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SUB-COMMITTEE ON STABILITY AND LOAD LINES AND ON FISHING VESSELS SAFETY 55th session Agenda item 7

SLF 55/INF.8

14 December 2012 ENGLISH ONLY

REVISION OF THE DAMAGE STABILITY REGULATIONS

FOR RO-RO PASSENGER SHIPS

The GOAL based Damage Stability project (GOALDS) - Derivation of updated probability of survival for passenger ships

Submitted by Denmark and the United Kingdom

SUMMARY

Executive summary: This document summarizes the work carried out in the GOAL based Damage Stability project (GOALDS) addressing the probability of survival (s factor) for passenger ships

Strategic direction: 5.1

High-level action: 5.1.1

Planned output: 5.1.1.5

Action to be taken: Paragraph 13

Related documents: SLF 45/3/3; SLF 46/INF.6; SLF 52/11/1; MSC 84/22/12; SLF 52/WP.3 and MSC 91/7/2

Introduction 1 This document provides information on the results of the "GOAL based Damage Stability" project (GOALDS). 2 The study has been partially funded by the European Commission under the 7th research Framework Programme Theme "Sustainable Surface Transport". 3 In the framework of GOALDS project, a new formulation for the probability of survival (s factor) for passenger ships was developed and is being issued for discussion. The derived formulation, which is supported by findings regarding the impact of water on deck (WOD) on ship's damage stability, is simple, rational and calculable, consistent with the Safe Return to Port philosophy and accounts for the ship scale.

SLF 55/INF.8

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Background 4 MSC 84 agreed to include a new item on "Damage stability regulations for ro-ro passenger ships" in the Sub-Committee's work programme. 5 The Sub-Committee, at its fifty-second session, discussed in detail the impact of the SOLAS 2009 amendments on the damage stability requirements for ro-ro passenger ships after the presentation of three European Union funded research projects (GOALDS, FLOODSTAND and EMSA2), and whether in this regard any amendment to SOLAS should be considered. 6 The Sub-Committee noted the general view of the SDS Working Group that more research and the evaluation of further studies were important and necessary before considering any possible additional measures. Following a request by the Sub-Committee, MSC 89 agreed to extend the target completion year for this item to 2013. 7 The Sub-Committee, at its fifty-third session, instructed the SDS Correspondence Group to further consider the impact of the SOLAS 2009 amendments on ro-ro passenger ships, as compared to the SOLAS 1990 regulations in association with the Stockholm Agreement, taking into account document SLF 52/WP.3, and any further relevant research results as they become available. Main contents of the GOALDS project 8 The GOALDS research project contained the following main sub-projects:

.1 extending the formulation introduced by resolution MSC.216(82) for the assessment of the probability of survival of passenger ships in damaged condition, based on the results of extensive numerical simulations;

.2 performing comprehensive model tests to investigate the process of ship stability deterioration in damaged condition and to provide a basis for the validation of the numerical simulation results;

.3 compiling damage statistics and probability functions for the damage location, length, breadth and penetration in case of a collision/grounding accident, based on a thorough review of available information regarding these accidents over the past 60 years worldwide;

.4 formulating a new probabilistic damage stability concept for passenger ships, incorporating collision and grounding damages, along with an alternative method for the calculation of ship survival probability;

.5 establishing new risk-based damage stability requirements for passenger vessels based on a cost-benefit analysis to establish the highest level for the required subdivision index;

.6 to demonstrate that a commercially viable passenger vessel could be built to a significantly higher Attained Index than set forth by current requirements; and

.7 investigating the impact of the new formulation for the probabilistic damage stability evaluation of passenger ships on the design and operational characteristics of a typical set of ROPAX and cruise vessel designs (case studies).

SLF 55/INF.8

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Main findings of this sub-project 9 A new formulation for the probability of survival (s factor) for passenger ships was developed and issued for discussion. The derived formulation, which is supported by findings regarding the impact of water on deck (WOD) on ship's damage stability, is simple, rational and calculable, consistent with the Safe Return to Port philosophy and accounts for the ship scale. 10 Validation studies on the proposed new model for the s factor demonstrated high correlation with all available results (particularly experimental data). The new s factor model accounts for any level and mode of subdivision, including the watertight envelop above the traditional bulkhead deck.

11 The new GOALDS s-factor, outlined in the annex, introduces new ship design parameters when compared to SOLAS 2009. The definition and calculation of the residual volume (VR) the proper treatment of openings and partial bulkheads and their effect on progressive flooding (submerged openings) and on the assumed range of positive stability (openings located above the final waterline), the evaluation of survival probability during the intermediate stages of flooding and the effect of external heeling moments need to be carefully addressed.

12 As a result of the above raised issues, it has been decided to propose the new GOALDS damaged stability formulation not as a replacement of the current SOLAS 2009 regulation, but as an additional requirement for passenger ships on top of SOLAS 2009. Action requested of the Sub-Committee 13 The Sub-Committee is invited to note the research carried out by the GOALDS project and included as an annex to this document, and to consider its findings within its work on the item on "Revision of damage stability regulations for passenger ships".

***

GOALDS-D-WP.7.3-SSRC-INF2 Paper–rev1 Page 1 of 16

Due date of Deliverable: 2012-10-31

Actual Submission Date: 2012-10-31

Jakub Cichowicz Odd Olufsen -document author/s-

Dracos Vassalos

[email protected]

-document approved by- -revision type-

2012-10-31

RE (please select one) 1

-date of last update- -distribution level-

1 dissemination level

PU Public PP Restricted to Programme Participants (including Commission Services) RE Restricted to a group specified by the Consortium (including Commission Services) CO Confidential, only for members of the consortium (including Commission Services)

Deliverable D 7.3-2

INF 2 Paper

Document Id. GOALDS-D-WP.7.3-SSRC-INF2 Paper–rev1

Grant Agreement No: 233876 Project Acronym: GOALDS Project Title: GOAL based Damage Stability

ANNEX SLF 55/INF.8

Deliverable D 7.3-2

GOALDS-D-WP.7.3-SSRC-INF2 Paper–rev Page 2 of 16

Disclaimer

The information contained in this report is subject to change without notice and should not be construed as a

commitment by any members of the GOALDS Consortium or the authors. In the event of any software or

algorithms being described in this report, the GOALDS Consortium assumes no responsibility for the use or

inability to use any of its software or algorithms.

The information is provided without any warranty of any kind and the GOALDS Consortium expressly

disclaims all implied warranties, including but not limited to the implied warranties of merchantability and

fitness for a particular use.

(c) COPYRIGHT 2009 The GOALDS Consortium

This document may be not copied and reproduced without written permission from the GOALDS Consortium.

Acknowledgement of the authors of the document shall be clearly referenced.

All rights reserved.

Document History

Document ID. Date Description

GOALDS-D-WP.7-SSRC-INF.2–rev2 2012-11-13 Updated document’s control sheet

GOALDS-D-WP.7-SSRC-INF.2–rev1 2012-10-31 submitted for approval

Deliverable D 7.3-2


Document Control Sheet

Title: INF 2 Paper

Abstract

This report summarises the work carried out in tasks 3.3, 3.4 and 3.5 of the project addressing survivability of collision and grounding damages, the formulation of the new GOALDS s factor as

well as means of integrating collision and grounding scenarios into a common standard for damage

stability.

Summary Report:

Introduction

The purpose of this report is to provide brief summary of the major achievements made within

tasks 3.3, 3.4 and 3.5. The report does not contain any implementation details as these could be found in other relevant deliverables of GOALDS (task 3.6). The ‘in a nutshell’ summary is intended

to form a basis for submission to the IMO as a part of the project’s dissemination activities (INF 2 paper).

State of the Art N/A

Value added to GOALDS

Dissemination of project results by submission to IMO

Achievements

N/A

Not achieved N/A

Input from other Deliverables The contents of this report highlights major developments as reported in D3.3, D3.4, D3.5 by the

SSRC as well as the report on task T3.6 prepared by DNV.

How the results relate to the overall goals of GOALDS

N/A

This executive summary may be published outside the GOALDS consortium. YES

Work carried out by Approved by

WP3 Partners Apostolos Papanikolaou, NTUA

- signature on file -

- signature of internal reviewer and date of acceptance -

Deliverable D 7.3-2


Erik Tvedt, DMA

- signature on file -

- signature of external reviewer and date of acceptance -

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GOALDS-D-WP.7.3-SSRC-INF2 Paper–rev1 Page 5 of 16

Table of contents

SURVIVABILITY OF COLLISION OR GROUNDING DAMAGES ...................................................... 6

PRACTICAL IMPLEMENTATION OF THE S-FORMULATION IN THE CALCULATION OF

SAMPLE SHIPS WITHIN GOALDS ......................................................................................................... 11

INTEGRATED STANDARD FOR DAMAGE STABILITY .................................................................... 15

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Survivability of collision or grounding damages

The s-factor is a measure of the probability of surviving collision and grounding1 damages. The

current formulation, valid for final stages of flooding is given as

25.0

max

16

16,min

12.0

12.0,min

RangeGZs (1)

where maxGZ is the maximum righting lever of the residual GZ curve (up to flooding angle) in

meters and Range stands for corresponding range of positive stability, in degrees, measured from

the angle of static equilibrium.

The above formula was developed during the EU project HARDER. Although such information is

not founded in SOLAS, the s-factor expression had been derived with use of an important concept

of the critical significant wave height, critHS . The relationship between the critHS and the s-factor is

given as

16

16,min

12.0

12.0,min44 max4 RangeGZ

sHScrit (2)

The HARDER critHS corresponds to the sea states at which 50% of the survivability tests would

result in capsize within 30 minutes long trial (full scale).

The notion of the critical significant wave height links the factor s to another important concept of

the capsize band – a range of sea states over which a transition from unlikely to certain capsizes

can be observed. Within the band the capsize rate fp (ratio of runs resulting in loss to the total

number of experiments performed at the particular sea state) undergoes usually smooth change

from 0 to 1. The function Sf Hfp , unique for the particular configuration, is usually

approximated as a sigmoid function.

These concepts, i.e. the factor s, the critHS and the capsize band (along with the problem of

floodwater accumulation inside the cargo spaces on RoPax vessels – so called water on deck issue), were further investigated within the WP3 of the GOALDS project.

Capsize band and water on deck

Extensive numerical studies performed on relatively large sample of ships – both passenger and

RoPax - confirmed HARDER observations that the capsize rate, fp , follows a sigmoid distribution.

However, the results showed also that the function HSfp f contracts towards its lower

boundary when duration of the experiments lengthens. This led to the conclusion that in the

limiting case of infinite time the function HSfp f would become a unit step function. That is,

the time realisations below certain sea state would never result in loss whereas all runs in higher

seas would lead to capsize. Based on this it was decided that the critHS should be associated with

1 Presently in SOLAS, the survivability of grounding damages is not rendered by the probabilistic

framework.

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the lower boundary of the capsize band and not the sea state corresponding to the capsize rate of

50%. This led to the following definition:

The critical significant wave height should correspond to the sea state at which the capsize rate equals 0.05 (5%).

It is noteworthy that small fp was favoured over the zero due to the asymptotic behaviour of the

capsize rate characteristics.

Figure 1 Contraction of the capsize band

The process of floodwater accumulation was examined on a basis of the surviving realisations. This

allowed maintaining the assumption of the ergodicity of the process (commonly adopted in

seakeeping problems). The qualitative assessment was performed by plotting 95th percentile of the floodwater mass recorded in cumulative time intervals.

The characteristics obtained with help of this technique showed that all the (unconditionally)

surviving cases were characterised by presence of a horizontal asymptote. On the other hand,

presence of a slant asymptote was a sign of an underlying progressive flooding which would lead to capsize observed while re-running the simulation with the longer duration.

Furthermore, although the limiting amount of floodwater would vary with sea-state the observed

variation was statistically insignificant. That is, the limiting amount recorded at sea states

exceeding the critHS , would fall within a confidence interval for the average amount recorded for

the critHS .

Deliverable D 7.3-2


Figure 2 Accumulation of floodwater within internal spaces of a cruise vessel. Presence of a slant asymptote indicates underlying progressive flooding (in fact in this particular case the vessel sinks in calm water. The characteristics of the capsizing runs lie outside the confidence interval of the “surviving” run.

The s-factor development

The first stage of the development aimed at identification of dominant parameters, which would allow for correlating of the measured critical significant sea states with the characteristics of the

specific damage cases. This was based on the response surface methodology and it is referred to

in the following as the Design of Experiments (DoE) technique.

The assessment showed clearly that the current parameters set, constrained to the maxGZ

and Range only, is insufficient for accurate regression model, at least in the following form

23max2

2

max10 RangeRangeGZGZHScrit (3)

where i are regression coefficients.

Prediction based on the above model was characterised by correlation coefficient of just 0.7.

Deliverable D 7.3-2


Figure 3 Tests for the completeness of the SOLAS parameters set. The response surface technique allowed for slight improvement in the predicted sea-state. Throughout investigation led to the identification of the following dominant parameters:

area under the GZ (up to flooding angle), GZA

residual metacentric height, fGM

range of positive stability, Range

residual volume, RV (a measure of deterioration of the watertight integrity)

Figure 4 Tests for the completeness of the GOALDS parameters set. The DoE and GOALDS predictions result in 0.99 and 0.89 correlation to the experimental data, respectively. Application of the DoE technique to the GOALDS parameters resulted in the 0.99 correlation to the

experimental data.

Deliverable D 7.3-2


It is noteworthy that the choice of the GOALDS parameters was not arbitrary but followed physical

and dimensional modelling. As a result, the following expression was established

][

2

13

1

mV

RangeGM

AHS R

e

GZcrit

(4)

where eGM is given as

0max

max,max

GZGMGM fe (5)

The angles max and 0 correspond to an angle at maximumGZ and the static equilibrium,

respectively.

The eGM parameter was introduced in a place of the actual GM in order to prevent an unrealistic

prediction in case sof very small righting levers at about static equilibrium.

The residual volume, RV is a difference between total volume of the watertight envelope and the

volume of the watertight spaces included in the damage definition.

The probability of surviving a collision damage is estimated by mapping the critHS through the

distribution of sea states recorded during the ship to ship collisions, that is

critGOALDS HSs 2.116.0expexp (6)

Outstanding issues

The GOALDS proposal for the s-factor has been derived for a sample of more than 20 ships,

distinct in size and an internal arrangement. The data used in the development came mainly from

numerical simulations but the finally proposed expression was benchmarked against the results of physical tests (see Figure 4). However, the available experimental data for cruise vessels provided

only one single valid point in this benchmark – all other points correspond to RoPax ships. Therefore, applicability of the formulation to cruise ships requires further validation studies.

The conducted physical and numerical experiments for grounding damages did not result in any

capsizes due to action of waves. All tested cases corresponded to either calm-water sinking (s=0)

for very large damage extents or significant residual stability (s=1). Therefore, the formula could not be properly validated for grounding damages.

Furthermore, the research did not address intermediate stages of flooding, the effect of external

moments or evacuation/abandonment aspects (the k-factor). For that reason, it is recommended

to use the formulations currently in force in order to accommodate for these factors.

Deliverable D 7.3-2


Practical implementation of the s-formulation in the calculation of sample ships within GOALDS The proposed s-factor has been used extensively in the calculation of risk control options on

sample ships within the GOALDS project as well as in the optimisations studies. The new s-factor formulation has been programmed in the NAPA software. An overview of the calculation process

carried out in order to arrive at the attained index AGOALDS is shown in Fig. 5.

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Fig. 5 Overview of calculation process

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The definitions and assumptions applied when performing these calculations are described in the

following.

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Variables and definitions

The definition of variables and their interpretation is shown in table 1.

Variable Definition

max. GZ from equilibrium to flooding angle

Range of the righting lever up to flooding angle

Effective area below the GZ curve, truncated by the an

unprotected opening or the vanishing angle

Residual volume - calculated as the total volume of the intact hull minus the volumes of compartments open to sea.

Actual GM at equilibrium

GMe As defined in equation 5

Static equilibrium heel angle

Angle of maximum GZ

Table 1 Variables and definitions

Intermediate stages of flooding

For calculating the s-factors at intermediate stages, equation (7) as defined by SOLAS Reg.II-1/7-

2.2 has been applied with the following conditions:

a) The following events during intermediate stages will not set the s-intermediate to 0:

- 15 degrees heel (Ref. Reg.II-1/7.2.2)

- Immersion of points such as horizontal escape route, vertical escape hatch, control

stations for watertight doors, or any opening fitted with weathertight mean of closure (Ref.

Reg.II-1/7.5.2 and 7.5.3)

b) Cross flooding and intermediate stages sequences, are calculated as in SOLAS 2009 and

according to the Explanatory Notes, except for the deviations presented in paragraph a)

above.

(7)

Final stage of flooding

With regards to final equilibrium stage, the effect of external moments, , as per SOLAS 2009

Reg.II-1/7-2 has been included as shown in equation (8)

si(GOALDS) = minimum {sintermediate,i or sGOALDS,i*smom,i}

(8)

Deliverable D 7.3-2


By the calculation procedure shown in Fig.5, calculation results both for index A according to

current SOLAS and AGOALDS are available for all calculations that have been carried out and show in general good agreement.

Integrated standard for damage stability

The concept of integration is derived from the most fundamental reasoning on risk tolerability. Namely, from the regulatory point of view it is a fairly routine assumption that a design must not

give rise to risk to life (or other pertinent loss) greater than some level considered tolerable, which

can be expressed as the following relationship ( 7 ).

criterionRiskRisk ( 7 )

The left hand side of the above equation can be expanded, leading to equation ( 8 ).

criteriongroundingcollision Riskriskrisk ( 8 )

In order to formalise such a standard, there must be an element addressing both of these hazards

in a consistent manner. It should be observed that either of hazard of collision or grounding results

to the event of loss of stability (in waves), after ingress of water through breach in hull integrity. While the source of hull breach, as well as its characteristics (location, length, etc.) differ between

them, the physical reason for the ultimate loss of life is the same - the loss of stability.

Therefore, it could be conceptualised that ship stability may be represented in exactly the same

manner as it is assumed in the current Regulation 6 of SOLAS2009, whereby a single value of R represents the probability of a ship surviving any among the mutually exclusive set of feasible

flooding scenarios.

The extension applied here is that the set of flooding cases is more comprehensive.

This allows postulating that the limit on the risk to life may be considered in the following form

( 9 ).

maxmaxmaxmax 11 NNRfNNpfRisk trequiredtcriterion ( 9 )

The components of risk due to collision and grounding can be expressed by analogical models, that is

max1 NAfrisk cccollision ( 10 )

max1 NAfrisk grgrgrounding ( 11 )

where f stands for frequency of a flooding scenario and A is the attained index of subdivision (for

collision and grounding scenarios) such a model leads to the proposed integrated standard as

given by the equation ( 12 ), which states that the probability of survival after flooding due to

collision OR grounding must not be less than a required global level R .

maxNRAA grgrcc ( 12 )

Deliverable D 7.3-2


where are weighting coefficients depending on the frequencies and grounding flooding scenarios.

It should be mentioned that the probabilities A in ( 12 ) are to be assigned according to the

respective formulations of SOLAS 2009 for cA (assuming appropriate corrections proposed in this

project), and the probabilistic concept of survivability for grA should be analogical to that for

collision damages2. Relevant details can be found in the project deliverable D5.2.

2 It should be noted that the GOALDS project resulted in proposals for the most important ingredients of the

probabilistic framework for grounding, i.e. p- and s- factors. However due to complexity of the formulations

with respect to practical applications to ship-like forms, the concept has not been implemented

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