Assessment of specific EU stability requirements for ro-ro passenger ships : publishable executive summary.
Date: 2019-04-09
Institutions: Directorate-General for Mobility and Transport
Subjects: carriage of passengers, fodder beet, report, risk management, technical specification, transport regulations, transport safety

Assessment of specific EU 
stability requirements for  
ro-ro passenger ships 

Publishable Executive Summary 

Written by DNV GL 
April – 2019 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
EUROPEAN COMMISSION 

Directorate-General for Mobility and Transport 
Directorate D — WATERBORNE 
Unit D.2 — Maritime Safety 

Contact: Lanfranco Benedetti 

E-mail: MOVE-MARITIME-TRANSPORT-AND-SAFETY@ec.europa.eu 

European Commission 
B-1049 Brussels 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
EUROPEAN COMMISSION 

Assessment of specific EU 
stability requirements for  
ro-ro passenger ships 

Publishable Executive Summary 

Directorate-General for Mobility and Transport  

Assessment of specific EU requirements for ro-ro passenger ships 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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Luxembourg: Publications Office of the European Union, 2019 

ISBN: 978-92-76-02100-1 
doi: 10.2832/682701 

© European Union, 2019 
Reproduction is authorised provided the source is acknowledged. 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Publishable executive summary 

Prepared by:  
Odd Olufsen 
DNV GL 

  Verified by: 
  Anne Marie Kristensen 

  Approved by: 
  Olav Rognebakke 

DNV GL 

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Revision history:  
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 Publishable executive summary 

Table of Contents 

Table of Contents ............................................................................................. 3 
Disclaimer ....................................................................................................... 3 
Motivation and introduction ................................................................................ 4 
The consortium ................................................................................................ 5 
Applicable regulations and mapping of fleet .......................................................... 5 
Definitions of sea areas: ................................................................................. 5 
Classes of ships ............................................................................................. 5 
Abbreviations used in the executive summary .................................................... 6 
Applicable regulations ....................................................................................... 7 
Mapping of the fleet .......................................................................................... 7 
Sample ships and results made available in the study ............................................ 8 
Calculation procedures ................................................................................. 11 
Wave height limitations in operation ................................................................. 13 
Implementation options .................................................................................. 14 
Implementation options related to level of R .................................................... 14 
Methods to account for wave height limitations ................................................ 15 
Deterministic requirements in addition to the probabilistic requirements .............. 15 
Analysis of impacts ......................................................................................... 16 
Comparison of risk ......................................................................................... 18 
Evaluation and comparison .............................................................................. 19 
Summary of findings ....................................................................................... 19 
References .................................................................................................... 21 

Disclaimer 

The  information  and  views  set  out  in this  report  are  those  of  the  authors  and  do  not 
necessarily  reflect  the  official  opinion  of  the  Commission.  The  Commission  does  not 
guarantee the accuracy of the data included in this study. Neither the Commission nor 
any  person  acting  on  the  Commission’s  behalf  may  be  held  responsible  for  the  use 
which may be made of the information contained therein.  

January 2019    3 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Publishable executive summary 

Motivation and introduction 

The objective of this study was to support the review of the EU Directive 2003/25/EC 
in  relation  to  the  status  of  the  international  regulations  as  set  forth  by  SOLAS 
Convention in its up to date version (amendment status 2020). The objective as given 
by the tender specification is to: 

“  compare  the  regulatory  framework  provided  by  Directive  2003/25/EC  with  that 
provided by the future SOLAS2020, identifying and providing evidence of any potential 
safety  gaps  between  the  two  sets  of  rules  and  to  identify  and  eventually  propose 
alternative  measures  that  could  close  safety  gaps  (towards  an  increased  safety)  by 
taking  into  account  the  overall  survivability  of  the  ship  (i.e.  considering  the 
contribution of all damage cases for collision) ” 

Directive  2003/25/EC  on  specific  stability  requirements  for  ro-ro  passenger  ships, 
dated 14 April 2003, sets forth the criteria and requirements known as the Stockholm 
Agreement (SA in short). The Stockholm Agreement was concluded 28 February 1996 
in pursuance of SOLAS 95 Conference Resolution 14 “Regional Agreements on specific 
stability  requirements  for  ro.ro  passenger  ships”  adopted  on  29  November  1995. 
These  requirements  address,  in particular,  the  possible  accumulation of  water  on  the 
ro-ro deck for flooding cases defined in accordance with the deterministic standards of 
SOLAS90  applicable  at  that  time.    It  was  at  the  time  assumed  that  the  SOLAS90 
criteria would ensure sufficient survivability in significant wave heights not exceeding 
1.5  m.  Consequently,  for  ro-ro  passenger  vessels  operating  in  areas  where  the 
significant wave heights are higher, the supplemental requirements of the Stockholm 
Agreement are required.  
Since  the  Stockholm  Agreement  was  developed,  tremendous  efforts  in  research  and 
subsequent  amendments  of  SOLAS  have  taken  place.  Some  essential  research 
projects  that  should  be  mentioned  are  the  partly  EU  funded  projects  HARDER  and 
GOALDS  as  well  as  the  EMSA  funded  projects  EMSA  I,  II  and  III.  HARDER  was  the 
main source for amendments to SOLAS damage stability requirements, often referred 
to  as  SOLAS2009,  where  the  probabilistic  concept  replaced  the  deterministic 
requirements  for  passenger  ships.  The  work  carried  out  in  EMSA  II  and  EMSA  III 
provided  the  basis  for  the  criteria  and  requirements  of  the  most  recent  amended 
SOLAS that will enter into force in 2020.  
In order to meet the objectives, and in accordance with the project specification, the 
following main tasks have been carried out and are described in the following: 

•  Applicable regulations and mapping of fleet.  
•  Sample ships and results made available in the study 
•  Operational wave height limitations in a probabilistic concept 
• 
•  Analysis of impacts 
•  Comparison of risks, implementation options 
•  Summary and observations 

Implementation options 

January 2019    4 

 
 
 
 
 
 
 
 
 Publishable executive summary 

The consortium 

The consortium carrying out these studies consists of the following member companies 
in alphabetical order: 

Brookes  Bell,  DNV  GL,  FORESHIP,  HEC,  INTERFERRY,  LMG  MARIN,  MEYER  TURKU, 
MSRC and NAP 

Applicable regulations and mapping of fleet 

Definitions1 of sea areas: 
International 
voyage  

 A  voyage  from  a  port  of  a  member  state  to  a  port  outside  that 
member state, or conversely 

Area A  

Area B  

Area C  

Area D 

A sea area outside area B, C and D 

A sea area which it is at no more than 20 Nautical Miles from the line 
of the coast but outside areas C and D 

Sea areas where the probability of exceeding 2.5 m significant wave 
height is smaller than 10 % over one year, and not more that than 5 
NM from the line of the coast. 

A  passenger  ship  engaged  on  domestic  voyages  in  sea  areas  where 
the probability of exceeding 1.5 m significant wave height is smaller 
than  10%  over  one  year,  and  not  more  than  3NM  from  the  line  of 
the coast. 

Classes of ships 

The classes of ships are given in relation to the sea area in which they are operating. 

Class A 

Class B 

Class C 

Class D 

A passenger ship engaged on domestic voyages in Areas A, B, C 
and D 

A  passenger  ship  engaged  on  domestic  voyages  in  Areas  B,  C 
and D 

A passenger ship engaged on domestic voyages in Areas C and D 

A passenger ship engaged on domestic voyages in Area D 

1 Refer to the directive 2017/2108/EU amending 2009/45/EC for complete definitions 

January 2019    5 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
                                          
 Publishable executive summary 

Abbreviations used in the executive summary 

A 

R 

Attained  subdivision  index  A  calculated  in  accordance  with  SOLAS 
Reg.II-1/B-1/7 

Required  subdivision  index  R  in  accordance  with  SOLAS  Reg.II-1/B-1/6 
(with amendments) 

s-factor 

Factor representing the probability for surviving a given damage, SOLAS 
Reg.II-1/B-1/7-2 (with amendments)  

SA 

Stockholm Agreement 

January 2019    6 

 
 
 
 
 
 
 
 
 Publishable executive summary 

Applicable regulations 

The  current  legislation  is  based  on  the  Directive  2009/45/EC  which  makes  the 
Directive 2003/25/EC mandatory for all new ships of classes A, B and C and for ships 
on International voyages visiting European ports. 

The Directive 2003/25/EC is based on some assumptions fundamentally different from 
other regulations concerning damage stability. The main assumption is that water may 
accumulate on the ro-ro deck in case of a damage. Hence, the Directive requires that 
the stability is assessed by assuming a certain amount of water on deck in the flooded 
condition.  The  water  accumulated  on  deck  is  quantified  based  on  the  freeboard  after 
damage and the limiting wave height applicable for the area of operation.  It is noted 
in  addition  that  compliance  may  be  documented  not  only  by  calculations  but  also  by 
model test.  

The criteria and requirements of the Directive 2003/25/EC were introduced at a time 
when  the  SOLAS90  was  in  force,  which  is  a  deterministic  damage  stability  standard 
(one-  or two-compartment flooding). When the probabilistic damage stability concept 
was  introduced  by  SOLAS2009,  the  Directive  was  kept  applicable  as  it  was  not 
considered  evident  that  the  amended  requirements  of  SOLAS2009  would  provide  the 
same  safety  level  as  Stockholm  Agreement.  By  the  adoption  of  SOLAS2020  the 
requirements  have  become  stricter  for  new  ships  built  from  the  year  2020  both  in 
terms of the formulation of survivability when the roro space is involved in a damage 
case as well as in terms of the required subdivision index R.  

Mapping of the fleet 

As  a  first  step,  the  fleet  of  roro  passenger  ships  operating  within  the  EU  in 
International  trade  and  domestically  in  classes  A,  B  and  C  was  mapped  by  using 
various  registers  of  ships.  Area  of  operation  included  e.g.    the  North  Sea, 
Mediterranean, Baltic, English Channel etc.  
The  main  sources  used  were  the  IHS  Fairplay/Seaweb  database  and  the  database  of 
reported  ships  provided  by  EMSA  supported  by  the  IHS  Fairplay/Seaweb  database. 
Based on the IMO numbers, the operation of the ships was checked by using the AIS 
data  for  one  year  of  operation.  For  verification  and  completion  of  this  information 
several additional databases were consulted as well as a survey among the members 
of INTERFERRY.  
For the year of 2016 the ro-ro passenger ships were categorized as follows:  

•  256 ships in International trade 

•  64 ships in Class A 

•  88 ships in Class B 

•  15 ships in Class C 

January 2019    7 

 
 
 
 
 
 
 
 
 
 Publishable executive summary 

Within each class of ships, a variety of designs was found such as single enders, small 
and  large  double  enders,  cruise  ferries  and  ferries  with  long  lower  hold.  There  are 
significant variations in design, size parameters and capacity. This demonstrates that 
the roro passenger ships are designed to meet specific operational specifications that 
reflect a specific business case or being part of the domestic infrastructure.   
The  mapping  of  the  fleet  was  used  as  a  basis  to  ensure  that  the  sample  of  ships 
subject to the detailed damage stability calculations are representative.  

Sample ships and results made available in the study 

18  sample  ships  were  initially2  made  available  for  investigation  by  damage  stability 
calculations.  The  ships  made  available  represent  the  main  characteristics  of  the  fleet 
of  the  roro  passenger  ships  operating  in  EU  waters.  Their  common  feature  is 
compliance  with the SA  mainly  by calculations.  Some  ships  have  also  been  approved 
by  use  of  model  tests.  In  addition,  either  SOLAS90  (deterministic)  or  SOLAS2009 
(probabilistic)  requirement  is  applied.  For  one  of  the  ships  the  IMO  Res.A265 
(probabilistic  prior  to  SOLAS2009)  has  been  applied.    A  summary  of  the  results  is 
shown in the following table. 

Explanation to the columns in the below table: 

POB:    

Persons on board. Total number of passengers and crew 

R SOLAS2009: 

Required index R according to SOLAS2009 

A SOLAS2009:  

Attained  index  A  according  to  SOLAS2009  and  based  on  current 
limiting GM Curves 

R SOLAS2020: 

Required index R according to SOLAS2020 

A SOLAS2020:  

Attained  index  A  according  to  SOLAS2020  and  based  on  current 
limiting GM curves 

A SOLAS2020 OPT:  Attained  index  A  according  to  SOLAS2020,  based  on  optimised 

limiting GM curve in relation to loading condition  

EU Class:  

Current  EU  Class  in  accordance  with  the  definitions  above.  Note 
that some ships may shift their class during a year of operation 

Hs:  

Reg.8:  

Limiting  significant  wave  height  for  which  compliance  with  the 
Stockholm Agreement has been documented 

Check  of  compliance  with  Reg.8,  the  deterministic  regulation  of 
SOLAS2020,  based  on  the  optimised  GM  limits.  OK  means  that 
compliance  is  achieved  for  all  damage  cases  investigated,  while 

2 A210 and B150 are new designs included for the Impact Analysis.  

January 2019    8 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
                                          
 Publishable executive summary 

N means that compliance is not achieved due to failure of one or 
more damage cases 

Regulation:  

The applicable regulation; SOLAS 90, IMO Res. A. 265 or SOLAS 
2009   

January 2019    9 

 
 
 
 
 Publishable executive summary 

Hs 

Reg.8 

Reg 

Table 1 Overview of sample ship results 

Id 

POB 

S
A
L
O
S
R

9
0
0
2

S
A
L
O
S
A

9
0
0
2

S
A
L
O
S
R

0
2
0
2

S
A
L
O
S
A

0
2
0
2

S
A
L
O
S
A

0
2
0
2

T
P
O

M1 
M2 
M3 
M4 
LMG1 
LMG2 
LMG3 
LMG4 
N1 
N2 
N3 
N4 
N5 
N6 
IF1 
IF2 
IF3 
IF4 

3000  0.82264  0.85483  0.87551  0.84093  0.85670 
3000  0.82264  0.82319  0.87550  0.81244 
2200  0.81088  0.87150  0.86645  0.85997 
2600  0.81101  0.80336  0.87040  0.78518  0.84850 
399  0.71125  0.75153  0.72200 
0.7412  0.76926 
718  0.73582  0.77917  0.76395  0.75799  0.79074 
1500  0.78125  0.78934  0.85099  0.78789  0.83040 
1032  0.75594  0.79364  0.80538  0.79364  0.82793 
2620  0.81184  0.69029  0.87067  0.67678  0.76437 
935  0.74158  0.79392  0.79258  0.78816  0.79501 
1825  0.79566 
0.8112  0.85785  0.80316  0.83665 
1800  0.78908  0.84021  0.85886  0.83618  0.86073 
650  0.73073  0.92137  0.75498  0.89745  0.90877 
200  0.69259  0.67310  0.72200  0.66082  0.67394 
1774  0.78027  0.78031  0.85685  0.76956  0.77807 
850  0.71805  0.78920  0.78137  0.78045  0.80977 
600  0.72356  0.72370  0.74838  0.70571  0.74828 
0.8118 
471  0.70386  0.80096  0.73137  0.79751 

s
s
a
l
C
U
E

I 
I 
I 
I 
B 
C 
B 
B 
A 
I/A 
B 
B 
B 
B 
I 
I 
I 
I 

m 
4.00 
4.00 
4.00 
4.00 
4.00 
2.50 
3.70 
4.00 
4.00 
4.00 
2.50 
3.25 
2.50 
2.50 
4.00 
4.00 
4.00 
4.00 

A210 
B150 

2000 
2000 

  0.86108  0.86172 
  0.86108  0.86130 

I 
I 

4.00 
4.00 

OK  S2009 
S90 
OK 
OK  S2009 
S90 
OK 
S90 
OK 
N  S2009 
OK  S2009 
OK  S2009 
S90 
N 
S90 
OK 
S90 
OK 
S90 
N 
S90 
N 
S90 
N 
S90 
OK 
N 
S90 
N  S2009 
IMO 
A265 
OK  S2020 
OK  S2020 

OK 

In  addition  to  the  sample  ships  provided  in  this  study,  roro  passenger  ship  designs 
used in previous studies, namely GOALDS and EMSA III, are referred to as well as the 
submission to IMO SDC3 by Denmark which includes calculation results for a number 
of  ferries  operating  in  Denmark3.      In  total,  the  calculation  results  for  27  ships  are 
provided and compared to the criteria of the different instruments. 

It  is  noted  that  LMG2,  LMG3  and  LMG4  comply  with  SOLAS2009  even  though  not 
required according to 2009/45/EC. 

3 Only DK2 is category B. The other ferries marked DK are class D.  

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 Publishable executive summary 

Table 2 Overview of reference ship results 

Id 

POB 

R 
SOLAS2009 

A 
SOLAS2009 

R 
SOLAS2020 

A 
SOLAS2020 

A 
SOLAS2020 
OPT 

G1 

G2 

E1 

E2 

E3 

E4 

3500 

2200 

3280 

1700 

625 

610 

0.83296 

0.79804 

0.83000 

0.77800 

0.72143 

0.72780 

DK1 

600 

0.72720 

DK2 

110 

0.68270 

DK3 

395 

0.71010 

DK4 

250 

0.69740 

DK5 

590 

0.72520 

DK6 

410 

0.70680 

0.83512 

0.80984 

0.85270 

0.77404 

0.76478 

0.95650 

0.75770 

0.69500 

0.89400 

0.68880 

0.88105 

0.86360 

0.87872 

0.85536 

0.74970 

0.75168 

0.75168 

0.72200 

0.72200 

0.72200 

0.74700 

0.72330 

0.82937 

0.80255 

0.83261 

0.83982 

0.72252 

0.74911 

0.83680 

0.75420 

0.71730 

0.66930 

0.78730 

0.64890 

0.7947 

0.8412 

0.78410 

0.74530 

0.80380 

0.72010 

Calculation procedures 

The calculations were carried out in several steps. Firstly, the ships were calculated in 
accordance  with  SOLAS2009  and  the  attained  A-index  compared  with  the  required 
index R of SOLAS2009. In the following steps, the attained index A was calculated in 
accordance  with  SOLAS2020  and  compared  with  the  new  required  R-index  according 
to SOLAS2020.  
The  first  round  of  calculations  carried  out  in  accordance  with  the  SOLAS2020  were 
based  on  the  existing  limiting  GM  curve  provided  by  the  stability  manual.    The 
relevant  GM  values  at  the  lightship  draught,  the  partial  draught  and  the  deepest 
subdivision draught as specified by the SOLAS regulations were selected on this basis.  
However,  it  was  seen  in  many  cases  that  there  were  quite  substantial  margins 
between the limiting GMs and the actual loading conditions. In the final step, the GM 
values  used  in  the  SOLAS2020  calculations  were  optimised  to  reflect  a  reduced  but 
still comfortable margin to the loading conditions. 
This  is  illustrated  in  the  example  below,  where  the  effect  of  selecting  the  GM  at  the 
light service draught dl is shown. 

• 

• 

If  the  GM  at  dl  is  selected  from  intact  stability  limit  the  attained  index  A  is 
0.81972 

If the GM at dl is selected at the possible highest level in accordance with the 
regulation the attained index A is 0.83135.  

The figure is also serving as an illustration on how the required GM varies for different 
regulations including the Stockholm Agreement.  

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Figure 1 Example of limiting GM values for different criteria 

The main results from these calculations including the reference ships are included in 
the figure below.  
The  figure  includes  the  level  of  R  adopted  as  SOLAS2020  and  the  results  from  the 
sample ship calculations in this study as well as reference ships from previous studies.  

•  The  light  blue  +  sign  indicates  the  A-index  for  the  sample  ships  in  this  study 

calculated for the existing limiting GM curves 

•  The dark blue triangular reflect the corresponding A-index for the sample ships 

in this study based on optimised GM limits  

•  The  green  strokes  show  the  initial  designs  in  previous  studies;  GOALDS  and 

EMSA III 

•  The  blue  squares  indicate  reference  ships  in  IMO  submission  SDC3/INF.4, 

based on initial GM limits 

•  The  red  squares  indicate  reference  ships  IMO  submission  SDC3/INF.4,  based 

on optimised GM limits 

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Figure 2 A-index for all ships in relation to level of R according to SOLAS2020 

Wave height limitations in operation 

The assessments carried out in accordance with the Stockholm Agreement are based 
on  two  important  parameters,  namely  the  significant  wave  height  in  the  areas  of 
operation (with 10 % probability for exceedance) and the freeboard after flooding. The 
assessments  are  carried  for  the  damage  cases  derived  in  accordance  with  the 
definitions of SOLAS90, e.g. one- or two-compartment standards depending mainly on 
the number of persons carried on board.  
Two  different  ways  of  including  the  critical  wave  height  in  a  probabilistic  framework 
were  suggested  in  this  study;  the  normalised  s-factor  and  the  expected  critical  sea-
state.  
The  method  identified  as  the  normalised  s-factor,  assumes  a  bi-linear  dependency 
between the range and the height of the GZ-curve as set forth by SOLAS2020 and the 
corresponding  critical  wave  height.  For  instance,  a  GZ-range  of  20  degrees  and  GZ-
height  of  0.2m  in  flooding  cases  involving  the  ro-ro  space  correspond  to  survival  in 
significant  wave  height  of  4.0m.  Following  the  suggested  new  method,  the  GZ-range 
of  10  degrees  and  GZ-height  0.1  m  should  correspond  to  survivability  in  significant 
wave height 2.0 m. Consequently, if a ship is operating in significant wave heights not 
exceeding 2.0 m, the s-factor for each damage case is calculated by use of the values 
derived  from  the  above.  The  corresponding  A-index  is  obtained  by  weighting  and 
summation  in  the  same  way  as  in  SOLAS  Reg.II-1/B-1/7  and  should  be  evaluated  in 
relation to the level of R as set forth in SOLAS2020. 

January 2019    13 

 
 
 
 
 
 
 Publishable executive summary 

The  second  method,  identified  as  the  “expected  critical  sea-state”,  is  based  on 
establishing the critical wave height for each damage case based on the GZ-range and 
the  GZ-height.  Each  damage  case/initial  condition  will  have  a  corresponding  critical 
wave  height.  The  critical  wave  heights  are  simply  replacing  the  s-factors  in  the 
calculations of the index of subdivision. The end result is a number that represents the 
expected critical sea-state which can be used directly in the assessment in respect of 
the  operation  in  an  area  with  known  sea-states  or  as  an  operational  limitation  as  in 
SA. 
The  application  of  both  methods,  in  spite  of  some  variations  between  the  sample 
ships,  did  not  show  a  significant  effect  when  accounting  for  operational  wave  height. 
The  second  method  is  technically  the  most  promising  but  would  need  thorough 
consideration of the application and acceptance criteria.   

Implementation options 

The implementation options were derived based on the considerations of the existing 
regulations both within EU and Internationally as well as input received from 
stakeholders.  

The implementation options are divided into three groups: 

• 

Implementation options related to the level of R  

•  Methods to account for wave height limitations  

•  Deterministic requirement in addition to the probabilistic requirements  

Implementation options related to level of R 

The options investigated for the level of R are as follows: 

•  SOLAS2020. 

•  SDC3 compromise. 

•  EMSA III proposal (EMSA 3.2)  

The  implementation  options  reflect  the  proposals  that  have  been  considered  in  the 
process leading to the level of R that was finally adopted as SOLAS2020. The proposal 
from  the  EMSA  III  study  was  forwarded  to  IMO  by  the  EU  flag  states.  However,  the 
EMSA  III  study  did  not  include  roro  passenger  ships  with  less  than  600  persons  on 
board  and  several  IMO  member  states  had  concerns  that  the  requirements  would  be 
too strict for smaller ships.  This led to the compromise identified as SDC3 which was 
approved but not adopted by MSC. The alternatives are shown in the figure below in 
relation  to  the  existing  level  of  R  according  to  SOLAS2009,  which  is  a  function  of 

January 2019    14 

 
 
 
 
 
 
 
 
 
 
 Publishable executive summary 

lifeboat  capacity.  Curves  for  no  lifeboats  and  75%  life  boat  capacity  are  included  for 
reference.  

Figure 3 Level of R – implementation options in relation to current SOLAS2009 

.  

Methods to account for wave height limitations 

The operational wave height is an essential parameter in the Stockholm agreement.  
As the Stockholm agreement is based on SOLAS90 and deterministic definition of 
damage cases, it cannot be directly implemented in a probabilistic concept.   
It was shown that the two methods suggested have a rather limited influence in the 
assessment of survivability. Therefore, the third option was to not consider any effects 
from the wave heights and use the same s-factor regardless of Class;  

•  use of the “normalised s-factor”  

•  use of the concept of “expected critical sea-state”  

•  no modification, use SOLAS2020 as is regardless of operational area 

Deterministic requirements in addition to the probabilistic 
requirements 

The implementation options listed here should be seen in relation the implementation 
options listed with respect to level of R. If SOLAS2020 is adopted, the deterministic 
requirement set forth by Reg. 8 (minor side damage) is already considered included. 
From the stakeholder consultations it was suggested that the current assumption 

January 2019    15 

 
 
 
 
 
 
 
 
 
 Publishable executive summary 

regarding damage penetration in SOLAS Reg.II-1/B-1/8 should be expanded to B/5.  
Retaining the Stockholm agreement is considered as the base line  

For the sake of completeness all options are listed:  

• 

retain Stockholm Agreement as set forth the by 2003/25/EC, as is 

•  use SOLAS2020 as is without any addition (covered by Reg.8) 

•  use SOLAS Reg.II-1/B-1/8 with B/5 penetration instead of B/10 

Analysis of impacts 

The  impacts  of  the  alternative  implementation  options  listed  above  were  studied  by 
using  five  sample  ships  representative  for  the  segments  of  the  fleet  operating  within 
EU  both  in  international  traffic  and  domestic.  For  each  of  the  sample  ships,  design 
changes  were  developed  and  assessed  with  respect  to  costs  and  risk.  Main  impacts 
were  identified  considering  the  results  of  EMSA III  study,  e.g.  changes  in  operational 
costs  (fuel,  harbour,  maintenance)  and  fuel  related  impacts  (air  pollution,  climate 
change). By assessing the RCOs using the same threshold of VPF (Value for Preventing 
a Fatality ~6 million Euros), the results are comparable to previous EMSA III study. 

The ships investigated in this study were:  

•  LMG1: A single ended ferry with 399 persons on board 

•  LMG2: A double ended ferry with 718 persons on board 

• 

IF3: A typical cargo ferry with long lower hold and 600 persons onboard 

•  A210 and B150: Large ferries with 2000 persons on board 

The analysis of implementation option with respect  to various formulations of R used 
the A-index directly in a risk model as a measure  of ship capsize. Risk reduction was 
quantified  by  applying  the  EMSA III  risk  model  for  roro  passenger  ships.  A 
corresponding  assessment  was  also  carried  out  for  four  roro  passenger  ships  in  the 
EMSA III study and since both assessments refers to the same basis, the results can 
be merged.  
The results from the Impact Analysis and the cost-benefit assessment are summarised 
as follows: 

•  LMG1 complies with the level of R-index according to SOLAS2020 as it is, while 
the  Risk  control  options  investigated  to  meet  the  higher  standard  of  SDC3 
exceed the cost threshold. 

•  LMG2 can comply with level of R according to all options while meeting the cost 

threshold 

• 

IF3  Complies  with  level  of  R  according  to  SOLAS2020  and  SDC3  in  its  current 
configuration. RCOs for meeting the EMSA3.2 exceed the cost threshold. 

•  A210 is designed for compliance with SOLAS2020 and is also meeting the level 

of R according to SDC3 but not EMSA 3.2 

January 2019    16 

 
 
 
 
 
 
 
 
 
 Publishable executive summary 

•  B150 is designed for compliance with SOLAS2020 and is also meeting the level 

of R according to SDC3 as well as EMSA3.2 

• 

Table 3 Summary of results from Impact assessment on sample ships 

Ship 

POB  A(Initial)  Highest 
A (RCO) 

R 
(SOLAS2020) 

LMG1 

399 

0.7412 

0.748  0.7220 

R 
(SDC3) 
0.7839  0.8392 

R 
(EMSA3.2) 

LMG2 

718  0.79074 

0.909  0.7640 

0.8120  0.8460 

IF3 

600  0.74828 

0.8154  0.7484 

0.8016  0.8436 

A210  2000 

0.8617 

0.8617  0.8611 

0.8611  0.8671 

B150  2000 

0.8749  0.89767  0.8611 

0.8611  0.8671 

RCO 
description 

Update 
opening 
arrangement 
Update 
opening 
arrangement 
Optimised 
GM limits 
Designed  for 
compliance 
Main 
made 
watertight 

deck 

Table 4 Summary of results from EMSA III 

Ship 

POB  A(Initial)  Highest 

A 
(RCO) 
0.8326  0.9152  0.8787 

3280 

0.8787 

0.8817 

R 
(SOLAS2020) 

R 
(SDC3) 

R 
(EMSA3.2) 

RCO 
description 

Baltic 
RoPax 
Med 
RoPax 

DE 
ferry 
SE 
mall 

1700 

0.8398  0.8809  0.8554 

0.8554 

0.8629 

610 

0.7947  0.8426  0.7497 

0.8025 

0.8438 

625 

0.8412  0.8604  0.7517 

0.8038 

0.8441 

incr.  by 

B 
0.8 m 
The ship had 
an 
ample 
margin 
w.r.t. R in its 
initial design 
Deck  raised 
0.3 m 
Deck  raised 
0.3 m 

The  Stockholm  Agreement  and  its  effect  on  overall  risk  was  found  to  be  more 
challenging  to  document.  It  was  observed  that  the  Stockholm  Agreement  in  most 
cases provides the strictest minimum GM requirement at the deepest draughts where 
the  results  are  dominated  by  the  freeboard  in  the  flooded  condition.  However,  the 
contribution to total survivability is not evident. Worth to note, in one case and for one 
risk  control  option  (reducing  freeboard)  it  was  seen  that  the  implementation  of 
Stockholm Agreement did not meet the cost threshold.  

Additional  calculations  of  the  suggested  methods  for  wave  height  limitations  were 
carried  out  on  the  sample  ship  LMG2  for  wave  heights  ranging  from  2.5m  to  4.0m, 
using  the  limiting  GMs  provided  by  the  Stockholm  Agreement  for  the  same  wave 

January 2019    17 

 
 
 
 
 
 
 
 
 Publishable executive summary 

heights.  While  the  Stockholm  Agreement  showed  a  significant  effect  on  the  limiting 
GM, the influence using the suggested methods was found to be minor.  
Risk  control  options  to  study  the  effects  from  deterministic  implementation  options 
were also considered. If longitudinal bulkheads protecting a large space is moved from 
B/5  outwards  to  B/10  compliance  with  SOLAS2020  level  of  R  can  be  achieved  while 
Stockholm Agreement cannot be complied with. Assuming a B/5 penetration in lieu of 
B/10  when  checking  compliance  with  SOLAS  Reg.II-1/B-1/8  was  found  to  be  non-
conclusive with respect to total survivability.   

Comparison of risk 

As  a  supplement  to  the  Impact  Analysis,  a  comparison  of  the  risk  levels  represented 
by the various implementation options for level of R was carried out. The collision risk 
can be expressed and quantified as a function of the attained index A. As the attained 
index  A  is  a  measure  for  the  probability  to  survive  collision  damages,  the  1-A  is 
representing the probability for not surviving the collision damages. Thus, the values 
of 1-A can be used as a measure of the risk level. Correspondingly, the level of R as 
set  forth  by  regulations  or  suggested  as  implementation  options  can  be  used  to 
represent the “target” risk level by the value of 1-R. 

Figure 4 Comparison of risk levels 

As all sample ships are in compliance with current regulations it was observed that: 

•  For  future  new  ships  with  1350  or  more  persons  on  board  SOLAS2020 
represents  a  significant  risk  reduction  compared  with  existing  ships,  i.e.  ships 
complying with SOLAS90+SA or SOLAS2009+SA. 

January 2019    18 

 
 
 
 
 
 
 
 
 Publishable executive summary 

• 

If  the  SDC3  level  of  R  is  implemented  there  would  be  also  a  risk  reduction  in 
the segment below 1,350 POB. 

Evaluation and comparison 

Evaluation  of  the  implementation  options  was  carried  out  by  reference  to  the 
methodology  described  in  the  EU  Better  Regulation  toolbox/3/.  The  parameters 
applied  in  the  evaluation  of  implementation  options  are  effectiveness,  efficiency, 
coherence  and  proportionality.  The  judgement  of  each  implementation  option  in 
relation  to  the  described  parameters  was  noted  to  be  subject  to  a  high  degree  of 
subjectivity.  If  another  group  of  experts  were  involved  the  outcome  could  be  very 
different.  

•  A  level  of  R  according  to  SDC3  was  found  slightly  more  favourable  than 

SOLAS2020.  

•  SOLAS2020  Reg  8  amended  to  B/5  was  found  slightly  more  favourable  than 

current Reg.8 when compared with current SA.  

•  The  expected  Hscrit  method  was  found  to  be  significantly  more  favourable  in 

comparison with the normalised s-factor method. 4 

Summary of findings 

The  current  regulatory  regime  is  complex  and  gives  several  options  to  achieve 
compliance in which the safety level is not easily comparable. 

The objective of this study was to compare the regulatory framework as provided by 
Directive  2003/25/EC  with  the  future  SOLAS2020.  The  results  from  the  sample  ship 
calculation  are  reasonable  clear  for  ships  carrying  approximately  1350  and  more 
persons  on  board.    Compliance  with  SOLAS2020  for  ships  having  a  capacity  larger 
than  1350  represents  a  feasible  solution  that  ensures  that  the  current  safety  level  is 
not  compromised.  For  ships  with  smaller  capacity,  less  than  1350,  the  conclusion  is 
not so evident. 

The  SOLAS90  standard  is  outdated  and  it  is  seen  that  its  application  does  not 
represent a uniform safety level. This is observed from the sample ships results where 
the  A-indices  for  SOLAS90  ships  are  scattered  and  seems  to  indicate  a  decoupling 
between passenger capacity and survivability. 

It is further observed that all regulations, both existing and new include a “gap” at 400 
persons onboard. The deterministic damage scenario; SOLAS90, Reg.8 of SOLAS2009 
and SOLAS2020 all include a step change from one-compartment to two-compartment 
damages when there are 400 persons or more onboard. 

4 The evaluation covers the two methods suggested in the study.  

January 2019    19 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
                                          
 Publishable executive summary 

The impact assessment shows that two of the ships in the smaller than 1350 segment, 
namely  LMG2  and  IF3,  meet  the  level  of  R  according  to  SDC3  cost-efficiently.  The 
LMG2 achieves a high A-index by modification of openings and IF3 by optimising the 
GM  limits.  The  smallest  vessel;  LMG1  meets  SOLAS2020  but  is  not  found  to  meet 
SDC3  by  risk  control  options  meeting  the  cost  threshold.  Several  RCOs  including 
change in breadth, side casing etc were investigated.  

From EMSA III, four ships subject to Impact assessment have risk control options that 
are found to meet the cost threshold and comply with SDC3. Two of them are in the 
region of less than 1000 persons on board.  

The most essential findings from this study that should be considered in the decision 
making are listed in the following. The order of sequence is arbitrarily. 

•  The requirements of the directive 2009/45/EC and 2003/25/EC can be replaced 
by the damage stability framework as per SOLAS2020 but with a level of R as 
per  SDC3  proposal  (same  as  R  in  SOLAS2020  for  ships  of  capacity  exceeding 
1350).  

•  Alternatively, the current regulations can be replaced by the requirements of SOLAS2020, 
provided  that  directive  2003/25/EC  (i.e.  the  Stockholm  Agreement)  is  retained  for  ships 
having a capacity of less than 1350 POB. 

•  Based on the sample ship results there is no evidence that adoption of deeper 
transverse penetration (B/5) in place of the B/10, as required by SOLAS Reg.8, 
would increase the overall survivability, expressed by the attained index A.  

•  The  sample  ship  calculations  do  not  show  that  wave-height  limitations 
accounted for by either the normalised s-factor or expected critical wave height 
have significant impact on the overall survivability as expressed by the attained 
index  A.  The  study  does  not  see  any  merit  in  introducing  separate 
requirements  with  respect  to  the  operational  wave-height  limitations  for 
damage stability in a probabilistic concept.  

January 2019    20 

 
 
 
 
 
 
 
 
 
 
 Publishable executive summary 

References 

/1/ IMO SDC4/INF.4 Small Ro/pax ship stability study submitted by Denmark  
/2/ EMSA III Report, Impact assessment with the EC IA 
/3/  European  Commission.  (2015a).  Better  Regulations  -  Guidelines.  Strasbourg: 
http://ec.europa.eu/smart-

from 

European 
Retrieved 
Commission. 
regulation/guidelines/toc_guide_en.htm 

January 2019    21 

 
 
 
 
 
 
 
 
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doi: 10.2832/682701