERS

DESTROYERS

DESTROYERS

DESTROYER ESCORT

GUIDED MISSILE FRIGATES

GUIDED MISSILE FRIGATES

FRIGATES

FRIGATES

AMPHIBIOUS COMMAND SHIPS

AMPHIBIOUS ASSAULT SHIPS

AMPHIBIOUS ASSAULT SHIPS

AMPHIBIOUS TRANSPORT DOCKS

AMPHIBIOUS TRANSPORT DOCKS

DOCK LANDING SHIPS

DOCK LANDING SHIPS

DOCK LANDING SHIPS

TANK LANDING SHIP

TANK LANDING SHIP

TANK LANDING SHIP (WWII)

AMPHIBIOUS CARGO SHIPS

MINE COUNTERMEASURE VESSELS

OCEAN MINESWEEPERS

AUXILIARY CRANE SHIPS

59,000

104,000

91,000

81,000

65,000

42,000

40,600

17,500

20,950

11,000

10,450

9,127

8,592

17,525

10,100

8,250

8,250

19,500

8,300

10,000

6,150

4,500

4,150

9,400

4,200

3,040

3,400

3,540

1,914

4,100

3,426

3,900

3,400

18,650

39,300

18,800

17,000

14,665

15,730

13,700

12,000

8,450

7,100

4,000

20,700

1,040

970

735

31,500

8,500

16,600

15,000e

9,500

9,000

9,000

5,300

4,500

4,000

4,000

2,960

3,040

7,900

7,000e

3,675

3,000e

5,300

6,900

5,000e

3,000e

2,256

2,100

4,400

2,100

1,400

1,400

1,450

1,342

2,200

1,715

2,020

1,715

7,360

11,500

6,700

8,350

8,300

8,000e

7,450e

6,150

5,200

3,400

2,000

7,650

1,500

1,340

5,300e

.70

.45

.45

.45

.45

.45

.70

.70

.70

.70

.70

.70

.70

.70

.70

.70

.70

.70

.70

.70

.70

.70

.70

.70

.70

.70

.70

.70

.70

.70

.70

.70

.70

.70

.75

.75

.75

.75

.75

.75

.75

.75

.75

.75

.75

.75

.75

664

895

1028

615

300

300

308

324

207

238

239

239

312

254

296

243

308

254

254

228

176

194

254

194

134

158

158

79

170e

131

131

131

220e

262

155

175

175

360e

348

174

108

82

30

312

40

40

300e

5

5

5

5

5

5

5

5

4e

4e

3

3

4

4e

4

3

5e

4e

4e

3

2

3

3

2

3

3

3

1

2e

2

2

2

5

5

5

5

5e

5e

5

5

4

4

4

5e

2e

2

5e

3

3

3

3

3

3

2

2

1

1

1

1

2

1

1

1

2

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

2

3

2

2

2

2

2

2

2

2

1

2

1

1

3

G-7




∆ AT CW AP


L L

OA

D

DIS

PL

AC

EM

EN

T

(L. T

ON

S)

LIG

HT

SH

IP F

RO

NT

AL

WIN

DA

GE

AR

EA

(Ft

)

WIN

D C

OE

FFIC

IEN

T

TO

TA

L P

RO

JEC

TE

D

AR

EA

OF

AL

L

PRO

PE

LL

ER

S (

Ft)

CU

RV

E F

OR

HU

LL

RE

SIST

AN

CE

SEE

FIG

UR

E G

-6

CU

RV

E F

OR

WA

VE

RE

SIST

AN

CE

SEE

FIG

UR

E G

-7

AD 15-19

AD 37-44

AE 21-25

AE 26-35

T-AF 58

AFS 1-7

T-AFS 8-10 (ex RN/RFA)

T-AG 194 (ex AGM-19)

AGF 11 (ex LPD-11)

AGF 3 (ex LPD-1)

T-AGM 10 (ex AP 145)

T-AGM 20 (ex AO-114)

T-AGM 23 (ex AG 154)

AGOR 14-15

AGOR 21-22

AGOR 23

AGOR 3, 9-10

T-AGOR 16

T-AGOR 7, 12-13

T-AGOR 8, 11

T-AGOS 1-26

T-AGS 21-22

T-AGS 26-27, 33-34

T-AGS 29, 32

T-AGS 38

T-AGS 39-40

AH 17

T-AH 19-20

AK 283

T-AK 1010

T-AK 2043

T-AK 2046

T-AK 267

T-AK 271

T-AK 280-282

T-AK 284-286, 295

T-AKB 1015, 2049

T-AKR 287-294

T-AKR 7

T-AKR 9

T-AKR (new)

T-AKX 3000-3004

T-AKX 3005-3007

T-AKX 3008-3012

AO 177-186

AO 51, 98-99

T-AO 105-109

DESTROYER TENDERS

DESTROYER TENDERS

AMMUNITION SHIP

AMMUNITION SHIP

STORE SHIP

COMBAT STORE SHIPS

COMBAT STORES SHIPS

MISC.

MISC. COMMAND SHIP

MISC. COMMAND SHIP

MISSILE RANGE INST.

MISSILE RANGE INST.(T2-SE-A2)

MISSILE RANGE INST. (C4-S-A1)

OCEANOGRAPHIC RESRCH SHIPS







OCEAN SURVEILLANCE SHIPS

SURVEYING SHIPS (VC2-S-AP3)

SURVEYING SHIPS

SURVEYING SHIPS

SURVEYING SHIP

SURVEYING SHIPS

HOSPITAL SHIP

HOSPITAL SHIPS

CARGO SHIPS (C2-S-B1)

MPS-CARGO SHIP

MPS-CARGO SHIP (CR-S-66a)

MPS-CARGO SHIP (LASH TYPE)

CARGO SHIPS (C4-S-B1)

CARGO SHIPS (C1-ME2-13a)

CARGO SHIPS (VC2-S-AP3)

CARGO SHIPS (C3-S-33a)

MPS-CARGO SHIPS (BARGE CARRIER)

MPS-VEHICLE CARGO SHIPS (SL-7)

VEHICLE CARGO SHIP (C3-ST-14A)

VEHICLE CARGO SHIP (C4-ST-67A)

VEHICLE CARGO SHIP

MPS-VEHICLE CARGO SHIPS



OILERS

OILERS

OILERS

18,400

20,500

16,000

18,000

15,540

18,000

16,792

21,626

16,912

15,000

17,120

24,710

17,015

1,915

1,437

2,433

1,370

3,860

1,370

3,886

2,285

13,050

2,800

4,330

21,235

15,800

15,500

44,875

11,000

22,600e

24,300e

49,000e

22,056

3,886

11,300

15,404

53,000e

55,000e

18,286

21,700

24,500

44,086

51,612

46,111

26,110

34,040

35,000

6,200

8,000

6,490

7,800

5,400

6,350

4,00Oe

5,020

8,350

8,300

5,000e

5,020

5,550

1,800e

1,080e

1,500e

1,100

4,500e

1,100

2,400e

2,800e

2,900e

2,000e

2,500e

4,050

3,500e

4,900

8,400e

4,375

5,600e

5,000e

9,000e

4,200

1,600

4,100

3,800e

9,000e

10,000

4,000e

4,100e

6,200e

9,800

10,000

9,800

6,300

5,480

5,480

.75

.75

.75

.75

.75

.70

.75

.70

.75

.75

1.00

.70

1.00

.75

.75

.75

.75

.75

.75

1.00

.75

.75

.75

.75

.75

.75

.75

1.00

.75

.75

.75

1.00

.75

.75

.75

.75

1.00

1.00

.75

.75

.75

1.00

1.00

1.00

1.00

1.00

1.00

136

136

187

216

198

216

156e

150e

175

175

200e

150e

200e

30e

40e

45e

35e

100

35e

50e

55e

120

55e

90e

200e

150e

115

330e

106

220e

210e

320e

150e

50e

119

130e

300e

500e

180e

200e

400e

280e

380e

350e

220

346

346

5

5

5

5

4

5

4e

4

5

4

5e

5e

5

4e

4e

4e

4e

4e

4e

4e

4e

5e

4e

4

4e

4e

5

5e

5

5e

5e

5e

5e

5

5

5e

5e

5e

5

5

5e

5e

5e

5e

5e

5

5e

2

2

2

2

2

2

2

2

2

2

2

2

2

1

1

1

1

1

1

1

1

2

1

1

2

2

2

3

2

2

2

3

2

1

2

2

3

3

2

2

2

3

3

3

3

3

3

G-8




∆ AT CW AP


L L

OA

D

DIS

PL

AC

EM

EN

T

(L. T

ON

S)

LIG

HT

SH

IP F

RO

NT

AL

WIN

DA

GE

AR

EA

(Ft

)

WIN

D C

OE

FFIC

IEN

T

TO

TA

L P

RO

JEC

TE

D

AR

EA

OF

AL

L

PRO

PE

LL

ER

S (

Ft)

CU

RV

E F

OR

HU

LL

RE

SIST

AN

CE

SEE

FIG

UR

E G

-6

CU

RV

E F

OR

WA

VE

RE

SIST

AN

CE

SEE

FIG

UR

E G

-7

T-AO 143-148

T-AO 187-204

T-AO 57, 62

AOE 1-6

T-AOG 78

T-AOG 81-82

AOR 1-7

T-AOT

T-AOT 1203-1205

T-AOT 134

T-AOT 149-152

T-AOT 165

T-AOT 168-176

T-AOT 181

T-AOT 50-76

AP 110

AP 121-127

AR 5-8

T-ARC 2, 6

T-ARC 7

ARL 24

ARS 38-43

ARS 50-53

AS 11, 17, 18

AS 19

AS 31-32

AS 33-34

AS 36-41

ASR 21-22

ASR 9, 13-15

ATF 91-160

T-ATF 166-172

ATS 1-3

T-AVB 3-4

AVM 1

WAGB 10-11

WAGB 281-282

WAGB 4

WHEC 35, 37

WHEC 379

WHEC 715-726

WMEC 165-166

WMEC 615-623

WMEC 76, 85, 153

WMEC 901-913

WMEC 6, 167, 168

YTB 752-836

OILERS

OILERS

OILERS

FAST COMBAT SUPPORT SHIPS

GASOLINE TANKERS (T1-M-BT2)

GASOLINE TANKERS (T1-MET-24a)

REPLENISHMENT OILERS

TRANSPORT OILERS (T5 type)

MPS-TRANSPORT OILERS

TRANSPORT OILERS (T2-SE-A2)

TRANSPORT OILERS (T5-S-12A)

TRANSPORT OILERS (T5-S-RM2A)

TRANSPORT OILERS

TRANSPORT OILERS

TRANSPORT OILERS (T2-SE-A1)

TRANSPORTS

TRANSPORTS

REPAIR SHIPS

CABLE REPAIR SHIP (S3-S2-BP1)

CABLE REPAIRING SHIP

SMALL REPAIR SHIP

SALVAGE SHIP

SALVAGE SHIP

SUBMARINE TENDERS

SUBMARINE TENDERS

SUBMARINE TENDERS

SUBMARINE TENDERS

SUBMARINE TENDERS

SUBMARINE RESCUE SHIPS

SUBMARINE RESCUE SHIPS

FLEET TUGS

FLEET OCEAN TUGS

SALVAGE & RESCUE SHIPS

MPS-AVIATION MAINTENANCE SUP.

GUIDED MISSILE SHIP

(CG) ICEBREAKERS

(CG) ICEBREAKERS

(CG) ICEBREAKERS

(CG) HIGH ENDURANCE CUTTERS



(CG) MED. ENDUR. CUTTERS (ATF)

(CG) MEDIUM ENDUR. CUTTERS

(CG) MED. ENDUR. CUTTERS (ATF)

(CG) MEDIUM ENDUR. CUTTERS

(CG) MED. ENDUR. CUTTERS (ARS)

LARGE HARBOR TUGS

36,000

40,000

25,500

51,000

6,047

7,000

37,700

39,000

44,000e

22,380

32,953

31,300

34,100

35,000

21,880

20,175

22,574

16,300

8,500

14,157

4,325

2,045

2,880

17,000

19,200

19,000

21,089

23,000

3,411

2,320

1,640

2,260

2,929

23,800

15,170

12,087

6,515

8,449

2,656

2,800

3,050

1,731

1,000

1,731

1,780

1,745

350

5,000e

6,750e

5,480

9,750

2,500e

2,500e

7,590

5,000e

4,500e

3,600e

4,000e

4,600e

4,600e

4,700e

3,600e

6,800

6,300e

5,460

2,250e

4,700e

2,320

1,500

2,000e

6,200

6,200

6,440

7,550

7,550

4,500e

1,200

1,100

1,700e

2,500

6,000e

5,300

4,500

3,150

3,400

1,600

1,600

2,000

1,200

1,400

1,500

1,300

1,500

560

1.00

1.00

1.00

1.00

1.00

1.00

1.00

.75

1.00

1.00

1.00

1.00

.75

.75

1.00

.75

.75

.75

.75

1.00

.75

.75

.75

.75

.75

.75

.75

.75

.75

.75

.75

.75

.75

1.00

.75

.75

.75

.75

.70

.70

.70

.75

.70

.75

.70

.75

.75

400e

420e

346

456

70e

67

274

180e

270e

135e

200e

210e

200e

270e

120e

200

216

136

72e

300e

30

56

80

136

136

140

136

136

100

50

43

120e

110

370e

136

280e

182

300e

50e

47e

154e

43

40e

56

55e

56

22e

5e

5e

5e

5

4e

4e

5

5e

5e

5e

5e

5e

5e

5e

5e

5e

4e

5

5

5e

4

5

5e

4

4

4

5e

5

3e

5

2

4e

5e

5e

4

4e

5e

5e

1e

1e

2e

2e

2e

2e

1e

5e

2e

3

3

3

3

1

1

3

3

3

2

3

3

3

3

2

2

2

2

1

2

1

1

1

2

2

2

2

2

1

1

1

1

1

2

2

3

2

2

1

1

1

1

1

1

1

1

1

G-9


Table G-3. Beaufort Scale.

Beau-fort No.

Knots DescriptionAvg. Ht.

(ft)Significant 1/3 Highest (ft)

Avg. Wave

Length (ft)

Minimum Duration (Hours)

Avg. Wave Height

(ft)*

0 < 1 Calm --- --- --- --- ---

1 1-3 Light air < 1 < 1 10 in 18 min ---

2 4-6 Light breeze < 1 < 1 6.7 (ft) 39 min ---

3 7-10 Gentle breeze < 1 < 1 20-27 1.7-2.4 (hr) 2 (3)

4 11-16 Moderate breeze

1.8-2.9 2.9-4.6 52-71 4.8-6.6 3½ (5)

5 17-21 Fresh breeze 3.8-5.0 6.1-8.0 90-111 8.3-10.0 6 (8½)

6 22-27 Strong breeze 6.4-9.6 10-15 134-188 12-17 9½ (13)

7 28-33 Moderate gale (high wind)

11-16 18-26 212-285 20-27 13½ (19)

8 34-40 Fresh gale 19-28 30-45 322-444 30-42 18 (25)

9 41-47 Strong gale 31-40 50-64 492-590 47-57 23 (32)

10 48-55 Storm 44-59 71-95 650-810 63-81 29 (41)

11 56-63 Violent storm 64-73 103-116 910-985 88-101 37 (52)

12 > 63 Hurricane > 80 > 128 --- --- 45 (-)

1. Figures shown are associated with the low and high wind speed within each force range.

2. Except for the far right-hand column, figures are for fully developed seas. Note that the more strenu-ous seas require a progressively longer duration to develop. The fully developed seas associated with 50-kt or stronger winds rarely occur. Average heights listed in the right-hand column are more repre-sentative of waves actually encountered under the stated wind conditions.

* For tow planning purposes, use “average height” column in computing added resistance due to waves. These are the more usual wave heights encountered, due to the long duration required to achieve the "fully developed sea" for the stated wind conditions. Figures in parentheses represent the occasional highest wave in the average spectrum. These occasional highest waves have little long-term impact on the towing resistance.

G-10


Figure G-3. Example 2 - Scenario.

Wind 25 knots000° R

DD 963 @ 7500 LT displacement

What is the maximum speed each Navy tug can achieve?

Solution: Compute hawser tension at 10, 8, 6, 4 knots and plot in Figure 3-3

Tow Speed Tow Resistance Hawser Resistance Total Pull Required

10 kts 173,449 lbs. negligible 173,449 lbs.

8 kts. 122,159 lbs. 1,500 lbs. 124,059 lbs.

6 kts. 82,336 lbs. 1,850 lbs. 84186 lbs.

4 kts. 53,044 lbs. 1,100 lbs. 54,144 lbs.

The attached Figure G-4 work-up shows hawser tensions for the 6- and 8-knot cases.

Figure G-5 is a replica of Figure 3-3, with this resistance curve plotted on it. This providesthe following likely maximum tow speeds for each of the tug types listed, with total hawseraverage tension.

Max, Tow Speeds Average Tension

T-ATF 166 7.6 kts 117,000

ARS 50 6.9 kts 98,000

G-11


Figure G-4. Example 2 - Worksheet.

SH

IP:

C

ALC

S B

Y:

LT. M

AR

K F

IVE

Item

Des

crip

tion

Sym

bol

Uni

tsS

ourc

e

1S

hip

Cla

ss (

AE

, CV,

etc

.)D

D 9

63D

D 9

63

2To

w S

peed

VT

OW

Kno

ts8

6

3To

w C

ours

eγ

Deg

rees

4To

w D

ispl

acem

ent

DLo

ng to

nsTa

ble

G-2

7500

7500

5F

ront

al W

inda

ge A

rea

AT

Sq.

feet

Tabl

e G

-244

0044

00

6W

ind

Dra

g C

oeffi

cien

tC

WTa

ble

G-2

0.70

0.70

7To

tal P

roje

cted

Are

a of

P

rope

llers

AP

Sq.

feet

Tabl

e G

-225

425

4

8C

urve

Num

ber

for

Hul

l R

esis

tanc

eTa

ble

G-2

33

9C

urve

N

umbe

r fo

r S

eaS

tate

Res

ista

nce

Tabl

e G

-21

1

10Tr

ue W

ind

Spe

edV

win

dK

nots

2525

11B

eauf

ort N

umbe

rTa

ble

66

12R

elat

ive

Win

d S

peed

VR

Kno

ts33

31

13H

eadi

ng C

oeffi

cien

tK

Sect

ion

G-1

1.0

1.0

14W

ind

Res

ista

nce

RW

Pou

nds

RW

=0.

0050

6(A

T)(

CW

)(V

R)2 (

K)

1697

214

977

15R

esis

tanc

e F

acto

rR

H/D

Figu

re G

-63.

32.

1

16H

ull R

esis

tanc

eR

HP

ound

sR

H=

1.25

(RH

/D)(

D)

3093

819

688

17S

ea S

tate

Res

ista

nce

RS

Pou

nds

Figu

re G

-713

500

1350

0

18P

rope

ller

Res

ista

nce

RP

Pou

nds

RP=

3.73

7(A

P)(

VT

OW

)260

749

3417

1

19To

tal S

tead

y S

tate

Tow

R

esis

tanc

eR

TP

ound

sR

T=R

W +

RH

+ R

S +

RP

1221

5982

336

20To

w H

awse

r R

esis

tanc

eR

WIR

EP

ound

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3-1

or 1

0% o

f RT

1900

1850

21To

tal T

ow H

awse

rTe

nsio

nR

Pou

nds

R=

RT +

RW

IRE

1240

5984

186

G-12


Figure G-5. Available Tension vs. Ship’s Speed for U.S. Navy Towing and Resistance Curve.

ResistanceCurve

Ava

ilab

le T

ensi

on

(lb

s)

BollardPull

Speed (knots)

G-13


Figure G-6. Hull Resistance Curve, RH/∆ vs. Tow Speed.

1 .0

2 .0

3 .0

4 .0

5 .0

6 .0

7 .0

8 .0

9 .0

1 0 .0

11 .0

1 2 .0

1 3 .0

1 4 .0

R (

LB

/L. T

ON

)H

/∆

Tow Speed in Knots

5

4

3

2

1

Curve Numbers

G-14


Figure G-7. Wave Resistance Curve RS vs. Wave Height and Wind Force.

Significant Wave Height (Ft.)

Wind Force (Beaufort No.)

Ad

ded

R R

esis

tan

ce (

Lb

.)S

3 4 5 6 7 8

140,000

130 ,000

120 ,000

110,000

100 ,000

90,000

80,000

70,000

60,000

50,000

40,000

30,000

20,000

10,000

0

5 10 15 20 25

3

2

1

Curve Num bers

G-15


the tug and tow may preclude towing acrossthe wind and seas under strenuous conditions.

G-1.3 Wind Resistance

The prediction of wind resistance is also sim-plified in the manual. The sea conditions as-sociated with the most significant winds gen-erally dictate towing into or close to the wind.The ability to precisely predict the reductionof tow resistance from a Force 10 wind offthe quarter is not too important. Furthermore,in those cases where there is insufficient pitchor duration of the strong winds to raise fully-developed waves, the tug will base operation-al decisions on actual observations of thetowline, not on the predicted assistance fromstrong stern winds.

Note 2: At higher wind strengths, Force 5 to7, (the latter with winds of 28 to 33 knots),the tow will be forced to head into the windbecause of the sea conditions. Therefore, themost severe weather expected should bechecked for head wind and seas to confirmtug and especially tow hawser selection.

G-1.4 Propeller Resistance

Ships of comparable size (displacement) andspeed have comparable propeller size. Forships not listed in Table G-2, select a compa-rable listed ship for propeller projected area.In the case above, there is no comparable shiplisted in Table G-2. The T-AGM 20 is as-sumed to have a similar hull shape as thetanker, since it has a similar speed/length ra-tio. The propeller projected area for theT-AGM 20 is 150 square feet. The displace-ment of the ship in question is 4.4 times aslarge as the T-AGM 20, so it will requireroughly 4.4 times the power for the samespeed. Therefore, estimate the propeller pro-jected area as 4.4 x 150 square feet, whichequals 660 square feet.

G-2 Floating Dry Docks

The following method for determining the to-tal tow resistance of non self-propelled float-ing dry docks is based on the now out-of-cir-culation Towing Non Self-Propelled FloatingStructures (Technical Publication NAV-DOCKS TP-DM-26, 1 October 1953). Thisprocedure, which has been successfully usedfor many years, is recommended for estimat-ing tow resistance for these types of craft. Ta-ble contains the various constants used in thefollowing formulas.

G-2.1 Frictional Resistance

The data used for determining frictional resis-tance are based upon a series of experimentson model and actual conditions. The resis-tance caused by the friction of water on thevessel’s wetted surface depends upon:

• Area of surface below the waterline

• Nature of surface

• Speed of tow.

Thus the formula for frictional resistance of avessel passing through water is:

R = f1 x S x (V/6)2

where:

R = Resistance in pounds

f1 = A coefficient depending on the shape of the ship’s hull (from Table G-4)

S = Area of the vessel’s wetted sur-face below the waterline, in square feet (from Table G-4)

V = Speed of tow in knots relative to still water.

G-2.2 Wave-Forming Resistance

Data for wave-forming resistance are basedon model tests and depend on:

G-16


• Area below water line (maximum crosssection)

• Form of bow and stern

• Speed of tow.

Thus the formula for wave-forming resistanceof a body passing through water is:

G = 2.85 x B x f2 x V2 x K

where:

G = Resistance in pounds

B = Cross-sectional area of vessel below waterline in square feet (from Table G-4)

f2 = A coefficient depending upon the configuration of the vessel’s bow and stern (from Table G-4)

V = Speed of tow in knots relative to still water

K = 1.2 (multiplying by this number adds 20 percent for additional resistance from rough water and eddies)


Data used for determining wind resistance arebased on a series of experiments on models.The resistance caused by wind blowingagainst a vessel depends upon:

• Cross-sectional area of vessel abovewaterline subjected to wind

• Speed of wind

• Speed of tow

• Shape of vessel subjected to wind.

Thus the formula for frictional resistancecaused by wind is:

W = C x .004 (Vw + V)2 x f3

where:

W = Resistance in pounds

C = Cross-sectional area of vessel above waterline in square feet (from Table G-4)

Vw = Speed of wind in knots

V = Speed of tow in knots, relative to still water

Table G-4. Drydock Towing Coefficients.

Ship Class f1 S f2 B f3 C

AFDB-1AFDB-4AFDM-1AFDM-3ARD-1ARD-2ARD-12AFDL-1AFDL-7AFDL-35AFDL-47AFDL-48YFD-7YFD-68 to 71

SectionSection3-Piece3-Piece1-Piece1-Piece1-Piece1-Piece1-Piece1-Piece1-Piece1-Piece3-Piece3-Piece

256′ x 80′240′ x 101′496′ x 116′488′ x 124′390′ x 60′486′ x 71′492′ x 81′200′ x 64′288′ x 64′389′ x 84′488′ x 97′400′ x 96′488′ x 124′474′ x 118′

.45 to .8

.45 to .8

.45 to .8

.45 to .8

.45 to .8

.45 to .8

.45 to .8

.45 to .8

.45 to .8

.45 to .8

.45 to .8

.45 to .8

.45 to .8

.45 to .8

23,00026,00050,00052,00020,00034,00040,00013,00019,00038,00046,00048,00052,00048,000

.3

.3

.6

.6

.2

.2

.2

.4

.4

.3

.5

.4

.6

.6

720900750800250370480220210780420

1,350800750

.7

.7

.67

.67

.61

.61

.61

.7

.7

.67

.7

.7

.67

.67

3,8004,5007,0007,8002,0003,7004,4001,4001,5001,9002,5002,5407,8007,300

G-17


f3 = A coefficient depending on the shape of vessel subjected to wind (from Table G-4).

G-2.4 Total Tow Resistance for Dry Docks

The total tow resistance for docks (RTOT) isthe sum of the frictional resistance, wave-forming resistance, and wind resistance. Thistotal tow resistance is then used in selectingthe tow ship and designing the tow connec-tion as described in Chapter 3. This does notinclude towline resistance when figuring totaltowline tension.

RTOT = R + G + W

G-2.5 Example

The following example is given to show theuse of the four resistance formulas alreadyoutlined.

The problem is to determine the extreme re-quirements for towing AFDL 1 Class floatingdry dock under all weather conditions. To il-lustrate this design, the following known fac-tors have been selected:

• Hurricane wind speed: 64 knots

• Towing speed during hurricane: 6 knots

• Bottom condition of dry dock — mod-erately rough and in need of cleaning:use f1 coefficient of 0.65

Substitute into resistance formulas, usingabove factors and coefficients fromTable G-4.

R = f1 x S (V/6)2

= 0.65 x 13,000 x (6/6)2

= 8,450 lbs.

G = 2.85 x B x f2 x V2 x K

= 2.85 x 220 x 0.4 x 62 x 1.2

= 10,835 lbs.

W = C x 0.004 x (Vw + V)2 x f3

= 1,400 x 0.004 x (64 + 6)2 x 0.7

= 19,208 lbs.

Total resistance

RTOT = R + G + W

= 8,450 + 10,835 + 19,208

= 38,493 lbs.

G-3 Barges

The previous section on towing resistance ofdry docks can be adapted for computing thetotal resistance of barges.

G-3.1 Frictional Resistance

The method is identical to the one used inSection G-2.1. The wetted surface (S), is sim-ply the barge’s length times beam (for bot-tom) plus perimeter times draft (for sides,bow, and stern).

G-3.2 Wave-Forming Resistance

The cross section area (B) equals beam timesdraft. For the typical rake-ended barge, usef2 = 0.2. This also is applicable to the com-paratively blunt ship-shaped bow of somebarges such as YFBNs and APLs. For square-ended barges, use f2 = 0.5.


Use the formula contained in Section G-2.3.The cross sectional area (C), is the freeboardtimes beam plus height times width of thedeck house or any deck cargo. Use f3 = 0.60as an average barge figure in the formula.

G-3.4 Total Barge Resistance

To calculate total tow resistance (RTOT), addthe frictional resistance, wave-forming resis-tance, and wind resistance from the previousthree sections.

RTOT = R + G + W

G-3.5 Example

Assume a berthing barge (YRBM) is to betowed. Dimensions are:

Length: 265 feet

G-18


Width: 65 feet

Draft: 7 feet

Hull Depth: 12 feet

Deck House: 220 ft. x 55 ft. x 25 ft.

Desired tow speed is 10 knots, maximumhead wind is 20 knots. Bottom conditions areaverage. The hull has rake-shaped ends.

G-3.5.1 Frictional Resistance

Estimate average length below the waterlineas 250 feet, with the bottom being 245 feet.

S = Wetted surface

= 7 x 2 (250 + 65) + (245 x 65)

= 20,335 square feet

Therefore:

R = .65 x 20,335 x (10/6)2

= 36,716 lbs.

G-3.5.2 Wave Forming Resistance

B = Cross sectional area

= 65 x 7

= 455

Therefore:

G = 2.85 x 455 x 0.2 x 102 x 1.2

= 31,122 lbs.

G-3.5.3 Wind Resistance

C = Frontal area

= 65 x (12 - 7) + (25 x 55)

= 1,700 square feet

Therefore:

W = 1,700 x .004 (20 + 10)2 x .6

= 3,672 lbs.

G-3.5.4 Total Resistance

RTOT = R + G + W

= 36,716 + 31,122 + 3,672

= 71,510 lbs.

Inspecting Figure 3-1 shows that this tow iswithin the capability of the T-ATF and ATS 1Classes, at the assumed towing speed of 10knots. Clearly, other towing ships would beadequate for this tow at lower speeds.

G-19



G-20


Appendix H

CHECKLIST FOR PREPARING AND RIGGING A TOW

The following checklist is designed to helpthe preparing activity ready a tow for sea. Itlists pre-tow preparations and general re-quirements which must be completed beforethe towing unit will accept the tow for sea. Ifthe preparing activity has questions concern-ing this checklist or preparations required toready the tow, it should communicate theseconcerns to the towing unit or its ImmediateSuperior in Command (ISIC). The preparingactivity is responsible for completing thischecklist. Items that are not applicable or can-not be accomplished must be cleared throughthe towing unit or its ISIC. All not applicableor not accomplished items shall be document-ed. Rationale for accepting the tow with notaccomplished items shall be documented as a

part of the completed Towing InspectionChecklist.

The command conducting the tow shouldconduct a preliminary pre-tow inspection assoon as possible to preclude misunderstand-ings and rework. In special situations, thestandards reflected in this checklist can be re-laxed and an “acceptable risk” tow accepted.The Commanding Officer of the towing shipand the ISIC must agree to all acceptable risktows, as such tows do not relieve them of re-sponsibility or safe practice. Acceptable risktows are not routine.

The Commanding Officer of the towing shipconducts a final inspection of the tow, accom-panied by a representative of the preparingcommand. Upon satisfactory completion ofthis inspection, the preparing activity setscondition ZEBRA on the tow and the towingship’s Commanding Officer accepts and signsfor the tow.

Note: For more information on preparing atow for sea, refer to Chapter 3 and 4.

H-1



H-2


H-3

TOWING INSPECTION CHECKLIST Vessel Name _____________________________________ Hull Number_____________________________________

Owner __________________________________________ P.O.C. and 24 Hour # _____________________________

Departure Port ___________________________________ Arrival Port _____________________________________

Receiving Activity Port _____________________________ P.O.C. and 24 Hour # _____________________________

Vessel Characteristics

Length: Beam: Displacement:

Draft fwd: Draft aft: Mean draft:

Freeboard fwd: Freeboard aft: Freeboard mid:

MTI: TPI: KG:

GM: Maximum Ht above WL:

Maximum Navigational Draft (include sonar domes, propellers, etc.):

Is craft designed and authorized to be ocean-towed in accordance with requirements set forth in this manual? _________

Provide rationale for accepting the tow with items not accomplished.___________________________________________

_________________________________________________________________________________________________

_________________________________________________________________________________________________

_________________________________________________________________________________________________

_________________________________________________________________________________________________

_________________________________________________________________________________________________

Use separate sheet if additional space is needed.

The tow described above is seaworthy in all respects. The material condition is noted. Copies of the master inventory and storage keys are receipted for. Representative of command having prepared the tow for sea Date


H-4



H-5

1. SHIP INFORMATION

Reference N/A Yes No

a. Is the booklet of general plans available?

Location of booklet:

b. Is damage control book, curves of forms, or other stability data available?

If yes, provide location:

c. Are liquid load diagrams and damage control flooding plates available on board?

If the answer is Satisfactory, provide location:

d. Are instructions posted in after steering for lining up hydraulic steering systems to hand pump?

e. Are plans and date of the last drydocking available? Date of last drydocking: Location of plans:

f. Were hull thickness recordings taken during last drydocking: 5-7.5

g. Is record of sonic drill test satisfactory?

If not, has a satisfactory report of ultrasonic testing been provided?

h. Has a list of equipage been provided to the towing activity?

Note: The preparing activity is responsible for providing a list of equipage assigned to the craft that is pilferable and must be on board at destination. Preparing and towing representatives’ signatures are required. Provide list on separate sheet.

i. List remaining HAZMAT on board:

j. If craft is a floating drydock, has it been inspected by a representative of NAVSEA?

If satisfactory, provide name of inspector and date of inspection:

k. Do you hold a signed copy of the inspection?


H-6

2. RIDING CREW

Reference N/A Yes No a. Will a riding crew be employed? If so, attach a copy of the directive

(message, letter, etc.) and proceed with the following checks.

Note: Riding crews are not ordinary practice for open ocean tows.

5-6

b. Authority that authorized a riding crew.

c. Is a copy of the authorizing message attached?

Number of crew members:__________________

d. Has a list of the riding crews been provided to the towing activity?

Note: A list of the riding crew is entered in towing ship’s diary (name, rate, SSN, and NOK; address and phone number of rider and NOK for civilians).

e. Are enough life rafts on board with emergency rations and water for the riding crew in the event that they have to abandon ship?

Location of life rafts:

f. Date life rafts were last tested/inspected: 5-9.2

g. Are a sufficient quantity of life jackets and life rings on board?

Number, type, and location

h. Means of communication with the towing ship:

Note: Both visual and radio are recommended.

i. Has the riding crew been trained in damage control and support systems?

Note: The preparing activity is normally responsible for such training.

5-9.2

j. Is habitability and sustenance sufficient from on-board assets? 5-9.2

3. SEAWORTHINESS

Reference N/A Yes No a. Does craft have a fixed rudder or a skeg?

b. Is craft ballasted?

Type and location of ballast:

5-7.3

5-7.2

c. If not, will craft require additional ballst?

d. Types of ballast required: 5-2.9

e. Describe where ballast will be placed and how much:

f. Draft after craft is in proper trim:

Forward:________________ Aft:_________________________

Max. navigational draft:

5-7.2

g. GM after craft is in proper trim:

h. KG after craft is in proper trim:

i. If GM is not known, “sally ship” to establish period of roll: Normally T = 2 Beam(ft) T (observed):

Note: This method to assess the adequacy of ship’s stability is fully explained in Section 5-7.3.

5-7.3


H-7

Reference N/A Yes No j. Are all sea valves closed and wired shut? 5-7.4

k. Is there a two-valve protection from the sea for all sea openings?

Note: Two-valve protection consists of either two valves wired shut or one valve and a blank flange. A list of all valves should be attached.

5-7.4

l. Is a list of sea valves attached?

m. Closely inspect, below decks, all drain piping which originates above the water-line and terminates within 20 feet of the waterline. Are there any loose connections or badly deteriorated spots in the piping?

5-7.4

n. Are all sounding tubes capped?

o. Is there a list of all sounding tubes attached? (Required)

p. Are all between-tank sluice valves closed?

q. Are all normally dry compartments dry?

r. Are all bilges free of oil and water?

s. Are there any broken, cracked or weak frames, longitudinals, plates, welds, or rivets?

5-7.5.1

t. Have repairs been made? 5-7.5.1

u. Has the hull structure been inspected to the best of your ability?

v. Type(s) of hull inspection conducted, including location: (e.g., ultrasonic interior, exterior, voids)

Note: All compartments should be entered and inspected.

w. Have all compartments been inspected?

x. Has steel wire or cable been used to secure all equipment to prevent any movement in heavy weather?

Note: All moveable equipment must be secured in place with wire or by welding. No fiber rope or line will be accepted.

5-7

y. Are all rudders locked?

Note: The rudders should be locked by using structural steel of acceptable size and quantity. The lock should transfer the rudder load from the yoke to structural members of the tow’s hull. Refer to Chapter 4 for typical configurations and sizing.

5-7.6

z. Type of locking device used:

aa. Are all shafts locked? 5-7.1.9

bb. Are propellers removed? 5-7.1.8

cc. Are shafts equipped with extra rings of packing in the gland to allow emergency repair during transit?

5-7.1.11

dd. Is the gland tightened to its tightest position but not two-blocked? 5-7.1.11

ee. Ensure that there is no leakoff at the stern tube. Can the stern tube packing gland be tightened at least two more inches before it is two-blocked?

Note: Leaving two more inches will allow additional sealing room should there be leakage. If this room is not available, it is a good indication that the packing has deteriorated to an unacceptable point.

5-7.1.11

ff. Are locking nuts tight on packing glands to prevent their backing off? 5-7.1.11

gg. Are all portholes sealed and covered with metal to prevent breakage? 5-7.9


H-8

Reference N/A Yes No hh. Are all vents that are subject to heavy weather flooding (e.g., air, fresh

water, fuel tank) sealed?

Note: Wood covers are not considered adequate. The recommended procedure is to remove and blank flange or weld close.)

5-7.9

ii. Do vents allow for the escape of air or gas?

Note: Vents to tanks and other closed spaces should be covered to prevent water entry, but not plugged so as to prevent the escape of air or gas. Plugging a vent allows pressure to build up within the tank if the temperature rises. Barge sides and decks have been known to bulge severely. If necessary, cover compartment vents with canvas socks that prevent water from entering yet allow air to escape.

5-7.9

jj. Are all hatches, scuttles, doors, and other watertight closures provided with pliable gaskets?

5-7.9

kk. Have weather decks and main transverse bulkhead watertight closures been chalk tested?

ll. Are all dogs on watertight closures operable and functioning as designed?

mm. Is forward one-fifth of craft designed to withstand constant pounding during transit?

If the answer is Unsatisfactory, bow should be shored properly.

5-7.5

nn. If the craft to be towed is a barge, and inspection reveals signs of serious deterioration, or the barge is suspected of being weakened, it may require shoring, particularly in the forward one-fifth of its length. Is shoring required?

Note: Steel “K” shoring should be installed on all longitudinals in forward and after compartments.

5-7.5.1

oo. Has shoring been accomplished?

pp. For LST-type tows, all of the following must be answered Satisfactory, or the vessel will not be accepted for ocean tow, even as a calculated risk:

7-7

i. Do the bow doors have hydraulic rams connected?

ii. Are mud flaps at the bottom of the doors secured?

iii. Are all dogs, heavy weather shackles, ratchet-type turnbuckles and strongbacks in place, tight and secure so that they cannot work free?

iv. Are bow ramp operating instructions posted in the hydraulic control room?

qq. If craft is equipped with a bow or stern ramp, is it secured in accordance with notes listed below? Note: YFU/LCUs are inherently unseaworthy due to wide beams and flat bottoms. A lift of opportunity should be used whenever possible. If it is absolutely necessary to tow these craft, the following must be strictly adhered to:

7-7

i. The bow ramp will be secured with a minimum of four angle straps on each side, welded on the outside of the ramp. The size of these straps should be at a minimum of 4” by 3/8” and overlap the bow ramp and sides of the craft at a minimum of 10”.

ii. All normal securing devices (i.e., ramp chains, dogs, and turnbuckles) are in place and in good mechanical order.

iii. All hatches, scuttles, and doors have good gaskets and all securing devices are in proper operating condition.


H-9

Reference N/A Yes No rr. Are 1-foot by 3-foot draft marks painted on the sides of the hull forward,

aft, and midships at the water’s edge to allow visual inspection for proper trim during transit?

5-7.1.6

ss. Are all lifelines in place and in good condition?

tt. Are ladders available for boarding on both port and starboard sides? Figure 5-7

uu. Do rungs go all the way to the WL?

vv. For unmanned ships with freeboard over 10 feet, are rungs welded to the sides?

ww. Is condition ZEBRA set throughout the tow?

If the answer is Unsatisfactory, list exceptions on separate sheet.

xx. Are damage control inspection routes marked by paint/diagrams and/or reflective tape?

5-8.4

yy. Is interior access sufficiently marked for DC teams?

zz. Shoring may be required to prevent damage to deck fittings, wirings, scuttles, doors, etc. Has this been accomplished?

4. FLOODING

Reference N/A Yes No a. Are amber (upper) and white (lower) alarms lights installed? 5-7.1.3

b. Are flooding alarm lights visible for 360º and centered forward on the tow?

Note: Are additional spares available for long tow?

5-7.1.3

c. Are both the low and high water flooding alarm lights rigged with two bulbs each?

5-7.1

d. Are flooding alarm lights rigged with a separate battery source?

Note: Flooding alarm lights must not be connected to navigational lights.

5-7.1.2

e. Are batteries sufficient to provide continuous operation for the duration of the tow?

5-7.1.2

f. Total amperage capacity:

Sufficient amperage must be calculated and available to cover the following:

(1) Wattage of the bulbs serviced

(2) Distance of bulbs from battery source (wiring losses)

(3) Duration of tow

g. Are flooding alarm lights rigged with flasher-type units? 5-7.1.3

h. Is all wiring connected to sensor indicator lights run below decks insofar as possible?

5-7.1.1

i. Is all wiring secured and protected from any chafing? 5-7.1.2

j. Is all topside wiring protected from weather damage? 5-7.1.2

k. Are flooding alarms rigged in all major compartments closest to the keel?

5-7.1.1

l. Do all below-waterline areas have alarms?

Note: If the answer is Unsatisfactory, attach a list of below-waterline areas that do not have alarms. Tanks and voids that can be flooded without sounding an alarm should be identified and the decision not to install alarms justified.

5-7.1.1


H-10

Reference N/A Yes No m. Is this list attached?

n. In large craft or in barges where compartments run athwartships, are flooding alarms rigged on both port and starboard sides?

5-7.1.1

o. Are flooding alarm sensors well-secured to fixed objects such as stanchions, drainage pipes, or ladders?

5-7.1.1

p. Is the lower indicator light wire rigged to the 1-foot flooding alarm sensors?

5-7.1.1

q. Is the upper indicator light wire rigged to the 3-foot flooding alarm sensors?

5-7.1.1

r. Are the batteries secured for heavy weather?

Note: If topside, batteries must be in a watertight box. The location should be carefully selected and secured from heavy seas. If possible, batteries should be inside the ship.

s. Is battery ventilation adequate?

5. DEWATERING

Reference N/A Yes No a. Is dewatering equipment required? 5-8.3.1

b. Are all main spaces accessible for adequate dewatering capability? 5-8.3.3

c. Is a list of spaces that are unreachable by dewatering equipment attached?

d. Location of pumps/generators/eductors:

e. Has equipment been tested?

f. Amount/location/size of hose:

g. Is adequate fuel available for pumps/generators? 5-8.3.2

6. FIRE FIGHTING

Reference N/A Yes No a. Is fire fighting equipment required? 5-8.2

b. Have pumps been demonstrated to have sufficient suction lift and discharge head?

5-8.2

c. Are at least two P-100s or operating fire pumps and all other necessary fire fighting equipment on board?

d. Is there enough P-100 fuel on board? 5-8.2

e. Is means for storage of fuel adequate?

7. NAVIGATION

Reference N/A Yes No a. Are proper navigation lights installed for towed unit? 5-7.7

b. Is each light rigged with two bulbs, so that if one burns out the craft still complies with COLREGS?

5-7.7

c. Is all wiring well-secured and protected from damage by the elements?

d. Is the tow equipped with a solar switch or time switch?

5-7.7


H-11

Reference N/A Yes No e. Are the batteries secured for heavy weather?

Note: If topside, batteries must be in a watertight box. The location should be carefully selected and secured from heavy seas. If possible, batteries should be inside the ship.

f. Is battery ventilation adequate?

g. Are the batteries charged with sufficient amperage available to keep the lights burning brightly for the duration of the trip?

5-7.7

h. Total ampere capacity of the bank: Sufficient amperage must be calculated and available to cover the following:

Table 5-4



(3) Duration of tow (taking into consideration the solar/time switch and length of the period of darkness).

i. Are day shapes rigged in accordance with COLREGS?

8. CARGO

Reference N/A Yes No a. Will craft have cargo on board?

b. If liquid cargo, give location and type (include any residual liquids):

c. Is solid cargo stowed below the main deck secured in position? If so, list location and type:

d. Is solid cargo stowed topside secured in position? If so, list location and type:

Note: All solid cargo on board must be well-secured from heavy weather. All cargo topside must be secured with wire straps and properly secured turn-buckles or equivalent securing devices. In some cases, shoring will be required.

e. Will cargo stowed on board adversely affect the stability of craft?

If so, revise stability calculations in Section 4 of this checklist.

f. Has a manifest of all cargo been prepared for the towing ship?

9. MAIN TOWING GEAR

Reference N/A Yes No a. Have towing attachment points and fairleads (including chocks/bullnose)

been non-destructively tested?

Note: Dye penetrant recommended.

4-5


H-12

Reference N/A Yes No b. Date of last test:

c. Test procedure(s) used (visual, dye, MT):

Note: If there is any evidence of damage, rust, misalignment, or other damage, visual inspection should not be relied on.

d. Has all chain in the towing bridle been measured in accordance with NSTM 581 and Appendix D?

Note: The towing bridle is normally chain on ocean tows. On some service craft, especially barges, wire has been successfully used. Wire should be used with extreme caution, however, due to problems with chafing.

4-6.6

e. Is the Annual Towing Machine/Towing Winch Certification on hand? 5-9.2

f. Does the vessel have a copy of its Tow Hawser Certification? 5-9.3

g. Is the Master’s Towing Certificate onboard (Commercial Vessels)? 5-9.4

h. Is towing bridle of sufficient size and strength, according to the restrictions listed below? The following restrictions apply:

4-6.6

(1) For service craft up to 500 tons, no less than 1 1/4” chain.

(2) For service craft above 500 tons, no less than 1 5/8” chain.

(3) For ships, the bridle must be equal in size to the ship’s anchor chain, but not less than 1 1/4”. Large ships do not need chain larger than 2 1/4” when towed by U.S. Navy towing ships. More powerful commercial tugs will require larger chain bridles.

(4) Non-magnetic chain and attaching hardware will not be used for towing bridles.

(5) Single leg bridles of ships must be anchor chain or larger, but not less than 1 5/8”.

(6) The length of each leg of the bridle from the towing attachment point to the flounder plate after rigging is completed must be equal to or greater than the horizontal distance between the attachment points.

(7) A bridle apex should be between 30 and 60 degrees, with 60 degrees the optimal angle.

(8) On some ships with high bows (e.g., CV, AD, AOR, AFS), it may be necessary to rig a one or two-shot chain pendant between the bridle flounder plate and the towing hawser.

Note: Preparing activity should check with the towing activity as to the desired rig.

i. Are all detachable links in the bridle legs and chain pendant locked with a hairpin?

Note: If not, the towing bridle is unsatisfactory.

4-6.6

j. Are all bridle legs of the same size chain and equal in length when rigging is complete?

Link count:

Note: To ensure accuracy, counting links prior to rigging and painting bench marks is the only positive method. Total links per bridle should be equal at the attachment point on the tow.

4-6.6


H-13


k. If a wire bridle is used, and there is a point of chafe on the tow, has sufficient chafing protection been provided?

Note: Chafing of wire bridles can be severe. Chafing protection must be used to prevent failures.

4-6.6

l. If towing pads do not exist and bitts or cleats must be used, are they substantial enough to handle the strain of towing?

6-2.6.2

m. Are fairlead chocks and/or bullnose substantial enough to handle strain of towing?

n. Is the tow bridle fairlead angle sufficiently straight to preclude excessive side loading to fairlead points?

o. If mooring bitts are used, state the condition of bitts and surrounding deck areas. If any doubt exists, request that the area be non-destructively tested.

6-2.6.2

p. Is the towing bridle rigged with a backup system? 4-6.6

q. If mooring bitts are used a bridle attachment points, has heavy channel iron been welded across the bitts to prevent the wire or chain from jumping out?

Note: A minimum of 4-inch channel iron is recommended.

6-2.6.2

r. Type of backup, cleats, bitts, padeye: 4-6.6

s. Distance from towing pad or bitts to backup point:

t. When using a chain bridle and sets of bitts as the towing point, it is preferable to terminate the chain before reaching the bitts, using wire to make the connection to the bitts. When load-sharing between two sets of bitts, take only one round turn around one barrel of the first set and lead the wire to the second set, where it is terminated with a round turn followed by “figure eights”. Has this been done?

4-6.6

u. Has all slack been taken out of the “figure-eights”? 4-6.6

v. Has all the slack been removed from the backup wires so that all parts will take an equal strain if the attachment points fail?

4-6.6

w. In most cases, the bridle legs are run through closed chocks before being connected to the towing pads or bitts. The lead angle from the connecting to the chocks must be fairly straight to prevent bending and failure of the chain where it passes through the chock. Does the towing rig conform to the above?

x. Is there sufficient and adequate metal thickness at all potential chafing points to prevent the bridle from cutting into the chocks, gunwale, or hull?

y. Is the size of the bridle retrieving pendant adequate (i.e., providing a 4:1 safety factor in lifting bridle weight, but no less than 5/8-inch rope?)

4-6.8

z. Is there an adequate number of wire clips securing the retrieval pendant?

Table 4-1

aa. When attached from the bow of the tow to the flounder plate, is there enough slack to allow the retrieval pendant to droop slightly with no strain when the unit is being towed?

4-6.8

bb. Are flounder plates and plate shackles of approved design, and rigged in accordance with this manual?

Appendices D and I

cc. Is there a clearance in excess of 1/16” in securing pins in plate shackles, flounder plates and other towing jewelry?

Note: If not, the rig is unacceptable.

Appendix I


H-14


dd. All plate and safety shackle pin nuts must be locked with a minimum of a 5/16-inch machine bolt through a drilled hole in the plate shackle nut and pin. Secure the machine bolt in place with jam nuts. It is highly recommended that the bolt be peened over. Has this been done?

4-6.1

Appendix I

ee. Lateral movement must be removed from the plate shackle connections by using washers or welding bosses on the plates. Has this been accomplished?

Note: Welding is not acceptable.

Appendix I

ff. Are all safety shackles of the approved types and materials listed in the Appendix D?

4-6.1

Appendix D

gg. If a multiple tow is planned (and you are the planning activity), have you checked to ensure that all the necessary equipment is available to rig and stream the tow in accordance with the appropriate towing method?

Note: Standard U.S. Navy practice allows three possible versions: the Christmas Tree, Honolulu, and Tandem rigs. Any rig selected must be rigged in accordance with this manual.

Appendix I

hh. Rig selected:

ii. Normally, an open-ocean tow has solid connecting jewelry, but in cases of damaged and some calculated risk tows (such as some SINKEXs), an emergency quick-disconnect method such as a pelican hook is advisable. If this is such a tow, is an emergency quick disconnect provided?

6-6.2.3

6-7.6

jj. If so, provide the method used:

kk. If an emergency quick disconnect is provided, will all jewelry fit through all fairleads through which it must pass (e.g., the bullnose)?

6-7.6

ll. Has the system been designed with a safety link? 4-10

mm. Identify the weakest element in the towing rig: Breaking strength of the weakest element:

10. ANCHORING

Reference N/A Yes No a. Has an emergency anchoring system been rigged? 5-8.5

b. Is anchor rig capable of holding the vessel in 60’ of water with at least 3:1 ratio of scope of depth?

5-8.5

c. Is there a need for a deeper anchoring system?

d. If so, what is the depth required?

e. Is the rig capable of meeting this deeper requirement with at least a 3:1 ratio of scope to depth?

f. Is it rigged for quick release? 5-8.5

g. Is it secured for heavy weather?

h. Has the anchor windlass brake been tested?

i. If plans have been made to anchor the tow at port of delivery, is power available to raise the anchor?


H-15

11. SECONDARY TOWING GEAR

Reference N/A Yes No a. Are the secondary towing system’s attachment and fairlead points

adequate to tow the vessel? 4-5

b. Is adequate chafing protection provided for the vessel’s secondary towing systems?

c. Is the secondary towing pendant or the ship’s emergency tow pendant at least 1 5/8” wire rope?

4-4

d. Is the secondary towing pendant stopped off in bights on one side of the tow? 4-4

e. Are the stops sufficient to hold in heavy weather, but accessible to allow cutting and light enough to be broken without damaging the towing pendant or tow?

4-4

f. Will the secondary pendant fall free without turns that will cause kinking as they pull out?

4-4

g. Is the secondary towing pendant fitted with a synthetic line messenger to facilitate passing it to the tug?

4-4

h. If the tow is unmanned, is polypropylene floating retrieval line (5”-8” circumference) attached to the end of the messenger with a small buoy secured at its end?

4-4

12. SPECIAL CONSIDERATIONS

Some types of tows require special consideration. For instance, YTBs, YTMs, and other self-propelled service craft were not designed to go to sea and are not very seaworthy. In these craft, the watertight envelope must be absolutely complete; they have low freeboards and water will constantly be breaking over them in moderate seas. Because of the constant pounding of the seas caused by their flat bottoms, submarines are not designed with towing in mind. Generally, a towing padeye is installed near the sail as a single towing point. See Section 7-5 and Appendix J of the U.S. Navy Towing Manual for data concerning submarine tows. Extensive information concerning towing of unmanned, defueled, nuclear powered submarines is contained in NAVSEAINST 4740.9 Series. (For unmanned, defueled, nuclear powered cruisers, see NAVSEAINST 4740.10 Series.) There are many hulls whose design will require special towing rigs. Additional work may be required to rig an applicable bridle to ensure safe delivery of a craft from port to port. This will require additional lead time to prepare the tow(s) for ocean transit. Submarines, wooden-hull mine sweepers, sailing craft, etc., fall into this category. When towing a sharp “V-shaped” hull that has a bullnose and a bulbous bow/sonar dome, the single leg bridle is the preferred method of rigging. Rig using at least two shots of the tow’s anchor chain if that chain is acceptable.


H-16

13. REMARKS:


H-17

H-18

H-2. SAMPLE CERTIFICATE OF SEAWORTHINESS/DELIVERY LETTER FIRST ENDORSEMENT 1. Upon inspection of the tow described above, the following unsatisfactory conditions were found,

which render the tow unseaworthy or not ready for towing (if none, so state). a. b. c. d. 2. (Cross out the statement which is not applicable). a. I find the tow described above in a condition satisfactory for towing, and hereby assume

responsibility for delivery to the port of destination prescribed in my sailing orders. b I will accept the tow as an acceptable risk only upon authorization of my operational commander. I

have notified my operational commander of the reasons for this action. Commanding Officer, USS Date SECOND ENDORSEMENT (To be accomplished only if an acceptable risk tow is acceptable to delivery authority). 1. The following conditions listed in the first endorsement remain uncorrected.

a. b.

2. It is requested that you accept this tow in the above condition as an acceptable risk. Representative of command having cognizance of towed unit.

Date

SL740-AA-MAN-010

H-19

THIRD ENDORSEMENT 1. As authorized by __________________________________________ (DTG reference of operational commander’s message) I accept this tow, with conditions existing as described in the second endorsement, as an acceptable risk for delivery to the port designated in my Sailing Orders. ___________________________________________________________________________________

Commanding Officer, USS Date ___________________________________________________________________________________

SAMPLE DELIVERY LETTER From: (Receiving Activity) To: (Commanding Officer of Towing Vessel) 1. Received custody of (describe tow) this date. Representative of Receiving Activity. Date

H-20

This page intentially left blank


Appendix I

TOWING RIGS

I-1 Introduction

This appendix includes towing plans anddrawings of towing equipment and riggingassociated with towing operations. Towingrigs can be made up in various configura-tions. Select the tow rig based on its past per-formance and the needs of the particular tow.Although most Navy tows are simple, single-tug, single-unit operations, some tows areconsiderably more complex, consisting of asingle tug with multiple towed units. Occa-sionally, the displacement of the towed unitrequires using more than one tug.

The enclosed drawings are intended to serveas both guidance and examples of typical towconfigurations. Exercise care in selectingcompatible components. Keep these impor-tant points in mind:

• Each leg of a bridle should be strongenough to assume the entire resistanceof the tow.

• When using underiders, using chainbridles and pendants will promote adeeper catenary and minimize interfer-ence with intermediate tows.

• Towing flounder plates and plate sha-ckles are designed to be fabricated easi-ly. Flounder plates and cheeks of plateshackles can be fabricated from com-mon steel (that is, ABS Grade A orASTM A-36). Pins must be machinedfrom 150,000 psi minimum yield mate-rial such as AISI 4140. When pins arefabricated, it is recommended that amaterial certification be required.

• Plate shackles shown in these drawingsare not necessarily suitable for beach

gear or heavy lifting rig applications.These efforts generally require more ro-bust hardware.

I-2 Single Tug, Single Tow Configurations

Three common variations of the single tug,single tow configuration are a single hawserwith pendant, a single hawser with bridle, andtowing alongside. A fourth variation, the Liv-erpool Bridle, is used in special circumstanc-es where extra control is required.

I-2.1 Pendant or Single Leg Rig

The pendant rig is the simplest and moststraightforward rig and generally is used foropen-ocean towing of ships with fine bows,sonar domes, bulbous bows or when the towis most stable in this configuration (see Fig-ure I-1). All of the components are linked in aseries. A distinguishing element of the pen-dant rig is the deployment of a single chafingpendant to a single attachment point on thetowed vessel. The pendant rig is usually usedfor emergency towing. Outboard of the tow’sfairlead, the chafing pendant usually is con-nected via a leading chain and/or a towingpendant to the tug’s hawser. The advantage ofthe pendant rig is its ease of connection.There is little, if any, likelihood of the pen-dant fouling on the cutwater or other outboardstructure

I-2.2 Bridle Rig

The bridle rig is characterized by a two-legged bridle instead of the single pendant onthe towed vessel (see Figures I-1 throughI-3). The length of each bridle leg should beapproximately equal to the beam of the towedvessel. The fitting at the apex usually is a

CAUTION

Each leg of a bridle should bestrong enough to assume the entireresistance of the tow.

I-1


Figure I-1. Towing Rigs (Plan View).

Angle is Less Than orEqual to 100 Degrees

(60 Degrees Preferred)Bitts

Bridle Rig

Pendant or Single Leg Rig

AnchorWindlass

Chain Stoppers

Flounder Plate

I-2


Figure I-2. Example of Chain Bridle with Chain Pendant.

Tow Wire

ounder Plate -

P late Shack le -

Underrider:1 " D . x 600' Leg5

8

ounder Plate -

1" D. Retrieving Wire

Abo ut 60°

58

58

Tow P nd ant1 " D . x 75' Leg

Tow Pend ant: 1 " D . x 75' Leg,Stud-Link Chain

P late Shack le -

P late Shack le -

P late Shack les -

Fl

Fl

N O TE

S ize and leng th o f cha in to bede te rm ined in each case by :• S ize and w e igh t o f tow• B eam o f tow• D is tance to be tow ed• Type o f w ea the r expected• E x ten t o f C ha fing

Figure I-18

Figure I-17

Figure I-17

Figure I-15, D etail B

Figure I-18

Figure I-15, D etail B

Plate Shackle Portand StarboardFigure I-17

Tow Shackle; P late orSafety Shackle - Figure I-16

e

*

*

*

*Used for M ultiple Tow s

I-3


Figure I-3. Example of Wire Bridle with Wire Pendant.

Tow Shackle; Plateor Safety Shackle

Flounder P late*Figure I-15, Detail B

Plate Shackle* - Figure I-18

Flounder P late -Figure I-15, Detail B

Plate Shackles - Figure I-18

TowingPadeyes

About 60°



Tow Wire

Tow Pendant: 1 5/8” D. X 75’ Leg(or 90’ 2-1/4” Chain to IncreaseUnderrider Depth)

Tow Pendant: 1 5/8” D. X 75’ Leg

Underrider*:1 5/8” D. X 600’ Leg

1 5/8” D. 6x37, W ire Rope,Thim bles Both Ends1” D. Retrieving W ire

*Used for M ultiple Tows

I-4


flounder plate with the two bridle legs con-nected at its base and the apex usually con-nected to the lead chain and/or towing pen-dant, which in turn is connected to the towhawser.

The bridle rig places more and heavier rig-ging outboard of the towed vessel. This canlead to rigging problems on the deck of thetow. Furthermore, the bridle rig, by defini-tion, uses two off-centerline fairleads. As aconsequence, if the tow does not track the tugdirectly astern, there may be an off-center dy-namic load. This load, while tending to beself-correcting, unbalances the loads on eachbridle leg. Therefore, each bridle leg must beof full towline strength. Finally a criticalproblem of the bridle rig occurs when turn-ing, or when the tow sheers off to the side ofthe tug’s track, and the bridle leg on the farside can ride against the cutwater of the tow,causing damage to itself as well as to the tow.

In many cases, the foredeck arrangement, hy-drodynamic characteristics or need to tow thevessel backwards does not permit the use of abridle rig. For example, aircraft carriers andLSTs have forecastle arrangements that re-quire using a pendant rig. Bridle rigs are com-monly used on ships with blunt bows andbarges.

I-2.3 Towing Alongside

Towing alongside or “towing on the hip” is aconfiguration often used in congested waters(see Figure I-4). Towing alongside offers ex-cellent control. This configuration is not rec-ommended for the open ocean, however, be-cause of motion between the tug and tow in aseaway. When complex maneuvering is re-quired, consider having harbor tugs to do thejob or assist during difficult phases of the ma-neuvers.

For towing alongside, the tug generally se-cures to one side of the tow, well aft on the

Figure I-4. Towing Alongside.

1. Bow or Backing Line.2. Tow ing Line (Power).3. Stern Breast or Turning Line.

I-5


Figure I-5. Liverpool Bridle.

1 5/8” Wire Pendant

3” Synthetic Lazy Jack50 Feet LongEye and Thimble Spliced in One End

3” Synthetic Lazy Jack100 Feet LongEye and Thimble Spliced in One End

Carpenter Stopper

Main Hawser tothe Stranded Ship

“H” Bitt

Port Leg StoppedOff Ready for Use

Secured toBitt or Through

Chock to Bitt

Current D irection

I-6


tow to increase the control effectiveness ofher propellers and rudder.

I-2.4 Liverpool Bridle

The Liverpool Bridle, as shown in Figure I-5,is a towline harness designed to permit a tow-ing vessel to maintain fine control over head-ing and position. The Liverpool Bridle isneeded in circumstances, typically strandings,where currents and weather make it impossi-ble for a conventionally rigged tug to main-tain its station in relation to the tow. The Liv-erpool bridle is particularly useful when theheading of the tug must be different than thedirection of application of towing force.

The Liverpool Bridle requires:

• A towing winch

• One carpenter stopper secured to thetowline

• Two pendants of 1 5/8-inch wire ropewith a soft eye spliced in one end andan eye with a thimble spliced in the oth-er end.

• Two 3-inch synthetic fiber lazy jacks:one 50 feet long and the other 100 feetlong, each with eye and thimble splicedin one end. The lazy jacks are retrievinglines only and take no strain.

One pendant is used on the starboard side, theother on the port side. By rigging a bridle oneither side of the tug, the towing point can beshifted from side to side to facilitate ship con-trol. The pendants should be long enough torun slack from the forward rail or shoulderbitts, which are closest to the pivot point ofthe ship, outboard and in over the quarter to apoint on the centerline about 20 feet abaft thetowing H-bitts. Thus configured, the point oftow is forward of the vessel’s normal pivotpoint, and the tug is able to maneuver to keepher head in the desired direction.

A typical application of a Liverpool bridle isshown in Figure I-6.

I-3 Single Tug, Multiple Unit Tow Configurations

Single tug, multiple unit tows consist of onetug and several tows; the connection andmakeup of the tows can be varied. The U.S.Navy currently uses four versions: the Christ-mas, Honolulu, Tandem, and Nested rigs.

I-3.1 Christmas Tree Rig

The Christmas Tree rig is used for open-ocean towing (see Figures I-7 through I-10).It requires a review of water depths and bot-tom conditions prior to use. The catenary ofthe towline from tug to the first tow and sub-sequent connecting wires must be deepenough to ensure that the underrider passessafely below the bow of the leading tow(s). Itis important to have adequate water depth toprevent grounding the towline. Using chainbridles and pendants will promote a deeperunderrider and minimize interference with in-termediate tows.

Harbor tug assistance usually is required tobreak up the Christmas Tree rig before enter-ing port. With the assistance of harbor tugs, itis feasible to break out one of the tows with-out disrupting the remainder. Although astrong rig, it is difficult to make up and dis-

CAUTION

When towing alongside, keep alllines taut until ready for streamingthe tow. This will prevent the towfrom pounding alongside the tugand ensure effective control of thetow.

CAUTION

In operating the Liverpool Bridle,limit the tension to the safe workingload of the bridle’s 1 5/8-inch wirerope pendant.

I-7


Figure I-6. Use of Liverpool Bridle on Stranding Salvage.

Current

Dir

ectio

n of

Pul

l

Tug

Hawser

Dotted Lines ShowReverse Set

Stranded Ship

I-8


Figure I-7. Christmas Tree Rig.

Un

der

rid

erA

dd

itio

nal

Tow

Co

nn

ecti

on

Can

Be

Mad

e

Tow

Wir

e

Tow

Pen

dan

tC

hai

nB

rid

leF

lou

nd

er P

late

wit

h P

late

Sh

ackl

esTo

wP

end

ant

Tow

Sh

ackl

e

I-9


Figure I-8. Example of a Christmas Tree Rig Configuration with Chain Bridle.

Flounder Plate - Figure I-15, Detail B

Plate Shackles -Figure I-17

1-5/8” Chain Pendant, 45’ Leg (Optional)

Underrider: 1-5/8” x 600’ Leg

Chain Bridle

NOTE

1” Retrieving Wire

Plate ShacklesFigure I-18

R e t r ie v in g w i re m a y b e e y e -sp liced over th im ble and shackled in to padeye in lieu of using a w ire rope socket. Ensure re trieva l w ire hangs slack at any conceivable tow -ing angle.

NOTE

S ize a n d len g th o f cha in to b e d ete r-m in ed in ea ch case b y:• S ize a n d w e igh t o f tow• B ea m o f to w• D istan ce to b e to w e d• Typ e o f w e ath er exp ec te d• E xte nt o f C h a fin g

I-10


Figure I-9. Example of a Christmas Tree Rig Configuration with a Wire Bridle.

Underrider: 1-5/8” x 600’ Leg,6 x 37 IW RC

Flounder Plate -Figure I-15 3 Plate Shackles -

Figure I-18

NOTE

C onsider the risk of underride rinte rfe rence w ith tow s. U se o fcha in com ponents w ill increasethe depth of the underrider. S ee F igure I-8 .

Wire Bridle1 5/8”6 x 37 IW RC

1” Retrieving Wire

NOTE

S ize and length o f cha in to bedete rm ined in each case by:• S ize and w e igh t o f tow• B eam of tow• D is tance to be tow ed• Type o f wea ther expected• E x ten t o f C hafing

I-11


connect and does not facilitate getting all ele-ments in step. Figure I-10 shows a series ofbarges at the pier, ready for streaming.

The forward most tow wire will be subject tothe total resistance of all of the attached as-sets. The strength of this gear must bechecked carefully.

I-3.2 Honolulu Rig

The Honolulu rig was developed for inter-island towing, where individual units of mul-tiple tows were delivered to or picked upfrom different ports (see Figure I-11).

The first tow streamed is connected to themain tow wire and streamed farthest aft. Ad-ditional tows are connected with auxiliarytow wires to quarter bitts or auxiliary drums.The Honolulu rig allows independent connec-tion of the two tows, disconnecting and con-trol are readily workable, and it is relativelyuncomplicated to get both tows in step withthe tug. Additionally, each tow wire is subjectto the resistance of only one asset.

I-3.3 Tandem Rig

The Tandem rig, with its close-coupled tows,is generally used only in congested waterswhere good control is required (see FigureI-12). This is the least desirable of the singletug/multiple tow arrangements, as it lacks theflexibility and control of the other rigs forbreak-up upon entering port.

The rig connects the tug to the first tow, withsubsequent tows connected to the one in frontof it. The intermediate towline connects thefirst tow to the second, and must allow aproper catenary depth to minimize the surg-ing action between the tug and first tow, andbetween the first and second tows. It is diffi-cult to keep all elements in step with this typeof rig. Similar to the Christmas Tree Rig, theforward most tow is subject to the forces ofall assets. It may be that the fittings availablefor tow points on the after end of the first toware insufficient to withstand the strain of sub-sequent tows. Remember that these must not

only survive the steady tension of the addi-tional tows, but also the dynamic tensions.These attachment points must be inspectedusing the same criteria for primary attach-ment points.

I-3.4 Nested Rig

A nested rig tow employs multiple tows se-cured alongside each other so they may betowed as a single unit. Advantages of using anested rig include maneuverability, ease ofpreparation, and ease of retrieval. Because thenested vessels can work against each otherand inflict considerable damage, this rig is tobe used only in protected waters. A nested rigis generally controlled by a tug tied alongsideor by specially designed pusher boats. Riderlines can be used, but a short scope should bemaintained to ensure adequate control. Caremust be taken to ensure barges do not breakfree during these operations.

When using any of the above rigs, use one ofthe flounder plate arrangements shown inFigures I-8 and I-9. Chain should be used asbridles when possible to reduce chafing. Wirebridles can be used if proper care is taken tominimize chafe points and it is calculated thatwire provides sufficient strength when usingthe christmas tree rig or the tandem rig. (Re-member that the forward most gear will besubject to the combined tow forces of all ofthe attached assets. This gear should be sizedaccordingly.)

I-4 Multiple Tug, Single Tow Configurations

It may be desirable to use more than one tugfor a single tow. Greater power, increasedtowing speed and better control may be ob-tained in a multiple tug tow. Multiple tugs aregenerally used to tow large ships, deep-draftlarge-displacement dry-docks, deep-draft bar-ges, or battle casualties.

I-12


I-4.1 Side-By-Side Towing

Figure I-13 shows side-by-side tugs towing asingle tow. Each towline should have its ownconnector and chafing fairlead. There is nouniversally preferred method of two-tug tow-line arrangement. Most operators prefer totow “side-by-side” with equal hawser scopesto avoid sweeping over the other tug’s tow-line. A few operators prefer different scopesto minimize the risk of tug collision. In suchcases, the more powerful tug is designatedlead tug, with a longer hawser scope. Thelead tug may use a longer lead chain to in-crease the catenary depth. This reduces thechance of interference, should the following

tug suffer some untoward event that results inits crossing the lead tug’s towline.

I-4.2 Steering Assistance

At times when a tug has a tow at short scopein restricted waters, steering assistance isneeded. This assistance can be provided byanother tug, normally a harbor tug, astern ofthe tow. Usually the steering tug’s main ef-fect is to restrain the movement of the tow,primarily in yaw. U.S. Navy towing shipsrarely perform this function. Use of steeringtugs varies widely, depending upon localpractice, tug design, and pilot preference. Noattempt is made herein to provide informationon steering tug connections.

I-13


Figure I-10. Three-Barge Tow in Christmas Tree Rig Ready for Streaming.

5” N

ylo

n E

asin

g-O

ut

Lin

e, P

ort

an

dS

tarb

oar

d(A

ll to

ws

sim

ilar)

Do

ck

Sp

acin

g 1

0’ t

o 4

0’,

to s

uit

Big

ht

of

5” N

ylo

n R

eeve

d T

hro

ug

hB

ow

Ch

ock

an

d A

rou

nd

Bit

tsF

or

Tow

ing

Ou

t o

f H

arb

or

Ch

ain

Bri

dle

Tow

Wir

e

Tow

Sh

ackl

e(P

late

or

Saf

ety)

Ext

ra-H

eavy

Sei

zin

g o

nT

hir

d B

igh

t

Tow

Pen

dan

t: 1

5/8

” D

. X 7

5’W

ire

Ro

pe.

Fo

rwar

d O

ne

Op

tio

nal

. Ch

ain

Pen

dan

tIs

Pre

ferr

ed w

ith

Ch

ain

Bri

dle

1 5/

8 D

. X 6

00’ L

eg. 6

x 3

7, H

igh

Gra

de

Plo

w S

teel

Wir

e R

op

eS

top

ped

Off

Ove

r th

e S

ide.

Flo

un

der

Pla

tes

for

Bri

dle

an

d U

nd

erri

der

Sto

pp

ed O

ff O

ver

the

Bo

w

1” R

etri

evin

gW

ire

DIR

EC

TIO

N O

F T

OW

I-14


Figure I-11. Honolulu Rig.

NO

TE

Use

of a

cha

in b

ridle

and

a ch

ain

pend

ant w

ill in

crea

seth

e ca

tena

ry o

f the

mai

n to

w

wire

.

Bri

dle

Mai

n T

ow

W

ire

Tug

Tow

Win

ch

Au

xilia

ry

Tow

Wir

eB

itts

Cap

stan

I-15


Figure I-12. Tandem Rig.

Tow

Pen

dan

t

Ch

ain

Bri

dle

Tow

Co

nn

ecti

on

Po

ints

Flo

un

der

Pla

te

To

wW

ire

Pla

teS

hac

kle

Ch

ain

Bri

dle

Tug

NO

TE

Use

ofa

chai

nbr

idle

and

ach

ain

pend

antw

illin

crea

seth

eca

tena

ryof

the

mai

nto

ww

ire.

I-16


Figure I-13. Two-Tug Tows.

FlounderPlate

ChainPendant

Flounder Platewith

Plate Shackles

Tow Wire

NOTE

The side-by-side towing arrangement shown here,with the tugs towing on unequal towline scopes, isnot necessarily preferred over an arrangementwhere the tugs use equal towline scopes. See Sec-tion I-4.1.

I-17


Figure I-14. Example of Chain Bridle and Pendant.

NO TE

Retriev ing w ire m ay be eye-sp liced over th im ble and shack-led into padeye in lieu of us ing aw ire rope socket. Ensure re-trieval w ire hangs s lack at anyconceivable tow ing angle.

Plate Shackle - as RequiredFigure I-16

Chain PendantSize and Length

to S uit Tow

Flounder P lateFigure I-15 , Deta il B

Chain Bridle -See Notes on

Figure I-2

Plate Shackles -See Figure I-17

1” Retriev ing W ire

I-18


Figure I-15. Flounder Plate.

2 1/8”

1/4”

40.8 LB. Plate

2 9/16”D. - 1 Hole

15”15”

2”

1 1/2”R.

7 1/2” 7 1/2”

3”R.

1-1/2”D. Hole forRetrieving Wire.

2 5/16”D.- 2 Holes

NOTE

Detail A - Flounder Plate M edium Steelfor Use w ith 2-1/2” Pin Shackle and 2-1/2” Shackles

Detail B -- Flounder Plate Medium SteelSimilar to Detail ‘A’ Except as Noted.

ABS Grade A, ASTM A-36 or Equal

2 5/16” D. - 3 Holes

In no case shou ld d iam ete r of flounder p la te holes be m ore than 1 /4 ” larger than the shackle p in d iam ete r. A 1/16” clearance on d iam eter is p re fe rred.

I-19


Figure I-16. Plate Shackle and Pin for 2-Inch Closed Socket.

Weld Nut to Pin,One Side Only

PinSee Detail B Below

40.8 Lb. MS Plate Spacers

3/8 - 16UNC - 2A Securing PinSecure with 2 Jam Nuts

Tack Weld Nut to Pin with WasherFace of Nut Here

7/16” Drill

7/16” x 9/16” Slot

9/16”

1/8” CLNeck 3/16”R. X 3/16” Deep

Alter to Suit Hawser Termination

3 5/16”

3/8”

3/16”

6”D. X 10.2 LB. (1/4”) Plate Boss2 Required

2 1/2 - 4UNC - 2B Nut, STL,4 Required.Slot 2 OnlySee Detail B Below

6”4”6”

40.8 Lb. (1”) MS Side Plates2 Required

2 9/16” D. Hole

3 1/4”R .

Detail ATow Plate Shackle

11”

5-5/16” 2-27/32”2-27/32”

2-1/2”D.

1-1/8”

Detail BShackle Pin - 2 Required

NOTES

1. P la te m ateria l: AB S G rade A. A S TM A-36 o r s im ilar2 . P in M ate ria l: A IS I 4140 o r sim ila r 150 ,000 P S I m in im um y ie ld3 . A djus tab le shackle w idth and p in leng th to suit haw ser term ination .

2 1/2 - 4UNC - 2A

I-20


Figure I-17. Plate Shackle and Pin.




3/8 - 16 UNC - 2A Securing PinSecure with 2 Jam Nuts


7/16” Drill

7/16” x 9/16” Slot

9/16”

1/8” CLNeck 3/16”R. X 3/16” Deep

2-3/8”

6” 4” 6”

3/8”

40.8 Lbs. (1”) MS Side Plates,2 Required

2-1/4 - 4 1/2 UNC - 2B Nut, STL,4 RequiredSlot 2 OnlySee Detail B Below

2-5/16”D. Hole

3”R.

Detail APlate Shackle for 1-1/2 - 2-1/4” Chain

9”

4-3/8”2-5/16” 2-5/16”

2-1/4”D. 2-1/4 - 4 1/2 UNC-2A


NOTES

1. P la te m ateria l: AB S G rade A , A S TM A -36, o r s im ilar.2 . P in m ate ria l: A IS I 4140 o r sim ila r 150 ,000 P S I m in im um y ie ld .

1”

I-21


Figure I-18. Plate Shackle and Pin.




3/8 - 16 UNC - 2A Securing PinSecure with 2 Jam Nuts


7/16” x 9/16” Slot

9/16”

1/8” CLNeck 3/16”R. X 3/16” Deep

Alter to Suit Wire Termination

1/4”

40.8 Lbs. (1”)MS Side Plates:2 Required

2-1/4 - 4 1/2 UNC - 2 B Nut, STL,4 Required,Slot 2 Only

6”4”6”

2-7/8”

2-5/16”D. Hole

3” R.

Detail APlate Shackle for 1-5/8”D. Wire Rope

10”

2-9/16” 4-7/8” 2-9/16”

2-1/4” D. 2-1/4 -4 1/2 UNC-2A


1. P la te M ateria l: A BS G rade A, A S TM A - 36, or S im ila r2 . P in M ate ria l: A IS I 4140 o r S im ilar 150 ,000 P S I M in im um Yield. 1”

I-22


Appendix J

EMERGENCY TOWING OF SUBMARINES

This appendix provides information on thetowing attachment points of several classes ofsubmarines. This information is provided toassist the tow ship in planning an emergency(that is, unplanned) tow of a submarine. Theinformation is not all-inclusive, but coversmost submarine classes. The principles canbe adapted to other submarine designs.

Every U.S. Navy submarine has a plan for be-ing towed that is described in the ship’s infor-mation book. In general, all submarines builtprior to the SSN 688, SSN 21, and SSBN 726Classes have similar towing arrangements;these earlier submarines are discussed here asone group. The SSN 688, SSN 21, and SSBN726 Class submarines are discussed separate-ly. Table J-1contains relevant technical datafor the 594, 616, 637, 688, 21, and 726 Class-es of submarines.

J-1 Submarines Prior to the 688 and 726 Classes

J-1.1 Tow Attachment Points

Most submarines built prior to the 688, 21,and 726 Classes have a tow pad at or near thebase of the forward end of the sail or attachedto the forward escape trunk. Lateral strengthis considerably reduced, so a tow fairleadmust be used. The hole size in the padeye is 29/16 inches in diameter in all cases.

Most of these submarines have retractablemooring cleats, forward fairlead chocks, andcapstans. Many have capstans and fairleadchocks aft as well. The inside dimensions ofall the chocks are 10½ x 16½ inches exceptfor chocks on the 594 Class (which have an 8-

inch diameter) and the 598 Class (which are7½ x 12 inches). The oldest SSNs (578 and585 Classes) have fairleads of insufficientstrength for towing. For these submarines, ei-ther the towing pendant will have to be cen-tered laterally by using the mooring cleats oran alternative tow connection will have to bemade. For all other submarines, the fairleadcan and should be used. The smaller fairleadsmust be checked carefully to confirm thattowing jewelry and chafing chain will passthrough the small dimensions provided.

Submarine capstans are designed to handlemooring lines and can withstand the breakingstrength of the mooring lines. The capstancan be used, with caution, as an emergencytowing connection if a tow pad is not avail-able. The capstan, however, is neither power-ful nor fast. It will generally provide a3,000-pound pull at 40 fpm and a 4,500-pound pull at creep. Accordingly, the capstanwill be of little use in passing the tow hawser.The tow ship should plan this procedure tominimize the use of the submarine’s capstan.

J-1.2 The Towing Rig

Most of the submarines in this group carrydesignated towing gear onboard. In general,this gear includes shackles, a pelican hook,and a wire chafing pendant of 1-inch diameteror larger. See Figure J-1 which is adaptedfrom a typical submarine towing plan. Theproof test of the rig is 80,000 pounds. Thistowing rig is designed for short intra-harbortows. It should not be used for plannedopen-ocean towing. The shackles shown in .

CAUTION

Do not tow submarines with thescrew-pin shackles or the pelicanhook provided with the submarine'stowing rig. The towing ship shouldsubst i tute appropriate safetyshackles with the required bolt-locking fitting.

J-1


Table J-1. Towing Arrangement for Higher-Population Submarine Classes.

Ship

/Cla

ss

Des

igne

dTo

w A

rran

gem

ent

(See

Tex

t Cav

eats

on

Use

)

Tow

Poi

ntL

ocat

ion/

Stre

ngth

(SW

L)

Fair

lead

Cho

ckSi

ze/S

tren

gth

(SW

L)

Cap

stan

Loc

atio

n,L

inep

ull,

Max

Pul

l,St

ruct

ural

Str

engt

h

Anc

hor

Loc

atio

nA

ncho

r w

t.C

hain

siz

e

SE

AW

OL

FSS

N 2

1 C

lass

LO

S A

NG

EL

ES

SSN

688

Cla

ss

ST

UR

GE

ON

SSN

637

Cla

ss(S

SN

671

AN

D

685

have

sim

ilar

tow

ar

rang

emen

ts

LA

YFA

YE

TT

ESS

BN

616

Cla

ss

Per

mit

SSN

594

Cla

ss

FR 1

2 P

ort

FR 1

6 S

twb

70,0

00 lb

s (e

a)

Aft

onl

y5.

5” x

11”

140,

000

lbs

Forw

ard.

Onl

y30

00 lb

/40

fpm

4500

lb m

ax70

,000

lbs

Aft

1985

lbs

7/8”

cha

in

Cle

ats

- 1

3/8”

wir

e br

idle

,pe

lica

n ho

ok, 3

1’ x

1 3

/8”

chaf

ing

pend

ant,

coup

ling

for

450’

x 5

” D

B n

ylon

haw

ser.

Tow

ing

gear

car

ried

abo

ard

Pade

ye -

fair

lead

cho

ck 1

7/8

”pe

lican

hoo

k w

ith 1

3/4

”sc

rew

pin

anc

hor

shac

kles

and

link

. To

win

g ge

ar m

aybe

car

ried

abo

ard

Two

Bax

ter

Bol

t typ

epa

deye

s, 1

” w

ire

brid

le le

gs,

each

with

pel

ican

hoo

k pl

usfl

ound

er p

late

. So

me

ship

sha

ve a

rrm

ts s

imil

ar to

SSN

63

7 C

L.

Pade

ye, p

elic

an h

ook

and

clev

is

FR 2

1 P

/S70

,000

lbs

(ea)

Aft

onl

y5.

5” x

11”

70,0

00 lb

s

Forw

ard.

Onl

y30

00 lb

/40

fpm

4500

lb m

ax70

,000

lbs

Aft

2800

lbs

3/4”

cha

in

FR 2

7 (a

t sai

l)47

,000

lbs

FR 4

350

,000

lbs

(ea)

FR 1

8(a

t for

war

des

cape

hat

ch)

47,0

00 lb

s

Fore

and

aft

10.5

” x

16.5

”47

,000

lbs

Fore

and

aft

10.5

” x

16.5

”50

,000

lbs

Fore

and

aft

8” d

ia47

,000

lbs

Fore

and

aft

3000

lb/4

0 fp

m45

000

lb m

ax25

,000

lbs

For

e an

d af

t6,

000

lb/4

0 fp

mun

spec

ifie

d m

ax36

,000

lbs

Fore

and

aft

3000

lb/4

0 fp

m45

00 lb

s m

ax25

,000

lbs

Aft

2800

lbs

3/4”

cha

in

Aft

2800

lbs

1”ch

ain

Aft

2800

lbs

3/4”

cha

in

TR

IDE

NT

SSB

N 7

26 C

lass

Cle

ats

- 2”

wir

ebr

idle

incl

udin

g co

uplin

gfo

r 45

0’ x

8 1

/2”

DB

nyl

onha

wse

r. N

ote:

ent

ire

tow

rig

stor

ed a

shor

e.

FR 1

5 P

/S70

,000

lbs

(ea)

Aft

onl

y5.

5” x

11”

70,0

00 lb

s

Forw

ard.

Onl

y30

00 lb

/40

fpm

4500

lb m

ax70

,000

lbs

Aft

4600

lbs

1” c

hain

Onb

oard

Em

erge

ncy

Tow

ing

Pend

ant -

1.1

25”

chaf

ing

chai

n,

and

1.25

” w

ire

rope

wit

h tw

o N

AT

O s

tand

ard

links

con

ceal

ed in

tr

ough

wit

h re

ady

acce

ss o

n po

rt

side

of

sail.

Cle

ats

- 1

5/8”

wir

e br

idle

in

clud

ing

flou

nder

pla

te p

rovi

ded

by th

e tu

g.

J-2


Figure J-1. SSN 637 Class Towing Gear (Harbor Towing Only).

WARNING

Do not use this towing rig for ocean tows. Screw pinshackles should never be used in ocean towing.

Piece # Name / Dimensions

PC–1PC–2PC–3

Shackle - Anchor, Screw Pin, 1-3/4″Pelican Hook 1-7/8″ Stock, For 1-1/4″ WireLink 1-3/4″ X 15″

NOTES:

1. PC 1 TO BE SIMILAR TO FIG. 6–208 NO. 950–2 OF CROSBY-LAUGHLIN CO., FORT WAYNE, INDIANA OR EQUAL.

2. PC 3 TO BE FORGED AT 2000–2200ºF AND COOLED SLOWLY. PREHEAT TO 400–600ºF BEFORE WELDING. WELDING TO BE FINISHED BEFORE HEAT TREATMENT. HEAT TREAT TO 1525–1575ºF. QUENCH IN OIL AND TEMPER AT 1200ºF TO GIVE PHYSICAL PROPERTIES AS FOLLOWS:

TENSILE STRENGTH – 125,000 MIN.YIELD STRENGTH – 95,000 MIN.

ELONGATION IN 2″ – 16% MIN.

3. PROOF TEST ASSEMBLY TO 80,000 LBS.

4. LINK PC 3 TO BE WELDED WITH ELECTRODE TY NT 4140 OF MIL-E-88979.

5. GALV PC 3 TO SPEC ASTM/A 153.

6. BEFORE GALV AND AFTER PROFF TESTING PC3 SHALL BE MPI INSPECTED.

WeldSee Note 2 and 4

3

3

1

9

1

4

4

4

16

8

1 " D.

See Notes 2 and 4

PC 1

PC 3

PC 2

PC 1

1 " R.

""

22°

Towing Eye

2 " D. Hole

To Submarine To Tug

Arrangement of Towing Gear

J-3


the submarines towing plans are 1¾-inchscrew-pin anchor shackles. Do not use theseshackles for towing. Use only comparablesafety shackles. Note that the standard towpad will accept the pin of a standard 2-inchsafety shackle. The tug should provide morerobust gear if time permits.

J-1.3 Chafing Pendant

The submarine’s own towing rig may includea short wire chafing pendant. It may be only a3/4-inch or 1-inch pendant, however, andmay not provide adequate chafing protectionfor a long-distance, deep-catenary tow, espe-cially in the fairlead chock. The tow shipshould provide its own chafing pendant ofsufficient length to make the final connectionto the tow hawser on the fantail of the towship. The pendant should be made up to in-clude a short length of chain to ride in thefairlead chock for chafing protection.

Some submarines may carry a 450-foot, 5-inch circumference nylon tow hawser. Thishawser is not recommended for use when atow ship can provide longer or heaviergear. In this regard, note the current limita-tions on the use of synthetic towing hawsersdiscussed in Appendix C.

J-2 SSN 688 Class Submarines

Submarines in the SSN 688 Class have notow pads or forward fairleads. There is asmall 5 1/2-inch x 11-inch fairlead aft. Theship is designed to be towed using a bridle at-tached to the forward pair of hinged mooringcleats. Each cleat has a safe working load of70,000 pounds. Figure J-2 is a diagram of ahinged cleat and Figure J-3 is a schematic ofthe towing rig carried onboard the SSN 688Class. It requires modification for use inopen-ocean towing.

The bridle is made up of two 15-foot lengthsof 1 3/8-inch, 6 x 37 galvanized IPS steelwire. The chafing pendant is 31 feet of 1 3/8-

inch wire and the intended towing hawser is450 feet of 5-inch circumference double-braid nylon with a 5 1/2-inch rope coupling ateach end. As noted previously, neither the in-tended pendant nor the hawser is recommend-ed for ocean towing of this submarine. Thetug should provide a 1 5/8-inch chafing pen-dant of sufficient length to make the hawserconnection on its own fantail.

Use of the 1 3/8-inch bridle provided for thissubmarine is acceptable for towing this class.The soft eyes in the bridle legs must be appro-priately lashed to ensure that they do notjump off the cleats. Use of a pelican hook isnot recommended for ocean tows unless aquick release is mandatory. If a pelican hookmust be used, it should be installed such thatthe jaw will open away from the submarine(towards the tug) if released in an emergency(see Figure J-3 for proper configuration).

J-3 SSBN 726 Class Submarines

These large submarines, like those of the SSN688 Class, are designed to be towed with abridle attached to the forwardmost pair ofmooring cleats (see Figure J-4). This bridle ismore robust than the bridle used on other sub-marines, but it is not carried onboard the sub-marine. The bridle and associated hardware isstored at Trident Refit Facilities.

Figure J-4 shows two 14-foot, 2-inch diame-ter wire bridle legs with soft eyes for connect-ing to the cleats. Unless the tow originates ata Trident Refit Facility, where the designedtowing rig is stored, this bridle may not beavailable. If an SSBN 726 Class must bepicked up in an emergency, the tug can easilymake up its own bridle rig using equal lengthlegs of at least 1 5/8-inch diameter wire, safe-ty or plate shackles and a flounder plate. Thechafing pendant should be at least 1 5/8-inch wire, although heavier wire is pre-ferred. The pendant should be long enough

J-4


Figure J-2. Hinged Cleat for SSN 688 Class.

J-5


Figure J-3. Towing Gear Arrangement for SSN 688 Class (Harbor Towing Only).

3 8/

3 8/

3 8/

J-6


to permit connection to the main tow hawseronboard the tow ship.

Because of the weight of the towing gear, aretrieving wire (100 feet of 5/8-inch wire) isrecommended, as shown in Figure J-4. Theretrieving wire will reach the capstan 32 feetaft of the cleats for rigging purposes. Other-wise, the retrieving wire is secured to the No.2 set of mooring cleats in such a way as topreclude it from being placed under strain un-der any possible towing bridle orientation.

To prevent damage from the flounder plate,the No. 1 and No. 2 main ballast tank ventcovers must be installed prior to rigging theSSBN 726 Class for tow.

J-4 SSN 21 Class Submarines

These large submarines have an on boardemergency towing pendant designed foremergency towing.

The emergency towing pendant assemblyconsists of a towing padeye, towing chock,chafing chain, wire rope and sockets, and two

North Atlantic Treaty Organization (NATO)standard links. An intermediate fitting in thetowing pendant is four feet above the hull onthe port side of the sail at fram 24 where thependant is stowed and faired to the sail. Thisfitting, consisting of a NATO standard link,allows a towing line to be attached. The entiretowing assembly is normally not visible. It isstowed in a trough, covered with Neat Dura-1material and faired to the hull and sail. SeeFigure J-5 for emergency towing pendant as-sembly details.

Under certain conditions, the ship may betowed using a bridle attached to the forwardpair of hinged mooring cleats. Each cleat hasa safe working load of 70,000 pounds. Thetowing ship can easily make up its own bridleusing appropriate lengths of at least 1 5/8-inch diameter wire, safety or plate shackles,and a flounder plate. The chafing pendantshould be at least 1 5/8-inch wire, althoughheavier wire is preferred. The pendant mustbe long enough to permit connection to themain tow hawser onboard the tow ship.

J-7


Figure J-4. Towing Arrangement for SSBN 726 Class.

J-8


Figure J-5. Emergency Towing Pendant Assembly for SSN 21 Class.

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To w in g C h ocka nd P a de ye

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N ATOS ta n da rd L in kw ith C ove r P la te s(2 P o s itio ns)

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J-9



J-10


Appendix K

COMMERCIAL TUG CAPABILITIES

K-1 Introduction

This appendix addresses considerations andfeatures of commercial ocean-going tugs,both foreign and domestic, that may be calledupon for planned or emergency use by theU.S. Navy. It provides information to assisttowing planners and to encourage careful se-lection of commercial tugs to fulfill Navy re-quirements.

K-2 Tug Characteristics

This section addresses features of ocean-go-ing tugs, with emphasis on salvage tugs. Thisis not to suggest that other types of tugs arenot capable of safely executing assignedtasks. In fact, specialized tugs are usuallymore economical to hire than fully equippedand fully manned salvage tugs. The salvagetug is used here, however, as the benchmarkby which to compare others, since it is themost versatile type of tug.

K-2.1 Salvage Tug Attributes

Salvage tugs are large, powerful, and ex-tremely seaworthy tugs. They can performmany different tasks and carry a wide varietyof equipment and material as well as a rela-tively large crew. They have the crews andequipment to execute salvage tasks and thehigh power needed to refloat stranded ves-sels. They are excellent in rescue missions;they possess sufficient speed to reach the ca-sualty promptly, the extra manpower and gearto make the tow connection under strenuousconditions, and the power to tow the casualtyto safety. Finally, salvage tugs have the pow-er, stores, and fuel capacity to make them ex-

cellent for long-distance tows of large shipsand heavy objects. In terms of capital costand operating expenses, each of the three sal-vage tug missions—salvage, rescue, and tow-ing—could probably be accomplished moreeconomically and efficiently by a tug special-izing in only one of these areas. No other typeof tug, however, can fulfill all three missions,under all kinds of circumstances, as well asthe salvage tug.

Not surprisingly, the lines separating the clas-ses of tugs are sometimes blurred by overlap-ping design features, and often by what own-ers choose to call their tugs. There is no uni-versal acceptance of any particular salvagetug description. In fact, few owners actuallyrefer to their salvage tugs as such, preferringsimply to list them as “tugs.” Some that arecalled “salvage tugs” may be low-poweredvessels intended for support of salvage opera-tions, often inshore, and would be totally un-suited for a rescue mission, long ocean tow,or stranding on an unprotected shore.

The problem of identifying tugs by type isfurther complicated by the advent of manyhigh-powered but very specialized supportcraft involved in the offshore oil indus-try. Consequently, there are anchor-handlingtugs, supply tugs, and anchor-handling/sup-ply tugs. These can be useful in an emergencysituation, but may have minimum crew sizes,limited cruising range, and a lack of the wideassortment of gear useful in rescue towing orsalvage.

The following sections describe the attributesof salvage tugs.

K-2.1.1 Length

Length is a major contributor to seaworthi-ness and provides for good arrangements andample storage for crew, stores, and equip-ment. Length promotes efficient free-runningspeed. The disadvantages of incrementallength are higher construction cost and less

K-1


maneuverability. Salvage tugs generally ex-ceed 200 feet in length.

K-2.1.2 Draft

Draft promotes seaworthiness and directionalstability against off-center towing forces andprovides for efficient propeller, design, andplacement. Salvage tugs, however, must workin shallow water around strandings, so theirdrafts must be compromised. Salvage tugsgenerally have drafts of 16 to 20 feet.

K-2.1.3 Freeboard/Depth

High freeboard forward improves seaworthi-ness. Freeboard aft is a compromise betweenthe desire to provide a work space that is safeand dry versus one that is located convenient-ly close to the work site, which is often nearthe waterline.

K-2.1.4 Beam

Beam improves stability, provides the inter-nal volume for storage and other functions,and promotes efficient work spaces. Toomuch beam, however, handicaps free-runningspeed and increases fuel consumption. Sal-vage tug beams are 45 feet or more.

K-2.1.5 Crew

The crew of a salvage tug is significantlylarger than the crews of other tugs. Commer-cial salvage tug crews vary from 15 to 25.Less tangible is the experience level of thecrew. The best salvage and towing people of-ten gravitate toward the salvage tugs;man-for-man, the experience level is oftensuperior in these ships.

K-2.1.6 Towing Equipment

Some salvage tugs have automatic towingmachines. Most commercial salvage tugshave at least an automatic rendering winch.This is an important clue to the capabilities ofsalvage tugs. Appendix L has a more com-plete discussion of towing machines andwinches. Section 4-2 discusses strength oftowing hawsers and related equipment.

K-2.1.7 Power

Power is obviously a critical attribute for tugsbecause it provides for prompt transit to thelocation of the casualty, assists in refloatingthe stranded ship, and facilitates towing thecasualty. The citation of horsepower ratingfor tugs varies; this must be understood tomake valid comparisons between tugs. Thissubject is addressed in Section K-2.2.

K-2.1.8 Bollard and Towline Pull

Bollard and towline pull are measures ofmaximum pull while dead in the water andavailable pull when the tow is underway.These attributes are also discussed in SectionK-2.2.

K-2.2 Power, Bollard Pull, and Towline Pull

Towing is a very competitive endeavor, withbusiness often sold on the basis of tug power.Custom, along with regional differences, dic-tates different methods for reporting a tug’sattributes, as described below.

K-2.2.1 Power

The power of a tug can be quoted in shafthorsepower, horsepower, indicated horse-power, or kilowatts, as follows:

Shaft Horsepower (shp) is the power deliv-ered to the propeller. Generally, only Navytugs use shaft horsepower to describe theirpower; this, however, is the truest measure ofpower delivered by the tug.

Horsepower (hp) is generally the brakehorsepower (bhp) of the tug’s propulsion en-gines—that is, the power delivered at the en-gines shaft (not propeller shaft). This descrip-tion ignores the reduction gear and propellershaft losses, which may be considerable.Most American owners and the worldwideoffshore oil industry use horsepower to de-scribe their tugs. Some foreign shipownersuse kilowatts as units of power. Kilowatts (1kW = 1.341 hp) may be assumed to be mea-sured at the engine.

K-2


Indicated Horsepower (ihp) originates fromthe days of reciprocating steam engines andignores heat, friction, valve, and engine-driv-en auxiliary losses within the engine. Further-more, some owners may add the generatorengines and thruster power to the total, so in-dicated horsepower may exceed horsepowerby a factor of 1.2 to 1.6 or more. Of course,an owner reporting in horsepower also mayadd generators and other power sources or us-ers to the total. Most European and Asian sal-vage operators report tug power in indicatedhorsepower and are reluctant to report other-wise for fear of losing a competitive advan-tage. It has been noted, however, that moreowners are now reporting in kilowatts toavoid the confusion between horsepower andindicated horsepower.

K-2.2.2 Bollard Pull

Bollard pull is the zero speed pulling capabil-ity of the tug. It is a measure of the usefulnessof the ship in a stranding scenario or in hold-ing a large tanker or aircraft carrier off a leeshore. Keep in mind, however, that bollardpull figures, like horsepower, may be open tointerpretation.

Ideally, bollard pull is tested when a tug isbuilt and certified by one of the classificationsocieties. Bollard pull tests are also some-times performed after major engine over-hauls. Tug owners whose tugs have been test-ed usually provide a copy of the certificateattesting to the bollard pull figure.

Bollard pull, like horsepower, is a sellingpoint for tugs and is sometimes overstated.For instance, there are rules of thumb for con-verting propeller power (shaft horsepower) tobollard pull, such as one ton pull per 100horsepower for a conventional propeller or1.2 to 1.5 tons pull per 100 horsepower for apropeller fitted with a nozzle. The owner maysave the cost of a bollard pull test and simplyapply one of the factors to convert propellerpower to bollard pull without ever knowing

what the real figure is. It is unlikely that theowner would ever select a conservative con-version factor.

European owners generally report bollardpull in their literature and reputable salvagetug owners are generally able to produce acertificate to document the test. Americanowners and the worldwide offshore oil sup-port industry, on the other hand, rarely reportbollard pull. When they do, the figure maynot have been validated by a test. Horsepoweris probably a more reliable measure amongships of these types.

K-2.2.3 Towline Pull

Bollard pull is not the only useful measure ofthe pulling capability of a tug. Except instranding cases, the objective of the tug is tomove its tow. In towing, some of the tug’spower is spent on overcoming the hull resis-tance of the tug itself and some is spent on thehydrodynamic resistance of the towing haw-ser. Bollard pull can be maximized by propel-ler and nozzle design, but only at the expenseof towline pull at towing speeds. This ad-versely impacts free-running speed and fuelusage. Most tug designs, however, are opti-mized for towing.

Tugs are generally expected to operate in the4- to 8-knot speed range. Modern tugs usuallyuse advanced propeller designs so that bollardpull still is quite high, but tug speed and fuelconsumption are significantly reduced. A tugoptimized for rescue towing, on the otherhand, would probably not employ nozzles,being more concerned with high speed run-ning to the casualty than in efficiency of thetow itself. Figure K-1 displays towline pullvs. speed for typical tug designs using con-trollable-pitch propellers turning inside noz-zles. The figure is adapted from Blight andDai, Resistance of Offshore Barges and Re-quired Tug Horsepower, OTC 3320, 10thOffshore Technology Conference Proceed-ings (Ref. AE).

K-3


Figure K-1. Towline Pull vs. Towing Speed for Tugs with Controllable-Pitch Propellers and Nozzles.

Ava

ilab

le T

ow

line

Pu

ll (L

To

ns)

Towing Speed (KTS)

Twin Screw

Single Screw

K-4


Figure K-2. Anchor-Handling/Supply Tug.

Figure K-3. Point-to-Point Towing Tug.

K-5


K-6

K-2.2.4 Maneuverability

Tugs are available with both ocean-goingtowing capabilities and enhanced maneuver-ing characteristics. Examples of these aretugs equipped with azimuthing Z-drive pro-pulsion or Voith propulsion systems. The azi-muthing Z-drive propulsion is trainablethrough 360 degrees and can be positioned inthe hull during design to provide either a sterndrive or a tractor tug. A tug such as PointChebucto has two azimuthing stern driveunits with a reported bollard pull of 64 tonnesand a speed of 12 knots.

The Voith-Schneider propeller generatethrust at right angles to the axis of rotationwhich, through control of the angle of attackof the vertical propeller blades, can be direct-ed through 360 degrees thus acting as bothpropeller and rudder. This permits abandon-ing the conventional stern propulsion positionand allows placing the propeller at the pointof best interaction between the vessel, propel-ler, and towing. With the Voith-Schneider in

the forebody there is free inflow and outflowin all directions and thrust forces act ahead ofthe vessel pivot point.

The main point of this discussion is that a tugshould be considered as a balanced design,with some tugs being more suitable for sometypes of tasks than other tugs. This point ap-plies to the task as well. Chartering a 20,000-ihp salvage tug to tow a 200-foot barge wouldbe just as inappropriate as sending a 5,000-hpplatform supply ship, with no tow hawser orwinch, on a rescue tow mission.

K-3 Ocean-Going Tugs for Hire

This section provides sample specificationsfor typical ocean-going tugs and statistics onthe number of tugs available for hire.

K-3.1 Ocean-Going Tug Examples

Figures K-2 through K-4 are drawings of typ-ical salvage tugs, point-to-point towing tugs,and anchor-handling/supply tugs. Table K-1provides data on these and other tugs.

Figure K-4. Salvage Tug.


Table K-1. Typical Commercial Salvage/Towing Vessels for HireCompared with US Navy Salvage Ship.

Name USSSafeguard

AtlanticSalvor

Fotiy Krilov Baraka II

Type USN Salvageand Rescue

Towing and Salvage

Salvage Salvage

Year 1985 1975 1989 1994

LOA (ft) 255 254 321.5 227

Beam (ft) 51 43.25 64 51

Draft (ft) 15.5 21.5 23.5 24.25

Horse Power 4200 8800 24482 16000

Bollard Pull(tons)

54 127 250 161

Max Speed (kts) 13.5 16 18 17

Name Smit Singapore

Otto Candies Star Sirius Salvigour

Type Towing and Salvage

Anchor Handling

Anchor Handling

Salvage

Year 1984 1985 1985 1990

LOA (ft) 247 140 213 218.1

Beam (ft) 50.1 42 47.5 48.2

Draft (ft) 25 20.1 24.25 20.7

Horse Power 13500 7200 9180 6600

Bollard Pull(tons)

188 100 112 110

Max Speed (kts) 13 14 12 16

K-7


K-8

K-3.2 Decline in Salvage Tug Availability

Traditionally, salvage and towing companiesmaintained their best ships “on station” wait-ing for a casualty to occur. The “station”could be a semipermanent strategic locationsuch as Jamaica, Gibraltar, Aden, or Sin-gapore, with backup by a shore base, or a sea-sonal location such as the North Sea in winteror the Cape of Good Hope during the South-ern Hemisphere’s winter. Work was contract-ed on the well-understood Lloyd’s OpenForm “No Cure—No Pay” terms, and usuallywent to the first tug to arrive.

Several factors have led to the decline of thetraditional “fire house” nature of the salvageand towing business. To list a few:

• Improved navigational aids resulted infewer casualties.

• The advent of large offshore oil struc-tures and VLCC and ULCC tankers re-quired construction of large, very pow-erful, and expensive salvage tugs.

• Increased ship size resulted in fewerships to potentially suffer casualties.Furthermore, since fewer ships wereoperating, marginal operators andcrews were gradually forced out.

• Crews demanded improved habitabili-ty, working conditions, and wages.

• The worldwide reduction in oil con-sumption caused a reduction in ship-ping and, therefore, casualties, in theearly 1980s.

• Owners of casualties tended to avoidthe “no cure—no pay” contract in favorof more price competitive bidding. Thisplaced the traditional salvage tug opera-tors at a disadvantage because of theirhigher equipment, labor, and standbycosts.

Consequently, tug owners sought routine,long-distance towing tasks to keep their ex-pensive assets at work. Others laid up their

ships or went out of business. Consequently,“stand-by” assets were greatly reduced.

K-3.3 Availability of Ocean-Going Tugs

A 1996 survey reported 221 tugs and 841supply tugs having 1,000 brake horsepower(bhp) or greater. Of these, 97 tugs and 52 sup-ply tugs claim 6,000 to 10,000 bhp and 18tugs and 2 supply tugs are listed at over10,000 bhp. The total numbers are probablyunderstated, since some well-known salvage/towing firms are not listed in the survey andonly a few former Communist bloc ships list-ed. On the other hand, the ships were listed asreported by the owners, without comment.Many of the smaller, less-powerful tugs areunsuited for any but the most benign tows. Inaddition, many quite powerful tugs, in the4,000- to 8,000-ihp range, are well under 150feet in length. The ships are optimized beauti-fully for point-to-point towing but may behandicapped seriously in a rescue tow scenar-io under strenuous sea conditions. Again, tugsmust be matched to particular missions verycarefully.

K-4 Obtaining Tug Assistance

This section provides guidance in obtainingcommercial tug assistance.

K-4.1 Emergency Tug Assistance

Since a Navy ship requiring emergency tow-ing assistance communicates with its opera-tional and administrative superiors by desig-nated means, it is helpful (subject to securityrestrictions) to query the UHF and VHFemergency channel frequencies to determineif competent assistance is available close by.Salvage tugs always monitor the distress fre-quencies; most other tugs monitor these chan-nels frequently. Availability informationalong with pertinent data on the tug and itsowners, is useful to the operational superiorsin resolving the problem.


K-4.2 Restrictions in Contracting

U.S. Navy ship Commanding Officers are notauthorized to commit the U.S. Government toindefinite obligations or claims. A Lloyd’sOpen Form contract requires arbitration in,and is subject to, the laws and courts of GreatBritain. The United States will not permit it-self to be subject to such requirements. Fur-thermore, even a per diem (fixed rate) salvagecontract involves an indefinite value. The netresult is that the Commanding Officer of aU.S. Navy ship is severely restricted in con-tracting for emergency assistance.

K-4.3 Contracting for Emergency Com-mercial Towing Assistance

If Navy towing assets are not available, theappropriate superior in the chain of commandcan arrange for emergency commercial tow-ing assistance in two ways:

• Contacting the cognizant U.S. Govern-ment procurement office. This officecan provide data on potential nearby as-sistance and arrange for an appropriateper-diem-type contract with the tug’sowners, who will immediately advisethe tug.

• Contacting the U.S. Navy Supervisor ofSalvage (Director of Ocean Engineer-ing - NAVSEA 00C) by message(COMNAVSEASYSCOM WASHING-

TON DC/00C) or by telephone at (202)781-1731 (DSN 326-1731).NAVSEA 00C can be reached 24 hoursa day through the NAVSEA DutyOfficer at (202) 781-3889 (DSN 326-3889). SUPSALV maintains standingsalvage contracts that can respond im-mediately worldwide. Frequently, theNavy salvage contractor subcontractswith the most appropriate salvage/tow-ing firm anywhere in the world. Thus,an available commercial tug can be di-rected to provide emergency assistancewith very little delay and without sub-jecting all parties to protracted legal ef-forts after the fact.

K-4.4 Arranging for Routine (Non-Emer-gency) Tows by Commercial Tugs

The tow planner will normally request thetow from the appropriate Navy operationalSurface Force Commander, who will arrangefor a U.S. Navy or Military Sealift Commandtow. If neither is available, the tow should bearranged through the local supply/procure-ment agency. In the latter case, if tows are ar-ranged infrequently, or the tow is technicallyunusual, obtaining advice/assistance fromSUPSALV is recommended.

K-9



K-10


Appendix L

TOWING MACHINERY

L-1 Introduction

For the purpose of tow planning, this appen-dix provides a brief overview of the differenttypes of towing machinery installed in U.S.Navy tugs and towing ships. It describes thecapabilities and limitations of the towing ma-chinery in these ships. This appendix is not asubstitute for specific design or operating da-ta contained in the technical manuals for theequipment installed in any given ship.

This appendix addresses the machinery usedin classic towing arrangement where the tugis attached to the tow by a fiber or wire haw-ser. It does not address tug-barge combina-tions (where the tug is mechanically attachedto the tow).

L-2 Background

Because the primary mission of a tug is tow-ing, the towing machinery must be carefullyselected, designed, operated, and maintained.The value of the towing machinery cannot beunderestimated. This point is supported bythe president of a major, privately owned Eu-ropean salvage and towing company whoonce reported that, for modern, high powertugs, the cost of the towing machinery at leastequals the cost of the ship’s entire main pro-pulsion plant.

L-2.1 Terminology

Automatic towing machinery evolved fromthe original towing winch. Application ofsteam power to the towing winch resulted infrequent use of the term towing engine. To-day, towing machine is the preferred term forautomatic towing machinery and is the oneused in the NSTM. A nonautomatic towing

winch is appropriately called a towing winch.The terms traction machine or traction winchare both used, depending on the number ofautomatic features installed.

L-2.2 Functions of Towing Machinery

All towing ships need a means for handlingthe towing hawser. The mechanism must beable to:

• Deploy/retrieve hawser• Attach the hawser to the tug• Adjust the deployed length of the haw-

ser• Stow the unused portion of the hawser• Provide for quick release while the

hawser is under tension • Minimize damage and wear to the haw-

ser while in use and while stowed.

L-2.2.1 Attachment of the Hawser to the Tug

Older, smaller tugs may have no more than abollard or bitts for attaching the hawser.Smaller European tugs often use a towinghook that swivels about a strong bearing on aplatform. More modern tugs generally com-bine the hawser securing function with thestorage and/or transport system.

L-2.2.2 Hawser Scope Adjustment

Paying out additional line when the hawser issecured to bitts can be accomplished by hand,but at considerable personnel risk. When us-ing a towing hook, which requires a perma-nent eye at the end of a hawser, paying out theline requires inserting a specific length of ad-ditional hawser. In each case, shortening thelength of deployed hawser is difficult and re-quires power assistance if the hawser is understrain. Modern ships combine the hawser ad-justment function into a powered winch trac-tion machine.

L-2.2.3 Storage of Unused Hawser

On smaller, older tugs, hawsers may be sim-ply “faked down” on deck or stored on reels,which may be powered. Since the advent ofwire hawsers, larger ocean tugs generally

L-1


combine the hawser securing, adjusting, andstorage functions into a self-contained winch.More recently, traction machines have beendeveloped to overcome problems inherent inthe typical winch. Two factors that led to thisdevelopment are:

• The advent of very powerful tugs(10,000 hp or more) require very long,heavy wire hawsers. These ships, notyet seen in the U.S. Navy, often havetwo hawsers and towing machines.Each hawser may be 72 mm (2-7/8inch) in diameter and up to 1800 meters(5900 feet) long. Each such hawserweighs about 38 long tons and requiresa massive reel for storage that must berobust enough to withstand direct appli-cation of tensile loads. Optimal locationof the towing point is at the main deck,on centerline, close to mid-length of theship. This is prime space for arrange-ment purposes and presents a signifi-cant drawback to stability when largeweights are needlessly located at thatheight. Consequently, these large tugsfrequently use traction machines to ad-just and hold the wire, while the unusedwire is stored at more appropriate loca-tions on relatively light storage reels.These reels need only sufficient powerto take up the slack between reel andtraction machine. Wire hawser tractionmachines are similar in principle andappearance to the fiber line machinesused by the U.S. Navy.

• The use of large, long, synthetic fiberhawsers. The poor compression rigidityof these hawsers precludes towing di-rectly from a storage reel because thepart of the line under tension would em-bed itself in the preceding layers ofstored line. Furthermore, synthetic linesare relatively bulkier than wire haw-sers, making reel-type storage impracti-cal. The unused fiber hawser is general-

ly stored in a bin or dedicatedcompartment, which may be adjacent tothe traction machine. The tractionmechanism operates on the hawser andseparates the hawser’s unloaded, storedportion from its deployed, tensionedportion.

L-2.2.4 Quick Release of the Hawser under Tension

Emergency conditions, such as the tow’ssinking or being set toward danger, requirequick release of the hawser, often while understrain. Fiber hawsers may be cut with an axe.Wire hawsers may be cut with an oxyacety-lene torch or power cutters. Cutting the haw-ser is hazardous and may be impossible in aheavy seaway. The towing hook has an ad-vantage in that it can be tripped, often re-motely, to release the hawser. For the typicalreel-type towing winch, the reel can be dis-connected from the driver mechanism so thatit will freewheel, allowing the hawser simplyto pull itself off the reel. The bitter end of thewire is easily disconnected by the momentumof the wire coming off the reel. Tractionwinches can generally be disconnected thesame way, but a rapidly-running, large-diam-eter fiber hawser presents significant hazardsto personnel and equipment. Unless the bitterend of the hawser is very close to the tractionmechanism, the unloaded portion of the haw-ser may have to be cut.

L-2.2.5 Protection of the Hawser

The hawser must be protected from two prin-cipal hazards. The first is damage and wear tothe hawser from scuffing, abrasion, small di-ameter bending, crushing of stored layers un-der loaded turns on a reel, and adverse envi-ronmental conditions. This damage is mini-mized by the careful arrangement of towingmachines and deck equipment. The secondprincipal concern is protection of the hawserfrom overload due to surges caused by rela-tive movements of tug and tow in a seaway.This is addressed in part by proper operating

L-2


parameters (speed, scope of hawser, andcourse) and often by including automatic pay-out and retrieval features in towing machin-ery. Both concerns are further addressed byusing towing machinery instrumentation thatprovides hawser tension and scope readouts.This instrumentation may operate indepen-dently of towing machinery. The next sectiondiscusses reasons for including automatic fea-tures on towing machinery.

L-3 Automatic Tension Control

This section provides a historical perspectiveand brief discussion of surge loading of tow-ing hawsers and the advantages of automatictensioning towing machinery.

L-3.1 Tow Hawsers Surge Loading

Most seamen do not perceive the surge mo-tions of ships at sea, because there is no refer-ence from which to measure the motion.When two ships are connected by a tow haw-ser, however, the affects of surge motion arequite apparent. Towing people have long beenaware of the relative motion of tug and tow inocean wave systems. For small tugs and/ortows, the hawser itself exerts considerable re-straint to the motion of the ships from theircompletely independent states. But if the tugand tow are both relatively large, a strenuoussea state can easily impart sufficient relativemotion to cause hawser failure.

L-3.1.1 Early Automatic Towing Machinery

Experienced tug seamen have known the dan-gers of load surges for at least a century.Steam power led to larger, more powerfultugs, and to the use of wire hawsers when ma-nila hawsers grew to unmanageable sizes. Assteam deck machinery was developed, it wasin course applied to a winch for the towinghawser. The throttle to the winch steam en-gine could be cracked open (by trial and er-ror) to provide an automatic feature to thewinch. When the steam pressure behind the

pistons was overcome by the tension of thehawser, the winch would pay out; likewise,slack would be taken in automatically whenthe load eased. Simple controls were added toquantify the set point and to limit the totalamount of wire paid out, or taken in, withouthuman intervention. Through this arrange-ment, large potential surges in hawser loadingwere significantly reduced with the “automat-ic” steam towing winch. This improved safe-ty and wire wear and permitted use of morepower than otherwise would have been avail-able.

L-3.1.2 Electric Towing Machinery

The introduction of diesel power to large tugsin the 1930s was a major advance for propul-sion power and endurance, but a setback forautomatic towing machinery. The steam-pow-ered winch was no longer an option. Electric-driven automatic towing machinery was de-veloped, but it tended to be relatively expen-sive and complex. While the U.S. Navy was aleader in the use of automatic towing machin-ery, beginning early in World War II, much ofthe rest of the world returned to nonautomatictowing machinery.

Arguments against the use of automatic fea-tures are often heard. Among other things, au-tomatic towng machines are thought to be in-accurate, unreliable, too heavy, too expen-sive, too noisy, too complex, and impossibleto maintain. Nevertheless, the arguments forautomatic towing machines are compellingwhen one understands the magnitude of surgetensions, as described below.

L-3.1.3 Wire Surge Example

Section 3-4.2 provides data on catenaries ofwire towing hawsers. As the strain increases,the catenary becomes flatter, with less“spring” available. In fact, if it were not forthe stretch of the wire itself, it can be shownthat a 1000-foot, 2-inch FC hawser, with asteady tension of 50,000 pounds, would breakif the tug and tow were separated by only an

L-3


additional 2 feet. Fortunately, the hawser hasconsiderable elasticity. Figure 3-13 comparestug-tow separation to hawser tension for1,000 foot and 1,800-foot hawser scopes. A1,000-foot length of 2-inch wire, with initialtension of 50,000 pounds, will have tensionincreasing to the wire’s safe working limit of187,000 pounds (.65 x 288,000) when the tugand tow are separated by an additional 9 feet,still a relatively low figure. Further stretchwill permanently damage the wire, and it willbreak when increased separation has reacheda total of 15 feet beyond the separation char-acterized by the 50,000-pound initial tension.The same wire, with initial tension of 100,000pounds, can absorb increased tug-tow separa-tion of only approximately 10 feet.

The figures for 1,800 feet of the same hawserat 50,000 pounds initial tension are somewhatmore advantageous. The system can absorb19 feet of increased tug-tow separation beforereaching its safe working limit. Overall, theability of wire hawsers to absorb changes inthe distance between tug and tow is relativelylimited, compared to probable ship motionsunder strenuous sea conditions.

L-3.2 Automatic Features on Towing Machines - General

The full-featured automatic towing can be setto maintain hawser tension within a selectedrange. It will pay out hawser if the hawsertension exceeds the set point, and will recoverhawser when tension falls below another setpoint. Typically, the total amount of hawserallowed to be paid out or retracted is limited.Some towing machinery will pay out, but notretract, automatically.

L-3.3 Limitations in Quantitative Under-standing

The responsiveness of actual U.S. Navy auto-matic towing machines to real dynamic load-ing of their towing hawsers is not well under-stood at present. The automatic payoutfeature does reduce the potential peak ten-

sion, but quantitative data on towing machinetime constants and responsiveness need study.The landmark work leading to the data con-tained in Appendix M is very recent. It signif-icantly improves the understanding of the dy-namic demands placed on the towing system.Further work is needed to better understandhow the automatic towing machine handlesthese dynamic demands; at-sea testing willundoubtedly be required to validate the modelpredictions. There is a distinct possibility thatthis work will ultimately result in loweringtraditional factors of safety—which are really“factors of ignorance”—while maintaining orimproving efficiency and safety in towing op-erations.

L-4 Types of Towing Machines

This section provides an overview of thetypes of towing machines used by the U.S.Navy, with reference to other types of ma-chines for technical interest.

L-4.1 Conventional Towing Winches and Machines

Conventional towing winches and machines,which store the unused hawser on a horizon-tal drum, are the most prevalent.

L-4.1.1 Drum Arrangements

Units may have one or two main drums; onefor each hawser if there is more than one. Inthe U.S. Navy, two-drum units have drumsside by side. Commercial tugs often have thesecond drum forward and above the firstdrum in a “waterfall” arrangement. Thedrums are generally capable of independentoperation. They may be equipped with levelwind apparatus and may be strong enough towithstand the breaking tension of the wire ap-plied directly onto the drum. Some U.S. Navyunits are equipped with one or two auxiliarydrums to accommodate work on mooringlines or long target-towing hawsers.

L-4


L-4.1.2 Drum Securing Features

Towing hawser drums can generally be se-cured with a pawl or “dog.” For control, abrake system is also provided.

L-4.1.3 Drum Prime Movers

The more sophisticated units use DC electricmotors to provide infinitely variable speedcontrol. Some newer machines use an electro-hydraulic arrangement. These machines havea very quick response time. The double drumunits may have two drive units that can beclutched separately (one to each drum) or intandem to a single drum for increased power.Less sophisticated units have a self-containeddiesel engine drive, connected through atorque converter and/or an appropriate me-chanical transmission.

L-4.1.4 Automatic Features

The most desirable automatic feature of atowing machine is the ability to increase thehawser scope when towline tensions exceed acertain level. All machines have brake sys-tems that will slip at some point, but the setlevel may not be very reliable and the drumcan be locked by a dog or pawl. The nexthighest level of sophistication is automaticpayout of the line when the tension exceeds aset level. There may be a limit on the totallength of hawser permitted to be paid out au-tomatically. Finally, the most sophisticatedmachines have an automatic reclaiming capa-bility, with a limitation on the net allowablelength to be reclaimed.

L-4.1.5 Instrumentation and Controls

All units can be controlled locally and manyhave a remote operation station. Instrumenta-tion generally includes cable tension, lengthof cable paid out, motor speed indicator, andautomatic pay out/reclaim set points. Some ofthe instrumentation may be repeated on thebridge.

L-4.2 Traction Winches

In the U.S. Navy, traction winches were intro-duced for use with the large synthetic hawsersthat gained popularity in the 1960s. Tractionwinches also are finding application withwire hawsers in powerful commercial tugs.

L-4.2.1 General Description

Traction winches have two parallel cylinderswith grooves sized to accept the intendedhawser (see Figure L-1). There are four ormore complete wraps of the hawser aroundthe two cylinders. Both cylinders are pow-ered, to transport the hawser. The orientationof the cylinders or drums can be either hori-zontal or vertical. In principle, tractionwinches are similar to capstans. The two-drum arrangement eliminates the axial skid-ding of the rope inherent in capstans and pro-vide grooved drums that improve support andreduce wear on the line.

Unlike drum-type winches, a long line can beloaded onto a traction winch at any pointwithin its total length. This is used for moor-ing purposes and was the reason for their firstmarine use—for control of mooring lines onlarge ships and for Single Point Mooringsused in the offshore oil industry.

L-4.2.2 Hawser Storage

Conventional winch designs are not used withfiber towing hawsers for two reasons—thelarge size required and problems inherent inwrapping and storing a tensioned, highlyelastic line on itself. Storing the untensionedfiber hawser on a drum is feasible, but storagebins are universally used. The traction winchcan easily pull the hawser from its storage lo-cation, via appropriate fairleads. Re-stowingthe hawser as it is recovered, however, ismore difficult and sometimes requireshands-on effort.

L-4.2.3 Traction Winch Operation

Traction winches are motor-driven and someare equipped with variable speed capability.They have brakes and clutches for control.

L-5


Figure L-1. Multi-Sheave Traction Winch.

Brake Hand Wheel

Power Block

Traction Heads

Brakes

Transfer Case

Pinch RollerAft

L-6


When the clutch is released, the winch can beoverhauled by the hawser to provide for freerelease of the hawser in an emergency. Sometraction winches have an automatic tensionpayout capability, but automatic reclaim israre on fiber line systems because of the haw-ser storage system described above.Controlsand Instrumentation

Traction winches have local and/or remotestation controls. Most have tension readoutsand some have hawser scope instrumentation(without stretch compensation). Some trac-tion winches have end-of-hawser warning orshutdown systems.

L-5 U.S. Navy Towing Machinery Descriptions

This section provides more detailed descrip-tions of specific towing machinery installedon U.S. Navy towing ships. This is not a sub-stitute for technical manuals for the specificmachines. Towing machinery installed onmine warfare ships is not addressed. In thefollowing sections, “AAJ” refers to Almon A.Johnson, Inc., a major designer and builder oftowing machines.

L-5.1 ARS 50 Class Towing Machinery

The ARS 50 Class is equipped with an AAJSeries 322 automatic towing machine which

Figure L-2. ARS 50 Towing Machinery.

L-7


has two side-by-side main drums, each capa-ble of spooling 3,000 feet of 2 1/4-inch wire(see Figure L-2). It has level winds that canbe adjusted to spool 2 1/2-inch wire as well.Power is provided by two 125 hp DC electricmotors, which can be connected singly or incombination to either drum. Each drum canheave a maximum 110,000 pounds at 37 fpmat an average layer. Maximum line speed is100 fpm. Each drum can be set for automaticoperation within the range of 25,000 to115,000 pounds. Automatic operation in-cludes payout and reclaim, with limits onmaximum and minimum hawser scope.

The ARS 50 has a Series 400 traction ma-chine located adjacent to, and forward of, theSeries 322 machine. The traction winch is de-signed for use with 3½-inch to 14-inch cir-cumference fiber line. It has a power blockthat back-tensions the line and assists intransporting the line to the storage bin. Thetraction winch has an automatic payout capa-bility, with a set range of 15,000 to 110,000pounds, but has no automatic reclaim capabil-ity. The machine requires some monitoring tocontrol the towline tension without graduallypaying out all the line, although it does have a“cable-off” device that will control the winch.Maximum heave is 110,000 pounds at 20fpm; maximum line speed is 90 fpm.

Both machines are totally enclosed within theship’s deck house. Normal operation is froman enclosed operating station in the aft por-tion of the space, which is equipped with allcontrols and instrumentation. Much of the in-strumentation is repeated in the pilot house.Emergency shutdown controls are located inthe towing machine compartment. The ARS50 towing machine has no auxiliary drum in-corporated into the design.

L-5.2 T-ATF 166 Class Towing Machin-ery

The T-ATF 166 Class is equipped with aSMATCO Type 1 towing winch and a Lake

Shore traction winch. The SMATCO winch isa single-drum machine capable of spooling2,500 feet of 2 1/4 inch wire. A level wind isprovided (see Figure L-3). There is no auto-matic payout or reclaim capacity in the initialdesign. Wire tension measurement is provid-ed by strain gauges in the winch foundation.There is a remote tension readout, but no in-strumentation for scope out of wire. Maxi-mum hawser heave-in is 179,000 pounds at14 fpm; maximum hawser speed is 280 fpmat 18,000 pounds tension on the first wrap. Atthe top wrap (twelfth layer) maximum linespeed is 775 fpm at 6,000 pounds tension.Maximum pull on the twelfth layer is 64,000pounds at 38 fpm.

A major difference between the SMATCOtowing winch and those found on other Navytowing ships is that the SMATCO is diesel-driven through an air-operated clutch, atorque converter, and a gear train. For variousreasons, towing is frequently accomplishedwith the drum locked on a “dog,” rather thanriding the brake. To increase hawser scope, oreven let it run free in an emergency, the en-gine must be started, engaged, and the loadtaken off the dog before the dog can be re-leased. The problem is aggravated by the factthat the pneumatic control system on theSMATCO winch can fail in the “open” posi-tion. In this event, there is no way to releasethe dog. However, if the winch is not dogged,loss of air will lead to free-wheeling and lossof the towline. Managing the hawser with thissystem is more difficult than with the stan-dard U.S. Navy towing machines.

Some T-ATF vessels have had their SMAT-CO towing winch modified by Almon A.Johnson, Inc., to allow for automatic opera-tion. This new configuration is labeled as anAAJ Type Series 332 towing winch. Modifi-cations include the replacement of the dieseldrive system with a closed-loop electro-hy-draulic drive, and the addition of a program-mable logic controller (PLC) based solid state

L-8


Figure L-3. T-ATF Towing Machinery (SMATCO Winch).

Tow Hawser

Level Wind ShaftDrive Shaft

Diesel Engine

L-9


L

control system. Hydraulic fluid flow andpressure for the hydraulic drive motor is sup-plied by a hydraulic power unit mounted im-mediately forward of the towing machine.Automatic operation is achieved by PLC con-trol of the hydraulic pump swash plate as de-termined by tow line scope and tension.

As shown in Figure L-4, the AAJ Type Series332 is a single-drum machine capable ofspooling 2,500 feet of 2 1/4-inch wire with alevel wind. It is capable of automatic opera-tion in a range of 30,000 pounds to 110,000pounds, and manual operation to 250,000pounds. The modified towing winch has aline speed rating of 0 to 36 feet per minute at110,000 pounds at the mid layer of the drum.The operator control panel is located on the01 level overlooking the fantail. A remote

panel located on the bridge shows line pull,line scope, and status lights and alarms.

The T-ATF 166 Class has a separate LakeShore traction winch suitable for fiber haw-sers up to 15-inch circumference. The hawseris stored in a below-deck storage room withappropriate fairleads to the winch. The winchhas no automatic functions. The Lake ShoreTraction Machine is electric motor-driven,with infinite speed adjustment available.Maximum line pull is from 175,000 pounds at12 fpm. No-load maximum line speed is 370fpm in payout, 134 fpm heaving in. The unitcan be declutched to permit the lines to runfree in emergencies. There is a manual braketo control disconnected payout. The winchwill hold and structurally withstand thebreaking strength of a 15-inch circumferencedouble-braided nylon hawser.

-10


Figure L-4. T-ATF Towing Machinery (Series 332 Automatic Towing Machine).

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L-12


Appendix M

ESTIMATING DYNAMIC TOWLINE TENSIONS

M-1 Introduction

This appendix addresses the impact of shipmotion on towline tension. This informationcan be used by the tow planner if sea condi-tions are known. More importantly, the datacan be used to predict acceptable risks of ex-treme dynamic towline loadings, rather thanrelying solely on traditional factors of safetythat are based on steady-state tensions.

M-1.1 Ship Motion

All seamen are aware of ship motions ina seaway, particularly rolling, pitching, andyawing. Three additional types of ship mo-tion—heave, sway, and surge—are somewhatless apparent. Each ship, therefore, experi-ences a total of six independent types of mo-tion (see Figure M-1). In a towing situation,both the tug and tow experience these mo-tions, so the towline between them is subject-ed to 12 independent motions. The towline al-so acts on both ships. These dynamic effectscan cause the towline to fail at unexpectedtimes, when average tensions are well withinapparently acceptable limits.

Traditionally, these dynamics could not bequantified. The problem was addressed by us-ing the conventional method for handling un-known quantities—applying a factor of safe-ty. In towing, the factors of safety are appliedto the steady-state towline tensions (as de-scribed in Chapter 3) and the new strength ofthe towline. The factors of safety used are pri-marily based on experience. Nonetheless,failures still occur.

M-1.2 Wire Towline Behavior

A heavy wire hawser forms a catenary be-tween the tug and tow. The catenary acts as aspring, flattening and deepening to compen-sate for relative motions between the tug andtow. In a steady-state condition, the shape ofthe catenary is easily estimated.

Questions exist about the cross-flow hydro-dynamic resistance on the wire as it rises andfalls. It has been suggested that, for the mo-tion frequencies found in most towing situa-tions, the wire towline does not have time tofully resume its former deep catenary whenthe tension eases before the next surge in ten-sion occurs. The net result over time is thatthe wire catenary remains flat, thereby pro-viding somewhat less spring than previouslythought. Following this line of thought, moreof the spring remaining in the system must beattributed to the elastic stretching of the wireitself. (See Section 3-4.3 for a discussion ofthe stretch of wire hawsers.)

M-1.3 Synthetic Towline Behavior

Fiber hawsers are much lighter than wirehawsers and do not form an appreciable cate-nary. They rely almost totally on their elasticstretch to meet constantly changing towingdemands. The advent of strong, highly elasticsynthetics, especially nylon, was expected tobe a boon to towing, because their elasticityeasily absorbed relative ship motion. Suchhawsers could be easily handled and em-ployed without a dedicated towing winch oran automatic towing machine. As the use ofnylon became more prevalent, however, un-explained failures were reported, often undertowing tensions far below the supposedstrength of the towline. As a result, factors ofsafety were increased to the point where theadvantages of nylon over wire hawsers werelost.

A separate problem with nylon was caused byits elasticity. The large amount of energystored in the stretched hawser is released ex-

M-1


plosively when the hawser fails. This oftenhas disastrous effects, especially on person-nel. Ultimately, the U.S. Navy restricted theuse of synthetic towlines.

The problems with nylon hawsers led to ma-jor studies of the mechanical and chemi-cal properties of rope. Basically, the studiesfound that the strength of such ropes is affect-ed by sunlight, chemicals, salt water, and,above all, the cyclic load history of the rope.NAVSEA's continuing investigation into theuse of improved and composite designs ofsynthetic hawsers has led to the approval for

general use of single and double braidedpolyester lines in all routine and emergencytowing applications with the exception of nu-clear towing. The specifications of polyesterline approved for use are provided in Appen-dix C.

M-2 Design of the Extreme Tension Study

This section briefly describes the project toassign quantities to towline dynamics. Thebehavior of a wire stretched in water betweenvariably distant endpoints is discussed first,

Figure M-1. Types of Motion.

M-2


because this knowledge is a prerequisite tounderstanding the ship motion problem.

M-2.1 Understanding Wire Towline Behavior

The challenge of understanding the motionsof two ships connected by a towline requireda significant escalation of ship motion theo-ries. A mathematical model was developed topredict the behavior of a wire towline and ac-count for the wire's normal mechanical prop-erties, plus the following factors:

• Cross-flow hydrodynamic drag on thewire that tends to flatten out the catena-ry and increase dynamic tensions

• The changing spring constant of thewire.

Tests were conducted in a model towing tankwhere the towline was pretensioned and oneend point could be moved longitudinally tosimulate the varying separation between tugand tow. The test results validated the numer-ical model describing the behavior of a wiretowline.

M-2.2 Motions of the Tug and Tow

A computer can predict statistics of ship mo-tion in a seaway, given ship characteristics,size and frequency of the ocean waves, angleof encounter with the waves, and ship speed.For towing, the motions of two ships connect-ed by the towline model are examined. Thisdoes not directly predict the towline tension,however, because the motions of both theseas and the ships are random. The statisticalnature of the effort does provide the probabil-ity that a tension will be exceeded during a24-hour period of towing.

Given a steady-state tension, and selecting aprobability of 0.1 percent, the program calcu-lates “extreme tension,” the tension level thathas one chance in a thousand of being ex-ceeded in 24 hours of towing. This is compa-rable to once in 1,000 days of towing—a verysmall risk. (Of course, the “once” can occur

in the first hour. There is always a risk.) Withthe low probability involved, however,extreme tensions can be compared to thestrength of the towline using a lower factor ofsafety than is otherwise required when the dy-namic effects are unknown. A factor of safetyof 1.5 is indicated by this study. In otherwords, for a wire in good condition, limitingthe extreme tension to 67 percent of the newbreaking strength is reasonable.

Until experience is gained in applying the da-ta to real-life tows, two factors of safety areapplicable to towing operations: 1.5 when dy-namic effects are quantified and the appropri-ate factor of safety from Table 3-2. Both mustbe checked. The more severe criterion mustbe considered the limit until significant quan-titative experience is gained with the dynamictheory. Tow tensions should be limited soneither criteria is exceeded.

M-2.3 Description of Physical Variables and Influences on Extreme Tension

The numerical model describing wire hawserbehavior was incorporated into the ship mo-tion program. Thousands of individual com-puter simulations were performed, using thefollowing variables:

• Size of the tug and tow

• Wave size, angle, and frequency

• Average towline tensions

• Weight and scope of towline used

• Towing speed.

Each of these variables is discussed below.

M-2.3.1 Size of Tug and Tow

Sea motions of both the tug and its tow areunique. It was therefore necessary to studythe problem for four different tug classes:T-ATF 166, ARS 38, ARS 50, and ATS 1.For each tug, the following tow sizes wereexamined:

• 3,200-ton FFG 1 Class frigate

M-3


• 650-ton YRBM berthing barge

• 6,707-ton DD 963 Class destroyer

• 20,000-ton AE 26 Class ammunitionship

• 40,000-ton LHA 1 Class assault carrier.

The motion characteristics of the ARS 50 andATS 1 were found to be so similar that theywere combined into one category. Althoughthe ARS 38 and ATS 1 Class vessels havebeen decommissioned, the data are still in-cluded here to demonstrate the scope of thestudy.

M-2.3.2 Wave Size, Angle, and Frequency

Ocean waves cause various motions in the tugand the tow, which in turn cause variations intowline tension. The ship motion having themost influence on towline tension is surge,but the other motions—sway, heave, roll,pitch and yaw—play roles as well. Althoughmethods for predicting most types of shipmotion have been used for some time, surgewas normally not addressed. Surge has beenincluded in these efforts.

Generally, the larger waves cause the greatesttension, but it is not only the size of any onewave that counts—ship position and motionat any given point depend on the several mostrecent waves. In addition to wave size, thewave frequency is influential. For very highfrequency waves, ships do not have time torespond to each wave, so the motions result-ing from such waves are small. At very lowfrequencies, ships move significantly, butthere is enough time for the catenary to ad-just. At somewhat higher frequencies, chang-es in catenary depth are restricted by thecross-flow drag of the water on the catenaryas it tries to rise and fall. This results in largerextreme tensions.

The wave height estimated by an experiencedseaman has been found to be approximatelythe average height of the third-highest waves,

called H1/3. Values of H1/3 used in the com-puter program for predicting extreme tensionsare as follows:

Wind Speed H1/3

15 knots 4.0 feet

20 knots 7.2 feet

25 knots 9.1 feet

30 knots 16.4 feet

Another important factor is the angle at whichwaves are encountered. Changing course toencounter waves on at a different angle cansometimes reduce towline tension. Some-times head seas are better; at other times, seasfrom 60 degrees are better. Computationswere based relative wave directions of “deadahead” (0 degrees) and 60, 120, and 180 de-grees.

M-2.3.3 Average Towline Tension

For a wire rope towline, the average (mean)towline tension is critical for predicting ex-treme tension, since it is the base to which thedynamic tension effects are added in the anal-yses. When average tension is low, the tow-line hangs in a deep catenary and can changeits depth to accommodate large ship motionswithout large changes in the tension. Whenthe average tension is high, the towline isnearly straight and can accommodate shipmotions only by stretching, which requireslarge increases in the tension of wire rope.

Methods for estimating average towline ten-sion appear in Section 3-4.1 and Appendix Gof this manual. One of the effects influencingaverage tension, the added resistance due towaves, cannot be estimated with great accura-cy. Results for added resistance, obtainedfrom the methods presented in Appendix G,are approximate. Because average tension iscritical for estimating extreme tension, espe-cially for wire rope towlines, it is preferableto use mean tension measured with an accu-

M-4


rate tension meter rather than using calculatedmean tension.

For the purposes of this study, mean towlinetensions were assumed to be the following:

• 10,000 pounds• 20,000 pounds• 40,000 pounds• 80,000 pounds• 120,000 pounds

M-2.3.4 Weight and Scope of Towline Used

The towline catenary depends upon theweight and scope of the wire used. All of thecomputations were based on the actual haw-sers used by each towing ship (see TableB-1). Computations also assumed that the fi-nal connection to the tow uses one shot of2¼-inch chain, with 20 feet on the deck of thetow and 70 feet extending outward from thetow's bow. Computations were made for haw-ser scopes of 1,000, 1,200, 1,500, 1,800 and2,100 feet.

M-2.3.5 Tow Speed

Speed contributes to extreme tension for tworeasons. First, the wave encounter frequencyfor head seas increases with incrementalspeed, thereby raising slightly the added re-sistance due to tensions. Secondly, and farmore significant, is that increased speed cre-ates higher average towline tension. It in-creases dynamic factors by raising the base towhich purely dynamic parameters are added,and creates a stiffer towline system (that is,one with less catenary). A stiffer system alsoincreases dynamic effects.

Because of the association between mean ten-sion and extreme tension, estimates of the lat-ter are based on accurate estimates of meantension rather than towing speed. The prima-ry effects of speed are automatically includedin the mean tension number. The less-impor-tant influences of speed were accounted for inthe study, however. Computations were basedon towing speeds of 3, 6, and 9 knots.

M-2.3.6 Yawing and Sheering

In towing terminology, “sheering” is themovement of the tow off to the side of thetowing track. This motion can be steady, withthe tow staying to one side, or unsteady, withthe tow moving from side to side and takingseveral minutes to go through a complete cy-cle. Occasionally, sheering is called “yaw-ing.” This term should not be confused with“yawing” in seakeeping terminology, whichis a variation in heading caused by waves.The effects of yawing are included in thecomputations, but effects of sheering are not.Section M-3.2.6 provides guidance for ad-dressing a badly sheering tow.

M-2.4 Display of the Data

To recap, calculations were based on:

• Three classes of tugs (T-ATF 166, andARS 50)

• Five tow sizes (FFG 1, YRBM, DD963, AE 26, and LHA 1)

• Four wind speeds (15, 20, 25, and 30knots)

• Three towing speeds (3, 6, and 9 knots)

• Five hawser scopes (1,000, 1,200,1,500, 1,800, and 2,100 feet)

• Four wave angles (0, 60, 120, and 180degrees)

The results of these numerous calculationsare displayed in 15 tables—one for each tug-tow combination (see Tables M-1 throughM-10). Each table, in turn, has 12 blocks—one for each wind speed/towing speed combi-nation. Each block contains four rows (for thefour wave angles) and five columns (for thefive hawser scopes). The end result for eachcombination is a curve number. This numberindicates which curve should be used to cal-culate extreme tension from average tension.One hundred different curves are presented inFigures M-2 through M-5.

M-5


When there is not an obvious choice, the pro-gram selects the curve number that best mini-mizes the error at higher tension ranges—thatis, at about 70 percent of the strength of thewire used by the tug. Precise accuracy athigher tension levels is not needed, sincethere is too much risk associated with towingat these tensions. Errors at lower levels arenot a problem, since the wire is not highlyloaded.

Fo r e x a mp le , f o r a T -ATF to wi ng a40,000-ton LHA at 3 knots with an 1,800-foothawser into head seas generated by 30-knotwinds, the table identifies curve number 6(see Table M-5). If the predicted averagetowline tension is 52,000 pounds, curve 6predicts extreme tension at 140,000 pounds(see Figure M-2). In other words, there isonly a 0.1 percent probability that a tension of140,000 pounds will be exceeded in a day oftowing under the specified conditions. As-sume that the tow now sheers out to one side,remaining off the tug's quarter for a signifi-cant period. The tug's towing winch tensionmeter now reads 70,000 pounds. Curve 6 pre-dic ts the extreme tension of 195 ,000pounds—still well below the allowable ten-sion for the T-ATF's towing hawser.

M-3 Use of the Data

This section presents guidelines on using theextreme tension curves.

M-3.1 Allowable Extreme Tension

Given an estimated or measured average tow-line tension, the curves provide an extremetension (dynamic plus average) that has onlyone chance in a thousand of being exceededin 24 hours of towing. The allowable tensionfor a given wire can therefore be much closerto the hawser's ultimate strength than can ten-sion computed relying on the traditional fac-tors of safety described in Section 3-4.1.5.Keeping extreme tension under 67 percent ofnew breaking strength is recommended. This

is equivalent to a factor of safety of 1.5. Eachship might draw a horizontal line on each ofFigures M-2 through M-5 at 67 percent of thecatalogue strength of its towing hawser. Thisrepresents the limit of acceptable extremetowline tension for that tug.

Again, the 1.5 safety factor described abovedoes not supersede factors of safety listed inTable 3-2. These latter factors of safety,which describe limits on average or steady-state tension, must still be checked. Towspeed and tow line tensions should be con-trolled such that neither factor of safety be ex-ceeded.

M-3.2 Interpolation Within the Tables

This section describes how to interpolate datawithin the tables for a particular set of cir-cumstances.

M-3.2.1 Ship Size

For tugs that are different from those de-scribed, use the next smaller ship listed. Therationale for this choice is that smaller shipsare generally affected more by a given seastate than larger ships. For towing shipssmaller than the 2,000-ton ARS 38, use theARS 38 as the basis for evaluating dynamictension. For tows different from the examplesused, use the next smaller tow unless the par-ticular tow's displacement is within 25 per-cent of that of the next larger vessel.

M-3.2.2 Tow Speed

Because extreme tension is calculated fromaverage tension, not towing speed, an incor-rect prediction of speed is not too serious. Ex-amination of the curves and tables will showthat the secondary effects of speed, at a givenaverage tension, are not great. Thus, withoutresulting in major error, the table values for 3knots can be applied to speeds from 1.0 to 4.5knots; similarly, the 6.0 knot table values canbe applied to speeds from 4.5 to 7.5 knots,and so forth. Again, it is far more important toknow the actual average tension than the ac-

M-6


tual speed. To find the maximum allowablespeed for a given scope, interpolation or ex-trapolation is acceptable.

M-3.2.3 Towing Hawser Scope

Shorter hawser scope results in a “stiffer”hawser system and higher dynamic compo-nents. To be conservative, enter the tableswith the next-lower scope (i.e., 1,500 feet fora 1,700-foot hawser scope). Extrapolating be-yond 2,100 feet is acceptable.

M-3.2.4 Wave Angle

Data in the tables are presented for relativewave directions of 0, 60, 120, and 180 de-grees. The data for 0 degrees can be used forhead seas and seas to angles of 40 degrees rel-ative. The 60 degrees results can be used forseas from 40 to 70 degrees relative. Resultsare not provided for predominantly beam seas(between 70 and 110 degrees relative) be-cause the tow's rolling and sheering presentmuch larger difficulties than towline dynam-ics for these angles. The 120 degrees resultscan be used for quartering seas between 110and 140 degrees relative, respectively, where-as the 180 degrees results are appropriate forfollowing seas between 140 and 220 degreesrelative.

M-3.2.5 Wind Strength and Wave Height

If the seas are not fully developed, the rela-tionship between wind speed and wave char-acteristics will be different from that used inthe computer program. Factors for which seaswould not be fully developed include smallfetch or changes in wind speed or direction,since it takes many hours for the sea state toreach equilibrium with the wind.

When seas are not fully developed, data forwind speeds corresponding to actual waveheights should be used (as listed in SectionM-2.3.2) instead of data for existing windspeeds. For example, a sudden 45-knot windcan develop waves estimated at 9 feet. In the

tables, use the data for a 25-knot wind speed,which assumes H1/3 at 9.1 feet.

M-3.2.6 Adjust Calculations for Sheering

A tow sheering badly to one side or the otherwill raise the average tension. This is due tosignificantly increased hydrodynamic resis-tance of the towline and (possibly) increasedresistance of the tow because of a relativelylong-term yaw angle from the course of thetug. Such sheering movements generally oc-cur at a low frequency, so that they in them-selves do not generate dynamic effects. Thetug, typically with a constant-torque enginesetting, will simply slow down to compensatefor the increased average resistance. The ef-fects of sheering were not included in the ex-treme tension model. With a sheering tow, thetow ship should observe the average tension,over a minimum of 30 seconds, when the towis at its extreme deviation from the tug'strack. This figure should be used on thecurves to determine the extreme tension. If abadly sheering tow is also rolling heavily, andhas a high bow, increasing the dynamic factorof safety to 2.0 is appropriate.

M-4 Response to Worsening Sea Conditions

When encountering rising seas, the towingship Commanding Officer has several op-tions.

M-4.1 Reduce Speed

Reducing speed is probably the single mosteffective action, because of the multiple ef-fects in extreme tension—reduction of tow-line stiffness (with consequent dynamic com-ponent reduction) and reduction of theaverage tension.

M-4.2 Increase Towline Scope

While not as effective as reducing tow speed,increasing towline scope is usually the firstaction taken, assuming adequate water depthand towline length. This reduces the stiffness

M-7


of the system and therefore reduces the dy-namic component of the extreme tension.

M-4.3 Change Course

Examination of the tables and curves revealsthat changing course to encounter the waveson a different relative heading can reducetowline tension. Sometimes seas from 60 de-grees relative are better than head seas. Thisis demonstrated in the ATS 1 Class examplebelow. In general, stern seas at a given aver-age tension are worse, but in some cases, thetug can reduce RPM and might still makeheadway with acceptable towline tensions.Specific examples will have to be worked outcarefully.

M-5 Examples

The following section provides additional ex-amples for using Tables M-1 through M-10and Figures M-2 through M-5.

Use of the extreme tension charts and curvesfirst requires a predicted or observed meantowing hawser tension. For the sake of sim-plicity, all of the following examples arebased on the tow of a 7500 LT DD 963 Classdestroyer into seas generated by a 25-knotwind. These are the same set of circumstanc-es used in Example 2 of Appendix G. Exam-ple 2 predicts the hawser tension for severalspeeds, including the hydrodynamic resis-tance of 2,000 feet of 2¼-inch wire towinghawser with one shot of 2¼-inch chain. It alsopredicts the maximum safe speed for each ofthe most common Navy towing ships.

This example shows fairly modest changes inhawser hydrodynamic resistance over the ten-sion range of interest. For the following ex-amples, therefore, the effects of differentscopes and different hawsers can be ignored.Alternatively, tow resistance alone can beconsidered and the wire resistance of the spe-cific hawser in use added back at the appro-priate points. However, the method used here

is simpler and will make the results somewhatconservative.

The tables are developed for each towing shipclass towing a DD 963 Class destroyer dis-placing 6,707 LT. The assumed tow, beingheavier at 7,500 LT, will experience some-what less motion; the results will slightlyoverstate extreme tensions but are sufficientfor estimating purposes.

M-5.1 ATS 1 Class

For the ATS 1 Class, Example 2 predicts amaximum tow speed of 7.2 knots with a totalhawser tension of 106,000 lbs.

In Table M-8, look at the 25-knot wind/6-knot tow speed block. Find the curve num-bers for several hawser scopes; look at thecurves at 106,000 pounds to find several pre-dicted extreme tensions as folllows:

The ATS 1 Class towing hawser has a newbreaking strength of 300,000 pounds. Using a1.5 dynamic factor of safety for evaluatingextreme tensions, the allowable extreme ten-sion is 240,000 pounds. Note that the predict-ed extreme tensions for hawsers of at least1,500 are all under 240,000 pounds. Note alsothat predicted extreme tension is reduced insome cases when the seas are met at 60 de-grees relative, rather than head-on.

Not shown here is the extreme tension whentowing downwind under these conditions.Assume tow speeds up to about 9 knots withthe same tension, because of the following

WaveAngle

0°0°0°0°60°60°60°60°

Scope

1,2001,5001,8002,1001,2001,5001,8002,100

CurveNo.

5432933313029

ExtremeTension

270,000 lbs.234,000 lbs.203,000 lbs.177,000 lbs.235,000 lbs.198,000 lbs.217,000 lbs.177,000 lbs.

M-8


wind and seas. Predicted extreme tension isbeyond the curve display limits of 400,000pounds for all towline scopes listed.

The steady state, or mean, tensions must alsobe checked against the safety factors listed inTable 3-2. When towing on automatic tensioncontrol, the minimum factor of safety is 3,and the allowable tension is:

360,000/3=120,000 lbs.

This is greater that the mean tension of106,000 pounds, so the tow described is with-in limits, the actual control being the towingcapacity of the ATS 1 at the speed of 7.2knots.

M-5.2 ARS 50 Class

The ARS 50 class uses the same tables as theATS 1 Class, therefore, the curve numberswill be the same. But the ARS 50 can tow the7500 LT DDG 963 Class destroyer at only 6.9knots with a mean hawser tension of 98,000pounds. Therefore, extreme tensions will beless than for the ATS 1 at 7.2 knots. For ex-ample, with a hawser scope of 1,800 feet, theextreme tension prediction is 186,000pounds. The ARS 50 has a stronger hawserthan the ATS 1, so the example needs to becarried no further to check factors of safety.The tow will be limited by the maximum tow-ing speed attainable by the ARS 50.

M-5.3 T-ATF 166 Class

Example 2 predicts that the T-ATF can con-duct the tow at 7.6 knots with a hawser ten-sion of 117,000 pounds. However, if theT-ATF tows without its automatic tensionfeature, the minimum factor of safety fromTable 3-2, would be 4, and the allowablemean tension is:

360,000/4 = 90,000 lbs.

This will limit the towing speed to about 6.9knots.

The extreme tension must also be checkedwith a mean tension of 90,000 pounds usingTable M-3.

Applying the dynamic factor of safety of 1.5,the maximum allowable predicted extremetension is 240,000 pounds. Therefore, pre-dicted extreme tensions from ship motion the-ory is satisfactory for this tow at 6.9 knots.The 90,000-pound steady-state tension condi-tion limits this tow.

WaveAngle

0°0°0°0°

Scope

1,2001,5001,8002,100

CurveNo.

433029

ExtremeTension

195,000 lbs.170,000 lbs.162,000 lbs.148,000 lbs.

M-9


Figure M-2. Extreme Tensions (Curves 0 to 24).

M-10



M-11


Figure M-4. Extr eme Tensions (Curves 50 to 74).

M-12



M-13


Table M-1. T-ATF Towing YRBM Barge Displacing 650 Tons.C

urve

Num

bers

for

Var

ious

Tow

line

Leng

ths

Not

e: N

umbe

rs li

sted

und

er e

ach

haw

ser

leng

th c

orre

spon

d to

cur

ves

foun

d in

Fig

ures

M-2

thro

ugh

M-5

. Giv

en th

e av

erag

eto

w h

awse

r te

nsio

n, th

ese

curv

es p

redi

ct th

e ex

trem

e te

nsio

n th

at h

as a

pro

babi

lity

of 0

.1 p

erce

nt o

f oc

curr

ing

in 2

4 ho

urs

ofto

win

g un

der

the

stat

ed c

ondi

tions

.

Rel

Wav

eD

ir

15 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed15

Kn

ot W

ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed15

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

79 79 81 89

51 2 79 86

1 1 2 53

26 26 51 77

26 26 76 76

51 77 86 64

1 51 81 87

26 26 52 86

26 26 2 80

26 26 51 77

1 51 60 37

26 1 82 35

26 26 53 34

26 26 52 82

26 26 77 81

Rel

Wav

eD

ir

20 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed20

Kn

ot W

ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed20

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

90 89 89 69

89 63 89 90

84 86 87 89

79 79 82 63

77 77 79 84

63 63 67 95

85 85 64 68

79 79 86 90

52 52 81 89

51 28 54 87

81 82 67 46

79 54 64 43

52 52 62 17

28 2 82 65

27 51 55 88

Rel

Wav

eD

ir

25 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed25

Kn

ot W

ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed25

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

94 68 70 97

68 90 91 94

90 66 90 68

89 88 89 67

87 86 88 90

69 67 70 99

90 89 91 96

88 87 65 93

60 84 88 68

56 80 62 90

16 15 71 24

62 61 69 97

83 83 66 71

55 80 63 69

4 53 61 68

Rel

Wav

eD

ir

30 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed30

Kn

ot W

ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed30

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

74 96 97 24

96 70 95 74

69 91 68 71

91 90 90 69

90 89 66 68

73 72 98 24

71 69 95 99

91 66 68 95

66 88 66 69

64 62 89 69

71 71 99 24

69 17 95 24

65 62 68 74

62 60 66 72

84 82 64 69

M-14


Table M-2. T-ATF Towing FFG 1 Frigate Displacing 3,200 Tons.

Cur

ve N

umbe

rs fo

r V

ario

us T

owlin

e Le

ngth

s

Not

e: N

umbe

rs li

sted

und

er e

ach

haw

ser

leng

th c

orre

spon

d to

cur

ves

foun

d in

Fig

ures

M-2

thro

ugh

M-5

. Giv

en th

e av

erag

eto

w h

awse

r te

nsio

n, th

ese

curv

es p

redi

ct th

e ex

trem

e te

nsio

n th

at h

as a

pro

babi

lity

of 0

.1 p

erce

nt o

f oc

curr

ing

in 2

4 ho

urs

ofto

win

g un

der

the

stat

ed c

ondi

tions

.

Rel

Wav

eD

ir

15 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed15

Kn

ot W

ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed15

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

26 1 76 76

26 26 26 76

26 26 26 26

26 26 26 26

0 26 26 26

26 27 51 77

26 26 76 51

0 26 26 76

0 26 26 76

0 26 26 26

26 26 71 83

26 26 51 53

0 26 76 77

0 26 26 51

0 26 26 76

Rel

Wav

eD

ir

20 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed20

Kn

ot W

ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed20

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

3 30 4 83

2 29 3 54

28 28 2 78

51 28 28 77

1 27 51 2

29 30 80 65

28 29 78 83

27 28 52 80

27 28 28 53

26 27 28 3

29 29 56 68

28 29 79 66

27 28 78 60

27 27 2 81

26 27 2 54

Rel

Wav

eD

ir

25 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed25

Kn

ot W

ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed25

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

13 61 64 68

7 83 83 90

79 31 54 11

3 30 31 81

30 29 52 54

8 57 66 70

5 33 63 68

32 30 55 64

30 30 4 10

29 29 3 56

36 7 66 73

33 32 63 70

31 30 82 67

30 30 54 64

29 29 53 61

Rel

Wav

eD

ir

30 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed30

Kn

ot W

ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed30

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

18 67 68 73

66 67 67 70

13 61 63 67

8 34 56 65

5 32 5 11

17 67 69 99

15 65 67 72

9 58 65 69

6 33 60 67

33 31 80 15

16 66 71 24

14 63 68 98

7 36 66 71

34 32 61 69

32 31 56 67

M-15


Table M-3. T-ATF Towing DD 963 Destroyer Displacing 6,707 Tons.C

urve

Num

bers

for

Var

ious

Tow

line

Leng

ths

Not

e: N

umbe

rs li

sted

und

er e

ach

haw

ser

leng

th c

orre

spon

d to

cur

ves

foun

d in

Fig

ures

M-2

thro

ugh

M-5

. Giv

en th

e av

erag

eto

w h

awse

r te

nsio

n, th

ese

curv

es p

redi

ct th

e ex

trem

e te

nsio

n th

at h

as a

pro

babi

lity

of 0

.1 p

erce

nt o

f oc

curr

ing

in 2

4 ho

urs

ofto

win

g un

der

the

stat

ed c

ondi

tions

.

Rel

Wav

eD

ir

15 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed15

Kn

ot W

ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed15

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

26 26 76 76

26 26 26 1

26 26 26 26

26 26 26 26

0 26 26 26

26 26 51 77

26 26 1 51

26 26 26 76

0 26 26 76

0 26 26 26

26 26 51 80

26 26 51 78

0 26 1 77

0 26 26 51

0 26 26 76

Rel

Wav

eD

ir

20 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed20

Kn

ot W

ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed20

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

3 29 3 6

2 29 52 4

51 28 2 3

51 27 27 77

1 27 1 28

2 29 4 61

28 28 3 82

51 28 77 79

1 27 28 78

26 27 51 52

28 29 80 67

51 28 4 63

1 28 3 82

26 27 2 80

26 27 28 53

Rel

Wav

eD

ir

25 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed25

Kn

ot W

ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed25

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

9 83 61 91

6 32 6 63

4 31 4 82

3 29 3 80

52 29 29 4

6 35 89 69

4 32 58 67

3 30 5 13

30 29 53 8

29 29 3 6

5 33 65 73

32 31 60 69

30 30 55 66

29 29 79 14

28 29 78 9

Rel

Wav

eD

ir

30 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed30

Kn

ot W

ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed30

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

17 67 68 72

15 63 66 69

10 6 60 66

7 33 5 13

5 31 4 8

16 66 68 98

13 62 67 72

7 34 63 68

5 32 81 16

32 31 5 13

15 65 19 24

9 62 67 98

6 34 63 71

33 32 82 69

32 31 6 16

M-16


Table M-4. T-ATF Towing AE 26 Displacing 20,000 Tons.

Cur

ve N

umbe

rs fo

r V

ario

us T

owlin

e Le

ngth

s

Not

e: N

umbe

rs li

sted

und

er e

ach

haw

ser

leng

th c

orre

spon

d to

cur

ves

foun

d in

Fig

ures

M-2

thro

ugh

M-5

. Giv

en th

e av

erag

eto

w h

awse

r te

nsio

n, th

ese

curv

es p

redi

ct th

e ex

trem

e te

nsio

n th

at h

as a

pro

babi

lity

of 0

.1 p

erce

nt o

f oc

curr

ing

in 2

4 ho

urs

ofto

win

g un

der

the

stat

ed c

ondi

tions

.

Rel

Wav

eD

ir

15 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed15

Kn

ot W

ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed15

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

26 26 1 76

26 26 26 76

26 26 26 26

0 0 26 26

0 26 26 26

26 26 76 77

26 26 1 51

0 26 26 76

0 0 26 26

0 26 26 26

26 26 51 53

26 26 51 52

0 26 1 51

0 0 26 51

0 0 26 76

Rel

Wav

eD

ir

20 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed20

Kn

ot W

ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed20

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

30 30 3 5

2 29 29 53

28 28 28 52

27 27 28 2

1 27 27 28

2 30 4 8

28 28 3 6

27 28 2 4

27 27 28 3

1 27 51 77

28 29 5 16

28 28 53 61

27 28 52 38

26 27 2 54

26 27 28 53

Rel

Wav

eD

ir

25 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed25

Kn

ot W

ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed25

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

7 35 8 15

5 32 51 12

4 31 3 7

3 29 30 5

30 29 29 4

35 34 12 68

33 32 6 16

31 31 4 11

30 29 31 7

29 29 30 80

34 34 62 21

32 32 8 69

30 31 5 15

29 29 4 13

29 29 3 8

Rel

Wav

eD

ir

30 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed30

Kn

ot W

ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed30

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

17 16 67 20

14 10 64 68

8 35 7 15

6 32 34 12

34 32 32 8

16 15 68 22

11 39 65 71

37 34 8 67

34 32 6 15

33 32 4 12

14 15 18 24

39 37 66 74

36 34 12 70

33 32 7 68

32 31 5 16

M-17


Table M-5. T-ATF Towing LHA 1 Displacing 40,000 Tons.C

urve

Num

bers

for

Var

ious

Tow

line

Leng

ths

Not

e: N

umbe

rs li

sted

und

er e

ach

haw

ser

leng

th c

orre

spon

d to

cur

ves

foun

d in

Fig

ures

M-2

thro

ugh

M-5

. Giv

en th

e av

erag

eto

w h

awse

r te

nsio

n, th

ese

curv

es p

redi

ct th

e ex

trem

e te

nsio

n th

at h

as a

pro

babi

lity

of 0

.1 p

erce

nt o

f oc

curr

ing

in 2

4 ho

urs

ofto

win

g un

der

the

stat

ed c

ondi

tions

.

Rel

Wav

eD

ir

15 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed15

Kn

ot W

ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed15

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

26 26 1 76

26 26 26 26

26 26 26 26

0 0 26 26

0 26 26 76

26 26 51 77

26 26 1 51

0 0 26 76

0 0 26

26

0 0 26 26

26 26 51 78

0 26 76 77

0 0 1 51

0 0 26 76

0 0 26 76

Rel

Wav

eD

ir

20 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed20

Kn

ot W

ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed20

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

52 29 3 5

2 28 2 53

28 27 28 52

51 27 27 2

1 1 27 28

2 29 4 8

51 28 52 6

1 27 2 4

1 27 28 3

26 27 51 52

28 28 4 15

51 28 3 11

1 27 52 81

26 27 2 54

26 27 28 53

Rel

Wav

eD

ir

25 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed25

Kn

ot W

ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed25

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

7 34 7 15

5 32 5 10

4 30 31 6

3 29 30 5

52 29 29 4

5 33 9 18

4 31 6 15

3 30 4 10

52 29 3 7

2 29 52 80

4 34 12 20

31 32 7 68

52 30 5 15

2 29 4 12

28 29 3 8

Rel

Wav

eD

ir

30 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed30

Kn

ot W

ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed30

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

17 15 66 20

13 8 63 18

8 34 6 15

6 32 4 10

4 31 32 7

14 15 68 22

9 37 64 20

6 33 7 17

5 32 5 15

4 31 4 11

12 13 18 24

38 38 15 22

35 35 9 70

33 33 6 18

32 32 5 15

M-18


Table M-6. ARS 50 or ATS 1 Towing YRBM Barge Displacing 650 Tons.

Cur

ve N

umbe

rs fo

r V

ario

us T

owlin

e Le

ngth

s

Not

e: N

umbe

rs li

sted

und

er e

ach

haw

ser

leng

th c

orre

spon

d to

cur

ves

foun

d in

Fig

ures

M-2

thro

ugh

M-5

. Giv

en th

e av

erag

eto

w h

awse

r te

nsio

n, th

ese

curv

es p

redi

ct th

e ex

trem

e te

nsio

n th

at h

as a

pro

babi

lity

of 0

.1 p

erce

nt o

f oc

curr

ing

in 2

4 ho

urs

ofto

win

g un

der

the

stat

ed c

ondi

tions

.

Rel

Wav

eD

ir

15 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed15

Kn

ot W

ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed15

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

83 83 88 89

80 78 86 89

51 77 78 82

1 1 51 53

26 26 51 51

79 80 88 41

77 53 89 90

1 1 83 89

26 26 52 86

26 26 77 54

77 53 89 36

1 51 88 35

26 1 84 34

26 26 54 7

26 26 78 60

Rel

Wav

eD

ir

20 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed20

Kn

ot W

ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed20

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

91 90 68 94

90 88 90 68

87 90 88 90

82 83 84 90

78 53 55 63

90 89 93 96

90 90 91 93

85 86 89 91

79 55 88 90

77 52 83 90

89 89 94 44

63 63 91 42

82 60 89 93

52 53 89 16

28 2 63 89

Rel

Wav

eD

ir

25 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed25

Kn

ot W

ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed25

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

95 93 95 98

92 91 92 95

67 67 90 68

89 89 65 91

89 88 88 90

94 92 96 22

68 91 92 96

90 66 91 93

89 89 90 68

63 63 88 91

92 68 97 24

91 90 94 98

90 89 91 71

88 88 90 93

59 86 90 67

Rel

Wav

eD

ir

30 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed30

Kn

ot W

ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed30

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

98 97 98 24

96 94 96 98

69 68 92 95

91 90 90 92

67 90 90 68

97 96 98 24

95 94 96 22

92 91 93 72

91 90 91 70

90 90 90 68

96 97 99 24

94 93 97 24

68 67 93 96

67 90 91 96

66 89 67 70

M-19


Table M-7. ARS 50 or ATS 1 Towing FFG 1 Frigate Displacing 3,200 Tons.C

urve

Num

bers

for

Var

ious

Tow

line

Leng

ths

Not

e: N

umbe

rs li

sted

und

er e

ach

haw

ser

leng

th c

orre

spon

d to

cur

ves

foun

d in

Fig

ures

M-2

thro

ugh

M-5

. Giv

en th

e av

erag

eto

w h

awse

r te

nsio

n, th

ese

curv

es p

redi

ct th

e ex

trem

e te

nsio

n th

at h

as a

pro

babi

lity

of 0

.1 p

erce

nt o

f oc

curr

ing

in 2

4 ho

urs

ofto

win

g un

der

the

stat

ed c

ondi

tions

.

Rel

Wav

eD

ir

15 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed15

Kn

ot W

ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed15

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

26 27 76 76

26 27 1 76

26 26 26 26

26 26 26 26

0 26 26 26

26 27 51 77

26 27 76 51

0 26 26 76

0 26 26 1

0 26 26 26

26 27 77 87

26 27 51 79

0 26 76 77

0 26 26 51

0 26 26 76

Rel

Wav

eD

ir

20 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed20

Kn

ot W

ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed20

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

4 32 80 61

52 30 78 55

2 28 77 53

51 28 28 52

1 28 51 77

30 31 82 89

2 30 79 61

28 28 3 55

27 28 2 79

1 28 2 78

29 31 60 92

29 30 55 91

28 28 53 61

27 28 77 82

27 28 77 80

Rel

Wav

eD

ir

25 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed25

Kn

ot W

ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed25

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

65 65 66 69

62 8 63 67

80 4 55 64

4 31 4 82

3 30 3 80

13 63 67 71

7 60 64 92

4 32 59 66

31 31 54 61

30 30 53 82

8 12 91 97

35 35 65 94

32 32 85 68

30 30 55 89

29 30 79 62

Rel

Wav

eD

ir

30 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed30

Kn

ot W

ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed30

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

70 19 71 73

68 67 68 71

64 62 65 68

10 6 60 90

81 33 55 61

19 18 71 99

66 67 68 96

13 63 67 93

7 35 63 91

5 33 56 65

18 18 72 24

15 66 69 98

9 61 90 95

36 34 63 93

34 32 83 91

M-20


Table M-8. ARS 50 or ATS 1 Towing DD 963 Destroyer Displacing 6,707 Tons.

Cur

ve N

umbe

rs fo

r V

ario

us T

owlin

e Le

ngth

s

Not

e: N

umbe

rs li

sted

und

er e

ach

haw

ser

leng

th c

orre

spon

d to

cur

ves

foun

d in

Fig

ures

M-2

thro

ugh

M-5

. Giv

en th

e av

erag

eto

w h

awse

r te

nsio

n, th

ese

curv

es p

redi

ct th

e ex

trem

e te

nsio

n th

at h

as a

pro

babi

lity

of 0

.1 p

erce

nt o

f oc

curr

ing

in 2

4 ho

urs

ofto

win

g un

der

the

stat

ed c

ondi

tions

.

Rel

Wav

eD

ir

15 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed15

Kn

ot W

ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed15

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

26 26 76 76

26 26 1 26

26 26 26 26

0 26 26 26

0 26 26 26

26 26 51 77

26 26 76 51

26 26 76 76

0 26 26 26

0 26 26 26

26 26 2 80

26 26 51 78

0 26 76 77

0 26 26 51

0 26 26 1

Rel

Wav

eD

ir

20 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed20

Kn

ot W

ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed20

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

56 4 30 3

79 3 29 77

28 28 77 78

51 27 51 77

1 27 51 2

52 30 80 65

2 29 53 82

51 28 52 54

1 27 2 78

1 27 28 52

2 30 56 68

28 29 54 64

27 28 53 83

26 27 77 80

26 27 2 53

Rel

Wav

eD

ir

25 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed25

Kn

ot W

ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed25

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

13 10 64 68

56 5 83 65

54 32 54 58

53 30 53 81

52 30 3 54

8 60 90 71

5 33 61 68

4 31 55 63

3 30 79 84

29 29 78 81

6 36 67 73

4 33 63 70

3 31 82 67

29 30 54 63

29 29 4 59

Rel

Wav

eD

ir

30 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed30

Kn

ot W

ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed30

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

69 68 69 73

66 65 67 70

13 8 63 67

83 34 81 63

6 33 5 11

18 18 70 98

15 64 91 72

9 7 64 69

6 33 82 66

5 32 55 14

17 17 71 24

13 64 68 98

7 65 36 71

5 33 59 69

32 32 56 66

M-21


Table M-9. ARS 50 or ATS 1 Towing AE 26 Displacing 20,000 Tons.C

urve

Num

bers

for

Var

ious

Tow

line

Leng

ths

Not

e: N

umbe

rs li

sted

und

er e

ach

haw

ser

leng

th c

orre

spon

d to

cur

ves

foun

d in

Fig

ures

M-2

thro

ugh

M-5

. Giv

en th

e av

erag

eto

w h

awse

r te

nsio

n, th

ese

curv

es p

redi

ct th

e ex

trem

e te

nsio

n th

at h

as a

pro

babi

lity

of 0

.1 p

erce

nt o

f oc

curr

ing

in 2

4 ho

urs

ofto

win

g un

der

the

stat

ed c

ondi

tions

.

Rel

Wav

eD

ir

15 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed15

Kn

ot W

ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed15

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

26 1 76 76

26 26 26 26

26 26 26 26

0 0 26 26

0 26 26 26

26 26 51 51

26 26 76 51

0 26 26 76

0 0 26 26

0 26 26 26

26 26 77 53

26 26 51 52

0 26 76 51

0 0 26 76

0 26 26 26

Rel

Wav

eD

ir

20 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed20

Kn

ot W

ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed20

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

3 31 32 80

2 29 3 79

28 29 28 52

51 27 28 77

1 28 51 51

29 31 4 10

2 29 3 81

51 29 77 79

1 27 28 78

1 28 28 77

2 30 55 66

28 29 79 61

27 29 52 82

26 27 2 54

26 27 2 53

Rel

Wav

eD

ir

25 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed25

Kn

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- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed25

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

9 37 9 17

6 34 6 13

4 33 4 82

3 30 31 80

30 30 30 79

37 36 63 70

34 33 7 17

32 32 5 13

30 30 4 82

30 30 3 55

36 36 15 96

33 33 10 70

31 32 81 65

30 30 79 62

29 30 53 83

Rel

Wav

eD

ir

30 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed30

Kn

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- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed30

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

19 18 18 72

16 13 67 70

11 37 8 16

7 34 6 13

5 33 4 83

18 17 69 98

14 11 66 72

8 36 10 68

35 33 7 16

34 33 5 13

16 17 70 24

12 40 67 98

38 36 13 71

35 33 8 68

33 32 6 16

M-22


Table M-10. ARS 50 or ATS 1 Towing LHA 1 Displacing 40,000 Tons.

Cur

ve N

umbe

rs fo

r V

ario

us T

owlin

e Le

ngth

s

Not

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umbe

rs li

sted

und

er e

ach

haw

ser

leng

th c

orre

spon

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cur

ves

foun

d in

Fig

ures

M-2

thro

ugh

M-5

. Giv

en th

e av

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eto

w h

awse

r te

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n, th

ese

curv

es p

redi

ct th

e ex

trem

e te

nsio

n th

at h

as a

pro

babi

lity

of 0

.1 p

erce

nt o

f oc

curr

ing

in 2

4 ho

urs

ofto

win

g un

der

the

stat

ed c

ondi

tions

.

Rel

Wav

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ir

15 K

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3 K

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ed15

Kn

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ind

- 6

Kno

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xim

ate

Tow

Spe

ed15

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

26 26 76 76

26 26 26 26

26 26 26 26

0 0 26 26

0 26 26 26

26 26 51 51

26 26 76 76

0 26 26 76

0 0 26 26

0 0 26 26

26 26 77 78

0 26 76 77

0 26 1 51

0 0 26 76

0 0 26 1

Rel

Wav

eD

ir

20 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed20

Kn

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ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed20

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

3 30 3 80

2 2 52 53

28 28 2 3

51 27 51 77

1 27 1 51

2 29 4 83

28 2 3 55

51 28 77 79

1 27 2 78

1 27 51 52

28 29 5 65

51 29 53 60

1 28 52 81

1 27 77 54

26 27 28 53

Rel

Wav

eD

ir

25 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed25

Kn

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- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed25

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

8 36 8 16

6 33 6 13

4 31 4 82

78 30 3 80

52 29 29 79

6 35 12 69

5 33 7 16

78 31 5 12

52 30 53 82

2 29 3 55

5 36 14 99

4 33 8 69

3 31 6 16

2 30 4 13

2 30 3 83

Rel

Wav

eD

ir

30 K

not

Win

d -

3 K

not

s A

ppro

xim

ate

Tow

Spe

ed30

Kn

ot W

ind

- 6

Kno

ts A

ppro

xim

ate

Tow

Spe

ed30

Kno

t W

ind

- 9

Kno

ts A

ppro

xim

ate

Tow

Spe

ed

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

1000

ft

1200

ft

1500

ft

1800

ft

2100

ft

0º 60º

120º

180º

68 17 18 72

15 10 14 69

9 36

7 16

7 33 5 13

3 32 4 8

16 16 19 74

13 39 66 71

7 35 9 68

5 33 66 15

4 32 5 13

15 45 20 24

10 41 17 73

7 36 12 70

5 34 7 68

32 33 5 15

M-23



M-24


Appendix N

REFERENCES

A. Naval Ship’s Technical Manual (NSTM) S9086-TW-STM-010, Chap-ter 582, Mooring and Towing, (S9086-TW-STM-010/CH-582), 30 November 1990.

B. Allied Tactical Publication ATP-43(A) (NAVY), Ship-to-Ship Towing, 1996.

C. The Wire Rope Users Manual, Ameri-can Iron and Steel Institute, Washing-ton, D.C., Third Edition, 1993.

D. General Specifications for Overhaul of Surface (GSO) Ships, U.S. Navy, Sec-tions 582 and 077, Naval Sea Systems Command, S9AA0-AB-GOS-010/GSO.

E. RR-C-271D, Amendment 1, Federal Specification, Chain and Attachments, Welded and Weldless, 29 November 1995.

F. Naval Ship’s Technical Manual (NSTM) S9086-UU-STM-010, Chapter 613, Wire and Fiber Rope and Rigging, S9086-UU-STM-010/CH613, Second Revision, 1 May 1995.

G. Naval Ship’s Technical Manual (NSTM)S9086-BS-STM-010, Chapter 50,Readiness and Care of Inactive Ships,S9086-BS-STM-010/CH050, SecondRevision, 18 December 1998.

H. American Bureau of Shipbuilding (ABS) 10, Rules for Building and Classing Steel Barges, Notice No. 2, 11 May 1993.

I. Code of Federal Regulations (CFR) Part 81 - 72 COLREGS: Implementing rules.

J. International Code of Signals, Commu-nicationing Ship-to-Ship, NWP 14-1 (Ref. 16)

K. Naval Ship’s Technical Manual (NSTM) S9086-CH-STM-030, Chap-ter 074, Gas Free Engineering, (S9086-CH-STM-030/CH-074), Third Revi-sion, 23 April 1998.

L. Knight's Modern Seamanship, 1989, 18th Edition.

M. Naval Warfare Publication (NWP)MSC Handbook for Refueling at Sea,NWP 14-2, Change 3, March 1986.

N. Code of Federal Regulations (CFR) 35, Panama Canal, Revised 1 July 1997.

O. Allied Tactical Publication ATP-15, Arctic Towing Operations, Articles 3406 and 4406 55.

P. NAVSEAINST 4740.9E, Towing of Un-manned Defueled Nuclear Submarines, 16 January 2001.

Q. International Maritime Organization (IMO), Resolution A.535(13), Recom-mendations on Emergency Towing Re-quirements for Tankers, 17 November 1983.

R. International Chamber of Shipping Oil Companies International Marine Fo-rum, Peril at Sea and Salvage: A Guide for Masters, 2nd Edition, September 1982.

S. Naval Education and Training Com-mand, NAVEDTRA 10122-E, The Boatswain's Mate First Class and Chief Rate Training Manual, 1982 Edition.

T. MIL-STD-1625C Safety Certification Program for Drydocking Facilities and Shipbuilding Ways for U.S. Navy Ships, Change 1, 30 December 1992.

N-1


U. Principles of Naval Architecture, 2nd Edition, The Society of Naval Archi-tects and Marine Engineers, 1988.

V. DOD-STD-1399-301A, Interface Stan-dard for Shipboard Systems Section, 301A Ship Motion and Attitude (Met-ric), 21 July 1986.

W. Naval Ship’s Technical Manual (NSTM) S9086-7F-STM-010, Chapter 997, Docking Instructions and Routine Work in Drydock, S9086-7F-STM-010/CH-997, Third Revision, 25 November 1996.

X. OPNAVINST 5100.19C (N45, 0579LD0571210), Navy Occupational Safety and Health (NAVOSH) Program Manual for Forces Afloat, Vol. 1-3, 19 January 1994.

Y. OPNAVINST 5100.23C, Navy Occu-pational Safety and Health (NAVOSH) Program Manual, 2 November 1992.

Z. US Navy Salvage Safety Manual, 0910-LP-107-7600, 25 December 1988.

AA. NAVSEA Interim MRC for ARS 50 Class Running Rigging

AB. MIL-C-24633A Notice 1, Chain, Stud Link, Anchor, Low Alloy Steel, Flash Bolt Welded, 22 April 1998.

AC. Naval Ship’s Technical Manual (NSTM) S9086-TV-STM-010, Chap-ter 581, Anchoring, S9086-TV-STM-010/CH-581, 24 November 1997.

AD. NAVSHIPS 0994-004-8010 Carpenter Stopper, Operation and Maintenance Instructions, 5 June 1970.

AE. Blight and Dai, Resistance of Offshore Barges and Required Tug Horsepow-er, OTC 3320, 10th Offshore Technol-ogy Conference Proceedings, 1978.

N-2


Appendix O

GLOSSARY

21-thread. A light line used to stop off ahawser or other heavy line.

Abrasion resistance. Material’s ability to re-sist exterior damage due to frictional contact.

Advance. Distance gained in the direction ofthe original course when turning a ship, mea-sured from the point at which the rudder isput over to the point where the ship haschanged heading 90 degrees.

Amidships. In or toward the middle of a ship.

Anchor shackle. A U-shaped fitting with pin.

Anchor windlass. The machine used to hoistand lower anchors.

Assisting command. A naval shipyard, pri-vate ship yard, or naval station which installstowing systems, supplies riding crews, andprovides other assistance.

Assisting tugs. Tugs used during slow speedmaneuvers, namely getting underway, dock-ing, and other harbor movements.

Athwartship. At right angles to the fore andaft centerline of a ship or boat.

Attachment point. Point of attachment be-tween the tow and the towed vessel. The at-tachment point transmits the towing loadfrom the towline to the vessel.

Automatic towing machine. A device whichmaintains safe tension on the hawser duringtowing without action by the operator.

Auxiliary towline. A tug’s spare or second-ary hawser used for multiple tows or second-ary functions such as target towing.

Auxiliary vessel. A vessel that maintains,supplies, or supports combatants.

Backing down. Using a stern throttle to rap-idly reduce the forward speed of a tug. A dan-gerous practice in towing due to the risk offailed tow lines or collision.

Bail. The part of a pelican hook or chain stop-per that holds the hook closed.

Ballast. The weight added to a ship or boat toensure stability; to pump sea water into emptyfuel tanks.

Barrel. The rotating drum of a capstan orwinch. Also, one of two standing posts of abitt.

Beach gear. A generic term for specializedground tackle, purchases, and ancillary equip-ment used to extract a grounded ship.

Beam. A ship’s breadth at its widest point;any of the heavy horizontal crosspieces of aship.

Beam sea. A sea that runs athwart the ves-sel’s course.

Beam wind. A wind that blows athwart thevessel’s course.

Bear down. To approach the target.

Beaufort No. A numerical value (from 0 to12) used for rating wind velocity, in ascend-ing strength.

Billboard. An inclined platform used to stowan anchor for rapid deployment.

Bird caging. The phenomenon of wires flar-ing out around the full diameter of a wirerope, with resulting kinks in the wires. Thiscan occur when there is a sudden release of aheavy load on a wire rope.

Bitt. A pair of metal posts to which mooringor towing lines are made fast.

Bitter end. The absolute end of a piece ofline or cable, especially the last link of anchorchain in the chain locker.

O-1


Bollard. Single posts secured to a wharf orpier and used for mooring vessels by meansof lines extending from the vessel.

Bollard pull. The maximum pulling powerthat a tug can generate with zero forwardspeed.

Bowline. A classic knot that forms a loop thatwill not slip or become tighter under tension.

Bow (of the) shackle. The curved end of ashackle.

Bow thruster. A propulsor at the bow of theship which aids in moving the bow sideways.

Breaking of a tow. The release of a towedvessel.

Breaking strength. The actual or ultimaterated load required to pull a wire, strand, orrope to destruction.

Breakwater. Structure that shelters a port oranchorage from the sea.

Bridles. A length of chain or wire extendingfrom the bow of a tow. Usually refers to therigging of a tow with two legs from the tow’sbow to a flounder plate.

Broach. To be turned broadside to a surf orheavy sea.

Bulbous bows. An extension of the bow of aship below the water line that is designed toreduce wave drag.

Bulkhead. Walls or partitions within a ship,generally referring to those with structuralfunctions such as strength or water-tightness.

Bullnose. Closed chock at the bow of a ship.

Bull rope. Colloquial term referring to a tow-ing hawser.

Bulwark. Section of a ship’s side continuedabove the main deck as a protection againstheavy weather.

BUSHIPS. Bureau of Ships, now Naval SeaSystem Command.

Cable. A heavy rope, chain, or wire of greatstrength. Applications include attachment toanchors and towing. Also a unit of length,equivalent to 120 fathoms or 720 feet.

Calculated risk. Accepting an operation ordecision based on less than satisfactory con-ditions. As applied to towing, accepting a towwhen the tow’s material condition, seaworthi-ness, weather, etc., makes the tow less thansatisfactory. This should be rarely used as abasis of acceptance of the tow.

Calm water resistance. The hydrodynamicresistance created by a tow without the influ-ence of waves created by the weather, tug,tow, or other outside influences; approxi-mates steady tension.

Caprail. Rounded radius on the stern of atowing vessel, over which the sweep of thetow wire rides.

Capstan. A revolving device with a verticalaxis used for controlled deployment and re-trieval of lines.

Careen. To cause a vessel to have a perma-nent list to one side. Specifically, as in a dry-dock, to rotate the dock 90!, placing one side-wall below the water line. This is done toreduce the beam to allow passage through ca-nals or other restricted waterways.

Carpenter stopper. A mechanical deviceconsisting of a cover that encloses a slidingwedge within the body that can be opened byknocking away a latch that holds them closed.Used for stopping off wire rope.

Catamaran. A twin-hulled vessel or boat onwhich the individual hulls are joined togetherby an above water line structure.

Catenary. The downward curve or sag of arope, wire, or chain suspended between twopoints.

Center of gravity (CG). The point in a shipwhere the sum of all forces and moments ofweight is zero.

O-2


Chafing. Wear or damage to a ship or shipmaterials due to friction.

Chafing gear. Material used to prevent chaf-ing and wear on both the hawser and the tug’sstructure.

Chafing pendant. A length of chain used toreduce chafing or wearing.

Chain bridle. Two legs of chain joined by aflounder’s plate extending from the bow of atug.

Chain connecting link. See “Detachablelink.”

Chain pendant. A single length of chain ex-tending from the bow of a tug used as a tow-ing connection element, usually fitted with aneye at one or both ends.

Chain shackle. A U-shaped fitting with a pinused for chain connections in a towing rig.

Chain stopper. A device used to securechain, thereby relieving the strain on thewindlass; also used to secure the anchor in thehoused position in the hawsepipe.

“Chinese” moor. Denotes that two ships arealongside each other in such a manner that thestern of one is facing the same direction as thebow of the other.

Chock. A heavy smooth-surfaced fitting usu-ally located near the edge of the weather deckthrough which wire ropes or fiber hawsersmay be led.

Cleat. An anvil-shaped deck fitting for secur-ing or belaying lines.

Clip, wire. Fitting for clamping two parts ofwire rope to each other.

Closed socket. A wire rope termination si-miliar to a padeye or ring.

COLREG. U.S. Coast Guard Rules of theRoad.

Compartment. Room or space on boardship.

Condition ZEBRA. The condition of maxi-mum watertight integrity of a ship.

Constructional stretch. The elongation of awire rope caused by a virgin rope’s helicalstrands constricting the core during initialloading. This property is no longer exhibitedafter several loadings.

Controllable pitch propeller (CPP). Ascrew propeller with separately mountedblades and in which the pitch of the bladescan be changed, and even reversed, while thepropeller is in operation.

Core. The axial member of a wire rope, aboutwhich the strands are laid. It may consist ofwire strand, wire rope, synthetic or natural fi-ber, or solid plastic.

Cotter keys. Also called cotter pins, are usedto secure or block nuts, clevises, etc. Driveninto holes in the shaft, the eye prevents com-plete passage, and the split ends, deformed af-ter insertion, prevent withdrawal. Cotter keysare not used in towing.

Crest. The top of a wave.

Cutwater. The stem of a ship, the forward-most portion of the bow, which cuts the wateras the ship moves.

Dewatering. Process used to remove floodwater from a ship.

Deshackling kit. A tool set used to assembleand disassemble detachable links. Tools in-cluded in these sets are hammers, punches,lead pellets, spare taper pins, and hairpins.

Detachable link. A joining link that can beopened and is used to connect chain to moor-ing, towing, or beach gear equipment.

Die lock chain. Chain formed by forging.

Dipped shackle, padeye. The placement of ashackle through a padeye or connection, asopposed to passing the pin of the shacklethrough opening in the padeye. The padeye isshaped to accept a shackle as described.

O-3


Discharge head. A measurement of the dis-charge pressure of a pump in feet of waterwhich takes into account friction losses andvelocity head.

Displacement. The weight of water displacedby a vessel, expressed in long tons.

Dog. A pawl; a device applied to the winchdrum to prevent rotation. See “On the dog.”

Draft. Depth of a ship beneath the waterline,measured vertically to the keel.

Drag. Forces opposing direction of motiondue to friction, profile, and other components.

Drift rate. The motion of a vessel caused bythe action of the wind, the sea, and the cur-rent.

Drogue. A device used to slow rate of move-ment, usually towed or attached astern of thevessel.

Drum. A cylindrical barrel, either of uniformor tapering diameter, on which rope is woundeither for operation or storage; its surfacemay be smooth or grooved.

Dye-penetrant test. An inspection methodused to detect weld surface discontinuances.

Dynamic load. Relating to energy or physicalforce in motion; as opposed to static load, aforce producing motion or change.

Dynamic tension. Resistance of the ship tobe towed, the tow hawser, and the verticalcomponent of wire catenary.This resistancecannot be accurately predicted.

Eductor. A pumping device which uses theflow of water through a restriction to create areduced pressure and cause the flow of waterout of a space or compartment.

End link. The last link in a length of chain.

EIPS wire. Extra Improved Plow Steel wire.

Elastic stretch. The elongation of a wire ropeor synthetic line caused by the deformation ofthe material during loading.

Extreme towline tension. The additive accu-mulation of the complex dynamic responsesof tug, tow, and towline.

Eye splice. A loop formed in the end of arope by tucking the strand ends over and un-der the strands of the standing part of therope. A thimble is often used in the loop.

Fairlead. Metal fittings which lead lines in adesired direction.

Fairlead chock. A chock with a roller(s) in-stalled to lead a line to a bitt or cleat.

Fake (faked down). To lay out a line length-wise in long, flat bights, so that when needed,it will pay out freely.

Fantail. The open deck area or topside over-hanging part of the deck at the stern of a ship.

Fatigue. The tendency for materials or devic-es to break under repeated (cyclic) loading.

Fenders. Energy-absorbing materials or de-vices used to reduce contact between vessels.

Fetch. The distance a wind blows over thesea surface without a significant change of di-rection. A factor in the buildup of waves.

Fiber core. Cord or synthetic fiber used asthe axial member of a rope.

Fillet weld. A weld that has a triangular crosssection, joining two surfaces that are perpen-dicular to each other.

“Fish hooks.” Outer wires of wire rope thatbreak and cause short ends to project from therope; a sign of wire rope deterioration.

Fish plate. See Flounder plate.

Fitting. A specially designed piece on aship’s deck used to control or secure a line orrope (e.g., chock, bitts, padeye, etc.).

Flood effect diagrams. Diagrams whichshow the effect of flooding of a particularcompartment.

O-4


Flounder plate. A triangular steel plate towhich bridle legs are connected, sometimescalled “fish plate.”

Forecastle. Raised foreward section of aship’s weather deck. This area contains mostof the ship’s deck machinery and tow fittings.

Freeboard. Distance from the weather deckto the waterline.

Free-running speed. Maximum speed of atug without a tow.

Free-spooling. To pay out scope by releasingthe brake and allowing the towing drum to ro-tate as a result of the drag of the tow, with thetow motor disengaged.

Freshening the nip. Paying out or hauling inthe hawser to move the contact point in orderto distribute wear on the hawser, stern roller,towing bows, H-bitts, winch drum, etc.

Frictional resistance. The force created byan object as it moves through a fluid such aswater or air.

Fuse pendant. A pendant of wire rope orchain specifically designed to fail at a knowntension. May be used to protect the rest of therigging arrangement. Also called a “weaklink.”

GM. See “Metacentric height.”

Grapnel. A small, 4-armed anchor usedmainly to recover objects in the water. Thisdevice may also be helpful in establishing amethod of boarding a vessel without assis-tance from the deck.

Grommet. An endless circle or ring fabricat-ed from one continuous length of strand orrope.

Ground tackle. General term for all anchor-ing equipment aboard ship.

Gypsy head. The horizontal drum of a winch,around which a rope is wound for heaving inor paying out.

H-bitt. Short steel posts mounted forwardand aft that are used to lead or stop off a towhawser. A hard point used for towing.

Hairpin. A metal pin which is used to securea detachable link.

Harbor towing. Includes docking/undock-ing, standby duty, and safety escort duty inprotected waters.

Hatch. Access opening in the deck of a ship,fitted with a hatch cover for watertight clo-sure.

Hawse pipe. Heavy casting through whichthe anchor chain runs from deck down andforward through ship’s bow plating.

Hawser. A heavy line or wire rope of over 5inches in diameter.

Headed fair. An expression meaning bearingtoward an object or an area. In towing, this re-fers to the tow bearing in the same directionas the tug.

Heave. Vertical displacement of a ship in aseaway, as distinct from pitching, which is es-sentially a rotation about an athwartships ax-is. Heave generally refers to an upwardmovement, bodily, of the entire ship. Also, tohaul in or retrieve a line or rope.

Helix. The twist or curvature of the individu-al strands of a wire rope.

High line. A single line rigged between twoships under way transferring stores.

Hockle. Kinking of one or more strands oftwisted fiber line or wires on a wire rope.

Hog (hogging). Deviation of the keel from astraight line, in which the keel is concavedownward.

Hogging strap. A restraining line exertingforce on the hawser to hold it close againstthe caprail and/or closer to the fantail.

Hookup. The process of making up the con-nections to tow a vessel.

O-5


Horizontal stern rollers. A large-diameterroller, set in the stern bulwarks on the center-line and faired to the caprail. Provides a mini-mum chafe point for the tow wire duringheave-in and payout.

Horsepower, brake. The power delivered atthe engine’s shaft.

Horsepower, indicated. Power measured indiesel engine cylinders by means of an instru-ment (the “indicator”), which continuouslyrecords the steam or gas pressure throughoutthe length of the piston travel.

Horsepower, shaft. Power transmittedthrough the shaft to the propeller. It is usuallymeasured aboard the ship as close to the pro-peller as possible by means of a torsionmeter.The power actually delivered to the propelleris somewhat less than that measured by thetorsionmeter.

Hydrodynamic resistance. The force exert-ed by the motion of fluids upon a body im-mersed in the fluid. As applied to towing: theresistance created by water as a body movesthrough it.

Hummock. An irregular ridge or hillock onsea ice.

IMO. International Maritime Organization.

IPS. Improved Plow Steel.

“In Irons”. An expression used by shiphan-dlers to indicate limited control in maneuver-ing the ship. In towing, this can be caused bya tow wire that is “captured” at the stern, re-ducing the effect of the rudder of the tug.

Inland towing. Point-to-point towing per-formed on inland waterways such as rivers.

“In step”. An expression used to indicate thatthe towing ship and its tow are each riding thecrests and troughs of waves simultaneously.

IWRC. Independent wire rope core. A wirerope used as the axial member of a larger wirerope.

Jack stay. Wire or line rigged for a specialpurpose, such as hanging seabags.

Jacob’s ladder. Portable ladder, with rope orwire sides and wooden rungs, slung over theside for temporary use.

Jam nuts. A second nut installed hard againstthe first nut to prevent rotary motion of thefirst nut.

Jaw width. The dimension of the opening be-tween the eyes of a shackle.

Jewelry. Gear used to fasten together systemcomponents.

Kenter detachable link. A type of connec-tion normally used to join two pieces of studlink or cast chain. See “Detachable link.”

Kink. A unique deformation of a wire ropecaused by a loop of rope being pulled downtight. It represents irreparable damage to andan indeterminate loss of strength in the rope.

Kort nozzle. A nozzle used to enclose thepropeller of a ship as a means of boostingpower.

Lateral control wire. An auxiliary wire usedto limit the motion of the tow hawser in theathwartships direction.

Lay. The direction of the twist of strands of arope.

Lay length. The distance measured parallelto the axis of the rope (or strand) in which astrand (or wire) makes one complete helicalrevolution about the core (or center).

Layer. A single thickness, coat, fold, wrap, orstratum. In towing, wraps of wire around atowing winch are counted as layers.

Lazy jacks. Small lines used to tend and re-cover the towline when rigging a recovery fora Liverpool bridle.

Leading pendant. A length of chain or wireused between the tow and the towing hawser

O-6


to ensure a safe distance during hookup anddisconnect.

Lee. An area that is sheltered from the wind.

Leeward. Away from the wind.

Level wind. A device used during retrieval ofa wire to move the wire along the length ofthe drum to allow it to be stored evenly on thedrum of a towing machine.

Lighter. To use a boat or barge to servicelarger ships in harbors, or to remove fuel orcargo from a stricken vessel.

Line. A term frequently applied to a fiber orsynthetic rope, especially if it moves or isused to transmit a force.

Links. A connecting component of towingsystems.

Liverpool bridle. A method of rigging a towhawser; most commonly used in refloating astranded ship. This method allows the towvessel to head into the predominant set whilestill pulling the strand directly to sea.

Load cell. An instrument for measuring ten-sion or torque.

Locking pin (keeper). Device used to holdor maintain a chain stopper, shackle, or othersimilar devices in a designated position.

Longitudinal. A term applied to the fore-and-aft frames of a ship. Generally, the fore-and-aft direction on a ship.

NDT (Non-Destructive Test). Various meth-ods of checking for imperfections in metals,especially welds.

Messenger. A light line used for hauling overa heavier rope or hawser.

Metacenter. The imaginary point throughwhich the force of buoyancy acts for smallangles of heel.

Metacentric height (GM). Distance betweenthe metacenter and the center of gravity of aship; a measure of stability.

Minimum bend radius. The safe minimumradius for a given diameter, material, andmethod of bending. Bends of less than this ra-dius may cause damage to the rope or line.

Moment arm. The perpendicular distancefrom the point of application of a rotationalforce to the line of action of the force.

Mortise. The opening of a shackle or detach-able link. The inside dimension, measuredacross the opening of a shackle or detachablelink.

MPI (Magnetic Particle Inspection). Anondestructive test, using a magnetic fieldand steel filings or particles to locate and de-fine flaws in steel structures.

Natural pivot point. The location on a tugabout which the tug turns in the horizontalplane. It is generally located on the centerlineof the ship about one-third of the ship’s lengthfrom the bow.

NAVSEA 00C. Naval Sea Systems Com-mand, Director of Ocean Engineering/Super-visor of Salvage and Diving, Washington,DC.

Nip. A sharp bend in a line or wire.

“Nipping” the wire. To periodically adjustthe scope of the wire to reduce the wear onany one point.

Norman pins. Steel pins mounted along theaft bulwarks of a ship that limit the forwardsweep of the tow wire.

OCIMF. Oil Companies International MarineForum.

Ocean towing. Point-to-point towing outsideof protected harbors.

Ocean tugs. Ocean-going vessels designedspecifically for towing.

Offset plate shackle. A device used to con-nect towing components of different sizes.

O-7


“On the brake.” Towing with the tow haw-ser restrained by the brake system of the tow-ing machine or winch.

“On the dog.” Towing with the winch havinga pawl engaged in the ratchet teeth of the tow-ing machine’s drum.

Open socket. A wire rope termination that isshaped similarly to a shackle; mates with aclosed socket.

OTSR. Optimum Track Ship Routing.

P-100. Self-priming, diesel-driven dewater-ing pumps that pump about 100 gallons perminute.

P-250. Gasoline-driven pumps used for dew-atering.

Padeye. A metal fitting welded to a deck orbulkhead designed to accept a chain or shack-le.

Parceling. Wrapping a line or wire withstrips of canvas.

Pawl. A device that engages cogs in a wheelallowing rotation in only one direction.

Pay out. To slack off on a line, or let it runout.

Pear-shaped detachable links. A detachablelink used to connect a small fitting or chain toa larger fitting or chain.

Pelican hook. A hook that can be openedwhile under strain by knocking away a lock-ing ring which holds it closed; used to pro-vide an instantaneous release.

Pendant (pendant rig). A single wire orchain that leads from the apex of a towing bri-dle to the towline; a single wire or chain thatleads from the bow of the tow to connect tothe tow hawser; a length of wire used as anunderrider wire in a “Christmas Tree” rig.

Pitch. Fore-and-aft angular motion of a ship’sbow or stern in a seaway about the athwart-ships axis. See also “sway” and “yaw.”

Plate shackle. A connecting device made upof two metal plates and bolts, used to connectthe towing pendant and the towline, or toserve as a connecting unit in other parts of atowing rig.

Point-to-point towing. Towing a vessel fromone harbor to another.

Popped core. The phenomenon of wires flar-ing out on one side of a wire rope, exposiongthe core of the wire. This can occur whenthere is a sudden release of a heavy load on awire rope.

Port. The left-hand side of a ship when look-ing forward; the opposite of “starboard”.

Poured socket. A wire rope termination in-stalled by pouring molten zinc over splayedwire, often referred to as “spelter socket.”

Power block (transport block). A portable,hydraulic motor-driven line sheave, provid-ing back tension to the traction winch.

Preventer. Any line, wire, or chain whosegeneral purpose is to act as a safeguard incase something else carries away.

Proof load. See page D-6, paragraph D-14for a discussion of proof load as it applies tochain and to other forged hardware.

Quarter. One side or the other of the stern ofa ship.

Racking. Horizontal movement of the shack-le which tends to force the jaws of the shackleagainst the padeye plate causing the jaws toopen.

Rail. An open fence or hand rail aboard ship.

Range. The layout of anchor chain in evenrows.

Range up. To reduce the range between towand tug, accompanied by the tendency for thetow to overtake the tug by sheering out to theside.

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Reaching pendant. Used between the towand the towing hawser to ensure a safe standoff during hookup or disconnect. (See also“Leading pendant.”)

Reeving. The threading of a line or wirethrough a block, sheave, or other parts of awire rope system.

Relative drift. The difference in the rates anddirections of motion of two vessels caused bytheir differing reactions to wind, sea, and cur-rent.

Repair lockers. Storage spaces within theship which contain damage control equip-ment for the repair and control of damage dueto battle, flooding, or fire.

Rescue towing. Saving a stricken ship at sea,or towing a disabled ship from the scene of asuccessful salvage to a safe refuge.

Reserve buoyancy. A measure of the capa-bility of a ship to be flooded or ballastedwithout sinking.

Resistance. A force that retards, hinders, oropposes motion.

Retrieval pendant. A wire rope leading fromthe deck of the tow to the end of the towingpendant or flounder plate to facilitate bring-ing the tow gear back onto the foredeck.

Riding lines. Lines used for greater manage-ability when the tow is brought close to thetug’s stern.

Rockwell C. A measurement of materialhardness.

Roll. Side-to-side angular motion of a shipabout its longitudinal axis. See also “pitch,”“sway” and “yaw.”

Roll period. A measurement of the time re-quired for a ship to roll from starboard to portand back to starboard or vice versa.

Roller chock. A chock fitted with a roller.

Saddle. A device on the stern of the towingvessel against which the bow of the tow canbe brought up hard and maintained in positionduring ice operations.

Safe haven. An area that can provide shelterfrom the sea and the weather.

Safe working load. The load for which arope, fitting, or working gear is designed.(See pg. for discussion.)

Safety factor. A multiple representing extrastrength over maximum intended stress.

Safety shackle. A connecting device similarto the common shackle except that the mor-tise is held closed by a nut and bolt.

Safety track. A T-shaped track running thelength of the submarine’s topside to whichpersonnel safety lines can be attached.

Sag (sagging). Deviation of the keel from astraight line when the keel is concave up-ward. Also, the concave curve of a towlinesaid to have catenary.

Sail. The part of a modern submarine extend-ing above the main deck or hull, housing theperiscope supports, various retractable masts,and the surface conning station or bridge.

Sail area. The vertical hull surface of a shipon which the wind exerts force.

“Sally the ship.” A term referring to thepractice of imparting a rolling motion to aship by the crew’s repeatedly moving fromone side of the ship to the other.

Salvage towing. Follows very closely after asalvage operation, such as fire fighting, flood-ing control, battle damage repair, or retractionfrom stranding.

Scope. The amount of towline streamed.

Screw. The propeller of a ship.

Screw-pin shackle. A type of shackle inwhich the pin passes through one side of the

O-9


shackle and threads into the other side of it toform a closure.

Scuttle. Small, quick-closing access hole.

Sea anchor. A device, usually made of woodand/or canvas, streamed by a vessel or boat inheavy weather in order to hold the bow orstern into the sea.

Secondary towline. An emergency towlinerigged on the tow prior to getting underway.It can be deployed rapidly without assistancefrom personnel on board the tow.

Section modulus. As used in reference towire rope, the effective area of the steel inwire rope multiplied by the modulus of elas-ticity of the steel.

Seize. To bind with small stuff, as one rope toanother or a rope to a spar.

Serving. To wrap small stuff tightly around arope that has been previously wormed andparceled.

Shackle. U-shaped metal fitting, closed at theopen end with a pin, used to connect wire,chain, and similar components.

Shaft horsepower. See “Horsepower, shaft.”

Sheave. A pulley with a rim, used to supportor guide a rope in operation.

Sheering. In towing, the tow’s meanderingfrom the towing vessel’s track. The tow maysheer out to a constant position on one side ofthe tug’s track, or it may swing from one sideto the other with a fairly long period of sever-al minutes or more.

Shoring. Process of placing props againststructure or cargo to prevent braking, sag-ging, or movement in a seaway, or to holdship upright in drydock.

Short stay. SA minimum distance betweentug and tow used during harbor operations;“to bring to short stay.”

Shot. A standard length of chain, 15 fathoms(90 feet).

SHP. Shaft horsepower. See “Horsepower,shaft.”

Side-slipping. Moving sideways through thewater.

SITREP. Situation Report. A special reportgenerally in a prescribed format, required tokeep higher authority advised. Required un-der certain predictable circumstances, but al-so may be required at any time.

Skeg. A portion of the underwater hull withsignificant longitudinal and vertical dimen-sions but without appreciable transverse di-mensions. Its purpose is to give directionalstability to the hull. On some moveable twin-skegged tows the skeg may be moved to in-crease directional stability and reduce yaw-ing.

Slip. To part from an anchor by unshacklingthe chain. To release completely or let runoverboard.

Small stuff. Any small-circumference lineused for general purposes.

Smit towing bracket. Two vertical platessimilar to a pair of free-standing padeyes withan elliptical pin fitted between them.

Snapback. The sudden recoil occurring whena line parts.

Snatch block. A type of fairlead that can beopened easily to insert a bight of line.

Socket. A wire rope termination attached byzinc or resin. Sockets poured with resin arenot approved for towing. See “Poured sock-et.”

Sound. To measure depth of water at sea orthe depth of a liquid in a ship’s tanks. Tostrike a chain link with a hammer to detectcracks or loose studs.

Spelter socket. See “Poured socket.”

O-10


Splay. To unlay and broom the bitter end of awire rope, usually done preparatory to attach-ing a socket.

Spliced eye. A wire rope termination formedby inlaying the rope and intertwining thestrands to form an eye.

Sponsoring command. The command thatrequires a tow, and is responsible for prepar-ing the towed vessel for sea.

Spooling. Winding a rope on a reel or drum.

Spring lay rope. A rope combining fiber andwire.

Spring line. See “Spring.”

Spring, stretcher. A pendant or grommetused to dampen towline surges.

Stability. Ability of a ship to right itself afterbeing heeled over.

Starboard. The right-hand side of a shipwhen looking forward. Opposite of “port.”

Static load. The force applied by deadweight,often referred to as the “average” or “mean”load.

Steady (or static) towline tension. Resis-tance of the ship to be towed, the tow hawser,and the vertical component of wire catenary.

Stem. The forward extremity of a ship’s hull.

Stern. The rear section of a ship.

Stern planes. The after horizontal controlsurfaces of submarine normally used to con-trol depth and angles.

Stern rollers. The horizontal and verticalrollers at the stern of a tug used to lead, cap-ture and control the tow hawser.

Stokes stretcher. A wire mesh container usedto transfer injured personnel through hatchesonboard ship.

Stopper. A short length of line wrappedaround a line to stop it from running.

Strongback. A wood or metal bar which isused to hold a patch or shoring in place.

Stud-link. A chain link with a bar fittedacross the middle to prevent the chain fromkinking.

Strap. A short working wire with a splicedeye at each end.

Strain. To draw or stretch tight; to injure orweaken by force, pressure, etc.; to stretch orforce beyone the normal, customary limits; tochange the form or size of, by applying exter-nal force.

Stream. To extend or increase the scope ofthe tow hawser.

Submersible pump. Watertight electricpump that can be lowered into a flooded com-partment to pump it out.

Suction lift. A measurement in feet of theability of a pump to raise water or liquid tothe intake of the pump that takes into accountfriction and entrance losses.

Swage. To connect, splice, or terminate wirerope by use of steel fittings installed underextremely high pressure.

Sway. Motion of a ship in which it is dis-placed laterally, as distinct from rolling. Seealso “pitch,” “roll,” and “yaw.”

Swivel. A removable anchor chain link fittedto revolve freely and thus keep turns out of achain.

SWL. See “Safe Working Load.”

Synthetic hawser. A line or pendant used fortowing, made from any of a group of continu-ous or synthetic fibers.

Termination. The fitting installed on the endof a wire rope or chain used in towing.

Thimble. A grooved metal buffer fitted snug-ly into an eye splice.

Tiller (tiller arm). Casting or forging at-tached to the rudder stock.

O-11


Timber packing. Large wooden planks usedto reinforce hull plating.

Towing bows. Transversely installed beamsor pipe that bridge the caprails on the after-deck of the tug.

Towing bracket. See “Smit Towing Bracket”or “Tow pad.”

Towing chock. Chock designed or dedicatedto use during a towing operation.

Towing command. The command that per-forms the tow.

Towing hawser. Generally, the main towlinethat is carried by the tug or the principal seg-ment of the towline.

Towing hook. Heavy steel hooks mounted onvertical pins used to hold the eye of a towhawser.

Towing machine. A towing winch with auto-matic features.

Towing pad. Large padeye to which a tow-line may be attached.

Towing rig. Describes the entire system ofcomponents that make up the connection be-tween the tug and the tow.

Towing winch. A basic winch used in towingthat stores, pays out, and heaves in the towinghawser to compensate for variations in tow-line tension.

Towline. See “Towing hawser.”

Towline fatigue. The weakening of a towlinedue to cyclic application of load.

Towline strength. The nominal breakingstrength of the tow hawser.

Towline tension. The stress imparted to atowline during a towing operation.

Tow point. The point on the tug where thetowline exerts its force. This may be thewinch, H-bitts, caprail, norman pins, or otherpoints, depending on the towing configura-tion.

Tow resistance. The total force resisting themovement of the tow.

Tow ship. A vessel specifically designed forocean towing.

Traction winch. A multi-sheaved device thatgenerates line tension. Tension is generatedby friction between the line and tractionheads.

Transfer. Distance travelled by a ship at rightangles to original course when turning.

Transverse. Lateral dimension or placement.

Tripping. When a frame or padeye experi-ences transverse loading, it may result in out-of-plane deformation such that it is no longerperpendicular to the deck or hull plating. Ithas the appearance of having “fallen over”and is said to be tripped. A structure in thiscondition has significantly reduced strength.

Tucks. In splicing, the insertion of the end ofa strand between the strands of a rope.

Turnbuckles. A metal device consisting of athreaded link bolt and a pair of opposite-threaded screws capable of being tightened orloosened and used for setting up standing rig-ging or stoppers.

Two-blocking. Term describing when thetwo blocks of a block-and-tackle have beendrawn together or tightened so that theytouch.

Two valve protection. Consists of either twovalves wired shut or one valve and a blankflange.

Ultrasonic inspection. A non-destructivetesting method that uses high frequencysound waves to check for material thickness,laminations, and defects or inclusions.

Underrider. The wire rope, chain, or combi-nation used as a pendant heavy enough topass under a leading tow to a trailing tow at asufficient depth not to foul on the leading tow.

Veer. To pay out.

O-12


Vertical stern rollers. Vertical rolling pinsmounted on the caprail of a tug to restrain thetow hawser sweep.

Voith-Schneider propeller. A propeller thatgenerates thrust at right angles to the axis ofrotation which, through control of the angleof attack of the vertical propeller blades, canbe directed through 360 degrees thus actingas both propeller and rudder.

Wallis brake. A wire brake used for keepinga steady load on a wire rope as it is installedon a drum.

Warping tug. A small boat used to controlthe heading and speed of a tow during con-nection of the tow line.

Water brake. A device attached to the sternof a vessel (usually in lieu of a propeller) thatprovides drag for directional stability.

Wetted surface. The area of the vessel belowthe waterline which is exposed to the sea.

Williams target sled. The target used mostfor gunnery exercises.

Winch. An electric, hydraulic, or steam ma-chine aboard ship used for hauling in lines,wire, or chain.

Windward. Toward the wind.

Wire rope. Rope constructed of wire strandstwisted together, as distinct from the morecommon, and weaker, fiber rope.

Wire rope pendant. A length of wire with atermination fitting at each end.

Y-gate. A piping connection with a large inletsection and two smaller outlet sections to per-mit hookup of two hoses to one pump outlet.

Yard tugs. Vessels that dock/undock, providestandby duty and safety duty services of har-bor towing.

Yawing. Failure of a vessel to hold a steadycourse because of forces of wind, sea, dam-age to vessel, etc. In towing, yaw angle is the

difference between the tow’s heading and thetug’s heading. Yawing can be manifested byan oscillation of the tow’s heading by a smallangle to either side of the base course, withthe tow remaining on the same track as thetug. See also “sheer,” “sway,” “pitch,” and“roll.”

Yield strength. A measure of the maximumstress that can be applied to a material with-out permanent deformation. This is the valueof the stress at the elastic limit for materialsfor which there is an elastic limit.

YTB class. The largest tugs used for harbortowing.

YTL class. Small size tugs which move smallcraft and unloaded barges from one berth toanother within a harbor.

YTM class. Medium size tugs which movevessels of all sizes from berth to berth withina harbor and assist vessels of all sizes in get-ting underway and mooring.

Z-drive propulsion. A mode of propulsionthat uses a propulsar which can be trainedthrough 360 degrees and can be positioned inthe hull during design to provide the optimumpropulsion.

O-13



O-14


Appendix P

USEFUL INFORMATIONP-1 Introduction

This appendix contains miscellaneous information useful during salvage operations. Ground re-action is measured in long tons. Freeing and lifting forces are measured in short tons.

P-2 Weights and Measures

This section lists general information needed for performing salvage calculations in both metric

Table P-1. System of Metric Measures.

LENGTH

1 meter (m)

1,000 meters

= 10 decimeters (dm)= 100 centimeters (cm)= 1,000 millimeters (mm)= 1 kilometer (km)

AREA

1 square meter (m2)

1 square kilometer

= 1,000,000 square millimeters (mm2)

= 10,000 square centimeters (cm2)

= 100 square decimeters (dm2)= 1,000,000 square meters

VOLUME

1 liter (l)

1 kiloliter (kl)

1 milliliter (ml)

= 10 deciliters (dl)= 100 centiliters (cl)= 1,000 milliliters (ml)

= 1 cubic decimeter (dm3)= 1,000 liters

= 1 cubic meter (m3)= 1 cubic centimeter (cc)

MASS

1 kilogram (kg) 1 gram (g)

1,000 kilograms

= 1,000 grams (g)= 1,000,000 micrograms (µg)= 1,000 milligrams (mg)= 100 centigrams (cg)= 1 metric ton (tonne)

FORCE

1 kilogram force (kgf) 1 newton (N) 1 kilonewton (kN)

1 meganewton (MN)

= 9.807 newtons (N)= 0.102 kgf= 1,000 newtons= 102 kgf= 1,000,000 newtons= 102,000 kgf= 102 tonnes force (tonnef)

and English systems. Use this material with salvage formulae found throughout this manual.

P-1


Table P-2. System of English Measures.

LENGTH

1,000 mils12 inches3 feet6 feet15 fathoms120 fathoms6,080 feet

= 1 inch (in)= 1 foot (ft)= 1 yard (yd)= 1 fathom (fm)= 1 shot of chain= 90 feet= 1 cable’s length= 720 feet= 1 nautical mile (NM)= 2,027 yards

AREA

144 square inches (in2) = 1 square foot (ft2)

VOLUME

1,728 cubic inches (in3)27 cubic feet (ft3)231 cubic inches277.27 cubic inches42 U.S. gallons1 cubic foot

= 1 cubic foot (ft3)

= 1 cubic yard (yd3)= 1 U.S. gallon (gal)= 1 imperial gallon= 1 barrel= 5.615 cubic feet= 7.48 U.S. gallons= 6.23 Imperial gallons

BOARD MEASURE

board feet

12 board feet

= Length in feet x width in feet x thickness in inches: there-fore:= 1 cubic foot

DRY MEASURE

1 pint = 0.5 quart = 33.6 in3

LIQUID MEASURE

16 ounces2 pints4 quarts

= 1 pint= 1 quart= 1 gallon

NOTE:English system dry measure and liquid measure quarts and pints are not equivalent volumes. All Imperial liquid measures are therefore larger than the corresponding U.S. measure by a factor of 277/231, or 1.2.

FORCE AND WEIGHT

7,000 grains (gr)16 ounces (oz)2,000 pounds2,205 pounds2,240 pounds

= 1 pound (lb)= 1 pound= 1 short ton = 1 metric ton (tonne) = 1,000 Kg= 1 long ton

P-2


P-3

Table P-3. Basic English/Metric Equivalents.

MEASURES OF LENGTH

1 millimeter1 centimeter1 meter1 meter1 kilometer1 kilometer1 kilometer1 kilometer

= 0.03937 inch= 0.3937 inch= 39.37 inches= 3.281 feet= 0.62 mile= 0.54 nautical mile= 1,094 yards= 3,281 feet

1 inch1 inch1 inch1 foot1 mile1 NM1 mile1 NM

= 25.4 millimeters= 2.54 centimeters= 0.0254 meter= 0.3048 meter= 1.6 kilometers= 1.85 kilometers= 1,609 meters= 1,853 meters

MEASURES OF AREA

1 square mm (mm2)

1 square cm (cm2)1 square meter1 square meter1 square kilometer

= 0.00155 square inch= 0.155 square inch= 10.76 square feet= 1.196 square yards= 0.386 square mile

1 square inch1 square inch1 square foot1 square yard1 square mile

= 645.2 square millimeters= 6.452 square centimeters= 0.0929 square meter= 0.836 square meter= 2.59 square kilometers

MEASURES OF VOLUME

1 cc or ml

1 cubic meter (m3)1 cubic meter1 liter1 liter

= 0.061 cubic inch= 35.3 cubic feet= 1.31 cubic yards= 61.023 cubic inches= 0.0353 cubic foot

1 cubic inch (in3)

1 cubic foot (ft3)

1 cubic yard (yd3)

1 cubic foot (ft3)

= 16.39 cc or ml= 0.0283 cubic meter= 0.764 cubic meter= 28.32 liters

LIQUID MEASURE

1 liter (l)1 liter (l)1 cubic meter

= 1.057 U.S. quarts= 0.264 U. S. gallons= 264.17 gallons

1 U.S. quart (qt)1 U.S. gallon (gal)1 U.S. gallon

= 0.946 liter= 3.79 liters= 0.0038 cubic meter

DRY MEASURE

1 liter (l) = 0.908 dry quarts 1 dry quart = 1.101 liters

MEASURES OF WEIGHT AND MASS

1 kilogram (kg)

1 tonne

1 tonne

1 milligram1 gram

1 newton1 meganewton

= 2.205 pounds mass

= 1.1023 short tons= 2205 pounds

= 0.9842 long tons

= 0.0154 grain= 15.432 grains

= 0.225 pounds force= 100.4 long tons= 112.4 short tons

= 224,799 pounds

1 pound mass (lbm)

1 short ton

1 long ton

1 grain

1 pound force (lbf)1 long ton1 short ton

= 0.454 kilograms= 454 grams

= 0.972 tonne= 907.2 kilograms

= 1.016 tonne= 1016 kilograms

= 64.8 milligrams= 0.0648 gram

= 4.448 newtons= 0.009964 MN= 0.008896 MN


Table P-4. Circular or Angular Measure.

60 seconds60 minutes90 degrees4 quadrants2 radians1 radian

= 1 minute of arc= 1 degree= 1 quadrant or right angle= 1 circumference= 1 circumference= 180

= 360 degrees

= 57.3 degrees

Table P-5. Common Pressure Conversions

MULTIPLY BY TO OBTAIN

Feet of seawaterFeet of fresh waterPsiPsiInches of mercury

Lb/in2

Atmospheres

Lb/in2

Atmospheres

0.4450.4342.252.30.492.0414.70.0710.0

psipsifeet of seawaterfeet of fresh water

lb/in2

inches of mercury

lb/in2

atmospheresmeters of seawater

Table P-6. Common Density Conversion


Lb/ft3

Kg/m3

m3/tonne

ft3/long ton

16.02

0.01602

0.0624

0.001

35.87

0.0279

kg/m3

g/cc

lb/ft3

g/cc

ft3/long ton

m3/tonne

ππ

P-4


Table P-7. General Conversion Factors.


Atmospheres

Barrels

Cubic centimeters

Cubic feet

Cubic feet/minute

Cubic inches

Cubic meters

Cubic meters/minute

76076.033.93433.1103329.92

1.03310,33214.7

1.06

5.615420.159

0.00026420.0338

28,3201,7280.028327.4828.320.178

0.028327.481.43

16.390.00057870.000016390.0043290.01639

61,02335.31264.26.291,0001

35.31

mm of mercury (mm Hg)cm of mercury (cm Hg)feet of fresh water (ffw)approx. ffwfeet of seawater (fsw)approx. meters of seawaterapprox. fswinches of mercury (in Hg)

kg/cm2

kg/m2

lb/in2 (psi)

tons/ft2

cubic feet (ft3)U.S. gallons (gal)kiloliters, cubic meters

gallons (U.S.)ounces

cubic cm (cc)

cubic inches (in3)

cubic meters (m3)U.S. gallons (gal)litersbarrels (bbl)

cubic meter/min (m3/min)U.S. gallons/min (gpm)bbl/hour

cubic cm (cc)

cubic feet (ft3)

cubic meters (m3)U.S. gallons (gal)liters (l)

cubic inches (in3)

cubic feet (ft3)U.S. gallons (gal)barrelsliters (l)kiloliters (kl)

ft3/min

P-5


P-6

Table P-7 (Continued). General Conversion Factors.


Feet

Feet of fresh water

Feet of seawater

Feet/second

Foot-lbs

Foot-tons (long tons)

Foot-tons (short tons)

Gallons (U.S.)

Gallons (Imperial)

Inch-Pounds

Kilograms

304.830.480.30480.0001645

0.02950.88270.030562.40.434

0.03030.90480.0312464.00.445

30.481.0970.59210.68180.01136

1.3550.138313830

3,036.70.003030.3

2,7110.002710.276

3,7850.13372311.20.0238

0.833

0.1131153

2.205

millimeterscentimetersmetersmiles (nautical)

atmospheresin Hg

kg/cm2

lb/ft2

lb/in2

atmospheresin Hg

kg/cm2

lb/ft2

lb/in2 (psi)

cm/seckm/hourknotsmiles/hourmiles/min

newton-meterskilogram-metersgram-centimeters

newton-metersmeganewton-metersmeter-tonne

newton-metersmeganewton-metersmeter-tonne

cubic cm (cc)

cubic feet (ft3)

cubic inches (in3)Imperial gallonsbarrels (bbl)

U.S. gallons (gal)

newton-metersgram-centimeters

pounds




Kilograms/m2

Kilograms/m3

Kilograms/cm2

Kiloliters

Kilometers

Kilometers/hour

Knots

Liters

Meganewtons

Meganewton-meters

Meganewtons/meter

0.2048

0.00142

0.0624

14.226

6.29264.235.31

3,2810.54

27.780.91130.5396

6,080.21.85320.51481.15161.689

61.020.03530.26420.00629

100.4112.4102101,954224,809

329.4368.8102

30.634.3102

lb/ft2

lb/in2 (psi)

lb/ft3

lb/in2 (psi)

barrels (bbl)U.S. gallons

cubic feet (ft3)

feetmiles (nautical)

cm/secfeet/secknots

feet/hourkilometers/hourmeters/secstatute miles/hourfeet/sec

cubic inches (in3)

cubic feet (ft3)U.S. gallons (gal)barrels (bbl) (oil)

long tons (lton)short tonstonnekilograms (kg)pounds (lb)

foot-tons (long tons)foot-tons (short tons)meter-tonne

long ton/ftshort tons/fttonne/meter

P-7




Meters

Meters/second

Miles (nautical)

Miles/hour

Millimeters

Millimeters of mercury

Newtons

Newtons/meter

Ounces

Ounces (fluid)

Pounds

39.373.2810.0005391.094

1.9443.2813.60.03728

1,853.151.8536,0802,0271.1516

44.7881.4671.6090.86840.447

0.03937

0.001320.004350.0044613.6

0.0193

0.225

0.1021.356

0.0625

1.8050.029570.03130.0078

0.454164.448

inchesfeetmiles (nautical)yards

knotsfeet/seckm/hourmiles/min

meters (m)kilometers (km)feet (ft)yards (yd)miles (statute)

cm/secfeet/minfeet/seckm/hourknotsmeters/sec

inches (in)

atmospheresfeet of seawater (fsw)feet of fresh water (ffw)

kg/m2

lb/in2 (psi)

pounds (lb)

kg/mlb/ft

pounds (lb)

cubic inches (in3)liters (l)quarts, liquid (qt)U.S. gallons (gal)

kilogramsouncesnewtons (N)

P-8


P-9



Pounds/ft2

Pounds/in2

Quarts, U.S. liquid

Square feet

Square inches

Square kilometers

Square meters

Square miles

Square yards

Tons (long)

Long tons/square inch

0.0004725

4.882

0.006944

0.0682.252.3703.11440.00050.000446

0.946

0.033457.75324

929

0.0929

144

6.4520.006944

0.38610.29155

10.761.196

2.59027,878,400

0.8361

1,0162,2401.121.0160.009964

2,240

1,574,5081,574.5157.515.44

atmospheres

kg/m2

pounds/in2 (psi)

atmospheresfeet of seawater (fsw)feet of freshwater (ffw)

kg/m2

lb/ft2

short tons/in2

long tons/in2

liters (l)

cubic ft (ft3)

cubic inches (in3)fluid ouncesgallons

square cm (cm2)

square meters (m2)

square inches (in2)

square cm (cm2)

square feet (ft2)

square milessquare nautical miles

square feet (ft2)

square yards (yd2)

square kilometerssquare feet

square meters (m2)

kilogramspoundstons (short)tonne (metric)meganewtons (MN)

lbs/in2 (psi)

kg/m2

tonne/m2

kg/cm2

meganewtons/m2




Long tons/foot

Tons (short)

Short tons/square inch

Short tons/foot

Tonne (metric)

Tonne/meter

Yards

1.123.333,333.732,693.60.0327

907.22,0000.89290.90720.008897

2,0001,406,1511,406.15140.6213.79

0.89290.2762,976.529,190.60.0292

0.9841.10232,2051,0000.009807

0.30.3366729,807

91.440.9144

short tons/foottonne/meterkg/mnewtons/meter (N/m)Meganewtons/meter (MN/m)

kilogramspoundstons (long)tonnes (metric)neganewtons (MN)

lb/in2

kg/m2

tonne/m2

kg/cm2

MN/m2

long ton/fttonne/meterkg/mnewton/meter (N/m)MN/m

long tonsshort tonspounds (lbs)kilogramsmeganewtons (MN)

long ton/ftshort tons/ftlb/ftnewtons/meter

centimetersmeters

P-10


Table P-9. Temperature Conversion

ABSOLUTE TEMPERATURERankine (R) = Degrees Fahrenheit + 460

Kelvin (K) = Degrees Celsius + 273

Table P-8. Power Conversion.


Horsepower 0.746 kilowatts

Kilowatts 1.3404 horsepower

BTU 778.2 foot-pounds

Foot-pounds 0.001285 BTU

BTU 0.0003930 horsepower hours

Horsepower hours 2,554 BTU

BTU 0.0002931 Kilowatt hours

Kilowatt hours 3,412 BTU

°F 9C5

-------- 32+=

°C 59--- F 32–( )=

P-11


Table P-10. Common Flow Rate Conversion.


Liters per second (lps)

Liters per minute (lpm)

Tons seawater per hour

Tonnes seawater per hour

Tons fresh water per hour

M3/hour

M3/sec

Ft3/min (cfm)

U.S. gallons per minute (gpm)

15.832.120.260.0353261.84.360.5830.276

0.9954.2950.5740.2710.9764.4750.5980.2821.0164.40.5880.2781.010.981.02515850.221187.480.47228.321.7141.6711.7410.000471.70.1340.0633.790.2290.2230.233

0.000060.228

gpmcfmgpmcfmgal/hourgpmcfmlps

m3/hourgpmcfmlps

m3/hourgpmcfmlps

m3/hourgpmcfmlpstons seawater/hourtons fresh water/hourtonnes seawater/hourgpmcfmgpmlpslpmtons seawater/hourtons fresh water/hourtonnes seawater/hour

m3/sec

m3/hourcfmlpslpmtons seawater/hourtons fresh water/hourtonnes seawater/hour

m3/sec

m3/hour

P-12


Appendix Q

HEAVY LIFT SAMPLE CALCULATIONS

Q-1 Introduction

This Appendix demonstrates sample calculations for the procedures outlined in Chapter 8, HeavyLift Transport. These calculations can be used to actually perform the heavy lift or to check thecontractor’s calculations. Because the heavy lift of the damaged USS COLE (DDG 67) is not onlythe most recent, but also the most complex of the heavy lift transport operations undertaken by theUS Navy, it has been used to show the calculations involved.

Q-2 Information

On 12 October 2000, while USS COLE was in the port of Aden, Yemen for refueling, terroristsbombed USS COLE using an explosive laden small boat which was deliberately driven into theport side of USS COLE and exploded causing structural damage. It was determined that the bestmethod for returning COLE to a port where the damage could be repaired was to use a heavy liftvessel.

Information relative to USS COLE used in the calculations to follow comes from data on ship’scharacteristics from the Trim and Stability Booklet and the Docking Drawing updated for ob-served condition of loading and damage. This information is summarized in Table Q-1.

Using the drafts of 26.5 ft forward, 22 ft aft for the damaged condition the following informationcan be derived from the DDG 51 Draft Diagram and Functions of Form (Figure Q-1). (This re-quires extension of the data to cover the area of interest. These extensions are shown as dashedlines on Figure Q-1). This displacement includes the free flooding water in the damaged compart-ments. This condition was needed to address the drafts to be cleared to get the ship over theblocks.

Determine the displacement and other parameters as follows:

Given: Draft Forward 26 feet 6 Inches

Draft Aft 22 feet 0 Inches

On the Draft Diagram and Functions of Form (Figure Q-1), draw a straight line connectingthese drafts and where it crosses the center of floatation scale, read

WARNING

When trim exceeds one foot, especiallyby the bow, a more rigorous analysis,preferably by a computer program,should be used to obtain the hydrostaticinformation.

Q-1


Displacement 10,700 Tons

Transverse Metacenter (KMt) 29.05 feet

Project a line horizontally from this point and where it crosses the other scales, read:

Tons per inch immersion 53.9 Tons/inch

Moment to alter trim one inch 1,532 foot-tons

Longitudinal Center of Buoyancy (LCB) 5.9 feet aft of

Project a line vertically, where it crosses the scale at the bottom (center of flotation curve)shows the center of flotation

LCF 23 feet aft of

Using the Displacement & Other Properties Table from the docking drawing or the Curvesof Form drawing, you can also get these values at the mean draft. For a damaged ship, es-pecially with a large amount of trim, a computer should be used to check this information.This was also verified by using the POSSE program and the NAVSEA Flooding CasualtyControl program (FCCS).

The next step is to determine the Longitudinal Center of Gravity, LCG, as follows:

Determine the trim between drafts:

(Draft aft -Draft fwd) = 26.5 ft - 22 ft = 4.5 ft fwd

Determine the trimming lever (TL)

Estimating the KG requires estimating weight changes from a known condition. ForCOLE heavy lift, we were given

Full Load Condition:

Dispacement 8,886 Tons

Draft(mean) 21.3 feet

KG 24.28 feet

Vertical Moment (KG x Displacement) 215,752 foot-Tons

TL12 trim( ) MT1××

Displacement-----------------------------------------------=

12 4.5( ) 1532( )10 700,-----------------------------------=

7.73 feet fwd =

Determine LCG TL LCB+=

7.73 f( ) 5.9 a( ) 1.83 feet fwd of =+=

Q-2


Q-3

This was a good start and was used on COLE because the ship was in the process of refu-eling to a full load condition. With compensated tanks, the ship would be a little heavier(sea water is heavier than fuel oil) and the KG a little lower than if the tanks were full offuel. The loads equate to 2,127 Tons at 12.68 feet.

To estimate a KG for the ship at 10,700 Tons

Observed Condition:

To estimate the KG, first bracket the range of centers of gravity. First, for a low level wewill use the group average of the loads (12.68 feet). For another level, we will use the es-timated VCG of the flooding water in the area between the observed drafts and the tanktop (14.00 ft).

Estimate the range of KG:

High level.

For the damaged condition, we also have to estimate the free surface effect of the floodingwater. Free surface equates to:

Observed Displacement 10,700 Tons

Full Load Displacement 8,886 Tons

Difference is flooding water 1,814 Tons

8,886 Tons 24.28 feet 215,752 foot-Tons

add 1,814 12.68 23,002

new high 10,700 22.31 238,754

8,886 Tons 24.28 feet 215,752 foot-Tons

add 1,814 14.00 25,396

new low 10,700 22.54 241,148

FSl b

3×12 ∇ 35 ft

3/ton××

----------------------------------------------

l 80 ft (length of flooding between Fr 174-254)

b 66.5 ft (beam of COLE)

80 ft 66.5 ft( )3 / 12 10700×× 35×

5.2 ft=

=

=

=

=


Therefore the virtual KG (taking into account the free surface effect of the flooding water)could range from:

The flooding water in this condition would run out of the ship as it is lifted. Once liftedthe displacement of COLE would be essentially the same as that of the ship prior to dam-age. Items known to be removed would be subtracted for the condition. To this is added,estimated weights for sand bags and equipment on the weather decks and damage materialin the overhead or trapped flooding water.

Estimate for USS COLE:

Note: The new KG is determined by dividing the sum of the moment column by the sumof the weight column (i.e. 215, 152 ÷ 8,886 = 24.21)

Full Load 8,886 Tons 24.28 feet 215,752 foot-Tons

Removals:

Fuel 60 00 10.00 feet 600 00

Crew and effects 40 00 50.000 0 2,000 000

Additions:

Trapped Flooding Water 80 00 10.00 feet 800 00

Sandbags and Salvage Equipment 20 00 60.00 00 1,200 000

Estimated Condition 8886 000 24.21 00 215,152 00000

KGv low 22.3 5.2 27.5 feetKGv high 22.54 5.2 27.74 feet=+=

=+=

Q-4


Figure Q-1. DDG 51 Draft Diagram and Functions of Form.

24

23

22

21

20

19

18

17

16

15

14

13

12

24

23

22

21

20

19

18

17

16

15

14

13

12

1525

1500

1450

1400

1300

1200

1100

1000

900

DR

AF

T IN

FE

ET

AB

OV

E B

OT

TO

M O

F K

EE

L A

T C

ALC

ULA

TIV

E D

RA

FT

MA

RK

S

D R A FT A FT

M O M E N T TOA LTE R T R IM 1 ”

D R A FT A FTFR 461

FO

OT

TO

NS

10000

9500

9000

8500

8000

7500

7000

6500

6000

5500

5000

29.0

28.95

28.9

28.85

28.8

28.7

28.6

28.5

28.4

28.3

28.2

28.1

28.0

53

52

51

50

49

48

47

46

45

44

43

42

42

TO

NS

FE

ET

AB

OV

E B

OT

TO

M O

F K

EE

L

TO

NS

LCFD ISPA C E M EN T IN S ALT W AT ER

T R AN S V ER S E M E TA C EN T E R

5

4

3

2

1

0 0

1

2

33

4

5

6

7

8

9

10

TO N S PE R IN C H IM M ER S IO N

L C B

A F T FW D

D R AF T F W D

FE

ET

FW

D

FE

ET

AF

T

D R A FT FW DFR 5

LC FA FT O F

2 0 1 0 0

D ISP LA C EM E N T A N D T R A N SV E R S E M E TAC EN T ER A R E R E A D D IR EC TLY AT P O IN T W H E R E A S TR A IG H T L IN E C O N N EC T IN G D R A FT S FO RWA R D A N D A FT C R O S SE S TH E S E S C A LE S . O TH E R FU N C TIO N S A R E R E A D O N A H O R IZO N TA L L IN E T H R O U G H TH IS P O IN T.

DDG 51 CLASSDRAFT DIAGRAM AND FUNCTIONS OF FORM

DR

AF

T IN

FE

ET

AB

OV

E B

OT

TO

M O

F K

EE

L A

T C

ALC

ULA

TIV

E D

RA

FT

MA

RK

S

26 .5

Q-5


Table Q-1. DDG 67 Information

LOA 504.5 feet

LBP 465.5 feet Note: BY DESIGN LBP=466 ft

Beam 66.5 feet

Damaged Fully Loaded

Draft Fwd 26.5 feet

Draft Aft 22.0 feet

Draft 24.25 feet 21.3 feet

Trim 4.5 feet

Displacement 10,700 tons 8,886 tons

KG 22.54 feet 24.21 feet

MT1 1,532 ft-ton/in. 1460 ft-ton/in.

TPI 53.9 ton/in. 52.1 ton/in.

LCB 5.9 ft aft 2.80 aft

LCG 1.83 ft fwd 0.62 fwd

LCF 23.00 ft aft 23.00 aft

Underwater Projections

Sonar Dome forward ~ 10 feet below the keel

Propellers ~ 5 feet below the keel

Length of Keel Block System 312 feet From Docking Drawing

Distance from aft end ofknuckle block to

147.26 feet From Docking Drawing

Distance from aft end ofknuckle block to LCG

147.88 feet Calculated

Distance from aft end ofknuckle block to LCF

124.26 feet Calculated

Q-6


Q-3 Draft-at-Instability

This section demonstrates the calculations to determine the draft-at-instability for the COLE land-ing on the blocks of BLUE MARLIN. If COLE is not leaning against the guide posts and landedon the keel and side blocks before the draft-at-instability is reached, the ship will roll off theblocks. See Section 8-5.2.3 for more information on these calculations. The following equationrepresents the balance of the buoyancy moment and the displacement moment. The draft at whichthese two are equal will be the draft-at-instability.

Table Q-2 shows the information required to perform this calculation. The displacement momentis a constant: ∆ x KG = 8886 tons x 24.21 feet = 21.5 x 104 ft-tons. For the damaged condition thedisplacement moment is 10,700 tons x 27.5 feet = 29.4 x 104 ft-tons.

The bouyancy moment is found for a range of drafts. Table Q-3 displays the results of this calcu-lation. Figure Q-2 shows these results graphically. Both KM and the residual buoyancy can befound from the draft diagram (Figure Q-1). In Figure Q-2, the intersection of the buoyancy mo-ment line and the displacement moment line represents the draft-at-instability for the exampleprovided. The draft-at-instability for this example is 19.1 feet, for COLE after the flooding waterruns out. However, the draft-at-instability during landing could be as much as 23.8 feet. Thedrafts of COLE in the damaged condition were 26.5 ft fwd and 22 ft aft with a mean draft of 24.25feet. COLE could go unstable if it was picked up on one end. For this reason, BLUE MARLINmatched the trim and list of COLE in the damaged condition for loading the ship.

Table Q-2. Draft at Instability Information.

Required Information Source

Draft Assume a series of drafts (19’ - 24’)

Residual Buoyancy (∆-Rkn) at Assumed Drafts Draft Diagram (see Figure Q-1)

Height of Metacenter (KM) at Assumed Drafts Draft Diagram (see Figure Q-1)

Original KG (KGo) Table Q-1

Displacement (∆) Table Q-1

Displacement Moment (lifted condition) 21.5 x 104 ft-tons

(flooded condition) 29.4 x 104 ft-tons

KM ∆ Rkn–( ) ∆KGo=

Q-7


Table Q-3. Draft at Instability Results.

Draftft.

ResidualBuoyancy

∆∆∆∆ - Rkn(tons)

Height of Metacenter above Keel,

KM(ft)

Residual Buoyancy Moment

KM · (∆(∆(∆(∆ - Rkn)(ft-tons)

19 7481 28.72 21.4 x 104

20 8090 28.80 23.3 x 104

21 8703 28.85 25.1 x 104

22 9330 28.91 26.9 x 104

23 9965 28.97 28.8 x 104

24 10,600 29.1 30.8 x 104

Q-8


Figure Q-2. Draft at Instability Results.

22 24 26 28

20

21

22

23

20

Dra

ft(f

eet)

M om ents x 10 ft-Ltons4

W eight M omentKG " ∆

KM ( - R )# ∆ kn

Draft at Instability= 19.1 ft

ResidualBuoyancy

M om ent

30

24

Draft at Instability23.8 ft

Damaged W eight M om ent

Q-9


Q-4 Draft-at-Landing Fore and Aft

This section demonstrates the calculations to determine the draft at landing for the COLE landingon the blocks of the BLUE MARLIN. The draft-at-landing acceleration takes into account a shipwith trim pivoting around the knuckle block. When the two moments are equal, the trim will beremoved and the ship will be landed fore and aft. See Section 8-5.2.3 for more information onthese calculations. Figure 8-9 depicts the relationship of LCB and LCG to the reaction of theCOLE landing on the knuckle block. The moments created by the buoyancy force (acting throughLCB) and the displacement force (acting through LCG) must be equal for the COLE to land foreand aft. These two moments are calculated and graphed to determine the draft at which this oc-curs. Table Q-4 shows the information necessary to make the calculations.

Two conditions will be considered. The first is for the ship in the flooded condition. The second isfor the ship in the lifted condition with the flooding water drained out.

For the first condition LCG is located 1.83 feet forward of amidships (see Table Q-1) whichequals a distance of 149.09 feet from the aft end of the knuckle block. The displacement momentabout the knuckle block is a constant 10,700 tons times 149.09 feet which equals 15.95 x 105 ft-tons. In Figure Q-3 this is a vertical line. The buoyancy moment is found for a range of drafts (Ta-ble Q-5) and is plotted as a line in Figure Q-3. The intersection of the two lines represents a draftat landing of 25.2 feet for the flooded condition.

For the second condition, LCG is located 0.62 feet forward of amidships (see Table Q-1) whichequals a distance of 147.88 feet from the aft end of the knuckle block. The displacement momentabout the knuckle block is a constant 8,886 tons times 147.88 feet which equals 13.14 105 ft-tons.In Figure Q-3 this is a vertical line. The buoyancy moments are the same as those plotted in theprevious paragraph. The intersection of the two line represents a draft at landing of 21.7 feet forthe dewatered condition.

For COLE, BLUE MARLIN was trimmed to match the trim of COLE so that COLE landed levelfore and aft to minimize the loading on the knuckle block and on the end of the skeg of COLE.This approach was taken due to the uncertainty in the longitudinal strength of COLE.

WARNING

When trim exceeds one foot, especiallyby the bow, a more rigorous analysis,preferably by a computer program,should be used to obtain the hydrostaticinformation.

Q-10


Table Q-4. Draft-at-Landing Fore and Aft Information

Information Source

Draft Drafts from 19 ft - 23 ft

Residual Buoyancy (∆ - Rkn) at Assumed Drafts Figure Q-1

LCB at Assumed Drafts Figure Q-1

LCG Table Q-1

Displacement (∆) Table Q-1

Distance from aft end of knuckle block to LCG Table Q-1

Displacement Moment (lifted condition) 13.14 x 105 ft-tons

(flooded condition) 15.95 x 105 ft-tons

Table Q-5. Draft-at-Landing Fore and Aft Results.

DraftDist.

to Knuckle Block (ft)

Dist LCB to (ft)

Dist LCB to Knuckle Block (ft)

Residual Buoyancy

∆∆∆∆ - Rkn(tons)

Residual Buoyancy Moment(ft-tons)

19 147.26 1.2 fwd 148.46 7481 11.11 x 105

20 147.26 0.9 aft 146.36 8090 11.84 x 105

21 147.26 2.2 aft 145.06 8703 12.62 x 105

22 147.26 3.8 aft 143.46 9330 13.38 x 105

23 147.26 5.0 aft 142.26 9965 14.18 x 105

24 147.26 6.0 aft 141.26 10600 14.97 x 105

Q-11


Figure Q-3. Draft-at-Landing Fore and Aft.

12 13 14 1519

20

21

22

23

11

Dra

ft

Residual Buoyancy Moment (10 ft-Ltons)5

Weight Moment

Residual BuoyancyMoment

Draft at Landing= 21.7

24

25

16

Draft at Landing (flooded condition) 25.2 ft

13.1

4

15.9

5

26

Q-12


Q-5 Keel Block Build and Loading

The height of the keel block row should be as low as possible to improve stability, minimize therequired submergence depth for onloading, and minimize the complexity of build of the keel andside blocks. It should be high enough to provide at least one foot of clearance under any hull ap-pendage, protrusion, or penetration. For COLE, propeller pits were cut in the deck of BLUEMARLIN so that a keel block height of 16 inches could be used.

It is necessary to evaluate the stress on the keel blocks to ensure that they are strong enough tosurvive the expected loading conditions of the transit. The stress on the blocks will be affected bythe loading condition of the asset and the dynamic motions of the heavy lift ship. To determine thestress on the blocks, it is necessary to look at these motions. Tables 8-4, 8-5, and 8-6 are used toevaluate the ship motions for the heavy lift ship and the validity of the contractor’s Ship MotionAnalysis. Sea State 7 (7m significant wave height) was the expected maximum condition for thetransit of the COLE. Expected ship motions as predicted by Ship Motion analysis are also present-ed for comparison in Table Q-6.

Table Q-6. Heavy Lift Ship (HLS) Blue Marlin Characteristics and Motions

Item Value Source

LOA 712 ft Load Manual

LBP 677 ft Load Manual

Beam 137.8 ft Load Manual

Draft 28.7 Load Manual

Maximum SubmergedDepth of Cargo Deck

32.8 ft

Maximum Cargo DeckLoad

27.5 mT m2

Displacement (∆) 65177 ton Load Manual

KG with DDG 67 39.08 ft Load Manual

LCG with DDG 67 349.25 ft fwd AP Load Manual

TCG with DDG 67 0.01 ft Port Load Manual

Gm with DDG 67 31.4 ft Load Manual

(z) Distance between DDG 67 KG and HLS KG = 30.17 feet aft(x) Distance between DDG 67 LCG and HLS LCG = 39.85 feet(y) Distance between DDG 67 TCG and HLS TCG = 17.0 feet

Q-13


* For Sea State 7

The roll period of the heavy lift ship can be estimated using

B = 137.8 ft

GM = 31.4 ft for HLS with DDG 67 loaded

Ship motion analysis gave Tr = 8.25 sec and 16.7o roll

Once the motions for the ship are determined, the acceleration factors that result from these mo-tions can be determined. Use the equations from Section 8-6.2.1 to determine these accelerationfactors.

Item Value from Table

Table Value from ShipMotion Analysis

Heave Acceleration 0.2 g 8-4 -

*Pitch Angle (P) 4o 8-5 4.38o

*Pitch Period (TP) 7 sec 8-5 5.47 sec

*Roll Angle (R) 20o 8-6 16.7o

*Roll Period (TR) 9.8 8-6(see below) 8.25 sec

Table Q-6. Heavy Lift Ship (HLS) Blue Marlin Characteristics and Motions (Continued)

TrCC B×( )

GM-----------------------=

CC 0.40 sec

ft-------- , Table 8-6, Note 3=

Tr

0.40sec

ft--------- 137.8 ft×

31.4 ft-------------------------------------------------------=

Tr 9.84 sec=

az 1 h0.0214 Px

Tp2

------------------------0.0214 Ry

Tr2

-------------------------+ + +=

az 1 0.20.0214 4 deg( ) 39.85 ft( )

7( )2-----------------------------------------------------------

0.0214 20 deg( ) (17.0 ft)

9.842

-----------------------------------------------------------+ + +=

Q-14


Ship Motion Analysis gave

az = 1.214 which will be used in the following computations.

The hand calculations confirm that the ship motion analysis results are reasonable. They are alsowithin the commercial rule of 20o roll with a 10 second period and 10o pitch in a 10 second peri-od.

Use this vertical acceleration factor to determine the loading on the keel blocks, DLk.

DLK = 10,788 tons (Note: This is sufficient to encompass the flooded condition of COLE at10,700 tons at loading)

Since the loading of the keel block row is relatively continuous for its length and uniform for itswidth, we will use the trapezoidal approximation method described in Section 8-6.2.5 to deter-mine the distribution. Figure 8-9 shows the geometric relation of the components of these calcula-tions. This figure is repeated as Figure Q-4 to show the specific relationships for the DDG 67.These dimensions are taken from the DDG 67 Docking Drawing. For the purposes of these calcu-lations, it is assumed that the continuous row of keel blocks will extend from roughly the after-most part of the DDG 67 skeg to the after limit of the sonar dome. The keel is 36 inches wide forthe majority of its length but narrows to 18 inches wide at the end of the skeg. Some exclusionsfor items such as the Prairie-Masker belts and hull penetrations/sea chests are also assumed.These exclusions will not affect the length of keel blocking (Lk) but must be considered whenevaluating the total effective contact area. Since these exclusions will not occur in the area ofLoadMax, they will not be included in those calculations. Note: If you consider that a normaldocking block of 48” wide by 40” long and that one or 2 blocks can be left out without apprecia-bly affecting the keel block loading, the assumption that the keel block row is continuous can beused unless 3 or more keel blocks are left out, especially near one end.

The maximum (LoadMax) and minimum (LoadMin) loads will be determined from this approxi-mation. The concern is the overall load carrying capacity of the keel block row, the maximum ex-

az 1 0.2 0.07 0.8+ + +=

az 1.35=

DLK waz=

DLK 8 886 tons, 1.214×=

Q-15


Figure Q-4. Load Distribution.

Load M in

OHA

SRPAP

LBP

FP

A

LoadMax

LBP = Length between perpendiculars of asset = 465.5 ft

SRP = Distance from AP to point from w hich distance to keel blocks is m easured

LCG = Asset’s longitudinal center of gravity

OHA = Distance from SRP to keel block

6B = = Approximate Center of Trapezoid

A = Distance from asset’s LCG (center of Gravity) to C (center of Blocking)b

AP = After Perpendicular

= Length of keel blockingLk

Lk

2= = Center of blockingC b

Lk

LCG

B

Lk

C b

Deck of Heavy Lift Ship

= 4.5 !

= 237.82 ft fwd of SRP

= 90 !

= 312 !

= 156 !

= 52"

((OHA + C ) LCG)(OHA + C ) - LCG = 90 + 156 - 237.82 = 8.18 ft aft

b

b

#

= 0

= 465.5 ft

Q-16


pected local stress on the keel blocks, and the load carrying capacity of the cargo deck of theheavy lift ship. The equation for LoadMax returns a value in tons per foot.

In a normal dry-docking, this would be used to evaluate the stress on the last block in the line.Since heavy lifts are often done with a continuous row of keel blocks, the last foot of blockingwill be evaluated. To determine the maximum stress on the last section of keel blocking, useLoadMax and the equation from Section 8-6.2.5.

LoadMaxDLK

LK----------- 1

AB----+

=

LoadMax10788 tons

312 ft-------------------------- 1

8.18 ft52 ft

----------------+ =

LoadMax 40.01 tons/ft=

LoadMinDLK

LK----------- 1

AB----–

=

10788 tons312 ft

-------------------------- 1 8.18 ft52 ft

----------------–

LoadMin 29.13 tons/ft=

SLoadMax

Ae-----------------------

2240 lbton

------------------×=

S 40.01 tons/ft 1 ft 2240 lb/ton××36 in 12 in×-------------------------------------------------------------------------------=

S 207.5 psi=

Q-17


The stress of 207.5 psi is acceptable for the entire keel block row as it is below the compressivelimit for Douglas Fir (370 psi). Recalculating for an 18-inch wide keelblock, the stress of 415 psiexceeds the 370 psi limit. It should be noted that this stress is above the limit set for a 18-inchkeel block at the end of the skeg when looking at knuckle loading. To spread the load over theblock, a 1-inch thick steel plate was installed on top of the knuckle block under the skeg. Sincethe keel block loading was so high (40.01 tons/ft), it was checked against the load carrying capac-ity of BLUE MARLIN’s cargo deck which is 27.5 mT/m2. The location was changed so that theend of the skeg landed over a transverse bulkhead and spreader beams were placed under the keelblocks in these areas to spread the load.

It should be noted that this calculation assumes that the keel blocks will bear the entire dead-weight and dynamic load of COLE. In reality, the side blocks will provide a significant contribu-tion to supporting the load of COLE.

Q-6 Side Blocks

The number of side blocks required will be calculated in a two step process. Step 1 will determinethe minimum number of side blocks required for loading of the asset and deballasting of theheavy lift ship. Step 2 will determine the number required for the transit.

Step 1. To calculate the number of side blocks needed for loading, refer to the equations in Sec-tion 8-7.2. The first consideration is to support the dead (or static) load. The two components ofthis loading are the assumed sharing of the vertical load (estimated at 15 percent) and the increasein this load when the BLUE MARLIN heels or rolls during loading. Sea State 4 will be the max-imum observed during the loading and blocking operation and the numbers for roll amplitude (R)and period (Tr) are assumed for this condition. From Table 8-6, BLUE MARLIN would roll ap-proximately 5 degrees in Sea State 4. Due to the damage the COLE was listed 2 degrees. There-fore, a reasonable angle for the loading operation was 7 degrees. The number of blocks neededfor one side for this weight and assumed keel angle is found by:

Where DLs = 0.5 x 0.15 x w = 0.5 x 0.15 x 8886 = 666 tons per side DLr = wSinR = 8886 sin7o = 1083 tons per side Sp = 800 psi for Douglas Fir Ae = 24 in x 36 in = 864 in2

As noted in Section 8-7.3, this number of side blocks is only for the loading operation. Specialconsideration should be given to selecting the locations for the initial side blocks for landing. Thelocations should be taken from the side block locations on the docking drawing for the best possi-bility of correct fit. The lowest side block with the least curvature should be selected to minimizethe height. Areas of damage should be avoided due to uncertainty of the shape or strength of thehull. On past heavy lifts, use of wedge material or air bags was required at loading because the

Nd

DLs DLr+

Sp Ae×--------------------------=

Nd666 1083 2240×+

800 864×---------------------------------------------= = 5.67 or 6 blocks per side

Q-18


asset landed out of position or the side blocks did not fit well to the hull. These blocks may needto be replaced or not counted in the final total of required side blocks.

Step 2. To determine the final side blocking and seafastening, the number of additional sideblocks that need to be added, both wind loading and dynamic loads from ship motions for thetransit must be considered. The magnitude of these forces will depend on the expected condi-tions. If the blocking build will take place at a site other than the load site, the conditions for thetransit to the building site must also be evaluated. If the build is to take place in an exposed area,the conditions at that site must be considered. The conditions for the complete transit to the finaldestination must also be evaluated. However, the expected conditions for all phases of the opera-tion must be evaluated to ensure a safe transit. For these example calculations, the transit condi-tions will be used.

To complete Step 2, first, the moment from wind forces is found using the recommended windsfrom section 8-5.1.1. This wind (86.8 knots) must be multiplied by a gust factor of 1.21 whichequals 105 knots. It is also necessary to know the area upon which this wind will act, assuming abeam wind. The area for the DDG 67 above the waterline is published in various sources, and anestimate of the below waterline area is made or an estimate of the entire sail area can be made.

As of superstructure = 40 x 190 = 7600 ft2

As above the water line = 22 x 506 = 11132 ft2

As below the water line = 22 x 466 ft = 10252 ft2

As = 28984 ft2

This area is used in the equations found in Section 8-7.2.5 to find the number of side blocks re-quired to resist the wind forces. The value, L3 is an approximation of the moment arm from thedeck of the heavy lift ship to the center of the projected area. The factor, 0.004, in the momentequation accounts for the conversion in units (using feet and knots).

L3 = 35 ft

For a 25 knot wind speed

For the 86.8 knot wind speed

Where L2 =11.25 ft for the inner row and 17 ft for the outer row

Mw 0.004 As= L3V2

Mw 0.004 28984× 35 252

25.4 105ft lbs–×=××=

Mw 0.004 28984× 35 1052

44.7 106ft lbs–×=××=

Nw

Mw

AeSpL2-------------------=

Q-19


For the 25 knot wind speed

This can be accounted for within the initial 6 side blocks.For the higher wind speed (105 kts)

The outer row of side blocks was chosen because they are easier and quicker to install. On theCOLE heavy lift, these blocks were installed first and immediately after loading in case theweather became worse during the period of final side blocking and seafastening. Next, theamount of additional side blocking for ship’s motion during transit must be computed. Using Ta-bles 8-4, 8-5, and 8-6 and some historical weather data, the motions of the heavy lift ship with theasset aboard are determined. For this example, sea state 7 is used as the maximum expected con-dition. The factors listed in Table Q-6 will be used to find the accelerations associated with roll-ing.

Ship Motion Analysis gave a roll of 16.7o and ay = 0.435

Nw25.4 10

5× 36 18 800 11.5×××---------------------------------------------------=

Nw 0.319 side blocks=

Nw44.7 10

5ft lbs–×

36 18 800 17×××-----------------------------------------------=

Nw 3.8 side blocks=

ay Sin R0.0107 Px

Tp2

------------------------0.0002 R

2y

Tr2

----------------------------0.0214 Rz

Tr2

------------------------+ + +=

ay Sin 20o( ) 0.0107(4° )(39.85 ft)

7( )2--------------------------------------------------

0.0002(20° )2(17.0 )

9.8( )2-------------------------------------------------

0.0214(20° ) 30.2 ft( )

9.8( )2---------------------------------------------------+ +

+=

ay 0.342 0.035 0.014 0.135+ + +=

ay 0.526=

Q-20


These accelerations can then be used to find the moment associated with rolling.

Once the moment is known, the number of sideblocks that are required to resist that moment canbe found. In this equation, L2 represents the distance from the centerline of the ship to the center-of the side block. This is the location through which the resultant force will act. While this num-ber will be different for every block, the value of 17.5 represents an average or a typical block.This information comes from the docking drawing.

Therefore, the combined total number of side blocks could be determined by combining step 1,total side blocks for loading (TSB1 = Nd + Nw = 5.67 + 0.32 = 6) and step 2, total side blocks fortransit loadings (TSB2 = Nw + Nr)

The DDG 67 docking drawing indicates that 15 to 21 side blocks are required in a normal dock-ing. This means that there will be insufficient room to install 27 side blocks and that spur shoreswill have to be used to resist the higher roll angles and dynamic overturning moments.

To determine the number of shores required, we will reassess the number of side blocks requiredfor ship’s motion (Nw). We will start with determining the assumed number of side blocks to sup-port the static angle of roll.

The position of the side blocks on the docking drawing are designed to resist angles of roll up to15 degrees. The assessment used should reflect the angle of roll under consideration (maximumstatic angle of roll from the ship’s motion analysis, i.e. 16.7.) The first term in the equation for Ayis SinR where R is maximum roll angle. The equation for DLr can be reworked using the maxi-mum angle of roll for R.

Mr W ay KG( ) 2240×××=

8886 tons 0.435 24.21 ft 2240 lbs/ft×××=

209.62 106× ft-lbs=

NrMr

AeSpL2-------------------=

Nr209.62 10

6× ft-lbs

36 in 24 in 800 lb/in2

17.5 ft×××------------------------------------------------------------------------------------=

Nr 17.3 per side=

Final total side blocks Nd Nw Nr+ +=

5.67 3.8 17.3+ +=

26.77 or 27 side blocks on each side=

Q-21


DLr = w SinR

= 8886 (sin 16.7o)

= 2553.5 tons

Spur shores must resist all angles above 15 degrees and should be spaced accordingly. The num-ber of shores required to resist dynamic loading during transit is then determined from the numberof side blocks and the maximum allowable reaction of the shores. The position of the shores andthe side blocks is also a factor in considering how many shores are required.

Then the number of shores can be reworked for the remainder of the dynamic load. This method-ology will give a reasonable idea of how the spur shores should be distributed. See Section 8-7.4for more information.

L2 is the average distance off centerline for the side blocks for ship motions. For COLE we usedside blocks in the outer row, L2 = 17.5 feet.

L3 is the average distance off centerline for shore spur locations against the hull of the COLE = 21feet

Therefore the total side blocking would consist of side blocks and spur shores. Side blocks equalto Nd + Nw + Nr = 5.67 + 3.8 + 8.3 = 17.33 or 18 per side. To this is added 12 spur shores perside.

Now that we know how many shores we needed, we need to determine how to make the shores.

To start, it is necessary to determine the maximum allowable stress of the shores. This is basedboth on material and geometry.

For USS COLE, heavy, steel I-beams were chosen for the spur shores. These were designed for aloading of 195 tons/shore to be installed under the intersections of the transverse and longitudinalback up structure to the shell plating as specified by NAVSEA O5P. The spur shores were cappedwith a steel spreader plate and 1” thick dense rubber.

To ensure that the spur shore could develop its full compressive yield strength (σy) without col-umn buckling, its was limited to 40.

Column strength

Nr2553.5 2240×800 24 36××---------------------------------- 8.3 sideblocks= =

Ns

Mr DLr– L2⋅σsL3

---------------------------------=

209.62 10

62553.5 2240 17.5××–×

195 2240 21××----------------------------------------------------------------------------------------=

12 shores per side =

Lr---

σcr Compressive yield strength PA---- if slenderness ratio,

Lr--- 40≤

=

Q-22


Noting that

Therefore the minimum cross sectional area of the shore would be

Buckling strength To ensure adequate buckling strength, the slenderness ratio, must be lessthan 40.

A(mm2)

FlangeWebFlange

300 x II(300-22) x 19300 x 11

3,3005,2823,300

11,882

σy 32 Ksi for mild steel=

P 195 tons=

AP

σcr-------

195Ton 22401b

Ton----------×

32000 psi------------------------------------------------- 13.65 in

2= = =

Chosen I beams were 300mm 300mm 11mm 19mm×××–

11 882,25.4( )2

------------------ 18.417 in2

=

Lr---

L unsupported length of spur shore b = flange width=

r least radius of gyration of the section d = depth of web=

rIA----=

where I moment of Inertia=

A cross sectional area of the shore=

Q-23


Properties of the I-beam

For x axis A(mm2) X(mm) M = AX(mm3) Ix = MX(mm4)

Upper flange

300 x 11= 3300

971850 286209825 33275

Web (300-22)x 19 = 5282

792300 118845000 34017841

Lower flange

300 x 11= 3300

18150 99825 33275

11,882 1782300 405154650 34084391

For y Axis A Y M Ix Iy

300 x 11 3300 150 495000 74250000 24750000

(300 - 22) x 19 5282 150 792300 118845000 158900

300 x 11 8300 150 495000 74250000 24750000

11882 1782300 267345000 49658900

Iybd

3

12-------- mm

4( )=

300112

------– 294.5=

3002

--------- 150=

112

------ 5.5=

IN Ix IyM

2

A-------–+ 405154650 34084391

1782300( )2

11882----------------------------–+= =

171894041 mm4

=

rIA----

17189404111882

--------------------------- 120.27 mm (minmum radius of gyration)= = =

Q-24


Using the minimum radius of gyration:

Therefore, shores have to be less than 8.48 ft in length or they have to be braced such that no un-supported length is greater that 8.48 ft. That is, spur shores cannot be longer than 17 ft if support-ed or 8.5 ft if unsupported. They are welded at the base to the cargo deck of the heavy lift ship.

IN Ix IyM

2

A-------–+=

267345000= 496589001782300( )2

11882----------------------------–+

267345000 49658900 2634500–+=

49658900=

rIA---- 64.65 mm (minimum radius of gyration)= =

Lr--- 40≤

Therefore L 40r≤

40 64.65mm( ) 2586mm

25.4mmin

-------------------------------=≤

101.8 inches

12 in/ft------------------------------=

8.48 ft=

Q-25


Q-7 POSITIONING OF SPUR SHORES

Once the number of spur shores is determined, the locations and orientation of the spur shoresneeds to be assessed. The locations are determined as to how high on the ship's hull they need tobe to overcome the overturning moment, Mo. An estimated starting point is with the shore at theturn of the bilge. Under the turn of the bilge, the hull is relatively flat, the shores have to be per-pendicular to the local hull curvature, and the shores will be at too great an angle, more than 45°.At angles greater than 45° the shores provide very little resultant force in the transverse directionand will tend to trip out. If the shores are too high above the turn of the bilge, they become toolong and will not support the column strength. If the point has to be high on the hull to overcomethe overturning moments, towers may have to be used.

Mo is created by the transverse dynamic force working through the ship's (i.e. COLE) center ofgravity. (See Figure Q-5)

Mo = (displacement) (ay)( Lo)

Where displacement = 8,886 tons

ay = 0.435 from motion analysis

Lo = distance between the ship's CG and the position of the shores on the hull in the verti-cal direction. = (ship's CG above its keel (KG) + Keel block height (Hkb)) - shore averageheight (Hs) = 15.54'

Mo = (8,886) (0.435)(15.54) = 60,068 ft-tons

The righting moment is developed by the resultant force that the spur shores can create in thetransverse direction against the hull. From the motion analysis, in a dynamic environment, theweight of the ship is more when the heavy lift ship pitches up and less when the heavy lift shippitches down. An example of this is when the heavy lift ship pitches down and rolls off the top ofa wave into a trough. The dynamic load factor in the vertical direction is az. When the heavy liftship pitches up, az increases the loading on the blocking system, (displacement x az). When theheavy lift ship pitches down, az decreases the loading on the blocking (displacement x (2-az). Theresultant of this force in the transverse direction is the loading on the blocking times the cosine ofthe angle of roll.

The lever arm Lr is the distance between the line of action of the downward force through the CGof the ship and the position of the shore on the hull in the transverse direction.

Lr = 20.5' - (sin 16.8° )((24.21' + 1.33') - 10')))

Mr = (displacement) (2-az) (cos 16.8°) Lr

Mr = (8886)(2-1.214)(cos 16.8°)(20.5 - 15.54 sin 16.8°) = 107,047 ft-tons

The righting moment is greater than the overturning moment, therefore this is an acceptable shoreheight. Next you look at the ship's structure to make sure that where the shores are positioned onthe hull aligns with back up structure such as a bulkhead, a web frame or a deck. When these po-sitions are met, the final consideration determines the orientation of the shore. As noted in thefirst paragraph above, the shore has to be perpendicular to the local hull curvature. Where theshore is located on the hull curvature to the cargo deck determines the angle of the shore. A goodmix of angles between 20° and 45° is recommended with at least two at each angle.

Q-26


Figure Q-5. Overturning Moment.

Q-27



Q-28

As of 7/23/02 R-1


Appendix R

CHECKLIST FOR PREPARING AN ASSET FOR HEAVY LIFT

The following checklist is designed to helpthe crew of a ship or other preparing activityprepare a vessel to be heavy lifted. It listsgeneral requirements, most of which must becompleted before the asset is delivered to thefloat-on site. If the preparing activity hasquestions concerning this checklist or prepa-rations required to ready the asset for heavylift, it should communicate these concerns asearly as possible to ensure a timely departure.The preparing activity should fully completethis checklist in time for the preloading con-ference. Items that are not applicable or can-not be accomplished must be cleared throughthe Loadmaster and Docking Observer.

The Docking Observer should conduct a pre-liminary inspection as soon as possible (prior

to the float-on date) to preclude misunder-standings and rework. In special situations,the standards reflected in this checklist can be“relaxed” if operational factors dictate thatgreater risk is acceptable and if all partiesagree. Any deviations from this checklistmust be accompanied by an appropriate justi-fication from the preparing activity.

The Docking Observer should conduct a finalinspection of the asset, accompanied by a rep-resentative of the preparing activity or the as-set as well as the Loadmaster and Indepen-dent Marine Surveyor. Upon satisfactorycompletion of this inspection, condition ZE-BRA should be set on the asset.

NOTE

For more information on preparinga vessel for heavy lift, refer toChapter 8.


R-3

ASSET INSPECTION CHECKLIST Asset Name _____________________________________ Hull Number_____________________________________

Owner __________________________________________ P.O.C. and 24 Hour # _____________________________

Departure Port ___________________________________ Arrival Port _____________________________________

Receiving Activity Port _____________________________ P.O.C. and 24 Hour # _____________________________

Heavy Lift Vessel Name ____________________________ P.O.C. and 24 Hour # _____________________________

Asset Characteristics Upon Arrival at Float-On Site

Length: Beam: Displacement:

Draft fwd: Draft aft: Mean draft:

Freeboard fwd: Freeboard aft: Freeboard mid:

MTI: TPI: KG:

GM: Maximum Ht above WL:

Maximum Navigational Draft (include underwater appendages; i.e., sonar domes, propellers, etc.):

Has the asset been prepared and is it authorized to be heavy lifted in accordance with requirements set forth in this manual?

Provide rationale for accepting asset with items not accomplished_____________________________________________

_________________________________________________________________________________________________

_________________________________________________________________________________________________

_________________________________________________________________________________________________

_________________________________________________________________________________________________

_________________________________________________________________________________________________

Use separate sheet if additional space is needed.

The asset described above is seaworthy in all respects. The material condition is noted. Representative of command having prepared the asset for lift Date


R-5

1. SHIP INFORMATION


a. Is the booklet of general plans available?


b. Is damage control book, curves of forms, or other stability data available?


c. Are liquid load diagrams and damage control flooding plates available on board?


d. Are instructions posted in after steering for lining up hydraulic steering systems to hand pump?

e. Are plans and date of the last drydocking available? If yes, provide location:

Date of last drydocking:

Note: A copy should be provided to the heavy lift ship as early as possible. An extra copy should be brought to the preloading conference.

f. Has a list of equipage been prepared?

Note: The preparing activity is responsible for providing a list of equipage assigned to the craft that is pilferable and must be on board at destination. Provide list on separate sheet.

g. List remaining HAZMAT on board (include all fuel and ammo):

2. RIDING CREW

Reference N/A Yes No a. Will a riding crew be employed? If so, attach a copy of the directive

(message, letter, etc.) and proceed with the following checks.

b. Authority that authorized a riding crew:

c. Number of crew members:___________________

d. Has a list of the riding crew been provided to the heavy lift vessel?

Note: A list of the riding crew is entered in towing ship’s diary (name, rate, SSN, and NOK; address and phone number of rider and NOK for civilians).

e. Are enough life rafts on board the heavy lift ship with emergency rations and water for the riding crew in the event that they have to abandon ship?

Location of life rafts:

f. Date life rafts were last tested/inspected:


R-6


g. Are a sufficient quantity of life jackets and life rings on board?

Number, type, and location:

h. Means of communication between the docked asset: and the heavy lift ship:

Note: Must be provided if riding crew is to live aboard asset.

i. Has the riding crew been trained in damage control and support systems?

Note: The preparing activity is normally responsible for such training.

j. Is habitability and sustenance sufficient from on-board the heavy lift ship or asset?

Note: Habitability and sustenance should be available on the asset if the riding crew is to live aboard.

3. SEAWORTHINESS

Reference N/A Yes No a. Draft after craft is in proper trim:

Forward: _________________ Aft: _____________________ Max. navigational draft:

8-5.2.2

8-3.6.1

b. GM after craft is in proper trim:

c. KG after craft is in proper trim:

d. If GM is not known, “sally ship” to establish period of roll: Normally T = 2 Beam(ft) T (observed):

5-7.3

e.

Displacement:

f. Provide a list of all tank soundings.

g. Has any temporary ballast been installed?

Type and location of ballast:

8-3.6.1

h. If not, will craft require additional ballast? 8-3.6.1

i. Type of ballast required:

j. Describe where ballast will be placed and how much:


R-7


k. Is condition ZEBRA set throughout the tow?

If the answer is Unsatisfactory, list exceptions on separate sheet.

l. Are all sea valves secured and tagged out? 8-3.6

m. Is a list of sea valves attached? 8-3.6

n. Are all sounding tubes capped? 8-3.6

o. Is there a list of all sounding tubes attached? (Required) 8-3.6

p. Are all between-tank sluice valves closed? 8-3.6

q. Are all normally dry compartments dry? 8-3.6

r. Are all bilges free of oil and water? 8-3.6

s. Have all compartments been inspected for loose equipment? 8-3.6

t. Has steel wire or cable been used to secure all equipment to prevent any movement in heavy weather?

Note: All moveable equipment must be secured in place with wire or by welding. No fiber rope or line will be accepted.

8-3.6

5-7

u. Are all rudders secured?

Note: The rudders should be secured to ensure that there will be no movement during rolling on the heavy lift ship.

8-3.6

v. Type of securing device used:

w. Are all portholes secured for heavy weather?

x. Are all watertight boundaries secured? 8-3.6

y. Are all hatches, scuttles, doors, and other watertight closures provided with pliable gaskets?

8-3.6

5-7.9

z. Have weather decks and main transverse bulkhead watertight closures been chalk tested?

aa. Are all dogs on watertight closures operable and functioning as designed?

bb. For LST-type assets, all of the following must be answered Satisfactory, or the vessel will not be accepted for lift:

i. Do the bow doors have hydraulic rams connected?

ii. Are mud flaps at the bottom of the doors secured?

iii. Are all dogs, heavy weather shackles, ratchet-type turnbuckles and strongbacks in place, tight and secure so that they cannot work free?

iv. Are bow ramp operating instructions posted in the hydraulic control room?

cc. If asset is equipped with a bow or stern ramp, all normal securing devices (i.e., ramp chains, dogs, and turnbuckles) must be in place and in good mechanical order.

dd. Are all lifelines in place and in good condition?


R-8


ee. Are there two means of egress for the asset?

Note: One egress must be a well constructed stair-type access. The second egress may be a temporary access such as a jacob’s ladder.

8-4.5

ff. Are damage control inspection routes marked by paint/diagrams and/or reflective tape?

5-8.4

gg. Is interior access sufficiently marked for DC teams?

4. ELECTRICAL POWER

Reference N/A Yes No a. If power is to be supplied by the heavy lift ship, has the power cable

connection been inspected to ensure compatibility?

Note: To ensure an adequate connection, a visual inspection should be conducted.

b. If the assets generators are to be run have the following items been accomplished?

c. Has provisions for cooling water been made?

d. Have cooling water pumps been demonstrated to have sufficient suction lift and discharge head?

e. Is sufficient fuel available on board the asset for the entire transit?

f. Is there sufficient ventilation for the riding crew to run the generators?

g. Has the free surface of the partially filled fuel tank (due to fuel expended during voyage) been included in the stability calculations (also check calculations in Transport Manual)?

5. FIRE FIGHTING

Reference N/A Yes No a. Has adequate fire fighting capability been provided?

b. If provided from the asset:

c. Have pumps been demonstrated to have sufficient suction lift and discharge head?

5-8.2

d. Are at least two P-100s or operating fire pumps and all other necessary fire fighting equipment on board?

5-8.2

e. Is there enough P-100 fuel on board? 5-8.2

f. Are there sufficient starting cartridge spares?

Note: 4 recommended.

5-8.2

g. Is means for storage of fuel adequate? 5-8.2

h.

If provided from the heavy lift ship:


R-9

Reference N/A Yes No i. Has the connection on board the heavy lift vessel been inspected

and been shown to be compatible?

Note: To ensure an adequate connection, a visual inspection should be conducted.

8-9.6

j. Is adeqaute fire hose available to reach from the proposed connection point to the asset’s connection point?

k. Is all hose protected against chafing?

l. Is all hose secured for heavy weather?

6. NAVIGATION

Reference N/A Yes No a. Have all required navigation lights been installed?

Note: Previous lifts have required a mast light due to increased height.

b. Is each light rigged with two bulbs, so that if one burns out the craft still complies with the COLREGS?

5-7.7

c. Is all wiring well-secured and protected from damage by the elements? 5-7.7

d. Is the light equipped with a solar switch or time switch?

e. Are the batteries secured for heavy weather?

Note: If topside, batteries must be in a watertight box. The location should be carefully selected and secured from heavy seas. If possible, batteries should be inside the asset.

f. Is battery ventilation adequate?

g. Are the batteries charged with sufficient amperage available to keep the lights burning brightly for the duration of the trip?

5-7.7

h. Total ampere capacity of the bank: Sufficient amperage must be calculated and available to cover the following:

Table 5-4



(3) Duration of transit (taking into consideration the solar/time switch and length of the period of darkness).

i. Are day shapes rigged in accordance with COLREGS?

7. CARGO

Reference N/A Yes No a. Is any ship equipment to be included as separate cargo on board the

deck of the heavy lift ship?

b. If so, has a list of this equipment been prepared?

Is this list attached?

c. Is this cargo properly stowed for sea in it’s container?


R-10


d. Has the removal of this equipment been included in all weight and stability calculations?

8. OTHER CONSIDERATIONS

Reference N/A Yes No a. Are safety nets provided around access brows?

b. Are sufficient mooring lines available for tug operations?

c. Is sufficient fendering available for tug operations and for contact with alignment columns?

8-4.1

d. Have provisions been made to extend scuppers and overboard discharges to beyond the deck of the heavy lift vessel (gray water, CHT, etc.)


R-11

9. REMARKS:

SL740-AA-MAN-010

R-12

SAMPLE CERTIFICATE OF DELIVERY LETTER FIRST ENDORSEMENT 1. Upon inspection of the asset described above, the following unsatisfactory conditions were found,

which render the asset not ready for heavy lift (if none, so state). a. b. c. d. 2. (Cross out the statement which is not applicable).

a. I find the asset described above in a condition satisfactory for heavy lift, and hereby assume responsibility for delivery to the port of destination prescribed in my sailing orders.

b. I find the asset described above in an unsatisfactory condition and will not

accept the vessel for heavy lift until these discrepancies are corrected. ___________________________________________________________________________________

Representative of command having Cognizance of lifted asset.

Date


R-2 As of 7/23/02



APPENDIX S - INDEX

AAAJ (Almon A. Johnson) . . . . . . . . . . . . L-7abrasion resistance, synthetic line . . . . C-2abrasion, synthetic line . . . . . . . . . . . . . C-5ABS, chain certification . . . . . . . . . . . . . D-1acceleration

dynamic load . . . . . . . . . . . . . . . . . 3-24getting underway . . . . . . . . . . . 6-1, 6-10

accepting the tow . . . . . . . . . . . . 5-26, 5-29acceptable risk . . . . . . . . . . . . . . . 5-29

acids, effect on line . . . . . . . . . . . . . . . . C-3acoustic arrays, special tows . . . . . . . 7-15AFDM, special tows . . . . . . . . . . . . . . 7-15alarm lighting requirements . . . . . . . . . . 5-9alarm, lights . . . . . . . . . . . . . . . . . . . . . . H-7alarms

audible . . . . . . . . . . . . . . . . . . . . . . . 5-9draft indicator . . . . . . . . . . . . . . . . . 5-6fire . . . . . . . . . . . . . . . . . . . . . 5-22, 6-18flooding . . 5-6, 5-8, 5-28, 6-18, H-7, H-8

schematic . . . . . . . . . . . . . . . 5-6, 5-7radiological . . . . . . . . . . . . . . . . . . 5-22

alkali, effect on line . . . . . . . . . . . . . . . . C-3Almon A Johnson

Series 322 automatic towing machine (ARS 50) . . . . 2-7, 2-8

Almon A. Johnson . . . . . . . . . . . . . . . . . L-7332 (T-ATF) . . . . . . . . . . . . . . 2-10, L-9Series 322 automatic towing

machine (ARS 50) . . . . . . . . L-7American Bureau of Shipping, see ABSanchor . . . . . . . . . . . . . . . . 5-24, 6-17, H-12

drogue . . . . . . . . . . . . . . . . . . . . . . 6-17during beaching . . . . . . . . . . . . . . . 6-30emergency . . . . . . . . . . . . . . . . . . . 5-24removing . . . . . . . . . . . . . . . . . . . . 6-27submarine . . . . . . . . . . . . . . . . . . . . 7-9windlass . . . . . . . . . . . . . . . . 6-27, H-12with a tow . . . . . . . . 5-21, 6-3, 6-4, 6-32

anchor chaininspection . . . . . . . . . . . . . . . . . . . . . D-2pendant . . . . . . . . 4-30, 6-7, 7-12, 7-13submarine . . . . . . . . . . . . . . . . . . . . 7-9towing in ice . . . . . . . . . . . . . . . . . . . 7-6

anchor windlass, preparing pendant . . 6-27anchor-handling tug . . . . . . . . . . . K-5, K-6

anchoring . . . . . . . . . . . . . . . . . . . . . . . 5-24emergency . . . . . . . . . . . . . . . . . . . 5-24tug in irons . . . . . . . . . . . . . . . . . . . 6-14with a tow . . . . . . . . 5-21, 6-3, 6-4, 6-32

approaching a drifting tow. . . . . . . . . . . 6-10Aramid lines . . . . . . . . . . . . . . . . . . . . . C-2arrays

see acoustic . . . . . . . . . . . . . . . . . . 7-15special tows . . . . . . . . . . . . . . . . . . . 7-1

ARS . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-39ARS 38 . . . . . . . . . . . . . 1-3, 2-7, 3-11, 4-9ARS 50 . . . . . . . . . . . . . . . . . . 1-3, 2-7, 2-8

available pull . . . . . . . . . . . . . . . . . . 3-11h-bitts . . . . . . . . . . . . . . . . . . . . 4-8, 4-9ice towing . . . . . . . . . . . . . . . . . . . . . 7-5stern characteristics/

features . . 4-36, 4-39, 4-42, 4-44tow wire. . . . . . . . . . . . B-10, B-12, B-13

ARS 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3ARS 7 . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3assistance, harbor operations. . . . . . . . 6-22assisting command. . . . . . . . . . . . . . . . . 5-3assisting tugs . . . . . . . . . . . . . . . . . . . . 6-22ATA . . . . . . . . . . . . . . . . . . . . . 1-1, 1-3, 2-7ATF . . . . . . . . . . . . . . . . . . . . . . . . .1-1, 2-7ATF 76 . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3ATM, see automatic towing machineATP-43 (NAVY) Ship-to-Ship Towing . . . 1-5ATR (rescue tug) . . . . . . . . . . . . . . . . . . 1-2ATS. . . . . . . . . . . . . . . . . . . . . . . . 1-3, 3-11

stern characteristics . . . . . . . . 4-9, 4-36attachment points . . . . . 4-7, 4-8, 4-13, H-9

bitts . . . . . . . . . . . . . . . . . . . . . . . . . . 6-9emergency . . . . . . . . . . . . . . . . . . . . 6-6inspection . . . . . . . . . . . . . . . . . . . . 5-26location . . . . . . . . . . . . . . . . . . . . . 6-16multiple tows . . . . . . . . . . . . . . . . . . . I-1NATO ships . . . . . . . . . . . . . . . . . . . -14submarines . . . . . . . . . . . . . . . .7-7, J-1

audible alarm . . . . . . . . . . . . . . . . . . . . . 5-9automatic towing

safety factors . . . . . . . . . . . . . . . . . . 4-2shortening scope . . . . . . . . . . . . . . 6-22underway . . . . . . . . . . . . . . . . . . . . 6-12

automatic towing machine . . . . . . . . . . . . . . . . . . . . 2-10, 3-9,

S-3


3-23, 3-26, 4-2, 4-7, 6-12, 6-20, 6-22, L-4, L-9ARS 50 . . . . . . . . . . . . . . 3-26, L-7, L-8heavy weather . . . . . . . . . . . . . . . . 6-19ice towing . . . . . . . . . . . . . . . . . . . . . 7-6safety factors . . . . . . . . . . . . . . . . . . .3-8submarines . . . . . . . . . . . . . . . . . . 7-10T-ATF . . .2-7, 3-26, L-7, L-9, L-10, L-11

axes . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-28cutting hawser . . . . .4-45, 6-30, E-6, L-2

Bbacking down with a tow . . . . . . . . . . . 6-17backup bitts . . . . . . . . . . . . . . . . . . . . . H-11backup securing system 4-29, 6-6, 6-9, H-11ballast . . . . . . . . . . . . . . . . . . . . . . . . . . H-4

trim . . . . . . . . . . . . . . . . . . . . . . . . .5-10stability . . . . . . . . . . . . . . . . . . . . . . 5-10

barge . . . . . . . . . . . . . . . . . . . . . . . . . . .5-14bridle . . . . . . . . . . . . . . . . . . . . . . . .6-16estimating resistance . . . . . . G-18, G-19limits or tow speed . . . . . . . . . . . . .6-18sample tow arrangements . . I-7, I-8, I-9, I-10, I-11, I-12, I-13, I-14, I-15, I-16, I-17,

I-18structural inspection 5-14, 5-15, 5-16, H-7vents . . . . . . . . . . . . . . . . . . . .5-21, H-6

battery . . . . . . . . . . . . . 6-19, H-7, H-8, H-9alarms/lights. 5-8, 5-9, 5-18, 5-21, 5-22,

5-28beaching a tow . . . . . . . . . . . . . . .6-29, H-6beaufort scale (number). . . . . . . . G-4, G-10bending fatigue, synthetic line . . . . . . . . C-2bhp (brake horsepower). . . . . . . . . K-2, K-8Bights . . . . . . . . . . . . . . . . . . . . . . . . . . .4-5bilges . . . . . . . . . . . . . . . . . . . . . . . . . . H-1

dewatering equipment . . . . . . . . . . .5-21billboard, anchors . . . . . . . . . . . . . . . . 5-24bird cage . . . . . . . . . . . . . . . . . . . . B-1, B-2bitts

attachment points. . 4-7, 4-8, 7-12, H-11backup . . . . . . . 4-29, 6-6, 6-7, 6-8, 6-9fairlead . . . . . . . . . . . . . . . . . . . 4-8, 4-9h-bitts . . . . . . . . . . . . . . . . . . . 4-8, 4-39towing . . . . . . . . . . . . . . . . . . . 6-14, 7-2

boardingderelict vessels . . . . . . . . . . . . 6-9, 7-12ladders . . . . . . . . . . 5-25, 5-26, 6-9, H-7

boarding crewbeaching a tow . . . . . . . . . . . . . . . .6-29dewatering . . . . . . . . . . . . . . . 5-23, 5-26retrieving pendant . . . . . . . . . . . . . .4-30

secondary pendant . . . . . . . . . . . . . . 6-4bollard. . . . . . . . . . . . . . . . . . . . . . . . . . . 4-8bollard pull . . . . . . . . . . . 3-24, K-2, K-3, K-4booklet of general plans . . . . . . . . . . . . H-3boom, cranes . . . . . . . . . . . . . . . . . . . . . 5-6bottom plating. . . . . . . . . . . . . . . 5-14, 5-17bow door. . . . . . . . . . . . . . . . . . . . 7-12, H-6bow ramp . . . . . . . . . . . . . . . . . . . 7-12, H-6bows, towing. . . . . . . . . . . . . . . . 4-36, 4-38brake horsepower (bhp) . . . . . . . . . K-2, K-8Brake, Wallis . . . . . . . . . . . . . . . . . B-5, B-6break test . . . . . . . . . . D-7, D-9, D-10, D-11

load. . . . . . . . . . . . . . . . . . . . . D-8, D-15breaking strength

bitts . . . . . . . . . . . . . . . . . . . . . . . . . . 4-8commercial stud link chain . . . . . . . D-9detachable link . . . . . . . . . . . . . . . . D-10DiLok chain . . . . . . . . . . . . . . . . . . . D-7hawser sizing . . . . . . . . . . . . . . . . . 3-27limits for nylon . . . . . . . . . . . . . . . . . 4-3NATO link . . . . . . . . . . . . . . . . . . . . 7-14Navy stud link . . . . . . . . . . . . . . . . . D-8pear shaped link . . . . . . . . . . . . . . D-11safety link . . . . . . . . . . . . . . . . . . . . 4-33shackles . . . . . . . . . . . . . . . . . . . . D-15stoppers . . . . . . . . . . . . . . . . . . . . . . E-2submarine deck fittings. . . . . . . . . . . 7-7synthetic line. . . . . . . . . . . . . . . C-4, C-6wire rope. . . . . . . . . . . . . . . . . . . . . B-11

bridle. . . . 4-25, 4-29, 4-30, 5-28, I-1, I-2, I-5beaching . . . . . . . . . . . . . . . . . . . . . 6-30chain . . . . . . . . . . . . . . . . . 4-1, D-1, D-2derelict vessels . . . . . . . . . . . . . . . . . 6-6examples . . . . . . . . . . . . . . . . . I-14, I-15fairleads . . . . . . . . . . . . . . . . 6-16, 6-17inspection . . . . . . . . . 6-19, H-10, H-11liverpool . . . . . . . . . . . . . . . . . . . . . . I-7passing . . . . . . . . . . . . . . . . . . . . . . 6-25quick disconnect . . . . . . . . . . . . . . . 6-33retrieval pendant. . . . . . . . . . . . . . . 4-30shortening the tow . . . . . . . . . . . . . 6-23submarines . . . . . . . . .7-7, 7-9, J-4, J-6wire . . . . . . . . . . . . . 4-29, I-4, I-11, I-12yawing tow . . . . . . . . . . . . . . . . . . . 6-16

broaching tow . . . . . . . . . . . . . . . . . . . . 6-30broken wires . . . . . . . . . . . . . . . . . . . . . . B-7bullnose . . . . . . . . . . . . . . . . . . . . . . . . 4-17bulwark . . . . . . . . . . . . . . . . . . . . . . . . . 6-7burying the wire . . . . . . . . . . . . . . . . . . . B-5

S-4


Ccable layers . . . . . . . . . . . . . . . . . . . . . 7-15caprail . . . . . . . . . . . 4-36, 4-37, 4-39, 4-42capstan . . . . . . . . . . . . . . . . . . . . . . . . 4-36

retrieval pendant . . . . . . . . . . . . . . 4-30submarines. . . . . . . . . . . . . . . . 7-7, J-1

capstans. . . . . . . . . . . . . . . . . . . . . . . . 5-22capture hook . . . . . . . . . . . 4-39, 4-41, 4-42cargo . . . . . . . . . . . . . . . . . . . . . . 5-28, H-9carpenter stopper 4-30, 4-33, 6-30, E-1, E-6catenary . . . . . . . . . . . . . . . . . . . . 3-4, 3-21

calculations . . . . . . . . . . 3-9, 3-10, 3-22chain. . . . . . . . . . . . . . . . . . . . . . . . . D-1curves 3-12, 3-13, 3-15, 3-16, 3-17, 3-18depth . . . .3-2, 3-9, 3-10, 3-21, 3-22, 6-1formula . . . . 3-9, 3-10, 3-21, 3-22, 3-23shallow water . . . . . . . . . . . . . . . . 6-29tension reduction . . . . . . . . . . . . 6-1, L-3towing in ice . . . . . . . . . . . . . . . . . . 7-5

Certificate of Seaworthiness 5-5, 5-26, H-15chafing . . . . . . . . . . . . 5-6, 6-16, 7-13, H-11

chain . . . . . . . .4-2, 4-27, 6-26, D-1, D-2electrical wiring. . . . . . . . . . . . . . . . 5-22gear . . . . . . . . . . . . . . . . . . . . . . . . 4-33on wire . . . . . . . . . . . . . . . . . . . . . . B-10reduction . . . . . . . . . . . . . . . . 4-27, 6-18submarine towing . . . 7-9, 7-10, J-1, J-4synthetic line . . . . . . . . . . . . . . . . . . C-3wire. . . . . . . . . . . . . . . . . . . . . . . . . 4-29

chafing chain . . . . . . . . . . . . . . . . . . . . 6-24chafing gear . . . . . . . 4-2, 4-33, 4-36, 4-37,. . . . . . . . . . . . . . . . . . . 4-42, 7-6, 7-10, C-5chafing pendant . . . . . . . . . . . . 4-1, I-1, J-1chafing protection . . . . . . . . . . . H-10, H-12chain . . . . . . D-2, D-3, D-4, D-5, D-6, D-16

anchoring . . . . . . . . . . . . . . . . . . . 5-24characteristics/types .D-2, D-5, D-7, D-8commercial stud link . . . . . . . . . . . . D-9connections . . . . . . . . . . . . . 4-21, 4-24cutting. . . . . . . . . . . . . . . . . . . . . . . 4-45DiLok . . . . . . . . . . . . . . . . . . . . D-1, D-5disconnecting . . . . . . . . . . . . . . . . 6-31emergency tow connections. . . 6-6, 6-7inspection . . . . . . . . . . . . . . . . . . . . H-10Navy die lock . . . . . . . . . . . . . . D-1, D-5Navy diel lock . . . . . . . . . . . . . . . . . D-1Navy stud link . . . . . . . . . . . . . D-1, D-8proof load . . . . . . . . . . . . D-4, D-6, D-15securing steering gear . . . . . . . . . . 5-18towing pendant . . . . . . . 4-1, 4-17, 4-27,

. . . . . . . . . . . . . 4-29, 6-3, 6-7, 6-8, 6-9chain bridle . . . . . . . . . . . . H-10, H-11, I-3, . . . . . . . . . . . . . . . . . . . . I-9, I-10, I-16, I-18

ice towing . . . . . . . . . . . . . . . . . 7-5, 7-6chain pendant . . . . . . 7-5, 7-6, I-3, I-10, I-17chain stopper . . . . . . . . . . . . . . . . . . . . 6-23chain stoppers . . . . . . . . . . 4-5, 4-11, 4-30, . . . . . . . . . . . . . . . . 4-34, 6-3, 6-4, 6-27, I-2chains . . . . . . . . . . . . . . . . . . . . . . . . . . D-1chalk test . . . . . . . . . . . . . . . . . . . . . . . . H-6chemical, synthetic line. . . . . . . . . . . . . C-3chinese stopper . . . . . . . . . . . . . . . . . . E-5chocks. . . . . . . . . . . . . . . . . . . . . 4-17, 4-18

fairlead . . . . . . . . . . . . . . . . . . . . . . 4-17Christmas tree rig . . . . . . . I-7, I-9, I-10, I-11cleaning

chain . . . . . . . . . . . . . . . . . . . . . . . . D-2synthetic line . . . . . . . . . . . . . . . . . . C-2wire rope . . . . . . . . . . . . . . . . . . . . . B-3

clips. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5secondary tow pendant. . . 4-4, 4-5, 4-6wire rope . . . . . . . . . . . . . . . . 4-31, 4-32

closed socket . . . . . . . . . . . . . . . 4-23, B-13coal tar, synthetic line . . . . . . . . . . . . . . C-3collision, avoiding . . . . . . . . . . . . . . . . . 6-28COLREGS . . . . . . . . . . . . . . . . . . . . . . H-9combat salvage. . . . . . . . . . . . . . . . . . . . 1-4combat towing . . . . . . . . . . . . . . . . . . . . 1-4combustible gas . . . . . . . . . . . . . . . . . . . 5-9combustible material . . . . . . . . . . . . . . 5-22commercial end link . . . . . . . . . . . . . . D-12commercial stud link chain . . . . . . . . . . D-9communicating, riding crew . . . . . . . . . 5-26communication . . . . . . . . . . . 6-1, 6-3, 6-10, . . . . . . . . . . . . . . . . . . . . 6-12, 7-8, A-2, H-4communications, electrical power. . . . . 5-22compartmentation . . . . . . . . . . . . . . . . 5-23compartments . . . . . . . . . . . . . . . . . . . . H-5condition ZEBRA . . . . . . . . . . . . . . . . . . H-7connection jewelry . . . . . . . . . . . . . . . . . 4-2constructional . . . . . . . . . . . . . . . . . . . . 3-23contingency planning . . . . . . . . . . . . . . A-3control, lateral . . . . . . . . . . . . . . . . . . . 4-44controllable pitch propeller . . . . . . . . . . 3-24controllable pitch propellers . . . . . . . . . 5-10conversion

factors . . R-5, R-6, R-7, R-8, R-9, R-10flow rate . . . . . . . . . . . . . . . . . . . . R-12genera conversion factors . . . . . . . . R-5general conversion factors . . . R-6, R-7,

S-5


R-8, R-9, R-10power . . . . . . . . . . . . . . . . . . . . . . R-11temperature . . . . . . . . . . . . . . . . . . R-11

Cordage Institute . . . . . . . . . . . . . . . . . C-1corrosion

chain . . . . . . . . . . . . . . . . D-2, D-3, D-4synthetic line . . . . . . . . . . . . . . . . . . C-2wire rope . . . . . . . . . . . . B-3, B-7, B-10

cotter keys (cotter pins) . . . . . . . . . . . . 4-21cracks, in chain . . . . . . . . . . . . . . . . . . . D-4cranes, towing . . . . . . . . . . . . . . . . 5-6, 5-14creep, synthetic line . . . . . . . . . . . . . . . C-2crew, accommodations . . . . . . . . . . . . .5-22crisscross stopper . . . . . . . . . . . . . .E-4, E-5crossover stopper . . . . . . . . . . . . . . . . . E-5curves of forms . . . . . . . . . . . . . . . . . . . H-3cuts, synthetic line . . . . . . . . . . . . . . . . . C-5cutting gear . . . . . . . . . . . . 4-44, 4-45, 6-33cutting the hawser . . . . . . . . . . . . 6-30, 6-33cyclic fatigue, synthetic line . . . . . . . . . . C-2

Ddamage

chain . . . . . . . . . . . . . . . . . . . . . . . . D-4synthetic line . . . . . . . . . . . . . . C-4, C-5

damage controlbook . . . . . . . . . . . . . . . . . . . . . . . . H-3equipment . . . . . . . . . . . . . . . . . . . .5-21routes . . . . . . . . . . . . . . . . . . . . . . . . H-3

damaged vessel . . . . . . . . . . . . . . . . . .7-15day shapes . . . . . . . . . . . . . . . . . . . . . . H-9deactivated submarines. . . . . . . . . . . . . 7-6decelerating with a tow . . . . . . . . . 6-1, 6-23delivery letter . . . . . . . . . . . . . . . 5-29, H-16derelict vessel . . . . . . . . . . . . 6-6, 6-9, 6-12detachable link. . . . . . . . . . . . . . . . . . . H-10

anchor connecting . . . . . . . . . . . . . .4-21commercial . . . . . . . . . . . . . . . D-11detachable end link . . . . . . . . . 4-21Kenter type . . . . . . . . . . . . . . . .4-21Navy type . . . . . . . . . . . . . . . . . 4-21pear-shaped . . . . . 4-16, 4-17, 4-21,. . . . . . . . . . . . . . . . . . . . . .4-24, D-5

specs . . . . . . D-3, D-4, D-5, D-10, D-11,. . . . . . . . . . . . . . . . . . D-16, D-17, D-18uses . . . . . . . . . 4-17, 4-21, 4-24, 4-29, . . . . . . . . . . . . . . . .4-34, 6-24, 6-27, D-1

dewatering . . . . . . . . . . . . . . . . . .5-23, H-8dewatering equipment . . . . . . . . .5-23, H-8DiLok chain . . . . . . . . . . . . . . .D-1, D-5, D-7dipped shackle, padeye . . . . . . . . . . . .4-11

disabled towing machine . . . . . . . . . . . 6-31disabled vessel . . . . . . . . . . . . . . . . . . . . 6-6discharge head. . . . . . . . . . . . . . . . . . . H-8disconnect, quick . . . . . . . . . . . . . . . . . 6-33disconnecting the tow . . . . 6-22, 6-23, 6-31displacement . . . . . . . . . . . . . G-7, G-8, G-9distance between tug and tow . . . . . . . 3-23distressed NATO ships . . . . . . . . . . . . 7-13divers . . . . . . . . . . . . . . . . . . . . . . 6-31, 7-9dog, towing machine . . 4-8, 6-20, 7-12, L-5dogs, doors/hatches . . . . . . . . . . . . . . . H-6doors . . . . . . . . . . . . . 5-21, 5-28, 7-12, H-6draft . . . . . . . . . . . . . . . . . . . . . . . . . . . . H-4

indicator . . . . . . . . . . . . . . . . . . 5-6, 5-9marks . . . . . . . . . . . . . . . . . . . . . . . 5-11

draft marks . . . . . . . . . . . . . . . . . . 6-18, H-7drag

hydrodynamic . . . . . . . . . . 3-4, 3-9, 3-21drag, propellers . . . . . . . . . . . . . . . . . . . 5-9drain piping. . . . . . . . . . . . . . . . . . 5-13, H-5dredge . . . . . . . . . . . . . . . . . . . . . . 5-4, 5-6dredge ladder . . . . . . . . . . . . . . . . . . . . . 5-6drift rate . . . . . . . . . . . . . . . . . . . .6-10, 6-11drifting tow . . . . . . . . . . . . . . . . . . . . . . 6-10drogue . . . . . . . . . . . . . . . . . . . . 6-17, 7-11drones . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1drydock

resistance . . . . . . . . . . . . . . G-16, G-18towing . . . . . . 6-16, 6-18, 7-15, H-3, I-12

drydocking plans . . . . . . . . . . . . . . . . . H-3dump scow . . . . . . . . . . . . . . . . . . . . . . . 5-6dyamic tension . . . . . . . . . . . . . . . . . . . M-3dye-penetrant . . . . . . . . . . . . . . . . . . . . D-4dye-penetrant test . . . . . . . . . . . . . . . . . 4-5dynamic load . . . . . . . 3-5, 3-24, 4-7, 4-25,. . . . . . . . . . . . . . . . . . . . . . . 6-18, D-1, D-2dynamic loading . . . . . . . . . . . . . . . . . . L-4dynamic tension . . . . . . . . . . .3-6, 3-7, 3-9, . . . . . . . . . . . . . . 6-14, 6-20, M-1, M-4, M-6

Eeductors . . . . . . . . . . . . . . . . . . . . . . . . . H-8elastic stretch . . . . . . . . . . . . . . . . . . . 3-23electrical power. . . . . . . . . . . . . . . . . . . 5-22elongation . . . . . . . B-1, C-2, C-5, D-2, D-4emergency

connection . . . . . . . . . . . . . . . . . . . . 6-6hawser . . . . . . . . . . . . . . 7-12, 7-13, C-1ship-to-ship towing . . . . . . . . . . . . . 6-24tug assistance. . . . . . . . . . . . . . . . . . K-8

emergency anchoring . . . . . . . . . 5-24, H-12

S-6


emergency release, NATO ships . . . . . 7-13emergency towing

hawser . . . . . . . . . . . . . . . . . . . . . . 6-24merchant ships. . . . . . . . . . . . . . . . 7-12procedures . . . . . . . . . . . . . . . . . . . 6-28safety . . . . . . . . . . . . . . . . . . . . . . . . A-2ship-to-ship. . . . . . . . . . . . . . . . . . . 7-13submarines . . . . . . . . . . . . 7-6, 7-7, J-1

end linkchain . . . . . . . . . . . . . . . . . . . . . . . . D-5thimble . . . . . . . . . . . . . . . . . . . . . . 4-26

end-for-end, towline . . . . . . . . . . . . . . . B-3ESSM . . . . . . . . . . . . . . . . . . . . . . . . . . 5-8external wear, synthetic line . . . . . . . . . C-4extinguishers . . . . . . . . . . . . . . . . . . . . 6-28extreme tension . . . . . . . . . . . 3-6, 3-7, 6-20eye splice . . . . . . . . . . . . . . . . . . . . . . . B-13

Ffactors of safety . . . . . . . . . . . . . . . .3-7, A-1

bitts . . . . . . . . . . . . . . . . . . . . . . . . . 6-8extreme tension . . . . . . . . . . . . . . . . 3-9padeye . . . . . . . . . . . . . . . . . . . . . 4-15shackles . . . . . . . . . . . . . . . . . . . . 4-19synthetic line . . . . . . . . . . . . . . . . . . 4-3towing elements . . . . . . . . . . . . 3-8, 4-1wire rope . . . . . . . . . . . . . . . . . . . . B-12

failure, recording . . . . . . . . . . . . . . F-1, F-2fairlead . . . . . . 4-7, 4-8, 4-9, 4-17, 6-7, H-10

chafing . . . . . . . . . . . . . . . . . . . . . . 4-29submarines . . . . . . . . . . . . . . . . 7-9, J-1vertical rollers . . . . . . . . . . . . . . . . . 4-39

fenderdisplacement . . . . . . . . . . . . . . . . . . 2-3friction damage. . . . . . . . . . . . . . . . . 2-6

fendering . . . . . . . . . . . . . . . . . . . . . . . . 2-3fenders . . . . . . . . . . . . . . . . . . . . . . . . . 2-3

foam . . . . . . . . . . . . . . . . . . . . . 2-3, 2-5harbor tugs . . . . . . . . . . . . . . . . . . . . 2-6pneumatic . . . . . . . . . . . . . . . . . 2-3, 2-5rubber. . . . . . . . . . . . . . . . . . . . 2-3, 2-4ship shell plating damage. . . . . . . . . 2-6YTBs . . . . . . . . . . . . . . . . . . . . . . . . 2-6

fiber core, wire rope . . . . . . . . . . . . . . 4-22fiber line . . . . . . . . . . . . . . . . . . . . . . . . C-1fire . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-28

access markings . . . . . . . . . . . . . . 5-24riding crew . . . . . . . . . . . . . . . . . . . . 5-6submarines. . . . . . . . . . . . . . . . . . . . 7-8

fire alarms . . . . . . . . . 5-9, 5-22, 6-18, 6-19fire extinguishers . . . . . . . . . . . . . . . . . 6-28

fire fighting . . . . . . . . . . . . . 5-22, 5-26, H-8fire-fighting equipment . . . 5-21, 5-22, 5-26, . . . . . . . . . . . . . . . . . . 5-28, 6-19, 6-28, H-8fire-fighting pumps . . . . . . . . . . . . 5-22, H-8firemain . . . . . . . . . . . . . . . . . . . . . . . . . 5-22fires . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6flemish eye . . . . . . . . . . . . . . . . . . . . . B-13float switches . . . . . . . . . . . . . . . . . . . . . 5-8floating retrieval line . . . . . . . . . . . . . . H-12flooding . . 5-6, 5-24, 5-26, 6-18, 6-19, 6-29

alarm lights . . . . . . . . . . . . . . . . . . . 5-7drain piping . . . . . . . . . . . . . . . . . . . 5-14indications. . . . . . . . . . . . . . . . . . . . 5-13

flooding alarm . . . . . . . . . . . . . . . . . . . . 5-8schematic . . . . . . . . . . . . . . . . . . . . . 5-6

flooding alarms . . . . . . . . 5-6, 5-7, 5-8, 5-9, 5-22, 5-23, 5-28, H-7, H-8flooding effect diagram . . . . . . . . . . . . 5-23flounder plate

bridle . . . 4-17, 4-27, 7-6, H-10, H-11, I-1examples . . . . . . . I-3, I-4, I-9, I-10, I-11, . . . . . . . . . . . . . . . . I-16, I-17, I-18, I-19retrieval pendant . . . . . . . . . . . . . . 4-30submarines . . . . . . . . . . . . . . . . . . . J-8target towing . . . . . . . . . . . . . . . . . . 7-2

flounder platesexamples . . . . . . . . . . . . . . . . . . . . . I-14

flow rate conversion . . . . . . . . . . . . . . . R-12foam, fire-fighting . . . . . . . . . . . . . . . . . 6-28formula

catenary depth . . . . . . . . . . . . .3-9, 3-22frames . . . . . . . . . . . . . . . . . . . . . . . . . 5-14frames, inspection . . . . . . . .5-13, 6-18, H-5framing . . . . . . . . . . . . . . . . . . . . . . . . . 6-19freeboard . . . . . . . . . . . . . . . 2-3, 5-4, 5-23free-wheeling

propeller . . . . . . . . . . . . . 5-9, 5-10, 6-16tow machine . . . . . . . . . . . . . . . . . . 6-30

freshening the nip . . . . . . . . . . . . . 4-42, C-3frictional resistance. . . . . . . . . . G-18, G-19frontal windage area . . . . . . . . . . . G-4, G-8fuel, emergency systems . 5-21, 5-24, 5-26, . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-28, H-8furniture . . . . . . . . . . . . . . . . . . . . . . . . 5-22fuse pendant . . . . . . . . . . . . . . . . . . . . 4-33

GGate Craft . . . . . . . . . . . . . . . . . . . . . . . 5-4generators. . . . . . . . . . . . . . . . . . . . . . . H-8getting underway . . . . . . . . . . . . . . . . . . 6-1gland, packing . . . . . . . . . . . . . . . . . . . . H-5

S-7


GM . . . . . . . . . . . . . . . . . . . . . . . . . . . . H-4gravity structures . . . . . . . . . . . . . . . . .7-15grease, wire rope . . . . . . . . . B-3, B-7, B-15grinding, chain . . . . . . . . . . . . . . . . . . . . D-4grommet, synthetic line . . . . . . . . . . . . .4-25ground reaction . . . . . . . . . . . . . . . . . . . R-1ground tackle . . . . . . . . . . . 4-30, 6-33, E-1gypsy head . . . . . . . . . . . . . . . . . 4-36, 4-40

Hhabitability . . . . . . . . . . . . . . . . . . . . . . . H-4hairpin, detachable links . . . . . . .4-21, 4-29,. . . . . . . . . . . . . . . . . . . . . . . . . . D-18, H-10half hitches, stoppers . . . . . . . . . . . E-4, E-5hand-spliced eye . . . . . . . . . . . . . . . . . 4-22harbor towing . . . . . . . . . . . . . . . . . . . . .1-2harbor tug . 1-3, 2-1, 2-6, 5-4, 7-15, G-9, I-5

assistance . . . . 5-3, 6-1, 6-3, 6-4, 6-22,. . . . . . . . . . . . 6-23, 6-30, 7-11, I-7, I-13

hatch . . . . . . . . . . . . . 5-21, 5-28, 7-12, H-6hawser . . . . . . . . . . . 4-2, 6-25, 6-26, 6-27, . . . . . . . . . . . 6-30, 7-5, 7-6, 7-13, H-10, L-1

breaking in . . . . . . . . . . . . . . . . . . . . C-4recording . . . . . . . . . . . . . . . . . . F-1, F-2submarines . . . . . . . . . . . . 7-7, 7-9, J-4synthetic line . . . . . . . . . . 4-2, 6-30, C-4target towing . . . . . . . . . . . . . . . . . . 7-3wire rope . . . . . . . . .4-2, 6-31, 7-6, B-12

hawser resistance . . . . . . . . . . . . . . . . . G-3hawser tension . . . . . . . . . . . . . . . . . . . G-4hawser, towing. . . . . . . . . . . . . . . . . . . . 4-2

log . . . . . . . . . . . B-1, B-5, C-1, C-4, F-1new rope . . . . . . . . . . . . . . . . . . .F-3operations . . . . . . . . . . . . . . F-3, F-4

post-operations entry . . F-3, F-4synthetic line . . . . . . . . . . . . . . . . . . C-1

abuses . . . . . . . . . . . . . . . . . . . . C-3kinks, hockles . . . . . . . . . . C-3, C-4log . . . . . . . . . . . . . . . .C-1, C-4, F-1new . . . . . . . . . . . . . . . . . . C-3, C-4nylon . . . . . . . . . . . . . . . . . . . . . 4-3polyester . . . . . . . . . . . . . . . . . . .4-3precautions . . . . . . . . . . . . . . . . C-6stowing. . . . . . . . . . . . . . . . . . . . C-3uncoiling or unreeling. . . . . . . . . C-3

wire rope . . . . . . . . . . . . . . . . . . . . . 4-2abuses . . . . . . . . . . . . . . . . . . . B-10carried by Navy ships. . . . . . . . B-10installation . . . . . . . . . . . . . . . . . B-5kinks, hockles . . . . . . B-3, B-4, B-10log . . . . . . . . . . . . . . . . B-1, B-5, F-1

new . . . . . . . . . . . . . . . . . . . . . . . B-5precautions . . . . . . . . . . . . . . . . B-10procurement . . . . . . . . . . . . . . . B-12re-reeling . . . . . . . . . . . . . . . . . . B-4stowing . . . . . . . . . . . . . . . . . . . . B-7unreeling . . . . . . . . . . . . . . . . . . . B-3

HAZMAT. . . . . . . . . . . . . . . . . . . . . . . . H-3h-bitts . . . . . . . . . . . . . . . . . . 4-2, 4-39, 4-44heading coefficient . . . . . . . . . . . . G-2, G-4heat resistance . . . . . . . . . . . . . . . . . . . C-2heat, synthetic line . . . . . . . . . . . . . C-2, C-5heaving line . . . . . . . . . . . . . . . . . . . . . 6-10heavy fenders . . . . . . . . . . . . . . . . . . . . . 7-6heavy weather . . . . . . . . . . 6-19, 6-20, 6-21heavy weather shackles, LST tows . . . H-6high level flooding alarms . . . . . . . .5-8, 5-9high weights . . . . . . . . . . . . . . 5-4, 5-6, 5-13hinged cleat . . . . . . . . . . . . . . . . . . . . . . J-5hitches, stoppers . . . . . . . . . . . . . . . . . . E-5hockle

synthetic line. . . . . . . . . . . . . . . C-3, C-4wire rope. . . . . . . . . . . . . B-3, B-4, B-10

hogging strap . . . . . . . . . . . 4-44, 4-46, 6-14Honolulu rig . . . . . . . . . . . . . . .I-7, I-12, I-15hook, towing . . . . . . . . . . . . . . . . . . . . . . 4-7horizontal stern rollers . . . . . . . . 4-36, 4-37horsepower. . . . . . . . . . . . . . . . . . . . . R-11horsepower, commercial tugs. . . . . . . . . K-2hose

dewatering . 5-22, 5-23, 5-24, 5-26, H-8fire . . . . . . . . . . . . 5-22, 5-26, 6-28, H-8

hullblanks . . . . . . . . . . . . . . . . . . . . . . . 5-13inspection . . . . . . . . . . . . . . . . . . . . H-5resistance G-2, G-3, G-4, G-7, G-8, G-9

hurricane . . . . . . . . . . . . . . . . . . . . . . . 6-19hydraulic steering gear . . . . . 5-18, H-3, H-6hydrodynamic resistance . . . . . . . . . . . . 3-4

Iice towing . . . . . . . . . . . . . . . . . . . .7-5, 7-6ice, synthetic line . . . . . . . . . . . . . . . . . C-3icebreaker. . . . . . . . . . . . . . . . . . . . 7-5, 7-6identification

chain . . . . . . . . . . . . . . . . . . . . . . . . D-1synthetic line. . . . . . . . . . . . . . . C-1, C-4wire rope . . . . . . . . . . . . . . . . . . . . . B-1

in irons . . . . . . . . . . . . . . . . 4-39, 6-14, 6-15in step. . . . . . . . . . . . . . . . . . . . . 6-18, 6-28indicated horsepower . . . . . . . . . . . . . . . K-3inland towing . . . . . . . . . . . . . . . . .1-3, 7-15

S-8


inner bottom . . . . . . . . . . . . . . . . . . . . 5-14inspection . . . . . . . . . . . . . 5-13, 5-14, 5-21, . . . . . . . . . . . . . . . .5-26, 6-19, A-2, B-3, B-7

chain. . . . . . . . . . . . . . . . . D-2, D-3, D-4operation orders . . . . . . . . . . . . . . . . 5-5synthetic line . . . . . . . . . . . . . . C-1, C-4wire rope . . . . . . . . . . . . . . . . . B-3, B-7

inspection checklist . . . . . . . . . . . . . . . . H-1inspection routes . . . . . . . . . . . . . . . . . . H-7instruction operational orders . . . . . . . . 5-5is . . . . . . . . . . . . . . . . . . . . . . . . . 4-36, 5-28

Jjack stay . . . . . . . . . . . . . . . . . . . . . . . 6-24jam nuts . . . . . . 4-19, 4-20, 4-23, D-5, H-11jewelry . . . . . . . . . . . . . . . . . . . . . . . . . 4-17

Kkenter detachable link . . . . . . . . . . . . . 4-21Kevlar . . . . . . . . . . . . . . . . . . . . . . . . . . C-2Kevlar stopper . . . . . . . . . . . . . . . . E-1, E-5kinking

synthetic line . . . . . . . . . . . . . . C-3, C-4wire rope . . . . . . . . . B-3, B-4, B-7, B-10

Lladders . . . . . . . . . . . . . . . . 5-25, 5-26, H-7Lake Shore Traction Winch . . . . . . . . . . L-9landing craft . . . . . . . . . . . . . . . . . . . . . . 5-4lateral control wire . . . . . . . . . . . . . . . . 4-44lazy jack . . . . . . . . . . . . . . . . . . . . . . I-6, I-7LCM6 . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4LCM8 . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4LCPL . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4LCU . . . . . . . . . . . . . . . . . . . 5-4, 7-12, H-6lead chain . . . . . . . . . . . . . . . . 4-1, 4-30, I-5lead chain pendant . . . . . . . . . . . . . . . . 4-2lead pendant . . . . . . . . . . . . . . . . . . . . 4-29lessons learned . . . . . . . . . . . . . . . . . . . 5-1letter of instruction . . . . . . . . . . . . . . . . . 5-5level wind . . . . . . . . . . . . . . . . . . . 4-39, L-4life jackets . . . . . . . . . . . . . . . . . . . . . . . H-4life rafts . . . . . . . . . . . . . . . . . . . . . . . . . H-4life rings . . . . . . . . . . . . . . . . . . . . . . . . . H-4lifelines . . . . . . . . . . . . . . . . . . . . . . . . . . H-7lifting operation . . . . . . . . . . . . . . . . . . . C-2lights. . . . . . . . . . . . . . 5-21, 5-22, 5-28, H-8lights, navigation

batteries . . . . . . . . . . . . . . . . . . . . . . 5-8line . . . . . . . . . . . . . . . . . . . . . . . . . 4-8, C-6line-throwing guns . . . . . . . . . . . . . . . . 6-12links . . . . . . . . . . . . . . . 4-1, D-3, D-5, D-18liquid load diagrams . . . . . . . . . . . . . . . . H-3

list . . . . . . . . . . . . . . . . . . . 5-10, 6-18, 6-29liverpool bridle. . . . . . . . . . . . . . . I-6, I-7, I-8Lloyd’s Open Form . . . . . . . . . . . . . . . . K-9locked . . . . . . . . . . . . . . . . . . . . . . . . . . 6-16locking . . . . . . . . . . . . . . . . . . . . . . . . . 5-14longitudinals . . . . . . . . . . . . . . . . . . . . . H-5loose studs . . . . . . . . . . . . . . . . . . . . . . D-4loss of power. . . . . . . . . . . . . . . . . . . . . 6-28low alarm lights . . . . . . . . . . . . . . . . . . . . 5-9low level alarm . . . . . . . . . . . . . . . . . . . . 5-8low level lights. . . . . . . . . . . . . . . . . . . . . 5-8LSMR . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4LST . . . . . . . . . . . . . . . . . . . . . 7-12, H-6, I-5lubricate . . . . . . . . . . . . . . . . . . . . . B-1, B-7lubrication . . . . . . . . . . . . . . B-3, B-10, B-15LWT . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4

Mmagnetic-particle . . . . . . . . . . . . . . . . . D-4maintenance . . . . . . . . . . . . . . B-3, C-2, D-2making turns with the target . . . . . . . . . . 7-2man overboard . . . . . . . . . . . . . . . . . . . 6-33maneuver . . . . . . . . . . . . . . . . . . . . . . . 6-14maneuverability. . . . . . . . . . . . . . 4-39, 6-21maneuvering . . . . . . . 6-14, 6-21, 6-28, 6-34manifest . . . . . . . . . . . . . . . . . . . . . . . . H-9marker buoy . . . . . . . . . . . . . . . . . . . . . 6-32marking access. . . . . . . . . . . . . . . . . . . 5-24measurement systems

circular . . . . . . . . . . . . . . . . . . . . . . R-4english . . . . . . . . . . . . . . . . . . . . . . R-1metric . . . . . . . . . . . . . . . . . . . . . . . . R-1

melting . . . . . . . . . . . . . . . . . . . . . . . . . C-5merchant ships . . . . . . . . . . . . . . . . . . . . 7-1

distressed . . . . . . . . . . . . . . . . . . . . 7-11message . . . . . . . . . . . . . . . . . . . . 5-29, H-3messenger . . . . . . . 4-4, 4-5, 5-28, 6-2, 6-5, . . . . . . . . . . . . 6-10, 6-11, 6-12, 6-13, 6-23, . . . . . . . . . 6-24, 6-25, 6-30, 6-32, 7-3, 7-10messenger line . . . . . . . . . . . . . . . . 4-6, 6-3metacresol . . . . . . . . . . . . . . . . . . . . . . . C-3Military Sealift Command . . . . . . . . . . . . 2-7mineral acids. . . . . . . . . . . . . . . . . . . . . C-3minesweeping devices . . . . . . . . . . . . . 7-15mini-ATC . . . . . . . . . . . . . . . . . . . . . . . . 5-4minimum plate thickness . . . . . . 5-15, 5-16missing studs . . . . . . . . . . . . . . . . . . . . . D-4MK1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4MK2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4MK2 . . . . . . . . . . . . . . . . . . . . . . . . . .65 5-4MK3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4

S-9


MK4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4MK4 40’ . . . . . . . . . . . . . . . . . . . . . . . . . 5-4MK4 50’ . . . . . . . . . . . . . . . . . . . . . . . . . 5-4MK5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4Molly Hogan. . . . . . . . . . . . . . . . . . . . . B-13mooring bitts . . . . . . . . . . . . . . . . . . . . H-11mooring cleats . . . . . . . . . . . . . J-1, J-4, J-7mooring line . . . . . . . . . . . . . . . . . . 6-3, 6-8mooring lines . . . . . . . . . . . . . . . . . . . . 5-28MSC. . . . . . . . . . . . . 1-3, 4-7, 5-2, A-1, B-1mud flaps . . . . . . . . . . . . . . . . . . . . . . . . H-6

NNATO . . . . . . . . . . . . . . . . . . . . . . . . . .7-13

link . . . . . . . . . . . . . . . . . . . . . . . . . 6-26ships . . . . . . . . . . . . . . . . . . . . 7-1, 7-14standard towing link . . . . . . . . . . . . 7-14towing link . . . . . . . . . . . . . . . . . . . 6-24

natural pivot point . . . . . . . . . . . . . . . . 6-14Naval Publications and Forms Center . B-12Naval Sea Systems Command . . . . . . . B-1Naval vessels . . . . . . . . . . . . G-7, G-8, G-9navigation . . . . . . . . . . . . . . . . . . . . . . . 5-3navigation lights 5-18, 5-26, 6-18, 6-19, H-8navigation track . . . . . . . . . . . . . . . . . . . 5-3NAVSEA . 1-3, 4-3, 4-25, 5-8, C-1, F-2, H-3NAVSEA 00C . . . . . . . . . . . 3-7, 5-21, 7-15,. . . . . . . . . . . . . . . . . . . . B-5, B-6, D-5, K-9Navy die lock chain . . . . . . . . . . . . D-1, D-5Navy stud link chain . . . . . . . . . . . D-1, D-8Nested rig . . . . . . . . . . . . . . . . . . . . I-7, I-12non-destructively tested. . . . . . . . . . . . . H-9norman pin. . . .4-42, 4-43, 4-45, 6-14, 6-20NR-1 . . . . . . . . . . . . . . . . . . . . . . . . . . .7-15nuclear vessel . . . . . . . . . . . . . . . . . . . . 7-4nylon . . . . . . . . . . 4-3, 4-25, 6-24, C-1, C-2,. . . . . . . . . . . . . . . . . . . . . C-3, C-5, C-6, J-4nylon line

abrasion resistance . . . . . . . . . . . . . C-2creep . . . . . . . . . . . . . . . . . . . . . . . . C-2fatigue . . . . . . . . . . . . . . . . . . . . . . . C-2heat resistance. . . . . . . . . . . . . . . . . C-2strength . . . . . . . . . . . . . . . . . . . . . . C-2

nylon towing hawser . . . . . . . . . . . . . . . .J-8O

Ocean Towing . . . . . . . . . . . . . . . . . . . . .1-3Orville Hook . . . . . . . . . . . . . . . . . . . . . .6-34overridden . . . . . . . . . . . . . . . . . . . . . . 6-28overriding . . . . . . . . . . . . . . . . . . . . . . . 6-33

PP-100 . . . . . . . . . . . . . . . . . . 5-22, 5-23, H-8

P-250 . . . . . . . . . . . . . . . . . . . . . .5-22, 5-23packing gland . . . . . . . . . . . . . . . . . . . . H-5padeye . . . . . . . . . . . . . . . . 4-8, 4-10, 4-12,. . . . . . . . . . . . . . . . . . 4-13, 4-15, 5-26, 6-6

chain stoppers . . . . . . . . . . . . . . . . 4-10dipped shackle . . . . . . . . . . . . . . . . 4-11

padeye design . . . . . . . . . . . . . . . . . . . 4-14paints . . . . . . . . . . . . . . . . . . . . . . . . . . 5-22paint-stripping compounds . . . . . . . . . . C-3Panama Canal . . . . . . . . . . . . 7-4, 7-5, 7-15paper . . . . . . . . . . . . . . . . . . . . . . . . . . 5-22passing a tow . . . . . . . . . . . . . . . . . . . 6-25passing the hawser . . . . . . . . . . 6-11, 6-13passing the target . . . . . . . . . . . . . . . . . . 7-3passing the tow . . . . . . . . . . . . . . . . . . 6-23passing the towline. . . . . . . . . . . . . . . . 6-10patrol boat . . . . . . . . . . . . . . . . . . . . . . . 5-4pawl . . . . . . . . . . . . . . . . . . . . . . . . . . . . L-5pelican hook . . . . . . . 4-5, 4-30, 6-24, 6-27,. . . . . . . . . E-1, E-6, H-12, J-1, J-3, J-4, J-6pendant . . . . . . . . . 4-27, 6-23, 6-25, 6-30,. . . . . . . . . . . . . . . . . . . . . 7-2, 7-9, D-2, I-7pendant leg rig . . . . . . . . . . . . . . . . . . . . I-2pendant rig . . . . . . . . . . . . . . . . . . . . . . . I-1pendants. . . . . . . . . . . . . . . . . . . . . . . . D-1personnel boats . . . . . . . . . . . . . . . . . . . 5-4PHMs . . . . . . . . . . . . . . . . . . . . . . . . . . 7-15picking up a tow . . . . . . . . . . . . . . . . . . . 6-1pile driver . . . . . . . . . . . . . . . . . . . . 5-4, 5-6pilot . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-22pipe structures . . . . . . . . . . . . . . . . . . . 7-15pivot point . . . . . . . . . . . . . . . . . . . . 6-15, I-7plate . . . . . . . . . . . . . . . . . . . . . . . H-5, H-11plate shackle . . . . . . 4-20, 4-21, D-6, H-11,. I-1, I-3, I-4, I-10, I-11, I-16, I-17, I-20, I-21,. . . . . . . . . . . . . . . . . . . . . . . . . . . . I-22, J-8platforms. . . . . . . . . . . . . . . . . . . . . . . . 7-15plating. . . . . . . . . . . . . . . . . . . . . 5-14, 6-19Point-to-Point Towing . . . . . . . . . . . . . . 1-3point-to-point towing tug . . . . . . . . K-5, K-6polyester . . . . . . . . . . .4-3, 4-25, 6-24, C-1,. . . . . . . . . . . . . . . . . . . . C-2, C-3, C-5, C-6polyester line

abrasion resistance . . . . . . . . . . . . . C-2creep. . . . . . . . . . . . . . . . . . . . . . . . C-2fatigue . . . . . . . . . . . . . . . . . . . . . . . C-2heat resistance . . . . . . . . . . . . . . . . C-2strength. . . . . . . . . . . . . . . . . . . . . . C-2

polypropylene . . . . . . . . . C-1, C-2, C-3, C-5polypropylene line

S-10


abrasion resistance . . . . . . . . . . . . . C-2creep . . . . . . . . . . . . . . . . . . . . . . . . C-2fatigue . . . . . . . . . . . . . . . . . . . . . . . C-2heat resistance . . . . . . . . . . . . . . . . C-2strength . . . . . . . . . . . . . . . . . . . . . . C-2

popped core . . . . . . . . . . . . . . . . . . B-1, B-2porthole . . . . . . . . . . . . . . . 5-21, 5-28, H-5precautions . . . . . . . . . . . . . . . . . . . . . . D-4pressure . . . . . . . . . . . . . . . . . . . . . . . . . R-4primary pendant . . . . . . . . . . . . . . . 4-5, 6-3projected area of propellers . . . . . .G-1, G-4,. . . . . . . . . . . . . . . . . . . . . . . . . . . . G-7, G-8proof load . . . . . . . . . . . . . . . . . . . . . . . . D-6propeller resistance . . . . . . . G-2, G-4, G-16propeller shaft . . . . . . . . . . . . . . . . . . . 5-12propeller shaft locking . . . . . . . . . . . . . 6-19propellers . . . . . . . . . . . 5-9, 5-10, 6-16, H-5PTF . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4pump . . . . . . . . . . . . 5-22, 5-23, 5-24, 5-26,. . . . . . . . . . . . . . . . . . 5-28, 6-28, 6-29, H-8Pusher boats . . . . . . . . . . . . . . . . . . . . . 2-6

Qquick disconnect . . . . . . . . . . . . . .4-7, H-12quick disconnect system . . . . . . . . . . . 6-33quick disconnection . . . . . . . . . . . . . . . 6-21quickly releasing . . . . . . . . . . . . . . . . . 5-28quick-release . . .4-7, 5-24, 6-27, 6-31, 6-33,. . . . . . . . . . . . E-1, E-6, H-12, J-4, L-1, L-2quick-release device . . . . . . . . . . . . . . 4-30

Rradiological. . . . . . . . . . . . . . . . . . . . . . . 5-9radiological alarms . . . . . . . . . . . . . . . . 5-22ramp chains . . . . . . . . . . . . . . . . . . . . . . H-6reaching pendant . . . . . . . . . . . . . . . . . 4-30receiving activity. . . . . . . . . . . . . . . . . . . 5-5recover the towline. . . . . . . . . . . 6-31, 6-32recovering

tow . . . . . . . . . . . . . . . . . . . . . . . . . . 6-4recovering a capsized target . . . . . . . . . 7-3recovering the target . . . . . . . . . . . . . . . 7-3recovery buoy . . . . . . . . . . . . . . . . . . . 6-30recovery pendant . . . . . . . . . . . . . . . . . . 7-4Reducing towline loads . . . . . . . . . . . . 3-10reduction gears . . . . . . . . . . . . . . . . . . 5-10reeling . . . . . . . . . . . . . . . . . . . . . . . . . . B-3refueling . . . . . . . . . . . . . . . . . . . . . . . . 6-21rejecting the tow . . . . . . . . . . . . . . . . . 5-29relative drift . . . . . . . . . . . . . . . . . . . . . 6-10releasing a tow . . . . . . . . . . . . . . . . . . . 6-1releasing the stopper . . . . . . . . . . . . . . . E-6

remotely operated boats . . . . . . . . . . . . . 7-1removing propellers . . . . . . . . . . . . . . . . 5-9replace wire rope . . . . . . . . . . . . . . . . . B-7replenishment . . . . . . . . . . . . . . . . . . . 6-21re-reeling. . . . . . . . . . . . . . . . . . . . . . . . B-4rescue and salvage . . . . . . . . . . . . . . . 5-22rescue towing . . . . . . . . . . . . . 5-14, 6-3, 6-6rescue tows. . . . . . . . . . . . . . . . . . . . . . . 5-6rescuing . . . . . . . . . . . . . . . . . . . . . . . . . 6-6resistance due to waves . . . . . . . . . . . . G-3Resistance hawser . . . . . . . . . . . . . . . . . 3-2Resistance propellers . . . . . . . . . . . . . . . 3-2Resistance tow . . . . . . . . . . . . . . . . . . . . 3-2resistance towline . . . . . . . . . . . . . . . . . G-2retrieval

buoy . . . . . . . . . . . . . . . . . . . . . . . . . 6-4line 6-4

retrieval pendant . . . . . . . . 4-30, 6-31, H-11retrieving a tow wire . . . . . . . . . . . . . . . 6-32retrieving line . . . . . . . . . . . . . . . . . . . . 6-23retrieving wire 5-28, 6-31, I-3, I-14, I-18, J-7rider lines . . . . . . . . . . . . . . . . . . . . . . . I-12riding crew . .4-30, 5-2, 5-5, 5-6, 5-24, 5-26, . . . . . 6-6, 6-14, 6-19, 6-28, 6-29, H-3, H-4riding line . . . . . . . . . . . . . 6-3, 6-5, 7-3, 7-5rivets . . . . . . . . . . . . . . . . . . . . . . . . . . . H-5roll period . . . . . . . . . . . . . 5-13, 6-18, 6-29route markings . . . . . . . . . . . . . . . . . . . 5-24rudder . . . . . . . . . . . . . . . . 5-14, 5-18, 5-19, . . . . . . . . . . . . . . 5-20, 6-14, 6-16, H-4, H-5rudder locking . . . . . . . . . . . . . . . . . . . . 6-19

Ssaddle . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6saddle method . . . . . . . . . . . . . . . . 7-5, 7-6safe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-8Safe Working Load (SWL) . 4-3, 4-19, 4-36, . . . . . . . . . . . . . . . . . . . 7-10, D-5, D-6, J-4safety . . . . . . . . . . . . . . . . . . . . . 6-28, 6-29, . . . . . . . . . . . . . . . . . . . 6-32, A-1, A-2, F-1safety factor . . . . . . . . . . 4-2, 4-7, 5-21, D-6safety link . . . . . . . . . . . . . .4-29, 4-33, H-12safety shackle . . . . . . . . . . . . . . . . . . . H-11sail . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-10salvage towing . . . . . . . . . . . . . . . 1-4, 5-14salvage tug . . . . . . . K-1, K-2, K-3, K-6, K-8salvage vessel . . . . . . . . . . . . . . . . . . . K-7Scope . . . . . . . . . . . . . 3-9, 3-10, 3-21, 3-22scope .4-7, 4-33, 6-17, 6-18, 6-20, 6-22, L-1screw-pin shackles . . . . . . . . . . . . . . . . D-5scuttle . . . . . . . . . . . 5-21, 5-28, 7-12, H-6

S-11


seaanchor . . . . . . . . . . . . . . . . . . . . . . 6-17drogue . . . . . . . . . . . . . . . . . . . . . . 6-17

SEA 00C . . . . . . . . . . . . . . . . . . . . . . . . .F-2sea chests . . . . . . . . . . . . . . . . . . . . . . 5-13sea openings . . . . . . . . . . . . . . . . . . . . . H-5sea state resistance . . . .3-2, G-2, G-3, G-4sea valves . . . . . . . . . . . . . . 5-13, H-4, H-5Seaborne-Propelled Targets . . . . . . . . . 7-4seaplane derrick . . . . . . . . . . . . . . . . . . .5-4seaworthiness . . . . . . . . . . . . . . . . . . . 5-26secondary pendant . . . . . . . . . . . . . . . H-12secondary tow . . . . . . . . . . . . . . . . . . . . 4-3secondary towing . . . . . . . . . . . . 5-14, H-12secondary towing pendant . . . . . . . . . . H-12secondary towing rig . . . . . . . . . . . . . . .5-21secondary towline . . . . . . 4-3, 4-4, 4-6, 5-26Section modulus . . . . . . . . . . . . . 3-22, 3-23securing . . . . . . . . . . . . . . . . . . . . . . . . . E-6SEPTARs. . . . . . . . . . . . . . . . . . . . . . . . 7-4service craft . . . . . . . . . . . . . . . . . 5-14, 6-18setting course . . . . . . . . . . . . . . . . . . . 6-17setting the stopper . . . . . . . . . . . . . . . . . E-6shackle . . 4-1, 4-19, 4-20, 4-24, 5-28, 7-9,. . D-1, D-5, D-6, D-13, D-14, D-15, J-3, J-4shaft bearings . . . . . . . . . . . . . . . . . . . 5-10shaft horsepower . . . . . . . . . . . . . . . . . . K-2shaft-locking device . . . . . . . . . . . . . . . 5-10shafts . . . . . . . . . . . . . . . . . . . . . . 5-10, H-5sheer . . . . . . . . . . . . . . . . . . . . . . . 6-17, 7-8sheering . . . . . . . . . . . . 3-5, 3-7, 6-16, 7-10sheers . . . . . . . . . . . . . . . . . . . . . . . . . . . I-5ship handling . . . . . . . . . . . . . . . . . . . . 6-12ship maneuvering . . . . . . . . . . . . . . . . .6-12ship-to-ship towing. . . . . . . . . . . . . . . . 7-14shock load . . . . . . . . . . . . . . . . . . . . . . . C-2shoring . . . . 5-14, 5-15, 5-16, 5-17, H-6, H-7short scope . . . . . . . . . . . . . . . . . . . . . . I-12short stay . . . . . . . . 6-3, 6-22, 6-28, 7-2, 7-3short-scope method . . . . . . . . . . . . 7-5, 7-6side-by-side towing . . . . . . . . . . . . I-13, I-17single lead pendant . . . . . . . . . . . . . . . 6-17single leg rig. . . . . . . . . . . . . . . . . . . . I-1, I-2single pendant . . . . . . . . . . . . . . . . . . . 4-27sink . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-28SINKEX . . . . . . . . . . . . . . . . . . . . . . . . .7-15sinking . . . . . . . . . . . . . . . . . . . . . . . . . .6-29skeg . . . . . . . . . . . . . . . . . . . . . . . 6-16, H-4slamming . . . . . . . . . . . . . . . . . . . . . . . 5-14sled . . . . . . . . . . . . . . . . . . . . . . . . . 7-3, 7-4

slipping the hawser. . . . . . . . . . . 6-30, 6-32slower speed . . . . . . . . . . . . . . . . . . . . 6-22sludge removal craft . . . . . . . . . . . . . . . . 5-4sluice valves . . . . . . . . . . . . . . . . . . . . . H-5SMATCO towing winch. . . . . . . . . . . . . . L-9Smit Towing Bracket. . . . . . . . . . . . . . . 7-12snap back . . . . . . . . . . . . . . . . . . . C-2, C-6socket . . 4-22, B-10, B-12, B-13, B-14, B-15solar switch . . . . . . . . . . . . . . . . . 5-18, H-8sonar buoys . . . . . . . . . . . . . . . . . . . . . . 7-1sounding tubes . . . . . . . . . . . . . . . . . . . H-5Spectra . . . . . . . . . . . . . . . . . . . . . . . . . C-2speed . . . . . . . . . . . . . . . . . 6-16, 6-18, 6-20speed/length ratio . . . . . . . . . . . . . . . . . G-3spliced . . . . . . . . . . . . . . . . . . . . . . . . . 4-22sponsoring command . . . . . . . . . . . . . . . 5-5spring pendants . . . . . . . . . . . . . . . . . . . 4-1springs . . . . . . . . . 3-24, 4-2, C-1, C-2, C-4SSBN . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-9SSBN 616 Class . . . . . . . . . . . . . . . . . . J-2SSBN 726. . . . . . . . . . . . . . . . . . . . . . . . J-1SSBN 726 Class. . . . . . . . J-2, J-4, J-7, J-8SSN 594 Class . . . . . . . . . . . . . . . . . . . . J-2SSN 637 Class . . . . . . . . . . . . . . . . J-2, J-3SSN 671 Class J-2SSN 685 Class . . . . . . . . . . . . . . . . . . . J-2SSN 688 Class . 7-9, J-1, J-2, J-4, J-5, J-6SSN 720 Class . . . . . . . . . . . . . . . . . . . . J-2stability . . . . . . . . 5-10, 6-29, H-3, H-9, L-2Steady resistance . . . . . . . . . . . . . . . . . . 3-2Steady tensions . . . . . . . . . . . . . . . . . . . 3-7Steady towline tension . . . . 3-27, 6-18, G-1steady-state tow resistance . . . . . G-2, G-4steering tug. . . . . . . . . . . . . . . . . . 6-17, I-13stern . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-15stern gland . . . . . . . . . . . . . . . . . . . . . . 5-10stern ramp . . . . . . . . . . . . . . . . . . . . . . H-6stern rollers . . . . . . . . . . . . 4-42, 6-14, 6-20stern tube . . . . . . . . . . . . . . . . . . . 5-10, H-5stopper . . . . . 6-22, 6-23, E-3, E-4, E-5, E-6stopper hitches . . . . . . . . . . . . . . . . . . . . E-6stoppers . . . . . . . . . . . . . . . . . . . . . . . . . E-1stowing . . . . . . . . . . . . . . . . . B-7, C-3, D-3stream . . . . . . . . . . . . . . . . . . . . . . .6-3, 6-5streaming the target . . . . . . . . . . . . . . . . 7-2strength . . . . . . . . . . . . . . . . . . . . . . . . . D-2stretch. . . . . . . . . . . . . . . . . . . B-1, C-2, D-2strongbacks . . . . . . . . . . . . . . . . . . . . . H-6structural. . . . . . . . . . . . . . . . . . . . . . . . 5-14structure . . . . . . . . . . . . . . . . . . . . . . . . H-5

S-12


stud link anchor . . . . . . . . . . . . . . . . . . . D-9stud link chain . . . . . . . . . . . . D-1, D-2, D-5submarine capstan . . . . . . . . . . . . . . . . .J-1submarine deck fittings . . . . . . . . . . . . . 7-7submarines . . . 6-17, 7-1, 7-6, 7-7, 7-8, 7-9,. . . . . . . . . . . . . . . 7-10, 7-11, H-13, J-1, J-4submersibles . . . . . . . . . . . . . . . . . . . . 7-15suction lift . . . . . . . . . . . . . . . . . . . . . . . H-8sunlight . . . . . . . . . . . . . . . . . . . . . C-3, C-5Supervisor of Salvage . . . . . . . . . . . . . . K-9supply tug. . . . . . . . . . . . . . . . . . . . K-5, K-6SUPSALV . . . . . . . . . . . . . . . . . . . . . . . K-9Surge . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5sustenance. . . . . . . . . . . . . . . . . . . . . . . H-4Swage . . . . . . . . . . . . . . . . . . . . . . . . . 4-22swaged . . . . . . . . . . . . . . . . . . . .4-22, B-13swaging . . . . . . . . . . . . . . . . . . . . . . . . 4-21SWATHs . . . . . . . . . . . . . . . . . . . . . . . 7-15SWL . . . . . . . . . . . . . . . . . . . 4-3, 4-19, 7-7synthetic. . . . . . . . . . . . . . . . . 4-8, 6-9, C-6synthetic fiber. . . . . . . . . . . . . . . . . . . . . F-1synthetic hawser . . . . . . . . . . 4-2, C-4, L-2synthetic line . . . . . . . 4-26, 4-45, 6-8, 6-26,. . . . . . . . 6-27, 7-6, C-1, C-2, C-3, C-5, E-2

abrasion . . . . . . . . . . . . . . . . . . . . . . C-5abrasion resistance . . . . . . . . . . . . . C-2creep . . . . . . . . . . . . . . . . . . . . . . . . C-2fatigue . . . . . . . . . . . . . . . . . . . . . . . C-2heat resistance. . . . . . . . . . . . . . . . . C-2strength . . . . . . . . . . . . . . . . . . . . . . C-2terminations . . . . . . . . . . . . . . . . . . 4-23

Synthetic spring . . . . . . . . . 3-10, 4-2, 4-25,. . . . . . . . . . . . . . . . . . . . . . . 6-1, 6-22, 7-10synthetic towing hawser. . . . . . . . . . . . . J-6Synthetic towlines . . . . . . . . . . . 3-23, 3-24system . . . . . . . . . . . . . . . . . . . . . . . . . . 6-6

TTandem . . . . . . . . . . . . . . . . . . . . . . . . . I-7Tandem rig. . . . . . . . . . . . . . . . . . I-12, I-16tank . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-21tank vents. . . . . . . . . . . . . . . . . . . . . . . 5-21tankers . . . . . . . . . . . . . . . . . . . . . . . . . 7-12tanks . . . . . . . . . . . . . . . . . 5-13, 5-28, 6-19target . . . . . . . . . . . . . . . . 7-1, 7-2, 7-3, 7-4target capsizes. . . . . . . . . . . . . . . . . . . . 7-4target sleds . . . . . . . . . . . . . . . . . . . . . . B-1target towing precautions. . . . . . . . . . . . 7-4targets . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1T-ATF 1-3, 4-7, 4-9, 4-39, 4-41, 4-42, 7-1, 7-5T-ATF 166 . . 2-7, 2-9, 3-11, B-10, B-12, L-9

T-ATF 166 Class . . . . . . . . . . . . . . . . . . L-7Temperature . . . . . . . . . . . . . . . . . . . . R-11Tension . . . . . . . . . . . . . . . . . . . . . . . . 3-22tension in the towline . . . . . . . . . . . . . . 6-20terminating the tow . . . . . . . . . . . . . . . . 6-22terminations . . . . . . . . . . . . 4-17, 4-21, 4-22thimble . . . . . . . . . . . . . . . 4-23, 4-25, 4-26thinners . . . . . . . . . . . . . . . . . . . . . . . . . C-3tiller arm . . . . . . . . . . . . . . . . . . . .5-18, 5-19tiller steering gear . . . . . . . . . . . . 5-14, 5-20time switch . . . . . . . . . . . . . . . . . . . . . . H-8total projected propellers . . . . . . . . . . . G-9Tow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-5tow

unmanned . . . . . . . . . . . . . . . . . . . . 6-4tow and be towed . . . . . 6-23, 7-6, 7-13, C-1tow bridle . . . . . . . . . . . . . . . . . . . . . . . 6-23tow conference . . . . . . . . . . . . . . . . . . . 5-29tow connection . . . . . . . . . . . . . . 7-10, 7-13tow hawser . . . . . . . . . . . . . . . . . . . . . . 6-33tow hawser resistance . . . . . . . . . . . . . G-4tow in step. . . . . . . . . . . . . . . . . . . . . . . 6-14tow machine . . . . . . . . . . . . . . . . . . . . . 6-31tow or be towed . . . . . . . . . . . . . . . . . . . A-2tow pad . . . . . . . . . . . . . . . . . . . . . .7-7, J-4tow pendant . . . . . . . . . . . . . . . . . . 6-33, I-9tow point . . . . . . 4-39, 6-12, 6-14, 7-9, 7-10tow resistance . . . . . . . . . . . . 6-1, G-1, G-3tow rig . . . . . . . . . . . . . . . . . . . . .5-18, 5-26Tow Ship

Design . . . . . . . . . . . . . . . . . . . . . . . 2-1Stern Arrangement . . . . . . . . . . . . . . 2-2

tow sponsor . . . . . . . . . . . . . . . . . . . . . . 5-3tow-and-be-towed . . . . . . . . . . . . . . . . 6-26Tow-and-Be-Towed By Naval Vessels . . 1-4towing . . . . . . . . . . . . . . . . . . . . . . . . . 5-22

stern . . . . . . . . . . . . . . . . . . . . . . . . . 7-9towing alongside . . . . . . . . . . . . . . . .I-5, I-7towing bow . . . . . . . . . . . . . . . . . 4-36, 4-38Towing Bracket . . . . . . 4-5, 4-8, 4-15, 4-16towing bridle . . . . . . . . . . . . . . . . . . . . . . J-6towing command. . . . . . . . . . . . . . . 5-3, 5-5towing delivery . . . . . . . . . . . . . . . . . . . 6-23towing drum . . . . . . . . . . . . . . . . . . . . . 6-32towing hawser . . . . . . .6-24, B-3, B-13, C-1Towing Hawser Log . . . . B-1, B-5, C-1, C-4, . . . . . . . . . . . . . . . . . . . . D-1, D-3, F-1, F-3towing hook. . . . . . . . . . . . . . . 4-17, L-1, L-2towing in ice . . . . . . . . . . . . . . . . . . . . . . 7-5towing machine. . . 4-5, 4-7, 4-36, 4-39, B-5

S-13


towing machine’s automatic. . . . . . . . . . 6-1towing machinery . . . . . . . . . . . . . . . . . . L-1towing on the hip . . . . . . . . . . . . . . 7-15, I-5towing operation . . . . . . . . . . . . . . . . . 7-10towing pad . . . . . . . . . . . . . . . . . . . . . . 6-24towing padeye . . . . . . . . . . . . . . . . H-13, I-4towing pads . . . . . . . . . . . . . . . . . . . . . H-10towing pendant . . . . . . . . . . . . . . . . . . 4-30towing point . . . . . . . . . . . . . . . . . . . . . . L-2towing procedures . . . . . . . . . . . . . . . . 6-24towing rescue. . . . . . . . . . . . . . . . . . . . 5-18towing resistance . . . . . . . . . . . . . . . . . . G-3towing rig . . . . . . . . . . . . 5-5, 5-21, 6-16, I-1towing ship. . . . . . . . . . . . . . . . . . . . . . . 5-2towing speed . . . . . . . . . . . . . . . . . . . . .6-17towing track . . . . . . . . . . . . . . . . . . . . . . 7-8towing watch . . . . . . . . . . . . . . . . . . . . 6-18towline . . 6-33, 7-3, 7-9, B-3, C-1, C-2, D-2

emergency . . . . . . . . . . . . . . . . . . . .6-4secondary . . . . . . . . . . . . . . . . . . . . 6-4

towline pull . . . . . . . . . . . . . . . . . . . . . . . K-3Towline resistance . . . . . . . . 3-3, 3-21, 3-26towline scope . . . . . . . . . . . . . . . . . 6-1, 6-14Towline tension . .3-1, 3-2, 3-4, 3-23, 4-13,. . . . . . . . . . . . . . . 6-1, 6-18, 6-23, 7-11, G-2towpoint . . . . . . . . . . . . . . . . . . . . . . . . 6-15trace . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1traceability . . . . . . . . . . . . . . . B-1, C-1, D-1track . . . . . . . . . . 5-29, 6-17, 6-20, 7-15, I-5tracking . . . . . . . . . . . . . . . . . . . . . . . . 6-16traction machine . . . . . . . . . . . . . . L-1, L-2traction winch . . . . . . . . . . . . . . 2-7, 4-5, 4-8,. . . . . . . . . . . . . . . . . . . . . . L-5, L-6, L-7, L-9trailing buoy . . . . . . . . . . . . . . . . . . . . . .4-5transfer . . . . . . . . . . . . . . . . . . . . . . . . .6-23transferring

freight . . . . . . . . . . . . . . . . . . . . . . . 6-21personnel . . . . . . . . . . . . . . . . . . . .6-21tow . . . . . . . . . . . . . . . . . . . . . 6-23, 7-13

transverse bulkhead . . . . . . . . . . . . . . . H-6trim. . . . . . . 5-9, 6-16, 6-18, 6-29, 7-15, H-4trimmed . . . . . . . . . . . . . . . . . . . . . . . . . 7-8tug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-2tug assistance . . . . . . . . . . . . . . . . . . . . K-8Tug Powering and Bollard Pull . . . . . . . 2-2tugs

assistance . . . . . . . . . . . . . . . . . 6-1, 6-3turnbuckles . . . . . . . . . . . . . . . . . . . . . . H-6two nuts . . . . . . . . . . . . . . . . . . . . . . . . . D-5two-valve protection. . . . . . . . . . . .5-13, H-5

type commander. . . . . . . . . . . . . . . . . . . 5-5typhoons. . . . . . . . . . . . . . . . . . . . . . . . 6-19

UUFB . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4ultraviolet light . . . . . . . . . . . . . . . . . . . . 4-3ultraviolet rays . . . . . . . . . . . . . . . . . . . . C-3uncoiling new hawsers . . . . . . . . . . . . . C-3underrider I-1, I-3, I-4, I-7, I-9, I-10, I-11, I-14underwater projections . . . . . . . . . . . . . . 7-9underway . . . . . . . . . . . . . . . . . . . . . . . . 6-3unmanned tow . . . . . . 5-6, 5-13, 5-22, 6-28unmanned vessels . . . . . . . . . . . . . . . . . 7-4Unreeling . . . . . . . . . . . . . . . . . . . . . . . . B-3unreeling new hawsers . . . . . . . . . . . . . C-3utility boats . . . . . . . . . . . . . . . . . . . . . . . 5-4

Vvane type steering gear . . . . . . . . . . . . 5-18vane-type steering gear . . . . . . . . . . . . 5-20Vectran . . . . . . . . . . . . . . . . . . . . . . . . . C-2vents . . . . . . . . . . . . . . . . . . . . . . . 5-28, H-6vertical rollers . . . . . . . . . . . . . . . 4-37, 4-39Voith-Schneider propeller . . . . . . . . . . . K-6volume . . . . . . . . . . . . . . . . . . R-1, R-2, R-3

WWallis Brake . . . . . . . . . . . . . . . . . . B-5, B-6water brake. . . . . . . . . . . . . . . . . . . . . . . 5-9waterline mark . . . . . . . . . . . . . . . . . . . . 5-9watertight closures . . . . . . . . . . . . 5-21, H-6wave forming resistance . . . . . G-16, G-17,. . . . . . . . . . . . . . . . . . . . . . . . . G-18, G-19wave resistance . . . . . . . . . . G-7, G-8, G-9Wave-induced tension . . . . . . . . . . . . . . 3-5weak link . . . . . . . . . . . . . . . . . . . . . . . 5-28weather . . . . . . . . . . 5-29, 6-18, 6-19, 6-21weather decks . . . . . . . . . . . . . . . . . . . H-6weights and measures . . . . . . . . . . . . . R-1weld . . . . . . . . . . . . . 5-14, 7-10, D-4, H-5wetted surface . . . . . . . . . . . . . . . . . . G-18wildcat . . . . . . . . . . . . . . . . . . . . . . . . . 6-27Williams Target Sled. . . . . . . . . 7-1, 7-2, 7-4wind coefficient . . . . . . . . . . . G-7, G-8, G-9wind drag coefficient. . . . . . . . . . . G-1, G-4Wind resistance . . . . . 3-2, G-2, G-4, G-16,. . . . . . . . . . . . . . . . . . . . G-17, G-18, G-19wind speed . . . . . . . . . . . . . . . . . . G-2, G-4windage area . . . . . . . . G-1, G-2, G-7, G-9wire . . . . . . . . . . . . . . . . . . . . . . . . 4-45, 6-9wire bridle . . . . . . . . . . . 4-29, I-4, I-11, I-12wire clips. . . . . . . . . . . 4-22, 4-29, 6-6, H-11wire hawsers. . . . . . . . . . . . . . . . . B-10, L-2

S-14


wire pendant . . . . . . . . . . . . . . . . . . I-4, 6-7wire rope . . 4-2, 4-7, 4-21, 4-22, 4-30, 4-31,. . . . . . . . . 4-32, 4-33, 5-18, 6-31, B-1, B-3,. . . . . . . . . . . . . . . B-5, B-13, B-15, E-1, F-1

characteristics . . . . . . . . . . . . . . . . B-12installing . . . . . . . . . . . . . . . . . . . . . . B-5measuring . . . . . . . . . . . . . . . . . . . . B-9nomenclature . . . . . . . . . . . . . . . . . B-8procurement . . . . . . . . . . . . . . . . . . B-12termination . . . . . 4-22, B-10, B-12, B-13

wire rope chafing pendant . . . . . . . . . . . J-6wire rope clips . . . . . . . . . . . . . . . . . . . B-13wire rope pendant . . . . . . . . . . . . . 4-1, 4-33wire rope towing hawser . . . . . . . . . . . . 7-6wiring . . . . . . . . . . . . . . . . . . . . . . . H-7, H-8wiring board . . . . . . . . . . . . . . . . . . . . . . 5-8

Xxylene. . . . . . . . . . . . . . . . . . . . . . . . . . . C-3

YYard tugs . . . . . . . . . . . . . . . . . . . . 2-6, 6-5

yaw . . . . . . . . . . . . . . . 3-5, 6-16, 6-17, 7-8YCU . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4YD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4YFNG . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4YFNX . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4YFU. . . . . . . . . . . . . . . . . . . . 5-4, 7-12, H-6yield strength . . . . . . . . . . . . . . . . . . . . D-6YM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4YNG . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4yoke arm steering gear . . . . . . . . . . . . . 5-14YPD . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4YSD . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4YSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4YTB. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6YTBs. . . . . . . . . . . . . . . . . . . . . . . . . . H-13YTL . . . . . . . . . . . . . . . . . . . . . . . . . 2-6, 5-4YTMs . . . . . . . . . . . . . . . . . . . . . . . . . H-13

ZZ-drive propeller . . . . . . . . . . . . . . . . . . K-6ZEBRA, condition . . . . . . . . 5-21, 5-28, H-7

S-15

usn towing manual

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