hm manual

Hydromax

Windows Version 14 User Manual

© Formation Design Systems Pty Ltd 1984 - 2009

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License and Copyright

Hydromax Program © 1985-2009 Formation Design Systems. Hydromax is copyrighted and all rights are reserved. The license for use is granted to the purchaser by Formation Design Systems as a single user license and does not permit the program to be used on more than one machine at one time. Copying of the program to other media is permitted for back-up purposes as long as all copies remain in the possession of the purchaser. Hydromax User Manual © 2009 Formation Design Systems. All rights reserved. No part of this publication may be reproduced, transmitted, transcribed, stored in a retrieval system, or translated into any language in any form or by any means, without the written permission of Formation Design Systems. Formation Design Systems reserves the right to revise this publication from time to time and to make changes to the contents without obligation to notify any person or organization of such changes. DISCLAIMER OF WARRANTY Neither Formation Design Systems, nor the author of this program and documentation are liable or responsible to the purchaser or user for loss or damage caused, or alleged to be caused, directly or indirectly by the software and its attendant documentation, including (but not limited to) interruption on service, loss of business, or anticipatory profits. No Formation Design Systems’ distributor, agent, or employee is authorized to make any modification, extension, or addition to this warranty.

Contents

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Contents

License and Copyright ...................................................................................................... iii Contents ............................................................................................................................. v About this Manual ............................................................................................................. 1 Chapter 1 Introduction....................................................................................................... 3

Input Model ............................................................................................................. 3 Analysis Types ........................................................................................................ 4 Analysis Settings ..................................................................................................... 4 Environment Options............................................................................................... 4 Stability Criteria ...................................................................................................... 5 Output...................................................................................................................... 5

Chapter 2 Quickstart .......................................................................................................... 7 Upright Hydrostatics Quickstart.............................................................................. 7 Large Angle Stability Quickstart............................................................................. 8 Equilibrium Condition Quickstart ........................................................................... 9 Specified Condition Quickstart ............................................................................. 10 KN Values Quickstart............................................................................................ 11 Limiting KG Quickstart......................................................................................... 12 Floodable Length Quickstart ................................................................................. 13 Longitudinal Strength Quickstart .......................................................................... 13 Tank Calibrations Quickstart................................................................................. 14

Chapter 3 Using Hydromax ............................................................................................. 16 Getting Started....................................................................................................... 16

Installing Hydromax.................................................................................... 16 Starting Hydromax ...................................................................................... 16

Hydromax Model................................................................................................... 17 Preparing a Design in Maxsurf.................................................................... 18 Opening a New Design ............................................................................... 21 Opening an Existing Hydromax Design File .............................................. 22 Updating the Hydromax Model................................................................... 23 Hydromax Sections Forming ...................................................................... 24 Checking the Hydromax model................................................................... 27 Setting Initial Conditions ............................................................................ 29 Working with Loadcases............................................................................. 32 Modelling Compartments............................................................................ 44 Forming Compartments .............................................................................. 54 Compartment Types .................................................................................... 58 Sounding Pipes............................................................................................ 59 Damage Case Definition ............................................................................. 61 Key Points (e.g. Down Flooding Points)..................................................... 63 Margin Line Points...................................................................................... 65 Modulus Points and Allowable Shears and Moments................................. 65 Floodable Length Bulkheads....................................................................... 66 Stability Criteria .......................................................................................... 66

Analysis Types ...................................................................................................... 66 Upright Hydrostatics ................................................................................... 68 Large Angle Stability .................................................................................. 70 Equilibrium Analysis .................................................................................. 76 Specified Conditions ................................................................................... 79 KN Values Analysis.................................................................................... 81 Limiting KG................................................................................................ 83 Limiting KG for damage conditions with initially loaded tanks................. 86

Contents

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Floodable Length ........................................................................................ 90 Longitudinal Strength.................................................................................. 93 Tank Calibrations ........................................................................................ 95 Starting and Stopping Analyses .................................................................. 98 Batch Analysis ............................................................................................ 99

Analysis Settings ................................................................................................. 101 Heel ........................................................................................................... 102 Trim........................................................................................................... 103 Draft .......................................................................................................... 105 Displacement............................................................................................. 105 Specified Conditions ................................................................................. 105 Permeability .............................................................................................. 106 Tolerances ................................................................................................. 106

Analysis Environment Options............................................................................ 108 Fluids Analysis Methods........................................................................... 108 Density of Fluids ....................................................................................... 111 Waveform.................................................................................................. 112 Grounding ................................................................................................. 113 Hog and Sag .............................................................................................. 115 Stability Criteria ........................................................................................ 115 Damage ..................................................................................................... 116

Analysis Output ................................................................................................... 116 Reporting................................................................................................... 116 Copying & Printing ................................................................................... 118 Select View from Analysis Data ............................................................... 120 Saving the Hydromax Design ................................................................... 120 Exporting................................................................................................... 121

Chapter 4 Stability Criteria ............................................................................................ 123 Criteria Concepts ................................................................................................. 123

Criteria List Overview............................................................................... 123 Types of criteria ........................................................................................ 126

Criteria Procedures .............................................................................................. 127 Starting the Criteria dialog ........................................................................ 127 Resizing the Criteria dialog....................................................................... 128 Working with Criteria ............................................................................... 128 Editing Criteria.......................................................................................... 130 Working with Criteria Libraries................................................................ 132

Criteria Results .................................................................................................... 134 Criteria Results Table................................................................................ 134 Report and Batch Processing..................................................................... 136

Nomenclature ...................................................................................................... 136 Definitions of GZ curve features............................................................... 136 Glossary..................................................................................................... 139

Chapter 5 Hydromax Reference .................................................................................... 141 Windows.............................................................................................................. 141

View Window ........................................................................................... 141 Loadcase Window..................................................................................... 143 Damage Window....................................................................................... 143 Input Window............................................................................................ 144 Results Window ........................................................................................ 145 Graph Window.......................................................................................... 147 Report Window ......................................................................................... 151

Toolbars............................................................................................................... 154

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File Toolbar............................................................................................... 154 Edit Toolbar .............................................................................................. 154 View Toolbar ............................................................................................ 154 Analysis Toolbar ....................................................................................... 155 Window Toolbar ....................................................................................... 155 Visibility Toolbar ...................................................................................... 155 Render Toolbar.......................................................................................... 155 Edge VIsibility Toolbar............................................................................. 156 Report Toolbar .......................................................................................... 156 View (extended) Toolbar .......................................................................... 156 Extra Buttons ToolbarToolbar .................................................................. 156

Menus .................................................................................................................. 156 File Menu .................................................................................................. 157 Edit Menu.................................................................................................. 158 View Menu................................................................................................ 160 Case Menu................................................................................................. 162 Analysis Menu .......................................................................................... 162 Display Menu............................................................................................ 165 Data Menu................................................................................................. 168 Window Menu........................................................................................... 168 Help Menu................................................................................................. 169

Appendix A: Calculation of Form Parameters............................................................... 170 Definition and calculation of form parameters.................................................... 170

Measurement Reference Frames ............................................................... 170 Nomenclature ............................................................................................ 171 Coefficient parameters .............................................................................. 171 Length ....................................................................................................... 172 Beam ......................................................................................................... 173 Draft .......................................................................................................... 174 Midship and Max Area Sections ............................................................... 175 Block Coefficient ...................................................................................... 175 Section Area Coefficient ........................................................................... 176 Prismatic Coefficient................................................................................. 176 Waterplane Area Coefficient..................................................................... 176 LCG and LCB ........................................................................................... 176 Trim angle ................................................................................................. 177 Maximum deck inclination........................................................................ 177 Immersion ................................................................................................. 178 MTc or MTi............................................................................................... 178 RM at 1 deg............................................................................................... 178

Potential for errors in hydrostatic calculations .................................................... 178 Integration of wetted surface area ............................................................. 179

Reference Designs ............................................................................................... 179 Reference Calculations........................................................................................ 180

Appendix B: Criteria file format.................................................................................... 182 Appendix C: Criteria Help............................................................................................. 184

Parent calculations............................................................................................... 184 Selecting a calculation in a criterion ......................................................... 184 Angle calculators r .................................................................................... 184

Parent Heeling Arms ........................................................................................... 185 Heeling Arm Definition ............................................................................ 186 Parent Heeling Moments........................................................................... 192

Parent Stability Criteria ....................................................................................... 194

Contents

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Criteria at Equilibrium .............................................................................. 194 GZ Curve Criteria (non-heeling arm)........................................................ 196 Heeling arm criteria (xRef) ....................................................................... 212 Heeling arm criteria................................................................................... 212 Multiple heeling arm criteria..................................................................... 224 Heeling arm, combined criteria................................................................. 230 Derived heeling arm criteria...................................................................... 233 Other combined criteria............................................................................. 237 Specific stand alone heeling arm criteria .................................................. 238 Stand alone heeling arm criteria................................................................ 239 Stand alone heeling arm combined criteria ............................................... 239

Appendix D: Specific Criteria ....................................................................................... 242 Dynamic stability criteria .................................................................................... 242

Capsizing moment..................................................................................... 242 Heeling arms for specific criteria - Note on unit conversion............................... 244

IMO Code on Intact Stability A.749(18) amended to MSC.75(69) .......... 244 IMO HSC Code MSC.36(63).................................................................... 246 USL code (Australia) ................................................................................ 248 ISO 12217-1:2002(E)................................................................................ 249 ISO 12217: Small craft – stability and buoyancy assessment and categorisation. ........................................................................................... 251

Appendix E: Reference Tables ...................................................................................... 254 File Extension Reference Table........................................................................... 254 Analysis settings reference table ......................................................................... 255

Index .............................................................................................................................. 256

About this Manual

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About this Manual

This manual describes how to use Hydromax to perform hydrostatic and stability analyses on you Maxsurf design. Chapter 1 Introduction Contains a description of Hydromax functionality and its interface to Maxsurf Chapter 2 Quickstart Gives a quick walk through the analysis tools available in Hydromax. Error! Reference source not found. Explains how to use Hydromax' powerful floatation and hydrostatic analysis routines to best advantage. Chapter 4 Stability Criteria Gives details of the stability criteria that may be evaluated with Hydromax. Chapter 5 Hydromax Reference Gives details of Hydromax' windows and each of Hydromax' menu commands. If you are unfamiliar with Microsoft Windows® interface, please read the owner's manual supplied with your computer. This will introduce you to commonly used terms and the basic techniques for using any computer program.

Chapter 1 Introduction

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Hydromax is a hydrostatics, stability and longitudinal strength program specifically designed to work with Maxsurf. Hydromax adds extra information to the Maxsurf surface model. This includes: compartments and key points such as downflooding points and margin line. Hydromax’ analysis tools enable a wide range of hydrostatic and stability characteristics to be determined for your Maxsurf design. A number of environmental setting options and modifiers add further analysis capabilities to Hydromax. Hydromax is designed in a logical manner, which makes it easy to use. The following steps are followed when performing an analysis:

• Input model

• Analysis type selection

• Analysis settings

• Environment options

• Criteria specification and selection

• Run analysis

• Output Hydromax operates in the same graphical environment as Maxsurf; the model can be displayed using hull contour lines, rendering or transparent rendering. This allows visual checking of compartments and shows the orientation of the vessel during analysis.

Input Model

Maxsurf design files may be opened directly into Hydromax, eliminating the need for time-consuming digitising of drawings or hand typing of offsets. This direct transfer preserves the three-dimensional accuracy of the Maxsurf model. Tanks can be defined and calibrated for capacity, centre of gravity and free surface moment. Tanks and compartments can be flooded for the purpose of calculating the effects of damage. A number of loadcases can be created. The loadcase allows static weights and tank-fillings to be specified and calculates the corresponding weights and centres of gravity as well as the total weight and centre of gravity of the vessel under the specified loading condition. Loadgroups may also be created and cross referenced into loadcases. Other input consists of: tank sounding pipes; key points, such as downflooding points, immersion and embarkation points; margin lines and section modulus.


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Analysis Types

Hydromax contains the following analysis tools: • Upright hydrostatics

• Large angle stability

• Equilibrium analysis

• Specified Condition analysis

• KN values and cross curves of stability

• Limiting KG analysis

• Floodable Length analysis

• Longitudinal Strength analysis

• Tank Calibrations Although common analysis settings are used where possible, different analyses may require different settings. For example: the upright hydrostatics analysis simply requires a range of drafts; whereas the longitudinal strength analysis requires a detailed load distribution. The analysis settings for each analysis type are explained in detail in the analysis synopsis below.

Analysis Settings

The analysis settings describe the condition of the vessel to be tested. For example, a range of drafts in the case of upright hydrostatics, or a range of heel angles for a large angle stability analysis. The following analysis settings are available:

• Heel

• Trim

• Draft

• Displacement

• Permeability

• Specified condition The analysis settings are specified prior to running the analysis. Settings that are not relevant to the selected analysis type are greyed out in the Analysis menu.

Environment Options

Environmental options are modifiers that may be applied to the model or its environment that will affect the results of the hydrostatic analysis.


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Depending on the analysis being performed, different environmental options may be applied to the Hydromax:

• Type of Fluid Simulation

• Density (of fluids)

• Wave form

• Grounding

• Hogging and sagging

• Intact and Damage condition

Stability Criteria

Hydromax has the capability to calculate compliance with a wide range of stability criteria. These criteria are either derived from the properties of the stability curve calculated from a Large Angle Stability analysis or from the vessel’s orientation and stability properties calculated from an Equilibrium analysis. Limiting KG and Floodable length analyses also use stability criteria. Hydromax has an extensive range of stability criteria to determine compliance with a wide range of international stability regulations. In addition, Hydromax has a generic set of parent criteria from which virtually any stability criterion can be customized.

Output

Views of the hull are shown for each stage of the analysis, complete with immersed sectional areas and actual waterlines. The centres of flotation, gravity and buoyancy are also displayed. Heeled and trimmed hullforms and water plane shapes may be printed. Results are stored and may be reviewed at any time, either in tabular form, or as graphs of the various parameters across the full range of calculation. All results are accumulated in the Report window (which can be saved, copied and printed), or output directly to a Word document. The criteria checks are summarised in tables listing the status (pass/fail) of each criterion as well as the margin. The criterion settings and intermediate calculation data may also be displayed if required. For a brief overview of the different analysis that Hydromax has available, continue reading Chapter 2 Quickstart.

Chapter 3 Using Hydromax

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Chapter 2 Quickstart

This chapter will briefly describe each analysis type and its output. For each analysis type, a list of the required settings as well as the available environment options is given. Hydromax contains the following analysis types

• Upright Hydrostatics

• Large Angle Stability

• Equilibrium Condition

• Specified Condition

• KN Values

• Limiting KG

• Floodable Length

• Longitudinal Strength

• Tank Calibrations Each analysis has different settings that may be applied

• Heel

• Trim

• Draft

• Displacement

• Specified condition

• Permeability

• Loadcase

• Tank and compartment definition

Hydromax offers different environment options that may be applied to the analyses • Fluid Densities

• Treatment of fluids in tanks: fluid simulation or corrected VCG

• Wave form

• Grounding

• Hog and sag

• Damage Hydromax offers an extensive range of stability criteria that are applicable to equilibrium, large angle stability, limiting KG and Floodable length analysis. Error! Reference source not found. will describe each of the analysis types, settings and environment options in more detail.

Upright Hydrostatics Quickstart

For Upright Hydrostatics, heel is fixed at zero heel, trim is fixed at a user defined value and draft is varied in fixed steps. Displacement and centre of buoyancy and other hydrostatic data are calculated during the analysis.


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Upright hydrostatics requirements • Range of drafts to be analysed

• VCG (for calculation of some stability characteristics such as GMt and GMl only)

• Trim Upright hydrostatic options

• Fluid Densities

• Wave form

• Hog and sag

• Damage

• Compartment definition (in case of damage) The results are tabulated and graphs of the hydrostatic data, curves of form and sectional area at each draft are available. For more detailed information please see: Upright Hydrostatics on page 68.

Large Angle Stability Quickstart

For the analysis of Large Angle Stability, displacement and centre of gravity are specified in the loadcase. A range of heel angles are specified and Hydromax calculates the righting lever and other hydrostatic data at each of these heel angles by balancing the loadcase displacement against the hull buoyancy and, if the model is free-to-trim, the centre of gravity against the centre of buoyancy such that the trimming moment is zero. Large angle stability requirements

• Range of heel angles to be analysed

• Trim (fixed or free)

• Loadcase or loadgroup

• Tank definition in the case of tank loads being included in the Loadcase (and/or for the definition of damage)

Large angle stability options

• Fluid Densities


• Wave form

• Hog and sag

• Damage

• Compartment definition (in case of damage)

• Key points

• Margin line and deck edge

• Analysis of stability criteria


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The key output value is GZ (or righting lever), the horizontal distance between the centres of gravity and buoyancy. A graph of these values at the various heel angles forms a GZ curve. Various other information is often overlaid on the GZ curve, including upright GM, curves for wind heeling and passenger crowding levers and the angle of the first downflooding point. These additional data depend on which (if any) stability criteria have been selected. A number of other graphs may be selected from the pull-down list in the graph window. Remember that you can access this data in tabular form by double clicking in the graph window:

• Dynamic stability curve (Area under GZ curve, integrated from upright)

• Variations of other hydrostatic and form parameters may be plotted against heel angle.

• Maximum safe steady heel angle

• The sectional area curve at each of the heel angles tested may also be displayed. Note that some of these graphs have parameters that may be adjusted in the Data Format dialog If large angle stability criteria have been selected for analysis, these results will also be reported in the criteria results table and they may lead to additional curves being displayed on the GZ curve. Downflooding angles for any key points, margin line and deck edge will also be computed and tabulated. For more detailed information please see: Large Angle Stability on page 70.

Equilibrium Condition Quickstart

Equilibrium Analysis uses the Loadcase, to calculate the displacement and the location of the centre of gravity. Hydromax iterates to find the draft, heel and trim that satisfy equilibrium and reports the equilibrium hydrostatics and a cross sectional areas curve. Equilibrium analysis requirements

• Loadcase or loadgroup


• Compartment definition and damage case (in case of damage) Equilibrium analysis options


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• Fluid Densities


• Wave form

• Hog and sag

• Grounding

• Damage


• Key points

• Margin line and deck edge

• Analysis of equilibrium criteria Equilibrium analysis result table lists the hydrostatic properties of the model. If a wave form has been specified there will be a number of columns; each column contains the results for a different position of the vessel in the wave as given by the wave phase value. The sectional area curve is also calculated, as is the freeboard to any defined key points, margin line and deck edge. Any equilibrium criteria will also be evaluated and their results reported. For more detailed information please see: Equilibrium Analysis on page 76.

Specified Condition Quickstart

In the specified condition each of the three degrees of freedom, for which the hydrostatic properties of the model are to be calculated, can be set. Specified Condition Requirements

• Specified Conditions Input Dialog

If fixed trim is specified, you may enter the trim or specify the forward and aft drafts (these are at the perpendiculars as specified in the Frame of Reference dialog). Specified Conditions options


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• Fluid Densities

• Wave form

• Hog and sag

• Damage

• Tank and Compartment definition (in case of damage) The output for the specified condition consists of a curve of cross sectional areas and hydrostatics of the vessel in the specified condition. For more detailed information please see Specified Conditions on page 79.

KN Values Quickstart

KN values or Cross Curves of Stability are useful for assessing the stability of a vessel if its VCG is unknown. They may be calculated for a number of displacements before the height of the centre of gravity is known. The KN data may then be used to obtain the GZ curve for any centre of gravity height (KG) using the following formula:

GZ = KN - KG * sin(Heel) where GZ is the righting lever measured transversely between the Centre of Buoyancy and the Centre of Gravity, and KG is the distance from the baseline to the vessel's effective Vertical Centre of Gravity. KN Values Analysis Requirements

• Range of displacements to be analysed



• Estimate of VCG (provides more accurate result if free-to-trim)

• TCG (if required) KN Values Analysis Options

• Fluid Densities

• Wave form

• Hog and sag

• Damage

• Tank and Compartment definition (in case of damage) Output is in the form of a table of KN values and a graph of Cross Curves of Stability. If the analysis is performed free-to-trim and an estimate of the VCG is known, this may be specified. The computed KN results will then give a more accurate estimate of GZ for KG close to the estimated VCG since the effects of VCG on trim have been more accurately accounted for. For more detailed information please see KN Values Analysis on page 81.


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Limiting KG Quickstart

The Limiting KG analysis may be used to obtain the highest vertical position of the centre of gravity (maximum KG) for which the selected stability criteria are just passed. This may be done for a range of vessel displacements. At each of the specified displacements, Hydromax runs several Large Angle Stability analyses at different KGs. The selected stability criteria are evaluated; the centre of gravity is increased until one of the criteria fails. Limiting KG Analysis Requirements




• Stability criteria for which limiting KG is to be found

• TCG (if required) Limiting KG Analysis Options

• Fluid Densities

• Wave form

• Hog and sag

• Damage

• Tank and Compartment definition (in case of damage)

• Laodcase (in case of initial loading of damaged tanks)

• Key points (if required for criteria)

• Margin line and deck edge (if required for criteria) A graph of maximum permissible GZ plotted against vessel displacement is produced as well as tabulated results indicating which stability criteria limited the VCG. If limiting curves are required for each of the stability criteria individually, this may be done in the Batch Analysis mode. A check will be made to ensure that any selected equilibrium criteria are passed, however at least one large angle stability criterion is required. Only relevant criteria will be used, i.e. if a damage case is chosen, only damage criteria will be evaluated; if the intact condition is used, only intact criteria will be evaluated. Some criteria, such as angle of maximum GZ, are very insensitive to VCG and may prevent the analysis converging. If the analysis is unable to converge for a certain displacement this will be noted and the next displacement tried. For more detailed information see Limiting KG on page 83.


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Floodable Length Quickstart

This analysis mode is used to compute the maximum compartment lengths based on user-specified equilibrium criteria. Floodable Lengths may be computed for a range of displacements; the LCG may be specified directly or calculated from a specified initial trim. In addition a range of permeabilities may be specified. The VCG is also required to ensure accurate balance of the CG against the CB at high angles of trim. As well as the standard deck edge and margin line immersion criteria (one of which must be specified) the user can also add criteria for maximum trim angle and minimum required values of longitudinal and transverse metacentric height. Floodable Length Analysis Requirements


• VCG

• Range of permeabilities to be analysed

• Trim (free- to- trim to either initial trim or specified LCG)

• Floodable length criteria to be tested

• Margin line and deck edge (required for criteria) Floodable Length Analysis Options

• Fluid Densities

• Wave form

• Hog and sag The output is in the form of tabulated Floodable Lengths for each displacement and permeability. The data is tabulated for each of the stations as defined in Maxsurf. The data is also presented graphically. For more detailed information please see Floodable Length on page 90.

Longitudinal Strength Quickstart

Hydromax calculates the net load from the buoyancy and weight distribution of the model. That data is then used to calculate the bending moment and shear force on the vessel. Longitudinal Strength Analysis Requirements


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• Loadcase (including distributed loads if required)


• Compartment definition and damage case (in case of damage) Longitudinal Strength Analysis Options

• Fluid Densities

• Treatment of fluids in tanks: fluid simulation is always used for Longitudinal Strength analysis

• Wave form

• Hog and sag

• Grounding

• Damage


• Allowable shear and bending moment The longitudinal strength graph and tables contain all information on weight and buoyancy distribution, the shear force and bending moment on the vessel. If defined, graphs of allowable shear and bending moment are superimposed on the graph. For more detailed information please see Longitudinal Strength on page 93.

Tank Calibrations Quickstart

Tanks can be defined and calibrated for capacity, centre of gravity and free surface moment (FSM). Fluid densities and tank permeabilities can be varied arbitrarily. Tank calibrations are for the upright (zero heel) vessel, but the vessel's trim may be specified. Hydromax uses its fluid simulation mode to calculate the actual position of the fluids in the tanks, taking into account the vessel trim. Tank ullages are measured from the top of the sounding pipe to the free surface of the liquid within the tank along the sounding pipe and in a similar manner, soundings are measured from the bottom of the sounding pipe to the free surface. Tank calibration analysis requirements

• Tank definitions

• Sounding pipe definition (if required)

• Sounding intervals for calibration levels

• Trim Tank calibration analysis options

• Fluid Densities

• Treatment of fluids in tanks: fluid simulation always selected

• Hog and Sag

• Damage: Intact case always selected For each tank, a table of capacities, volumes etc. is calculated. These results are presented in both tabular and graphical forms.


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For more detailed information please see Tank Calibrations on page 95.


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This chapter describes • Getting Started

• Hydromax Model

• Analysis Types

• Analysis Settings

• Analysis Environment Options

• Analysis Output

Getting Started

This section contains everything you need to do to start using Hydromax • Installing Hydromax

• Starting Hydromax

Installing Hydromax

Install Hydromax by inserting the CD and running the Setup program, then follow the instructions on screen.

Note: Before installing any program from the Maxsurf suite for the first time, please read the purchase letter (also referred to as installation manual).

Starting Hydromax

After installation, Hydromax should be accessible through the Start Menu. Simply select Hydromax from the Maxsurf menu item under Programs in the Start menu.

Windows Registry

Certain preferences used by Hydromax are stored in the Windows registry. It is possible for this data to become corrupted, or you may simply want to revert back to the default configuration. To clear the Hydromax preferences, start the program with the Shift key depressed. You will be asked if you wish to clear the preferences, click OK, doing this will reset all the preferences. The following preferences are stored in the registry:


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• Colour settings of contours and background

• Fonts

• Window size and location

• Size of resizing dialogs (alternatively, these may be reset by holding down the shift key when activating them)

• Density of fluids

• Heel angles for large angle stability, KN and Limiting KG analyses

• Permeabilities for floodable length analysis

• Location of files

• Units for data input and results output

• Convergence tolerance (Error values)

• Maximum number of loadcases

• Reporting preferences

Note: The default density for the fluid labelled "Sea Water" is stored in the windows registry. All hydrostatic calculations use this. Check the density of seawater after resetting your preferences. It is recommended to save your customized densities with your project using the File | Save Densities As command.

Hydromax Model

This section describes how to open a Maxsurf model in Hydromax and provides some important information to ensure that your model is correctly interpreted by Hydromax.

• Preparing a Design in Maxsurf

• Opening a New Design

• Opening an Existing Hydromax Design File

• Updating the Hydromax Model

• Hydromax Sections Forming

• Checking the Hydromax model After checking the Hydromax model, the next step is to check the Hydromax settings and initial analysis conditions.

• Setting Initial Conditions Depending on the analysis performed, you may need to set up the following additional model data:


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• Working with Loadcases

• Modelling Compartments

•

• Forming Compartments

• Compartment Types

• Damage Case Definition

• Sounding Pipes

• Key Points (e.g. Down Flooding Points)

• Margin Line Points

• Modulus Points and Allowable Shears and Moments

• Stability Criteria

Preparing a Design in Maxsurf

There are several important checks that must be carried out in Maxsurf before opening a design in Hydromax:

• Setting the Zero Point

• Setting the Frame of Reference

• Surface Use

• Skin Thickness

• Outside Arrows

• Trimming

• Coherence of the Maxsurf surface model

Setting the Zero Point

Ensure that the zero point is correctly setup in Maxsurf. A consistent zero point and frame of reference should be used for the model throughout the Maxsurf suite. In Hydromax you have the option of displaying longitudinal measurements such as LCB or LCF from the model zero point or amidships.

Setting the Frame of Reference

It is vital that the Frame of Reference is correctly setup in Maxsurf before attempting to analyse the model in Hydromax. The Frame of reference should not be changed in Hydromax. The frame of reference defines the fore and aft perpendiculars, the baseline and the datum waterline; midships is automatically defined midway between the perpendiculars. By convention, in the profile and plan views, the vessel’s bow is on the right. The perpendiculars define the longitudinal positions of the vessel’s draft marks and cannot be coincident. The base line is the datum from which the drafts and KG are measured.

Surface Use

In Maxsurf you can choose between two types of surface use

Hull Hull surfaces are used to define the watertight envelope of the hull.


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Internal structure Internal structure surfaces are used for all other surfaces (any surfaces which do not make up the watertight envelope) and also surfaces which are to be used in Hydromax to define the boundaries of tanks and compartments that have complex shapes.

The following table describes the difference between each surface use in Hydromax: Included: Hull Shell Internal

Structure Hydrostatic sections

Selection of tank/compartment boundaries Skin thickness applied to the surface

Verify that all surfaces that are to be used as tank/compartment boundaries are defined as Internal Structure. If a surface is defined as internal structure, it is not included as part of the hull shell by Hydromax, i.e. internal surfaces will be ignored in the forming of hydrostatic sections.

Skin Thickness

If skin thickness is to be used in hydrostatic calculations, ensure that the thickness and projection direction have been specified for the hull shell surfaces. Thickness can be specified differently for each hull surface, resulting in more accurate hydrostatics. To activate skin thickness in Hydromax ensure that the “Include Skin Thickness” option is selected when reading the file or calculating the hull sections.

Note Tank boundaries made from internal structures surfaces do not have skin thickness. To include skin thickness, the internal structure surface should be placed to model the inside of the tank if the tank wall has significant thickness.

Skin thickness for hull surfaces will be treated so that the hull sections go to the outside of the plate whilst any tanks are trimmed to the inside of the plate.

Outside Arrows

The surfaces’ outside arrows define the orientation of the surfaces. Ensure that you have used the Outside Arrows command from the Maxsurf Display menu to define which direction points outwards (towards the seawater) for each surface. The surface direction may be flipped by clicking on the end of the arrow.

Trimming

Ensure that all surfaces are trimmed correctly. At any longitudinal position on the hull, you should have completely closed transverse sections or sections with at most one opening (e.g. the deck).


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Correct Section with no opening.

Correct section with one opening: this section will be closed across the top.

Also see:

Hydromax Sections Forming on page 24 Checking the Hydromax model on page 27

Coherence of the Maxsurf surface model

Hydromax will generally have no problem correctly interpreting your design as long as the following requirements for the Maxsurf model are observed:

• Make sure that each surface touches its adjacent surfaces at its edge, preferably by bonding the edges together

• Where surfaces intersect, trim away the excess regions of the surface; e.g. the part of the keel that is inside the hull and the part of the hull that is inside the keel

• Do not have surfaces that cannot be closed in an unambiguous fashion, i.e. a maximum of one gap in a transverse section through the hull.

• Remember that the inner portions of each intersecting contour will be trimmed off

• Check surface use; internal structure surfaces are ignored when forming the hull sections in Hydromax

Note: For groups internal structure surfaces that will be used to define tank (or compartment boundaries) the same requirements apply.

Also see: Checking the Hydromax model on page 27.


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Opening a New Design

File opening in Hydromax is window specific, i.e. Hydromax will automatically look for compartment definition files when you are in a Compartment Definition window and a loadcase in a Loadcase window. To open a design for analysis, ensure that the design view window is active, then select Open Design from the File menu. Choose a Maxsurf design file (.msd). The following dialog will appear:

Calculate new Sections

Choosing Calculate Sections will calculate the specified number of sections through the hull. These will then be used for the Hydrostatics calculations. The meaning of (ignore existing data, if any) is explained in Opening an Existing Hydromax Design File.

Include Plating Thickness

At this stage, any surface thickness specified in the Maxsurf Surface Properties dialog may be included.

Use Trimmed Surfaces

If the Maxsurf model has trimmed surfaces, the Use Trimmed Surfaces item should be ticked.

Stations

When calculating stations, you may select how many stations should be used. Reducing the number of stations will speed up the analysis time but reduce the accuracy, conversely increasing the number of stations will increase the analysis time but lead to higher accuracy results. The first option allows you to use the station grid created in Maxsurf. This is extremely useful for hulls that have features such as keels or bow thrusters that need to be accurately modelled and may need a locally denser station spacing to do so. It also allows designs with significant longitudinal discontinuities in their sectional areas to have stations specified either side of the discontinuity, avoiding any errors inherent in the integration of evenly spaced stations. For example, if it was known that a design had a significant discontinuity in its sectional area curve at amidships, by specifying one station 1mm aft of amidships and one station 1mm forward of amidships this discontinuity can be modelled very accurately. The upper limit for the number of stations is 200.


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Surface Precision

The Surface Precision options has two functions: • Setting for calculating the hydrostatic sections

• Setting used to form new compartments or tanks. The precision at which the design was saved in Maxsurf is included in the Maxsurf design file (.msd). Hydromax recognises this precision setting and will and set the Surface Precision button accordingly.

Note: Maxsurf surface trimming information may vary for different precisions. Therefore it is recommended not to change the precision setting when opening the Maxsurf design file in Hydromax.

Note: The accuracy of the results depends much more on the number of sections than the accuracy at which the sections are calculated. Reducing the precision of the sections can greatly improve performance, usually at relatively small impact on the accuracy of the hydrostatics.

Opening an Existing Hydromax Design File

After saving the Maxsurf design file for the first time in Hydromax, a “Hydromax Design file” (.hmd) is created. The Hydromax design file will consist of the hydrostatic sections and all input data such as loadcases, compartment definition, key points, sounding pipes etc. Hydromax also allows saving of all input and output files into individual files. To open an existing design, there are two options:

• Double click on the .hmd file from any Windows explorer window

• Use the Hydromax Open command form the file menu and select the .msd file


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An existing Hydromax design consists of a number of files with different file extensions.

When Hydromax opens a .msd file, it will look for a .hmd file with the same name as the .msd file. For example: when opening OSV.msd, the OSV.hmd file is found. The Calculate Sections dialog now has the option to read the sections from the file.

Ø Ensure “Read existing data and sections” is selected and click OK.

Hydromax will now open the .hmd file. This contains hydrostatic sections information and all input information from last time the .hmd file was saved, i.e. compartment definitions, loadcases, damage cases, key points etc.

Notes: 1) When selecting “Read existing data and sections (do not update geometry)” the Maxsurf surface information is not recalculated. This means that changes to the hull shape in the Maxsurf Design file, are not automatically incorporated. You will load your existing sections, loadcases and compartment definitions etc. See: Updating the Hydromax Model on page 23 for more information. 2) Calculate new sections (ignore existing data, if any) means that Hydromax will recalculate the hull sections and ignore any data stored in the .hmd file. You will have to reload your individual loadcases and compartment definition files etc after you have selected this option and pressed OK. Do not choose this option if you wish to keep the additional Hydromax data and you have not yet saved them as individual files as if the model is saved in Hydromax the .hmd file will be overwritten and any existing data lost. For more information on file properties and extensions in Hydromax, please see: File Extension Reference Table on page 254.

Updating the Hydromax Model

To update the hydrostatic sections to the latest Maxsurf Design File, select “Recalculate Hull sections” in the analysis menu after reloading the Maxsurf Design File with the “read existing data and sections from file” option selected. This function can also be used to include/exclude surface thickness or change the number of sections and to change use/not use trimmed surfaces without reloading the Maxsurf Design File. The “Recalculate Hull Sections” command recalculates Hull surfaces as well as Tank Boundary surfaces (Internal Structure surfaces in Maxsurf). Any tanks and loadcases will also be updated with this command.


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Note: Changes to the Maxsurf design are only recalculated after the new Maxsurf design has been re-loaded into Hydromax. This means that if the model is simultaneously being edited in Maxsurf and Hydromax, it is necessary to: 1) save and close the model in Hydromax 2) save in Maxsurf 3) open in Hydromax, using “Read existing data and sections” to make sure the loadcase, compartment definition etc remain part of the Hydromax design file. 4) use the “Recalculate Hull Sections” from the analysis menu.

Hydromax Sections Forming

Hydromax works by applying trapezoidal integration to data calculated from a series of cross sections taken through the Maxsurf model surfaces. Hydromax will automatically form these sections, called “Hydromax sections”, “hydrostatic sections” or just “sections”. Hydromax deals only with sections that are completely closed, or can be unambiguously closed. This section outlines the section forming process used in Hydromax and may be helpful when preparing a Maxsurf design for Hydromax. Whilst it is always preferable to give Hydromax a completely closed model with no ambiguities, Hydromax will try to resolve any problems with the model definition in the manner outlined in the following sections.

Note: The golden rule is that for any longitudinal position, the section must be made up of closed, non-intersecting (and non-self-intersecting) contours. In practice, one opening is acceptable and this will be automatically closed with a straight line.

Furthermore, contours cannot be contained wholly within another contour.

The same is true for groups of internal surfaces that have been selected to define a tank boundary.

Where a section consists of an open shell (e.g. a hull surface with no deck), Hydromax will automatically close the section with a straight line connecting the opening ends.

If, however, the section is made up of two line segments, (e.g. having both a gap at the centreline as well as an open deck), an ambiguity exists as to how the two line segments will be connected. This is not an acceptable shape.


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In the example above, if either the top or bottom gap had been closed in Maxsurf the design would cease to be ambiguous. Multiple surfaces that are trimmed correctly, bonded together or use compacted control points will not cause any problems when opened in Hydromax. Hydromax will form a closed section through multiple surfaces by linking the curve segments together.


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A section through a multihull containing a single closed contour

A section comprising two closed contours

Hydromax will link curve segments together if they are only separated by a small amount. The user cannot change these tolerances, because there are too many dependencies in the program. Where surfaces intersect, Hydromax will make an attempt to remove excess portions of the curve to form a single continuous contour. However this is not always possible so it is much better practice to trim the model correctly manually.

Ambiguous Sections (e.g. decks, bulwarks)

A common example of ambiguous sections is a model with multiple decks. Hydromax will have difficulties distinguishing the intended main deck.

Hydromax closes the outside contour and trims remnants


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The example above has bulwarks; generally these will be treated correctly by Hydromax and removed, but this depends on the height of the bulwark relative to the rest of the section. To prevent ambiguities it is recommended to trim the bulwark in Maxsurf. If the bulwark’s volume is expected to influence the hydrostatic calculations, the bulwark’s volume has to be properly modelled in Maxsurf by modelling both the outside and the inside of the bulwark.

Checking the Hydromax model

Before starting any analysis you should check whether Hydromax has been able to correctly interpret your design. The following tools are available to validate the Hydromax model.

• Show Single Hull Section

• Checking the Sectional Area Curve

• Using Rendering to Check the Model

Note: Sections that are not formed correctly cause the majority of problems with Hydromax models. Therefore, checking your sections after opening the design in Hydromax is strongly recommended. Incorrect sections in the model will give incorrect results. These sections should be continuous with no gaps and no unexpected lines. In particular, look closely at intersections between surfaces to make sure that Hydromax has interpreted the shape correctly.

Show Single Hull Section

In the body plan view, you can step through the sections one-by-one to verify that they have been correctly calculated. This is done by selecting Show Single Hull Section in Body Plan view from the Display menu. You can then click in the inset box to view the sections, the left and right arrow cursor keys will enable you to step through the sections one-by-one. This works the same as the Maxsurf body plan window and is an extremely powerful tool to validate your Hydromax model. For more information see the Maxsurf manual.


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Checking the Sectional Area Curve

Another way of checking the Hydromax model is to perform a specified condition analysis at quite deep draft and look carefully at the sectional area curve in the graph window. If this displays any unexpected spikes or hollows Hydromax may not have correctly interpreted the hull shape. This is not a foolproof method since it does not necessarily highlight problems in the non-immersed part of the hull.

This Cross Sectional Area curve indicates there may be a problem with section forming from 12 m to 16 m.

Using Rendering to Check the Model

The model may also be rendered, which makes it easier to see if there are any areas of the model which have not been properly defined. Select Render from the Display menu whilst in the perspective view and turn on the sections:


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Note: In rare instances incorrect rendering may occur. This does not necessarily mean that the model is incorrect. As long as the sections are formed correctly, the model is correct.

Setting Initial Conditions

All Hydromax calculations are performed in the frame of reference of the model. Hydromax uses the aft perpendicular and forward perpendicular together with the baseline and the zero point for all calculations and gives the results in the units specified in the display menu.

Note: Before you run any analysis using Hydromax, it is important that you set up the required initial conditions for the design.

Coordinate System

Hydromax uses the Maxsurf coordinate system:

Longitudinal +ve forward -ve aft Transverse +ve starboard -ve port Vertical +ve up -ve down


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View window View direction Body plan From the stern, looking fwd Plan From above, Port side above the centreline (this

the opposite direction to Maxsurf) Profile From Starboard, bow to the right.

Frame of Reference and Zero Point

It is essential that a frame of reference be specified. This should be done in Maxsurf and not in Hydromax. Draft and trim are measured on the forward and aft perpendiculars. If these are not in the correct positions, some analysis results will be meaningless or may even fail to complete. See: Setting the Zero Point and Setting the Frame of Reference on page 18.

Note: Changing the zero point in Maxsurf will not update the compartment definition, loadcase and other input values. Changing the zero point after you have started analysing the model in Hydromax is not recommended.

Customising Coefficients

In Hydromax you may choose between the length between perpendiculars and the waterline length for the calculation of Block, Prismatic and Waterplane Area Coefficients. You may also select the draft, beam and sectional area to be used for calculation of these coefficients. The LCB and LCF can be displayed in the Results windows relative to the specified Zero Point, Amidships location, Aft Perpendicular, Fwd Perpendicular or from the Aft, Middle or fwd end of the actual waterline. You can also specify whether you want the forward (towards the bow) or the aft (towards the stern) to have a positive sign. Finally you can chose whether you want the LCB and LCF to be displayed as a length or as a percentage of the waterline or LPP length as specified in the Length for Coefficients.


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Data | Coefficients dialog

Setting Units

The units used may be specified using the Units command. In addition to the length and weight (mass) units, units for force and speed (used in wind heeling and heeling due to high-speed turn etc. criteria) and the angular units to be used for areas under GZ curves, may also be set. The angular units for measuring heel and trim angles are always degrees. Units may be changed at any time.

Other Initial Conditions

See:


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Fluids Analysis Methods on page 108 Density on page 111

Working with Loadcases

Loadcases define the loading condition of the vessel. Static weights that make up the vessel lightship are specified here as well as tank filling levels, expressed as either a percentage of the full tank capacity or as a weight. Loadcases automatically contain all the tanks defined in the Tank definition. Loadgroups are special loadcases that contain no tanks. These may be used to define groups of fixed weights (such as the steel weight or lightship weight) in a single location which may then be cross-referenced into a loadcase. Any changes to the loadgroup are then automatically incorporated into any loadcases that reference them. A loadgroup is included in a loadcase simply by specifying the loadgroup name in the “Item Name” column. The loadcase will normally update the column totals automatically as weights or tank loadings are changed. The exception to this is if tanks have not yet been formed or the vessel is still rotated from the result of an analysis. If the loadcase does not update, click on the update Loadcase button and ensure that the hull is at the DWL by selecting “Set vessel to DWL”:

Creating a new Loadcase File

To create a load case, switch to the loadcase view by selecting Loadcase from the Loadcase sub-menu in the Window menu. Then select “New Load Case” from the File menu or press Ctrl+N. A new load spreadsheet will be displayed in the Loadcase window. The default loadcase will contain a lightship entry and an entry for each tank (with a default filling of 50%).


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The tabs in the bottom of the window can be used to skip through the different loadcases in the design.

Create New Loadcases based on Template

To avoid rework, an existing loadcase may be used as a template when creating a new loadcase. To do this,

Ø In the loadcase window, select the Loadcase you wish to use as a template

Bring the loadcase you wish to use as a template to the front for example by clicking on the tab on the bottom

Ø select File | New

First, you will be asked for a new Loadcase name after which the following dialog appears:


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A new loadcase will appear in one of the blank (…) loadcase tabs. If there are no blank tabs left, you will either have to close an existing loadcase, or add more loadcases using the Case | Max. Number of Loadcases command.

Note The template is only used during the creation of the loadcase. Once a loadcase has been created from a template loadcase, changes made in the template are NOT automatically changed in the loadcase derived from it.

Naming and Saving a Loadcase

A loadcase can be given any name by saving it to a separate file where the loadcase filename will be used as the loadcase name and displayed on the tab in the loadcase window. Alternatively,

Ø Select Edit Loadcase from the Case menu

Ø Changing the name in the Loadcase Properties dialog.

The next time you use the File | Save Loadcase command you will be asked to confirm the loadcase file name.

Loading a Saved Loadcase

You can load a saved loadcase into your loadcase window by:

Ø Select an empty tab in the loadcase window that you wish to load the loadcase into

Empty tab.

If there are no empty tabs, you should either increase the maximum number of loadcases (see below), or close an existing loadcase.

Ø Select File | Open Load Case


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Ø Select the .hml file you wish to open.

Setting the Maximum Number of Loadcases

The maximum number of loadcases (up to twenty-five) that can be loaded in Hydromax at any one time is set by selecting “Max. Number of Loadcases” from the Case menu. You may then enter the maximum number of load cases you require.

You must restart Hydromax for this change to take effect. In most cases, you will only need to set this once to the maximum number of loadcases you are ever likely to use. For convenience of use, a sensible number is recommended. Each loadcase can be selected and used for analysis. Each may be saved and loaded independently, effectively allowing you as many loadcases as you require.

Note: When loading a design that has more loadcases than the maximum you have currently set in Hydromax, you will receive a warning and the file will not be loaded. You must increase the maximum number of allowable loadcases and restart Hydromax before you can load the design.

Closing a Loadcase

Ø Select the tab of the loadcase you wish to close in the Loadcase window

Ø Select File | Close Load Case

Adding and Deleting Loads

To add an extra load to the loadcase,

Ø Select Add Load from the Edit menu or press Ctrl+A.

A new load will be inserted into the table above the currently selected row. You can repeat this process for as many loads as you wish. If you want to remove a load from the table, simply click anywhere in the row you want to remove, and choose Delete Load from the Edit menu (or highlight the complete row by clicking the grey cell to the left of the row and press the Delete key). If you wish to delete several loads simultaneously, click and drag so that all of the loading rows that you wish to delete are selected, then select Delete Load.

Editing Loads

Click on the cell containing the load name and type in a name for this load, for example "Lightship", and press the Tab key to go to the next column in the table (or simply click directly in the cell you wish to edit). For each item in the list you can specify a quantity. This is used to calculate the total weight of that item. For example: if the item was “crew” with a weight per unit, you could specify the quantity and unit weight, and the total weight of crew would be automatically calculated. The weight of each item should be entered in the next column.


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The weight must always be positive. If for some reason you wish to have an upward (negative) load, you can do so by entering a negative quantity – this can be useful if you want to apply a pure moment to the model by applying equal magnitude, but opposite sign loads to the vessel in the loadcase. Tab to the next column and enter the horizontal lever for the item. After you type in this number, press enter and the total LCG will be automatically re-calculated and displayed in the bottom row of the table. The CG position will also be shown and updated in the View windows if Large Angle Stability, Longitudinal Strength or Equilibrium analysis are selected.

Note: Levers, as with all other measurements in Hydromax, are measured from the Zero Point.

Loadcase Sorting

A number of tools are available for controlling the order in which items and tanks occur in the loadcase. You may move selected items and tanks up and down in the loadcase; you may also sort selected items by name, fluid type (for tanks) etc.

Insert row | Delete row | Sort rows | Move row(s) up | Move row(s) down

Sort selected columns

After moving loads, subtotals and subsubtotals, you may have to use Analysis | Update Loadcase ( button) to update the subtotals and subsubtotals. To ensure data consistency, Hydromax does this automatically prior to running an analysis.

Loadcase Formatting

Hydromax allows you to improve the presentation of the Load Case window by adding blank, heading or sub-total lines in the table.

Adding Component or Heading Lines Components or headings can be included in a load case by preceding the text with a period (.) character.

Adding Blank Lines A blank line can be added into the load case by placing a dollar ($), apostrophe (‘) or full-stop(.) character in the Item Name field.


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Adding Totals or Subtotals A subtotal can be displayed for several loads within a load case. To do this the item name field must commence with the word ‘total’ or ‘subtotal’.

Sub-subtotals Sub-sub-totals may also be inserted. Sub-subtotals must start with the text “subsubtotal”.

Grouping Similar Tanks Use the move items UP or Down commands in the Edit menu to adjust the row order in the loadcase.

Quantity and Unit mass for sub total rows

If a sub total includes only tanks, then the quantity and unit mass items will be included. The unit mass is the sum of all the masses of the full tanks and the quantity is the sum of the masses divided by the sum of the full tank masses. When tanks are grouped by fluid type this can be useful for calculating the total tank capacity for that fluid type.

Loadcase Colour Formatting

Different colours can be defined for fixed mass items and tanks; alternatively, tanks may be displayed in the same colour as the fluid they contain (As defined in Analysis | Fluids dialog).

Ø View | Colour menu when Loadcase window is frontmost

Loadcase format

It is possible to select which columns are displayed in the loadcase window. Use the Display | Data Format dialog:


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The Relative density and Fluid Type which allow you to override the default tank densities as defined for each tank in the Compartment Definition window. This can be useful for vessels such as product carriers which may have cargos of different types of fluids with different densities. Moment columns (mass * lever) can be displayed if desired.

Longitudinally Distributed Loads

Distributed loads can be entered in the Loadcase window in the aft limit and forward limit cells. The aft limit and forward limit columns only appear when Longitudinal Strength analysis is selected and the distributed loads will only have an effect on the results in this analysis mode. The “Long. Arm” column defines the longitudinal position of the centre of the load; the fore and aft limits define the longitudinal extents of the load.

If the longitudinal arm is changed in the Loadcase window, the forward and aft limits will be moved by the same amount. For an evenly distributed load, the centre of gravity should be midway between the forward and aft limits.


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Evenly distributed loads. Red = green and divided in the centre.

For trapezium shaped distributed loads the centre of gravity is not midway between the boundaries, but within the middle third 1/3 of the centre.

Trapezium shaped distributed load. Red = Green divided within middle 1/3 of centre.

Note: Since the load is distributed as a trapezium, the centre of gravity should lie within the middle third between the forward and aft limits of the load, at these extrema, the load distribution becomes triangular. Tanks will be automatically treated as distributed loads for the longitudinal strength calculations.

Tank Loads

When you create tanks using the compartment definition, they will be automatically included in the loadcases (but not in Loadgroups which do not contain tanks).


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Tanks have a quantity value, expressed as a percentage of the full capacity and a weight column. Tank level can be given as either a percentage of full capacity, volume, a sounding or a weight.

The tank Unit Mass is the tanks mass at 100% filling.

When a tank is changed in the Compartment definition table, question marks may be shown in the loadcase momentarily while the tank’s new volumetric properties are being calculated. To update the loadcase for changes in tank loads, select Update Loadcase from the Analysis menu or toolbar.

Updating tank values in the loadcase

Irrespective of whether you have updated the values in the Loadcase Condition, the Loadcase will be automatically updated as the first step of any analysis using the Loadcase information. Also see:

Update Loadcase on page 164

Loadcase cross-referencing; Loadgroups

It is possible to cross-reference one loadcase from another. This is useful if you wish to define a detailed lightship mass distribution but do not want to have it displayed in full in each loadcase. It also means that this lightship mass distribution would only need to be defined and edited in one location instead of in each loadcase. To prevent the problems of recursively including the same loadcase and also prevent tanks from being included more than once, we have defined the following rules:

• A special type of Loadcase called a Loadgroup has been defined.

• A Loadgroup does not contain tanks

• Only a Loadgroup can be referenced

• Only a Loadcase can reference a Loadgroup.

• A Loadcase can reference any number of Loadgroups

• A Loadgroup is referenced in a Loadcase by typing the name of the Loadgroup to be referenced in the Item column

• You can factor the referenced Loadgroup by changing the value of the Quantity column in the Loadcase.

• Loadgroups may be analysed in the same way as Loadcases – but remember the tanks are implicitly empty in a Loadgroup.

For the example above this means that the lightship mass distribution would be defined as a Loadgroup and then this Loadgroup could be referenced in any number of loadcases. The Loadcase properties dialog (Case menu) is used to define a loadcase as a Loadgroup:


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This lightship Loadgroup contains the lightship mass distribution along the ship. The Lightship load group can then be cross-referenced into any loadcase


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The referenced Loadgroup is automatically calculated and the appropriate values included in the Loadcase:

Note: Loadgroup naming The cross-referencing of loadgroups in a loadcase is case insensitive.

Loadcase density override

It is now possible to override the default tank fluid densities as defined in the Compartment definition window. This allows you to load the same tanks with different fluids in different Loadcases – as might be the case for a product carrier, for instance. By default use tank defined densities:


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Type in a valid (>0.0) specific gravity and it will override the tank value:

Type in any string that doesn’t begin with an “L” for the fluid and it will revert back to the tank value:

Type in some thing that begins with an “L” and it will revert back to the “Private” density of the loadcase item.


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Free surface correction

If the corrected VCG fluid option has been chosen, the Loadcase will sum the free surface moments, divide by the total displacement to obtain the VCG correction and adjust the VCG accordingly to obtain the corrected fluid VCG.

Fluid simulation If the Fluid simulation option is selected in the analysis menu, no correction is made to the upright VCG. Instead, at every step of the analysis, Hydromax calculates the actual position of the fluid in the tanks taking into account heel and trim, making the tanks’ free-surface parallel to the sea surface, thus the actual vessel CG is recalculated accounting exactly for the static shift of the fluids in slack tanks.

When the corrected VCG method is selected in the analysis menu, it is possible to choose the type of free surface moment to be applied for each tank in a Hydromax Loadcase. The options available are

Maximum Hydromax will use the maximum free surface moment of the tank in upright condition for all fluid levels.

Actual Hydromax uses the free surface moment for the current fluid level of the tank in upright condition.

IMO Hydromax uses IMO MSC75.(69) Ch 3.3 for the calculation of the free surface moment. This method approximates the movement of fluid due to heeling and is based on the fluid shift in a 50% full rectangular, box-shaped-tank. For other shapes and fillings of tanks it will not correctly approximate the free surface moment.

User specified A user specified value is used for all levels and heel angles.

Workshop structure

Workshop can save a Loadgroup that contains the masses of all the structural parts. This can be loaded into Hydromax and referenced in any Loadcase.

Modelling Compartments

This section will describe in detail how to model different types of tanks and compartments. Besides a general explanation on how to model tanks using the compartment definition table, this section contains a number of important sections that the user should be aware off when modelling tanks:

• Number of Sections in Tanks on page 57

• Tank and Compartment Permeability on page 52

Creating a Compartment definition file (.htk)

Ø Select the Compartment Definition table by clicking on the Compartment Definition tab at the bottom of the Input window.

Ø Select New Compartment Definition from the File menu


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This will give you a new set of compartment definitions with one default tank.

Adding and Deleting Compartments

Before you can start adding compartments, make sure you have created a Compartment definition file, see above. Compartments may be added or deleted by

Ø Select Add or Delete Compartment from the Edit menu.

Add will add a tank after the currently selected compartment and Delete will delete the currently selected compartment(s). The accelerator keys Ctrl+A and the Delete key may also be used to add and delete entries respectively.

Modelling Box Shape Tanks

Simple tanks and compartments are created by specifying six values that define a box-shaped boundary for the tank. This box will be called the Boundary Box. The boundary box is made up of the fore and aft extremities of the tank, the top and bottom, and the port and starboard limits of the tank. Each value defines one of the six planes of the tank. The column headings in the Compartment Definition table include terms such as 'F Bottom, 'A Top', 'F Port' and 'A Starboard'. The 'F' and 'A' abbreviations stand for Forward and Aft, in other words the two ends of the compartment. You will notice that aft columns contain the word "ditto". This means that the value is identical at the aft end of the tank to the forward end, resulting in a parallel tank. When the “Update Loadcase” command from the Analysis menu is used, or an analysis started, Hydromax will form the sections that define the tanks and compartments. This is done by finding the intersection of the tank bounding box and the hull. Thus it is not necessary to make the tanks fit the hull manually – this is done automatically by Hydromax.

Box shaped compartments can be formed from the numerical values in the compartment definition table.

See Longitudinal Extents of Boundary Box on page 57 for some recommendations regarding setting the boundary box.


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Modelling Tapered Tanks

The default is for compartments to have parallel sides. If you wish to define tapered compartments, it is possible to enter different transverse and vertical values for the points defining the forward and aft ends of the compartment. If a different value is entered in one of the “ditto” columns, a tapered tank will result. Tanks can be tapered or sloped in Plan or Profile views. Hydromax does not have a mechanism for creating a sloped tank boundary in the Body Plan view.

By changing the “ditto”-input fields, tapered tanks can be formed

Note: Tapering can be done in Plan and in Profile view. Tapered tanks in Body Plan view have to be created using a boundary surface. See Modelling Tanks Using Boundary Surfaces on page 47.

Linked Tanks

Tanks and compartments may be linked. This means that although they are defined as separate tanks, they act as a single tank with a common free surface. To link tanks, compartments or non-buoyant volumes, first make them the same type as the parent and give them the same name. The easiest way to do this is to copy and paste the name from the Name column of the parent row into the Name column of the linked tank row. They may then be linked to the parent by typing l or linked in the Type column. Linked tanks and compartments do not have to be physically linked in space. However, the fluid in a linked tank or damaged compartment is always assumed to be able to flow freely between the linked volumes.


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Modelling Tanks Using Boundary Surfaces

Tanks, compartments and non-buoyant volumes may have their boundaries defined by surfaces as well as being constrained to particular dimensions. This allows for the modelling of arbitrarily shaped tanks.

Forming tanks using boundary surfaces

The surfaces to be used to define the tank boundaries are selected by clicking in the Boundary Surfaces column in the middle of the Compartments Definition table. A dialog will appear that allows you to select which surfaces form the boundary of the tank. If a tank uses boundary surfaces, the cell in the Boundary Surfaces column is coloured blue.


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If you wish to use a Maxsurf surface to define a tank or compartment, tick next to the surface name in the Boundary Surface list. Note that symmetrical surfaces appear twice as there will be a starboard and a port side copy of the surface. The Starboard surface is first in the list and the Port surface second. The port surface is also identified with the suffix (P) after the name.

Note: Only internal structure surfaces appear in the boundary surfaces list. Symmetrical surfaces are duplicated, with the port-side surface having “(P)” appended to the surface name. After selecting the internal surfaces, it is necessary to type in the extents of the boundary box. Hydromax will automatically set the “Fore” and “Aft” limits of the boundary box to just within the longitudinal limits of the Boundary Surface. This ensures that at least 12 sections are inserted in the tank.

Also see: Forming Compartments on page 54 Number of Sections in Tanks on page 57 Longitudinal Extents of Boundary Box on page 57

Modelling External Tanks

External tanks may not be modelled in Hydromax. However, it is normally possible to add "Hull" surfaces in the Maxsurf model, which will enclose the external tanks. The tanks can then be modelled in Hydromax.


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Additional box-shaped hull surfaces used to define deck tanks

Modelling Non-Buoyant Volumes

Non-buoyant volumes are effectively permanently flooded compartments. These parts of the hull can normally be modelled using trimmed hull surfaces. However, there are occasions where it is more convenient to use non-buoyant volumes. In some cases, where the volume to be flooded forms sections within the hydrostatic section, this is the only option, e.g. waterjet ducts. The choice whether to use trimmed surfaces or non-buoyant volumes is primarily determined by the length of the non-buoyant volume relative to the length of the vessel.

Using trimmed hull surfaces When the length of the non-buoyant volume, relative to the length of the model, is large enough; the non-buoyant volume can be calculated accurately from the hull sections. If possible, trimmed surfaces should be used. The picture below is a good example of when to use trimmed surfaces.

Propeller tunnels modelled with trimming surfaces

Using tank type: Non-buoyant volume In some cases using trimmed surfaces is just not possible. For example, when the sections of the non-buoyant volume are entirely enclosed within the hull sections (as is the case for a water jet duct) the use of a non-buoyant volume is the only way in which these features can be modelled.


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Water-jet ducts modelled as non-buoyant volumes

Another occasion when non-buoyant volumes should be used, is when the length of the compartment relative to the length of the hull is too small to calculate its volume from the hull sections. A good example of this is a bow thruster on a long ship. If the vessel is very long, and the thruster duct is of small diameter, there may not be sufficient sections to model it accurately (even if you use the maximum of 200 sections for the Hydromax model). In this case you are better off modelling the thruster duct as internal structure and using these surfaces to define a non-buoyant volume. For example: in the image below the bow thruster volume is only calculated with one section.

For more information, see Number of Sections in Tanks on page 57. Tip: Besides increasing the number of sections through the bow thruster from 1 to 12, modelling the thruster duct as a non-buoyant volume has the additional advantage of being able to specify a Tank and Compartment Permeability, and hence also account for the thruster.


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Bow thruster tube modelled as two non-buoyant volumes

Tanks within Compartments

When a tank is defined within a compartment, Hydromax will automatically deduct the volume of the tank from the compartment volume using a “linked neg. (negative) compartment”. This is necessary for damage cases where the compartment is flooded and the volume of the tank should be treated completely separately from the compartment. Linked negative compartments are deleted and recreated whenever a tank or compartment is added, deleted or modified. Negatively linked compartments are displayed on the bottom of the Compartment Definition table solely for reference purposes and are not under direct user control. This means that linked negative compartments cannot be added, deleted or modified. Linked negative compartments are named based on both the parent compartment as well as the tank from which the linked negative compartment was derived. For example a linked negative compartment might be named “Compartment3 (Stbd Hydr Oil)” to reflect that it is derived from the intersection of Compartment3 with the Stbd Hydr Oil tank.

Tanks Overlapping

As mentioned earlier in this manual, only compartments and non buoyant volumes or tanks can overlap with each other. Tanks or compartments of the same type (eg two tanks) can not overlap. A tank and a non-buoyant volume are also not allowed to overlap. Hydromax will first try to form tank sections and then check whether these sections overlap tank sections of adjacent tanks. When two conflicting or overlapping tanks or compartments are detected during the forming process, you will receive an error message:

Notice that the compartment definition row number of the tank is given in brackets i.e. tank #8 intersects tank #3.


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Troubleshooting Overlapping Tanks Sometimes the reason for the conflict can be quite simple: eg an overlapping boundary box. However, when you are modelling tanks using boundary surfaces, the surface boundaries act as a boundary between two adjacent tanks and the bounding box extents are allowed to overlap. In these cases, it can be quite difficult to see why the tanks overlap, especially if you have a large number of tanks already defined.

By temporarily deleting all tanks except for the one that does not form, it often becomes clear why the tank overlaps. In the case of the image above, the tank’s fwd most section goes all the way to the CL (probably because the fwd boundary box extent is just fwd of the boundary surfaces or exactly on the edge of a boundary surface). This causes this particular tank to “overlap” with surrounding tanks.

Procedure to Fix Overlapping Tanks:

Ø Save Model

Ø Go into Comp def window

Ø Save comp def

Ø Delete all tanks except for one you wish to investigate

Ø form tanks, inspect tank sections

Ø Try to fix tank definition, eg by selecting additional boundary surfaces

Now that you know how to fix it..

Ø Close comp def file. Do NOT save!!

Ø Open saved Comp def file

Ø Fix compartment.

Ø Save & move on to next compartment.

Tank and Compartment Permeability

Tanks may have two permeabilities; one, which is used when the tank is intact, and the other when it is damaged. Compartments and non-buoyant volumes have only one permeability, thought it is listed in both columns. The compartment permeability is applied when the compartment is flooded in a damage condition and the non-buoyant volume permeability is applied at all times since it is always flooded.


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In the case of damaged tanks and compartments, the permeability fraction is also applied to the free-surface-moment contribution of that tank or compartment.

Permeability of Compartments As opposed to tanks, compartments typically have structure (other than plate stiffeners) and equipment inside. In case of large variations in permeability within a compartment it is recommended to model separate linked compartments with separate permeability to increase accuracy. For example an engine room with engines and auxiliaries at the tanktop could be divided up in a lower- and an upper engine room compartment. The lower compartment will have a permeability of, for example, 60% and the upper compartment a permeability of 95%. Depending on the level of accuracy required, the engines and equipment could also be modelled individually as empty tanks.

Relative Density of Tank Fluids

Relative Density (Specific Gravity) values can be typed directly into the Relative Density column of the Compartment Definition table.

Alternatively the fluid type can be entered into the Fluid Type column, either as the name or as one of the single letter codes (when entering the name, auto complete is used, so it is normally only necessary to type the first few letter of the name). If a fluid type is entered, the relative density value is obtained from the value specified in the Density dialog. Whenever values are changed in the Density dialog (see Density of Fluids on page 111), all entries for that fluid in the compartment definition are automatically updated. If the tank defines a cargo tank that will carry different liquid cargoes, the default density specified here in the compartment definition may be overridden in the loadcases.

Tanks and Surface Thickness

If you have specified that Hydromax should include the surface thickness, the tanks, compartments and non-buoyant volumes will correctly account for the surface thickness and its projection direction: the tanks will go to the inside of the hull shell.

Note: Thickness of boundary surfaces are not taken into account, hence you should design these surfaces to the inside of the tank.

Compartment and Tank Ordering

The tank definition order can be adjusted in a similar way to loads in the loadcase. Select the rows you wish to use and use the Edit | Move Items Up or Down commands (there is no provision for sorting tanks alphabetically). Groups of linked tanks and compartments will be moved together.

Compartment and Tank Visibility

When creating complicated tank plans, it is often useful to check individual tanks. Selected tanks may be displayed in the following manner:


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Ø Define a damage case

Ø Select only damaged tanks and compartments for display, turn off the display of intact tanks and compartments.

Ø Select whether you want to see the tank outline or the tank sections (tanks sections are preferable when checking that tanks have been formed correctly since it is these sections which are used to determine the tank volume and other properties).

Ø Choose the damage case from the Analysis toolbar

Ø Set any of the tanks and compartments you wish to be visible to damaged in the damage case window.

You can make the damage case window quite small and tile it next to the perspective view. Use this to quickly turn tanks on and off by changing their damage status.

Using a damage case to quickly change the tank and compartment visibility

Forming Compartments

Tanks and compartments are formed automatically by Hydromax (once the tank extents and any boundary surfaces have been defined) by selecting Recalculate Tanks and Compartments from the Analysis menu. The formed status of a tank (yes or no) is shown in the last column of the compartment definition table. This section describes the internal tank-forming process that Hydromax uses to form tanks. First a step-by-step outline of the tank forming process is given, followed by the tank section insertion process. Understanding these processes may assist you in rare situations where the tank forming does not work as expected.

Step-by-Step Tank Forming Process

As an example, the starboard waterballast tank below will be created using boundary surfaces.


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An example of a port and starboard waterballast tank with a pipe tunnel at the centreline. The water ballast tanks have a margin plate on the side.

Hydromax uses three input items to form the compartment • Boundary surfaces (if defined)

• Boundary box

• Hydromax Hull sections

Starting position The starboard tank margin plate is modelled using an Internal Structure surface from Maxsurf.

Starting point: Hydromax Hull sections with an internal surface and a bounding box

Also see: Modelling Tanks Using Boundary Surfaces on page 47 and the Maxsurf manual on internal structure surfaces

Step 1: Close Internal Structure Surface

Hydromax will close the Internal Structure Surface contour by drawing a straight line between the ends of the opening.


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Hydromax uses the same method for forming the tank section from the boundary surfaces as for forming the hydrostatic sections through the hull. As with the hull sections, the surfaces selected to form the tank boundary must form closed section contours at all longitudinal positions through the tank. The area inside the selected surfaces will define the tank contour. Make sure that the boundary surfaces:

• Form a closed section contour, or

• There is no more than one opening – the opening will be closed with a straight line

Note: Hydromax will close the section contour of the selected boundary surfaces only. Often a tank is not formed as expected because only one side of the internal structure surface was selected for example the portside (p). Another common cause of unexpected results is trimming. If you selected “use trimmed surfaces” while opening the Maxsurf model, Hydromax will use the trimmed internal structure surface. Usually the internal structure surfaces are best to be left untrimmed.

Step 2: Clip to Boundary Surface Using the closed surface section contour Hydromax can now form a closed compartment section. The tank or compartment looks like this at this stage:

Step 3: Clip to Hull Hydromax will clip the compartment section to the hull.


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Step 4: Clip to Boundary Box Finally the compartment section is clipped to the boundary box. The boundary box is formed from the numerical input in the Compartment definition table.

Number of Sections in Tanks

The volume of a tank or compartments is calculated by integrating section properties along the length of the tank. Thus it is important to have a sufficiently large number of sections to accurately model the tank. Hydromax will normally place twelve sections between the forward and aft limits defining the tank. If this results in a section spacing greater than the spacing for the hull spacing, additional sections will be inserted into the tank so that the tank section spacing match the hull section spacing. Also see

Longitudinal Extents of Boundary Box on page 57

Longitudinal Extents of Boundary Box

For tanks near the ship’s extremities it is good practise to set the “Fore” and “Aft” limits in the compartment table to just inside the hull surface (say 1mm). The following example illustrates why:

• If the boundary box is set like this:

The number of hull sections is dependent on the section spacing in the model.


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• But if the boundary box is set just inside the forward limit of the bulbous bow:

To recap – Near the ship’s extremities, the longitudinal extents should not be set to extreme values, they should be set to just inside the extents of the hull surfaces to ensure that at least 12 sections are used to calculate the tank volumes. For internal structure surfaces that are used as boundary surface, Hydromax will automatically set the “Fore” and “Aft” limits of the boundary box to just within the longitudinal limits of the boundary surface. This ensures that at least 12 sections are inserted in the tank. Note that transversely and vertically there are no such restrictions. Also see

Number of Sections in Tanks on page 57 Forming Compartments on page 54

Compartment Types

Five compartment types can be created using the Compartment Definition table - tanks, linked tanks, compartments, linked compartments and non-buoyant volumes.

Tanks Will be included in the tank calibration output and are automatically added to the loadcase.

Linked Tanks Will have their volume added to the parent tank with the same tank name. They do not have a separate entry in the loadcase. In addition, if a tank is damaged, any tank that it is linked to will also be regarded as damaged. Tanks need not be adjoining to be linked, they can be remote from one another. In this case the tank linking simulates tanks with cross connections.

Compartments Are only used to specify compartmentation for damage. They are not included in the tank calibration output and will not be added to the loadcase.


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Linked Compartments Work in the same way as linked tanks. This allows you to damage a complex compartment configuration by linking compartments together and damaging the parent compartment.

Non-Buoyant Volumes Are only used to specify compartments of the vessel which are permanently flooded up to the static waterline. They are ideal for defining water-jet ducts, moon pools, etc. and essentially behave as damaged compartments. They are not included in the tank calibration output and will not be added to the loadcase.

To change the type of a tank, type the first character of the tank type (t, c or n) in the Type column of the Compartment Definition table and then press Enter. This will automatically set the tank/compartment to the correct type.

Sounding Pipes

Hydromax allows sounding pipes to be defined for each tank. One sounding pipe per tank is permitted and up to nine vertices per sounding pipe, allowing inclined, bent or curved sounding pipes to be modelled. Hydromax creates a default sounding pipe when the tank is formed (either by running an analysis, or using one of the following commands: Analysis | Recalculate Tanks and Compartments; or Analysis | Update Loadcase. The default sounding pipe is placed at the longitudinal and transverse position of the lowest point of the tank. If the lowest point of the tank is shared between several locations (e.g. the bottom of the tank is flat either longitudinally or transversely) the default sounding pipe location is placed at the aft-most low point and as close to the centreline as possible. The top of the sounding pipe is taken to be level with the highest point of the tank and the default sounding pipe is assumed to be straight and vertical. Automatically created sounding pipes will be recalculated if the tank geometry changes. However, once the sounding pipe has been edited manually, any changes to the sounding pipe due to tank geometry changes will also have to be made manually.

Edit Sounding Pipes

To customise a sounding pipe, you need to use the Sounding Pipes table in the Input window, shown below.


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You can activate this window by selecting from the Windows | Input | Sounding Pipes menu, by clicking on the tabs at the bottom of the Input window, or by clicking on the

icon in the window toolbar. To add vertices to create a bent sounding pipe, make the sounding pipe type User Defined, then click on the first row of a particular sounding pipe and choose Edit | Add or use the Ctrl+A key combination. A new row will be added to the sounding pipe and the longitudinal position, offset and height of the vertex can be edited. Unwanted vertices can be deleted by clicking on the relevant row in the table and selecting Edit | Delete or by hitting the Delete key. Note that each successive vertex in a sounding pipe must be no higher than the previous vertex i.e. it is not acceptable to have S-bends in the sounding pipes.

Calibration Increment

Hydromax allows user definable increments (or: intervals) for tank soundings. This is done by specifying a numerical value for the increment for each tank in the Calibration Spacing column of the Sounding Pipes Input window.

Ø Type the value of the desired calibration increment in the Calibration Spacing cell for the tank calibration you wish to modify.

If no increment is entered, Hydromax uses its default value based on a reasonable division of the depth of the tank. In this case the Sounding Pipes table will display “Auto” in the Calibration Increment column for the tank.


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Note Increments are measured along the sounding pipe, not along the vertical axis of the tank. If the sounding pipe is inclined or if it has multiple angles, soundings will step evenly along the inclined length of the sounding pipe.

Damage Case Definition

In all but the floodable length and tank calibration analysis modes, Hydromax is capable of including the effects of user-defined damage. Hydromax allows the user to set up a number of damage cases. Volumes that are permanently flooded should be defined as non-buoyant volumes.

Adding a Damage Case

To add a damage case, make the Damage window active and select Add Damage Case from the Case menu. You may specify a name for the Damage Case in the dialog. Each new damage case will have a column in the Damage Window and a tick may be placed to indicate which tanks and compartments are damaged for that particular Damage Case. The new damage case is added after the currently selected damage case column, to insert a damage case immediately after the intact case, select the intact case column. Several damage cases may be added in one go by selecting a number of columns.

Deleting a Damage Case

To delete damage cases, simply select the columns to be deleted in the Damage Window and select Delete Damage Case from the Case menu. Note that it is not possible to delete the intact case.

Renaming a Damage Case

The name of the current damage case may be changed by selecting Edit Damage Case when the damage case window is active, the current damage case is selected from the Analysis toolbar – see below.


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Selecting a Damage Case

The current damage case is selected from the Analysis toolbar.

The Loadcase and View windows will reflect the damage defined in the current damage case. To perform analyses for the intact vessel, select Intact as the current damage case. Any subsequent analyses will take into account the damaged compartments. Note that carrying out a Tank Calibration analysis will force the intact case to be selected. This is also the case for the Floodable Length analysis which effectively sets up its own longitudinal extent of damage. When tanks have been damaged, their weights and levers are no longer displayed in the Loadcase window and the word ‘Damage’ is displayed in the quantity column. This is because Hydromax uses the “Lost buoyancy” method rather than “Added mass”.

Note: Hydromax uses the “Lost buoyancy” method rather than “Added mass”. Flooding is considered to be instantaneous up to sea level. Any tank fluids are treated as having been completely replaced by seawater up to the equilibrium waterline. Hydromax assumes that all compartment definition has been done after the tanks have been defined. If you have linked tanks or compartments or added tanks within compartments after the definition of a damage case, you should toggle the damage status of the damaged tanks. This is simply done by copying all the damage case data to a spread sheet, turning off all damage in all the damage cases (use the fill down command) and then pasting back in the original data from where it was stored in the spreadsheet.

Displaying Damage Cases

When a damage case is selected, all damaged tanks and compartments will be displayed in damaged tank or damaged compartment colour respectively. These colours can be specified in the View | Colour menu. In the Loadcase Window damaged tanks are displayed with the label 'Damaged' in the Quantity column, and all values set to zero.


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The Loadcase Window displays damaged tanks and excludes them from any calculations.

Key Points (e.g. Down Flooding Points)

Key points such as downflooding points and hatch openings can be defined in Hydromax using the Key Points window. The points may be displayed in the Design View window and will be displayed in different colours depending on whether or not they are immersed. Immersed key points will be displayed in the same colour as flooded tanks or compartments. Key points may be placed asymmetrically, a positive offset is to starboard and a negative offset is to port. Vessels which have symmetrical key points on starboard and port sides must have both key points added to the table. There are several types of Key Points:

• Down Flooding points

• Potential Down flooding points

• Embarkation points

• Immersion Points Only downflooding points are used in determining the downflooding angle, which is used in criteria evaluation. The other types of points have their freeboard measured but are not used for the evaluation of the downflooding angle and are for information only.

Adding Key Points

To start adding downflooding points go to the Key Points table, select New Key Points from the File menu. You will be given a default point. To add additional key points to the table, choose Add from the Edit menu or press Ctrl+A. A new point will be inserted below the currently selected row in the table.


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Deleting Key Points

To delete a Key point, click anywhere in the row of the point to be deleted and select Delete. To delete more than one point at a time, click and drag over the rows you want deleted.

Select Delete from the Edit menu, and the selected rows will be deleted.

Editing Key Points

Key points are defined by entering a name, a longitudinal position, a transverse offset from the centreline, and a height. Click in any cell and enter the name or value you require. All points are entered relative to the zero point. The type of Key Point may be selected from the combo-box in the Type column of the Down Flooding Points table in the Input window:

Links to Tanks or Compartments

Downflooding points may be linked to tanks or compartments. Select the tank or compartment from the combo-box in the Linked to column of the Down Flooding Points table in the Input window:

Downflooding points that are linked to tanks or compartments, which are damaged in the currently selected damage case, will be ignored when computing the downflooding angle. These downflooding points will appear italicised and an asterisk (*) is postfixed to the downflooding point’s name in the DF Angles table of the Results window:


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The downflooding angles for each of the points are displayed in the results window. The downflooding angles are computed during a large angle stability analysis; the freeboards after an Equilibrium or Specified Condition analysis. Immersed points are highlighted in red in the Freeboard column. In addition to the Key Points results, immersion angles or freeboards (depending on the analysis) are also given for the margin line and deck edge. In the Name column the longitudinal position where immersion first takes place (or the lowest freeboard) is given.

Note: Linking a downflooding point to a tank does not mean that Hydromax will consider a tank damaged when the downflooding point is submerged. This form of automatic flooding is not supported in Hydromax yet.

Margin Line Points

The margin line is used in a number of the criteria. Hydromax automatically calculates the position of the margin line 76mm below the deck edge when the hull is first read in. If necessary, the points on the margin line may be edited manually in the Margin Line Points window (the deck edge is automatically updated so that it is kept 76mm above the margin line). It is only necessary to modify the height value of the margin line points. Once this has been done for all the points that need to be changed, selecting Snap Margin Line to Hull in the Analysis menu will project all of the points horizontally onto the hull surface, ensuring that the margin line follows the hull shape precisely. Asymmetric margin lines and deck edges are not supported. Points may be added or deleted as required using the procedure described in Adding Key Points and Deleting Key Points on page 64.

Modulus Points and Allowable Shears and Moments

The Modulus window can be used to enter maximum allowable shear forces and bending moments for each section. One or more points can be entered in this window. Allowable shear force and/or bending moment can be specified at each point. The modulus value is not currently used as deflections are not calculated.


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To start a table of allowable shear forces and bending moments, bring the Modulus table to the front and choose New Modulus Points from the File menu with the Modulus window frontmost. The allowable values can be saved and recalled as text files by using Open and Save from the File menu. New allowable values can be inserted by selecting Add from the Edit menu and entering a longitudinal position as well as an allowable shear and/or moment. Points may be added or deleted as required using the procedure described for the key points. These allowable values are displayed as lines on the longitudinal strength graph.

Floodable Length Bulkheads

Bulkheads entered in the Input window are used for Floodable Length analysis in order to optionally plot the compartment lengths in the floodable length graph for easy verification that the critical compartment lengths are not exceeded. The Bulkheads are automatically sorted by longitudinal position. For more information see Floodable Length on page 90.

Stability Criteria

Stability criteria may be evaluated after a Large Angle Stability analysis and after an Equilibrium analysis. Stability criteria are required to perform a limiting KG and Floodable Length analysis. Please refer to Chapter 4 Stability Criteria starting at page 123 for information on defining and selecting criteria.

Analysis Types

After specifying the input values and checking the Hydromax model, the analysis can be performed. In this section the different analysis types available in Hydromax will be described. The following analysis types are available in Hydromax:

• Upright Hydrostatics


• Equilibrium Analysis

• Specified Conditions

• KN Values Analysis

• Limiting KG


•

• Longitudinal Strength

•

• Tank Calibrations

Also, some general information is given on:


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•

• Starting and Stopping Analyses

•

• Batch Analysis The required analysis settings and environment options will be discussed separately and in more detail in the next two sections of this chapter. Following each analysis, one or more graphs may be shown – select the graph to be displayed from the pull-down menu in the Graph window. The Data Format dialog can be used to specify what is displayed in some graphs and tables; the available options depends on the current results table or graph:

Data format dialog for Upright hydrostatics table and graph

Data format dialog for Large angle stability analysis, max. safe heeling angle graph


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Upright Hydrostatics

Upright hydrostatics lets you determine the hydrostatic parameters of the hull at a range of drafts, at zero or other fixed trim.

Choosing Upright Hydrostatics

Select Upright Hydrostatics from the Analysis Type option in the Analysis menu or toolbar.

Upright Hydrostatic Analysis Settings

The following analysis settings apply for Upright Hydrostatic Analysis: • Draft from the Analysis menu, specify range of drafts for analysis

• Trim from the Analysis menu, you may specify a fixed trim for all drafts A range of drafts for upright hydrostatic calculations can be specified using the Drafts command from the Analysis menu.

Initial and final drafts can be entered, together with the number of drafts to be used. The Vertical Centre of Gravity is also required for the calculation of GM etc. This is specified as KG, i.e. from the baseline, which is not necessarily the vertical zero datum. When a design is first opened, the initial draft defaults to the draft at the DWL in Maxsurf. Similarly the VCG defaults to the height of the DWL.

Upright Hydrostatics Environment Options

The following environments can be applied to the upright hydrostatics analysis: • Density from the Analysis menu

• Wave Form (if any)

• Hog and Sag

• Damage (or Intact) from the Analysis toolbar


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Upright Hydrostatic Results

The curves of form are shown on a separate graph and the sectional area may be show for any of the drafts: see Select View from Analysis Data on page 120.


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Large Angle Stability

Large angle stability lets you determine the hydrostatic parameters of the hull at a range of heel angles either with or without trim or free-to-trim.

Choosing Large Angle Stability

Select Large Angle Stability from the Analysis menu or toolbar.

Large Angle Stability Settings

The following analysis settings apply for Large Angle Stability Analysis: • Displacement and Centre of Gravity using the Loadcase window

• Heel from the Analysis menu, select range for analysis

• Trim (fixed or free) from the Analysis menu If criteria are being evaluated, the heel range and heel angle steps should be chosen accordingly, to ensure accurate evaluation of the criteria.

Note You can select positive heel direction (port or starboard). However, you can enter negative values and test full 360 degrees of stability if you wish. Some criteria require calculations of GZ at negative heel. The criteria are only evaluated on the side of the graph that corresponds to positive heel angles. For example: when using a -180 to 180 heel range, the results may be two angles of vanishing stability, the one that would be reported in the criteria would be the one with a positive heel angle (even if the one at negative heel occurred at an angle closer to zero). Also see: Heel on page 102 in the Analysis Settings section.

Large Angle Stability Environment Options

The following environments can be applied to the large angle stability analysis: • Fluid simulation of tank fluids centre of gravity

• Density


• Hog and sag (if any)



Large Angle Stability Results

Large Angle Stability Analysis results are:


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• Hydrostatic data table for each angle of heel

• GZ curve

• Dynamic stability (GZ area) curve

• Graph of hydrostatic parameters against heel angle

• Graph of max. safe steady heel angle

• Stability Criteria evaluation

• Downflooding angles to key points, deck edge and margin line

• Curve of areas at each heel angle

Dynamic stability Graph A graph of the GZ area integrated from upright may be plotted, features such as downflooding angle are also included on the graph.


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Graph of maximum safe steady heeling angles for sailing vessels These calculations are derived from the value of GZ at a critical heel angle, for example the angle of downflooding or angle of deck edge immersion. Once a GZ curve has been calculated, you can display the maximum safe heeling angle curves by selecting the graph type in the pull-down menu.


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The parameters for the calculation can be modified in the Display | Data Format dialog (this graph must be selected in the topmost window):

Analysis options for the calculation of Maximum steady heel angles (Display | Data Format).

The first part of the dialog is almost exactly the same as the “Angle of equilibrium - derived wind heeling arm” criterion. This allows you to specify the critical condition that should not be exceeded due to a gust or squall. MCA require downflooding but you can include additional criteria if desired. You can also change the shape of the heeling arm curve and the gust ratio.


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In the lower-left, you can specify the squall wind speeds (you can add any number) The default gives three wind speeds of 30, 45 and 60kts. Finally you can adjust the axis limits. This is because normally you will have computed a GZ curve for a wider heel range than you would wish to display in this graph – it is uncommon to sail a vessel with a steady heel angle of greater than 40 degrees. It can often be useful to duplicate this criterion in the GZ criteria that are evaluated. This will give you the same result as for the gust limiting line.


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The same safe angle of heel to prevent downflooding in the event of a gust (16.5 deg) is found.

To obtain smooth curves, the GZ curve should be calculated at small intervals of heel, especially at the lower heel angles – typically steps of 1degree. Under some circumstances, it may not be possible to evaluate the curves, the most common reason for this is that the GZ curve has not been calculated up to a sufficiently high angle of heel and downflooding angle cannot be found. Full details of the calculations can be found in: Sailing Yacht Design: Practice. ed. Claughton, Wellicome and Shenoi. Adison Wesley Longman 1998. ISBN 0-582-36857-X STABILITY INFORMATION BOOKLET available from the MCA. www.mcga.gov.uk

Stability Criteria Evaluation The criteria results are displayed in the Criteria tab in the results window. For more information on how to customize the display of the criteria results, please refer to the Results Window on page 145 in the reference section.

Important: For important information on varying displacement while evaluating criteria, see: Important note: heeling arm criteria dependent on displacement on page 192.

Downflooding Angle After a Large Angle Stability analysis, the Key Points Data table lists the downflooding angles of the margin line, deck edge and defined Key Points. In addition, the first downflooding point is marked on the large angle stability graph. Only the positive downflooding angles are displayed, hence if there is any asymmetry, the large angle stability analysis should be carried out heeling both to starboard and to port. For the margin line and deck edge the longitudinal position at which immersion first occurred is provided.

Downflooding points that are linked to tanks or compartments that are damaged in the currently selected damage case, will be ignored when computing the downflooding angle. These downflooding points will appear italicised, and an asterisk (*) is postfixed to the downflooding point’s name in the Key Point Data table of the Results window.

A downflooding angle of zero degrees indicates that the key point is immersed at zero degrees of heel.

Also see: Select View from Analysis Data on page 120.


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Equilibrium Analysis

Equilibrium analysis lets you determine the draft, heel and trim of the hull as a result of the loads applied in the table in the Loadcase window. The analysis can be carried out in flat water or in a waveform.

Choosing Equilibrium Analysis

Select Equilibrium from the Analysis Type option in the Analysis menu.

Equilibrium Analysis Settings

• Displacement and Centre of Gravity using the Loadcase window Also see:

Setting the Frame of Reference on page 18

Equilibrium Analysis Environment Options

The following environments can be applied to the Equilibrium analysis: • Fluid simulation of tank fluid centre of gravity

• Density


• Hog and Sag (if any)


• Grounding (if any)

• Criteria

Equilibrium Results

Equilibrium Results are: • Hydrostatic data

• Freeboard of key points, deck edge and margin line

• Criteria evaluation

• Wave phase animation

• Curve of areas


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Hydrostatic data

Height/freeboard above free surface The freeboard of each Key Point is also calculated. The freeboard is for the vessel condition currently displayed in the Design view and is recalculated after each Equilibrium and Specified Conditions analysis. The freeboard calculated is the vertical distance of the Key Point above the local free surface; hence the local free surface height if a waveform is selected will be taken into account.

Freeboard of key points.

Negative freeboards, i.e. where the Key Points are immersed are displayed in red. The longitudinal positions at which the minimum freeboard for the margin line and deck edge occurred are also specified.

Stability Criteria Evaluation The criteria results are displayed in the Criteria tab in the results window.


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Equilibrium Animation in Waves If performed in conjunction with analysis in waves, the Equilibrium analysis will automatically phase-step the waveform through a complete wavelength. This gives ten columns of results, one for each position of the wave crest. If necessary the results of this phase stepping can be animated giving a simple, quasi-static simulation of the hull motion in waves (Display | Animate).

Note: This simulation only includes static behaviour at each wave phase, and does not cover dynamic or inertial forces. This can be done using Seakeeper.

Equilibrium Concept

The definition of equilibrium is “Position or state where object will remain if undisturbed”. You can distinguish equilibrium into two types:

• Stable, when disturbed the object will return to its equilibrium position

• Unstable, when disturbed the object will not return to its equilibrium position

With ships, an unstable equilibrium can exist when the KG > KM, i.e. the centre of gravity is above the metacentre (negative GMt). In real world a ship in unstable equilibrium will roll from the upright unstable equilibrium position to a position of stable equilibrium and assume an “angle of loll”. Since Hydromax starts the equilibrium analysis in upright position, it has no way of determining whether the equilibrium is stable or unstable. This means that unstable equilibrium may be found instead of the stable equilibrium. Therefore it is recommend to check the value of GMt yourself after doing an equilibrium analysis or perform a Large Angle Stability analysis and look at the slope of the GZ curve through the equilibrium heel angle.

Stable equilibrium Unstable equilibrium


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Unstable equilibrium

Stable equilibrium ”Angle of loll”

The graph above shows the results of a Large Angle Stability analysis for a vessel with negative initial GMt. In practice this vessel would have a loll angle of approximately 25 degrees. If an equilibrium analysis is performed for this vessel with the transverse arm set to zero, Hydromax will find the unstable equilibrium position with zero degrees of heel. In practice, it is desirable to find the stable equilibrium position. To do this, first ensure that the tolerances (Edit | Preferences) are set as sensitive as possible. This will ensure that the smallest possible heeling moment is required to find stable equilibrium position. Then create a very small heeling moment by offsetting one of the weight items in the loadcase window TCG by just a fraction. The equilibrium analysis will now find the stable equilibrium position.

Note: It is good practice to always perform a Large Angle Stability analysis as well as the equilibrium analysis to check if the vessel is in stable or unstable equilibrium. This is most likely to occur if the VCG is too high and the vessel has negative GM when upright. The problem can be overcome by offsetting the weight of the vessel transversely by a small amount.

Specified Conditions

Specified Condition analysis lets you determine the hydrostatic parameters of the vessel by specifying the heel, trim and immersion. Heel can be specified by either the angle of heel or the TCG and VCG. Trim can be specified by the actual trim measurement, or the LCG and VCG. Immersion can be specified by either the displacement or the draft.

Choosing Specified Conditions

Select Specified Conditions from the Analysis Type option in the Analysis menu or toolbar.


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Specified Conditions Settings

The settings required for Specified Condition analysis are: • Specified Conditions from the Analysis menu

Three Sets of variables are provided, labelled Heel, Trim and Immersion. One choice must be made from each of these groups. Hydromax will then solve for the vessel hydrostatics at the conditions specified.

Values from the current loading condition can be inserted into the Centre of Gravity and Displacement fields by clicking on the Get Loadcase Values button. Also see:

Setting the Frame of Reference on page 18 Specified Conditions on page 105 in the Analysis Settings section.

Note: If the fluid simulation has been turned on in a previous analysis mode, then the VCG obtained from the loadcase will not include the free surface correction; the “Get Loadcase Values” button will return exactly the displacement and CG as displayed in the current loadcase window.

The specified condition analysis itself ignores tank fillings and does no correction to VCG.

Specified Conditions Environment Options

The following environments can be applied to the Specified Condition analysis: • Density




Specified Conditions Results

The specified conditions results are the same as equilibrium analysis results except that criteria are not evaluated, i.e. hydrostatic data and key points freeboard are calculated.


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KN Values Analysis

KN Values Analysis allows you to determine the hydrostatic properties of the hull at a range of heel angles and displacements to produce the cross curves of stability diagram.

Choosing KN Values Analysis

Select KN Values from the Analysis Type option in the Analysis menu or toolbar.

KN Values Analysis Settings

The analysis settings required for KN Values analysis are: • Heel from the Analysis menu, select range for analysis

• Trim (fixed or free) from the Analysis menu

• Displacement from the Analysis menu, select range for analysis and specify estimate of VCG if known

The heel angles used may differ from those used in the Large Angle Stability and Limiting KG analyses. To set the range of angles, select Heel from the Analysis menu. A range of displacements for KN calculations can be specified using the Displacement command from the Analysis menu. Initial and final displacements can be entered, together with the number of displacements required.

Displacement range dialog

Trim dialog


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The VCG can also be entered (specified from the vertical zero datum). Traditionally, KN calculations are calculated assuming the VCG at the baseline (K). However if the analysis is being calculated free-to-trim and an estimate of the VCG is known, the accuracy of the KN calculations (for VCGs in the vicinity of the estimated VCG) may be improved by calculating the GZ curve using the estimated VCG position – this will reduce the error in the trim balance due to the vertical separation of CG and CB because this vertical separation is specified more accurately than simply assuming the VCG at the baseline. If a VCG estimate is specified, the KN values are still presented in the normal manner with the KN values calculated as follows:

KN(φ) = GZ(φ) + KG_estimated sin(φ)

For information on Trim settings for KN Analysis, see: Trim for KN, Limiting KG and Floodable Length analyses on page 104. Also see

KN Value Concepts on page 83

KN Values Analysis Environment Options

• Density




KN Values Analysis Results


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KN Value Concepts

The righting lever, GZ, may be calculated from the KN cross curves of stability (at the desired displacement) for any specified KG using the following equation: .

GZ = KN - KG sin(φ)

Note: KN values can also be referred to as “Cross curves of stability”.

Limiting KG

Limiting KG analysis allows you to analyse the hull at a range of displacements to determine the highest value of KG that satisfies the selected stability criteria. GZ curves are calculated for various KG values. After each cycle, the selected criteria are evaluated to determine whether the CG may be raised or must be lowered.

KK

B

M

B’

NN

G Z


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When comparing the results of a limiting KG analysis to that of a Large Angle Stability analysis, it is essential that the same heel angle intervals are used and that the free-to-trim options and CG are the same. Some criteria, notably angle of maximum GZ, are extremely sensitive to the heel angle intervals that have been chosen.

Choosing Limiting KG

Select Limiting KG from the Analysis Type option in the Analysis menu or toolbar.

Limiting KG Settings

The initial conditions required for Limiting KG analysis are: • Displacement from the Analysis menu, select range for analysis

• Heel from the Analysis menu, select range for calculation of GZ curves

• Trim (fixed or free) from the Analysis menu The range of displacements to be used is set in the same way as they are set in the KN analysis. The heel angles used may differ from those used in the Large Angle Stability and KN analyses. To set the range of angles, select Heel from the Analysis menu. See Large Angle Stability on page 70 for further details. For information on Trim settings for Limiting KG Analysis, see: Trim for KN, Limiting KG and Floodable Length analyses on page 104.

Note: Since Limiting KG can be quite a time consuming analysis, you may wish to use a smaller number of heel angles than for the Large Angle Stability calculations. (However this will cause some loss of accuracy.) Limiting KG calculations will be significantly faster if the trim is fixed.

Limiting KG Environment Options

• Fluid simulation of tank fluid centre of gravity

• Density




• Criteria

Limiting KG Results

Limiting KG analysis results are • Limiting KG values, for each displacement and the limiting criterion.

• Limiting KG vs displacement graph The Limiting KG value is measured from the baseline, which is not necessarily the same as the zero point.


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The Limiting KG analysis also checks that any selected equilibrium based criteria are passed at each VCG that it tries. However, you must still have at least one Large Angle Stability criterion selected. Criteria are only evaluated on the positive side of the GZ curve, so if there is any form of asymmetry, it may be necessary to run the analysis heeling the vessel to both starboard and port (this can be done automatically in the Batch Analysis).

After a Limiting KG analysis has completed, the results in the Criteria results table display “Not Analysed”, this is because they do not necessarily refer to the final KG and would be misleading. If you require the limiting KG for each criterion individually or wish to perform a Large Angle Stability and Equilibrium analysis at each of the displacements and the corresponding limiting KG, this can be done in the Batch Analysis. Some criteria may depend on the vessel displacement and or vessel’s VCG. Where these values are explicit in the criterion’s definition in Hydromax, the correct values of displacement and VCG will be used in the evaluation of these criteria. However, problems can arise if the criterion is only available in its generic form – most commonly heeling arm criteria where the heeling arm is specified simply as a lever and not as a moment. In this case, since the heeling arm is not related to the vessel displacement in its definition within Hydromax, the heeling arm will remain constant for all displacements (where it is perhaps desired that the heeling arm should vary with displacement. For example in the case where the heeling moment, rather than the heeling arm is constant).


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Important: For important information on varying displacement while evaluating criteria see Important note: heeling arm criteria dependent on displacement on page 192.

Also see: Convergence Error on page 106 in the Analysis Settings section.

Limiting KG Concepts

Hydromax will iterate to a KG value that just passes all criteria you have specified in the criteria dialog. Hydromax will start with a set start KG value (e.g. 1 meter), run a large angle stability analysis and check the selected criteria. If any of the criteria fail, Hydromax will lower the KG and try again. If the criteria pass, Hydromax will raise the KG value and try to make the criteria fail. Hydromax will continue doing this until the limiting KG value has been iterated to within 0.1mm. If this tolerance is not achieved in a certain number of iterations, Hydromax will move on to the next displacement. When performing a Limiting KG analysis, Hydromax will evaluate any equilibrium-based criteria that are selected for testing and act accordingly. However, at least one GZ-based criterion must also be selected. This is because to perform a sensible search, Hydromax must have at least one criterion that will improve by reducing the VCG; Hydromax assumes that raising the VCG will make criteria more likely to fail and that reducing the VCG will make the criteria more likely to pass. This is not necessarily the case for equilibrium-based criteria such as freeboard requirements or for GZ-based criteria such as Angle of maximum GZ; if only these types of criteria are selected, Hydromax may have difficulty in finding a true limiting KG and specify convergence errors.

Limiting KG for damage conditions with initially loaded tanks

The set up of the Limiting KG analysis parameters has been modified to facilitate setting up the required TCG when calculating the Limiting KG for a damaged vessel where liquid cargo tanks initially carrying cargo or ballast water are damaged. Hydromax assumes that damaged tanks lose all liquid cargo or ballast that they may have been carrying and their buoyancy is lost from the vessel – analysis is done by the lost buoyancy method rather than the added mass method. For Limiting KG calculations for a damaged vessel where some of the damaged tanks were initially non-empty, it is often required to specify a required TCG. This is because under most circumstances, the intact vessel is upright (zero heel). The tanks would generally provide a transverse moment that must be balanced by the mass of the vessel, which must therefore be offset. Note that we are only concerned about the tanks that will be damaged and that initially contain cargo or ballast; this is because when they are damaged the ballast or cargo is assumed to be totally lost from the vessel. (Although seawater enters these damaged areas, this is not seen as an additional mass because damage is computed by the lost buoyancy method.) Two methods of specifying the required TCG are possible. The second method was available in older versions of Hydromax and it is the first method that provides the additional functionality:


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1. Current loadcase specifies initial loading of damaged tanks: This means that the currently selected Loadcase will be used to define the volume of cargo or ballast in tanks before damage is applied. If this method is selected Hydromax will look at the mass and CG of cargo or ballast in tanks which will be damaged during the analysis. This is used to compute required TCG. Note that all results and input data will be assumed to be for the intact vessel. That is the specified displacement will be that of the intact vessel and that the resulting LCG, TCG and KG will also be for the intact vessel. If the vessel has an off-centre intact TCG, this can be specified below (if the vessel is symmetrical and initially upright, this should be zero).

2. The second option is for the used to specify the required TCG directly. This functionality has been in Hydromax for many years. In this case, however the specified displacement and CG corresponds to that of the intact vessel with damaged tanks empty. i.e. the mass and CG of the intact vessel after deducting the masses of cargo or ballast in any tanks that will be damaged.

Example calculations

It is probably simplest to explain this functionality by means of an example. The following sample calculations demonstrate how the new Limiting KG options may be used. A vessel with a port-side tank that are initially full will have this tank damaged. We wish to find the maximum VCG that the intact vessel may have in order to pass the selected stability criteria. Initial tank loadings

First we need to define how much cargo is in the tanks that will be damaged. This is done by defining a loadcase and switching to the intact mode to specify the tank filling levels. Here we have specified that the tank is 80% full before the damage is applied.

Use a loadcase to specify the initial quantities of fluids in tanks

Setting the Displacements

Secondly we need to define the displacement range we wish to calculate the Limiting KG for. This is done in the Displacements dialog:

Displacement dialog


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Setting the Trim options

We now need to specify the trim options we wish to use. In this case we shall use free to trim, but with an initial vessel trim of 0.25m by the stern. Importantly we shall also specify that the current loadcase should be used to determine the required TCG and because the vessel is symmetrical, the specified TCG is zero:

Trim and TCG specification

Running the Analysis

We now need to select the damage case to be evaluated, the stability criteria that need to be passed and a suitable range of heel angles to be computed to evaluate the criteria. We also need to determine which way we should heel the vessel and in doubt should try heeling the vessel in both directions to see which will give the worst result. In this case large port-side tanks are to be damaged; these are filled significantly above the waterline so loss of ballast from these tanks will cause a list to Starboard, so the analysis should be done in this direction. Results from Limiting KG analysis

Limiting KG results

Validation of results

The results can be validated by completing a Large Angle Stability analysis with the specified displacement and CG. It must be remembered that these are KG results not VCG so when checking the VCG must be calculated. In this case the baseline (K) is at –356.845mm


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Model baseline

Computed VCG values

We can now set up a loadcase for one of the displacements. Remember that these are the intact vessel displacement and CG:

Loadcase to check calculated Limiting KG

When the analysis is run, it can be seen that (as expected) the stability criterion is passed with a very small margin.


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Criterion is passed with a small margin

Floodable Length

The Floodable Length analysis allows you to calculate the longitudinal distribution of maximum length of compartments that can be flooded with the vessel still passing specified equilibrium criteria. The results are presented as the maximum length of compartment plotted (or tabulated) against the longitudinal position of the compartment’s centre. Traditionally the criterion of margin line immersion is used to compute the Floodable Length curve. The Floodable Length may be computed for a range of displacements and compartment permeabilities.

Choosing Floodable Length

Ø Select Floodable Length from the Analysis Type option in the Analysis menu or toolbar.

Floodable Length Analysis Settings

The initial conditions required for Floodable Length analysis are: • Trim (free-to-trim, either initial trim or specified LCG)

• Displacement, select range and specify VCG

• Permeability, select range

• Bulkhead location (if applicable) The analysis is always carried out free-to-trim, but the centre of gravity can either be specified directly in the Trim dialog or it is computed from the specified initial trim. For information on Trim settings for Floodable Length Analysis, see: Trim for KN, Limiting KG and Floodable Length analyses on page 104. The range of displacements to be used is set in the same way as they are set in the KN and Limiting KG analyses. The VCG must also be specified since the Floodable length analysis is very sensitive to accurate trim calculations. This means that the vertical separation of CG and CB is accounted for in the trim balance. The permeability dialog is used to specify the permeabilities to be used for the Floodable Length analysis; the permeability is applied over the entire length of the vessel and is also applied to the free-surface when calculating the reduction of waterplane area and inertia.


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This permeability is unrelated to the permeability when defining compartments and is only used for floodable length calculations.

Floodable Length Environment Options

• Density



• Damage: no damage case may be selected as this is automatically defined by the analysis. The Intact condition is automatically selected and the Damage toolbar is disabled

• Criteria from the Analysis menu, select which criteria should be evaluated Criteria must be specified from the analysis menu. These are used to compute the Floodable Lengths.

Note that internally, Hydromax will treat the vessel sinking or the trim exceeding +/-89º as a criterion failure.

Floodable Length results

The results of the analysis are given in tabulated format at the stations defined in the Maxsurf Design Grid as well as graphical format. The tabulated data is linearly interpolated from the graphical data. (The raw graph data can be accessed by double clicking the graph.) There are several graph plot options available in the Data | Data format dialog (when the floodable length graph is topmost). The vessel profile (centreline buttock) may also be displayed. All compartment standards up to the maximum specified will be plotted.


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Floodable lengths graph options: • Fix the y-axis so that it is the same scale as the x-axis.

• Plot the different compartment standards up to a specified maximum value.

• Vessel profile (shown in light grey)

• Floodable Length Bulkheads locations are specified in a table in the Input window. The graph updates in real time as you adjust the bulkhead locations so once you have calculated the floodable lengths, you can quickly adjust the bulkhead locations so that the vessel meets the required compartment standard.

If the analysis is unable to find a condition where the vessel passes the selected criteria, the following dialog will be displayed. The vessel sinking or the criteria failing in the intact condition could cause this.

Floodable Length Concepts

The analysis is performed by defining a flooded compartment, with the centre of the compartment at a section under investigation. The length of this flooded compartment is increased section-by-section until one of the criteria is failed. The compartment is then moved progressively forward along the vessel. This process may be visualised by turning on the display of the Hydromax sections.


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Note: Speed versus Accuracy The analysis will be both considerably more accurate and slower with a larger number of sections in the Hydromax model; it is recommended that a minimum of 100 sections be used for most situations. The speed of the analysis can be increased quite considerably by increasing the allowable tolerances in the Edit | Preferences dialog.

Longitudinal Strength

Longitudinal Strength lets you determine the bending moments and shear forces created in the hull due to the loads applied in the Loadcase window. The analysis can be carried out in flat water or in a specified waveform.

Choosing Longitudinal Strength

Select Longitudinal Strength from the Analysis Type option in the Analysis menu or toolbar.

Longitudinal Strength Settings

The initial conditions required for Longitudinal Strength analysis are: • Displacement and Centre of Gravity using the Loadcase window

• Distributed loads using the Loadcase window When the Longitudinal Strength analysis mode is selected, two extra columns appear in the Loadcase window. These are used to specify the longitudinal extents of the load. A trapezium shaped distributed load is derived from the centre and fore and aft extents of the load. See the Loadcase Longitudinally Distributed Loads section on page 38 for more details.


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Longitudinal Strength Environment Options

• Density


• Hog and Sag


• Grounding (if any)

• Criteria, allowable shears and moments from Input window Note that Hydromax will always use the fluid simulation method when performing a longitudinal strength analysis. For more information on how Hydromax can take fluids in tanks into account see Fluids Analysis Methods on page 108.

Longitudinal Strength Results

The output from the longitudinal strength calculations is a graph of mass, buoyancy, damage and non-buoyant volumes and grounding loads. From these, the net load, shear force and bending moment along the length of the hull are computed. If defined, allowable shear forces and bending moments are overlayed on the graph. Downward acting masses, such as normal masses in the loadcase or lost buoyancy due to damage, are given positive values. Upward acting forces such as buoyancy and grounding reactions are given negative values.

Name of Curve Description Mass Vessel mass / unit length Buoyancy Buoyancy distribution / unit length = immersed cross sectional


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area * density. Damaged tanks and compartments reduce the buoyancy.

Grounding Grounding reaction Damage/NBV Loas buoyancy due to damaged tanks and compartments and

Non-Byoyant Volumes (NBV) Net Load Mass + Buoyancy + Grounding + Damage (and NBV) Shear

Shear Force = ∫x

AftSt

dxx)(NetLoad

Moment Bending Moment = ∫−

x

AftSt

dxx)(ShearForce

Allowable shear and moment

Allowable shear and bending moments as specified in the input Modulus table.

This data is also displayed in the “Long. Strength” tab in the Results window. You can display this table by choosing Longitudinal Strength from the Results sub-menu under the Window menu; alternatively double-clicking in the graph will give you all the data as plotted.

Note Make sure you have defined sections in your model in Maxsurf. Without this, the longitudinal strength table will be empty.

Note: For the purposes of strength calculations, any point loads in the loadcase will be applied as a load evenly distributed 100mm either side of the position of the load. Tanks are taken into account as distributed loads as well based on their mass distribution that is calculated from the tank sections.

Tank Calibrations

Tank Calibration allows you to determine the properties of the tanks you have defined in the Compartment window, at a range of capacities.


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Choosing Tank Calibrations

Select Tank Calibrations from the Analysis Type option in the Analysis menu or toolbar.

Tank Calibration Input

• Tank definitions and boundaries

• Permeability

• Fluid type All required Tank Calibration Analysis input can be specified in the Compartment Definition table. Also see:

Relative Density of Tank Fluids on page 53

Tank Calibration Settings

• Trim, fixed trim

Tank Calibration Environment Options


• Density

Tank Calibration Results

In the Window | Graphs menu each tank can be selected for display in the Graph window. For more information see Chapter 5 Hydromax Reference.


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Sounding pipes and tank calibration results

If the vessel is trimmed, there are ranges of tank volumes that will show the same sounding/ullage. (The same effect can occur if the sounding pipe does not reach the lowest or highest point in the tank – remember that this can change as the vessel trims, which is effectively what is happening in the figures below). These points occur when the tank is near empty or near full, see below (increasing the trim, will exacerbate this phenomenon):

Figure a Zero trim

Figure b Trim by bow, near-empty

tank

Figure c Trim by bow, near-full tank

Figure a shows a sounding pipe that extends the whole height of the tank, with the vessel at zero trim. Here all tank filling levels will have a valid sounding. Figure b shows the vessel with (bow down) trim and a small amount of fluid in the tank. Here there will be a range of tank filling levels which all show zero sounding. Figure c shows the vessel with the same trim, but with the tank nearly full. Here there will be a range of tank filling levels that all show maximum sounding.


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These effects will be noted in the tank calibration results if they are extreme enough since Hydromax always adds calibrations at 1%, 97.9%, 98% and 100% full; if the 1% level does not intersect the sounding pipe, the sounding will be given as zero. Similarly if the 97.9%, 98% and 100% full levels do not intersect the sounding pipe, the maximum sounding will be displayed, see below. In the results out lined in red, there are four results which all have a sounding of 1.0m but different capacities – the fluid levels are all above the top of the sounding pipe. In the blue results, the last two results are below the bottom of the sounding pipe, giving soundings of 0.0m but different capacities (the last but one calibration point is the fluid remaining in the tank when the sounding is 0.0m).

Tank calibrations for severely trimmed vessels; sounding pipe does not cover full range of tank capacities. The profile view of the tank in the trimmed vessel is shown on the right; the sounding pipe is in the middle of the

tank and extends from the bottom to the top of the tank.

In a similar way, if the sounding pipe extends above or below the maximum and minimum fluid levels, you will get readings which have the same capacity but different soundings.

User specified sounding intervals

With the addition of user specified tank calibration intervals, it is possible to specify the calibration intervals that you require. These will start at a sounding of zero (rather than an ullage of zero). Note that in addition to the specified soundings, levels of 1%, 97.9%, 98% and 100% full will also be added if they have not already been included in the specified soundings. The 97.9% and 98% levels are given because it is at 98% that the free surface moment is made zero.

Starting and Stopping Analyses

To start the analysis, choose Start Analysis from the Analysis menu or toolbar. Hydromax will step through the parameter ranges specified, floating the hull to equilibrium conditions where required. Hydromax will redraw the contents of the windows to display the current hull position for each iteration. Calculations may be interrupted at any time by selecting Stop Analysis from the Analysis menu or toolbar.


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If you have stopped the analysis, you can resume calculation by selecting Resume Analysis from the Analysis Menu or toolbar. There may be a slight time delay on all of these operations while the current cycle is finished. You can also switch application by clicking in the window of any background program. Hydromax will continue to calculate in the background although its speed will be reduced. The drawing of the vessel at each step of the analysis can be quite time consuming. If you are not interested in seeing the progress of the analysis, switch to a table window and maximise it to speed up the analysis. Should the analysis take longer than about 45 seconds, Hydromax will flash and beep to indicate that the analysis has been completed. The start, pause and resume functions are also available in the Analysis toolbar:

Batch Analysis

Batch Analysis Concepts

Hydromax has basic batch processing capability. With a single command, Hydromax will run Large Angle Stability and Equilibrium analyses for all combinations of load and damage cases. Further, Limiting KG and KN calculations can be made for each damage condition. There are other options which allow the analysis to be performed heeling to both port and starboard. For the Limiting KG analysis you may also check the Limiting KG for each criterion individually. You may also choose to perform a Large Angle Stability and Equilibrium analysis at the final VCG. The aim of the batch processing function is to:

• Provide the user with a simple and consistent way of carrying out Large Angle Stability and Equilibrium analyses on a large number of load and damage cases.

• Facilitate time consuming Limiting KG analyses, especially where results for all individual criteria are required.

• Enable Limiting KG and KN analyses to be performed automatically for all damage cases.

• Facilitate testing with heel to port and starboard for vessels with asymmetric loading and/or damage conditions (or hulls).

• Facilitate export of the data from Hydromax and import into MS Excel for post processing and report generation.

• Provide all relevant results and the data required to be able to reproduce the runs, i.e.: analysis parameters, file name etc.

Before you can perform a Batch Analysis it is recommended that you run a number of Analyses manually to check whether the Model has been defined correctly and all Analysis Settings and Environment conditions have been set correctly.

Batch Analysis – Procedures

Once the loadcases, damage cases, key points, criteria and analysis parameters for the required analyses have been set up, the Batch Analysis is started


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• Analysis | Start Batch Analysis

Batch analysis runs all combination of loadcases and damage cases.

Tip: Under most operating systems, minimising Hydromax can reduce the time required to perform the calculations. This is because time consuming redrawing of the design windows, graphs and tables is avoided.

Batch Analysis Settings

Analysis parameters such as trim, heel angles etc. are set in the normal way for each analysis type included in the Batch analysis. For example, if you want the Large Angle Stability to use a fixed trim of 0.5 m:

• first select the Large Angle Stability analysis type from the analysis menu

• set the trim to Fixed trim and 0.5 m

• then select Analysis | Batch Analysis

Batch Analysis Environment Options (Criteria)

Any Analysis Environment Options specified prior to a Batch Analysis will be used during the Batch Analysis. Any criteria that have been set are evaluated at the end of each analysis and the results of these are also output to the text file.


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Important: For important information on varying displacement while evaluating criteria, see Important note: heeling arm criteria dependent on displacement on page 192.

Batch Analysis Results

Before analysis starts, you will be prompted to enter the name and location of the file where Hydromax will write the results of the batch analysis. Once the analysis is complete, this tab delimited text file may be imported directly into MS Excel for further processing. Because the analyses are simply carried out one after the other, it is not possible to go back to the results for a specific analysis from within Hydromax; only the results of the final analysis will be stored in Hydromax. At the bottom of the dialog is a check box which allows users to select whether the results of a batch analysis should go to the Report window in Hydromax as well as the batch analysis text file. When the option for Sending the results to Word is selected in the Edit | Preferences dialog, the batch analysis will automatically create a Word document.

Warning: Sending the results to the Report can slow down analysis considerably and also consume considerable system resources. For large batch analysis, it is advisable not to include the results in the report. The report is stored in memory and if you have insufficient memory, it is possible that your computer will become very slow to respond and under some circumstances with certain operating systems even cause Hydromax to crash.

Also see: Reporting on page 116.

Analysis Settings

In the previous sections opening and preparing a model in Hydromax was discussed together with descriptions of the different Analysis types. This section will describe the following analysis settings:

• Heel

• Trim

• Draft

• Displacement

• Specified Conditions

• Permeability Hydromax will allow specification of only those analysis settings that apply to the currently selected analysis type.


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In hydrostatic analysis, there are three degrees of freedom: Trim, Heel and Draft. Hydromax matches the trim, heel and draft with the vessel’s mass and centre of gravity or visa versa. This way the volume of the displaced hull matches the required mass and the centres of gravity and buoyancy lie one above the other in a vertical line. For example: it can match a specified heel, trim and draft by varying the displacement and centre of gravity; or it can match a specified displacement and centre of gravity by varying the heel, trim and draft. Combinations of both are also possible. The following table is a very simplified representation of the degrees of freedom and their weight counterpart: Degree of Freedom Weight 1 Draft Displacement 2 Trim Longitudinal Centre of Gravity (LCG) 3 Heel Transverse Centre of Gravity (TCG)

In fact it is a rather more complicated situation than that suggested by the table above, because vertical centre of gravity is also important and also because most of the variables are coupled. The various analysis types and settings can be thought of as setting one variable in each pair to a fixed value and deriving the others from the analysis. For example: the Upright Hydrostatics analysis consists of fixing heel and trim and stepping through a series of fixed drafts. In this case the LCB and TCB (and therefore the required LCG and TCG) are calculated from the underwater hullshape at each draft. For an equilibrium analysis all degrees of freedom are derived from the centre of gravity and Displacement. In the Specified Condition Analysis any combination of the variable pairs may be specified.

Heel

The Heel dialog from the analysis menu is used to specify the range of heel angles to be used for Large Angle Stability, KN and Limiting KG analyses. Heel angles between -180° and +180° may be specified. The heel steps must be positive. If only one set of steps is required, simply put 0 in the other steps. If there is any asymmetry in the vessel due to either: hull shape, key points, loading, damage, etc., and there is any doubt as to which will be the worst heel direction, then the analysis should be carried out for both heel to starboard and heel to port to find the most pessimistic condition. If all the heel angle intervals are 10 deg or less, Hydromax will fit a cubic spline to the GZ curve and use this to interpolate for values between the tested heel angles. If any step is greater than 10 deg, Hydromax will not do any curve fitting and linear interpolation will be used.


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Note: For the angle of equilibrium to be found (when analysing criteria), it is essential that the GZ curve crosses the GZ=0 axis with positive slope. It is possible that the GZ at zero heel may be very slightly positive (due to asymmetry or rounding error) for this reason, it is advisable to test at least one negative heel angle, at say -5 degrees, to ensure that the equilibrium angle is identified. It is good practise to start the heel range at an angle of approximately -30°. This is to allow roll back angle criteria to be evaluated correctly.

Note: The heel angles to be used are specified independently for each analysis mode. This can be a source of apparent differences in the results from the different analyses.

Trim

For most analyses you may specify whether the vessel is free-to-trim or has fixed trim. Select Trim in the Analysis menu to bring up the Trim dialog.

Specification of different trim options is dependent on the type of analysis currently selected.


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Trim may be specified for Upright Hydrostatics, Large Angle Stability, KN Analysis Limiting KG, Floodable Length and Tank Calibrations. (For the Specified Condition analysis, the trim may be specified in the Specified Conditions dialog.) Equilibrium and Longitudinal Strength analyses always use a free trimming (and free heeling) analysis so that there is no trimming (or heeling) moment applied to the vessel at the final equilibrium.

Trim for KN, Limiting KG and Floodable Length analyses

The trim dialog is also used to specify the centre of gravity of the vessel when required:

Trim dialog

Fixed trim (KN and Limiting KG analyses only). The analysis is carried out with the specified fixed trim; the vessel is not free-to-trim as it heels. Although considerably faster, this analysis will tend to over-estimate ship stability properties such as GZ.

Free-to-trim using a specified initial trim value Using this method, for each displacement, the LCB of the intact vessel at the specified trim and zero heel is computed. The LCG is calculated using this value and the VCG. Calculations at each heel angle of the large angle stability analysis are then done free-to-trim using the derived LCG and VCG. Thus, for each displacement, the upright, intact vessel trim will be the same, but the LCG will be different.

Free-to-trim to a specified LCG value With this method, a specified constant LCG is maintained for each displacement. This LCG is then used to compute the free-to-trim vessel orientation at each heel angle as the large angle stability analysis is performed. Thus, for each displacement, the LCG will be the same, but the upright vessel trim will be different.

VCG for trim balance The VCG, measured from the vertical zero datum (not necessarily KG), may be specified. For KN analysis, the VCG will only have an effect if the analysis is free-to-trim. It will be used to determine the LCG if an initial trim value is specified. It will also be used to improve the accuracy of the KN results.


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For Floodable Length calculations, which are always calculated free-to-trim, the VCG will be used to calculate the LCG if an initial trim value is specified. Also, because the analysis is very sensitive to trim, the VCG is needed to provide an accurate balance of the trimming moment. (As the trim angle increases the longitudinal movement of the centre of gravity due to its vertical position becomes more important.) In the case of the Limiting KG analysis, the actual VCG is used and the VCG input field will state “not applicable”.

TCG value The TCG option allows you to specify an off-centreline centre of gravity for Limiting KG and KN calculations. This is especially useful when evaluating the Limiting KG of a damaged vessel that had cargo or ballast in tanks which are subsequently damaged. The TCG can be either specified directly or calculated from the tank loadings defined in the current loadcase.

Draft

The draft dialog is used to specify the range of drafts to be used for the Upright hydrostatics analysis.

The VCG specified in the draft dialog is used for the calculation of upright stability characteristics such as GMt only, and is specified in terms of KG – i.e. from the baseline, which is not necessarily the vertical zero datum.

Displacement

The displacement dialog is used to specify the range of displacements to be used for the KN, Limiting KG and Floodable Length calculations.

Specified Conditions

The specified conditions analysis setting is only available for the specified condition analysis. See Specified Conditions on page 79.


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Permeability

The Permeabilities are set in a table in the Permeability dialog. Use the Add and Delete buttons to add or delete rows from the table. The permeabilities may be sorted by double clicking on the permeability column heading. The last set of permeabilities used will be recalled from the registry when Hydromax is started.

The Permeability dialog is used to specify the permeabilities to be used for the Floodable Length analysis; the permeability is applied over the entire length of the vessel. This permeability is unrelated to compartment, tank or non-buoyant volume permeability and is only used for floodable length calculations.

Individual Permeability of Tanks and Compartments

The individual permeability of each compartment (or tank) is specified in the Compartment definition table. The compartment, tank and non-buoyant volume permeabilities are used when calculating the effects of damage, and/or calculating the weights of fluids in tanks in the loadcase. Also see:

Modelling Compartments on page 44

Tolerances

In the Edit | Preferences dialog of Hydromax, calculation tolerances can be set. This defines the tolerances that Hydromax uses to determine when to finish iteration during


• Equilibrium analysis

• Specified conditions

• KN calculations


• Longitudinal Strength Ideal tolerances can range between 0.00001% and 0.1% (1 gram in 10 tonnes of displacement). Acceptable tolerances can range from 0.001% to 1.0%. Acceptable tolerances should always be greater than Ideal tolerances.

Convergence Error

Hydromax will attempt to solve most analysis to within the ideal tolerance. If this is not achieved within a certain number of iterations, but the acceptable error has been achieved, Hydromax will continue. If convergence to within the acceptable error has not been achieved, Hydromax will display a warning.


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One of the most common causes of non-convergence is if the specified displacement exceeds the volume of the completely submerged vessel and it sinks. Also convergence may be poor if the trim angle approaches ±90°. If Hydromax thinks that it is likely that the model has sunk (waterplane area is zero at the current condition) the following dialog will be displayed. The specified displacement and the actual displacement at the current iteration are provided for information.

Note This warning is not displayed during batch analysis, instead the warning is written in the batch file.

The warning is also not shown when accessing Hydromax from a VBA macro using the Automation interface

If there is a convergence problem, which appears not to be due to sinking, then the following dialog will be displayed.

This problem can sometimes occur if the specified displacement is extremely small and the vessel has a large flat bottom, producing a highly non-linear waterplane area vs. draft plot. Other causes of non-convergence can be non-linear moment to trim vs. trim angle curve or moment to heel vs. heel angle curve.


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Note: There are occasions when convergence will not necessarily occur within the maximum allowable number of iterations. If Hydromax fails to converge it will give you a warning, but will allow you the option of continuing the search. If you choose to continue, Hydromax will search for the equilibrium position indefinitely. If the search is unsuccessful after a reasonable period of time, you can interrupt Hydromax by pausing the analysis.

The analysis will also fail to converge if the trim becomes excessive. All analyses other than Floodable Length will fail if the trim exceeds +/-45º; in the case of the Floodable Length analysis, this limit is increased to +/-89º.

Analysis Environment Options

The analysis can be performed in different environments; this section describes the analysis environment options available in Hydromax in more detail:

• Fluids Analysis Methods

• Density

• Waveform

• Grounding

• Hog and Sag


• Damage

Fluids Analysis Methods

Hydromax allows you to specify two different ways of simulating any fluids contained in tanks or compartments. Selecting Fluids in the Analysis menu opens the Fluids Analysis dialog. It is possible to specify the range of filling levels for which free surface moments should be applied in the loadcase. This functionality is accessed through the Analysis | Fluids dialog:


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Fluid Analysis dialog

If the corrected the VCG method is used, the FSM is applied if the filling level is within the exclusive range specified; i.e. if the filling level is less than or equal to the lower limit or the filling level is greater than or equal to the upper limit, the free surface moment will be zero. The upper limit is clearly stated by IMO as 98%, but the code provides some flexibility in interpretation for the lower limit. You may set different limits for each of the different free surface moment types other than “User Specified”. (see IMO IS Code)

3.3.2 Free surface effects should be considered whenever the filling level in a tank is less than 98% of full condition. Free surface effects need not be considered where a tank is nominally full ,i.e. filling level is 98% or above. 3.3.10 The usual remainder of liquids in empty tanks need not be taken into account in calculating the corrections, provided that the total of such residual liquids does not constitute a significant free surface effect.

In addition it is possible to ignore the free surface moment if the VCG correction for a single tank, due to the free surface moment is less than a specified amount. This requires that a nominal minimum displacement be specified. This is applicable to the “IMO” free surface moment type only. (see IMO IS Code)

3.3.9 Small tanks which satisfy the following condition using the values of "k" corresponding to an angle of inclination of 30°, need not be included in the correction:

m01.0/ min <∆fsM

where fsM is the free surface moment of the tank in question and min∆ is

the ship displacement at the minimum mean service draft of the ship without cargo, with 10% stores and minimum water ballast, if required.

Note: Tank Calibration results In the tank calibration results the free-surface moment based on the transverse second moment of area of the tank waterplane is given for all filling levels. This is because the actual free surface moment to be used to determine the VCG in a loadcase depends on the method being used and also the heel angle in question (in the case of the IMO correction).


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Note: Calculation of GM GM values always use the centre of gravity corrected for free surface moments even if the “simulate fluid” option has been chosen. Note that the upright free surface moments as shown in the loadcase are used, not those from the actual second moment of area of the inclined tank waterplane.

Note Most documented stability criteria assume that the corrected VCG method has been used. Although the computational potential is available, authorities have not adopted this more accurate calculation of the shift in centre of gravity due to fluid movement.

Fluid analysis method: Use corrected VCG

Tank capacities and free surface moments are calculated for the upright hull (zero trim and zero heel). The effective rise in VCG due to the tanks' free surface is calculated by summing the free surface moment of all the tanks and dividing by the total vessel displacement (the free surface moment to be applied is specified in the loadcase). This method should be used when compiling a stability booklet for a design, as it corresponds with the traditional approach used by naval architects and classification societies worldwide. It is reasonably accurate at low angles of heel and trim. In this case, the loading window will include a column for free surface moment and cells for corrected fluid VCG. These values are automatically calculated from the maximum free surface moments of the tanks, calculated in the upright condition. There are several FSM types available. For more information, see Working with Loadcases on page 32.

Fluid analysis method: Simulate fluid movement

This method is a faithful simulation of the static movement of the centre of gravity of the fluid in each tank. Every tank is rotated to the heel and trim angle being analysed. Hydromax iterates to find the fluid level for the rotated tank at the specified capacity. The new centre of gravity is calculated for each tank and used in the analysis. The new LCG, VCG and TCG are calculated for the whole design and used in the calculation of GZ, KG, and GM. This approach is used when the stability of a vessel is being investigated and the closest possible simulation of the hull's behaviour is required. It is particularly useful at high angles of heel or trim, or with tanks whose heeled water plane area may be significantly different from the upright case (i.e. tall narrow tanks, or wide shallow tanks). The penalty of using this approach is that the calculation time is longer, however the results are significantly more accurate.


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When fluid simulation method is selected, free surface moments and corrected fluid VCG are normally not displayed in the loadcase.

When selected, fluid simulation is used for analyses that use a loadcase, i.e. Large Angle Stability, Equilibrium Condition and Longitudinal Strength (the Longitudinal Strength analysis always uses fluid simulation). When fluid simulation is used in one of these analyses, the actual fluid level in the tank, filled to the volume specified in the loadcase, will be displayed in the View window. Otherwise the complete tank will be shown.

Density of Fluids

Where necessary, the density of sea water (the fluid in which the vessel is floating) and fluids commonly carried on board can be adjusted using the Density dialog. Density using the current units, or non-dimensional relative density (specific gravity), may be specified. Alternatively, density may be specified using Barrels as the unit of volume. Conversions are performed automatically. Specific gravity is calculated relative to a fluid having a density of 1000.0 kg/m3.

By assigning a code to the fluid you can easily apply the fluid type in the Compartment Definitions table. Tanks that have been specified as containing one of these fluids will be updated automatically when the density of the fluid is changed in the Density dialog. Tank calibrations results and loading conditions will also be updated.


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Note The vessel's hydrostatics are always calculated assuming the vessel is floating in the fluid labelled "Sea Water". This is the first fluid in the list printed in bold font. If the vessel is to float in a different fluid, it is necessary to change the density of this fluid. Note that only the custom fluids may have their names changed. Thus, if you wanted to carry out an analysis for a vessel in fresh water, you would change the density of "Sea Water" to 1000.0 kg/m3.

Saving and Loading Densities

Densities listed in the Density table can be saved and loaded using the File menu. The densities file may be edited manually if desired. There is one row for each of the 18 fluid types. The four columns, each separated by a tab character. These are fluid name, fluid code, specific gravity, colour respectively (the colour is in hexadecimal for the red, green, blue components and are probably much more easily edited in the Density dialog. The name and code for the first entry, Sea Water, cannot be changed (any changes made will be ignored). All other entries may be edited (the same restrictions area applied as when editing through the Density dialog).

Sea Water S 1.0250 6D00FF00FF00 Water Ballast B 1.0250 6D006D00FF00 Fresh Water W 1.0000 FF005F005F00 Diesel D 0.8400 FF005B00FF00 Fuel Oil F 0.9443 6D00FF006D00 Lube Oil L 0.9200 7F007F007F00 ANS Crude C 0.8883 3F003F003F00 Gasoline leaded G 0.7499 FF0000007F00 Unlead. Gas. U 0.7499 FF007F007F00 JFA J 0.8203 7F007F00FF00 MTBE M 0.7471 F600FA00C900 Gasoil GO 0.8524 FF00FF007F00 Slops SL 0.9130 FF006F00FF00 Custom 1 C1 1.0000 D6000300D600 Custom 2 C2 1.0000 D600D6000300 Custom 3 C3 1.0000 0300D600D600 Custom 4 C4 1.0000 D60003000300 Custom 5 C5 1.0000 DF00DF00DF00

If you make an error, you can always reset the densities to their default values in the Densities dialog. Also see:

Windows Registry on page 16

Waveform

Hydromax is capable of analysing hydrostatics and stability in arbitrary waveforms as well as for a level water plane. To specify a waveform, select the Waveform command from the Analysis menu:


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The water plane can be specified as flat, or as a sinusoidal or trochoidal waveform. If a waveform is specified, the wavelength, wave height and phase offset can be specified. The wavelength defaults to the waterline length of the hull at the DWL. If the wavelength is modified the wave height defaults to a standard metric wave, equivalent to:

Once a wavelength has been set, the wave height can be modified to give a non-standard height. The phase offset governs the position of the wave crest aft of the forward end of the DWL, as a proportion of the wavelength. The phase offset varies between 0 and 1, both of which correspond to a wave crest at the forward end of the DWL. For example, a phase offset of 0.5, with a wavelength equal to the waterline length, will give a single wave crest at amidships.

Grounding

Grounding is an additional analysis environment option for the Equilibrium or Longitudinal Strength analysis. It is possible to specify grounding on one or two points of variable length. The Equilibrium analysis will determine whether the hull is grounded or free floating and will trim the hull accordingly. Damage can be specified concurrently with grounding. If the vessel touches one or both grounding points, this will be reflected in the results:

The displacement column will show the total grounding reaction force in brackets; the sum of the buoyancy and the grounding reactions equals the loadcase displacement.


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The effective centre of gravity will be modified by the grounding reactions – a mass is effectively being removed from the vessel; this will bring the effective centres of gravity and the centre of buoyancy in line vertically. The value of KG, GMt and GMl are all calculated to the effective centre of gravity. Remember that KG is measured in the upright vessel reference frame (normal to the baseline); whilst GMt and GMl are the actual vertical separation of the metacentres above the centre of gravity in the trimmed reference frame normal to the sea surface.

Note: Grounding points are considered to span the transverse extents of the hull and therefore constrain the heel to zero. The length of the grounding points is only used when considering the load distribution for Longitudinal Strength analysis and not to determine the pivot point. The vessel is considered to pivot at the centre of the grounding point.

When two grounding points are entered, the first point (edit boxes on the left) must refer to the forward grounding point; the second grounding point is the aft grounding point.

Note: Fixed zero heel during grounding analysis The equilibrium analysis will only consider the longitudinal balance of moments, i.e. the vessel will not be balanced in heel and the vessel will remain upright (zero heel) even if the transverse metacentric height is less than zero.


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Hog and Sag

Hydromax has the option to apply hog or sag during the calculations.

Hog or sag is distributed in a parabolic curve centred at either the amidships location, or a specified longitudinal position relative to the zero point. This is called the “centre of deflection”. When hog is specified the centre of deflection and frame of reference at that location remain stationary and the ends of the hull are deflected downward.

When sag is specified the centre of deflection and frame of reference at that location remain stationary and the ends of the hull are deflected upwards.

Note: Hog and sag apply to all analysis modes including tank calibrations, which will vary slightly with changes in hog and sag.

Stability Criteria

Stability criteria may be seen as the “environment of authorities” that the ship will be deployed in.


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For more information see Chapter 4 Stability Criteria starting at page 123.

Damage

You can specify whether the model is to be analysed in intact or damaged condition using the Analysis Toolbar. Also see:

Damage Case Definition on page 61

Analysis Output

Hydromax will produce the following output data: • Hydromax model visualisation

• Result data tables per analysis

• Graphs per analysis

• Report

o Report window

o Streamed directly to a Word document

o Report Templates In this section:

•

• Reporting

• Copying

• Select View from Analysis Data

• Saving the Hydromax Design

• Exporting

Reporting

Hydromax has several options to do your reporting: •

• Batch Analysis text file and/or streaming to Report window

• Automatically generate a report in the Report Window for each analysis run

• Automatically Streaming results to Word

• Manually copy and paste tables and graphs from the Results Window and Graph Window

The most efficient method depends on the number of loadcases and damage cases you have to analyse and the output you require. Form small number of loadcases and damage cases you can do a manual copy and paste of the results into a report. This then allows you to validate the results at the same time.


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For large numbers of cases, it is recommended to use batch analysis. Batch Analysis results saved as text files do not include graphs. Select the option to send the results to the report window if you require Graphs. Additionally, if the option to Stream the report to Word has been selected in the Edit | Preferences dialog a word document is automatically generated after a Batch Analysis.

Streaming results to Word

It is possible to stream the Analysis results directly to Word. To do this: • Edit | Preferences

• Select the option to Send the Report to Word

This will send the Report document to Word instead of to the Report window. After you have run an analysis a Word document is created and opened automatically. This also applies to Batch Analysis.

Report Templates

Hydromax offers the ability to customise reports through a Report Template. This feature is only available when sending reports to Microsoft Word. With report templates, instead of just dumping the results of each analysis into a Word document, it is possible to use template keywords to specify where in the document the analysis results go and where each element of the output (such as graph, tables, etc) is placed. This gives you much greater control over how the analysis results are output than with the normal Send Report to Word option and allows you to customise your own report template document. To turn on Report Templating you need to select it in the Preferences dialog box. Simply tick the box ‘Use Word Templating’. Please note that Send Report to Word must be enabled before you can enable this option. See the dialog box below as an example:


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The Word Template File specified should be in .dot or .dotx/dotm (for Word 2007) format and will be used when creating any future reports. You can use one of the sample templates provided, or you can build your own template. Two Report Templates have been included to get you started: StabilityBooklet.dot

This is an example of a complete Stability Booklet template – this document is the default Word Template file for new users and is recommend for users wanting to quickly create a Stability Booklet. Users can start with StabilityBootlet.dot and then use it customise their own report template.

HMReportTemplate.dot This document is a good starting point for creating your own customised template. It contains an introduction to how templates are created and configured. It also includes all of the basic analysis blocks and variables to get you started.

Both of these templates contain macros and toolbar items to make life easier when you design your own template. These allow you to easily add and remove the analysis keyword blocks.

Note: To edit a report template in Microsoft Word you will need to start Microsoft Word and then open the template directly using the File menu. Simply double-clicking on a template document opens up a new document based on the template (which is not what you want).

The location of these report templates varies depending on which operating system you are using. On Windows XP/Server 2003 the default location for the report templates is:

• C:\Program Files\Maxsurf 14\Report Templates\ On Windows Vista, due to new security changes we’ve had to move this to an alternative location that every user has write access to – so you can find it at:

• C:\Users\Public\Documents\Maxsurf\Maxsurf14\Report Templates\

Tips:

See: Copying Tables on page 119 for tips on how to include the table header in a copy paste to for example Excel Graph Formatting on page 150 for tips on how to format your graph prior to copying to another application. Data Format on page 165 for tips on how to specify what should be displayed and customise how to display tables (vertical or horizontal).

Copying & Printing

A range of options for transferring data from Hydromax to other programs such as spreadsheets and word processors is provided through copy and paste functions. This data transfer works both ways: e.g. copying and pasting data to and from Excel spreadsheets allows you to use the full spreadsheet capabilities of Excel on your Hydromax model.


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Copying Hull Views

Pictures of the hull in the View windows may be copied to the Clipboard using the Copy command from the Edit menu. The image copied is as per the image displayed in the Hydromax view window. These pictures can then be pasted into other applications or the Hydromax Report window. To copy a simple bitmap image of the view at the current resolution, use Ctrl+I; additionally, a bitmap of the current image may be saved by pressing Ctrl+Shift+I

Copying Tables

Tables may be copied to the clipboard. Simply select a cell, row, column, range of cells or the whole table and then choose the Copy command or Ctrl+C. The data copied from the table will be placed on the clipboard and can then be pasted into a spreadsheet or word processor for further work.

Note: Copying data from the table with the Shift key depressed, will also copy the column headings.

Printing

Each of the windows in Hydromax may be printed. Simply bring the window you wish to print to the front and choose Print from the File menu. Views of the hull in the View window may be printed to scale as in Maxsurf. Prior to printing you may wish to set up the paper size and orientation by using the Page Setup command from the File menu.

Print Preview

The page to be printed is initially displayed in print preview mode. To print the page click the Print button, otherwise click the Cancel button. The printing may be forced to be black and white. Choose the Colours button and select the options required. Note that the print preview is not refreshed after these changes, but the selection will be reflected in the printout. The titles may be edited by clicking the Titles button.

Graph Printing to Scale

When printing the graph, it is possible to ensure that the graph is plotted to a sensible scale so that measurements can be made directly from the graph. To do this, hold the shift key down when selecting the print command for the graph. You will be asked if you want to print the graph to scale or to fill the page:


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The scale used will depend on the length units that are currently selected. If these are metric, then the graph will be plotted so that the grid lines are at one of the following intervals (If the current length units are imperial then similar intervals will be used, but they will be inches instead of cm.): 1.0cm, 2.0cm, 2.5cm, 5.0cm.

Exporting a Bitmap Image

You may also export a bitmap of the rendered perspective view with the File | Export | Bitmap Image command.

Select View from Analysis Data

For most analyses, each step from the analysis can be visualised when the analysis has completed. For example: the angle of downflooding can be visualised by returning to the Stability table in the results window, selecting the column at the required heel angle and select “Select View From Data” in the Display menu.

In the View window the hull will be displayed in the selected position. This can also be done for Upright Hydrostatics and the different wave phase calculations for an Equilibrium analysis in a waveform. The Select View from Data can also be used to display the Curve of Areas graph for each intermediate analysis stage, see Graph type on page 148.

Saving the Hydromax Design

Hydromax design data may be saved • Saving in a Hydromax Design File

• Saving Input Files separately

Saving in a Hydromax Design File

To save the design in one file, ensure that the View window is topmost and select Save from the File menu. The Hydromax data is saved in a .hmd file with the same name as the design.

Saving Input Files separately

In addition to saving all the data together, the data in the individual tables such as loadcases, damage cases, compartment definition, key points etc., may also be saved separately. For more information on file properties and extensions in Hydromax, please see: File Extension Reference Table on page 254.


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Note Although all Hydromax model data is saved in the .hmd file automatically every time you press Save from any of the design windows, it is recommended to also save the Hydromax input files separately. This gives the option of loading common data into different design files. E.g. for comparing the characteristics of vessels which have only minor differences in hull shape and identical tank layouts and loadcases.

Saving Loadcases to a File Once you have set up a loading spreadsheet, you can save it in a file on disk. This allows the same loading spreadsheet to be recalled at any time for use with the same design or with any other hull. To save the loadcase table, ensure the Loadcase window is topmost on the screen and choose Save Load Case from the File Menu. Selecting this option saves all the loads displayed in the current tab in the Loadcase window.

Saving Damage Cases to a File Bring the Damage window to the front and select Save Damage Cases or Save Damage Cases As from the file menu.

Saving Compartment Definitions to a File To save a compartment definition to a file, bring the Input window to the front and choose the compartment definition table; select Save Compartment Definition from the File menu. You will be asked to name the file and select where it is to be saved.

Saving Input Window Tables To save a input window table to a file, bring the Input window to the front and choose the required input table; select Save from the File menu. You will be asked to name the file and select where it is to be saved.

Saving Results to a File

Once you have performed an analysis, the data generated may be saved as a text file. This allows for further calculations to be done in a spreadsheet or for formatting to be done in Word, Excel or other programs. To save the data, ensure the Results window is topmost on the screen and choose the table containing the data you wish to save. Select Save or Save As from the File Menu. Selecting this option saves all the data currently displayed in the Results window. The Results files are saved as tab delimited text, meaning that they can be read directly into spreadsheets such as Excel with values being placed in individual spreadsheet cells.

Exporting

The data export function in Hydromax is similar to Maxsurf. Some Hydromax-specific export features are described below.


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Data export dialog in Hydromax.

DXF export Contains all lines displayed in the active design window as closed poly-lines. In addition, each tank, compartment and non-buoyant volume is exported on a separate layer. This export function is particularly useful to export tank arrangement drawings.

Note: The layer name is the same as the compartment name, so it is important to have unique compartment names.

For more information on data export of DXF and IGES, please see the “Output of Data” section in the Maxsurf manual.

Exporting the Model to Hydromax Version 8.0

After Hydromax version 8, a major change to the Hydromax file structure was made. Hydromax models created in versions greater than version 8.0 can be exported using the File | Export menu so that it is compatible with Hydromax version 8.0. All key points will become downflooding points in the version 8 file and any tank sounding pipe information will be lost.

http://www.fdsfiles.com/webmanuals/maxsurf/msmanual.htm#output_of_data

Chapter 4 Stability Criteria

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This chapter describes how stability criteria are used in Hydromax. Stability criteria are evaluated for Large Angle Stability, Equilibrium and Limiting KG calculations. A fixed sub-set of criteria is used for the Floodable length analysis and these criteria are accessed in their own, simplified dialog. The following sections will be discussed:

• Criteria Concepts, an overview of what capabilities Hydromax offers with regards to stability criteria.

• Criteria Procedures, explanation how to work with the Hydromax criteria dialog to create your own custom set of criteria.

• Criteria Results, criteria evaluation results

• Nomenclature, explanation of terms and definitions See also:

• Appendix B: Criteria file format

• Appendix C: Criteria Help

• Appendix D: Specific Criteria

Criteria Concepts

Hydromax includes a wide range of template criteria (or: parent criteria) as well as pre-defined custom criteria such as IMO, HSC, DNV, ISO and more. Hydromax uses a single dialog to control all the stability criteria. This makes it quick and easy to set which criteria should be included for analysis and to change criteria parameters. It is also possible for users to create their own custom sets of criteria. Users may save, import and edit their criteria sets. These custom criteria files may be easily transferred via email. Criteria may be identified as intact or damage criteria (or both). This ensures that the correct criteria are evaluated and displayed during normal and batch analysis. Although all criteria are displayed in the criteria table, only criteria that are applicable are added to the report; i.e.: if the intact case is being computed, only the criteria that are selected for evaluation during an intact analysis will be evaluated and added to the report, similarly for the damage cases. Criteria results are added to the Report after a Large Angle Stability or Equilibrium analysis. However, only the applicable criteria are added to the report (although all are displayed in the Results table); i.e. after an Equilibrium analysis only those criteria that are evaluated from Equilibrium data are added, and after a Large Angle Stability analysis only GZ based criteria are added to the report. Help information relating to the use and parameters of each criterion is displayed in the lower right hand corner of the dialog.

Criteria List Overview

Hydromax includes a wide range of criteria. These criteria are listed using in a tree control on the left-hand side of the criteria dialog. This section describes how this list of criteria can be divided up in to Parent heeling arms, Parent criteria, predefined custom criteria and user created custom criteria. This section also explains how all criteria can be divided up into two different criteria types: equilibrium and GZ curve based.


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The criteria tree list

Parent Calculations This folder contains calculations that are required for certain criteria parameters, for example, the roll-back angle required for the IMO IS code Severe wind and rolling (weather) criterion. These calculations may be referenced in certain criteria.

Parent calculations in Hydromax Criteria dialog

Parent Heeling Arms In most cases a ship is subject to specific heeling moments. Those heeling moment are then used in a number of different criteria. The Hydromax criteria list contains Parent Heeling Arms that can be copied into a custom criteria folder and then cross-referenced into the stability criteria.


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The advantage of using cross-referenced Heeling Arms is that a heeling arm is now defined (and edited) in only one place. This ensures that all criteria which use a specific heeling arm use exactly the same heeling arm. Another benefit is that, since the heeling arm is defined in one place, it is only displayed once in the GZ graph and not duplicated for each criterion that uses it. Furthermore some newer heeling arm criteria are only available for cross-referenced heeling arms and a greater variety of heeling arm definitions are available through cross-referencing.

Parent Criteria The Parent Criteria group contains all the parent criteria types that are available in Hydromax. Each parent criterion allows you to perform a specific calculation; these are the fundamental criteria from which criteria for specific codes are derived.

Parent criteria are special in that you cannot rename, delete or add criteria to the Parent Criteria group. Also the parent criteria settings cannot be saved, they will always revert to their default values when Hydromax is restarted. This is because the parent criteria are intended for use as templates from which you can derive your own custom criteria. This is done by dragging the required parent criteria in to the “My custom criteria” group or any other group you create.

To distinguish the Parent criteria from your derived criteria, they are displayed in bold text in the Criteria list.

Predefined Custom Criteria A number of criteria files containing criteria for specific codes are supplied with Hydromax. These may be found in the “HMSpecificCriteria” folder. This folder can be found in the Maxsurf root directory: c:\program files\Maxsurf. Most specific criteria are locked; those that are not locked require your ship design data to be input. Also see Working with Criteria Libraries on page 132 Appendix D: Specific Criteriaon page 238.

Custom Criteria You can create your own set of criteria in the tree as well. This is explained in the section on Working with Criteria on page 128.


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Types of criteria

There are two fundamental types of criteria:

Equilibrium criteria Equilibrium criteria are evaluated after an Equilibrium analysis and refer only to the condition of the vessel in its equilibrium state For example: margin line immersion tests, freeboard measurements, trim angle, metacentric height, etc. This type of criterion is also used by the Floodable Length analysis. Equilibrium

criteria can be recognised by the icon.

Criteria derived from measurements of the GZ curve. These are calculated after a Large Angle Stability analysis and during a Limiting KG analysis. For example, area under GZ curve between specified limits, angle of maximum GZ, etc. These criteria are often referred to as Large Angle Stability (LAS) or GZ criteria.

Note that there is some cross-over between the criteria types, notably angle of equilibrium heel. This can be measured from the GZ curve by looking for an up-crossing of the GZ=0 axis. The equilibrium heel angle is also a fundamental output of the Equilibrium analysis. The same also applies for GMt. For this reason, in some criteria sets some criteria are included twice, once in the form of an Equilibrium criterion and again as a Large Angle Stability criterion. For a criterion to be used in the search for maximum VCG in the Limiting KG analysis, it must be a LAS criterion. This is because it is only this type of criteria that is more likely to pass as VCG is reduced. A check is also made to ensure that any selected Equilibrium criteria are passed, but they cannot be included directly in the search algorithm. You will notice that different icons are used to differentiate between different types of criteria. These icons are derived from the parent criterion type. The different types of criteria and their icons are described below:

Folder icon, create separate folders to store related criteria. All folders must have unique names (even if the parent folders have different names).

Equilibrium criterion. These criteria are evaluated only after an equilibrium analysis has been performed.

GZ criterion. These criteria make measurements from the GZ curved obtained from a Large Angle Stability analysis.

GZ area criterion

GZ criterion with heeling arm

GZ area criterion with heeling arm

GZ criterion with several heeling arms and their combinations

GZ area criterion with several heeling arms and their combinations

Combined GZ criterion. These criteria perform several individual tests on the GZ curve. e.g. STIX.

Combined GZ heeling arm criterion. These criteria perform several individual tests on the GZ curve including a heeling arm. e.g. Weather criterion.

See next: Criteria Procedures


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Criteria Procedures

This section describes how to work with the stability criteria dialog. • Starting the Criteria dialog

• Resizing the Criteria dialog

• Working with Criteria

• Editing Criteria

• Working with Criteria Libraries

Starting the Criteria dialog

The criteria dialog allows you to select which criteria are selected for inclusion in the analysis and change their parameters. To bring up the Criteria dialog, select Criteria from the Analysis menu:

or use the Criteria button, , in the analysis toolbar:


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The criteria dialog is shown below:

Note: The Floodable Length analysis uses its own set of criteria. The criteria command will bring up the Floodable Length Criteria dialog when the Floodable Length analysis is selected.

Resizing the Criteria dialog

The dialog may be resized and a vertical and horizontal slider can be used to resize the width of the Criteria List and the height of the Criterion Details areas. Note that if, in the unlikely event that the dialog items vanish due to resizing the dialog, the dialog size can be reset by holding down the “Shift” key when you open the dialog. This behaviour is the same as all other resizing dialogs.

Working with Criteria

In the Concepts section it was explained how the criteria are listed in a tree list. This section explains how to create and customise your own criteria from the Parent Heeling Arms and Criteria provided with Hydromax.


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Using the Criteria Tree List

The tree works in much the same way as the file folders in Windows Explorer:

Ø Click on the “+” sign to expand the folder (or double click on it).

Ø Click on the “-” sign to collapse the group (or double click on it).

Ø Click on an item’s name or icon to select it

Ø Once selected, click again on the on the item’s name to edit its name

Some short-cut keys for the tree list: Tree control smart keys Function Alt+Keypad * Recursively expands the current group

completely Right Arrow or Alt+Keypad + Expands the current group Left Arrow or Alt+ Keypad - Collapses the current group Up Arrow Move one item up tree Down Arrow Move one item down tree Space Include criterion for analysis

Criteria Tree Right-click Context Menu

Several options are available by right-clicking on a criterion or criterion group:

Criterion right-click menu

Include for Analysis: Toggle whether the criterion (or all criteria within the group) should be evaluated.

Intact: Toggle whether the criterion (or all criteria within the group) should be evaluated for intact conditions.

Damage: Toggle whether the criterion (or all criteria within the group) should be evaluated for damaged conditions.

Lock: Toggle whether the criterion (or all criteria within the group) are locked. If a criterion is locked, this prevents inadvertent editing of its parameters. Locking is used for criteria belonging to specific codes where the required values are fixed.


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Add Group: Add a new criterion group.

Cut: Cut the criterion (or whole criterion group) to the clipboard. This may then be pasted into another location in the tree.

Copy: Copy the criterion (or whole criterion group) to the clipboard. This may then be pasted into another location in the tree.

Paste: Paste the criterion (or whole criterion group) from the clipboard to the selected location

Rename: Renames the criterion or group. This may also be done by selecting the label, then clicking again in the label.

Delete: Deletes the criterion or all the criteria and sub-groups within the group.

Defining new Custom Criteria and Groups

New custom criteria sets may be created by first creating a new criterion group and then dragging the desired criteria into the criterion group. By holding down the Ctrl button a copy of the criterion being dragged is created (unless it is a parent criterion, in which case a copy will be made regardless of whether the Ctrl key is held down or not). Alternatively use the Copy and Paste functions from the right-click context menu (see above). It is extremely important to ensure that all criteria groups have unique names. If duplicate group names exit, then loading the criteria file may cause unexpected results. As criteria (and new groups) are loaded they are inserted into the first group that is found with a name that matches the name of the group to which the criterion should belong. If there are groups with the same name, all criteria that should be in a group of that name will end up in the first one and none in the second.

Moving Criteria

Criteria may be moved from one group to another by dragging them with the left-mouse-button or by using the cut and paste functions in the right-click context menu (see above). Note that if you drag a criterion from the Parent Criteria group a copy will be made and the original will not be deleted.

Copying criteria

You can use the Criteria Tree Right-click Context Menu to copy and paste criteria. Alternatively, you can hold down the CTRL-key while moving the criteria you will copy the criteria.

Selecting the Criteria for Analysis

Criteria may be selected for analysis by ticking the tick box to the left of the criterion. Other functions are available from a menu activated when the right button is clicked on your mouse. To select an entire group, right-click on the group and choose Include for Analysis from the menu.

Editing Criteria

The specific details for a criterion are displayed in the table in the top-right of the dialog:


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Criterion details table

To edit the parameters for a specific criterion, click on the criterion’s name in the tree and the criterion’s parameters will be displayed in the table on the right. Edit the parameters as required and then select the next criterion to be edited from the tree, or click the dialog’s Close button. Please note that the criteria are updated as you change their data and that there is no “Cancel” function for this dialog. If in doubt, use the File | Save Criteria command to save a copy of your current criteria selection and data before making any changes in the Criteria dialog. The parameters that may be adjusted have a white background; those which cannot be edited, have a grey background. The values that are required for passing a criterion are in bold.

Check Boxes in Criteria Properties Section of Criteria Dialog

There is some subtly different behaviour for the check boxes in the dialog depending on their context. In most cases there will be group of related options used to define a criterion parameter. For example the limits for an upper integration range or the individual criteria to be evaluated for a more complex criterion:

In both of these cases the selection is cumulative and none of the selections are mutually exclusive. However, at least one must be selected.

In other cases, where the items are mutually exclusive, the check boxes act as radio buttons and only one may be selected. This occurs, for example, with the “Value of GMt at” criterion:


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Finally a check box can be used to select whether a specific effect should be included, for example, GZ curve reduction in the wind heeling criteria:

Criterion Pass/Fail Test

There are some subtle differences between the wordings for different criteria. For example one criterion may state “Shall be greater than…”, whereas another may state “Shall not be less than…”. Hydromax allows you to make this distinction by selecting the required comparison from a combo-box in the criterion row of the details table:

Description Symbol Logical test Shall be greater than > Greater than Shall not be less than ≥ Greater than or equal to Shall be less than < Less than Shall not be greater than ≤ Less than or equal to

Damage and Intact

Criteria may be defined as intact or damage stability criteria (or both). Intact criteria are only evaluated for the intact case and damage criteria are evaluated when a damage case has been selected (irrespective of whether there are actually any damaged compartments or tanks in the damage case). Criteria that are defined for both are always evaluated. A third option which is not yet implemented is WOD (Water on deck) this checkbox has no effect. These options may either be set using the right-click menu or by ticking the appropriate boxes in the bottom of the dialog:

Intact and Damage tick-boxes.

Working with Criteria Libraries

It is possible to load and save the criteria. The parent criteria, built into Hydromax are not saved, only the criteria that you create or import will be saved.

Default Criteria Library File

When starting, Hydromax will try to open the default criteria library file called: “Hydromax Criteria Library.hcr” from the directory in which the Hydromax program resides. By default this is c:\program files\Maxsurf\ Hydromax Criteria Library.hcr. If this file cannot be found, you will be prompted to locate a criteria file: You may select an alternative file or click the Cancel button to proceed and be given the default criteria, which consists of the Parent criteria and a “My Custom Criteria” group.


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The default criteria library will be automatically updated every time the criteria dialog is closed. Even if you loaded an alternative file, updates will be saved in the default criteria library, either overwriting the existing one or creating a new one.

Note It is good practise to save the criteria file with the project in the project folder. That way, when at a later stage you need to re-analyse the project, all criteria are still available. See Saving Criteria below.

Saving Criteria

It is also possible to save the criteria into a new file. This can be useful when you are defining new custom sets of criteria that you wish to keep separate or when defining criteria sets for different vessels. Choose Save Criteria As from the File menu. This will simply export all the custom criteria (parent criteria are not saved) to the specified file. Further updates will, however, continue to be saved to the default criteria library file that was opened when Hydromax was first started, so if you want to save any further changes you will have to resave as described above.

Importing Criteria and Specific Criteria Files

New criteria may be added to your criteria list by importing them – choose Import Criteria from the File menu. You will then be asked if you wish to keep the existing criteria:

If you choose “Yes” your existing criteria will be kept, if you choose “No”, all existing criteria except the parent criteria will be removed and replaced by those in the file you are opening. The default criteria library will be over-written with the new criteria so if you wish to keep any custom criteria that you may have added to your default criteria library, you must save them in a new file first. Note that when keeping your existing criteria, it is important to ensure that the group names in the file you are importing are not the same as those that already exist. If this does occur, the imported criteria will be found in the original groups, not in the new groups. A number of criteria containing criteria for specific codes are supplied with Hydromax. These may be found in the “HMSpecificCriteria” folder. You can import several criteria files in one go using Shift, or Ctrl select to select multiple files in the Open Hydromax Criteria dialog.


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Criteria File Format

The criteria are saved in a Hydromax criteria file with the extension .hcr. The file is a normal PC text file, which may be edited manually so as to generate custom criteria. The typical format of the file is given in the following file: c:\Program Files\Maxsurf\\HMCriteriaHelp\CriteriaHelp.html. Editing this file will also allow you to add your own help text or associate rich text format help files (rtf) files with your criteria.

Criteria Results

After a Large Angle Stability or Equilibrium analysis, criteria are evaluated and the results displayed in the Stability Criteria table in the Results window. Criteria can also be re-evaluated without having to redo the analysis when “Close and Recalculate” is selected in the criteria dialog. This allows you to edit criteria parameters or selected criteria and re-evaluate using the existing analysis results. After calculation the relevant criteria are also added to the Report.

Criteria Results Table

The tested criteria are listed one above the other. Intermediate values are displayed. Values that could not be calculated, e.g.: angle of vanishing stability, angle of equilibrium, etc., have n/a in the Actual and/or Value column. This is normally due to an insufficient range of heel angle having been used. Results may be displayed in “Verbose” or “Compact” format (see above). The format for the results table and the report are specified separately. Chose the Display | Data Format command when the Stability Criteria results are displayed:


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Stability criteria results window: compact format

Stability criteria results window: verbose format


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Report and Batch Processing

As noted earlier, only the relevant criteria results are added to the Report and/or Batch file. Criteria that are not relevant, i.e. any criteria that have a “not analysed” result, are not added to the Report (although they are displayed in the Criteria Results table). For example damage criteria during intact analysis or Equilibrium criteria during a Large Angle Stability analysis are not added to the report. Also see

Reporting on page 116 Batch Analysis on page 99

Nomenclature

This section gives a brief description of the various values that are determined by Hydromax in the evaluation of criteria. There are two distinct types of criteria:

Equilibrium criteria Equilibrium criteria are evaluated after an Equilibrium analysis and refer only to the condition of the vessel in its equilibrium state For example: margin line immersion tests, freeboard measurements, trim angle, metacentric height, etc. This type of criterion is also used by the Floodable Length analysis. Equilibrium

criteria can be recognised by the icon.

Criteria derived from measurements of the GZ curve. These are calculated after a Large Angle Stability analysis and during a Limiting KG analysis. For example, area under GZ curve between specified limits, angle of maximum GZ, etc. These criteria are often referred to as Large Angle Stability (LAS) or GZ criteria.

Note: The metacentre is always (even for Large Angle Stability criteria) computed directly from the vessel’s hydrostatic properties (i.e. water-plane inertia and immersed volume) at the specified heel angle and not from the slope of the GZ curve. This gives an accurate result that is not dependent on the heel angles and intervals tested during the analysis.

Definitions of GZ curve features

Some typical GZ curves are shown below, the third graph shows the GZ curve with a heeling arm overlayed.


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Typical GZ curve

Unusual GZ curve with double peak


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GZ curve with heeling arm superimposed

GZ Definitions

The table below defines how Hydromax calculates the various features of the GZ curve: Angle of vanishing stability

The angle of vanishing stability is the smallest positive angle where the GZ curve crosses the GZ=0 axis with negative slope.

Angle of vanishing stability with heeling arm curve

The angle of vanishing stability with a given heeling arm is the smallest positive angle where the GZ curve crosses the heel arm curve and where the GZ-Heel Arm curve has negative slope.

Downflooding angle

The downflooding angle is the smallest positive angle at which a downflooding point becomes immersed.

Equilibrium angle The equilibrium angle is the angle closest to zero where the GZ curve crosses the GZ=0 axis with positive slope.

Equilibrium angle with heeling arm curve

The equilibrium angle with a given heeling arm is the angle closest to zero where the GZ curve crosses the heel arm curve where the GZ-Heel Arm curve has positive slope.

First peak in GZ curve

In some cases, the GZ curve may have multiple peaks; this often occurs if the vessel has a large watertight cabin. The angle of the first peak is the lowest positive angle at which a local maximum in the GZ curve occurs.


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GML or GMT Vertical separation of the longitudinal or transverse metacentre and centre of gravity. The location of the metacentre is computed from the water-plane inertia, not the slope of the GZ curve. Note that the centre of gravity used is the upright centre of gravity corrected by the free surface moments of partially filled tanks in their upright condition, rotated to the specified heel (and trim) angle.

GZ Curve The curve of vessel righting arm (GZ) plotted against vessel heel angle

Heeling arm curve A curve of heeling lever, which is superimposed on the GZ curve. This is typically used to assess the effects of external heeling moments, which are applied to the vessel. These include the effects of wind, passenger crowding, centripetal effects of tuning, etc. Depending on the moment that they represent, the heeling arm curves will have different shapes. The heeling arms are never allowed to be negative; if the cos function goes negative, the heeling arm is made zero. If the heeling arm has a power of cos greater than zero, the heeling arm is forced to be zero at heel angles greater than 90° and less than -90°.

Maximum GZ Positive angle at which the value of GZ is a maximum Maximum GZ above heeling arm curve

Positive angle at which the value of (GZ - heel arm) is a maximum

Glossary

The table below describes some commonly used terms: φ Angle of heel measured from upright.

Deck Slope / maximum slope

The maximum slope of an initially horizontal, flat deck at the resultant vessel heel and trim. i.e. combined effect of heel and trim.

Gust Ratio Used for some wind heeling criteria, the Gust Ratio is the ratio of the magnitude of the gust wind heeling arm to the steady wind heeling arm.

g = 9.80665ms-2 1998 CODATA recommended value for standard acceleration of gravity

Roll back angle A negative heel angle change. Often a roll back angle is measured from some equilibrium position; the resulting heel angle after the roll back has been applied is more negative than the original. Commonly used in wind and weather criteria to account for the action of waves rolling the vessel into the wind. If a criterion uses a roll back angle, it is often necessary to calculate the GZ curve for negative angles of heel.

Chapter 5 Hydromax Reference

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This chapter contains brief descriptions of the tools available in Hydromax: • Windows

• Toolbars

• Menus

Windows

Hydromax uses a range of graphical, tabular, graph and report windows. • View Window

• Loadcase Window

• Damage Window

• Input Window

• Results Window

• Graph Window

• Report Window

View Window

The View window displays the hull, frame of reference, immersed sections of the hull and any compartments, and the centroids of gravity, buoyancy, and flotation. These positions are represented by: c b centre of buoyancy c g centre of gravity c f centre of flotation K location of keel (K) for KN

during KN analysis You can choose which type of view is displayed by selecting from the Window menu or the View toolbar. The Zoom, Shrink, Pan and Home View commands from the View menu may be used and work in exactly the same way as in Maxsurf. If a Perspective view is shown, you may also use the Pitch, Roll and Yaw indicators to change the angle of view. Please refer to the Maxsurf manual if you are unfamiliar with these functions. You may set the visibility of the various display elements by using the Visibility command from the Display menu. Two sets of visibility flags are maintained, one is used for all analyses other than tank calibration and the other is used for when the tank calibration analysis is selected. If a view window is visible when an analysis is being carried out, it will display the hull shape using the correct heel trim and immersion for the current step of the analysis. After an analysis, the Select View from Data command in the Display menu may be used to move the hull to a selected position from the Results window.


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The view of the tanks, compartments and non-buoyant volumes can be toggled between an outline view and a view of the sections.

Perspective view

In the perspective view, the model may be rendered.

The rendered view also enables tanks and compartments to be more easily visualised, especially when the hull shell is made transparent.

The rendering options are to be found in the Display menu, with further lighting options in the Render toolbar. Please refer to the Maxsurf manual for more information on the different rendering options available in perspective view.

Note: Fastest performance will be achieved by reducing the amount of redrawing that is required from Hydromax. For this reason, it is best to turn off sections, and especially waterlines, when performing an analysis. You may then turn them on again after the analysis has completed. For fastest performance, e.g. when running in Batch mode, minimise the Hydromax window so that no redrawing occurs.


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Loadcase Window

In the Loadcase window a spreadsheet table of all loads and tanks is displayed.

Using the tabs on the bottom of the window allow you to quickly browse through the different loadcases. Hydromax allows you to improve the presentation of the Load Case window by adding blank, heading or sub-total lines in the table. For more information see Working with Loadcases on page 32. The columns that are displayed may be selected using the Display | Data Format dialog.

Damage Window

The Damage window is used to specify which tanks and compartments are flooded in each damage case. There is always an Intact case, which cannot be edited, this is the default condition. If flooded volumes are required in the intact case they should be defined as non-buoyant volumes.


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Input Window

The Input window contains tables where the additional Hydromax design data is entered. The tables in the Input window contain the:

• Compartment Definition

• Sounding Pipes

• Key Points

• Margin Line Points

• Modulus Points

• Bulkhead loacations

The input window contains tabs on the bottom that allow you to quickly browse through the different input tables.

Compartment Definition

This table can be used to define the tanks and compartments in the Hydromax models. For more information see Modelling Compartments on page 44 in the Analysis Input section.

Sounding Pipes

This table is used to define the tank sounding pipes and calibration intervals. Default values are provided but these may be edited if necessary.

Key Points

There are several types of Key Points: • Down Flooding points

• Potential Down flooding points

• Embarkation points

• Immersion Points Only downflooding points are used in determining the downflooding angle, which is used in criteria evaluation.

Margin Line Points

The margin line is used in a number of the criteria. Hydromax automatically calculates the position of the margin line 76mm below the deck edge when the hull is first read in. If necessary, the points on the margin line may be edited manually in the Margin Line Points window (the deck edge is automatically updated so that it is kept 76mm above the margin line).

Modulus Points

This table is used to define the allowable limits for shear force and bending moment during the longitudinal strength calculations.


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Bulkheads

See Floodable Length Bulkheads on page 66.

Results Window

The Results window contains ten tables, one for each of the different analysis types plus criteria results and key points results tables. When switching mode, the currently selected results table will change to reflect the current analysis mode. Note that results are never invalidated if analysis options are modified – it is up to the user to ensure that the results are recalculated as necessary.

Setting the Data Format

It is possible to configure Hydromax so that only the results that you wish to see are displayed. To do this, choose Data Format from the Display menu.

A dialog similar to the one above will appear. Items that are selected with a tick will be displayed in the Results window and on any printed output. Items that are not selected are still calculated during the analysis cycle, but are not displayed. You may change the display format at any time after the analysis without having to redo the calculations. The data available for display depends on the analysis.

Data Layout

Most analysis data can be formatted vertically or horizontally to fit better on the screen or the printed page. For example, with Upright Hydrostatics, the data can be formatted so that each draft has a column of results, or so that each draft is on a separate row.


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To change the format, select Data Format from the Display menu, and select either the horizontal or vertical layout button.

Key Points Data Result Window

Key points data is calculated for Large Angle Stability, Equilibrium and Specified condition Analysis. The DF angle column is only visible when the analysis mode is set to Large Angle Stability and the Freeboard column is only displayed when the analysis mode is set to Equilibrium or Specified condition.

Stability Criteria Result Window

If stability criteria are turned on in the analysis menu, they will be evaluated during Large Angle Stability, Limiting KG and Equilibrium analyses. The results of the criteria evaluation are presented in this table after Large Angle Stability and Equilibrium analyses. Criteria results are not displayed in this table after a Limiting KG analysis. The results may be displayed in compact format:


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Alternatively, the results can be displayed in verbose format, where all the intermediate calculations are shown, by selecting the desired format in the Display | Data format dialog.

Graph Window

The Graph window displays graphs, which show the results of the current analysis. Hydromax will automatically display the graph that displays the result of the current

analysis when you select Graph from the Windows menu or press the toolbar button. Alternatively you can select a specific graph using the Windows | Graphs menu item. Only the graphs that are applicable to the current analysis can be displayed. Graphs can be copied using the Edit | Copy command.


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Depending on the analysis mode, different graphs are available.

Upright Hydrostatics Analysis: • Hydrostatics

• Curves of Form

• Curve of areas – different graph for each draft tested (selected using Display|Select view from data)

Large angle stability Analysis • Righting Lever (GZ)

• Curve of areas – different graph for each heel angle tested (selected using Display|Select view from data)

• Max steady heel angle

• Large angle stability (hydrostatic data other than GZ)

• Curves of Form

• Dynamic stability (GZ area)

Equilibrium Analysis: • Curve of areas

Specified condition Analysis: • Curve of areas

KN Values Analysis: • Cross curves (KN)

Limiting KG Analysis: • Limiting KG

Floodable length Analysis: • Floodable length

Longitudinal strength Analysis: • Longitudinal strength

• Curve of areas

Tank Calibration • One graph for each tank

For many graphs you can select what is plotted and other options with the Display | Data Format dialog.

Graph type

Hydromax can graph many types of data depending on the type of analysis being performed. These graphs include Upright Hydrostatics, Curves of Form, Curve of Areas, Righting Lever (GZ curve), Longitudinal Strength, Floodable Length and Tank Capacities. These can all be displayed via the Graphs item in the Windows menu. Tip: You can use the Select View from Analysis Data option (page 120) to see the Curve of Areas for each heel angle and/or intermediate stage during the analysis.


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Interpolating Graph Data

To display an interpolated value from one of the curves, use the mouse to click anywhere on the curve. The data in the lower left corner of the window will change to display the curve name and co-ordinates of the mouse on the curve. Click anywhere on the dashed line and drag it with the mouse; as you move the cursor the interpolated values will be displayed.

Note: In case multiple curves are plotted in the same graph you can switch between the curves by clicking on them. Hydromax will ignore the exact position you click on the curve to allow reading all related interpolated values along the black dashed line.

GZ Graph

The GZ value, Area and corresponding heel angle can be measured by using the slider; the slider data is displayed at the bottom of the Graph window. The area is integrated from zero heel angle to the location of the graph slider.

Note: Because the horizontal axis scale is always in degrees, the area is always given in units of length.degrees and cannot be displayed in units of length.radians.


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Note The lower integration limit is always zero (irrespective of the equilibrium angle). Thus if you require the area between two limits, you must subtract the area at the lower limit from the area at the higher limit.

Curve fitting for GZ graph

A curve fit will be performed if all the heel angle intervals are less than or equal to 10˚. If this is the case, a parametric cubic spline is used to fit a smooth curve through the calculated GZ data at the specified heel angles. This ensures that the fitted line goes exactly through the calculated GZ points. If you wish to prevent this curve fitting, add a heel angle interval of greater than 10˚ as the final step. This can sometimes be useful if you expect a discontinuity in the GZ curve.

Graph data

The graphed data can be obtained by double clicking on the graph. Since the graph data contains more data points than most tables in the results window, this double click can be extremely helpful to export the analysis data to for example Excel fro further processing. Especially in the case of the sectional area curve, where there is no tabular data available. Also see: Copying Tables on page 119.

Graph Formatting

When you are in the Graph window you can use the View | Colour dialog to change the colours of the curves in the graph as well as the background. The View | Font command allows you to change the text size and font size.

Copying Graphs

You can copy the contents of the Graph window using the Copy command or Ctrl+C. Note that the picture is placed in the clipboard as a meta-file which can be resized in Word or Excel.


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Note When the graph is pasted in Microsoft Word®, the graph can be edited by right clicking on the graph and selecting “edit picture”.

Report Window

Hydromax contains a Report window. This window is used to create a progressive summary of the analyses that have been carried out. This report can be edited via Cut, Copy and Paste; printed, saved to and recalled from a disk file.

Report Window Page Setup

When you are in the Report window, the File | Page setup command allows you to customise the page orientation and size you wish to use for reporting. This is important because, inserted tables will be automatically formatted to fit the current page set up. However, once the tables have been placed into the report, their formatting will not be changed by changes to the print set up. Hence it is often most convenient to select the desired report page set up before any analyses have been made. You can for example choose the landscape Page Setup prior to running an analysis to make the tables fit better. Hydromax will split most results tables so they fit the specified page set up. However, both Loadcase and Criteria results tables will not be split.

Editing a Report

The Report window has it's own toolbar permanently attached to the view, as well as a ruler showing you tab stops, indentation and margin widths. Underneath all of this you have your actual editing area. As the built-in report window only has basic editing and formatting functionality, it is recommended that the report window be used only to accumulate the results. Once all the results have been gathered in the report window, these should be saved and opened in a word processor such as Microsoft Word or Open Office for formatting:

• set the results tables up as you want them to appear in the report (the report uses the same column widths, fonts etc.); do the same for the graph widow;

• choose an appropriate paper size for the report (the tables will be split to fit this paper size, so choosing a wide paper size will prevent all but the widest tables from being split);

• copy and paste the Hydromax report into Microsoft word. Use the Format | Autoformat function in Word (with the default settings) to set the correct styles for the different levels of heading in the document, this will facilitate generating a table of contents and also allows you to re-format the various styles (or import a custom set of styles using the style organiser in Word).


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The information below is provided for reference, but it is strongly recommended not to use any of the formatting commands in the Report window. The toolbar has a number of buttons that allow you to change either the current settings, or the section of text that is currently highlighted. The toolbar contains the following items:

Font combo box Use this to change the current font

Font Size combo box Use this to change the current font size

Bold Use this to toggle the Bold style

Italic Use this to toggle the Italic style

Underline Use this to toggle the Underline style

Colour Use this to set Text Colour

Left Justify Use this to set Left Justification

Centre Justify Use this to set Centre Justification

Right Justify Use this to set Right Justification

Bullet Use this to toggle Bullet Points

The Ruler comes in two formats, in metric and in inches - the format you have displayed on your screen depends on the current Dimension Units you have (use Units in the Display menu to change this). The format shown below is metric.


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The Ruler allows you to set left, right, centre, and decimal tab stops. The tab stops are very useful for creating columns and tables. A paragraph can have as many as 20 tab positions. The 'left' tab stop indicates where the text following the tab character will start. To create a left tab stop, click the left mouse button at the specified location on the ruler. The left tab stop is indicated on the ruler by an arrow with a tail toward the right. The 'right' tab stop aligns the text at the current tab stop such that the text ends at the tab marker. To create a right tab stop, click the right mouse button at the specified location on the ruler. The right tab stop is indicated on the ruler by an arrow with a tail toward the left. The 'centre' tab stop centres the text at the current tab position. To create a centre tab stop, hold the shift key and click the left mouse button at the specified location on the ruler. The centre tab stop is indicated on the ruler by a straight arrow. The 'decimal' tab stop aligns the text at the decimal point. To create a decimal tab stop, hold the shift key and click the right mouse button at the specified location on the ruler. The decimal tab stop is indicated on the ruler by a dot under a straight arrow. To move a tab position using the mouse, simply click the left mouse button on the tab symbol on the ruler. While the mouse button is depressed, drag the tab to the desired location and release the mouse button. To clear a tab position, simply click on the desired tab marker and drag it off the ruler. Normally, a tab command is applicable to every line of the current paragraph. However, if you highlight a block of text before initiating a tab command, the tab command is then applicable to all the lines in the highlighted block of text.

Keyboard Support for Reports

In addition to menu support, there are also several useful keystrokes that are available while editing the report. These are listed below for convenience:

Ctrl+B Toggle Bold on/off Ctrl+U Toggle Underline on/off Ctrl+PageUp Position at the top of the report Ctrl+PageDown Position at the bottom of the report Ctrl+Enter Insert a page break

Opening and Saving the Report

The report can be saved to a file or read in from a file using the Save and Open Menu commands with the report window highlighted. This is useful if you wish to append an analysis to a report that had been calculated at some time in the past. (Load in the old report, perform the analyses; the new results will be appended to the end of the report which may then be resaved).


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Pasting images into the report

Sometimes, it is desirable to insert schematic images of the vessel into the report. This is very easily done, by copying an image from one of the design views and then pasting it into the report at the desired location. The image copied is as per the image displayed in the Hydromax view window. Ensure that the colors selected will be easily visible in the white background of the report view. Depending on which Microsoft operating system you are using (notably Win98), the image may not maintain its aspect ratio and may be pasted into the report as a square. To overcome this problem, paste the image into Microsoft Word first, then copy it from Word back into the Hydromax report window.

Toolbars

Hydromax has a number of icons arranged in toolbars to speed up access to some commonly used functions. You can hold your mouse over an icon to reveal a pop-up tip of what the icon does.

File Toolbar

The File toolbar contains icons that execute the following commands: New – Open – Save – Cut – Copy – Paste – Print

Edit Toolbar

The Edit toolbar contains icons that execute the following commands: Add Row - Delete Row | Sort Loadcase Rows – Move Loadcase/Tank Row up – Move Loadcase/Tank Row Down

View Toolbar

The View toolbar contains icons that execute the following commands: Zoom – Shrink – Pan – Home View – Rotate – Assembly window.


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The Rotate command is only available in the Perspective window. The Assembly window is not available in Hydromax.

Analysis Toolbar

The Analysis toolbar contains icons for selecting the current analysis, loadcase and damage case: Analysis Type – Current Loadcase – Current Damage Case

The Analysis toolbar also contains icons that execute the following commands: Criteria (dialog) | Start Analysis – Pause Analysis – Resume Analysis | Update Tank Values in Loadcase The “Update Tank Values in Loadcase” is exactly the same as the menu command for “Recalculate Tanks and Compartments on page 164.

Window Toolbar

Allows quick switching between commonly used windows: Perspective – Plan – Profile – Body Plan | Loadcase – Damage Case | Compartment – Downflooding – Margin Line – Modulus – Bulkheads | Results for Current Analysis – Criteria Results – Key Point Results | Graph – Report

Visibility Toolbar

The Visibility toolbar contains icons that show or hide various items in the graphical views: Sections – Datum Waterline – Waterlines | Key Points – Margin Line | Tanks – Damaged Tanks – Compartments – Damaged Compart. – Linked Negative Compartment. – NBV – Tank Names – Tank Sections – Tank Outlines | Show/Hide Grid * NBV = Non Buoyant Volume

Render Toolbar

Render – Render transparent – Toggle custom light 1 – Toggle custom light 2 – Toggle custom light 3 – Toggle custom light 4 – Customise light settings


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Edge VIsibility Toolbar

Hull Edges – Internal Edges – Feature Edges – Bonded Edges

Report Toolbar

Spool results to report

View (extended) Toolbar

Set Home View – Colour – Font – Preferences(unused) – Properties

Extra Buttons ToolbarToolbar

Add surface areas to loadcase – Preferences | Heel – Trim – Draft – Displacement – Displacement – Specified Condition – Permiability – Fluid simulation – Densities – Waveform – Hog/Sag – Grounding – Batch Analysis Data Format – Units – Coefficients – Set to DWL – Set View from Data – Hide Grid – Show Grid Only – Show Grid and Labels – Visibility Dialog – Show Single Section This toolbar provides a number of buttons for commonly used commands in case you should wish to customise your toolbars.

Menus

The following section describes all of the menu commands available in the Hydromax program.


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• File Menu

• Edit Menu

• View Menu

• Case Menu

• Analysis Menu

• Display Menu

• Data Menu

• Window Menu

• Help Menu

File Menu

The File menu contains commands for opening and saving files and printing.

New

Creates a new table for whichever input table is frontmost, e.g: when the Loadcase Condition is the frontmost window, the New command will create a new loading condition. When the Compartment Definition table is frontmost, New creates a new compartment definition.

Open

When no design is open, selecting the Open command will show a dialog box with a list of available Maxsurf designs. Select the design you wish to open, click the Open button. The requested design will be read in and its hull shape calculated for use in Hydromax. If a design is already open, the Open command will open whichever file corresponds to the frontmost input window.

Close

The Close command will delete the data in the frontmost window. Hydromax will ask whether you wish to save any changes. Selecting Close when one of the design view windows is frontmost will close the current Maxsurf design.

Save

Selecting Save will save the contents of the frontmost window to a file on the disk.

Save As

Selecting Save As performs the same function as save but allows you to specify a new filename preventing the original file from being overwritten.

Import

Allows import of file types other than Maxsurf design files

nuShallo Allows direct import of a nuShallo pan file.

Export

Selecting Export enables you to export a Hydromax file as a variety of different file formats such as:


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DXF or IGES. DXF exports sections as closed poly-lines. In addition, each tank, compartment and non-buoyant volume is exported on a separate layer (the layer name being the same as the compartment name, so it is important to have unique compartment names). IGES exports the NURB surface data. See the Maxsurf manual for more information.

Hydromax v8.0 file Also allows users to export Hydromax files that are compatible with earlier versions of Hydromax.

Export Bitmap Allows you to export the rendered image as a bitmap file at the specified resolution. This command is only available when the Perspective window is frontmost with rendering turned on.

Import Criteria

Imports criteria from the selected criteria files. Current criteria may be kept or discarded.

Save Criteria As

Exports the current criteria set to the specified file. It is good practice to save the criteria library with each project in a project folder. Note that a branch of the criteria tree may be saved in its own file by right-clicking on the branch folder in the Criteria dialog tree. The whole library may be saved by right clicking on the root “Criteria” branch; this is not normally necessary as this is done after any major changes to the criteria definition.

Load Densities

Loads density table data previously saved from Hydromax – can be useful for synchronising the densities on several computers.

Save Densities As

Saves the Fluid densities table data, see Density of Fluids on page 111.

Page Setup

The Page Setup dialog allows you to change page size and orientation for printing.

Print

The Print command allows you to print the contents of the frontmost window on the screen.

Exit

Exit will close Hydromax and all the data windows. If you have any data or results, which have not been saved to disk, Hydromax will ask you if you wish to save them before quitting.

Edit Menu

The Edit menu contains commands for working with tables.

Undo

Undo may be used with desk accessories, but cannot be used on Hydromax drawing windows or data windows.


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Cut

Cut may be used in the Report window but cannot be used on Hydromax drawing or data windows.

Copy

The Copy command allows you to copy data from any of the windows, including the design view, input tables, results tables and graph window.

Paste

Choose the Paste command to Paste data into the Loadcase window or other input tables, or the Report window. Paste cannot be used in the View, Graph or Results windows.

Select All

Selects the entire Report.

Fill Down

Copies text in a table down a column like a spreadsheet.

Table

Performs operations on Hydromax's Report window.

Insert New Table Create a new table in the Report.

Insert Row Insert a new row into the current table in the Report.

Split Cell Split the currently selected cell into two separate cells in a table in the Report.

Merge Cells Merge the selected cells in a table into a single cell in the Report.

Delete Cells Delete current cell, column or row or a range of cells, columns or rows in the Report.

Row Positioning Set Justification for the current table row or an entire table in the Report.

Cell Border Set Cell Border Width for a single cell or range of cells in the Report.

Cell Shading Set Cell Shading Percentage for a single cell or a range of cells in the Report.

Show Grid Toggle table grid lines in the Report.

Add

The Add command is used to add an entry to the input tables (Load, tank, margin line point etc.).

Delete

The Delete command will delete rows from the input tables. If no rows are selected, the last row in the window will be deleted, otherwise all selected rows will be deleted.


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Sort Items

Sorts the selected rows in the Loadcase window

Move Items Up

Moves the selected rows up (if possible) in the Loadcase and Compartment definition tables.

Move Items Down

Moves the selected rows down (if possible) in the Loadcase and Compartment definition tables.

Add Surface Areas

This command automatically adds the surface areas and centres of gravity of all hull surfaces into the current loading condition. This is useful for estimating the initial weight of hull plating.

Preferences

The Hydromax preferences dialog allows you to set your analysis tolerances (or: error values) and select the option to stream the report to a Microsoft Word document. Also see:

Tolerances on page 106 Streaming results to Word on page 117.

View Menu

The View menu contains commands for controlling the views in the graphics windows.

Zoom

The Zoom function allows you to examine the contents of the design view windows in detail by enlarging the selected area to fill the screen.

Shrink

Choosing Shrink will reduce the size of the displayed image in the design view windows by a factor of two.

Pan

Choosing Pan allows you to move the image around within the View window.

Home View

Choosing Home View will set the image back to its Home View size.

Set Home View

Choosing Set Home View allows you to set the Home View in the View window. To set the Home View, use Zoom, Shrink, and Pan to arrange the view, then select Set Home View from the View menu.


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Rotate

Activates the Rotate command, which is a virtual trackball which lets you freely rotate a design in the Perspective view window.

Colour

The Colour function allows you to set the colour of lines, labels, and graphs. Remember to always be careful when using colour. It is very easy to get carried away with bright colours and end up with a garish display that is uncomfortable to work with. In general it is best to use a neutral background such as mid grey or dull blue and use lighter or darker shades of a colour rather than fully saturated hues. From the scrollable list, select the item whose colour you wish to change. The item’s current colour will be displayed on the left of the dialog. To change the colour click in the box and select a new colour from the palette. When Loadcase window is frontmost, Colours for the loadcase items can be set. See Loadcase Colour Formatting on page 37.

Font

Font command allows you to set the size and style of text.

The text style chosen will affect the display and printing of all text in the Report, Loadcase, Graph, Curve of Areas, and Results windows.

Toolbar

Allows you to turn the Toolbars on and off.

Status Bar

Allows you to turn the Status Bar on and off at the bottom of the screen.

Properties

Displays the properties sheet, which may be used to view parameters of selected objects (such as tanks).


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Full Screen

Maximises screen usage.

Case Menu

Commands associated with the Loadcases and Damage cases

Edit Loadcase

Edit the properties of the current Loadcase (name and whether it is a loadcase or Loadgroup). Loadcases are created, opened and closed through the file menu. See Working with Loadcases on page 32.

Add Damage case

Add another damage case

Delete Damage case

Delete the selected damage cases

Edit Damage case

Edit the properties of the selected damage case

Max. number of Loadcases

Specify the number of loadcase tabs – this requires a restart to activate the changes made.

Analysis Menu

The Analysis menu can be used to change the current analysis mode. It also contains commands to set the input data and analysis settings and environment options required for the current analysis.

Note: It is good practice when preparing to run analysis to work down the Analysis menu starting at the top and checking all of the settings and environment options.

Heel

Selecting Heel allows you to specify the three ranges of heel angles that you wish Hydromax to step through. Separate ranges are used for Large Angle Stability, KN and Limiting KG analyses.


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Trim

Allows the specification of the trimming mode to be used for the analysis. This can be fixed trim; free-to-trim to loadcase; free-to-trim specifying initial trim value and free-to-trim specifying LCG position.

Draft

The range of drafts used for the analysis of upright hydrostatics can be set using this command. KG for the upright hydrostatics is also specified in this dialog.

Displacement

The range of displacements used for the analysis of KN values, Limiting KG and Floodable Length can be set using this command. The vertical centre of gravity to be used for KN and Floodable Length analyses is specified here.

Specified Condition

Allows you to specify Heel, Trim, CG, Displacement and Draft for the Specified Condition analysis.

Permeability

The range of permeabilities used for the Floodable Length analysis are set using this command.

Fluids

Allows you to specify whether to use Corrected VCG method or Simulate Fluid Movement method when treating the fluid contained in slack tanks. See Fluids Analysis Methods on page 108.

Density

This command allows you to set the density of fluids used in the analysis. See Density on page 111.

Waveform

The Waveform command allows you to perform analysis for a flat waterplane or sinusoidal or trochoidal waveforms.

Hog and Sag

Allows you to define the amount of hog or sag to be applied to the hull when calculating the vessel’s hydrostatics.

Criteria

The criteria menu item will bring up the criteria dialog. This allows you to specify which criteria will be checked during the analysis. See Criteria on page 123.

When the floodable length analysis is selected, the criteria command will bring up a Floodable Length Criteria dialog with criteria that only apply to floodable length analysis.

Grounding

Specifies grounding on one or two points of variable length for use with the Equilibrium and Longitudinal Strength analyses.


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Update Loadcase

Checks for changed tanks and makes sure that any tanks and compartments that have not been formed are correctly calculated. It then updates the loadcase with the correct capacities and free surface moments for the tanks. Also recalculates totals and sub-subtotals after a row sorting or moving command. Also see:

Tank Loads on page 39

Recalculate Tanks and Compartments

Forces all tanks and compartments to be re-formed from their initial definition. This command also updates the loadcase. If any of the tank boundaries are made up from boundary surfaces, it is better to use “Recalculate Hull Sections” after re-opening the Maxsurf model to make sure the latest internal structure surfaces are being used as well.

Recalculate Hull Sections

Deletes all existing hull, tank and compartment sections and recalculates them from the hull surface data and compartment definition. This is particularly useful if the underlying Maxsurf model has been modified, if you wish to recalculate at a different precision, or if you wish to modify whether skin thickness or trimming options are applied.

Note: To be able to update the Hydromax model to changes made in Maxsurf see Updating the Hydromax Model on page 23 for a step-by-step procedure you can follow.

Snap Margin Line to Hull

Project all of the margin line points horizontally onto the hull surface, ensuring that the margin line follows the hull shape precisely. Also see:

Margin Line Points on page 65.

Set Analysis Type

Choose the analysis type you wish to use from the sub-menu.

Start Analysis

Selecting Start Analysis causes Hydromax to start performing the specified analysis. The analysis may be halted at any time by choosing Stop Analysis from this menu, also.

Resume Analysis

If you have halted analysis by choosing Stop Analysis, Resume Analysis may be used to restart the calculation from the point where it was interrupted.

Stop Analysis

This command halts the analysis at the current iteration. Note that the analysis may not have been completed and in the case of large angle stability, equilibrium condition and KN values, any data displayed for the final iteration may be incorrect.


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Start Batch Analysis

Hydromax will run the selected analyses for all combinations of load and damage cases using the batch processing command. Results are written to a tab delimited text file as specified by the user at the start of the analysis.

Spool to Report

Send the results of the analysis to the report upon completion. This should be turned on before commencing the analysis to ensure that results are added to the report when the analysis is completed.

Display Menu

The Display menu contains commands for controlling the data, which are displayed in the graphics and other windows.

Data Format

Data Format allows you to choose which data are tabulated and graphed (Upright Hydrostatics, Stability, Equilibrium and Specified Condition). A dialog box allows you to choose from a range of stability variables. See Setting the Data Format on page 145.

Hydrostatic results Data format dialog

Used to select display options for Criteria results:

Criteria table Data format dialog


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Used to select which columns are displayed in the Loadcase window:

Loadcase Data format dialog

When the Max. Safe heeling angle angles graph is shown as a result of a Large Angle Stability analysis the Data Format dialog may be used to customise the graph layout:

Max safe heeling angle Data format dialog

May be used to customise the Floodable length graph:

Floodable length Data format dialog


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Set Vessel to DWL

Rotates the vessel back to upright and to DWL after an analysis has been completed (or Select View from Data used). This is required for automatic update of the Loadcase (note that if you do not rotate back to the DWL, the Loadcase will not update while editing – only when start another analysis). This is to ensure that tank data in the Loadacase are for the vessel in the upright condition, not for tanks with the vessel at the final heel and trim of the last analysis.

Select View from Data

This function may be used to synchronise the display in the Design View window with one of the sets of data in Results window. The view may be set from any of the results from Upright Hydrostatics, Large Angle Stability or Equilibrium analyses. Simply highlight the column or row that corresponds to the condition you wish to view and select “Select View From Data”; the Design View will change to match the condition in the selected row or column in the Results window.

Visibility

The visibility of tanks, compartments, labels, hull contours, and other items in the design view may be set by using this dialog.

Grid

The grid submenu allows you to hide the grid or show the grid with or without station grid labels. The grid can only be displayed when the vessel is in upright position on its design waterline. The option to display the grid will be greyed out when the ship is currently displayed in, for example, a trimmed state at the end of an equilibrium analysis. Switching analysis type puts the boat back into upright position on its design waterline.

Show Single Hull Section in Body Plan

Selecting the Show Single Hull Section item from the Display menu will change the display in the Body Plan window to show only one section through the hull, as well as a control box, similar to the one in Maxsurf, in the top right corner of the window. The section being displayed can be chosen by clicking on the section indicators at the top of the control box. Alternatively, the section chosen can be changed by pressing the left or right cursor keys on your keyboard. This allows you to rapidly step through the hull sections from bow to stern. Also see:

Show Single Hull Section on page 27

Render

When the Perspective window is the current view for the model the Render option may be toggled on and off to render the surfaces.

Render Transparent

When the Perspective window is the current view for the model the Render Transparent option may be toggled on and off. Render Transparent makes the hull surfaces of the model semi transparent so that the rendered tanks and compartments within the model may be viewed.


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Animate

This command is available for any analysis that steps through several steps. For example, when a waveform has been specified and an equilibrium analysis is selected or after a Large Angle Stability analysis over a heeling range. Selecting Animate will animate the stability sequence in the design View window, through the range of heel angles specified. You may set the initial viewing position in the Perspective View window using the Pitch, Roll and Yaw indicators. When Hydromax has finished calculating the frames the sequence may be replayed by moving the mouse from side to side. Clicking the mouse button will terminate the animation. If animation is chosen after an Equilibrium Analysis has been performed in waves, the animation will automatically cycle through the full range of wave phases, giving a simple visual simulation of the motion of the hull through the wave. Hold the shift key down while selecting the command to save the animation.

Data Menu

Units

The units used may be specified using the Units command. In addition to the length and mass units classes, units for speed (used in wind heeling and heeling due to high-speed turn etc. criteria) and the angular units to be used for areas under GZ curves, may also be set. The angular units for measuring heel and trim angles are always degrees. See Setting Units on page 31 for more information.

Coefficients

Allows you to customise how you wish to calculate the coefficients as well as the display format for the LCB and LCF. See Customising Coefficients on page 30 for more information.

Design Grid

Access to the Design Grid is intended for information only. You are not expected to change the Design Grid in Hydromax.

Frame of Reference

Access to the Frame of Reference is intended for information only. You are not expected to change the Frame of Reference in Hydromax. If the position(s) of the Baseline and/or Perpendiculars need to be changed from those defined in the Maxsurf model, they may be changed using the Frame of Reference command. It is highly recommended that the correct frame of reference be set in Maxsurf prior to loading the design into Hydromax. This will ensure that a consistent frame of reference is used in all the programs. See: Setting the Frame of Reference on page 18.

Window Menu

For the items in this menu, each represents a Hydromax window. Selecting the item brings the appropriate window to the front.

Cascade

Displays all the Windows behind the active Windows.


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Tile Horizontal

Layout all visible windows across the screen.

Tile Vertical

Layout all visible windows down the screen.

Arrange Icons

Rearranges the icons of any iconised window so that they are collected together at the bottom of the Maxsurf program window.

View Direction

Select the desired view direction from the sub-menu. The selected design window will then be brought to the front.

Loadcase

Brings the Loadcase window to the front. The Loadcase window allows you to enter a series of component weights, together with their longitudinal and vertical distances from the zero point. These inputs are used to calculate the total Displacement and Centre of Gravity for Stability, KN and Equilibrium analysis.

Input

Choose from the Input item to bring the desired Input window to the front and display the Compartment Definition, Key Points, Margin Line Points or Modulus table.

Results

Choose from the Results item to bring the desired Results window to the front and display the desired table.

Graph

Brings the selected Graph window to the front. The Graph window displays a number of different graphs, depending on which analysis mode is currently active.

Help Menu

Provides access to Hydromax Help.

Hydromax Help

Invokes Hydromax Help.

Hydromax Automation Reference

Invokes the Automation Reference help system.

Online Support

Provides access to a wide range of support resources available on the internet.

Check for Updates

Provides access to our website with the most recent version listed.

About Hydromax

Displays information about the current version of Hydromax you are using.

Appendix A

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Appendix A: Calculation of Form Parameters

This Appendix explains how the calculation of form parameters (CB, CP, AM, etc.) is achieved in Hydromax, and investigates why differences with other hydrostatics packages may occur.

Definition and calculation of form parameters

Below is a summary of the definitions of basic vessel particulars and form parameters used in Hydromax.

Measurement Reference Frames

Results in Hydromax are given from the vessel’s zero point. However, because Hydromax treats trim exactly (the hull is rotated not sheared when trim occurs), there are two frames of reference:

Ship or upright frame of reference The “ship” or “upright” reference frame is that of the upright vessel with zero-trim. Here the baseline is horizontal and the perpendiculars are vertical. “Longitudinal” measurements are made parallel to the baseline and “vertical” measurements are perpendicular to the baseline.

World or trimmed frame of reference The “world” or “trimmed” reference frame is that of the trimmed vessel. Here the baseline is no longer horizontal and neither are the perpendiculars vertical. “Longitudinal” measurements are made parallel to the horizontal, static waterline and “vertical” measurements are perpendicular to the waterline

Rotated reference frame (red) and measurements in the two reference frames: Measurements in the upright vessel reference frame (green) and trimmed reference frame (blue)

The majority of measurements are given in the “ship” frame of reference. These include longitudinal centres of gravity, floatation and buoyancy (LCG, LCF, LCB); and measurements from the keel such as KB and KG. Measurements such as GM are measured in the “world” frame of reference, i.e. GM is the true vertical separation of the metacentre and the centre of gravity with the vessel inclined. It is for this reason the LCG and LCB values in the “ship” frame of reference are not the same if there is any vertical separation between the CG and CB even though the vessel is in equilibrium; it is the LCG and LCB in the “world” reference frame that are the same.

Appendix A

Page 171

Nomenclature

Amax Maximum immersed cross-sectional area to waterline under investigation

Ams Immersed cross-sectional area to waterline under investigation amidships

A Immersed cross-section area: Amax or Ams as selected by user

AWP Area of waterplane at the waterline under investigation BOA Overall beam of whole vessel (above and below

waterline) BWL Maximum waterline beam at design waterline B Maximum beam of waterline under investigation b Waterline beam of station under investigation GM Metacentric height: vertical distance from centre of

gravity to metacentre, measured in the trimmed reference frame

KB Distance from keel (baseline) to centre of buoyancy, measured normal to the baseline.

KG Distance from keel (baseline) to centre of gravity, measured normal to the baseline.

LOA Length overall LCB Longitudinal Centre of Buoyancy, measured in upright

reference frame, parallel to baseline. LCF Longitudinal Centre of Floatation, measured in upright

reference frame, parallel to baseline. LCG Longitudinal Centre of Gravity, measured in upright

reference frame, parallel to baseline. LWL Length of design waterline LBP Length between perpendiculars L length of waterline under investigation T0 Draft from some arbitrary baseline (normally the lowest

point on the design) T Maximum immersed depth (draft) of hull t Draft (immersed depth) of station under investigation ∇ Immersed volume of displacement at waterline under

investigation

Coefficient parameters

There are several options for calculating hullform coefficients. These can be modified in the Data | Coefficients dialog shown below:

Appendix A

Page 172

Length

The datum/design waterline or DWL is a waterline near which the fully loaded design is intended to float under normal circumstances. The forward perpendicular is normally defined as the intersection of the DWL with the bow. The after perpendicular is normally defined as the position of the rudder post, or possibly the transom. Several lengths may be defined: the LBP is the length between perpendiculars, this may be different from the length of the DWL (LWL) and in general, will also be different from the LOA (overall length). In some cases, particularly for resistance prediction purposes, it may be more appropriate to define an effective length of the underwater body, features such as bulbous bows and overhangs can make the LBP, LWL and LOA quite different. In addition, for calculations at drafts other than the DWL, it may be appropriate to use the actual waterline length at that draft (L).

Some of the more common lengths that may be used to characterise a vessel.

In Hydromax you may choose between the length between perpendiculars and the waterline length for the calculation of Block, Prismatic and Waterplane Area Coefficients. Select Coefficients from the Display menu:

Appendix A

Page 173

Beam

It is normal to use the maximum waterline beam for calculation of coefficients, and this may be of the DWL or the waterline under consideration. However, there may be times when it is appropriate to use the maximum immersed beam (e.g. submarine, vessel with tumble-home or blisters). For the calculation of section area coefficients it is normal practice to use the beam and draft of the section in question.

Vessel with tumble-home

Catamarans and other multihull vessels pose another difficulty. In some cases the overall beam is of importance, in others, the beam of the individual hulls may be required.

Hydromax uses the total waterline beam of immersed portions of the section for calculation of block coefficient and other form parameters. For the case of a monohull this will be the normal waterline beam. For catamarans this will be twice the demihull beam (remember that the total displaced volume is used and hence the block coefficient is the same as that of a single demihull). For the section shown below, the beam used would be the sum of B1, B2 and B3.

Multihull beams

You may choose which beam should be used from the following list:

In the reported hydrostatics, you can select various beams:

Appendix A

Page 174

Calculated beams

The values “Beam extents” are those that measure the beam across the maximum port and starboard extents of the vessel. For a catamaran this would be from the outside of the port demihull to the outside of the starboard demihull. For a monhull, this would simply be the distance from the port side to the starboard side. The other beam values are calculated by summing the breadth of waterline crossings as described above. For a monhull without tunnels, this will be the same as the extents value, but for a multihull, it will be less than the extents value. Hydromax uses these values for computing coefficients.

Draft

The draft is normally specified from a nominal datum. Normally this datum is the lowest part of the upright hull. However, for vessels with raked keel lines or yachts, the datum may be elsewhere. In Hydromax drafts are defined from the datum line. However, there are also occasions when the immersed depth of the section is a more relevant measure of draft, this is often the case when form parameters are calculated.

Hydromax uses the depths that stations extend below the waterline for calculation of form coefficients. Both depths are measured in upright position. You may select which depth should be used for the calculation of form parameters, including the option of measuring the draft to the baseline – this gives the option of ignoring appendages such as fin keels when determining the draft to be used to calculate the form parameter (if the baseline is defined to the bottom of the canoe body for example). It should be noted that the section area will, however, include the appendages.:

Appendix A

Page 175

Draft measurements

Draft measurement at heel angle When the vessel is heeled, the draft is measured through the intersection of the upright waterline and the centreline, perpendicular to the heeled waterline (see figure below). Essentially the draft is measured along the heeled and trimmed perpendiculars on the centreline. It is for this reason that as the heel approaches 90degrees, the draft becomes very large.

Draft measured along the inclined perpendicular lines

Midship and Max Area Sections

It is current usual practice to define the midship section as midway between the perpendiculars, however for some vessels it is defined as the midpoint of the DWL. For vessels with no parallel mid-body, the section with greatest cross-sectional area may also be of particular interest. In Hydromax, the position midway between the perpendiculars is defined as midships. When computing form coefficients, such as CP and CM, you may select which section area should be used: Hydromax uses the station with the maximum immersed cross-sectional area at the waterline under consideration.

Block Coefficient

Principles of Naval Architecture defines the block coefficient as: "the ratio of the volume of displacement of the moulded form up to any waterline to the volume of a rectangular prism with length, breadth and depth equal to the length, breadth and mean draft of the ship at that waterline." However, the actual definitions of the length, beam and draft used vary between authorities. Length may be LBP, LWL or some effective length. The beam may be at amidships or the maximum moulded beam of the waterline; or may be defined according to another standard – this may be important for hulls with significant tumble-home or blisters below the waterline.

Hydromax uses the length beam and draft as selected in the Coefficients dialog to compute the block coefficient. The beam used is that obtained by summing the immersed waterline crossings of the specified section.

TBLCB ⋅⋅

∇=

Appendix A

Page 176

Section Area Coefficient

Principles of Naval Architecture defines the midship coefficient as: "The ratio of the immersed area of the midship station to that of a rectangle of breadth equal to moulded breadth and depth equal to moulded draft at amidships." It should be noted that, for sections that have significant tumble-home or blisters below the waterline, the midship section coefficient can be greater than unity. In Hydromax midships is midway between the perpendiculars.

The section area coefficient used by Hydromax, is calculated at either the station with maximum cross-sectional area or the midship section area (as defined in the Coefficients dialog). The beam and immersed depth of the selected section is used unless the draft to baseline option has been selected in which case this draft is used.

Options for Section area coefficient

tbA

CM ⋅=

Prismatic Coefficient

Principles of Naval Architecture defines the prismatic coefficient as: "The ratio between the volume of displacement and a prism whose length equals the length of the ship and whose cross-section equals the midship section area." Again the definition of midship section and vessel length depend on the standard being used.

Hydromax uses the selected length and the selected immersed cross-section area Amax or Ams.

ALCP ⋅

∇=

Waterplane Area Coefficient

Principles of Naval Architecture defines the waterplane area coefficient as: "The ratio between the area of the waterplane and the area of a circumscribing rectangle."

Hydromax uses the length and beam as selected.

BLA

C WPWP ⋅

=

LCG and LCB

Hydromax allows you to fully customise how you want to display the LCB and LCF values. See Customising Coefficients on page 30 for more information.

Appendix A

Page 177

The LCG and LCB are calculated in the “ship” or “upright” frame of reference; see Measurement Reference Frames on page 170. When the vessel is free-to-trim, the LCG and LCB will be at the same longitudinal position in the global coordinate system, but not in the frame of reference. Therefore a difference between the LCG and the LCB value will occur when the vessel is trimmed. This is explained in the figure below:

Effect of vertical separation of CG and CB on LCG and LCB measured in the Ship reference frame

Note: LCG and LCB are calculated in the vessels’ frame of reference and therefore will have different longitudinal positions when the vessel is trimmed then for when it is upright.

This is the same for differences in TCG and TCB values due to heeling.

Trim angle

The trim angle as defined by:

−= −

pp

fa

L

TT1tanθ

where: θ is the trim angle; Ta , Tf are the aft and forward drafts at the corresponding perpendiculars and LPP is the length between perpendiculars.

Maximum deck inclination

The inclination angle is a combination of heel and trim angle. Hydromax calculates the steepest slope of the deck when the ship is trimmed and/or heeled. Deck camber and initial deck slope are not taken into account. For example:

Appendix A

Page 178

The Max deck inclination is the maximum slope of the deck when combining the trim and heel angle of the vessel, assuming the deck inclination is zero when the vessel is in upright position.

Immersion

The weight required to sink the model one unit-length below its current waterline. The unit-length can be either in cm or inch depending on your unit settings.

MTc or MTi

The required moment to make the vessel trim one unit-length. That can be either cm or inch depending on your unit settings.

RM at 1 deg

The righting Moment at 1 degree heel angle, calculated by

)1sin(**GMtDisplRM =

Potential for errors in hydrostatic calculations

There are a number of potential sources of error when calculating the hydrostatic properties of immersed shapes. These mainly occur from the integration method used, and occur in both hand calculations, and most automatic calculations carried out by computers. Both methods use numerical integration techniques, which are normally either based on Simpson's rule or the Trapezium rule. As with all numerical integration schemes, the accuracy increases as the step size is reduced, hence computer calculations offer an enormous advantage compared with hand calculations, due to the increased speed and accuracy with which these calculations may be carried out. With hand calculations, it is normal to use perhaps 21 sections and perhaps 3-5 significant figures; with computer calculations, it is quite feasible to use 200 sections or more with 10s of significant figures. These effects are noted from comparing the results of different hydrostatics packages on the same hullform. In general, differences for basic parameters such as displacement etc. are under 0.5% (note that, in general, agreement of hand calculations to within 2% is considered good). Differences in derived form parameters may show considerable variation. However, this is primarily due to differences in the definitions used – see discussion above. The 0.5% error discrepancy noted above, may be attributed to a number of causes:

Appendix A

Page 179

• Convergence limits when balancing a hull to a specified displacement or centre of gravity.

• Different number of integration stations used, and their distribution. Where there are large changes in shape, such as near the bow and stern, the stations should be more closely spaced. This can be of particular importance if the waterline intersects the stem profile between two sections.

• Differences in the hull definition, and number of interpolation points used to define each section. If the surface is exported as DXF poly-lines then the precision used and the number of straight-line sections used to make up the poly-line are important.

• The integration method used: trapezium, Simpson, or higher order methods.

Integration of wetted surface area

At first glance, it may seem that wetted surface area may be calculated by simply integrating the station girth along the length of the hull, in a similar way that one might integrate the station cross-sectional area along the length of the hull to obtain the volume. However, this is not the case, and the wetted surface area can only be accurately found by summing elemental areas over the complete surface. Further, the error due to integrating girths along the vessel length cannot be removed simply by increasing the number of integration stations. The only accurate numerical method is to sum the areas of individual triangles interpolated on the parametric surface. The differences are easily shown by considering the surface area of half a sphere. This is given analytically by: 22 RA π= , where R is the radius of the circle. It may be shown that the area obtained by integrating the girth of the sphere along its length is given by:

2

22' R

Aπ

= , note that this is with an infinite number of integration steps, and hence the

integration of section girths underestimates by error factor of 27.1/45.02

22

2

== πππR

R, or

approximately 27%. However, for normal ship hulls the differences will be much less, due to the greatly reduced longitudinal curvature. Surface areas calculated by the 'Calculate Areas' dialog in Maxsurf are the most accurate, since they are derived from the actual parametric definition of the surface. Those calculated by Hydromax and most other hydrodynamics packages, which use a number of vertical stations to define the hull, will be subject to the error described above.

Reference Designs

A folder of reference hull shapes is included with Maxsurf and Hydromax. These designs are of simple geometric shapes and can be used to validate calculations performed by Hydromax. Below is a table of results derived analytically from these shapes compared with results obtained from Maxsurf and Hydromax at different precisions.

App

endix A

Pag

e 180

Reference Calculations

Hyd

rost

atic

s ca

lcul

atio

ns fo

r var

ious

refe

renc

e de

sign

s, c

ompa

riso

n of

Max

surf

and

Hyd

rom

ax w

ith a

naly

tical

val

ues

sphere 10m

diam at 5m

draft

V

olum

e m

^3

WP

Are

a m

^2

VC

B

m

LC

B

m

Tra

ns. I

m^4

L

ong.

I m

^4

Vol

ume

WP

Are

a T

rans

. I

Lon

g.

I A

naly

tical

ly d

eriv

ed

261.

7993

9 78

.539

82

-1.8

75

0 49

0.87

3852

49

0.87

385

% e

rror

%

err

or

%

erro

r %

er

ror

Hyd

rom

ax H

igh

Prec

isio

n 26

0.49

98

78.3

81

-1.8

74

0 48

8.68

0726

9 48

9.14

247

-0.5

0%

-0.2

0%

- 0.45

%

- 0.35

%

Hyd

rom

ax L

ow P

reci

sion

26

0.34

279

78.3

57

-1.8

74

0 48

8.56

4741

48

8.93

873

-0.5

6%

-0.2

3%

- 0.47

%

- 0.39

%

Max

surf

Hi P

reci

sion

26

1.53

2 78

.341

-1

.875

0

490.

57

485.

761

-0.1

0%

-0.2

5%

- 0.06

%

- 1.04

%

Max

surf

Low

Pre

cisi

on

257.

105

77.8

49

-1.8

71

0 48

3.19

1 48

0.89

-1

.79%

-0

.88%

- 1.

57%

- 2.

03%

10m Cylinder 10m diam. at 5m draft

Vol

ume

m^3

W

P A

rea

m^2

V

CB

m

L

CB

m

T

rans

. I m

^4

Lon

g. I

m^4

V

olum

e W

P A

rea

Tra

ns.

I L

ong.

I

Ana

lytic

ally

der

ived

39

2.69

9 10

0 -2

.122

0

833.

3333

33

833.

3333

3 %

err

or

% e

rror

%

er

ror

%

erro

r H

ydro

max

Hig

h Pr

ecis

ion

391.

991

100

-2.1

21

0 83

3.33

3333

83

3.33

333

-0.1

8%

0.00

%

0.00

%

0.00

%

Hyd

rom

ax L

ow P

reci

sion

39

1.99

1 10

0 -2

.121

0

833.

3333

33

833.

3333

3 -0

.18%

0.

00%

0.

00%

0.

00%

M

axsu

rf H

i Pre

cisi

on

392.

522

100

-2.1

22

0 83

3.33

3 83

3.33

3 -0

.05%

0.

00%

0.

00%

0.

00%

M

axsu

rf L

ow P

reci

sion

38

9.87

4 10

0 -2

.118

0

833.

333

833.

333

-0.7

2%

0.00

%

0.00

%

0.00

%

App

endix A

Pag

e 181

Box 20m

long 10m

beam at 5m draft

Vol

ume

m^3

W

P A

rea

m^2

V

CB

m

L

CB

m

T

rans

. I m

^4

Lon

g. I

m^4

V

olum

e W

P A

rea

Tra

ns.

I L

ong.

I

Ana

lytic

ally

der

ived

10

00

200

-2.5

0

1666

.666

666

6666

.666

7 %

err

or

% e

rror

%

er

ror

%

erro

r H

ydro

max

Hig

h Pr

ecis

ion

1000

20

0 -2

.5

0 16

66.6

6666

6 66

66.6

667

0.00

%

0.00

%

0.00

%

0.00

%

Hyd

rom

ax L

ow P

reci

sion

10

00

200

-2.5

0

1666

.666

666

6666

.666

7 0.

00%

0.

00%

0.

00%

0.

00%

M

axsu

rf H

i Pre

cisi

on

1000

20

0 -2

.5

0 16

66.6

67

6666

.667

0.

00%

0.

00%

0.

00%

0.

00%

M

axsu

rf L

ow P

reci

sion

10

00

200

-2.5

0

1666

.667

66

66.6

67

0.00

%

0.00

%

0.00

%

0.00

%

Parabolic W

igley type Hull, LWL=15m

,B=1.5m,D=0.9375

Vol

ume

m^3

W

P A

rea

m^2

V

CB

m

L

CB

m

T

rans

. I m

^4

Lon

g. I

m^4

V

olum

e W

P A

rea

Tra

ns.

I L

ong.

I

Ana

lytic

ally

der

ived

9.

375

15

-0.3

52

0 1.

9287

5 16

8.75

%

err

or

% e

rror

%

er

ror

%

erro

r H

ydro

max

Hig

h Pr

ecis

ion

9.36

4 14

.985

-0

.352

0

1.92

527

168.

4685

-0

.12%

-0

.10%

- 0.

18%

- 0.

17%

H

ydro

max

Low

Pre

cisi

on

9.35

1 14

.98

-0.3

52

0 1.

9241

8 16

8.37

73

-0.2

6%

-0.1

3%

- 0.24

%

- 0.22

%

Max

surf

Hi P

reci

sion

9.

372

14.9

99

-0.3

51

0 1.

927

168.

63

-0.0

3%

-0.0

1%

- 0.09

%

- 0.07

%

Max

surf

Low

Pre

cisi

on

9.30

2 14

.942

-0

.351

0

1.91

16

7.62

1 -0

.78%

-0

.39%

- 0.

97%

- 0.

67%

Appendix B

Page 182

Appendix B: Criteria file format

The criteria are saved in a Hydromax criteria file with the extension .hcr. The file is a normal PC text file, which may be edited manually so as to generate custom criteria. The typical format of the file is given below: Please refer to the file C:\Program Files\Maxsurf\HMCriteriaHelp\CriteriaHelp.html for a full list of all the parameters for all the different criteria types. Hydromax Criteria File [units] LengthUnits = m MassUnits = tonne SpeedUnits = kts AngleUnits = deg GZAreaGMAngleUnits = deg [end] [criterionGroup] GroupName = Specific Criteria ParentGroupName = root [end] [criterionGroup] GroupName = My Custom Criteria ParentGroupName = root [end] [criterionGroup] GroupName = STIX input data ParentGroupName = Specific Criteria [end] [criterion] Type = CTStdAreaUnderGZBetweenLimits RuleName = STIX input data CritName = GZ area to the lesser of downflooding or… CritInfo = Area under GZ curve between specified heel… CritInfoFile = HMCriteriaHelp\StixHelp.rtf Locked = true GroupName = STIX input data TestIntact = true TestDamage = false Test = false Compare = GreaterThan UseLoHeel = false UseEquilibrium = true UseHiHeel = false UseFirstPeak = false UseMaxGZ = false UseFirstDF = true UseVanishingStab = true LoHeel = 0.0 HiHeel = 30.0 RequiredValue = 0.000 [end]

Appendix B

Page 183

[criterion] Type = CTStdAngleOfVanishingStab RuleName = STIX input data CritName = Angle of vanishing stability CritInfo = Calculates the angle of vanishing stability… CritInfoFile = HMCriteriaHelp\StixHelp.rtf Locked = true GroupName = STIX input data TestIntact = true TestDamage = false Test = false Compare = GreaterThan RequiredValue = 0.0 [end] The file must have “Hydromax Criteria File” in the first row. The first section of the file is the units section and this specifies the units that are to be used in the file. There are two angular units: AngleUnits Specifies the units for angular measurements,

e.g. range of stability GZAreaGMAngleUnits Specifies the angle units used for area under

GZ graph and for GM. The criteria then appear after the units section and as many criteria as required may be included. The common parameters for all criteria are as follows: Type Describes the type of criterion RuleName Text which specifies the rule to which the

criterion belongs CritName Text which specifies the criterion’s name CritInfo Verbose description of the criterion Locked Whether the criterion may be edited in

Hydromax or not. If Locked is set to true, it is not possible to edit the criterion’s parameters in Hydromax

The other parameters that may be set depend on the criterion type.

Appendix C

Page 184

Appendix C: Criteria Help

In this Appendix all individual Parent Criteria are explained in detail. This information can also be found in the lower right of the Criteria Dialog in the Criteria Help section. In this section:

• Parent Heeling Arms

• Parent Heeling Moments

• Parent Stability Criteria For all general help on criteria or working with the criteria dialog, see Chapter 4 Stability Criteria on page 123.

Parent calculations

Special calculations are provided for some criteria parameters. This allows for complex calculations to be cross referenced into criteria. Currently this has only been implemented for the IMO roll-back angle calculation used in the IMO code on Intact Stability, severe wind and rolling (weather) criterion. If there are any other calculations that you would like implemented, please contact [email protected] with details of the required calculations. The new parent calculations are listed above the parent heeling arms:

Parent calculations in Hydromax Criteria dialog

As with other criteria and heeling arms, you should make a copy of the parent calculation by dragging it to your custom criteria folder.

Selecting a calculation in a criterion

Using a calculation in a criterion is very similar to using a heel arm: • Define your custom calculation by copying it from the parent list.

• In the criterion select the required calculation from the pull down list:

Angle calculators r

These calculators produce an angular measurement and may be referenced by the following criteria:

Criteria that currently support roll-back angle calculations

Heeling arm criteria (xRef)

Ratio of areas type 2 XRefHeelRatioOfAreas2

Combined heeling arm criteria (xRef)

Combined criteria (ratio of areas type 2)

XRefHeelGenericWindHeeling

Heeling arm criteria (stand alone)

Ratio of areas type 2 - general wind heeling arm

CritHeelRatioOfAreas2

Heeling arm, Combined criteria (ratio of areas CritHeelGenericWindHeeling

mailto:[email protected]

Appendix C

Page 185

combined criteria (stand alone)

type 2) - general wind heeling arm

Heeling arm, combined criteria (stand alone)

Combined criteria (ratio of areas type 2) - wind heeling arm

CritHeelWindHeeling

IMO roll-back angle calculator

The IMO roll back angle calculator calculates the roll back angle as per the severe wind and rolling (weather) criterion as defined in the IMO Code on Intact Stability. The input parameters may be specified by the user or calculated by Hydromax for the vessel in the upright condition for the current loadcase. The block coefficient is calculated with the current user settings for length and beam (not necessarily the waterline beam which another parameter required for the calculation). The method used for the k-factor can be one of three options: “Round bilge: k = 1.0”, “Sharp bilge: k = 0.7” or “Tabulated value for k” – these are auto completed so you only need to type the first letter.

Input parameters for IMO roll-back angle calculation

Parent Heeling Arms

As with the criteria, there is a list of parent heeling arms, from which custom heeling arms may be derived:

Available heeling arms and moments

Appendix C

Page 186

To learn how to cross reference these heeling arms into criteria, please see Heeling arm criteria (xRef) on page 212.

Heeling Arm Definition

This section describes how to define heeling arms and is valid for both the parent heeling arms that can be cross referenced into the heeling arm criteria, and for the Old heeling arm criteria where the heeling arm is specified for each criterion separately. There are several heeling arms that are used for the criteria. They are defined below.

• General heeling arm

• General heeling arm with gust

• General cos+sin heeling arm

• User Defined Heeling Arm

• Wind

• Turning

• Lifting heeling

• Towing heeling

• Forces heeling arm

• Trawling heeling arm

• Areas and levers

• Important note: heeling arm criteria dependent on displacement

Note: When you are working with the parent heeling arms, make sure you copy them into a custom heeling arms folder before editing them. Same as for the Parent criteria, the Parent heeling arms will be reset to their default values each time you start up Hydromax.

General heeling arm

The general form of the heeling arm is given below:

)(cos)( φφ nAH = where: φ is the heel angle, A is the magnitude of the heeling arm,

ncos describes the shape of the curve. Typically n=1 is used for passenger crowding and vessel turning since the horizontal lever for the passenger transverse location reduces with the cosine of the heel angle. For wind n=2 is often used for heeling because both the projected area as well as the lever decrease with the cosine of the heel angle. However, some criteria, such as IMO Severe wind and rolling (weather criterion) have a heeling arm of constant magnitude, in this case n=0 should be used. Make sure you read Important note: heeling arm criteria dependent on displacement on page 192.

General heeling arm with gust

Some criteria require a Gust Ratio, this is the ratio of the magnitude of the wind heeling arm during a gust to the magnitude of the wind heeling arm under steady wind.

Appendix C

Page 187

steady

gust

H

HGustRatio =

Both the steady and the gust heel arm have the same shape.

)(cos)( φφ nsteady AH =

)(cos)( φφ ngust GustRatioAH ××=

where: φ is the heel angle, A is the magnitude of the heeling arm,

ncos describes the shape of the curve. It should be noted, that in this case, the definition of gust ratio is the ratio of the heeling arms. Some criteria specify the ratio of the wind speeds; if it is assumed that the wind pressure is proportional to the square of the wind seed, the ratio of the heel arms will be the square of the ratio of the wind speeds.

General cos+sin heeling arm

Some criteria, notably lifting of weights, require a heeling arm with both a sine and cosine component:

( ))(sin)(cos)( φφφ mn BAkH += It should be noted that provided the indices are both unity, the same heeling arm form may be used for computing towing heeling arms of the form:

( ))sin()cos()( δφδφφ +++= BAkH in this case a constant angle (in the case of towing, the angle of the tow above the horizontal) is included. It may be shown that this is equivalent to:

( ))sin()cos()( φφφ DCkH += where:

)(tan1 2

2

δα −+=

RC

, )tan( δα −= CD , 222 BAR += and AB

=αtan

Make sure you read Important note: heeling arm criteria dependent on displacement on page 192.

User Defined Heeling Arm

A user-defined heeling arm may be used in the criteria. With the heeling arm, the user can specify the number of points and the shape of the heeling arm curve. This heeling arm can then be cross-referenced into any of the heeling arm criteria. First, the number of points is specified and then for each point the angle and magnitude of the curve can be specified. These should be comma delimited for example <45 , 1.2> for a heeling arm magnitude of 1.2 meters at 45 degrees angle of heel. (To aid input of the data, if only one value is supplied it is taken as the heel angle – and the magnitude is left unchanged, and if a value preceded by a comma is given, this is taken as the magnitude – and the heel angle is left unchanged.) A single coefficient may be adjusted and this is used as a multiplication factor (whist the shape of the curve remains unchanged).

Appendix C

Page 188

Passenger crowding heeling arm

The magnitude of the heel arm is given by:

)(cos)( φφ npaspc

MDnH

∆=

where:

pasn is the number of passengers M is the average mass of a single passenger D is the average distance of passengers from the vessel centreline ∆ is the vessel mass (same units as M ) The heeling arm parameters are specified as follows: Option Description Units number of passengers: nPass

Number of passengers none

passenger mass: M Average mass of one passenger mass distance from centreline: D

Average distance of the passengers from the centreline

length

cosine power: n Cosine power for curve - defines shape none

Wind heeling arm

In the case of the wind pressure based formulation, the wind heeling arm is given by: ( )

)(cos)( φφ nw g

HhPAaH

∆−

=

where: a is a constant, theoretically unity A is the windage area at height h ∆ is the vessel mass P is the wind pressure H is the vertical centre of hydrodynamic resistance to the wind force In the case of the wind velocity based formulation, the wind heeling arm is given by:

Appendix C

Page 189

( ))(cos)(

2

φφ nw g

HhAvaH

∆−

=

where: a is now effectively an average drag coefficient for the windage area multiplied by the air density and has units of density v is the wind speed. And the other parameters are described as above. Option Description Units constant: a Constant which may be used to modify

the magnitude of the heel arm, normally unity for pressure based formulation or 0.5 ρair CD for the velocity formulation; where ρair is the density of air and CD is an average drag coefficient for the windage area

none for pressure based formulation; mass/length3 for velocity based formulation

wind model Pressure or Velocity (type “P” or “V”) wind pressure or velocity

Actual velocity of pressure - depends on wind model

mass/(time2 length) or length/ time

area centroid height: h Height of user defined total or additional windage area

length

total area: A User may specify either a total windage area

length2

additional area: A Or, an area to be added to the windage area computed by Hydromax based on the hull sections

length2

height of lateral resistance: H

There are four options for specifying H (all options are calculated with the vessel upright at the loadcase displacement and LCG): User specified

length

H = mean draft / 2 H is taken as half the mean draft. length H = vert. centre of projected lat. u'water area

H is taken as the vertical centre of underwater lateral projected area.

length

H = waterline H is taken as the waterline length cosine power: n Cosine power for curve - defines shape none

Turning heeling arm

The magnitude of the heel arm is derived from the moment created by the centripetal force acting on the vessel during a high-speed turn and the vertical separation of the centres of gravity and hydrodynamic lateral resistance to the turn. The heeling arm is obtained by dividing the heeling moment by the vessel weight. The heeling arm is thus given by:

)(cos)(2

φφ nt h

Rgv

aH =

where (in consistent units):

Appendix C

Page 190

a is a constant, theoretically unity v is the vessel velocity R is the radius of the turn h is the vertical separation of the centres of gravity and lateral resistance The heeling arm parameters are specified as follows: Option Description Units constant: a Constant which may be used to modify the

magnitude of the heel arm, normally unity none

vessel speed: v Vessel speed in turn length/time turn radius: R Turn radius may be specified directly length turn radius, R, as percentage of LWL

Or, as some criteria require, as percentage of LWL

%

Vertical lever: h There are four options for specifying h (all options are calculated with the vessel upright at the loadcase displacement and LCG): User specified

length

h = KG h is taken as KG - position of G above baseline in upright condition

length

h = KG - mean draft / 2 h is taken as KG less half the mean draft. length h = KG - vert. centre of projected lat. u'water area

h is taken as the vertical separation of the centres of gravity and underwater lateral projected area.

length


Lifting heeling arm

This is used to simulate the effect of lifting a weight from its stowage position. The magnitude of the heel arm is given by:

[ ])sin()cos( )( φφφ vhM

H lw +∆

=

where: M is the mass of the weight being lifted h is horizontal separation of the centre of gravity of the weight in its stowage position and the suspension position v is vertical separation of the centre of gravity of the weight in its stowage position and the suspension position ∆ is the vessel mass (same units as M ) The heeling arm parameters are specified as follows: Option Description Units Mass being lifted: M Mass of weight being lifted mass vertical separation of suspension from stowage position: v

Vertical separation of suspension point from weight’s original stowage position on the vessel. This value is positive if the suspension position is above the original stowage position.

length

horizontal separation of suspension from stowage position: h

Horizontal separation of suspension point from weight’s original stowage position on the vessel This value is positive if the

length

Appendix C

Page 191

horizontal shift of the weight should produce a positive heeling moment.

Towing heeling arm

The magnitude of the heel arm is given by:

[ ])sin()(cos )( τφτφφ +++∆

= hvgT

H ntow

where: T is the tension in the towline or vessel thrust, expressed as a force. h is horizontal offset of the tow attachment position from the vessel centreline v is vertical separation tow attachment position from the vessel’s vertical centre of thrust ∆ is the vessel mass n is the power index for the cosine term which may be used to change the shape of the heeling arm curve τ is the (constant) angle of the towline above the horizontal. It is assumed that the towline is sufficiently long that this angle remains constant and does not vary as the vessel is heeled. The heeling arm parameters are specified as follows: Option Description Units tension or thrust: T Tension in towline or vessel thrust force vertical separation of propeller centre and tow attachment: v

Vertical separation tow attachment position from the vessel’s vertical centre of thrust. This value is positive if the towline is above the thrust centre.

length

horizontal offset of tow attachment: h

Horizontal offset of the tow attachment position from the vessel centreline. This value is positive if the offset is in the direction of the tow.

length

angle of tow above horizontal: tau

Angle of tow above the horizontal angle


Forces heeling arm

This heeling arm can be used to model up to two forces acting on the vessel forces, such as those applied due fire-fighting or manoeuvring using thrusters. The magnitude of the heel arm is given by:

( ) ( )[ ])(cosh )(cosh 1

)( 212211 φφφ nn

forces HAHAg

H −+−∆

=

where:

1A and 2A are two forces acting on the vessel, expressed as a force, not a mass.

1h and 2h are the vertical heights (from the zero point) at which these forces act.

1n and 2n define the shapes of the heeling arms created by the two forces.

H is the assumed vertical position of the vessel’s centre of lateral resistance (or the centre of rotation from which the forces are applied) ∆ is the vessel mass g is acceleration due to gravity

Appendix C

Page 192

Trawling heeling arm

This heeling arm can be used model the effects of trawl net snagging as defined in Annex G of the Australian NSCV requirements :

)(cos)(sng trawl φφ n

mym

H+∆⋅

=

where: m is a mass parameter determined from the breaking load of the trawl gear and the downwards angle of the trawl net. y is the transverse distance of the line of action of the trawl wire from the vessel centreline

n defines the shape of the heeling arm. ∆ is the vessel mass

Areas and levers

Some criteria require the evaluation of above and below water lateral projected areas and their vertical centroids. The user may also specify additional areas and vertical centroids or the total areas and vertical centroids. In all cases the vertical centroids are given in the Maxsurf/Hydromax co-ordinate system; i.e.: from the model’s vertical datum, positive upwards. The lateral projected area and its centroid of area are calculated for the upright vessel (zero heel) at the draft and trim defined in the loadcase or trim dialog. The area is calculated from the hydrostatic sections used by Hydromax; thus, increasing the number of sections will increase the accuracy of the area calculation; further, only “Hull” surfaces are included in the calculation - “Structure” surfaces are ignored. The vertical position of the keel, K, is assumed to be at the baseline (as set up in the Frame of Reference dialog), even if the baseline does not correspond to the physical bottom of the vessel.

Important note: heeling arm criteria dependent on displacement

Some heeling arm criteria are dependent on the displacement of the vessel for the calculation of the Heeling Arm. For example, the value “A” in:

)(cos)( φφ nAH = ,is manually calculated from:

∆=M

A , where

M = heeling moment ∆ = displacement. For these types of heeling arms you should use the various heeling moment curves that are available – see below:

Heeling moment curves

Parent Heeling Moments

Heeling moments work the same way as Parent Heeling Arms in that they can be cross referenced into criteria. The advantage of using heeling moments is that they provide a constant heeling moment (varying heeling arm) as the vessel displacement changes (due to different loadcases or during a limiting KG analysis).

Appendix C

Page 193

These are in addition to the existing specific heeling arm curves for passenger crowding, wind heeling etc., which take account of the vessel displacement as required. The following heeling moments are available in the Hydromax criteria dialog:

• General heeling moment

• General cos+sin heeling moment

• General heeling moment with gust

• User Defined Heeling Moment

General heeling moment

The general form of the heeling moment is given below. It allows you to specify a constant heeling moment as opposed to a constant heeling arm:

)(cos)( φφ nAH

∆=

where: φ is the heel angle, A is the magnitude of the heeling moment (mass.length) and ∆ the vessel displacement

(mass); thus ∆A is the magnitude of the heeling arm (length).

ncos describes the shape of the curve. Typically n=1 is used for passenger crowding and vessel turning since the horizontal lever for the passenger transverse location reduces with the cosine of the heel angle. For wind n=2 is often used for heeling because both the projected area as well as the lever decrease with the cosine of the heel angle. However, some criteria, such as IMO Severe wind and rolling (weather criterion) have a heeling arm of constant magnitude, in this case n=0 should be used.

General cos+sin heeling moment

Some criteria, notably lifting of weights, require a heeling moment with both a sine and cosine component:

( ))(sin)(cos)( φφφ mn BAk

H +∆

=

where: φ is the heel angle, A and B the magnitudes of the cosine and sine components of the heeling moment

(mass.length) and ∆ the vessel displacement (mass); thus ∆A and

∆B are the magnitude of the

heeling arm (length). It should be noted that provided the n and m indices are both unity, the same heeling moment form may be used for computing towing heeling moments of the form:

( ))sin()cos()( δφδφφ +++∆

= BAk

H

in this case a constant angle (in the case of towing, the angle of the tow above the horizontal) is included. It may be shown that this is equivalent to:

( ))sin()cos()( φφφ DCk

H +∆

=

where:

Appendix C

Page 194

)(tan1 2

2

δα −+=

RC

, )tan( δα −= CD , 222 BAR += and AB

=αtan

General heeling moment with gust

Some criteria require a Gust Ratio, this is the ratio of the magnitude of the wind heeling arm during a gust to the magnitude of the wind heeling arm under steady wind.

steady

gust

H

H=GustRatio

The general form of the heeling moment is given below. It allows you to specify a constant heeling moment as opposed to a constant heeling arm. Both the steady and the gust heel moment have the same shape.

)(cos)( φφ nsteady

AH

∆=

)(cosGustRatio)( φφ ngust

AH ××

∆=

where: φ is the heel angle, A is the magnitude of the heeling moment (mass.length) and ∆ the vessel displacement

(mass); thus ∆A is the magnitude of the heeling arm (length).

ncos describes the shape of the curve. It should be noted, that in this case, the definition of gust ratio is the ratio of the heeling arms. Some criteria specify the ratio of the wind speeds; if it is assumed that the wind pressure is proportional to the square of the wind seed, the ratio of the heel arms will be the square of the ratio of the wind speeds.

User Defined Heeling Moment

With the User Defined Heeling Moment, the user can specify the number of points and the shape of the heeling moment curve. Defining User Defined Heeling Moments works in much the same as for User Defined Heeling Arm. This heeling moment can then be linked into a Heeling arm criteria (xRef) for evaluation.

Parent Stability Criteria

The parent criteria are divided up into different categories depending on their basic types.

Criteria at Equilibrium

These criteria are calculated after an equilibrium analysis and relate to the equilibrium position of the vessel after the analysis. The equilibrium criteria are only displayed in the report if you run an equilibrium analysis.

Maximum value of Heel, Trim or Slope at Equilibrium

This criterion may be used to check the value of maximum Heel, Pitch or Maximum Slope (compared with an originally horizontal and flat deck). Option Description Units

Appendix C

Page 195

The angle of Choose from the following (case insensitive auto-completion is used): Heel Pitch MaxSlope

deg

Shall be less than / Shall not be greater than

Permissible value deg

Minimum Freeboard at Equilibrium

Checks whether the minimum freeboard is greater than a minimum required value. This could be used to check margin line or downflooding point immersion. Option Description Units The value of Choose from the following (case

insensitive auto-completion is used): Marginline DeckEdge DownfloodingPoints PotentialDfloodingPoints EmbarkationPoints ImmersionPoints

length

Shall be greater than / Shall not be less than

Permissible value length

Maximum Freeboard at Equilibrium

Check that the maximum freeboard is less than a maximum required value. This could be used to check that an embarkation point is sufficiently close to the waterline. Option Description Units The value of Choose from the following (case

insensitive auto-completion is used): Marginline DeckEdge DownfloodingPoints PotentialDfloodingPoints EmbarkationPoints ImmersionPoints

length



To check that the freeboard lies within a specified range, use a combination of both forms of the minimum/maximum freeboard criteria.

Value of GMT or GML at Equilibrium

This criterion is used to check that the GM (transverse or longitudinal) exceeds a specified minimum value. Option Description Units The value of Choose from the following (case

insensitive auto-completion is used): GMtransverse GMlongitudinal)

length

Appendix C

Page 196



GZ Curve Criteria (non-heeling arm)

These criteria, calculated from the GZ curve, are calculated from the Large Angle Stability analysis in Hydromax.

Value of GMt at

Finds the value of GMt at either a specified heel angle or the equilibrium angle. The criterion is passed if the value of GMt is greater then the required value. GMt is computed from water-plane inertia and immersed volume (not the slope of the GZ curve as this is inaccurate if the heel angle resolution is insufficient). Option Description Units Value of GMt at either specified heel angle User specified heel angle deg angle of equilibrium See Nomenclature deg Shall be greater than / Shall not be less than


Value of GZ at

Finds the value of GZ at either a specified heel angle, first peak in GZ curve, angle of maximum GZ or the downflooding angle. The criterion is passed if the value of GZ is greater then the required value. Option Description Units Value of GZ at either specified heel angle User specified heel angle deg angle of first GZ peak See Nomenclature deg angle of maximum GZ See Nomenclature deg first downflooding angle

See Nomenclature deg



Value of Maximum GZ

Finds the maximum value of GZ within a specified heel angle range. The criterion is passed if the value of GZ is greater than the required value. If you want to check the value of GZ at a certain angle you can set both specified angles as the required angle. If any of the calculated angles for the upper limit are less than the lower limit, they will be ignored when selecting the lowest. If all the upper limit values are less than the lower limit, then the criterion will fail. This functionality is to allow criteria such as “The maximum GZ at 30deg or greater”.

Note: Upper limit and analysis heel angle range It is required that the range of heel angles specified for the Large Angle Stability analysis is equal, or exceeds, the upper range heel angle specified in the criterion.

Option Description Units Value of maximum GZ in the range from the greater of

Lower limit for heel angle range, the greater of the following:

specified heel angle User specified heel angle deg angle of equilibrium See Nomenclature

Appendix C

Page 197

to the lesser of Upper limit for heel angle range, the lesser of the following:

specified heel angle User specified heel angle; this should normally be specified and be less than or equal to the upper limit of the range of heel angles used for the Large Angle Stability analysis.

deg

angle of first GZ peak See Nomenclature deg angle of maximum GZ See Nomenclature deg first downflooding angle




Value of Maximum GZ

Value of GZ at Specified Angle or Maximum GZ below Specified Angle

If the angle at which maximum GZ occurs is greater than a specified value, the value of GZ at the specified angle is calculated. Otherwise the value of maximum GZ is calculated. The required GZ value depends on the angle at which the maximum occurs, see graph below. Option Description Units heel angle at which required GZ is constant

If the angle of maximum GZ is greater than or equal to this value, the required value of GZ is constant and is taken at this specified angle. Otherwise the required value of maximum GZ varies as a hyperbolic function with the angle of maximum GZ. This is

0φ .

deg

Appendix C

Page 198

Option Description Units required value of GZ at this angle is

Required value of GZ at the heel angle specified above. This is ( )0φGZ .

length

limited by first GZ peak angle

Angle at which GZ is measured may be limited to the location of the first peak in the GZ curve.

deg

limited by first downflooding angle

Angle at which GZ is measured may be limited to first downflooding angle.

deg


Permissible value. length

If

0maxφφ ≥GZ

then ( )0φGZ must be greater than the specified, constant value.

If 0maxφφ <GZ

then maxGZ must be greater than ( )0

0

max

φφφ

GZGZ

where:

0φ is the specified angle at which the required GZ value becomes a constant

maxGZφ is the heel angle at which the maximum GZ of value occurs

( )0φGZ is the GZ value at 0φ and

maxGZ is the maximum value of GZ.

Variation of required GZ with angle of maximum GZ

The angle at which the GZ was measured is listed in the results.

Value of RM at Specified Angle or Maximum RM Below Specified Angle

As above (Value of GZ at specified angle or maximum GZ below specified angle) except the righting moment rather than the righting lever is specified, measured and compared. The righting moment RM is given by:

gGZRM ρ∇= where: ∇ is the vessel volume of displacement ρ is the density of the liquid the vessel is floating in

g is acceleration due to gravity = 9.80665m/s2

GZ is the righting lever.

Appendix C

Page 199

Ratio of GZ Values at Phi1 and Phi2

Calculates the ratio of the GZ values at two specified heel angles. The criterion is passed if the ratio is less then the required value.

( )( )2

1Ratioφφ

GZGZ

=

Option Description Units Ratio of GZ values at phi1 and phi2 Phi1, first heel angle, the lesser of

First heel angle, the lesser of the following:

specified heel angle User specified heel angle deg angle of first GZ peak See Nomenclature deg angle of maximum GZ See Nomenclature deg first downflooding angle


Phi2, second heel angle, the lesser of

Second heel angle, the lesser of the following:

specified heel angle User specified heel angle deg angle of first GZ peak See Nomenclature deg angle of maximum GZ See Nomenclature deg first downflooding angle



Permissible value %

Ratio of GZ values at phi1 and phi2

Appendix C

Page 200

Angle of Maximum GZ

Finds the angle at which the value of GZ is a maximum positive value, heel angle can be limited by first peak in GZ curve and/or first downflooding angle. The criterion is passed if the angle is greater then the required value. Option Description Units Angle of maximum GZ limited by first GZ peak angle

The angle of maximum GZ shall not be greater than the angle at which the first GZ peak occurs

deg

limited by first downflooding angle

The angle of maximum GZ shall not be greater than the angle at which the first downflooding occurs

deg



Angle of Equilibrium

Finds the angle of equilibrium from the intersection of the GZ curve with the GZ=0 axis. The criterion is passed if the equilibrium angle is less then the required value. Option Description Units Angle of equilibrium Shall be less than / Shall not be greater than


Ratio of equilibrium heel angle to the lesser of

The equilibrium angle and the lesser of the selected angles are compared. If the ratio is less than the required value, then the criterion is passed. Using a ratio gives more flexibility, e.g.: it is possible to check that the equilibrium angle does not exceed half (or any other fraction) the downflooding angle. The user may choose the type of Key point to define the downflooding angle (downflooding point, potential downflooding point, embarkation point, immersion point). If the equilibrium angle is negative, the user is advised that the vessel should be heeled in the opposite direction and the criterion is failed. Option Description Units Ratio of equilibrium angle to the lesser of: spec. heel angle Specified heel angle deg angle of margin line immersion

Angle of first immersion of the margin line deg

angle of deck edge immersion

Angle of first immersion of the deck edge deg

first flooding angle of the

Smallest immersion angle of the specified type of Key Point

deg

angle of first GZ peak Angle of first local peak in GZ curve deg angle of max. GZ Angle at which maximum GZ occurs deg angle of vanishing stability

Angle of vanishing stability deg


Permissible value %

Appendix C

Page 201

Equilibrium heel angle satisfies either

This criterion is nothing more than two “Ratio of equilibrium heel angle to the lesser of” criteria. The actual criterion is passed if either of the individual criteria is passed. This type of criterion is used to formulate criteria such as:

The maximum allowable angle of equilibrium is 15 degrees in the damage condition, but this can be allowed to increase to 17 degrees if the deck edge is not immersed.

Angle of Downflooding

Finds the angle of first downflooding. The criterion is passed if the downflooding angle is greater then the required value. Option Description Units Angle of downflooding Shall be greater than / Shall not be less than


Angle of Margin Line Immersion

Finds the first/minimum angle at which the margin line immerses. The criterion is passed if the smallest angle at which the margin line immerses is greater then the required value. Option Description Units Angle of margin line immersion Shall be greater than / Shall not be less than


Angle of Deck Edge Immersion

Finds the first/minimum angle at which the deck edge immerses. The criterion is passed if the smallest angle at which the deck edge immerses is greater then the required value. Option Description Units Angle of deck edge immersion Shall be greater than / Shall not be less than


Angle of Vanishing Stability

Finds the angle of vanishing stability from the intersection of the GZ curve with the GZ=0 axis. The criterion is passed if the angle of vanishing stability is greater then the required value. Option Description Units Angle of vanishing stability Shall be less than / Shall not be greater than


Range of Positive Stability

The angular range for which the GZ curve is positive is computed. The criterion is passed if the computed range is greater then the required value. Option Description Units Range of positive stability from the greater of Lower limit

Appendix C

Page 202

Option Description Units specified heel angle User specified heel angle deg angle of equilibrium See Nomenclature deg to the lesser of Upper limit of the range first downflooding angle


angle of vanishing stability




GZ Area between Limits type 1 - standard

The area below the GZ curve and above the GZ=0 axis is integrated between the selected limits and compared with a minimum required value. The criterion is passed if the area under the graph is greater than the required value. Option Description Units GZ area between limits type 1 - standard from the greater of Lower limit for integration, from greatest

angle of

specified heel angle User specified heel angle deg angle of equilibrium See Nomenclature deg to the lesser of Upper limit of integration, from lesser

angle of

specified heel angle User specified heel angle deg spec. angle above equilibrium

User specified heel angle above the equilibrium heel angle

deg



immersion angle of Marginline or DeckEdge





Permissible value length.angle

Appendix C

Page 203

GZ area between limits type 1 - standard

GZ area between limits type 2- HSC monohull type

The area under the GZ curve is integrated between the specified limits. However the required minimum area depends on the upper integration limit. The required area is defined below and is based on the area required for IMO MSC.36(63) §2.3.3.2 and IMO A.749(18) §4.5.6.2.1. The criterion is passed if the computed area under the graph is greater then the required value. The required area is defined as follows:

If 2max φφ ≥ : required area = 2A ;

If 1max φφ ≤ : required area = 1A ;

If 2max1 φφφ << : required area = ( )max2

12

212 φφ

φφ−

−−

+AA

A;

Where:

maxφ is the upper integration limit;

1A is the area under the GZ curve required at the specified lower heel angle 1φ ; and 2A is the

area under the GZ curve required at the specified higher heel angle 2φ . For example, if the lower angle was 15° and the required area at this angle was 0.07m.rad and the upper angle was 30° and the required area at this angle was 0.055m.rad, then the required area would be given by:

( )max301530

055.007.055.0 φ−

−−

+=A

or simplifying: ( )max30 001.055.0 φ−+=A

Appendix C

Page 204

Variation of required area with upper integration limit

Option Description Units GZ area between limits type 2- HSC

monohull type

from the greater of Lower limit for integration, from greatest angle of

specified heel angle User specified heel angle deg angle of equilibrium See Nomenclature deg to the lesser of Upper limit of integration, from smallest

angle of



deg





lower heel angle Minimum angle that requires a GZ area greater than... Until this angle the required GZ area is constant

deg

required GZ area at lower heel angle

Value of GZ area that is required until the lower heel angle

length.angle

higher heel angle Angle from which the required GZ area remains constant onwards

deg

required GZ area at higher heel angle

Value of GZ area that is required from the higher heel angle onwards

length.angle



Appendix C

Page 205

GZ area between limits type 2 - HSC monohull type

GZ area between limits type 3 - HSC multihull type

The area under the GZ curve is integrated between the specified limits. However the required

minimum area depends on the upper integration limit ( maxφ ). The required area is defined below and is based on the area required for IMO MSC.36 (63) Annex 7 §1.1. The criterion is passed if the computed area under the graph is greater than the required value.

required area = ( )max11 /φφA ; Where:

maxφ is the upper integration limit;

1A is the area under the GZ curve required at the specified heel angle 1φ .

For example, if the specified angle ( 1φ ) was 30° and the required area at this angle ( 1A ) was 0.055m.rad, then the required area would be given by:

( )max/30055.0 φ=A

Appendix C

Page 206

Variation of required area with upper integration limit

Option Description Units GZ area between limits type 3 - HSC

multihull type

from the greater of Lower limit for integration, from greatest angle of

specified heel angle User specified heel angle deg angle of equilibrium See Nomenclature deg to the lesser of Upper limit of integration, from lesser

angle of



deg





higher heel angle Heel angle at which required GZ area is specified

deg

required GZ area at higher heel angle

Value of GZ area that is required until the higher heel angle

length.angle



Appendix C

Page 207

GZ area between limits type 3 - HSC multihull type

Ratio of GZ area between limits

This criterion calculates the ratio of the two areas between the GZ curve and the GZ=0 axis.

Ratio = ( )2 Areaabs

1 Area =

( )

( )

∫

∫

φφ

φφ

φ

φ

φ

φ

dGZ

dGZ

4

3

2

1

abs

, where “abs” means the absolute value of.

Option Description Units Ratio of GZ area between limits Area 1 from the greater of Area 1 lower integration limit, 1φ

specified heel angle User specified heel angle deg angle of equilibrium See Nomenclature deg Area 1 to the lesser of Area 1 upper integration limit, 2φ deg

specified heel angle User specified heel angle deg angle of first GZ peak See Nomenclature deg angle of maximum GZ See Nomenclature deg first downflooding angle See Nomenclature deg angle of vanishing stability See Nomenclature deg Area 2 from the lesser of Area 2 lower integration limit, 3φ

specified heel angle User specified heel angle deg angle of first GZ peak See Nomenclature deg angle of maximum GZ See Nomenclature deg first downflooding angle See Nomenclature deg angle of vanishing stability See Nomenclature deg

Appendix C

Page 208

Option Description Units Area 2 to Area 1 upper integration limit, 4φ

specified heel angle User specified heel angle deg Shall be greater than / Shall not be less than

Permissible value %

This criterion is designed to be calculated on the positive side of the GZ curve only; GZ areas below the GZ=0 axis on the negative heel angle side of the GZ curve are not considered positive. Typically, Area 1 would be from equilibrium to vanishing stability and Area 2 would be from vanishing stability to 180 deg, see graph below. In the example below, the lower and upper integration limits for Area 1 are equilibrium and vanishing stability, respectively and the limits for Area 2 are vanishing stability and 180 deg.

Ratio of GZ area between limits – Example 1

In the following example the upper limit for Area 1 has been set to the downflooding angle. The limits for Area 2 remain unchanged.

Appendix C

Page 209


In the final example, the lower integration range for Area 2 has been reduced to the downflooding angle. Note that Area 2 is now A1 – A2.


Ratio of positive to negative GZ area between limits

This criterion calculates the ratio of GZ area above the GZ=0 axis to that below the axis in the given heel angle range. Option Description Units

Appendix C

Page 210

Option Description Units Ratio of positive to negative GZ area

between limits

in the heel angle range from User specified lower limit heel angle deg to User specified upper limit heel angle deg Shall be greater than / Shall not be less than

Permissible value %

Ratio = ( )2 Areaabs

1 Area ,

where “abs” means the absolute value of. And the areas are defined as follows: If both heel angle limits are ≥ zero: Area 1 is the total area between the GZ curve and GZ=0 axis, where the value of GZ > 0; Area 2 is the total area between the GZ curve and GZ=0 axis, where the value of GZ < 0. Area 1 is positive, Area 2 is negative.

Ratio of positive to negative GZ area between limits. Positive heel: lower limit = 0deg, upper limit = 180deg.

If both heel angle limits are < zero: Area 1 is the total area between the GZ curve and GZ=0 axis, where the value of GZ < 0; Area 2 is the total area between the GZ curve and GZ=0 axis, where the value of GZ > 0. Area 1 is positive, Area 2 is negative.

Appendix C

Page 211

Ratio of positive to negative GZ area between limits. Negative heel: lower limit = -180deg, upper limit = 0deg.

If the lower heel angle limit < zero, and the upper heel angle limit > zero (the upper limit is assumed to be greater than the lower limit): Area 1 is the total area between the GZ curve and GZ=0 axis, where the value of GZ > 0 for heel angles ≥ 0 plus the area between the GZ curve and GZ=0 axis, where the value of GZ < 0 for heel angles < 0; Area 2 is the total area between the GZ curve and GZ=0 axis, where the value of GZ < 0 for heel angles ≥ 0 plus the area between the GZ curve and GZ=0 axis, where the value of GZ > 0 for heel angles < 0. Area 1 is positive, Area 2 is negative.

Ratio of positive to negative GZ area between limits. Positive and negative heel: lower limit = -180deg, upper limit = 180deg.

Appendix C

Page 212

Heeling arm criteria (xRef)

The cross-reference heeling arm criteria are set up to allow you to define heeling arms or heeling moments in a central location and then cross-reference or link them into the criteria. The criteria themselves work much the same as the Heeling arm criteria (page 212), except for the fact that you don’t have to specify the heeling arm for each criterion separately, but can simply select which heeling arm you wish to apply. After you have defined your heeling arms, these can be cross-referenced into new heeling arm criteria:

The heeling arms are cross-referenced simply by selecting the desired heeling arm from the pull-down list:

For information on defining heeling arms or moments, see Parent Heeling Arms on page 185.

Heeling arm criteria

The preferred method is to use the xRef heeling arm criteria rather than the stand alone heeling arm criteria. This is because a wider range of heeling arm formulations is available and for some criteria, they only exist in xRef form. The heeling arm criteria available in the Hydromax Criteria dialog are listed below. Also available are:

Appendix C

Page 213

• Multiple heeling arm criteria; these are where the same criterion is applied to up to three heeling arms and/or combinations of these heeling arms

• Heeling Arm, combined criteria; these are where several criteria are applied to the same heeling arm

Value of GMT at equilibrium - general heeling arm

Calculates the transverse metacentric height (GMT) at the intersection of the GZ and heel arm curves. The criterion is passed if the GMT value is greater then the required value. GMT is computed from the waterplane inertia and the displaced volume at the equilibrium heel angle.

Ratio of GMT and heeling arm

Calculates the following ratio and the criterion is passed if the ratio exceeds the specified value. )()sin( φφ HAGM >

Where the heel angle, φ, is the lesser of: a user-specified heel angle; angle of margin line immersion; angle of deck edge immersion; or first flooding angle of the specified key point type. In addition, this angle may also be multiplied by a user-specified factor. The specified cross-referenced heel arm is then evaluated at this heel angle to give: )(φHA . Finally, The transverse GM is taken at a user-specified heel angle or angle of equilibrium (without heel arm).

Ratio of GMt and heel arm criterion

Value of GZ at equilibrium - general heeling arm

Calculates the value of the GZ curve at the equilibrium intersection of the GZ and heel arm curves. The criterion is passed if the GZ value is greater then the required value.

Appendix C

Page 214

Value of GZ at equilibrium - general heeling arm

Value of maximum GZ above heeling arm

Finds the maximum value of (GZ - heel arm) at or above a specified heel angle. The first downflooding angle may be selected as an upper limit. The criterion is passed if the value of (GZ - heel arm) is greater then the required value.

Appendix C

Page 215

Value of maximum GZ above heeling arm

The upper limit may be specified as a certain percentage of the selected limits. This is applied to all selected upper angle limits, including “specified heel angle”. However this option would normally be used to specify an upper limiting angle of “half the angle of margin line immersion”.

Maximum ratio of GZ to heeling arm

This criterion calculates the maximum ratio of GZ : Heeling arm (for the same heel angle) within the range of heel angles specified. The value of GZ at this heel angle must be greater than zero. If the heeling arm is zero or negative in the range, then the point with maximum positive GZ (where the heeling arm ≤ 0.0) will be selected. The upper limit may be specified as a certain percentage of the selected limits. This is applied to all selected upper angle limits, including “specified heel angle”. However this option would normally be used to specify an upper limiting angle of “half the angle of margin line immersion”. Examples:

Upper limit is 50% of angle of margin line immersion (43° / 2 = 21.5°). In the range 0° to 21.5°, the maximum ratio of GZ:heel arm occurs at 21.5°. At this heel angle the value of GZ is 0.553m and the heel arm 0.930m giving a ratio of

59%.

Appendix C

Page 216

In this case a constant heeling arm is used, thus the maximum ratio occurs at the angle of maximum GZ (62.4°). At this heel angle the value of GZ is 1.122m and the heel arm 0.5m giving a ratio of 224%.

Finally, the downflooding angle is 94.3°, at this heel angle the heel arm is zero (thus the ratio infinite). Hence the criterion is passed. The angle and value of GZ is given for the location where it is a maximum (in the region where the heel arm is zero; the exact value will depend slightly on the heel angles tested in the Large Angle Stability analysis.)

Appendix C

Page 217

The same is true if an unusual user-defined heeling arm is used. In this case the heeling arm is zero between 50° and 70°. Hence the maximum ratio reported is infinity and occurs at the angle where GZ is maximum in this heel angle

range.

Minimum ratio of GZ to heeling arm

This criterion calculates the minimum ratio of GZ : Heeling arm (for the same heel angle) within the range of heel angles specified. And checks that this ratio is greater than a specified value. This criterion can be used to check that the GZ is at least as great as the heeling arm over the specified range. If a heeling arm with zero amplitude is used, the same criterion may be used to check that the GZ is positive over the specified range. The upper limit may be specified as a certain percentage of the selected limits. This is applied to all selected upper angle limits, including “specified heel angle”. However this option would normally be used to specify an upper limiting angle of “half the angle of margin line immersion”.

Ratio of GZ values at phi1 and phi2 - general heeling arm

Used to check the ratio of GZ values at two points on the GZ curve. The heel arm is used to define the equilibrium angle and the heel angle where (GZ - heel arm) is maximum. The criterion is passed if the ratio is less than the required value.

Ratio =

( )( )2

1

φφ

GZGZ

Angle of maximum GZ above heeling arm

Calculates the heel angle at which the difference between the GZ curve and the heeling arm is greatest (GZ - Heel Arm is maximum, positive). The criterion is passed if the angle is greater then the required value.

Appendix C

Page 218

Angle of maximum GZ above heeling arm - general heeling arm

Angle of equilibrium - general heeling arm

Calculates the angle of equilibrium with the specified heeling arm. The equilibrium angle is the smallest positive angle where the GZ and heeling arm curves intersect and the GZ curve has positive slope. The criterion is passed if the equilibrium angle is less then the required value.

Angle of equilibrium - general heeling arm

Appendix C

Page 219

Angle of equilibrium ratio - general heeling arm

Calculates the ratio of the angle of equilibrium (with the specified heeling arm) to another, selectable angle. The angle of equilibrium is computed as described in §Angle of equilibrium - general heeling arm.

Ratio = specified

mequilibriu

φφ

The other angle used to compute the ratio may be one of the following: Required angle for ratio calculation Auto complete text Marginline immersion angle MarginlineImmersionAngle Deck edge immersion angle DeckEdgeImmersionAngle Angle of first GZ peak DownfloodingAngle Angle of maximum GZ MaximumGZAngle First downflooding angle FirstGZPeakAngle Angle of vanishing stability with heel arm VanishingStabilityWithHeelArmAngle

Angle of vanishing stability - general heeling arm

Calculates the location of the first intersection of the GZ curve and heel arm curve where the slope of the GZ curve is negative. The criterion is passed if the angle is greater then the required value. This criterion should not be confused with the range of positive stability.

Angle of vanishing stability - general heeling arm

Range of positive stability - general heeling arm

Computes the range of positive stability with the heeling arm. [Range of stability] = [Angle of vanishing stability] – [Angle of equilibrium] The criterion is passed if the value of range of stability is greater then the required value.

Appendix C

Page 220

Range of positive stability - general heeling arm

GZ area between limits type 1 - general heeling arm

Computes the area below the GZ curve and above the heel arm curve between the specified heel angles. The criterion is passed if the area is greater than the required value.

Area = ( )∫ −

2

1

)(arm heel)(φ

φφφφ dGZ


Appendix C

Page 221


The area between the GZ curve and heel arm and the area under the GZ curve is computed (Area 1). The required value is based on a constant plus a proportion of the area under the GZ curve (Area 2). The criterion is passed if the ratio is greater than the required value.

Area 1 = ( )∫ −

2

1

)(arm heel)(φ

φφφφ dGZ

;

Area 2 = ∫4

3

)(φ

φφφ dGZ

;

2 Areaconstant1 Area k+≥


Ratio of areas type 1 - general heeling arm

The ratio of the area between the GZ curve and heel arm and the area under the GZ curve is computed. This criterion is based on the area ratio required by various Navies’ turning and passenger crowding criteria. Type 1 stands for which areas are being integrated to calculate the ratio (see graph). The criterion is passed if the ratio is greater than the required value.

Area 1 = ( )∫ −

2

1

)(arm heel)(φ

φφφφ dGZ

;

Area 2 = ∫4

3

)(φ

φφφ dGZ

;

Appendix C

Page 222

Ratio = 2 Area1 Area



This criterion is used to simulate the effects of wind heeling whilst the vessel is rolling in waves. Because of the many different ways in which this criterion is used it has several options for defining the way in which the areas are calculated. If a gust ratio of greater than 1.0 is used, the vessel is assumed to roll to windward (under the action of waves with the steady wind pressure acting on it, then roll to leeward under a gust. Hence the rollback angle is taken from the equilibrium angle with the steady wind heeling arm, but the integration for Area 1 is taken from the equilibrium with the gust wind heeling arm. The roll back may be specified as either a fixed angular roll back from the angle of equilibrium with the steady wind heel arm or can be rolled back to the vessel equilibrium angle ignoring the wind heeling arms (i.e.: where the GZ curve crosses the GZ=0 axis with positive slope).

Note The Large Angle Stability analysis heel angle range should include a sufficient negative range to allow for the rollback angle. For more information see: §Heel.

Area 1 = ( )∫ −

2

1

)(arm heelgust )(φ

φφφφ dGZ

Area 2 = ( )∫ −2

1

)()(arm heelgust φ

φφφφ dGZ

Appendix C

Page 223




The ratio of the area under the GZ curve to the area under the heel arm curve is computed. This criterion is based on the area ratio required by BS6349-6:1989. The criterion is passed if the ratio is greater than the required value. Areas under the GZ=0 axis are counted as negative.

Area GZ = ∫2

1

)(φ

φφφ dGZ ;

Area HA = ∫2

1

)(arm heelφ

φφφ d ;

Ratio = HA AreaGZ Area

Appendix C

Page 224


Multiple heeling arm criteria

These criteria are used to check the effects of combinations of up to three heeling arms and their combinations, for example passenger crowding, turning, wind. The combined heeling arms are computed by adding the values of the individual heeling arms at each heel angle.

Ratio of GZ values at phi1 and phi2 - multiple heeling arms

Checks the ratio of GZ values as per §Ratio of GZ values at phi1 and phi2 - general heeling arm with the specified heeling arms.

Appendix C

Page 225

Ratio of GZ values at phi1 and phi2 - multiple heeling arms

Angle of equilibrium - multiple heeling arms

Checks the equilibrium heel angle as per §Angle of equilibrium - general heeling arm with the specified heeling arms.

Angle of equilibrium - multiple heeling arms

GZ area between limits type 1 - multiple heeling arms

Checks the area under the heel angle as per §GZ area between limits type 1 - general heeling arm with the specified heeling arms.

Appendix C

Page 226



Checks the area under the heel angle as per §GZ area between limits type 2 - general heeling arm with the specified heeling arms.

Area 1 = ( )∫ −

2

1

)(arm heel)(φ

φφφφ dGZ

;

Area 2 = ∫4

3

)(φ

φφφ dGZ

;

2 Areaconstant1 Area k+≥

Appendix C

Page 227


Ratio of areas type 1 - multiple heeling arms

Checks the area under the heel angle as per §Ratio of areas type 1 - general heeling arm with the specified heeling arms.

Appendix C

Page 228

Ratio of areas type 1 - multiple heeling arms

Subdivision Index s-factor - MSC_216(82).rtf

The Subdivision Index s-factor as described in IMO MSC.216(82) is computed. Several extra options are presented to the user.

Appendix C

Page 229

Option Description Units Subdivision Index s-factor –

MSC.216(82)

Vessel type : Passenger, Cargo, User

The type of vessel being analysed. This is used to determine default parameters and which s-factors should be computed.

Upper angle of range: lesser of

The lowest of the selected angles can be used to specify the upper limit of the range of positive stability. The beginning of the range of positive stability is taken as the first positive equilibrium angles

first downflooding angle




Immersion angle of Marginline or DeckEdge


s-Final Parameters for computing the s-Final factor

Max. GZ limit Upper limit of allowable maximum GZ value when computing s-Final

length

Range limit Upper limit of allowable range of positive stability when computing s-Final

deg

K-factor min. heel Theta_min used to determine K deg

K-factor max. heel Theta_max used to determine K deg

s-Intermediate Parameters for computing the s-Intermediate factor

Max. GZ limit Upper limit of allowable maximum GZ value when computing s-Intermediate

length

Range limit Upper limit of allowable range of positive stability when computing s- Intermediate

deg

Max. allowable equilibrium heel angle

Maximum allowable equilibrium heel angle after damage. If the equilibrium heel angle exceeds this value then s-Intermediate is zero.

deg

s-Moment Parameters for computing the s-Moment factor

intact displacement at subdivision draft

Displacement of the intact vessel at the subdivision draft

mass

GZ reduction Reduction to be applied to maximum GZ

length

Passenger heel Link to passenger heeling moment mass.length

Appendix C

Page 230

moment

Wind heel moment Link to wind heeling moment mass.length

Select survival craft heel moment

Link to heeling moment that defines the effect of launching survival craft

mass.length


Permissible minimum value for s-factor

Vessel type: If Passenger is selected, then s-Intermediate and s-Moment factors are computed. For the s-Final factor, the minimum and maximum heel angles are set to 7 and 25 deg. respectively. The criterion result is then the minimum value of s-Final and (s-Intermediate . s-Moment). If Cargo is selected, then only the s-Final factor is computed and in this case, the minimum and maximum heel angles are set to 15 and 30 deg. respectively. If User is selected, then all three s-factors are computed as for the Passenger ship, and any values for the s-Final factor minimum and maximum heel angles may be specified. s-Final = K. {GZmax / limitGZmax . Range / limitRange}1/4 where: K = 1 if equilibrium heel <= Theta_min K = 0 if equilibrium heel >= Theta_max K = {(Theta_max – equilibrium heel) / (Theta_max – Theta_min)}1/2

s-Intermediate = {GZmax / limitGZmax . Range / limitRange}1/4 if equilibrium heel > Max. allowable equilibrium heel angle then s-Intermediate = 0 s-Moment = (GZmax – GZ reduction) . Displacement / Mheel where: Mheel is the maximum of the three selected heeling moments. The result is the minimum of s-Final and (s-Intermediate . s-Moment). All s-factors are in the range 0 <= s <= 1

Heeling arm, combined criteria

Several criteria require the evaluation of several individual criteria components. Although it is possible to evaluate these criteria by evaluation of their individual components, for simplicity the common combinations have been combined into single criteria.

Note: At least one of the individual criteria has to be selected.

Combined criteria (ratio of areas type 1) - general heeling arm

This is a combined criterion where three individual criteria must be met. These are: 1. Angle of steady heel must be less than a specified value. The Angle of steady heel is obtained as per §Angle of equilibrium - general heeling arm. 2. The area ratio must be greater than a specified value. The area ratio is evaluated as per § Ratio of areas type 1 - general heeling arm 3. The ratio of the value of GZ at equilibrium to the value of maximum GZ must be less than a specified value.

Appendix C

Page 231

Combined criteria (ratio of areas type 1) - general heeling arm

Combined criteria (ratio of areas type 2) - general wind heeling arm

This is a widely applicable wind heeling criterion in its most generic format. The heeling arm is specified simply by a magnitude and cosine power. Optionally, a gust wind can be applied. 1. Angle of steady heel must be less than a specified value. The angle of steady heel is obtained as per Angle of equilibrium - general heeling arm. 2. The area ratio must be greater than a specified value. The area ratio is evaluated as per Ratio of areas type 2 - general heeling arm. 3. The ratio of the value of GZ at equilibrium to the value of maximum GZ must be less than a specified value.


Appendix C

Page 232

Area definition

If required, a reduction of the GZ curve may be applied. If this is done, all calculations are done using a reduced GZ’ curve which is computed at each heel angle as follows:

)(cos)()(' φφφ mBGZGZ −= This criterion may be used to evaluate the following specific criteria (as well as many others of similar format):

• US Navy DDS079-1: §079-1-c(9) 1, §079-1-c(9) 4,

• Royal Navy NES 109: §1.2.2, §1.3.5, §1.4.2 Initial impulse and Wind heeling criteria

• RAN A015866: §4.4.4.2, §4.8, §4.9.5

• IMO A.749(18) Code on intact stability: §3.2

• IMO MSC.36(63) High-speed craft code §2.3.3.1

• ISO/FDIS 12217-1:2002(E) Small Non-Sailing Boats §6.3.2

Appendix C

Page 233

Derived heeling arm criteria

For these criteria, the magnitude of the heeling arm is derived (rather than specified directly) from a required relationship between the GZ curve and the heeling arm curve. The shape of the heeling arm (e.g. cos1.3) must be specified. The heeling arm is normally derived from a GZ value, GZ area or angle of equilibrium requirement. The criterion is then evaluated by comparing some requirement of the derived heeling arm with a specified value.

GZ derived heeling arm

This criterion is used to calculate the amplitude of a heeling arm derived from the value of GZ at a certain heel angle. The GZ value used to define the heeling arm is the GZ at one of the following heel angles:

• specified angle of heel

• angle of first peak in GZ curve

• angle at which maximum GZ occurs

• angle of first downflooding

• immersion angle of margin line or deck edge The heeling arm is then calculated as described by the equation below, and is then compared with a minimum required value.

φαφn

GZA

cos=

where: A Amplitude of heeling arm n Shape of heeling arm (n = 0 for constant heeling arm) φ Specified heel angle

φGZ Value of GZ at specified heel angle

α Required ratio = φφ HAGZ /

GZ area derived heeling arm type 1

This criterion is used to calculate the amplitude of a heeling arm derived from the area under the GZ curve between specified limits. The area under both the GZ and heeling arm curves is integrated between the same specified limits, see below. Lower integration limit, 1φ :

• specified angle of heel

• angle of equilibrium Upper integration limit, 2φ :

• spec. heel angle

• spec. angle above equilibrium

• angle of first GZ peak

• angle of max. GZ

• first downflooding angle

• angle of vanishing stability It is also possible to specify a minimum heel angle for the upper integration limit. Any negative areas (due to negative GZ) up to this minimum upper integration heel angle will be deducted from the total area under the GZ curve.

Appendix C

Page 234

The amplitude of the heeling, which satisfies the equation below arm is then found and compared with a minimum required value.

α

φφφ

φ

φφ

φ

∫∫ =

2

12

1

d d cos

GZA n

A Amplitude of heeling arm n Shape of heeling arm (n = 0 for constant heeling arm) φ heel angle GZ GZ curve α Required ratio

GZ area derived heeling arm type 2

This criterion is used to simulate the effects of wind heeling whilst the vessel is rolling in waves. Because of the many different ways in which this criterion is used it has several options for defining the way in which the areas are calculated. With the wind pressure acting on it, the vessel is assumed to roll to windward under the action of waves and then roll to leeward. The rollback angle is taken from the equilibrium angle with the wind heeling arm. A heeling arm of prescribed shape is found such that the specified area ratio is met. The amplitude of the heeling arm is then compared with a required minimum value. The roll back may be specified as either:

• a fixed angular roll back from the angle of equilibrium with the wind heel arm;

• roll back to the vessel equilibrium angle ignoring the wind heeling arms (i.e.: where the GZ curve crosses the GZ=0 axis with positive slope); or

• roll back to a specified heel angle.


Area 1 = ( )∫ −2

1

)(arm heel)(φ

φφφφ dGZ

Area 2 = ( )∫ −2

1

)()(arm heelφ

φφφφ dGZ


Appendix C

Page 235

GZ area derived heeling arm (type 2) - general heeling arm

Angle of equilibrium - GZ derived wind heeling arm

The derived wind heeling criterion is used to check that the steady heel angle due to wind pressure exceeds a certain value. The steady heel arm is derived from a gust of specified ratio. The wind gust will cause the vessel to heel over to the lesser of a specified heel angle, angle of the first GZ peak, angle of maximum GZ or the first downflooding angle. The vessel is assumed to be safe from gusts up to the specified ratio, if the angle of steady heel is greater than the angle. This means that the lesser of: a specified heel angle, first peak in GZ curve, angle of maximum GZ or the first downflooding angle, should be large enough to withstand a gust from a steady wind heeling angle larger than ….

Angle of equilibrium - derived wind heeling arm

Appendix C

Page 236

Ratio of equilibrium angles - GZ area derived heeling arm

This criterion is used to compare the equilibrium angles with two different heeling arms. The first equilibrium angle, φ1, is the angle of equilibrium with a derived heeling arm. The second equilibrium angle, φ2, is the angle of equilibrium with a specified heeling arm. The derived heeling arm is chosen such that the areas, A1 and A2, are in the specified ratio. There are several options which can be used to define the upper and lower ranges for the area integrations. The specified heeling arm is specified by an amplitude and cosine power; the same cosine power is used for both the specified and the derived heeling arms.

Ratio of equilibrium angles - derived heeling arm

Area 1 = ( )∫ −2

1

)(arm heel)(φ

φφφφ dGZ

Area 2 = ( )∫ −2

1

)()(arm heelφ

φφφφ dGZ

Ratio of areas = 2 Area1 Area

φ1 = Angle of equilibrium with heeling arm derived from required area ratio (purple heeling arm) φ2 = Angle of equilibrium with specified heeling arm (orange heeling arm) The criterion is passed if the ratio φ2 : φ1 is less than the required value. Thus if it is required that φ2 be less than φ1, then the ratio φ2 : φ1 must be less than unity. Option Description Units A Magnitude of specified heeling arm length

Appendix C

Page 237

n Cosine power to describe shape of both specified and derived heelning arms

required area ratio Area1 / Area2

The required area ratio used to find the derived heeling arm magnitude

options Specify lower integration limit for Area1 deg options Specify upper integration limit for Area1 deg options Specify lower integration limit for Area2; the

upper integration limit is always the angle of equilibrium with derived heel arm

deg

required value Specifies the maximum allowable ratio of equilibrium heel angle with the specified heel arm to the equilibrium heel angle with the derived heel arm (phi2 / phi1). This value is normally less than or equal to 100%, indicating that the equilibrium heel angle with the specified heel arm must be less than the equilibrium heel angle with the derived heel arm


Other combined criteria

Other criteria, which do not easily fall into the categories above, are found here.

Other criteria - STIX

The stability index criterion or STIX criterion as described in ISO/FDIS 12217-2:2002(E) is used to assess the stability of sailing craft. The required input parameters are described below. Please refer to ISO/FDIS 12217-2:2002(E) for exact definitions of parameters and how they should be calculated. Option Description Units delta Adjustment to STIX rating, either 0 or 5.

5=δ if the vessel, when fully flooded with water, has reserve buoyancy and positive righting lever at a heel angle of 90º . 0=δ in all other cases.

AS, sail area ISO 8666 Sail area as defined in ISO 8666. Note that no additional windage areas are calculated by Hydromax for this criterion.

length2

height of centroid of AS

Height of sail area centre of effort from model’s vertical datum (not necessarily the waterline, this is not the same as the STIX variable CEh which is measured from the waterline, positive up).

length

LH, length Hull length as defined by ISO 8666. This may be either specified or calculated by Hydromax. Hydromax calculates this parameter as the overall length of the vessel (all hull surfaces) in the upright, zero trim condition.

length

Appendix C

Page 238

Option Description Units BH, beam of hull Hull beam as defined by ISO 8666. This

may be either specified or calculated by Hydromax. Hydromax calculates this parameter as the overall beam of the vessel (all hull surfaces) in the upright, zero trim condition.

length

LWL, length waterline Hull waterline length in the current load condition as defined by ISO 8666. This may be either specified or calculated by Hydromax. Hydromax calculates this parameter as the waterline length of the vessel (all hull surfaces) at zero heel and at the loadcase displacement and centre of gravity; if the analysis is carried out free-to-trim, the waterline of the trimmed vessel is used.

length

BWL, beam waterline Hull waterline beam in the current load condition as defined by ISO 8666. This may be either specified or calculated by Hydromax. Hydromax calculates this parameter as the waterline beam of the vessel (all hull surfaces) at zero heel and at the loadcase displacement and centre of gravity; if the analysis is carried out free-to-trim, the waterline of the trimmed vessel is used.

length

height of immersed profile area centroid

Height of centre of the lateral projected immersed area of the hull from model’s vertical datum (not necessarily the waterline, this is not the same as the STIX variable LPh ); may be specified or calculated by Hydromax. Hydromax calculates this parameter at zero heel and at the loadcase displacement and centre of gravity; if the analysis is carried out free-to-trim, the waterline of the trimmed vessel is used.

length


Hydromax uses the numerical STIX rating value rather than the STIX design category.

Hydromax calculates the various factors and STIX rating according to ISO/FDIS 12217-2:2002(E). Note that a downflooding angle is required to calculate the STIX index. Hence, if no downflooding points are defined, or defined downflooding points do not immerse within the selected heel angle range, the angle of downflooding is taken to be the largest heel angle tested. This affects the calculation of the Wind Moment and Downflooding factors.

Specific stand alone heeling arm criteria

These criteria provide some specific stand alone heeling arm criteria. They are included for compatibility with criteria sets defined in earlier versions of Hydromax, but it is highly recommended to use the equivalent xRef criteria with the desired heeling arms.

Appendix C

Page 239

Stand alone heeling arm criteria

Angle of equilibrium - passenger crowding heeling arm

Calculates the angle of equilibrium with the heeling arm due to passenger crowding applied. The heeling arm is calculated from the number, weight and location of the passengers, see §Passenger crowding.

Angle of equilibrium - high-speed turn heeling arm

Calculates the angle of equilibrium with the heeling arm due to high speed turning applied. The heeling arm is calculated from the turn radius, vessel speed and height of the vessel’s centre of gravity, see §Turning.

Ratio of areas type 1 - general cos+sin heeling arm

This is a very similar criterion to § Ratio of areas type 1 - general heeling arm; the only difference being the shape of the heel arm. In this criterion the heel arm has both a sine and a cosine component. This is used to simulate the effects of lifting weights and is used by several Navies. The modified form of the heeling arm is given below, for further information also see §General cos+sin heeling arm

( ))(sin)(cos)( φφφ mn BAkH +=

Area 1 = ( )∫ −

2

1

)(arm heel)(φ

φφφφ dGZ

;

Area 2 = ∫4

3

)(φ

φφφ dGZ

;


Stand alone heeling arm combined criteria

Combined criteria (ratio of areas type 1) - passenger crowding

This criterion is essentially the same as its generic form: Combined criteria (ratio of areas type 1) - general heeling arm, however the heel arm is the specific passenger crowding form.

Combined criteria (ratio of areas type 1) - high-speed turn

This criterion is essentially the same as its generic form: Combined criteria (ratio of areas type 1) - general heeling arm, however the heel arm is the specific high-speed turning form.

Combined criteria (ratio of areas type 1) - general cos+sin heeling arm

The lifting criterion is the same as the Combined criteria (ratio of areas type 1) - general heeling arm except that the heel arm has both a cos and sin component.

Appendix C

Page 240

Combined criteria (ratio of areas type 1) – cos+sin heeling arm

Combined criteria (ratio of areas type 1) - lifting weight

This criterion is essentially the same as its generic form: Combined criteria (ratio of areas type 1) - general cos+sin heeling arm, however the heel arm is the specific lifting of a heavy weight form.

Combined criteria (ratio of areas type 1) - towing

This criterion is essentially the same as its generic form: Combined criteria (ratio of areas type 1) - general cos+sin heeling arm, however the heel arm is the specific towing form.

Combined criteria (ratio of areas type 2) - wind heeling arm

This criterion is exactly the same as §Combined criteria (ratio of areas type 2) - general wind heeling arm except that the magnitude of the heeling arm is automatically calculated from the wind pressure (or velocity), projected area and area lever information.

Appendix C

Page 241

Area definition


Appendix C

Page 242

Appendix D: Specific Criteria

In Hydromax, we have tried to distil the essence of the various stability criteria and present them in their simplest form whilst preserving the physical significance of the stability characteristic under assessment. In some cases, what is essentially the same criterion, is presented in quite different ways by different regulatory bodies. In Hydromax we have always sought to keep the physical significance transparent in the formulation – for this reason, constants such as acceleration due to gravity are explicitly shown in the formulations and consistent units are used – thus removing the need for obscure constants with strange units. In this section we look at some common criteria and demonstrate how they may be evaluated in Hydromax.

Dynamic stability criteria

In some cases the criteria are expressed in terms of the so-called dynamic stability curve. This is the integral of the GZ curve where the ordinate is the area under the GZ curve integrated from zero to the heel angle in question. Remembering this relationship and that the slope of the dynamic stability curve is the value of GZ it is often possible to reformulate the same criterion in terms of one based on the GZ curve.

Capsizing moment

Often a capsizing moment is determined from the dynamic stability curve by drawing a line through the origin which is tangent to the GZ area curve. This is the dynamic heeling arm curve (blue) and is the integral of a constant value heeling arm. The capsizing moment is taken as the magnitude of GZ at this tangent heel angle 2φ . The problem is to reformulate this so that this capsizing moment can be found from the GZ curve:

Dynamic stability curve and Dynamic heeling arm.

From the figure above we can see that the slopes of both curves are the same at 1φ and 2φ ; from this we can deduce that the value of GZ and Heeling arm are the same at these angles. Furthermore, at 2φ , the values are the same indicating that the areas under each curve from 0 to

2φ are the same. Finally since the dynamic heeling arm is a straight line with constant slope we know that the corresponding heeling arm is a constant value. From these facts we can derive the following GZ and heeling arm curves:

Appendix C

Page 243

Stability curve, Area 1 corresponds to the area under the heeling arm curve up to the second intercept

Stability curve, Area 2 corresponds to the area under the GZ curve up to the second intercept

Knowing that Area1 = Area2 we can deduce that Area 3 = Area 4 in the figure below:

Appendix C

Page 244

The magnitude of the heeling arm must be chosen so that Area 3 = Area 4

So the capsizing moment can also be determined by finding the heeling moment that gives Area3 = Area4. This can easily be done in Hydromax using the GZ area derived heeling arm type 2 criterion.

Heeling arms for specific criteria - Note on unit conversion

There are quite a few different ways in which different authorities define their heeling arms. The approach that has been taken in Hydromax is to reflect the physics of what is generating the heeling moment. Be careful as some criteria specify heeling arms and some specify heeling moments or “moments” in mass.length. All Hydromax criteria use a heeling arm since this is what is ultimately plotted on the GZ curve. To obtain the heeling arm from the heeling moment, it is

necessary to divide by vessel weight ( ∆g ); and in the case of “moments” in mass.length, it is necessary to divide by vessel mass. Hydromax uses an internal conversion of knots to m/s based on the International Nautical mile which is defined as exactly 1852m (International Hydrographic Conference, Monaco, 1929). Thus 1 knot = 1852/3600 = 0.5144444... m/s. (Note that the UK nautical mile is 6080ft = 1853.184m; giving a conversion multiplier for knots to m/s of 0.51477333...) In the following section, the conversions for some common criteria have been explained.

IMO Code on Intact Stability A.749(18) amended to MSC.75(69)

3.1.2.6 - Heeling due to turning Heeling moment defined by:

−∆=2

196.02

0 dKG

LV

M tonneR [kNm]

Where:

RM = heeling moment in tonne.m

0V = service speed in m/s L = length of ship at waterline in m

tonne∆ = displacement in tonne

Appendix C

Page 245

d = mean draft m KG = height of centre of gravity above keel in m

Hence the heeling arm, gMH RR ∆= /1000 [m], is given by:

−=∆

−∆

=2

196.01000

21000196.0

20

20 d

KGLgV

gd

KGLV

HR [m]

Where: g = standard acceleration due to gravity = 9.80665 m/s2

∆ = displacement in kg The heeling arm in Hydromax is defined as:

hRg

VaH R

2

= [m],

Where: V = vessel speed in m/s R = radius of turn in m h = height of centre of gravity above centre of lateral resistance in m a = non-dimensional constant (theoretically unity) Thus equating the required IMO heeling arm to the Hydromax heeling arm, we obtain:

−=2

196.02

02 d

KGLgV

hRg

Va

Equating similar terms:

−=2d

KGh

0VV = and assuming that the ratio of the turn radius to the vessel length is 5.1:1, we obtain:

%510=

LR

and

9996.0%510196.0 =×=a

Note that it suffices that 196.0=RL

a and any ratio of turn radius to vessel length and constant

a that satisfies this relationship may be chosen, the choice of a ratio of 5.1:1 merely gives a constant approaching the theoretically correct value of unity.

3.2 - Severe wind and rolling criterion (weather criterion) Heeling arm defined by:

tonnew g

PAZl

∆=

81.91 1000 [m]

Where:

1wl = heeling arm in m P = wind pressure in Pa

Appendix C

Page 246

A = projected lateral windage in m2

Z = vertical separation of centroids of A and underwater lateral area in m


81.9g = IMO assumed value of gravitational acceleration - 9.81m/s2

The heeling arm in Hydromax is defined as:

∆−

=g

HhPAaHw

)(

[m]


∆ = displacement in kg h = height of centroid of A in m

H = height of centroid of underwater lateral area in m

a = non-dimensional constant (theoretically unity) Thus equating the required IMO heeling arm to the Hydromax heeling arm, we obtain:

tonnegPAZ

gHhPA

a∆

=∆−

81.91000)(


ZHh =− and

99966.0

81.980665.9

81.9

===gg

a

IMO HSC Code MSC.36(63)

Annex 6 1.1.4 - Heeling moment due to wind pressure Heeling moment defined by:

PAZM v 001.0= [kNm] Where:

vM = heeling moment in kNm P = wind pressure in Pa A = projected lateral windage in m2

Z = vertical separation of centroids of A and underwater lateral area in m

Hence the heeling arm, gMH vv ∆= /1000 [m], is given by:

gPAZ

gPAZH R ∆

=∆

=1000

001.0 [m]


∆ = displacement in kg The heeling arm in Hydromax is defined as:

Appendix C

Page 247

∆−

=g

HhPAaHw

)(

[m] Where: g = standard acceleration due to gravity = 9.80665 m/s2




∆=

∆−

gPAZ

gHhPA

a)(


ZHh =− and

0.1=a

Annex 7 1.3 - Heeling due to wind Heeling arm defined by:

tonne

PAZHL

∆=

98001 [m]

Where:

1HL = heeling arm in m P = wind pressure in Pa A = projected lateral windage in m2

Z = vertical separation of centroid of A and half the lightest service draft in m

tonne∆ = displacement in tonne The heeling arm in Hydromax is defined as:

∆−

=g

HhPAaHw

)(

[m]



H = height of half the lightest service draft in m



ZHh =−

Appendix C

Page 248

and

00068.1

8.980665.9

9800=

∆∆

=∆∆

=tonne

ga

Where the effect of wind plus gust is required, the factor a should be multiplied by the gust factor – typically 1.5. Hence, in the case of wind plus gust, a becomes 1.50102

USL code (Australia)

USL C.1.1.3 - Wind heeling moment USL wind heeling “moment” is specified as:

)(000102.0 HhPAM −= [tonne.m]

Where: h = height of centroid of A in m


P = wind pressure in Pa A = projected lateral windage in m2

Thus the heeling arm is given by:

∆−=

1000)(000102.0 HhPAH

[m]

The heeling arm in Hydromax is defined as:

∆−

=g

HhPAaH

)(

[m]


∆ = displacement in kg a = non-dimensional constant (theoretically unity) Thus equating:

∆−=

∆−

=1000

)(000102.0)(

HhPAg

HhPAaH

simplifying and rearranging:

0002783.180665.9102.00.1000000102.0 =×=××= ga

USL C.1.1.4 - Heeling moment due to turning USL wind heeling “moment” is specified as:

Lhv

M tonneskts∆=2

0053.0 [tonne.m]

Where:

ktsv = vessel speed in knots


Appendix C

Page 249

h = height of centre of gravity above centre of lateral resistance in m L = waterline length of vessel in m

Thus the heeling arm is given by:

0.10001

0053.02

×∆

∆=

Lhv

H tonneskts

[m]

Where: ∆ = displacement in kg The heeling arm in Hydromax is defined as:

hRg

VaH

2

= [m],

Where: V = vessel speed in m/s R = radius of turn in m h = height of centre of gravity above centre of lateral resistance in m a = non-dimensional constant (theoretically unity) Thus equating the required USL heeling arm to the Hydromax heeling arm, we obtain:

0.10001

0053.022

×∆

∆=

Lhv

hRg

Va tonneskts

simplifying and rearranging:

0.10001

5144.01

3.53.522

2

LR

gVv

LR

ga tonneskts =∆

∆=

finally, with g = 9.80665 [ms-2]:

LR

a 196424.0=

Assuming that the ratio of the turn radius to the vessel length,%509=

LR

gives a value for a:

999798.0%509196424.0 =×=a

Note that it suffices that 196424.0=

LR

a, and any ratio of turn radius to vessel length and

constant a that satisfies this relationship may be chosen, the choice of a ratio of 509% merely gives a constant approaching the theoretically correct value of unity.

ISO 12217-1:2002(E)

This section explains how the ISO 12217-1 code calculates the heeling arm and how you can replicate this calculation with a Hydromax criterion. “6.3.2 Rolling in beam waves and wind The curve of righting moments of the boat shall be established up to the downflooding angle or the angle of vanishing stability or 50°, whichever is the least, using annex D. The heeling moment due to wind, MW, expressed in newton metres, is assumed to be constant at all angles of heel and shall be calculated as follows:

Appendix C

Page 250

MW = 0.3 ALV * (ALV / LWL + TM)* vW2

Where LWL is the waterline length; TM is the draft at the mid-point of the waterline length, expressed in metres; vW = 28 m/s for design category A, and 21 m/s for design category B; ALV is the windage area as defined in 3.3.7, but shall not be taken as less than 0.55*LH * BH.”

Basically they are using moment = force * lever, where

the force is calculated as 0.3 * ALV * vW2, and

the lever is (ALV / LWL + TM) This lever is a bit confusing so let’s concentrate on that. Hydromax’ wind heeling arm calculation uses H for the vertical height of the hydrodynamic centre (underwater area) and h as the vertical height of the aerodynamic centre (windage area) – all measured consistently from the zero point, positive up. Thus the lever is (h-H) in Hydromax should be the same as the (ALV / LWL + TM) lever from ISO. You can calculate (ALV / LWL + TM) manually and then make sure the (h-H) value in Hydromax is the same by specifying:

Velocity based heeling arm; H = 0.0; h = (ALV / LWL + TM); a = 0.3 kg/m3

Note: the centre of the windage area -h- applies to the additional windage area or the total windage area depending on which option you have selected. Make sure you check your total windage lever in the intermediate results in the criteria results tab of the Results window.

For example, supposing we have a vessel with the following characteristics: Displacement 105.7 tonne = 1037 kN LH 24 m BH 5 m LWL 21.1 m TM 1.9 m vW 28 m/s for design category A ALV 72 m2 ( this is greater than 0.55 LH BH = 66 m2)

Thus according to the ISO 12217 formula, the heeling moment is given as: MW = 0.3 * 72 * (72 / 21.1 + 1.9) * 282 = 89961 Nm

Thus the heeling arm = MW / Displacement = 89961 / 1037000 = 0.0868 m

The input for Hydromax requires: Total area A = 72 m2; area centroid height: h = ALV / LWL + TM = 72 / 21.1 + 1.9 = 5.312 m; a = 0.3 kg/m3

giving the expected result for heeling arm amplitude:

Appendix C

Page 251

Intermediate results for the wind heeling arm.

ISO 12217: Small craft – stability and buoyancy assessment and categorisation.

This section gives some details on implementing the ISO 12217 stability criteria in Hydromax. See also the note on converting units for the definition of the heeling arms in ISO 12217-1:2002(E).

Part 1: Non-sailing boats of hull length greater than or equal to 6m

In many cases the user must determine the required pass value for the criteria, which depends on the category and length of vessel being tested. In most cases the default required value would exceed the worst case. 6.1.2: Downflooding height Minimum freeboard to downflooding points must be determined from Figures 2 and 3 (Section 6.1.2) and entered into the required value field; the default value is set at 1.42m which is slightly greater than the height required for a category A vessel of 24m in length. 6.1.3: Downflooding angle Must be greater than a certain value as determined according to the design category; see Tables 3 and 4 (Sections 6.1.3, 6.2). The default value is set to 49.7 6.2: Offset-load test There are several ways of evaluating this criterion:

1. Define a heeling arm and calculate the intersection of the heeling arm with the GZ curve to determine the angle of equilibrium.

2. Specify a loadcase with the offset load specified and carry out an equilibrium analysis. Verify that the angle of equilibrium does not exceed the maximum permissible value.

An additional requirement in this section is that a specified freeboard must be exceeded. 6.3: Resistance to wind and waves Determine the windage area and lever and enter them in the appropriate fields in the criterion. Also determine the required wind speed and roll-back angle (depending on the design category) and enter these values. In Hydromax, there is no option for placing the height, H, of the centre of lateral resistance at the bottom of the vessel, so this must be specified manually (it is measured from the model zero point, positive upwards). 6.3.3: Resistance to waves This criterion comprises two parts, one to check that the righting moment is sufficient and a second to determine whether the righting lever is sufficient. 6.4: Heel due to wind action

Appendix C

Page 252

Determine the parameters required for calculation of the wind heeling moment as per 6.3, but note the different wind speeds to be used. Determine the limiting heel angle from Table 4 (Sections 6.2)

Part 2: Sailing boats of hull length greater than or equal to 6m

6.2.2: Downflooding height Minimum freeboard to downflooding points must be determined from Figure 2 (Section 6.2.2) and entered into the required value field, the default value is set at 1.42m which is slightly greater than the height required for a category A vessel of 24m in length. 6.2.3: Downflooding angle Must be greater than a certain value as determined according to the design category, see Tables 3 (Sections 6.2.3). The default value is set to 40 6.3: Angle of vanishing stability Determine the required angle of vanishing stability which depends on design category and vessel displacement. The default value is 130. 6.4: Stability index (STIX) Determine the required STIX value depending on the design category, see Table 5 (Section 6.4.9). Also specify the sail area and vertical position of the sail area centroid and enter these values in the appropriate fields in the criterion. If desired you can specify the other values or let Hydromax calculate them for you. 6.5: Knockdown-recovery test The test can be approximated by examining the angle of vanishing stability in the flooded condition. If the flooded vessel has positive GZ at the knockdown angle, it should self right. 6.6.6: Wind stiffness test Determine the wind heeling moment as defined in 6.6.6 for the wind speed of interest (Table 6, Section 6.6.7). Convert this to a heeling lever. Calculate the GZ curve with the crew seated to windward, this criterion will then look at the angle of equilibrium of the vessel under the applied wind heeling arm.

Part 3: Boats of hull length less than 6m

These criteria are evaluated after an equilibrium analysis under the specified loading condition. Non-Sailing Boats: 6.2.2: Downflooding-height tests Determine the required downflooding height and specify the appropriate loading condition. The criterion is evaluated after an equilibrium analysis. 6.3: Offset-load test This criterion is most effectively evaluated by performing an equilibrium analysis with the required offset loading condition Sailing Boats: 7.2: Downflooding height Minimum freeboard to downflooding points must be determined from Figure 2 (Section 6.2.2) and entered into the required value field, the default value is set at 1.42m which is slightly greater than the height required for a category A vessel of 24m in length. 7.5: Knockdown-recovery test The test can be approximated by examining the angle of vanishing stability in the flooded condition. If the flooded vessel has positive GZ at the knockdown angle, it should self right. 7.6.6: Wind stiffness test

Appendix C

Page 253

Determine the wind heeling moment as defined in 6.6.6 for the wind speed of interest (Table 6, Section 6.6.7). Convert this to a heeling lever. Calculate the GZ curve with the crew seated to windward, this criterion will then look at the angle of equilibrium of the vessel under the applied wind heeling arm.

Appendix C

Page 254

Appendix E: Reference Tables

This appendix contains the following reference tables: • File Extension Reference Table

• Analysis settings reference table

File Extension Reference Table

The following table lists files that are used in Hydromax. The .hmd file contains all the additional information that defines the Hydromax model and you need only save this file when working in Hydromax. However, if you wish to transfer loadcases or compartment definitions from one model to another, this can be done by going to the appropriate window and saving it to a separate file. File Extension Description Maxsurf Design .msd Contains control point and surface information. E.g.

precision, flexibility, thickness, outside arrows, trimming, colour

When opening a .msd file Hydromax looks for a .hmd file with the same name.

Hydromax Design .hmd Contains hydrostatic sections information and all Input information that may also be stored separately in the files below

The .hmd file does not contain: - Maxsurf surface information - Links to or information on the Stability Criteria Library - Links to or information on the Results tables - Links to or information on the Report

Separate Input files Extension Description Loadcase .hml Each loadcase can be saved separately Compartments .htk The compartment definition can be saved separately Damage cases .dcs The damage case definition can be saved separately All Input window tables .txt All tables in the input window can be saved as text

files. Downflooding/embarkation points, margin lines, sounding pipes and modulus

Output files Extension Description All Result Window tables .txt Result tables can be saved separately

Results tables can not be opened in Hydromax

Report .rtf The report can be saved separately

Library Extension Description Hydromax Criteria Library .hcr The library is not related to the Hydromax Design File,

i.e. is not model related. The library is loaded when the program starts, not when the model is opened. For more information see the section on criteria.

Appendix C

Page 255

Analysis settings reference table

The following table can be used as a reference to the various analysis settings for each analyses type. Analysis Settings

Analyses type Trim Heel Draft Displace-ment

LCG TCG VCG

Upright stability S Upright R result n/a n/a For GM etc.

Large Angle Stability

S / FTTLC R result LC LC LC LC

Equilibrium result result result LC LC LC LC Specified Condition S S S S / LC S / LC S / LC S / LC

KN values S / FTT R result R S / FTT

S / LC4 S1

Limiting KG S / FTT R result R S / FTT

S / LC4 result2

Floodable Length FTT Upright result R FTT n/a S3

Tank Calibration S Upright n/a n/a n/a n/a n/a

Where, result Cannot be specified – they are a calculated resul S Specific (fixed, single) value to be set by user R Varied within Range specified by user LC Calculates values from loadcase – specifies displacement and COG only FTTLC Free-to-trim to loadcase CG FTT Free-to-trim to LCG calculated from a specific initial trim angle or

specified LCG (and VCG) 1 The VCG is used in two ways in the KN analysis. a) The VCG only has an effect on the results if the analysis is free-to-trim. b) The GZ curve is calculated for the specified VCG and then the normalised KN curve is calculated as KN = GZ + VCG*SIN(heel).

2 The VCG is not required for the Limiting KG analysis. When calculating the LCG from a specified trim and displacement, the current VCG is used. 3 The VCG is required for the floodable length analysis because of its effect on trim. During the floodable length analysis, the trim can be substantial and the vertical separation of CG and CB needs to be taken into account. 4 The TCG may be specified directly of derived from the lost cargo / ballast water in damaged tanks from the current loadcase.

Index

Page 256

Index

A

About Hydromax........................................ 169 Add Damage case....................................... 162 Add Load...................................................... 35 Add Surface Areas ..................................... 160 Allowable shears and moments.................... 65 Analysis

Menu ...................................................... 162 Output..................................................... 116 Settings................................................... 255 Toolbar ................................................... 155

Analysis in waves......................................... 78 Analysis type

Equilibrium............................................... 76 Floodable Length...................................... 90 KN Values Analysis ................................. 81 Large Angle Stability ............................... 70 Limiting KG ............................................. 83 Longitudinal Strength............................... 93 Specified Conditions ................................ 79 Tank Calibrations ..................................... 95 Upright Hydrostatics ................................ 68

Animate ...................................................... 168 Arrange Icons ............................................. 169 Automation Reference................................ 169

B

Batch Analysis.............................................. 99 Beam .......................................................... 173 Block Coefficient ....................................... 175 Boundary Box .............................................. 45 Bulkheads............................................. 66, 145

C

Calibration Increment................................... 60 Cascade....................................................... 168 Case

Menu ...................................................... 162 Cell Border ................................................. 159 Cell Shading ............................................... 159 Centre of buoyancy .................................... 141 Centre of flotation ...................................... 141 Centre of gravity......................................... 141 Check for Updates...................................... 169 Closing a Loadcase....................................... 35 Coefficient parameters ............................... 171 Coefficients,

calculation of .......................................... 168 Hydrostatic ............................................... 30

Colour......................................................... 161

Compartment Definition ...................... 44, 144 New .......................................................... 44 Saving..................................................... 121

Compartment types ...................................... 58 Compartments .......................................... 58 Linked ...................................................... 59 Linked Tanks............................................ 58 Non-Buoyant Volumes............................. 59 Tanks ........................................................ 58

Compartments, add, delete ................................................ 45 Forming .................................................... 54

Convergence Error ..................................... 106 Coordinate system........................................ 29 Copy ................................................... 119, 159 Copying Graphs.......................................... 150 Copying Tables .......................................... 119 Corrected VCG........................................... 110 Creating a Compartment definition file........ 44 Creating a new Loadcase File ...................... 32 Criteria........................................................ 163 Criteria File Format.................................... 134 Criteria Libraries ........................................ 132 Criteria,

Import ..................................................... 158 Save As................................................... 158

Cut .............................................................. 159

D

Damage ................................................ 61, 116 Damage Case

Add........................................................... 61 Delete ....................................................... 61 Display ..................................................... 62 Rename..................................................... 61 saving ..................................................... 121 Select ........................................................ 62

Damage Window........................................ 143 Data Format........................................ 145, 165 Data layout ................................................. 145 Data Menu.................................................. 168 Delete Cells ................................................ 159 Delete Damage case ................................... 162 Density ............................................... 111, 163 Design Grid ................................................ 168 Design Preparation ....................................... 18 Design,

coherence.................................................. 20 Saving..................................................... 120

Displacement...................................... 105, 163 Display Menu ............................................. 165

Index

Page 257

Downflooding Angles .................................. 75 Downflooding points............................ 63, 144

Linking to tanks or compartments............ 64 Draft ..................................... 68, 105, 163, 174 DWL............................................................. 68 DXF export................................................. 122 Dynamic Stability......................................... 71

E

Edge Visibility Toolbar.............................. 156 Edit Damage case ....................................... 162 Edit Loadcase ............................................. 162 Edit Menu................................................... 158 Edit Toolbar................................................ 154 Edit,

Add......................................................... 159 Delete ..................................................... 159 Move Items Down.................................. 160 Move Items Up....................................... 160 Sort Items ............................................... 160

Equilibrium............................................... 9, 76 Equilibrium Condition.................................... 9 Export ......................................................... 157 Export Bitmap ............................................ 158 Exporting.................................................... 121 External Tanks.............................................. 48 Extra Buttons Toolbar ................................ 156

F

File Extension Table................................... 254 File Menu ................................................... 157 File Toolbar ................................................ 154 File,

Close....................................................... 157 Exit ......................................................... 158 Hydromax Version 8.0 ........................... 122 New ........................................................ 157 Open ................................................. 21, 157 Save ........................................................ 157 Save As................................................... 157

Fill Down.................................................... 159 Floodable Length.......................................... 13 Floodable Length Criteria dialog ............... 163 Flooding ....................................................... 62 Fluid analysis method................................. 108 Fluid VCG............................................ 44, 111 Fluids.......................................................... 163 Font ............................................................ 161 Form parameters......................................... 170 Frame of Reference ........................ 18, 30, 168 Free Surface Moment ........................... 44, 110 Freeboard...................................................... 77 Full Screen.................................................. 162

G

Graph.......................................................... 169 Curve of Areas ....................................... 148 Curves of Form ...................................... 148 Data interpolation................................... 149 double click ............................................ 150 get data ................................................... 150 Righting Lever (GZ)............................... 148 Type........................................................ 148

Graph colours ............................................. 150 Graph Formatting ....................................... 150 Graph Printing to Scale .............................. 119 Graph Window........................................... 147 Graphs ........................................................ 148 Grid ............................................................ 167 Grounding .......................................... 113, 163 GZ .................................................................. 9

H

Heel .................................................... 102, 162 Heeling Moments ....................................... 192 Help Menu.................................................. 169 Hog and Sag ....................................... 115, 163 Home View ........................................ 141, 160 Horizontal lever............................................ 36 Hull Sections

Recalculate ............................................. 164 Hydromax v8.0 file .................................... 158

I

Immersion .................................................. 178 Immersion Angles ........................................ 75 Import ......................................................... 157 Initial Conditions.......................................... 29 Input ........................................................... 169 Input Tables, saving ................................... 121 Input Window............................................. 144 Insert New Table ........................................ 159 Insert Row .................................................. 159 Installing Hydromax..................................... 16 ISO 12217-1 ............................................... 249

K

Key points ............................................ 63, 144 adding....................................................... 63 Data .......................................................... 75 deleting..................................................... 64 editing....................................................... 64 Results .................................................... 146

KN Values.............................................. 11, 81

L

Large Angle Stability ............................... 8, 70

Index

Page 258

lateral projected area .................................. 192 LCB, LCG .................................................. 176 Length ........................................................ 172 Libraries ..................................................... 132 Limiting KG ........................................... 12, 84 Linked negative compartments .................... 51 Loadcase............................................... 32, 169

Adding and Deleting loads....................... 35 Distributed loads ...................................... 38 Editing loads............................................. 35 Free surface correction ............................. 44 maximum number .................................... 35 Renaming ................................................. 34 saving ..................................................... 121 Update ...................................................... 40

Loadcase Colour Formatting ........................ 37 Loadcase Formatting .................................... 36

Blank lines................................................ 36 Grouping tanks ......................................... 37 Headings lines .......................................... 36 Totals........................................................ 37

Loadcase Sorting .......................................... 36 Loadcase Template....................................... 33 Loadcase Window...................................... 143 Loadcase, cross referencing ......................... 40 Loadcase, density ......................................... 42 Loadcase, Distributed Loads ........................ 38 Loadcase, formatting, column selection....... 37 Loadcase, max. number.............................. 162 Loadcase, Tank loads ................................... 39 Loadgroup .............................................. 32, 40 Loadgroup, Workshop structure................... 44 Loading a Saved Loadcase........................... 34 Longitudinal Strength............................. 13, 93

M

Margin Line points ............................... 65, 144 Margin Line, Snap to hull .......................... 164 Max. Area Section...................................... 175 Maximum deck inclination......................... 177 Maximum shears and moments.................... 65 Measurement reference frames .................. 170 Menus......................................................... 156 Merge Cells ................................................ 159 Midship Section.......................................... 175 Modulus points........................................... 144 Modulus Window......................................... 65 Moment to trim........................................... 178

N

Non-Buoyant Volume Definition................. 44

O

Online Support ........................................... 169

Outside arrows ............................................. 19 overlap.......................................................... 51

P

Page Setup.................................................. 158 Pan...................................................... 141, 160 Paste ........................................................... 159 Permeability ........................... 13, 50, 106, 163 Perspective view......................................... 142 Precision, surface ......................................... 22 Preferences ........................................... 16, 160 Print ............................................................ 158 Print Preview.............................................. 119 Printing....................................................... 119 Printing to scale.......................................... 119 Prismatic Coefficient.................................. 176 Properties.................................................... 161

R

Ratio of equilibrium angles – GZ area derived heeling arm............................................. 236

Reference Calculations............................... 180 Reference Designs...................................... 179 Relative Density ................................... 53, 111 Render ........................................................ 167 Render Transparent .................................... 167 Report Toolbar ........................................... 156 Report Window .......................................... 151

Keystrokes.............................................. 153 Reporting.................................................... 116 Results ........................................................ 169 Results Window ......................................... 145 Results, saving............................................ 121 Resume Analysis .................................. 99, 164 Righting Moment ....................................... 178 Rotate ......................................................... 161 Row Positioning ......................................... 159

S

Safe steady heeling angles............................ 72 Save ............................................................ 121 Saving Densities......................................... 112 Section Area Coefficient ............................ 176 Section, show single................................... 167 Sectional Area Curve ................................... 28 Sections, Forming......................................... 24 Select All .................................................... 159 Select View from Data ....................... 120, 167 Set Analysis Type....................................... 164 Set Home View .......................................... 160 Set Vessel to DWL..................................... 167 Shift Key ...................................................... 16 Show Grid .................................................. 159 Show single hull section............................... 27

Index

Page 259

Shrink ................................................. 141, 160 Simulate fluid movement ........................... 110 Skin Thickness ............................................. 19 Sounding Pipes..................................... 59, 144

Calibration Increment............................... 60 Edit ........................................................... 59

Specific Gravity.................................... 53, 111 Specified Condition........................ 10, 79, 163 Specified Conditions, dialog ...................... 105 Split Cell..................................................... 159 Spool to Report........................................... 165 Stability booklet ......................................... 110 Stability criteria ............................................ 66 Stability Criteria Results ............................ 146 Stability criteria, angle calculators ............. 184 Stability criteria, Angle of deck edge

immersion............................................... 201 Stability criteria, Angle of downflooding... 201 Stability criteria, Angle of equilibrium ...... 200 Stability criteria, Angle of equilibrium -

general heeling arm ........................ 218, 219 Stability criteria, Angle of equilibrium - GZ

derived wind heeling arm....................... 235 Stability criteria, Angle of equilibrium - high-

speed turn heeling arm ........................... 239 Stability criteria, Angle of equilibrium -

multiple heeling arms ............................. 225 Stability criteria, Angle of equilibrium -

passenger crowding heeling arm ............ 239 Stability criteria, Angle of margin line

immersion............................................... 201 Stability criteria, Angle of maximum GZ .. 200 Stability criteria, Angle of maximum GZ

above heeling arm .................................. 217 Stability criteria, Angle of vanishing stability

................................................................ 201 Stability criteria, Angle of vanishing stability -

general heeling arm ................................ 219 Stability criteria, Areas and levers ............. 192 Stability criteria, capsizing moment ........... 242 Stability criteria, check boxes .................... 131 Stability criteria, Combined criteria (ratio of

areas type 1) - general cos+sin heeling arm................................................................ 239

Stability criteria, Combined criteria (ratio of areas type 1) - general heeling arm ........ 230

Stability criteria, Combined criteria (ratio of areas type 1) - high-speed turn ............... 239

Stability criteria, Combined criteria (ratio of areas type 1) - lifting weight................... 240

Stability criteria, Combined criteria (ratio of areas type 1) - passenger crowding ........ 239

Stability criteria, Combined criteria (ratio of areas type 1) - towing............................. 240

Stability criteria, Combined criteria (ratio of areas type 2) - general wind heeling arm231

Stability criteria, Combined criteria (ratio of areas type 2) - wind heeling arm ............ 240

Stability criteria, copying criteria............... 130 Stability criteria, criteria library file........... 132 Stability criteria, damage and intact settings

................................................................ 132 Stability criteria, defining custom criteria.. 130 Stability criteria, equilibrium ..................... 194 Stability criteria, General cos+sin heeling arm

................................................................ 187 Stability criteria, General heeling arm ....... 186 Stability criteria, glossary........................... 139 Stability criteria, Gust ratio ........................ 186 Stability criteria, GZ area between limits type

1 - general heeling arm........................... 220 Stability criteria, GZ area between limits type

1 - multiple heeling arms........................ 225 Stability criteria, GZ area between limits type

1 - standard............................................. 202 Stability criteria, GZ area between limits type

2 - general heeling arm........................... 221 Stability criteria, GZ area between limits type

2 - multiple heeling arms........................ 226 Stability criteria, GZ area between limits type

2- HSC monohull type............................ 203 Stability criteria, GZ area between limits type

3 - HSC multihull type ........................... 205 Stability criteria, GZ area derived heeling arm

type 1...................................................... 233 Stability criteria, GZ area derived heeling arm

type 2...................................................... 234 Stability criteria, GZ curve features ........... 136 Stability criteria, GZ definitions................. 138 Stability criteria, GZ derived heeling arm.. 233 Stability criteria, GZ, non-healing arm ...... 196 Stability criteria, heeling arm definition..... 186 Stability criteria, heeling arm dependency on

displacement........................................... 192 Stability criteria, heeling arm units ............ 244 Stability criteria, Heeling due to arbitrary

forces ...................................................... 191 Stability criteria, Heeling due to bollard-pull

................................................................ 191 Stability criteria, Heeling due to lifting of

weights ................................................... 190 Stability criteria, Heeling due to passenger

crowding................................................. 188 Stability criteria, Heeling due to towing .... 191 Stability criteria, Heeling due to trawling .. 192

Index

Page 260

Stability criteria, Heeling due to turning .... 189 Stability criteria, Heeling due to wind........ 188 Stability criteria, IMO Code on Intact Stability

A.749(18) ............................................... 244 Stability criteria, IMO HSC Code MSC.36(63

................................................................ 246 Stability criteria, IMO roll back angle

calculator ................................................ 185 Stability criteria, importing ................ 132, 133 Stability criteria, ISO 12217....................... 251 Stability criteria, list ................................... 123 Stability criteria, Maximum Freeboard at

equilibrium ............................................. 195 Stability criteria, Maximum ratio of GZ to

heeling arm............................................. 215 Stability criteria, Maximum value of heel,

pitch or slope at equilibrium................... 194 Stability criteria, Minimum Freeboard at

equilibrium ............................................. 195 Stability criteria, Minimum ratio of GZ to

heeling arm............................................. 217 Stability criteria, moving criteria................ 130 Stability criteria, Other criteria - STIX ...... 237 Stability criteria, parent criteria.......... 125, 194 Stability criteria, pass/fail test .................... 132 Stability criteria, Range of positive stability

................................................................ 201 Stability criteria, Range of positive stability -

general heeling arm ................................ 219 Stability criteria, Ratio of areas type 1 -

general cos+sin heeling arm................... 239 Stability criteria, Ratio of areas type 1 -


multiple heeling arms ............................. 227 Stability criteria, Ratio of areas type 2 -


general heeling arm ................................ 223 Stability criteria, Ratio of GMT and heeling

arm.......................................................... 213 Stability criteria, Ratio of GZ area between

limits....................................................... 207 Stability criteria, Ratio of GZ values at phi1

and phi2.................................................. 199 Stability criteria, Ratio of GZ values at phi1

and phi2 - general heeling arm............... 217 Stability criteria, Ratio of GZ values at phi1

and phi2 - multiple heeling arms............ 224 Stability criteria, Ratio of positive to negative

GZ area between limits .......................... 209 Stability criteria, report and batch processing

................................................................ 136

Stability criteria, results.............................. 134 Stability criteria, saving.............................. 133 Stability criteria, selecting for analysis ...... 130 Stability criteria, Survivability Index -

MSC_216(82).rtf .................................... 228 Stability criteria, tree list ............................ 129 Stability criteria, User Defined Heeling Arm

................................................................ 187 Stability criteria, USL code........................ 248 Stability criteria, Value of GMt at.............. 196 Stability criteria, Value of GMt at equilibrium

- general heeling arm.............................. 213 Stability criteria, Value of GMt or GMl at

equilibrium ............................................. 195 Stability criteria, Value of GZ at ................ 196 Stability criteria, Value of GZ at equilibrium -

general heeling arm ................................ 213 Stability criteria, Value of GZ at specified

angle or maximum GZ below specified angle ....................................................... 197

Stability criteria, Value of maximum GZ... 196 Stability criteria, Value of maximum GZ

above heeling arm .................................. 214 Stability criteria, Value of RM at specified

angle or maximum RM below specified angle ....................................................... 198

Start Analysis ....................................... 98, 164 Start Batch Analysis ................................... 165 Starting Hydromax ....................................... 16 Status Bar ................................................... 161 Stop Analysis ....................................... 98, 164 Streaming results to Word.......................... 117 Surface Use .................................................. 18

T

Table........................................................... 159 Tank

adding, deleting ........................................ 45 Fluids........................................................ 53 Ordering ................................................... 53 Permeability ....................................... 50, 52 Saving..................................................... 121 Surface Thickness .................................... 53 Visibility................................................... 53

Tank Calibrations ................................... 14, 96 Tank Type

external ..................................................... 48 linked........................................................ 46 simple ....................................................... 45 tapered ...................................................... 46

tanks overlap...................................................... 51

Tanks Recalculate ............................................. 164

Index

Page 261

Tanks within Compartments ........................ 51 Tanks,

boundary surfaces..................................... 47 complex .................................................... 47 Non-Buoyant Areas.................................. 49 Recalculate ............................................. 155

TCG, Limiting KG, KN ............................. 105 Tile Horizontal ........................................... 169 Tile Vertical................................................ 169 Tolerances .................................................. 106 Toolbars.............................................. 154, 161 Trapezoidal integration ................................ 24 Trim.................................................... 103, 163

Fixed....................................................... 104 Free-to-trim to a specified LCG value ... 104 Free-to-trim using a specified initial trim

value ................................................... 104 Trim angle .................................................. 177 Trimmed surfaces, checking......................... 19

U

Undo........................................................... 158 Units ..................................................... 31, 168 Update Loadcase ........................................ 164 Upright Hydrostatics ................................ 7, 68

V

Validate Hydromax model ........................... 27 VCG for trim balance................................. 104 View (extended)Toolbar ............................ 156 View Direction ........................................... 169 View Menu................................................. 160 View Toolbar.............................................. 154 View Window ............................................ 141 Visibility..................................................... 167 Visibility Toolbar ....................................... 155

W

Waterplane Area Coefficient...................... 176 Wave definition .......................................... 112 Wave height................................................ 113 Waveform................................................... 163

sinusoidal................................................ 113 trochoidal................................................ 113

Wavelength................................................. 113 Wetted surface area, integration of............. 179 Window Menu............................................ 168 Window Toolbar ........................................ 155 Windows Registry ........................................ 16 Word, report streaming to .......................... 117 Word, report templates............................... 117

Z

Zero Point......................................... 18, 30, 36

Zoom .................................................. 141, 160