ce_11_06 - iacs proposals on minimum power for eedi

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18 March 2011 To: CONSTRUCTION AND EQUIPMENT SUB-COMMITTEE CE(11)06 Copy: Marine Committee All Full and Associate Members (For Information) CONSIDERATION OF IACS PROPOSALS ON MINIMUM POWER REQUIREMENTS FOR SHIPS SUBJECT TO EEDI Action required: Members are invited to review the draft IACS submission to IMO on “Minimum propulsion power to ensure safe manoeuvring in adverse conditions” intended for consideration during the MEPC 62 EEDI discussion, attached as Annex A to this circular. The secretariat will appreciate Members’ comment on the contents of the paper and on the appropriateness of ICS co-sponsoring the IACS proposal. Comment should be addressed to the undersigned and copied to [email protected]. During the meeting of the Construction and Equipment Sub-Committee on 14th March 2011, the Sub-Committee gave its preliminary consideration to the draft MEPC submission by IACS on the topic of “Minimum propulsion power to ensure safe manoeuvring in adverse conditions”. This document proposes draft interim Guidelines to determine whether adequate propulsion power has been provided to enable safe manoeuvring in adverse conditions in the context of future ships designed to achieve mandatory EEDI values. The Sub-Committee noted that IACS has proposed a simplified assessment to be used as a first phase pending the development of more comprehensive guidelines. Having also noted the short time between receipt of this paper and the date of the Sub-Committee meeting, the Chairman requested the IACS paper to be circulated for further consideration and comment together with an earlier working paper understood to contain more comprehensive background information. The two papers are attached as Annexes to this circular. The secretariat has participated in the discussion on this proposal with IACS and other industry organisations. It is understood that the intention of the simplified approach is to provide a base document for initial consideration to facilitate the main EEDI initiative to be taken forward at MEPC 62, with those aspects of the guidelines addressing the minimum power consideration to be subject to further consideration at a later time.

Members are invited to review and comment on the draft submission. In particular, Members are invited to consider:

a) Whether ICS should formally co-sponsor the paper subject to further development following MEPC 62;

b) Whether ICS should offer verbal support to the paper at MEPC 62; and c) Whether specific revisions/improvement would be necessary prior to supporting

the paper. Members’ attention is drawn to the overview of the basic IACS proposal outlined in paragraphs 12 to 17 on page 5 of the paper. The general intent of the proposed simplified approach is that a ship should be able to maintain a minimum speed in adverse conditions, and that the parameters for the speed to be attained and the associated environmental conditions should be defined in the IMO guidelines along with guidance on verification. Alistair Hull Technical Manager

CE(11)06 - Annex A - IACS draft paper to MEPC-62 2011-03-09

MARINE ENVIRONMENT PROTECTION COMMITTEE 62nd session Agenda item 5

MEPC 62/5/y 8 April 2011 Original: ENGLISH

REDUCTION OF GHG EMISSIONS FROM SHIPS

Consideration of the Energy Efficiency Design Index for New Ships

Minimum propulsion power to ensure safe manoeuvring in adverse conditions

Submitted by IACS [BIMCO, ICS, Intercargo, Intertanko, OCIMF, WSC]

SUMMARY Executive summary:

This document presents draft interim guidelines to determine whether available propulsion power is sufficient to enable safe manoeuvring in adverse conditions.

To facilitate an early implementation, a simplified assessment is suggested as verification procedure in a first phase and which can be accomplished with tools that are available today. The simplified assessment is a subset of the comprehensive assessment which is based on the full draft interim guidelines but, due to its complexity, is only suggested for use in a later phase.

Strategic direction:

7.3

High-level action:

7.3.2

Planned output:

7.3.2.1

Action to be taken:

Paragraph 16

Related documents:

MEPC 61/24, MEPC 61/5/32, MEPC 61/5/3 EE-WG 1/4, MEPC 60/WP.9, MEPC 59/4/2, MSC.137(76)

Introduction

1. At MEPC 61 the debate on safety issues related to the EEDI focussed on safe manoeuvring in adverse conditions. Some delegations argued that – in order to reduce installed power - ship designers may choose to reduce a ship's design speed to achieve the required EEDI. To avoid negative effects on safety, such as under-powered ships, the IACS proposal for a provision to the draft regulations, contained in document MEPC 61/5/32, was agreed to be included in [square brackets] for further consideration as follows:

"For each ship to which this regulation applies, the installed propulsion power shall not be less than the propulsion power needed to maintain the manoeuvrability of the ship under adverse conditions as defined in the guidelines to be developed by the Organization."

2. IACS also informed the Committee that first draft guidelines will be developed and submitted to MEPC 62 for further consideration. Therefore, IACS established a project team to develop first draft guidelines and conducted a workshop with other stakeholders to discuss the impact and the practicability of the proposed procedures.

3. This paper presents the interim results of the work conducted.

- 2 - MEPC 62/5/y The Challenges

4. Standards for ship manoeuvrability are only defined for calm environment, in IMO resolution MSC.137(76) and MSC/Circ.1053. Compliance is checked by sea trials. For manoeuvring in adverse conditions, no rule, guideline or other reference exist. In particular

a. no agreed definition of standard manoeuvres exists which, if being carried out successfully in adverse conditions, would demonstrate that the vessel is capable of safe manoeuvring in these conditions.

b. adverse conditions are not defined in this context

c. model experiments with adverse weather are possible, but may not be available for routine ship design purposes because few facilities exists with the required capabilities

d. numerical simulation tools are not considered to be mature enough to routinely analyse this scenario, and this was recently reported by the Manoeuvring Committee to the final report to the 25th ITTC in 2008.

5. Due to the complexity of the issue and a lack of established practice, it is expected that work to understand and assess manoeuvrability of vessels in adverse conditions will continue for some time before accepted methods are established and robust tools will become available.

Proposal for two approaches towards verification

6. Recognizing the above, IACS suggests two approaches, with a simplified assessment in a first phase and a comprehensive assessment in a later phase. The simplified assessment procedure considers simplifications and it can be performed using available tools. Once experience has been gained with the simplified assessment and more robust tools are available, trial use of the comprehensive assessment should be considered. This phase-in may be linked to planned EEDI implementation phases.

a. The simplified assessment considers the advance of a vessel only in head waves and wind and determines the required propulsion power taking into account calm water hull and appendage resistance, added resistance in waves and air drag. The simplified assessment – briefly described in paragraphs 9 to 12 - is assumed to be ready for trial use once acceptance criteria have been agreed by the Committee.

b. The comprehensive assessment considers the full manoeuvring of a vessel and it includes the simplified assessment as a subset. In addition, the comprehensive assessment may be performed in two levels of sophistication: a static assessment and a time-dependent assessment. The comprehensive assessment, described in Annex I still requires more research before application can be attempted.

Proposal for definition of adverse conditions

7. Adverse conditions corresponding to sea states 7 to 8 were selected based on assumed reasonable probability levels, results from interviews with masters and one casualty report. For ease of reference, the proposed range of conditions is shown in the table below.

Probability Return period

Sea state

Sig. wave height (m)

Wave period (s)

Beaufort Mean wind speed (knots)

2% one week 7 7.5 7.5 to 14.5 9 45 0.5% one month 8 9.8 8.5 to 13.5 10 51.5

8. A wave height of 8 m and a wind force Bft 9 were reported to be adverse conditions for a large tanker by an experienced master who was interviewed by IACS. And sea states 7 to 8 were documented in a casualty report by the Australian Transport Safety Bureau, no 243, which showed that these conditions can be considered to be adverse but still allow for safe

- 3 - MEPC 62/5/y manoeuvring. A range of environmental conditions is suggested for discussion before an adequate probability level and associated conditions can agreed by the Committee.

The simplified assessment in brief

9. The process of verifying a ship having sufficient installed power to enable safe manoeuvring in adverse conditions will be one of submitting a calculation to demonstrate that the required speed can be attained at the defined adverse conditions.

10. The simplified assessment requires calculating the advance of a vessel only in head waves and wind and determines the required propulsion power taking into account calm water hull resistance and appendage resistance, added resistance in waves and air drag. A worked example for the advance speed assessment is contained in Annex III for a VLCC in fully loaded condition, acknowledging the uncertainties involved. All terms for this assessment may be approximated by simple formulae or using tabulated values or model experiments.

11. The basic assumption is that the dimensioning criterion is advance speed in waves and, implicitly, that turning and course keeping can be achieved if advance speed is maintained. This assumption is true for vessels with low above-water lateral area, typical for bulk carriers and oil tankers, but may be questioned for other vessels which are known to have reduced manoeuvring capability in strong gale force winds, such as fully loaded container vessels. However, it is also assumed that for these vessels due to their relatively high installed engine power, manoeuvrability in adverse conditions can be maintained. The latter assumption needs to be checked once the comprehensive assessment can be trialled.

12. The simplified assessment is assumed to be ready for trial use once acceptance criteria have been agreed by the Committee. In particular, the required minimum speed needs to be determined and it is believed that this can be done by systematic calculations on existing vessels with lower-than-average installed power to check if they can obtain the required speed.

Overview on annexes

13. Annex I presents the full draft interim guidelines to determine whether propulsion power is sufficient to ensure safe manoeuvring in adverse conditions. These guidelines are considered to be complete but also sufficiently open for later amendments due to their goal-based style.

14. Although the full guidelines are not needed for the suggested use of the simplified assessment within a first phase of use, the complete draft interim guidelines are documented to guide needed research and development activities in the near-term.

15. Background to the draft interim guidelines is contained in Annex II and a worked example for the simplified assessment is presented in Annex III.

Recommendations

16. The Committee is invited to take note of the work conducted and provide guidance as to 1) whether the simplified assessment can be considered for use as an interim measure, and 2) if further work is warranted.

17. The Committee is also invited to consider informing the relevant SLF correspondence group on the discussion on safe manoeuvring in adverse conditions as this may be linked to the current debate at SLF focussing on new intact stability criteria and related procedures for their assessment.

*************

- 4 - MEPC 62/5/y

ANNEX I

DRAFT INTERIM GUIDELINES TO DETERMINE WHETHER PROPULSION POWER IS

SUFFICIENT TO ENSURE SAFE MANOEUVRING IN ADVERSE CONDITIONS

Purpose

1. The purpose of these guidelines is to assist Recognized Organisations in the verification of the Energy Efficiency Design Index (EEDI) and to facilitate, at the same time, that vessels are capable of safe manoeuvring even in adverse conditions. These guidelines will support ship designers and ship builders to develop energy-efficient and safe new vessels.

2. These guidelines define a goal-based framework and procedures to determine whether the propulsion power is sufficient to ensure safe manoeuvring in adverse conditions.

Assumptions

3. The guidelines only apply to those ship types defined in the Annex to MEPC.1/Circ.681.

4. The guidelines apply to vessels with unrestricted navigation.

5. The vessel is considered to have been properly prepared by the crew to face adverse conditions, e.g., cargo secured and vessel correctly ballasted (i.e., heavy ballast). Therefore, cargo-related effects are not included in the guidelines.

6. No full scale tests are possible to be performed to test the vessel’s manoeuvring capability in adverse conditions. Therefore, model experiments and numerical simulations are accepted as equivalent tools to conduct the test programs defined in these guidelines.

Goal

7. The vessel shall have the necessary propulsion power [and steering capability1] to ensure safe manoeuvring in adverse conditions.

.1 safe manoeuvring means the ability to turn the vessel into a more desirable position relative to the weather, and at least to maintain this position without drifting over ground once the turn is completed.

.2 adverse conditions mean an unfavourable combination of wind and waves.

Functional requirements

8. The vessel should have the ability to perform the following missions in the defined adverse environmental conditions:

.1 Turn within defined time period and maintain [a][safe][any][required] course at a defined minimum speed

.1 The selection of the course may be limited due to navigation restrictions and this course may lead to an unfavourable heading of the vessel towards the waves.

9. Additional missions are identified but considered to be included in the above mission. These are survival in open seas with maintaining a favourable heading towards the waves, providing shelter for rescue operations, if the master decides to do so, and preparation for emergency towing.

1 Required rudder performance for calm environment is specified in MSC.137(76) and MSC/Circ.1053.

- 5 - MEPC 62/5/y 10. Manoeuvring in port is not considered in these guidelines due to the availability of tug assistance in port in case of adverse conditions.

11. Two standard manoeuvres are considered to be representative for the manoeuvrability of a vessel in adverse conditions and these reflect the above defined mission requirements.

Verification - acceptance criteria

12. The vessel should fulfil the following criteria2 for the standard manoeuvre “turning ability:”

.1 Time for completing a 180 degree turn is less than [15][30] minutes

.2 The maximum advance distance in wave direction is less than f * 5L, with f = [1.2][1.5] reflecting that a turning circle in waves is larger in diameter and/or advance than in calm water.

13. The vessel should fulfil the following criteria3 for the standard manoeuvre “course keeping and advance speed:”

.1 The minimum advance speed is [2][4] knots through water.

.2 The steering gear needs to balance the wind and wave force and moment and is defined as average deviation from the course and is less than ± [5][10] degrees.

14. Environmental conditions reflect adverse North Atlantic conditions3 and these are defined by the following parameters:

Probability Return period

Sea state

Sig. wave height (m)

Wave period (s)


2% one week 7 7.5 7.5 to 14.5 9 45 0.5% one month 8 9.8 8.5 to 13.5 10 51.5

Wind speed at 20 m above water surface

15. For vessels with restricted navigation, environmental conditions need to be agreed with the Administration, taking operational area and restrictions into account.

Verification - procedures

16. Verification of compliance by means of assessment procedures may be conducted by model experiments and/or numerical simulations. Two verification procedures are defined with different levels of sophistication as follows.

17. Advance speed assessment should be applied to vessels with a design Froude number below [0.2][0.3]4 and with a ratio of the above-water lateral area to the total lateral area incl. the rudder area smaller than [0.65][0.75]5, taking the loading condition resulting in the largest ratio.

18. The test program for the advance speed assessment is defined as follows:

2 It is noted that all figures given for the acceptance criteria are suggestions by IACS and these need to be validated using expert opinion, numerical and / or model tests before agreed by the Committee. Values given also need to be consistent with each other. 3 Following early feedback, a range of environmental conditions assumed to represent adverse conditions is offered for discussion. The adequate probability level needs to be discussed by experts and agreed by the Committee. 4 It is noted that the figures given are suggestions by IACS and these need to be validated using expert opinion, numerical and / or model tests before agreed by the Committee. Setting an appropriate threshold value requires systematic analysis of existing ship designs with due respect to submerged rudder area. 5 It is noted that the figures given are suggestions by IACS and these need to be validated using expert opinion, numerical and / or model tests before agreed by the Committee. Setting an appropriate threshold value requires comparison of existing stability information and performing systematic static performance assessments.

- 6 - MEPC 62/5/y

.1 Tests are performed at one loading condition representative for maximum cargo intake

.2 Maximum available power is supplied to the propellers and the rudder is in the neutral position

.3 Wind at maximum speed

.4 Irregular short-crested waves with maximum significant wave height and zero up-crossing periods varied as [7.5,] 8.5, 9.5, 10.5, 11.5, 12.5, 13.5 [,14.5] s

.5 head waves

.6 steady motion

.7 assessment parameters:

Required power for the defined minimum advance speed given in 13.1

.8 the vessel has passed the test if required power is smaller than available power

19. The comprehensive performance assessment is applicable to all vessels and requires performing the test programs listed below. Only for vessels with design Froude number below [0.2][0.3], the method used for testing may neglect all time-dependent and dynamic effects, which is considered to be acceptable for vessels for which dynamic coupling of motions in waves with manoeuvring (e.g., due to broaching) is not relevant. It is noted that the comprehensive assessment includes the simplified assessment as a subset.

20. The test program for the standard manoeuvre “turning ability” is performing a turning circle of 360 degrees6

.1 Tests are performed at two draft conditions representative for heavy ballast and maximum cargo intake

.2 Maximum available power is supplied to the propellers and the maximum rudder angle is set

.3 Wind at maximum speed with 3 directions (aligned with wave direction and ±30 degrees from the wave direction


.5 only one wave direction needs to be tested


turning time per 360 degrees turn

maximum distance in the wave propagation direction per 360 degrees turn

.7 A number of runs shall be performed for different realisations of the same wave conditions, ensuring the fulfilment of criteria for assessment parameters, as given in 12,

6 A turning circle of 360 degrees will avoid testing for different wave directions. However, if test facilities do not allow for a 360 degrees turning circle testing, a 180 degrees turn is considered an alternative with wave directions varied from 0 to 180 degrees and step size of 15 degrees tested.

- 7 - MEPC 62/5/y

with satisfactory engineering accuracy7. Alternatively, several turning circles may be performed following each other using the same realisation of the wave conditions.

21. The test program for the standard manoeuvre “course keeping and advance speed” is

.1 Tests are performed at two loading conditions representative for heavy ballast and maximum cargo intake

.2 Maximum available power is supplied to the propellers and the rudder angle is adjusted to achieve the desired course, up to its maximum angle if necessary.



.5 Wave directions 0 to 180 degrees, with 15 degrees step size


average forward speed and course deviation

.7 A number of runs shall be performed for different realisations of the same wave conditions, ensuring the fulfilment of criteria for assessment parameters, as given in 13, with satisfactory engineering accuracy14.

Documentation

22. Tests need to be documented including but not limited to the following:

.1 description of the vessel’s main particulars

.2 description of the vessel’s relevant manoeuvring and propulsion systems

.3 description of test program and test results

.4 description of applied test method with references

References

MSC.137(76) (2002) Standards for ship manoeuvrability

MSC/Circ.1053 (2002) Explanatory notes to the Standards for ship manoeuvrability

MSC/Circ.707 (1995) Guidance to the master for avoiding dangerous situations in following and

quartering seas

IACS (2001) recommendation 34 – standard wave data

The manoeuvring committee (2008) Final report and recommendations to the 25th ITTC

Australian Transport Safety Bureau, June 2007, Marine occurrence investigation No. 243.

***

7 Satisfactory engineering accuracy means a 95% fulfilment of criteria. For example: if 19 runs out of 20 satisfy the norms for the average forward speed, turning time and distance per turn, the criteria are considered to be satisfied.

- 8 - MEPC 62/5/y

ANNEX II

BACKGROUND TO DRAFT INTERIM GUIDELINES

General

1. The draft interim guidelines were written following the draft generic guidelines for developing [IMO] goal-based standards (GBS) contained in the annex of MSC 87/5. The following figure shows the structure of the draft interim guidelines and its elements, which closely follow the general hierarchy of the GBS.

Goal

Functional requirementsmissionsstandard manoeuvres (are selected to be representative)

Verificationacceptance criteria (quantitative, for checking compliance)

test programs(are verification procedures)

Tier I

Tier II

Tier III

Assumptions

2. Current manoeuvrability standards at IMO are seen as a lower bound to the requirements on manoeuvrability in adverse conditions. However, the current level of manoeuvrability in adverse conditions has never been checked and is not explicitly known. Therefore, it may be possible that existing vessels will be identified to be “underpowered” when the newly proposed assessment is applied for test purposes.

3. As part of the work, IACS developed a draft questionnaire to guide interviews with masters of typical merchant vessels. The purpose of these interviews were to identify events which masters associate with adverse conditions and to learn more on best practices in such conditions. The interview campaign was performed asking a small number of masters and chief officers with more than 15 years of professional experience and active on all types of vessels. Their responses were mostly used to select the environmental conditions.

4. In adverse conditions, masters voluntarily reduce speed to decrease ship motions and, thus, to avoid damages to the ship and its cargo. In addition, added resistance in waves slows down the vessel. Lower ship motions also contribute to better manoeuvrability with higher forces on the rudder. In addition, existing rules (e.g. on lashing) assume that the master has the ability to avoid adverse conditions and to control ship motions. Therefore, too extreme environmental conditions for testing manoeuvring capability may be inconsistent with existing rules.

Goal

5. The recent debate at IMO, see MEPC 61/24, paragraph 5.28, resulted in a text to be included in [square brackets] for further consideration as follows:

"For each ship to which this regulation applies, the installed propulsion power shall not be less than the propulsion power needed to maintain the manoeuvrability of the ship

- 9 - MEPC 62/5/y

under adverse conditions as defined in the guidelines to be developed by the Organization."

6. The IACS project team developed the goal formulation reflecting the above and aimed at more clearly defining on high level objectives for safe manoeuvring in adverse conditions.

7. It is noted that propulsion power alone is not sufficient to guarantee safe manoeuvring in adverse conditions. An effective rudder is also needed. At this stage is assumed that required rudder performance as specified in MSC.137(76) and MSC/Circ.1053 is sufficient and no additional requirement is considered.

8. Since the required level of safety for manoeuvrability in adverse conditions is not defined today, the goal formulation does not contain such element. However, as a starting point casualty reports from the IHS database have been checked to identify the frequency of occurrence of grounding events in adverse conditions.

9. Casualty reports after 1981 for bulk carriers, container vessels, general cargo ships and tankers built after 1981 with a minimum gross tonnage of 1,000 were selected when the accident severity was labelled “serious.” Casualties which may have been caused by lack of available propulsion power in adverse conditions were identified as grounding accidents in adverse conditions without any cause listed (which means that lack of propulsion power could have been the case). This resulted in 64 events in open sea conditions. The following table shows the identified events and event frequencies. It is clear from this first review that general cargo vessels have the highest frequency for such events, followed by bulk carriers and tankers.

Ship type Number of events. estimated ship years frequency Bulk carrier 19 187050 1,02E-04 Container vessel 6 131080 4,58E-05 General cargo ship 27 194851 1,39E-04 Tanker 12 118204 1,02E-04 Total 64 631185 1,01E-04

10. Another approach to identify the current state of installed power and potentially linked events of lack of available propulsion power in adverse conditions is built on the idea that vessels having less than average installed power may be susceptible to missing manoeuvring capability in adverse conditions. As example, bulk carriers and oil tankers built in the last decade and larger than 40.000 DWT were analysed and the vessels with lowest installed power were visually selected. These low-powered vessels have significantly lower installed power compared to the fleet average, see the following figures. A cross-check of casualty information with ship data showed that

a. Involved tankers were small and medium-sized tankers up to Aframax size. They have all been more than 10 years in service and had less-than average installed power, see figure below. No casualties have been recorded in this context for tankers of Suezmax size or for VLCCs.

b. Involved bulk carriers were mostly small and medium sized. Most have been more than 10 years in service. However, no clear trend emerged regarding their installed power, see figure below. In particular, the two largest bulk carriers involved in groundings with heavy weather had more then average installed power.

11. This first analysis shows that smaller vessels have a higher probability for “grounding in heavy weather” with 37% of bulk carriers and tankers smaller than 40.000 DWT, and another 39% between 40.000 DWT and 80.000 DWT, and only 24% larger than 80.000 DWT.

- 10 - MEPC 62/5/y

Crude oil tankers (delivered between 2001-01-01 and 2010-12-31)

y = 9,2383x0,6263

R2 = 0,8985

y = 7,5843x0,6232

R2 = 0,9265

0

5.000

10.000

15.000

20.000

25.000

30.000

35.000

0 50.000 100.000 150.000 200.000 250.000 300.000 350.000

DWT

Ma

in e

ng

ine

po

we

r (k

W)

all vessels low-powered vesselsrecorded casualties (delivered before 2000) average all vesselsaverage low-powered vessels

Bulk carriers (delivered between 2001-01-01 and 2010-12-31)

y = 8,1933x0,6124

R2 = 0,9716

y = 22,698x0,5411

R2 = 0,8642

0

2.000

4.000

6.000

8.000

10.000

12.000

14.000

16.000

18.000

20.000

40.000 80.000 120.000 160.000 200.000 240.000

DWT

Mai

n e

ng

ine

po

we

r (k

W)

all vessels > 40000 DWT low-powered vesselsrecorded casualties (also delivered before 2000) average low-powered vesselsaverage all vessels (>40000 DWT)

Functional requirements

12. Functional requirements provide the criteria to be satisfied in order to meet the goals. Five missions (open sea transit, restricted navigation-space operation, rescue operation, towing operation and port operation) were identified and required manoeuvres were listed. It became clear that operation in restricted navigation space dominates the other missions. In other words, a vessel capable to manoeuvre safely with restricted navigation space, which involves potentially also unfavourable headings, is assumed to be able to master the other missions, too.

- 11 - MEPC 62/5/y 13. One exemption is the operation in port which is assumed to be assisted by tugs and, therefore, is not considered any further in this context.

14. Necessary manoeuvres involve course keeping, track keeping, turning, propulsion, stopping, keep heading, station keeping. In the next step, standard manoeuvres were defined to reflect all required manoeuvring capabilities. Eventually, only two standard manoeuvres were identified to be representative for the manoeuvrability of a vessel in adverse conditions and reflecting the defined missions: turning ability and course keeping with advance speed.

15. It is underlined that it was always the aim of the IACS project team to consolidate the number of manoeuvres such that resulting standard manoeuvres can be checked with reasonable effort.

Verification - acceptance criteria

16. To check whether a vessel is capable of successfully performing a standard manoeuvre, quantitative acceptance criteria were defined relating to each standard manoeuvres. It is noted that the figures given are suggestions by IACS and these need to be validated using expert opinion, numerical simulation and / or model experiments before agreed by the Committee. And all figures need to be consistent with each other.

17. The turning ability is described by the time needed and the advance distance. Both criteria reflect the need to manoeuvre safely even with restricted navigation space. It is expected that the maximum time allowed for turning may also depend on ship size. Results from interviews also underline that time for action is limited to a few hours if the vessel is close to coast. If the vessel is on anchorage, it takes up to 1.5 hours to lift the anchor and to start picking up minimum speed.

18. The course keeping and advance speed capability is described by the minimum speed through water and the average static course deviation. Setting the minimum speed in this context is essential as it affects setting the other parameters as well. It was considered that a vessel needs to leave the coast by a couple of miles in few hours aiming to have more navigation space and then being able to turn the vessel into more favourable heading.

19. Results from interviews with experienced masters showed that they reduce speed up to a minimum to avoid damages to the hull and cargo. This minimum speed for adverse conditions has been stated to be between 4 knots, which is considered to be the minimum needed to ensure manoeuvrability, and up to 8 knots for a large container vessel.

20. The environmental conditions to be considered were selected based on the widely accepted IACS wave data (recommendation 34), mainly because these North Atlantic environmental conditions are used as reference in the IMO GBS on oil tankers and bulk carriers. This means that wave conditions were identified based on their probability and that related wind conditions were set independently.

21. Adverse environmental conditions were selected based on assumed reasonable probability levels, results from interviews with masters and one accident report. Probability levels of 2% to 0.5% corresponding to return periods of 1 week to 1 month appear reasonable. A wave height of 8 m and a wind force Bft 9 were considered to be adverse conditions for a large tanker by experienced masters. And sea states 7 to 8 were recorded in the “Pasha Bulker” casualty report. In these conditions, many vessels safely manoeuvred and, therefore, these conditions can be assumed to be adverse but not overwhelming.

“On 8-9 June, 2007, the adverse condition with wind up to storm force (Beaufort force 10) occurred off the coast near Newcastle, Australia. There were 41 ships anchoring at the port area during the adverse condition. A number of ships attempts to ride out the adverse condition and the majority dragged their anchors. The substantial ship queue increased the risks in the anchorage and resulted in one ship grounding (Pasha Bulker), another near grounding, a near collision, and a number of close-

- 12 - MEPC 62/5/y

quarters situations at the time. At the end, 40 ships managed to weight anchors or cut anchors and put to sea. This case provides the evidence that the installed power and rudder on these ships are sufficient to successfully manoeuvre in the adverse condition, which is close to North Atlantic conditions with a return period between one week and one month and defined by sea state 7 to sea state 8. On the other hand, it also provides the evidence that the defined adverse condition is actually occurring close to coast. Reference: Australian Transport Safety Bureau, June 2007, Marine occurrence investigation No. 243”

22. Therefore, a range of environmental conditions assumed to be representative for adverse conditions is offered for discussion. They differ in their probability of occurrence, or return period, see Figure below

23. Sea state 8 is seen as on the edge towards extreme conditions and smaller vessels might be overwhelmed already. The lack of manoeuvring performance for particular vessels in extreme conditions is known to their masters and they aim avoiding these situations. For example, a fully loaded container vessel will not be able to turn against extreme wind forces. This could potentially lead to setting different environmental criteria for different ship types and / or sizes which was, however, not considered in the current proposal due to a lack of evaluation results for different ship types and sizes.

24. For vessels with restricted navigation, environmental conditions need to be adapted taking operational area and restrictions into account.

Verification

25. Two verification approaches have been identified. These differ in their complexity and necessary resources. Test programs describe in detail which tests should be performed. Since no full scale tests can be performed, either model experiments and/or numerical simulations need to be conducted according to the test programs.

26. Test programs describe all necessary conditions for conducting the tests, such as, e.g., loading condition, engine and rudder settings, wind force and directions, wave height, periods and directions as well as the assessment parameters which directly relate to the acceptance criteria. In addition, a proposal to evaluate uncertainty from results in irregular waves is made.

27. Criteria to decide whether an individual vessel may be assessed with the simplified advance speed assessment have been identified and these relate to ship speed and to windage effect which is proportional to the ratio of above waterline lateral area and below waterline lateral

- 13 - MEPC 62/5/y area. The quantitative values for the criteria have not been finalised. Indeed, it is suggested to consider using the advance speed assessment for all ships in a first phase to gain experience before switching to the more difficult but comprehensive assessment.

28. The basic assumption for the advance speed assessment is that the dimensioning criterion is advance speed in waves and, implicitly, that turning and course keeping can be achieved if advance speed is maintained. This assumption is true for typical bulk carriers and oil tankers but may be questioned for fully loaded container vessels which are known to have reduced manoeuvring capability in strong gale force winds. However, it is assumed that due to their relatively high installed engine power, the impact of the EEDI would not lead to negative effects on safety too soon. The latter assumption needs to be checked for vehicle carriers, ferries and cruise vessels.

29. This simplified assessment comprises only the equation of steady motion in longitudinal direction and tools are available today to make it work. A worked example for the advance speed assessment is contained in Annex II for a VLCC in fully loaded condition, acknowledging the uncertainties involved. Forces include calm water hull resistance, rudder resistance, air drag, and added resistance in waves. All terms may be approximated by simple formulae or using tabulated values or simple model tests.

30. The comprehensive assessment following the full draft interim guidelines require many more tests to be performed and, therefore, they are considered not to be practical today. They may also be used to guide rule-making. This would require a larger number of numerical simulations per ship type with a number of ship sizes. Regression formulae may yield the desired trends for manoeuvrability as function of main ship parameters. However, the eventual success of this exercise was questioned by experts and, therefore, is not guaranteed.

- 14 - MEPC 62/5/y

ANNEX III

EXAMPLE FOR ADVANCE SPEED ASSESSMENT8

Introduction

The basic assumption of this simplified assessment is that the dimensioning criterion is advance

speed in waves and, implicitly, that turning and course keeping can be achieved if advance

speed is maintained. This simplified assessment comprises only the equation of steady motion

in longitudinal direction. It is only applicable to vessels below Froude number and below a lateral

area ratio given in the guidelines.

Procedure

The principle of the assessment is that the required propeller thrust, defined as a sum of bare

hull resistance in calm water cwR , resistance due to appendages appR , aerodynamic resistance

airR , and added resistance in waves awR ,

cw air awT R R R +Rapp, (1)

can be provided by the vessel’s propulsion system. The calm-water resistance can be

calculated neglecting the wave resistance as 2cw

1(1 )

2F sR k C Sv , where k is the form factor,

2

0.075

log Re 2FC

the friction resistance coefficient, Re /s ppv L is the Reynolds number, is

water density, S is the wetted area of the bare hull, sv is the ship speed and is the kinematic

density of water.

Aerodynamic resistance can be calculated as 2air air a F w

1

2R C A v , where airC is the aerodynamic

resistance coefficient, a is the density of air, FA is the frontal projected area of the hull and wv

is the relative wind speed.

The added resistance in waves awR can be derived from model tests, potential or viscous flow

computations or empirical formulae.

In order to check whether the required thrust can be provided by the engine, the required

advance ratio of the propeller J is found from the requirement

2 2 2a P T /T u D K J J , (2)

where TK J is the thrust coefficient curve. After this, the required rotation speed of the

propeller is found from the relation

a Pn u JD , (3)

8 This example for an advance speed assessment was prepared by Germanischer Lloyd.

- 15 - MEPC 62/5/y and the required power is then defined from the relation

3 5P Q2DP n D K J . (4)

It should be noted that for diesel engines, the available power is also limited due to the torque-

speed limitation of the engine maxQ Q n , thus an additional requirement to be checked is

D max2Q P n Q n . (5)

Example of Simplified Assessment

The proposed procedure is applied to the tanker KVLCC2 at full load which has been widely

tested before in calm water manoeuvring tests and benchmarking exercises

(http://www.simman2008.dk). The main data is shown in the following two tables:

Table 1: main particulars and loading conditions for test vessel KVLCC2 Full

Load Heavy Ballast

Light Ballast

Draught midship Tm, m 20.8 10.0 8.0

Displ. volume V, m3 3.126·105 1.236·105 1.099·105

Long. distance of CG from AP, m

171.20 171.613 176.27

Mass, t 3.200·105 1.267·105 1.127·105

Projected frontal area AF, m2

1356.7 1651.0 1767.0

Lateral area AL, m2 4005.7 6593.0 7260.2

Projected rudder area AR, m2

122.9 84.6 61.6

Parameter Definition Source Value Used

FA projected frontal area ship data 1356.7 m2

S submerged surface area of bare hull

ship data 27457.7 m2

airC coefficient of aerodynamic resistance

wind tunnel test, RANSE simulation or empirical formulae

1.0

PD propeller diameter ship data 9.86 m

k form factor model tests, viscous flow calculations, empirical formulae

0.22

( ), ( )T QK J K J propeller curves open-water propeller tests, propeller series, numerical calculations

Fig. 1

maxQ n engine torque/speed limiting curve

engine passport Fig. 2

sv ship speed assessment requirement [3.0 knots] 1.543 m/s

wv relative wind speed sum of wind speed [51.5 knots] and ship speed [3.0 knots]

28.0 m/s

w propeller wake fraction

model tests, viscous flow calculations, empirical formulae

0.4

density of water 1025.0 kg/m3

a density of air 1.2 kg/m3

- 16 - MEPC 62/5/y

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80

J

KT

10KQ

etha0

0

500

1000

1500

2000

2500

3000

3500

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4

n,1/s

Q,k

N.m

Fig.1. typical open-water propeller curves Fig. 2. typical limiting torque curve maxQ n

2. Calculation of calm-water resistance

Re /s ppv L 4.330108

FC 20.075 log Re 2

1.7103

cwR 20.5(1 ) F sk C Sv 69.63 kN

3. Calculation of aerodynamic resistance

airR 2

air a F w

1

2C A v

640.15 kN

5. Calculation of added resistance in waves

Added resistance in waves was computed wit a potential seakeeping code; here the maximum

added resistance over peak wave periods in the range 8.5 to 13.5 s with the significant wave

height 9.8 m was used, awR =1157.6 kN

6. Calculation of the required thrust

T cw air awR R R 1867.4 kN

7. Calculation of the required advance ratio and rotation speed

The advance speed of the propeller is calculated as a s (1 )u v w resulting in au equal to 0.926

m/s. The required advance ratio of the propeller J is found from equation (2), rewritten as

T

2 2 2a P

ln lnK J T

J u D , where the dependence 2

Tln /K J J , Fig. 3, is calculated from the open-

water propeller curve, and the right-hand side 2 2a Pln /( )T u D is equal to 3.084 []. From the

plot in Fig. 3, the required advance ratio J is found as 0.114 and then the required rotation

speed a Pn u JD as 0.822 1/s.

- 17 - MEPC 62/5/y

-6.0

-4.0

-2.0

0.0

2.0

4.0

6.0

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

J

ln(K

T/J

**2)

Fig. 3. Dependence 2T /K J J

8. Calculation of the required power

For the determined J , QK is found from the open-water propeller curve in Fig. 1; then the

required delivered power on the propeller is found:

QK Fig. 1 0.0293

DP 3 5P Q2 n D K J 9.74 MW

The required propulsion power is less than the delivered propulsion power at design speed of

18.2 MW, compare table 1 in Annex VI.

9. Check of the torque/speed limitation

Q D 2P n 1886.5 kNm

maxQ n Fig. 2 1904.1 kNm

Thus, the additional criterion maxQ Q n is fulfilled.

In summary, the vessel has passed the advance speed assessment.

***

MEPC-62-5-x-EEDI-minimum-power-rev-5.doc 2011-02-22

MARINE ENVIRONMENT PROTECTION COMMITTEE 62nd session Agenda item 5

MEPC 62/5/y 8 April 2011 Original: ENGLISH

REDUCTION OF GHG EMISSIONS FROM SHIPS

Consideration of the Energy Efficiency Design Index for New Ships

Minimum propulsion power to ensure safe manoeuvring in adverse conditions

Submitted by IACS [BIMCO, CESA, CLIA, ICS, Intercargo, Interferry, Intertanko, WSC]

SUMMARY Executive summary:

This document proposes draft interim guidelines to determine whether available propulsion power is sufficient to ensure safe manoeuvring in adverse conditions.

Strategic direction:

7.3

High-level action:

7.3.2

Planned output:

7.3.2.1

Action to be taken:

Paragraph 26

Related documents:

MEPC 61/24, MEPC 61/5/32, MEPC 61/5/3 EE-WG 1/4, MEPC 60/WP.9, MEPC 59/4/2, MSC.137(76)

Introduction

1. At MEPC 61 the debate on safety issues related to the EEDI continued and it focussed in particular on safe manoeuvring in adverse conditions. Member states delegations argued that ship designers may choose to reduce a ship's design speed to achieve the required EEDI, which would result in reduced installed power. In order to avoid adverse affects on safety, such as under-powered ships, IACS proposed to include a provision into the draft regulations in document MEPC 61/5/32. IACS also informed the Committee that first draft guidelines will be developed and submitted to MEPC 62 for further consideration.

2. “The vessel shall have the necessary propulsion power to enable safe manoeuvring in adverse conditions” is easily said but difficult to prove. Standards for ship manoeuvrability are defined in resolution MSC.137(76), but these are restricted to calm environment. MSC/Circ.1053 gives additional explanatory notes for the test of ship’s manoeuvrability.

3. IACS established a project team to develop guidance and conducted a workshop with other stakeholders to discuss the impact and the practicability of the proposed draft guidelines.

4. IACS also documented in EE-WG 1/4 acceptance criteria and environmental conditions which relate to voluntary class notations for redundant propulsion systems.

Overview of challenges

5. There exists no agreed definition of manoeuvres which, if being carried out successfully in adverse conditions, would demonstrate that the vessel is capable of safe manoeuvring in these conditions. Nor are adverse conditions defined in this context. And model tests as well as numerical simulations have been focussing on manoeuvring in calm water, except for research work summarised by the Manoeuvring Committee in the final report to the 25th ITTC in 2008.

- 2 - MEPC 62/5/y 6. To address the challenges, the following conceptual model was established. Using best practices, incident reports and available literature, see Annex II, goal, mission requirements and acceptance criteria for safe manoeuvring were established. The definition of adverse conditions also benefited from best practices but mainly builds upon available long-term wave climate data. To determine the necessary propulsion power for defined manoeuvres in defined environmental conditions, test programs were developed for the purpose of verification.

The vessel shall have the necessary propulsion power to enable safe manoeuvring in adverse conditions

safe manoeuvring

adverse conditions

necessary propulsion power

mission scenarios

manoeuvres and criteria

wave / wind conditions

test programs

good seamanship

Proposal

7. This document proposes draft interim guidelines to determine whether propulsion power is sufficient to ensure safe manoeuvring in adverse conditions, for those ships that are defined in MEPC.1/Circ.681, Annex, Section 1. Therefore, an amendment of MEPC.1/Circ.681 is proposed in Annex, Section 2.5.1, as follows:

Delivered propulsion power needs to be sufficient to pass manoeuvring tests as defined in the guidelines developed by the Organisation.

8. The draft interim guidelines are presented in Annex I.

Discussion

9. Current manoeuvrability standards at IMO are seen as a lower bound to the requirements on manoeuvrability in adverse conditions. However, the current level of manoeuvrability in adverse conditions has never been checked and is not explicitly known. Therefore, it is assumed to be possible that existing vessels will be found not to comply with the proposed criteria on manoeuvring in adverse conditions.

10. In adverse conditions, masters voluntarily reduce speed to decrease ship motions and, thus, to avoid damages to the ship and its cargo. In addition, added resistance in waves slows down the vessel. Lower ship motions also contribute to better manoeuvrability with higher forces on the rudder. In addition, existing rules (e.g. on lashing) assume that the master has the ability to avoid adverse conditions and to control ship motions. Therefore, too extreme environmental conditions for testing manoeuvring capability may be inconsistent with existing rules.

11. Current debate at IMO SLF also focuses on new intact stability criteria and related procedures for their assessment. It is noted that for vessels sailing with reduced advance speed, vulnerability to parametric roll may be increased. Therefore, it is suggested to inform the relevant SLF correspondence group on the current discussion at MEPC on safe manoeuvring in adverse conditions.

12. As part of the work, IACS developed a draft questionnaire to guide interviews with masters of typical merchant vessels. The purpose of these interviews were to identify events

- 3 - MEPC 62/5/y which masters associate with adverse conditions and to learn more on best practices in such conditions. Results from these interviews were used to develop the mission requirements and acceptance criteria and they are summarised in Annex III. [material to be provided later]

13. A first analysis of recorded casualties for bulk carriers, container vessels, general cargo vessels and tankers showed that groundings in adverse conditions which may have been caused by lack of propulsion power happened at a frequency of 1E-04 per ship year. The results of the analysis are summarised in Annex IV.

14. Relevant environmental conditions were selected for vessels in unrestricted service and by keeping IMO GBS reference conditions in mind. The sea state associated with adverse condition was selected following interviews and with particular reference to one well-documented casualty which is summarised in Annex V.

15. The draft interim guidelines contain a high level goal, mission requirements and acceptance criteria as well as test programs to determine whether an individual ship’s propulsion power is sufficient for safe manoeuvring in adverse conditions. Since no full scale tests can be performed, either model tests and/or numerical simulations need to be conducted according to the test programs.

16. The initial discussion at IMO MEPC working group meetings implicitly assumed that a lower threshold for propulsion power could be identified using a new approach. However, in the course of work, it turned out that this lower threshold may be too difficult and too time consuming to determine. Instead, the newly developed procedure only determines whether installed power is sufficient for safe manoeuvring in adverse conditions but it does not deliver explicitly the minimum power needed.

17. Test programs for verification were selected to include relevant missions and, at the same time, limit the number of tests. However, even though only two test programs are proposed in the draft interim guidelines, conducting the required tests for an individual ship is assumed to be time-consuming and expensive. In addition, manoeuvring in adverse conditions is a topic of current research and, therefore, test facilities and/or numerical simulation tools may not be available to a majority of ship designers and ship yards. Furthermore, any future rule development would require many more tests to derive trends per ship type and size. In addition, model tests are needed to verify the accuracy of numerical simulation tools.

18. Considering reasonable assumptions for selected ship types and sizes, the test programs can be simplified and requirements for necessary tools reduced. However, these simplifications typically include higher safety margins and may lead to higher requirements for the individual vessel.

19. Therefore, a three-level approach is proposed for verification with

Level 1: advance speed assessment, only applicable for vessels at lower design Froude number and with a low windage effect, under the assumption that turning and course keeping can be achieved by these vessels if advance speed is maintained

Level 2: static performance assessment, only for vessels at lower design Froude number, under the assumption that dynamic effects, such as broaching, will not occur

Level 3: dynamic performance assessment, suitable for all vessels

20. If a vessel has passed the assessment according to level 1, no further assessment is required. The same logic applies to passing level 2 assessment. On the other hand, a vessel which failed to pass level 1 assessment is very likely not to pass level 2 assessments without design modification.

21. A static performance assessment has been conducted, acknowledging the uncertainties involved, and the results are given in Annex VI. It is underlined that the example

- 4 - MEPC 62/5/y only addresses the test program for course keeping which includes an assessment of achieved speed. Another static performance assessment is needed for addressing the turning ability test program.

22. The method for static performance assessment is based on equations for equilibrium of longitudinal force and of transverse force as well as of the yaw moment, taking into account forces and moments due to wind, wave, drift, propeller and rudder. The principal challenge for this simplified assessment is the determination of rudder forces and moments at very low ship speeds which is beyond state-of-the-art prediction tools.

23. Following the first tests using the static performance assessment, it turned out that rudder effectiveness strongly influences manoeuvring in adverse conditions and, therefore, should be considered in conjunction with propulsion power in this context.

24. An advance speed assessment has been conducted, acknowledging the uncertainties involved, and the results are given in Annex VII. It is underlined that the example only addresses the test program for advance speed assessment.

25. The advance speed assessment is based on the equation for longitudinal motion only and computes required trust for given longitudinal forces. Forces include calm water hull resistance, rudder resistance, air drag, and added resistance in waves. All terms may be approximated by simple formulae or using tabulated values or simple model tests.

Recommendation

26. The Committee is invited to note the proposal and to take action as appropriate.

*************

- 5 - MEPC 62/5/y

ANNEX I

DRAFT INTERIM GUIDELINES TO DETERMINE WHETHER PROPULSION POWER IS

SUFFICIENT TO ENSURE SAFE MANOEUVRING IN ADVERSE CONDITIONS

Purpose

1. The purpose of these guidelines is to assist Recognized Organisations in the verification of the Energy Efficiency Design Index (EEDI) and to facilitate, at the same time, that vessels are capable of safe manoeuvring even in adverse conditions. These guidelines will support ship designers and ship builders to develop energy-efficient and safe new vessels.

2. These guidelines define a goal-based framework and procedures to determine whether the propulsion power is sufficient to ensure safe manoeuvring in adverse conditions.

Assumptions

3. The guidelines only apply to those ship types defined in the Annex to MEPC.1/Circ.681.

4. The guidelines apply to vessels with unrestricted navigation.

5. The vessel is considered to have been properly prepared by the crew to face adverse conditions, e.g., cargo secured and vessel correctly ballasted (i.e., heavy ballast). Therefore, cargo-related effects are not included in the guidelines.

6. The effects of currents which are typically not linked to waves and wind have not been included in these guidelines for reasons of simplicity. It is assumed that this could be done at a later stage when more experience has been gained with these guidelines.

7. No full scale tests are possible to be performed to test the vessel’s manoeuvring capability in adverse conditions. Therefore, model tests and numerical simulations are accepted as equivalent tools to conduct the test programs defined in this guideline.

Goal

8. The vessel shall have the necessary propulsion power [and rudder effectiveness]1 to ensure safe manoeuvring in adverse conditions.

.1 safe manoeuvring means the ability to turn the vessel into a position towards the weather and at least to maintain this position without drifting over ground.

.2 adverse conditions mean an unfavourable combination of wind and waves associated with North Atlantic conditions and a return period of [one week][one month]2.

Mission requirements

9. The vessel should have the ability to perform the following missions in the defined adverse environmental conditions:

.1 Stay off the coast to avoid grounding

1 Following the first tests using the static performance assessment, it turned out that rudder effectiveness strongly influences manoeuvring in adverse conditions and needs to be considered in this context. 2 A range of environmental conditions assumed to be representative for adverse conditions is offered for discussion. The adequate return period in this context needs to be discussed by experts and agreed by the Committee.

- 6 - MEPC 62/5/y

.1 Turn within defined time period and maintain a course to leave coastal area at a defined minimum speed

.2 The selection of the course may be limited due to navigation restrictions and this course may lead to an unfavourable heading of the vessel towards the waves.

.2 Survival in open sea

.1 Turn within defined time period and maintain a favourable heading towards the waves

.3 providing shelter for rescue operations

.1 is considered a combination of above missions and, therefore, no additional requirement is needed

.4 prepare for emergency towing

.1 is considered a combination of above missions and, therefore, no additional requirement is needed.

.5 manoeuvring in port

.1 is not considered in these guidelines due to the availability of tug assistance in port in case of adverse conditions

Acceptance criteria

10. The verification of compliance requires performing tests following defined test programs with standard manoeuvres and defined manoeuvring criteria. The verification will demonstrate whether a vessel with given propulsion power will pass the manoeuvring tests. (In other words, the minimum power to pass the tests is not explicitly determined. This would require additional test runs for level 2 and 3 assessments.)

11. Two standard manoeuvres are considered to be representative for the manoeuvrability of a vessel in adverse conditions and reflecting the above defined mission requirements: turning ability and course keeping.

12. The vessel should fulfil the following manoeuvring criteria3 for the standard manoeuvring test on turning ability:

.1 Time for completing a 180 degree turn is less than [15][30]4 minutes

.2 The maximum advance distance in wave direction is less than f * 5L, with f = [1.2][1.5]5 reflecting that a turning circle in waves is larger in diameter and/or advance than in calm water.

13. The vessel should fulfil the following manoeuvring criteria6 for the standard manoeuvring test on course keeping:

.1 The minimum speed is [2][3]7 knots over ground.

3 It is noted that the figures given are suggestions by IACS and these need to be validated using expert opinion, numerical and / or model tests before agreed by the Committee. Values given need to be consistent with each other. 4 It is expected that the maximum time allowed for turning depends on ship size. 5 The maximum advance distance needs to be consistent with the other values considered in this context. 6 It is noted that the figures given are suggestions by IACS and these need to be validated using expert opinion, numerical and / or model tests before agreed by the Committee. Values given need to be consistent with each other.

- 7 - MEPC 62/5/y

.2 The steering effort needs to balance the wind and wave force and moment and is defined as maximum deviation from the course and is less than ± [5][10]8 degrees.

14. Environmental conditions reflect adverse North Atlantic conditions9 and these are defined by the following parameters:

Return period10

Sea state Sig. wave height (m)

Wave period (s)


[One week 7 7.5 7.5 to 14.5 9 45] [One month 8 9.8 8.5 to 13.5 10 51.5]

Wind speed at 20 m above water surface

15. For vessels with restricted navigation, environmental conditions need to be agreed with the Administration, taking operational area and restrictions into account.

Verification - general

16. Verification of compliance by means of test programs may be conducted by model tests and/or numerical simulations. A three-level verification is defined as follows:

Level 1: advance speed assessment

Applicable to vessels below Froude number of [0.2][0.3]11 and with a low windage effect, defined as ratio of the above-water lateral area and the total lateral area incl. the rudder area smaller than [0.65][0.75]12, taking the loading condition which results in the largest ratio.

Level 2: static performance assessment

Applicable to all vessels below Froude number of [0.2][0.3]11

Level 3: dynamic performance assessment

Applicable to all vessels

Verification level 1 – advance speed assessment

17. The basic assumption of this simplified assessment is that the dimensioning criterion is advance speed in waves and, implicitly, that turning and course keeping can be achieved if advance speed is maintained. This simplified assessment comprises only the equation of steady motion in longitudinal direction.

7 It is assumed that the vessel needs to leave the coast by a couple of miles in a few hours with the aim to have more navigation space and then to turn the vessel into more favourable heading. 8 It is noted that the figures given are suggestions by IACS and these need to be validated using expert opinion, numerical and / or model tests before agreed by the Committee. 9 North Atlantic environmental conditions are defined as reference for the IMO GBS on oil tankers and bulk carriers. IACS Rec. 34 is widely accepted for structural design assessment and the related probability levels. Its use for assessing manoeuvring performance may be questioned and should be investigated in the future. However, due to a lack of proven alternatives, IACS Rec. 34 will be used in this context to derive the reference environmental wave conditions. As no wind conditions are associated with wave conditions given in IACS Rec. 34, related wind condition were set independently. 10 Following early feedback within IACS, a range of environmental conditions assumed to be representative for adverse conditions is offered for discussion. The adequate return period in this context needs to be discussed by experts and agreed by the Committee. 11 It is noted that the figures given are suggestions by IACS and these need to be validated using expert opinion, numerical and / or model tests before agreed by the Committee. Setting an appropriate threshold value requires systematic analysis of existing ship designs with due respect to submerged rudder area. 12 It is noted that the figures given are suggestions by IACS and these need to be validated using expert opinion, numerical and / or model tests before agreed by the Committee. Setting an appropriate threshold value requires comparison of existing stability information and performing systematic static performance assessments.

- 8 - MEPC 62/5/y 18. The test program is defined as follows:

.1 advance speed assessment

.1 Tests are performed at one loading condition representative for maximum cargo intake

.2 Maximum available power is supplied to the propellers and the rudder is in the neutral position

.3 Wind at maximum speed


.5 head waves

.6 steady motion


Required power for the defined minimum advance speed given in 13.1

.8 If the vessel has passed the assessment, no further assessment according to level 2 or 3 is required.

Verification levels 2 and 3 – performance assessment

19. Level 2 and level 3 verifications follow the same test program but use different assumptions and simplifications. In particular, level 2 verification builds on a static performance assessment of the vessel which neglects all time-dependent and dynamic effects. This is considered to be acceptable for vessels for which dynamic coupling of motions in waves with manoeuvring (e.g., due to broaching) is not relevant. Level 3 verification is considered to be applicable to all cases without restriction.

20. For each standard manoeuvre defined above, a test program needs to be conducted:

.1 Turning circle of 360 degrees13

.1 Tests are performed at two draft conditions representative for heavy ballast and maximum cargo intake

.2 Maximum available power is supplied to the propellers and the maximum rudder angle is set



.5 only one wave direction needs to be tested

.6 steady turning motion


13 A turning circle of 360 degrees will avoid testing for different wave directions. However, if test facilities do not allow for a 360 degrees turning circle testing, a 180 degrees turn is considered an alternative with wave directions varied from 0 to 180 degrees and step size of 15 degrees tested.

- 9 - MEPC 62/5/y

turning time per 360 degrees turn

maximum distance in the wave propagation direction per 360 degrees turn

.8 A number of runs shall be performed for different realisations of the same wave conditions, ensuring the fulfilment of criteria for assessment parameters, as given in 12, with satisfactory engineering accuracy14. Alternatively, several turning circles may be performed following each other using the same realisation of the wave conditions.

.9 If the vessel has passed the assessment, no further assessment according to a higher level is required.

.2 Course keeping

.1 Tests are performed at two loading conditions representative for heavy ballast and maximum cargo intake

.2 Maximum available power is supplied to the propellers and the rudder angle is adjusted to achieve the desired course, up to its maximum angle if necessary.



.5 Wave directions 0 to 180 degrees, with 15 degrees step size

.6 steady motion with constant course


average forward speed and course deviation

.8 A number of runs shall be performed for different realisations of the same wave conditions, ensuring the fulfilment of criteria for assessment parameters, as given in 13, with satisfactory engineering accuracy14.

.9 If the vessel has passed the assessment, no further assessment according to a higher level is required.

Documentation

21. Tests need to be documented including but not limited to the following:

.1 description of the vessel’s main particulars

.2 description of the vessel’s relevant manoeuvring and propulsion systems

.3 description of test program and test results

.4 description of applied test method with references

***

14 Satisfactory engineering accuracy means a 95% fulfilment of criteria. For example: if 19 runs out of 20 satisfy the norms for the average forward speed, turning time and distance per turn, the criteria are considered to be satisfied.

- 10 - MEPC 62/5/y

ANNEX II

SELECTED REFERENCES

MSC/Circ.707 (1995) Guidance to the master for avoiding dangerous situations in following and

quartering seas

MSC.137(76) (2002) Standards for ship manoeuvrability

MSC/Circ.1053 (2002) Explanatory notes to the Standards for ship manoeuvrability

IACS (2001) recommendation 34 – standard wave data

ANEP-79 (2007) Controllability and safety in a seaway

The manoeuvring committee (1999) Final report and recommendations to the 22nd ITTC



Australian Transport Safety Bureau, June 2007, Marine occurrence investigation No. 243.

W. Blendermann (1996) Wind loads on ships – collected data from wind tunnel tests in uniform flow,

Report 574, IfS Hamburg

W. Blendermann (1995) Estimation of wind loads on ships in wind with a strong gradient, Proc., Vol.1,

Part A, 271-277, Copenhagen

J.P. Hooft & J.B.M. Pieffers (1988) Manoeuvrability of frigates in waves, Merine Technology 25(4) 262-

271

L.L. Martin (1980) Ship manoeuvring and control in wind, SNAME Transactions 88

F.H.H.A. Quadvlieg & P. van Coevorden (2008) Manoeuvring criteria: more than IMO A.751 requirements

alone

S.L. Toxopeus & G.B. Loeff (2002) Steering dast vessels with pods, HIPER 2002, Bergen

A.J. Tuite & M.R. Renilson (1999) The controllability of a small vessel operating in severe following seas,

Int. Shipbuild. Progress 46(446) 129-140

B. Wagner (1972) Untersuchungen zur Frage des effektiven Zusatzwiderstandes durch den Wind auf der

Grundlage von Modellversuchen für Unter- und Überwasserschiffe, Report 286, IfS Hamburg

B. Wagner (1973) Einfluß des Momentenausgleichs durch das Schiffsruder bei der Ermittlung des

effektiven Zusatzwiderstandes durch den Wind, Report 293, IfS Hamburg

B. Wagner (1981) Beitrag zu den Steuereigenschaften von Einschraubenschiffen mit und ohne äußeren

Kraftangriff, Report 414, IfS Hamburg

J. Xing-Kaeding (2004) Unified approach to ship seakeeping and manoeuvring by a RANSE method, PhD

Thesis, IfS Hamburg

- 11 - MEPC 62/5/y

ANNEX III

SUMMARY OF INTERVIEWS RELATED TO BEST PRACTICES

Introduction

As part of the work, IACS developed a draft questionnaire to guide interviews with masters of

typical merchant vessels. The purpose of these interviews were to identify events which masters

associate with adverse conditions and to learn more on best practices in such conditions.

Results from these interviews are summarised below.

[the material prepared was lost by a hard disk crash and is now being recovered]

- 12 - MEPC 62/5/y

ANNEX IV

FIRST ANAYLSIS OF RECORDED CASUALTIES

Introduction

Available casualty reports from the IHS database have been checked to identify the

frequency of occurrence of grounding events in adverse conditions, with the aim to compare

these with other accident categories and their occurrence frequency.

Casualty reports after 1981 for container ships, bulk carriers, tankers and general cargo

ships built after 1981 with a minimum gross tonnage of 1,000 were selected when the

accident severity was labelled “serious.”

Results

Casualties which may have been caused by lack of available propulsion power in adverse

conditions were identified as grounding accidents in adverse conditions without any cause

listed (which means that lack of propulsion power could have been the case). This resulted

in 64 events in open sea conditions. The following table shows the identified events.

Ship type number of events. estd. ship years frequency Tanker 12 118204 1,02E-04 Bulk carrier 19 187050 1,02E-04 Container vessel

6 131080 4,58E-05

General cargo ship

27 194851 1,39E-04

Total 64 631185 1,01E-04

Discussion

Assuming that the above listed 64 casualties for grounding in adverse conditions without any

cause were indeed caused by lack of propulsion power, and using a rough estimate of the

ship years for the period 1982 to 2010 (29 years) and a world fleet of 20,000 ships (bulk

carrier 6450; tanker 4076; container 4520; general cargo ships 6719; all IHS-Status

Delivered) ≈630.000 ship years, a casualty frequency of 1.0E-4 per ship year is calculated.

- 13 - MEPC 62/5/y

ANNEX V

SUMMARY OF SAMPLE CASUALTY REPORT

Adverse conditions with Beaufort forces 7-12 have occurred at ports around the world as

reported in the investigations of incidents [1, 2, 3, 4, 5, 6].

On 8-9 June, 2007, the adverse condition with wind up to storm force (Beaufort force 10)

occurred off the coast near Newcastle, Australia [1]. There were 41 ships anchoring at the

port area during the adverse condition. A number of ships attempts to ride out the adverse

condition and the majority dragged their anchors. The substantial ship queue increased the

risks in the anchorage and resulted in one ship grounding (Pasha Bulker), another near

grounding, a near collision, and a number of close-quarters situations at the time. At the end,

40 ships managed to weight anchors or cut anchors and put to sea. The grounding of Pasha

Bulker was due to master’s inadequate understanding of heavy weather ballast, anchor

holding power and the limitations of Newcastle’s weather exposed anchorage. A tug was

sent out to assist Pasha Bulker, but was then directed not to do so due to the dangerous

swell of more than 9 m.

The above real case scenario provides the evidence that the installed power and rudder on

these ships are sufficient to successfully manoeuvre in the adverse condition, which is close

to North Atlantic conditions with a return period between one week and one month and

defined by sea state 7 to sea state 8. On the other hand, it also provides the evidence that

the defined adverse condition is actually occurring at ports around the world.

References

1. Australian Transport Safety Bureau, June 2007, Marine occurrence investigation No. 243.

2. Marine Accident Investigation Branch of UK, February, 2008, Report No. 3/2008.

3. Gard AS, September 2008, Loss prevention circular No 13-08.

4. Marine Accident Investigation Branch of UK, January, 2009, MAIB Safety Bulletin 1/2009.

5. Marine Accident Investigation Branch of UK, January, 2009, Report No. 2/2009.

6. Marine Accident Investigation Branch of UK, December, 2009, Report No. 25/2009.

- 14 - MEPC 62/5/y

ANNEX VI

EXAMPLE FOR STATIC PERFORMANCE ASSESSMENT15

Introduction

A simplified assessment using safety margins for uncertain terms may greatly reduce required

time for the determination of minimum power to ensure safe manoeuvring in adverse conditions.

The following example only addresses the test program for course keeping. Another simplified

assessment would be needed for addressing the turning ability test program.

Brief overview of method

A method for the simplified assessment of the course keeping test program is based on

equations for equilibrium of longitudinal force and of transverse force as well as of the yaw

moment, taking into account forces and moments due to wind, wave, drift, propeller and rudder.

The basic equations are as follows:

s w e d R 0X X X X X T+ + + + + = , (1)

s w e d R 0Y Y Y Y Y+ + + + = , (2)

s w e d R 0N N N N N+ + + + = , (3)

where X and Y denote force projections on the x- and y-axes, respectively and N denotes

moments with respect to the z-axis. sX , sY and sN are steady still-water hydrodynamic

reactions, wX , wY and wN are wind loads, eX , eY and eN are characteristic loads due to wave

action at the encounter frequency, dX , dY and dN are characteristic drift loads due to waves,

RX , RY and RN are forces and moment due to the rudder and T is the propeller thrust.

The test vessel is called KVLCC2 and it has been widely tested before in calm water

manoeuvring tests and benchmarking exercises (http://www.simman2008.dk). The main data is

shown in the following two tables:

Table 1: main particulars and loading conditions for test vessel KVLCC2 Full

Load Heavy Ballast

Light Ballast

Draught midship Tm, m 20.8 10.0 8.0

Displ. volume V, m3 3.126·105 1.236·105 1.099·105

Long. distance of CG from AP, m

171.20 171.613 176.27

Mass, t 3.200·105 1.267·105 1.127·105

Projected frontal area AF, m2

1356.7 1651.0 1767.0

Lateral area AL, m2 4005.7 6593.0 7260.2

Projected rudder area AR, m2

122.9 84.6 61.6

15 This example for a static performance assessment was prepared by Germanischer Lloyd.

- 15 - MEPC 62/5/y Sample result for course keeping test program

Tests are performed at two loading conditions (full load and ballast). Maximum available power

is supplied to the propeller and the rudder angle is adjusted to achieve the desired course, up to

its maximum angle if necessary. Wind is set at maximum speed (only one direction, aligned with

wave direction). Irregular short-crested waves were generated with maximum significant wave

height and zero up-crossing periods (varied from 8.5, 9.5, 10.5, 11.5, 12.5 to 13.5 s); wave

directions were varied from 0 to 180 degrees, with 15 degrees step size. (To produce higher

resolution pictures, we have used a step size of 1 degree.) The course keeping test program

checks a steady motion with constant course for the following two assessment parameters:

minimum speed and course deviation and typical results are shown in Fig. 1

Figure 1: typical result for test vessel KVLCC2

For each ship speed and wave direction, the required propulsion power is compared with the

available total propulsion power (Fig. 1, black line labelled with 1) as well as with the torque-

limited propulsion power (boundary 2 of the green area) according to eq. (5) in Annex VII. There

are also combinations of ship speed and wave direction when the rudder in not effective any

more. These are typically stern quartering conditions and these are shown as red-shaded area

labelled with 3. The intersection of the available power curve and the rudder-ineffectiveness

area show the wave and wind conditions when the course cannot be kept. If the resultant sector

is larger than the defined allowed course deviation, the vessel will not fulfil the criterion on

course keeping.

- 16 - MEPC 62/5/y Note that area 5 in Fig. 1, corresponding to following and quartering waves, is not attainable if

starting directly from the zero-speed condition: in order to accelerate to the required speed

(above 6.5 m/s), the ship has to start at the zero speed and accelerate in following and

quartering wind and waves, where the rudder is inefficient (area 3); thus the vessel will loose

control and will be turned by the wind and waves from the desired course. If such operational

parameters can be achieved (e.g. through acceleration in head waves, area 4, and turning away

from waves), the sailing would be unstable: if the speed drops due to encountering a large wave

or master action, the ship will move into the red area and loose control; it will be quickly turned

by wind and waves (the considered vessel will be turned against wind and waves).

The figure below compares the rudder inefficiency area and limiting power curve between light

(left) and heavy (right) ballast loading conditions. Note that heavy ballast improves significantly

course keeping in adverse conditions due to the increased effective rudder area. Due to less

resistance in calm water and in waves, the heavy ballast condition also improves advance

speed in head waves compared to the fully loaded condition.

Figure 2: typical result for test vessel KVLCC2 in two loading conditions

***

- 17 - MEPC 62/5/y

Annex VII

EXAMPLE FOR ADVANCE SPEED ASSESSMENT16

Introduction

The basic assumption of this simplified assessment is that the dimensioning criterion is advance

speed in waves and, implicitly, that turning and course keeping can be achieved if advance

speed is maintained. This simplified assessment comprises only the equation of steady motion

in longitudinal direction. It is only applicable to vessels below Froude number and below a lateral

area ratio given in the guidelines.

Procedure

The principle of the assessment is that the required propeller thrust, defined as a sum of bare

hull resistance in calm water cwR , resistance due to appendages appR , aerodynamic resistance

airR , and added resistance in waves awR ,

cw air awT R R R= + + , (1)

can be provided by the vessel’s propulsion system. The calm-water resistance can be

calculated neglecting the wave resistance as 2cw

1(1 )

2F sR k C Svρ= + , where k is the form factor,

( )2

0.075

log Re 2FC =

− the friction resistance coefficient, Re /s ppv L ν= is the Reynolds number, ρ is

water density, S is the wetted area of the bare hull, sv is the ship speed and ν is the kinematic

density of water.

Aerodynamic resistance can be calculated as 2air air a F w

1

2R C A vρ= , where airC is the aerodynamic

resistance coefficient, aρ is the density of air, FA is the frontal projected area of the hull and wv

is the relative wind speed.

The added resistance in waves awR can be derived from model tests, potential or viscous flow

computations or empirical formulae.

In order to check whether the required thrust can be provided by the engine, the required

advance ratio of the propeller J is found from the requirement

( )2 2 2a P T /T u D K J Jρ= , (2)

where ( )TK J is the thrust coefficient curve. After this, the required rotation speed of the

propeller is found from the relation

( )a Pn u JD= , (3)

16 This example for an advance speed assessment was prepared by Germanischer Lloyd.

- 18 - MEPC 62/5/y and the required power is then defined from the relation

( )3 5P Q2DP n D K Jπρ= . (4)

It should be noted that for diesel engines, the available power is also limited due to the torque-

speed limitation of the engine ( )maxQ Q n≤ , thus an additional requirement to be checked is

( ) ( )D max2Q P n Q nπ= ≤ . (5)

Example of Simplified Assessment

The proposed procedure is applied to the tanker KVLCC2 at full load which is used in Annex VI.

1. Input parameters:

Parameter Definition Source Value Used

FA projected frontal area ship data 1356.7 m2

S submerged surface area of bare hull

ship data 27457.7 m2

airC coefficient of aerodynamic resistance

wind tunnel test, RANSE simulation or empirical formulae

1.0

PD propeller diameter ship data 9.86 m

k form factor model tests, viscous flow calculations, empirical formulae

0.22

( ), ( )T QK J K J propeller curves open-water propeller tests, propeller series, numerical calculations

Fig. 1

( )maxQ n engine torque/speed limiting curve

engine passport Fig. 2

sv ship speed assessment requirement [3.0 knots] 1.543 m/s

wv relative wind speed sum of wind speed [51.5 knots] and ship speed [3.0 knots]

28.0 m/s

w propeller wake fraction

model tests, viscous flow calculations, empirical formulae

0.4

ρ density of water 1025.0 kg/m3

aρ density of air 1.2 kg/m3

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80

J

KT

10KQ

etha0

0

500

1000

1500

2000

2500

3000

3500

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4

n,1/s

Q,k

N.m

Fig.1. typical open-water propeller curves Fig. 2. typical limiting torque curve ( )maxQ n

- 19 - MEPC 62/5/y 2. Calculation of calm-water resistance

Re /s ppv L ν 4.330⋅108

FC ( ) 20.075 log Re 2

−⋅ − 1.7⋅10−3

cwR 20.5(1 ) F sk C Svρ+ 69.63 kN

3. Calculation of aerodynamic resistance

airR 2

air a F w

1

2C A vρ

640.15 kN

5. Calculation of added resistance in waves

Added resistance in waves was computed wit a potential seakeeping code; here the maximum

added resistance over peak wave periods in the range 8.5 to 13.5 s with the significant wave

height 9.8 m was used, awR =1157.6 kN

6. Calculation of the required thrust

T cw air awR R R+ + 1867.4 kN

7. Calculation of the required advance ratio and rotation speed

The advance speed of the propeller is calculated as a s (1 )u v w= − resulting in au equal to 0.926

m/s. The required advance ratio of the propeller J is found from equation (2), rewritten as

( )T

2 2 2a P

ln lnK J T

J u Dρ= , where the dependence ( ) 2

Tln /K J J⎡ ⎤⎣ ⎦ , Fig. 3, is calculated from the open-

water propeller curve, and the right-hand side 2 2a Pln /( )T u Dρ⎡ ⎤⎣ ⎦ is equal to 3.084 [−]. From the

plot in Fig. 3, the required advance ratio J is found as 0.114 and then the required rotation

speed ( )a Pn u JD= as 0.822 1/s.

-6.0

-4.0

-2.0

0.0

2.0

4.0

6.0

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

J

ln(K

T/J

**2)

Fig. 3. Dependence ( ) 2T /K J J

- 20 - MEPC 62/5/y 8. Calculation of the required power

For the determined J , QK is found from the open-water propeller curve in Fig. 1; then the

required delivered power on the propeller is found:

QK Fig. 1 0.0293

DP ( )3 5P Q2 n D K Jπρ 9.74 MW

The required propulsion power is less than the delivered propulsion power at design speed of

18.2 MW, compare table 1 in Annex VI.

9. Check of the torque/speed limitation

Q ( )D 2P nπ 1886.5 kN⋅m

( )maxQ n Fig. 2 1904.1 kN⋅m

Thus, the additional criterion ( )maxQ Q n< is fulfilled.

In summary, the vessel has passed the advance speed assessment.

***

ce_11_06 - iacs proposals on minimum power for eedi

Documents

iacs paper

paper subject

minimum power consideration

draft iacs submission

members comment

subcommittee meeting

preliminary consideration

initial consideration