Stability and safety of ship

ELSEVIER OCEAN ENGINEERING BOOK SERIESVOLUME 9 STABILITY AND SAFETY OF SHIPS Volume I - Regulation and Operation... ELSEVIER OCEAN ENGINEERING BOOK SERIESVOLUME 9 STABILITY AND SAFETY OF

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STABILITY AND SAFETY OF SHIPS

Volume I - Regulation and Operation

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ELSEVIER OCEAN ENGINEERING BOOK SERIES

VOLUME 9

STABILITY AND SAFETY OF SHIPS

Volume I: Regulation and Operation

LECH K KOBYLINSKI

Technical University of Gdansk, Poland and Foundation for Safety of Navigation and Environment Protection

SIGISMUND KASTNER

Bremen University of Applied Sciences, Germany

OCEAN ENGINEERING SERIES EDITORS

R Bhattacharyya

usNaval Academy,Annapolis, MD, USAM.E McCormickThe John Hopkins University,Baltimore, MD, USA

2005 ELSEVIER Amsterdam - Boston - Heidelberg - London - New York - Oxford - Paris

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© 2003 L Kobylinski and S Kastner.

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This book is dedicated to the seafarers that lost their lives at sea.

SERIES PREFACE

In this day and age, humankind has come to the realization that the Earth's resources are limited In the 19th and 20th Centuries, these resources have been exploited to such an extent that their availability to future generations is now in question In an attempt to reverse this march towards self-destruction, we have turned our attention to the oceans, realizing that these bodies of water are both sources for potable water, food and minerals and are relied upon for World commerce In order to help engineers more knowledgeably and constructively exploit the oceans, the Elsevier Ocean Engineering Book Series has been created.

The Elsevier Ocean Engineering Book Series gives experts in various areas of ocean technology the opportunity to relate to others their knowledge and expertise In a continual process, we are assembling world- class technologists who have both the desire and the ability to write books These individuals select the subjects for their books based on their educational backgrounds and professional experiences.

The series differs from other ocean engineering book series in that the books are directed more towards technology than science, with a few exceptions Those exceptions we judge to have immediate applications to many of the ocean technology fields Our goal is to cover the broad areas of naval architecture, coastal engineering, ocean engineering acoustics, marine systems ~ngineering, applied oceanography, ocean energy conversion, design

of offshore structures, reliability of ocean structures and systems and many others The books are written so that readers entering the topic fields can acquire a working level of expertise from their readings.

We hope that the books in the series are well-received by the ocean engineering community.

Rameswar Bhattacharyya Michael E McCormick

Series Editors

FOREWORD

Naval architecture for a long time concentrated on problems that have a direct impact onthe ship's economics, i.e resistance and powering The importance of stability wasrecognised and shipbuilders from the earliest times knew well that ships have to survivethe perils of the sea Nevertheless, because of a lack of understanding of stabilityprinciples, the losses of ships due to capsizing or foundering were enormous but seafarerswho considered the losses unavoidable accepted this situation

Gradually the understanding of stability developed, but it was not before the second half

of the twentieth century that the tools for "investigating dynamic behaviour of the ship in aseaway became available Until then, stability was investigated in a quasi-static way andthe main problem was development of the methods of calculation of the rightingmoments curve

Nowadays, safety of shipping is the focus of attention In order to promote safety at seathe International Maritime Organisation - IMO was created, (until 1982 called the Inter-governmental Maritime Consultative Organisation - IMCO) This United Nations Agencyfrom the very beginning of its work recognised the necessity to set up internationalstability safety standards This fact increased worldwide interest in stability problems

In many countries research programmes were initiated, and scientists throughout theworld, directly or indirectly, participated in the work of IMO on the development ofstability standards A number of scientific reports were prepared on stability problemsand published in scientific or technical magazines, or presented to IMO Severalinternational conferences, symposia and workshops, particularly devoted to stability andsafety of ships, were organised with hundreds of papers presented The amount ofknowledge on stability, accumulated over the years, is now enormous There is, however,

a lack of publications containing the review of.the knowledge in this particular field.The intention of this book is to fill this gap and to present, as far possible, the state of theart focused on the regulatory, operational and theoretical aspects of intact stability Thebook is addressed to readers who are interested in promoting safety against capsizing,who are involved in research on, and practical application of stability regulations on aninternational or national level, to ship operators and designers and members of themaritime administrations The initiative to write this book belonged to the late N B.Sevastianov, professor at the Kaliningrad Institute of Technology (Russia)

The book is divided in two volumes, I and 2 (These correspond to Volumes 9 and 10 ofthe Elsevier Ocean Engineering Series) The first volume (authored by L Kobylinski and

S Kastner with subtitle "Regulation and Operation") describes the state of the art in thefield of intact ship stability It is focused on how intact safety is promoted; it considersstability regulations; its current state is given an historical perspective The methods used

to develop these regulations are carefully examined Besides regulations, the first volumeaddresses the operational aspect of stability: ocean environment and ship behaviour aredescribed as they are seen from the bridge A large amount of graphical material allows

using the presented information for practical guidance Special attention is paid to board stability measurements and their accuracy •

on-The second volume (authored by V L Belenky and N B Sevastianov with the subtitle

"Risk of Capsizing") is a gathering of today's knowledge for tomorrow's development It

is focused on how risk and reliability can be applied for evaluation and regulation of theintact stability First, the framework of future risk-based stability regulations isconsidered Then the book examines physical phenomena associated with stability lossincluding broaching, greenwater influence and breaking waves action in order to evaluatethe risk of capsizing in different situations Much attention is paid to the mechanics ofcapsizing: as it seems to be necessary for interpretation and validation of numericalsimulation results The latter is meant to facilitate confident applicability of thesemethods for new ship designs

Volume 9: L Kobylinski and S Kastner

Stability and Safety of Ships Volume 1: Regulation and OperationISBN - 0-08-043001-5

Volume 10: V L Belenky and N B Sevastianov

Stability and Safety of Ships Volume 2: Risk of Capsizing

ISBN - 0-08-044354-0

PREFACE

This book focuses on the state-of-the-art in the field of promotion of stability safety Itincludes regulatory and operational aspects of intact stability of ships Ships must be safeagainst capsizing at sea Although capsizing accidents do not happen often nowadays, astability accident is one of the worst things that can happen to a ship In most cases itinvolves loss of life, often all hands aboard and total loss of the ship and her cargo.Catastrophic heel leads to losing cargo, structural damage and serious danger to humanlife

Safety against capsizing or loss of stability accident may be secured by regulatory andoperational means Stability regulations or requirements allow designing stable ships But

it is obvious that no ship can be built that cannot be capsized by mismanagement or badoperation Therefore, operational measures are equally important for the safety as designrequirements This book reviews knowledge, experience and information gathered in bothareas for the last 50 years and presents it in a systematic manner

The authors anticipate that the potential readers of this book are familiar with the basicstability theory and practical methods of calculation Therefore, only very briefreferences to the general stability concepts are included in Part 1 and Part 2 of this book

It is the view of the authors that damage stability problems should be dealt withseparately, therefore they are not included here

Part 1 (written by Professor Lech K Kobylinski, Technical University of Gdansk) onregulatory aspects of intact stability presents the progress on setting stability standardsfrom work at IMO, based on numerous contributions from a large number of shippingnations It discusses various methods used for the purpose of developing stabilitystandards and provides a critical review of standards currently in use As it is obviouslyimpossible to assure safety only by design measures, the importance of operationalrequirements and of the human factor is stressed Prospects of developing improvedstandards of safety against capsizing in various situations and the newest trends toachieve enhanced safety at sea that take into account the above mentioned factors arediscussed

This part is addressed mainly to ship designers, officers of national maritimeadministrations, surveyors and plan reviewing engineers of classification societiesallowing them a better understanding of the background of stability requirements theyshould respect It is addressed also to scientists and administrative personnel who work

on the development of new, or the improvement of, existing safety rules involvingstability Students studying ship stability problems may find useful material for furtherstudy These professionals are assumed to be interested in current national andinternational stability regulations as well as the scientific background of the regulationsthat are in force today

Part 2 (written by Professor Sigismund Kastner, University of Applied Sciences Bremen)

is addressed to shipmasters, nautical ship officers, students of maritime and navalacademies, port authority officials, surveyors and engineers at shipyards, operators andnautical personnel, in particular to lecturers and students of nautical schools It can bealso recommended to ship designers and administrators The structure of Part 2 is based

on his guest lectures at the Wodd Maritime University (WMU) in Malmo (Sweden) TheWMU was established on behalf of the International Maritime Organisation (IMO) in

1983 This lecture entitled "Ship Dynamics and Stability" was given for students inMaritime Education and Training (MET) for almost 2 decades

The safe ship needs the responsible master to make decisions coping with the severe seaenvironment Seafarers have a different background and experience than ship designers,although they both contribute to safe and economic shipping The shipmaster operates the

vessel the shipyard has delivered, hence the specific terms operational stability andsafety were designated The master has to cope with a number of problems with respect

to ship stability The correct loading to fulfil the requirements must be assured Stabilityestimates can diverge from the real ship status due to inherent inaccuracies.Environmental forces are not specifically known whilst at sea Stability risk cannot bejudged solely by experience Operational stability and safety needs special measures,such as awareness of the human factor and enhanced maritime education and trainingwith specific guidance for the ship operator Tools are the development of safetyscenarios in severe situations, ship motion characteristics made available on the bridge,sensor support on the hydrostatic and hydrodynamic status of the ship, and safetymanagement and decision systems with computer support

It has been a demanding but fascinating task to co-operate among the authors and theeditor from four different countries, with the publisher located in another country Theauthors appreciate the support of organisations, such as DAAD (Bonn) in fundingUniversity co-operation and meetings The authors want to express their warmest thanks

to all persons, colleagues and friends "Yho supported them with their comments,discussion, advice, and active involvement at the different stages of writing this book

We appreciate language aid and preliminary proof-reading carried out by SzymonKobylinski (Part 1) and Gregor Berns (Part 2) We are especially grateful to Robert M.Conachey, who performed the language editing Qfthe whole manuscript

We also wish to express sincere thanks to our wives Maryna Kobylinski and MarleneKastner, for their understanding and patience

We are confident that the span of material covered in this new book on stability andsafety of ships can be widely used for reference, study and training in the shippingcommunity, from ship designers to ship operators, from administrators to researchers.Opinions expressed are those of the respective authors and not necessarily oforganisations and institutions they have ever been affiliated with

L Kobylinski, S Kastner,

April, 2003

The views and opinions expressed in this book are solely and strictly those of the authors and do not necessarily reflect those of Technical University of Gdansk, Foundation for Safety of Navigation and

TABLE OF CONTENTS

Series preface vii

Foreword ix

Preface xi

Part 1 Development of stability standards Chapter 1 Historical development and basic stability concepts 3

1.1 History of stability and safety 3

1.2 General 10

1.3 Measures of stability 10

1.4 Effect of heeling moments 15

1.5 Effect of shifting of the centre of gravity 19

1.5.1 Transverse shifting of loads 19

1.5.2 Vertical shifting of loads 21

1.6 Effect of adding or removing loads 22

Chapter 2 Development and present status of stability standards 25

2.1 Concepts of safety and early attempts to establish stability standards 25

2.21MO work on development of stability standards 36

2.3 Status of the international intact stability standards for various types of ships 39

2.3.1 General 39

2.3.2 General recommended intact stability.criteria for passenger and cargo ships 40

2.3.3 Special criteria for certain types of ships 42

2.3.4 Compulsory stability requirements under provisions of SOLAS convention 49

2.4 Operational and constructional requirements in IMO instruments 51

2.5 Review ofIMO instruments related to stability 52

2.6 Possible methods of developing stability standards 52

Chapter 3 Standards based on the consideration of heeling moments 57

3.1 General 57

3.2 Factors causing heeling and influencing ship's stability 58

3.3 Heeling moments caused by shifting the position of the centre of gravity 59

3.3.1 Free surfaces of liquids 59

3.3.2 Icing 61

3.3.3 Water absorption 62

3.3.4 Crowding of passengers on one side 62

3.3.5 Loose goods 63

3.3.6 Water in deck well 66

3.3.7 Suspended loads 70

3.4 Heeling moments caused by external pulling forces 70

3.4.1 Heeling moment created in turning 70

3.4.2 Heeling moments created by a towing hawser 73

3.4.3 Heeling moment created by fishing gear 75

3.4.4 Heeling moment created by the anchor cable 75

3.4.5 Heeling moment at replenishment at sea 76

3.5 Effect of wind and seaway 76

3.5.1 Practical models of the wind effect 76

3.5.2 Wind velocity 78

3.5.3 Wind heeling moment 82

3.5.4 Calculation of rolling amplitude used in the weather criterion 86

3.5.5 The applicability of the weather criterion 89

Chapter 4 Statistical methods of developing stability standards 91

4.1 General 91

4.2 Method of J Rahola 91

4.3 Method applied for development ofIMO stability standards 93

4.4 Results of the analysis of intact stability casualty records and stability parameters 95 4.5 Discrimination analysis 101

4.6 Regression analysis 104

4.7 Statistical evaluation ofthe effectiveness of stability criteria 107

Chapter 5 Probabilistic approach to the development ofstability standards 111

5.1 Introduction 111

5.2 Definition of capsizing and of stability accident 112

5.3 Long-term probability of capsizing 115

5.4 Short-term probability of capsizing 117

5.5 Wave climates 119

5.6 Capsizing scenarios 121

5.7 Probability of capsizing and stability criteria 125

5.8 Risk assessment 127

5.9 Acceptable level of risk 128

Chapter 6 Model tests of capsizing 133

6.1 General 133

6.2 Conditions of similarity and preparation of models 135

6.3 Model tests of capsizing in open waters 138

6.4 Methodology and results of experiments on capsizing in open waters 139

6.4.1 Basic techniques 139

6.4.2 Experiments performed by the University of Hamburg team 140

6.4.3 Experiments performed by the Gdansk Technical University 142

6.4.4 Experiments performed by the University of California 143

6.4.5 Experiments performed by Hokkaido University 144

6.4.6 Results of capsizing experiments in open waters 145

6.5 Model tests of capsizing in towing and seakeeping tanks 149

6.5.1 Tests performed in various countries 149

Contents xv

6.5.2 General observations and guidelines on model tests of capsizing 150

6.5.3 Results of systematic model tests of capsizing in the Hamburg Ship Model Basin 153

6.5.4 Systematic model tests of capsizing carried out in Japan 155

6.5.5 Capsizing model tests in breaking waves 159

6.5.6 Model tests performed in Canada 161

6.5.7 Model tests in beam waves 164

6.5.8 Model tests in following waves 164

Chapter 7 Stability regulations - future outlook 167

7.1 Stability criteria - state of art 167

7.2 System approach to safety against capsizing 168

7.3 System safety assessment 170

7.4 Importance of operational factors 171

7.5 New design philosophy Formal safety assessment 172

7.6 Concluding remarks 174

Part 2 Operational aspects of stability and safety Chapter 8 Operational stability - hydrostatics and hydrodynamics 177

8.1 Ship operation as an interaction process 177

8.2 Ship stability in practice 178

8.3 Basic principle of stability 179

8.4 Hydrostatics and dynamics in ship stability 180

8.5 Definition of ship stability using quasi-static moment balance 182

8.6 Learning from disasters or transfer of theoretical achievements? 184

Chapter 9 Sea environment 191

9.1 The ship in the marine environment : 191

9.2 Wind 191

9.3 Variations in level of sea surface 193

9.4 Regular waves 194

9.4.1 The trochoid 194

9.4.2 Higher order waves Stokes and Airy theory 195

9.5 The sinusoidal wave 197

9.5.1 Basic relationships to describe regular waves in deep water 197

9.5.2 Normal dispersion of a wave field 199

9.5.3 Orbital motion of water particles in a wave 200

9.6 Irregular waves 20 1 9.7 Spectrum formulae by Pierson/Moskowitz and Bretschneider 204

9.8 The JONSW AP seaway spectrum 205

9.9 Maximum wave height in stationary random sea 206

9.10 Long-term statistics of irregular seaway 210

9.11 Wave data from observations 211

9.12 Wave climate 214

Chapter 10 Roll excitation and influence of speed and heading 217

10.1 Motion directions of rigid body 217

10.2 Mass moment of inertia 220

10.3 Linear restoring moment 221

10.4 Natural roll period 222

10.5 Roll damping 223

10.6 GM - To relationship and the rolling period test 225

10.7 Different modes of roll excitation in a seaway 228

10.8 Ship roll in beam seas ·228

10.9 Roll in beam seas at large amplitudes 232

10.10 GZ-variation in longitudinal waves · ·234

10.11 The encounter period of ship and waves 239

10.12 The encounter frequency 243

10.13 Wave group of two regular waves ··· · 243

10.14 Wave encounter of a ship in irregular seas 247

10.15 Wave energy and encounter spectra 251

10.16 Relevant frequencies ofthe spectrum of encounter 252

10.17 The bandwidth of the transformed seaway spectrum 255

10.18 Irregular time series of wave encounter 257

Chapter 11 Resonance and large roll motion · ·261

11.1 Roll resonance 261

11.1.1 Resonance from external excitation in beam seas 262

11.1.2 Parametric roll resonance in following and stem quartering seas 265

11.1.3 Practical method to avoid roll resonance 267

11.1.4 General steps by the master of avoiding resonance 270

11.1.5 Effective GM$ at large roll · ··273

11.1.6 Taking notes on extreme roll ··· ·277

11.2 Modes of capsize in irregular seas : 278

11.2.1 Free running model tests to study capsize in irregular seas 278

11.2.2 Capsizing mode 1: low cycle resonance 280

11.2.3 Capsizing mode 2: pure loss of stability 283

11.2.4 Capsizing mode 3: broach and capsize 285

11.2.5 Detailed dynamics of ship capsize 286

11.2.6 Videos on capsizing model tests 289

11.3 Statistical precision of determining the probability of capsizing in random seas 290 11.3.1 How predictable is capsizing in extreme random seas? 290

11.3.2 Binomial, Poisson and exponential distribution 293

11.3.3 Probability of time until capsize 294

11.3.4 Probability background for random trials 296

11.3.5 Testing of capsizing hypothesis 297

11.3.6 Statistical error type 1 299

11.3.7 Statistical error type II 301

11.3.8 Conclusions for preventing rare events · ·302

Contents xvii

Chapter 12 Forces due to roll motion • 305

12.1 Roll acceleration 305

12.2 Acceleration forces due to roll depending on location within the ship 309

12.3 Acceleration forces on cargo 312

12.4 Resultant force from all motion degrees offreedom 313

12.5 Approximation of dynamic loads on cargo 316

12.6 Simulation of dynamic behaviour of ship and cargo 318

12.7 Ships lost after shifting of cargo and corresponding operational conditions 320

Chapter 13 Measurement and accuracy of stability status 323

13.1 Decision systems based on measurements 323

13.1.1 Purpose of stability measurements 323

13.1.2 Load computer for mass calculations and hydrostatics 325

13.1.3 Loading management supported by measurements 327

13.1.4 Automatic ship inclining to measure the metacentric height GM 328

13.1.5 Monitoring of operational stability 331

13.1.6 Voyage data recorder for monitoring casualties 334

13.1.7 Ship routeing 334

13.1.8 Measurement of actual ship stability in waves 337

13.1.9 Mathematical decision systems and artificial intelligence 338

13.1.10 Economic advantages of stability control systems 341

13.2 Accuracy of the estimation of ship stability status 342

13.2.1 Historical background 342

13.2.2 Basic requirements for a measuring system in ship inclining 343

13.2.3 Theory of ship inclining measurements with a pendulum 343

13.2.4 Dynamic response of heel gauge aboard the ship 344

13.2.5 Correct reading of bridge pendulum 348

13.2.6 Laboratory testing of gauge accuracy 349

13.2.7 Measuring errors : 349

13.2.8 Accuracy of heel measurement 351

13.2.9 Accuracy of heel measurement for ship yard inclining 353

13.2.10 Practical length of pendulum 354

13.2.11 IMO requirements for ship inclining test 355

13.2.12 Conclusions on heel measurement with pendulum 356

13.2.13 Error statistics of operational ship inclining 358

Chapter 14 Safety management and operational requirements 359

14.1 Safety management of ship stability 359

14.1.1 Need to introduce a ship stability management system 359

14.1.2 Tools of an efficient stability management 360

14.1.3 The Master's range of judgement for operational stability assessment 360

14.1.4 Seakeeping guidance and survivability criteria 362

14.2 Guidelines on the in-service ship stability 368

14.2.1 Purpose of guidelines for operational stability 368

14.2.2 Loading and stability manua1 369

14.2.3 Guidelines on the management of ship stability 370

14.2.4 Guidance to the Master for avoiding dangerous situations in following and quartering seas 371

14.2.5 International safety management code (ISM) 378

14.3 The human factor maritime education and training 379

14.4 Operational stability in the future- a wishful forecast 382

References 383

References on international documents 404

Documents IMO 404

Documents of other international organisations 406

Stability requirements of various countries 406

Subj ect index 409

Part 1

Development of Stability Standards

Chapter 1

Historical Development and Basic Stability Concepts

1.1 History of Stability and Safety

Seafaring was always a dangerous enterprise involving serious risk of losing life andproperty, and also risk of pollution ofthe environment

Looking back at the history of seafaring, one may find that in old times perils of the seawere well recognised and great risks to which ships were subjected at sea were in a wayaccepted In fact, even in the nineteenth century people risking a sea voyage consideredthemselves to be very fortunate if they arrived safely at the port of destination and for that

a vote of thanks to God had to be offered The reflection of this situation could be foundeasily in the literature, art and tales of seamen but also in the reports on casualties,although systematic statistics of casualties have been carried out only recently

The industrial revolution of the nineteenth century and rapid expansion of seatransportation, seafaring and shipbuilding that followed caused the issue of marine safety

to become more important From one side, in view of the growing number of ships at sea,

a very high risk involved in seafaring could not· be accepted On the other hand, progress

in marine technology provided realistic possibilities to improve safety against capsizing

or foundering

From the oldest times shipbuilders were fully aware that ships must be stable at sea.Seneca in the first century A.D wrote: " Navis bona dicitur, non que prestiosis coloribuspicta est sed stabilis et firma et iuncturis aquam exc1udendibus spissa, ad ferendumincursum maris solida, velox et non sentiens ventum "(quote after Gleijeses [1945]).The knowledge of how to build safe ships was, however, based solely on experience that, inturn, was based on methods of "trial and error" where "errors" were sea disasters Lessonsfrom sea disasters materialised in rough recommendations on appropriate proportions anddimensions of the ship's hull and its construction that would safeguard stability and goodseakeeping qualities These recommendations were passed from generation to generation ofshipbuilders and were guarded in extreme secrecy Naval architecture was really a craft andnot a science Only in the second half of the nineteenth century did science began to affectshipbuilding appreciably, although Bouguer [1746] laid down the fundamentals of navalarchitecture much earlier

In view of the lack of knowledge about the basic laws concerning stability of floatingbodies, the first recommendations on how to build safe ships referred to stability in theindirect way by requiring sufficient height of the deck above water With the properrecommendations regarding distribution of weights and the form of the underwaterportion of the ship, this in fact, secured sufficient stability in most cases.

The oldest traces of safety recommendations refer to the prevention of overloading of ships,i.e to the freeboard if we use the modem terminology In a document found in Tunisia dated

to the first century B.C., containing the contract for transportation of goods by sea, theskipper solemnly promised not to take any additional load over the agreed quantity Theload line mark was known already in the middle ages The Venetian code of maritime lawfrom 1255 required the insertion of the load line mark in the form of an iron cross-nailed tothe ships' side [Krappinger 1964]

In the second half of the eighteenth century Lloyd's Register of Shipping issued the firstrecommendation on the magnitude of the freeboard - it required 2 to 3 inches per foot ofthe height of the hold Lloyd's subsequently amended the recommendation Also theLiverpool Underwriters Society had issued other more elaborate recommendations muchearlier [Cowley 1988]

Wooden ships, however, were built according to well-grounded, traditional andexperienced practices and were comparatively safe The introduction of steel as amaterial for ships' hulls was an important new development, but with no previousexperience, it caused the number of casualties to quickly increase The public reaction tohigh losses forced the British Government to form the Marine Department of the Board

of Trade, but its resources were small and activity limited Only in 1864, in view offurther pressure of public opinion, a committee was created to investigate this situation.The committee presented its report in 1867 proposing draft freeboard standards

In the following years, there was a rapid development of freeboard rules In thisconnection, the name of Samuel Plimsoll (1824 - 1898) has to be mentioned He led thecampaign aimed at increasing the safety of ships and proposed the load line mark in theform used to present days known as the "Plimsoll disc" [Alderman 1972] The chronicle

of events related to the development ofload line rules is as follows:

1876 - Merchant Shipping Act which required positioning of the load mark on all Britishships over 80 GRT

1885 - Creation of Load Lines Committee with Lloyd's Register of Shipping, whichdeveloped the first load line tables

1894 - Second Merchant Shipping Act containing load lines rules compulsory in Britain

up tb 1930.

1903 - See-Berufsgenossenschaft issued first German regulations on load lines

1927 - Load Lines Committee prepared draft international load lines rules

1930 - First International Convention on Load Lines adopted (LL Convention)

It has to be stressed that in spite of the passing of the two important Merchant ShippingActs of 1876 and 1894 under pressure of public opinion and in spite of the SamuelPlimsoll campaign, the opinion of legislators was against introducing any regulations In

1866 the Head of the Marine Department, Thomas Gray at a conference, expressed thephilosophy of the legislators in the following terms: "there can be no question thatgovernment interference is not only unnecessary, but may really become vicious if itattempts to attain an end by official inspection and supervision that can be better attained

by the development of free healthy competition and by the self-interest and emulation ofthe trader, since it fetters the development of trade, it stands in the way of theadvancement of science, and it interferes to the prejudice of the liberty of the subject ".The Board's Permanent Secretary, at the same meeting, said that: "they must look to self-interest and not to government regulations, as the great element of safety of life on boardship" The ship owners agreed with him that: "ship owner and ship master together arevery much better judges of what ought to be done to a ship than anybody else canpossibly be" (quoted after [Cowley 1988])

Recalling these opinion that result from liberal ideas of the nineteenth century, one mustremember appalling conditions present on board cargo and passenger ships, wheresometimes one third of the emigrants died during the voyage and numerous casualtiesoccurred Legislators and ship owners gave up only under great pressure from publicagitation in response to the high death toll

The development of the freeboard rules only in an indirect way inadequately securedsafety against capsizing The LL Convention referred directly to one aspect of stabilityonly, viz it required the master must be supplied with information concerning stability.The most important international instruments, viz International Convention for theSafety of Life at Sea (SOLAS Convention) did not include requirements concerningstability either, with the exception of a similar provision as in the LL Convention

The history of SOLAS Conventions was very turbulent The SOLAS Conventions fromthe very beginning included subdivision and damage stability requirements that were to agreat extent influenced by sea disasters

It is known that by the Middle Ages, it was required in China that junks must be fittedwith collision bulkheads in order to secure surVivability in case of collision Hulls ofwooden ships were rather resistant to damage and as it was comparatively easy to plumb

a hole, the installation of watertight bulkheads was considered not important Along withthe substitution of steel for wood in hull construction the situation changed and damagestability became important elements of safety

The British Merchant Shipping Act from 1854 included probably the first requirementsconcerning subdivision It required that passenger ships be fitted with a collisionbulkhead and two bulkheads around the machinery space In 1891, the Committee of theBritish Board of Trade proposed subdivision and damage stability rules for passengerships (no one bothered at the time about cargo ships and their crews) where a two-compartment standard was required The rules were, however, considered by themaritime world unnecessarily severe and were never implemented Only after severalserious disasters, where ships foundered due to lack of proper subdivision, did publicopinion force maritime authorities to take actions (ON WO foundered in 1894 with 250lives lost, 1897 ELBE with 355 lives lost, 1912 - TITANIC *with 1513 lives lost, 1913-

*) Different sources quote different number of lives lost The number 1513 is quoted after Encyclopedia

EMPRESS OF IRELAND with 1024 lives lost) The TITANIC disaster particularlycaused sharp reaction of the public Although many lives were lost at sea in minorcasualties, public opinion was always much more sensitive to serious casualties involvingheavy losses than to regular losses of lesser magnitude Moreover the TITANIC was aflagship and was claimed to be unsinkable and was on her maiden voyage with manypersonalities on board It was that which shook the marine world and the general public.The main cause of heavy loss oflife was insufficient life boat capacity, however.

The Court of Formal Investigation ofthe casualty recommended that boatage be providedfor all persons on board as well as effective subdivision to standards determined by thenewly appointed Bulkheads Committee The final recommendation was that the UnitedKingdom should call an International Conference to consider and possibly agree upon anInternational Convention

Between 12 November 1913 and 20 January 1914 the first International Conference onthe Safety of Life at Sea took place but the prepared text of the Convention was neverratified because of the outbreak of the First World War It was not until 1929 the SOLASConference took place and adopted subdivision and damage stability regulations basicallyfollowing the rules of its unratified predecessor Further International Conferencesadopted the 1948, 1960 and 1974 Conventions, Protocols to the Conventions and severalamendments

The 1960 SOLAS Conference adopted an important recommendation requestingIMCO**) to initiate work on the development of subdivision and damage stabilityregulations based on probabilistic approach both for passenger and cargo ships, whichsubsequently were developed and adopted by the IMO Assembly by Resolution A.265(VIII) The 1960 SOLAS Conference recommended also that IMO should develop intactstability standards for passenger, cargo ships and fishing vessels IMCO, (IMO) was thesole United Nations agency responsible for marine safety It commenced its work in 1959after its convention came into force This was an important turning point in the promotion

of maritime safety, and IMO through its Committees and Subcommittees started

developing safety requirements in various fields of maritime activity, inter allia in the

field of subdivision, load lines and stability

As it was already mentioned the SOLAS Conventions did not directly refer to intactstability, except that they included the provision concerning stability information that has

to be supplied to the master

Adoption of the afore-said recommendation appeared to be an important turning point inthe work on the development of stability standards as for the first time the need forinternational stability standards was articulated and also a scientific approach to thedevelopment of safety standards was recommended At the same time the subdivision anddamage stability requirements of the 1960 SOLAS Convention were strongly criticised asbased on vague assumptions involving several "factors" intended to take account of shipcharacteristics in an approximate way Nevertheless a long time passed until the

**) IMCO- Intergovernmental Maritime Consultative Organisation In 1982, it changed its name to the International Maritime Organisation -IMO In the text, references are made to IMO irrespective of whether

preference for a probabilistic approach to subdivision was fully recognised andprobabilistic subdivision standards were developed [IMO, Resolution A.265(VIII)].Further work on subdivision and damage stability concentrated on the development ofstandards for cargo ships that subsequently were included in the amendments to theSaLAS Convention In view of several serious casualties with Ro-Ro ferries and inparticularly after the casualties of the HERALD OF FREE ENTERPRISE, attention wasalso drawn to the safety problems of Ro-Ro ships and respective amendments to theSaLAS Convention were developed and adopted After the ESTONIA disaster, furtheramendments to the SaLAS Convention were adopted related to the safety of Ro-Ropassenger ships.

Development of regulations securing safety against capsizing encountered seriousproblems This might not be simple, because of the extreme difficulty in dealing with thecomplicated phenomena of motion of ships amongst the waves Also, opinions wereexpressed that the responsibility for securing sufficient stability should be left to themaster With a series of stability accidents, particularly with small vessels and with theview that many new ships with proportions and arrangements different from those ofconventional ships had been built the need to develop intact stability criteria was moreobvious

Safety against capsizing was, however, recognised a long time ago and theoretical andpractical investigations of stability problems have a long history

Probably Bouguer [1746] in his previously mentioned book already was the first tointroduce the concept of metacentric height as a measure of stability Jean Bernouilli[1714], Euler [1749], Attwood [1796] and others referred to stability without, however,proposing any standards In particular Daniel Bernouilli [1757] developed the theory ofrolling which was followed up to the middl~ of the nineteenth century The first whointroduced the concept of dynamic stability was Moseley [1850]

The metacentric height was considered as a, sufficient measure of stability up to 1870.The tragedy of the naval ship "CAPTAIN" which capsized in Biscay Bay during a squalldrew attention of naval architects to stability at large angles of heel This casualty isworth recalling

"CAPTAIN" was a low-built ship built by Coles Her righting arm curves are shown infig.I.I In the same figure the righting arm curves of the ship "MONARCH" are shown

"MONARCH" built by Reed was of traditional design having a high freeboard.Metacentric heights of both ships were not very different, but the range of righting armcurves was widely different Both ships were sailing alongside in Biscay Bay in moderateweather conditions when during a short squall accompanied by heavy rain "CAPTAIN"capsized and disappeared almost instantly taking with her all hands to the bottom of thesea [Brown 1981]

Admiral Reed warned the British Admiralty during the construction of CAPTAIN thather righting moments curve is insufficient but his warnings were not heard After thedisaster, the importance of stability at large angles of heel was recognised, and therighting moment curve was widely known as Reed's curve [Reed 1868]

By the end of the nineteenth century the first criteria regarding minimum values ofmetacentric height and of some other stability parameters were proposed Theseproposals are discussed in detail in Chapter 2.1 The proposals were, however, neverofficially accepted and remained as loose recommendations without any legal power Theactivity in developing and proposing such criteria was always greater after seriousstability casualties occurred For example, in 1894 during the stormy night of 22/23December, six German fishing boats capsized and foundered in the North Sea Followingthese casualties the German Professional Mariners' Association initiated investigationsthat finally resulted in recommending minimum values of the righting arms for fishingvessels [Herner, Rusch, 1952].

It has to be noted that in 1939, Rahola developed a method of establishing minimumvalues of stability parameters based on the analysis of casualty records [Rahola 1935,1939] The criteria recommended by him were used for a long time in several countriesuntil 1968, when an international recommendation on stability criteria was finallydeveloped by IMO, using a basically similar method

The first official national standards and requirements concerning stability were developedand introduced in 1947 by the Russian Register of Shipping They were based on theprinciple of equalisation of the wind heeling moment wi'th the righting moment of theship (see Chapter 2.1)

After IMO had started working on the development of the international standards theactivity in the field of stability of ships increased greatly Work of the Organisation ondevelopment of stability standards is discussed thoroughly in Chapter 2.2 This workultimately resulted in adoption of several recommendations and codes that includedstability standards for various types of ships This was possible, because researchprogrammes on stability were initiated in many universities and research organisationsthroughout the world

Until the end of the 1950's stability was treated in a static or quasi-static way andresearch was concentrated on the improvement of methods of calculation of righting armcurves and on evaluation of static or dynamic heeling moments Rolling of ships in waveswas considered on the basis of the Froude-Krylov method, which assumed regular waveand small inclinations After the famous paper by St Denis and Pierson [1953] had beenpublished, the tool was available to investigate stability of ships in a seaway where the

ship could be treated as a dynamic system The probabilistic approach to safety againstcapsizing was also pursued and nonlinear phenomena investigated.

The results of these investigations were published in numerous papers and presented atspecialised international conferences on stability The first International Conference onStability of Ships and Ocean Vehicles (STAB) was organised in Glasgow in 1975.Subsequently, further STAB Conferences were held in Tokyo in 1982, in Gdansk in

1986, in Naples in 1990, in Melbourne, Florida in 1994, in Varna in 1997 and inLaunceston, Tasmania in 2000 The eighth STAB Conference is scheduled for the year

2003 and it will be held in Madrid In 1990 also the International Stability Forum wascreated with the objective to pursue work on stability problems internationally

Apart from the STAB conferences, several international symposia and workshops werealso organised in a few countries, with some meeting regularly In Kaliningrad (Russia)the Workshop on Physical and Mathematical Modelling of Vessel's Stability in a Seawaywas held in 1993 That was followed two years later by the Symposium on Ship Safety in

a Seaway in memory of Professor N B Sevastianov In 1993 also, the u.S Coast Guardorganised a Vessels Stability Symposium in New London, Connecticut

In 1995, the first International Workshop on Contemporary Problems of Stability andOperational Safety of Ships was organised in Glasgow This was followed by the secondone in Osaka (1996), the third in Crete (1997), the fourth in St Johns (1998), and the fifth

in Trieste (2001) Also the International Towing Tank Conference (ITTC) created theStability Committee to study first of all problems related to mathematical modelling and

to model tests of stability

Comprehensive research programmes on stability were accomplished in severalcountries The results of these programmes are elaborated on in subsequent chapters.However, two such programmes sponsored by the British and Norwegian governmentswere aimed at developing "rational" or "improved" criteria and included a wide range ofsubjects The results of the British SAFES HIP project were presented at a speciallyorganised international conference organised by RINA in 1986 Planning andsupervision of the Norwegian project was performed by an international scientificCommittee consisting of several specialists on stability problems

It is obvious that the main cause of the increased activity in the field of was the fact thatIMO started in 1962 work towards development of stability standards Although theresults achieved in this work are remarkable and from a practical point of view anintroduction of the international stability standards resulted in increased safety againstcapsizing, there are still many problems to be solved until an ultimate solution, which isnot yet available, can be obtained

This tremendous effort which certainly resulted in a much better understanding ofstability problems and capsizing phenomena showed, however, that problems of stability

of ships in a seaway including safety against capsizing are extremely complicated and thetask of development of criteria of surviving based on risk of capsizing taking intoconsideration all possible situations which may be encountered during the vessel'slifetime is still far from being accomplished

Chapter 2

Development and Present Status of Stability Standards

2.1 Concepts of Safety and Early Attempts to Establish Stability Standards

In the past the ability to build ships that were safe and had good seakeeping qualities wasbased entirely on experience gained over a long time and passed on from generation togeneration The dimensions and proportions of the ship to be built, ensuring stability andseaworthiness, were estimated on the basis of this experience If an accident happened,the shipbuilders learned from their lesson and improved the construction of subsequentships

This was the oldest concept of safety, where safety was achieved by the "trial and error"method

This traditional way of building ships has survived to this day in many developingcountries, where small ships have been built without any drawings and calculations andthe design was solely based on experience This method however, cannot be accepted anymore, although lessons from accidents still have to be taken in order to improve shipdesign for safety We may only mention the HERALD OF FREE ENTERPRISE;ALLEXANDER KIELLAND or ESTONIA casuc;lltiesfollowing which several measuresaimed at increasing safety were undertaken

The method where safety was related to ship size and proportions was used byclassification societies not so long ago, where their regulations specifying hull scantlingswere related to ship parameters Krappinger [1967] defined this concept of safety as theassignment of hardware and this concept is often used as a basis of simple safetyrequirements up to this day

A more advanced concept of safety does not include assignment of dimensions orproportions of an object, but assignment of its physical properties In respect to stability,this means assignment of values of metacentric height or of the righting arms at variousangles of heel The method of estimation of these values could be, however, the same, i.e.the trial and error method All older stability criteria or recommendations were actuallybased on this method

The method of establishing criteria in the form of the hardware could be improved ifthere were sufficient statistical data and if these data are methodically and scientificallyanalysed There are known cases of the application of this method comparatively recently(e.g IMO, Resolution A.207 (VII»