intact stab

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For reasons of economy, this document is printed in a limited number. Delegates are kindly asked to bring their copies to meetings and not to request additional copies.

INTERNATIONAL MARITIME ORGANIZATION

IMO

E

MARITIME SAFETY COMMITTEE 78th session Agenda item 24

MSC 78/INF.5 16 December 2003 ENGLISH ONLY

WORK PROGRAMME

Revision of the Code on Intact Stability

Submitted by Germany

SUMMARY Executive summary:

This document informs on a Formal Safety Assessment on making mandatory the stability criteria contained in the IMO Code on Intact Stability (IS Code), carried out by Germany

Action to be taken:

Paragraph 2

Related documents:

MSC 78/24/1

1 The following Formal Safety Assessment is directed exclusively to the cost-benefit relation of the proposal to make the design criteria of the IS Code mandatory as contained in document MSC 78/24/1. It does not address the substance or appropriateness of the criteria themselves, nor does it consider the cost-benefit relation of other possible measures for enhancing the safety against capsizing of ships. Action requested of the Committee 2 The Committee is invited to take note of the information provided in the context of its consideration of document MSC 78/24/1.

***

MSC 78/INF.5

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ANNEX

Formal Safety Assessment on the

Making Mandatory of Stability Criteria contained in the

IMO Code on Intact Stability

MSC 78/INF.5 ANNEX Page 2

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Table of contents

Introduction and scope of Formal Safety Assessment................................................................. 4

Identification of hazards................................................................................................................. 5

• General mechanism of stability accidents ............................................................................ 5

• Stability accidents (case studies) .......................................................................................... 6

• "Lime Bay" .......................................................................................................................... 6 • "Sun Breeze"......................................................................................................................... 8 • "Dongedijk" .......................................................................................................................... 9 • "X" (anonymous report) ..................................................................................................... 10 • "Rautz"................................................................................................................................ 11 • Present status of the IMO Intact Stability criteria .............................................................. 12

• Relation to SOLAS and other Conventions........................................................................ 12 • Status perceived by ship owners and mariners ................................................................... 13 • Status perceived by carriers (charterers) and shippers ....................................................... 13 • Status perceived by flag State authorities........................................................................... 14 • Status perceived by port State authorities........................................................................... 14 • Status perceived by classification societies and underwriters ............................................ 14 • Status perceived by naval architects ................................................................................... 14 • National stability criteria .................................................................................................... 15

• Australia.............................................................................................................................. 15 • Germany ............................................................................................................................. 15 • Japan ................................................................................................................................... 16 • Sweden................................................................................................................................ 17 • USA .................................................................................................................................... 17 • Common practice of ship stability management ................................................................ 18

• Ships with critical operational stability .............................................................................. 18 • The role of the owner, the charterer and the shipper .......................................................... 19 • On-board stability monitoring and assessment................................................................... 20 • Practical consequences of deficient departure stability ...................................................... 22 • Summary of hazard identification ...................................................................................... 23

Risk assessment ............................................................................................................................. 24

• Methodology....................................................................................................................... 24

• Hazard and Operability Study (HAZOP) ........................................................................... 25 • Event Tree Analysis of stability accidents (ETA) .............................................................. 26 • Average cost of stability accidents and monetary risk ....................................................... 29 • Estimated consequences of mandatory IMO Intact Stability criteria ................................. 30

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• Indirect influence of mandatory criteria ............................................................................. 30 • Reduction of calculated risk ............................................................................................... 31 • Summary of risk assessment............................................................................................... 31

Risk control options ...................................................................................................................... 32

• Improvement of ship design and equipment....................................................................... 32

• Ship design ......................................................................................................................... 32 • Equipment for control of stability....................................................................................... 33 • Improvement of ship operation........................................................................................... 34

• Enforcement of SOLAS Regulation VI/2 (information from the shipper)......................... 34 • Review of loading and stowage procedures ....................................................................... 34 • Review of education and training of masters and deck officers ......................................... 34 • Enhancement of administrative supervision....................................................................... 35

• Flag state control ................................................................................................................ 35 • Port state control (PSC) ...................................................................................................... 36 • Revision of the IMO Code on Intact Stability .................................................................... 36

• Re-structuring the IS-Code................................................................................................. 36 • Mandatory status of the stability criteria ............................................................................ 38 • Summary of risk control options ........................................................................................ 38

Cost-benefit assessment ................................................................................................................ 39

• Benefit of mandatory intact stability criteria ...................................................................... 39

• Regulatory consequences ................................................................................................... 40

• Revision of the IMO Intact Stability Code ......................................................................... 40 • Revision of SOLAS Chapter II-1 ....................................................................................... 40 • Revision of national regulations ......................................................................................... 41 • Consequences for ship design and classification................................................................ 41

• Consequences for ship operation ........................................................................................ 41

• Strengthening of legal demands on shippers and carriers .................................................. 41 • Standardisation of key shipboard operations regarding stability management .................. 42 • Optional supervision by port state authorities .................................................................... 42 • Summary of cost-benefit assessment.................................................................................. 42

Recommendations for decision making ...................................................................................... 43

Literature....................................................................................................................................... 44


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Introduction and scope of Formal Safety Assessment The Code on Intact Stability for All Types of Ships Covered by IMO Instruments (IS-Code), was adopted by the IMO Assembly in Resolution A.749(18) in 1993 and amended by Resolution MSC.75(69) in 1998. It is a non-mandatory code. The IS-Code in its present form contains general provisions against capsizing, distinguished design criteria for all ships and for certain types of ships, and specific guidance on certain issues related to stability. The structure of the IS-Code is shown by its chapters as follows: Chapter 1 – General Chapter 2 – General provisions against capsizing and information for the master Chapter 3 – Design criteria applicable to all ships Chapter 4 – Special criteria for certain types of ships Chapter 5 – Icing considerations Chapter 6 – Considerations for watertight integrity Chapter 7 – Determination of light-ship displacement and centres of gravity Annex 1 – Detailed guidance for the conduct of an inclining test Annex 2 – Recommendations for skippers of fishing vessels on ensuring a vessel's endurance in

conditions of ice formation Annex 3 – Determination of ship's stability by means of rolling period test (for ships up to 70 m

in length) The presently non-mandatory status of the IS-Code is considered as unsatisfactory in the light of its importance for appropriate ship design and safe ship operation. Thus a proposal for re-structuring the IS-Code is envisaged having in view • a mandatory part A, containing all design criteria, • a recommendatory part B, containing guidance and explanations, and • a recommendatory part C, containing explanatory notes on compliance with the criteria. This step would require an appropriate amendment to SOLAS and/or ILLC Conventions. IMO has decided to back future decisions on safety regulations by a specific Formal Safety Assessment (FSA). FSA is "a structured and systematic methodology, aimed at enhancing maritime safety, including protection of life, health, the marine environment and property, by using cost-benefit assessment". The FSA methodology shall consist of the five steps: 1. Identification of hazards 2. Risk assessment 3. Risk control options 4. Cost-benefit assessment 5. Recommendations for decision making

The following Formal Safety Assessment is directed exclusively to the cost-benefit relation of the envisaged decision to make the design criteria of the IS-Code mandatory. It does not address the substance or appropriateness of the criteria themselves, nor does it consider the cost-benefit relation of other possible measures for enhancing the safety against capsizing of ships.

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Identification of hazards General mechanism of stability accidents The purpose of the existing Intact Stability Code, as lined out in its paragraph 1.1, is to "recommend stability criteria and other measures for ensuring the safe operation of all ships to minimise the risk to such ships, to the personnel on board and to the environment". The nature of this risk is not specified, but can be generally assumed as the risk of capsizing. Consequently, the Code provides stability criteria, which are to be uniformly used for ship design, for ship approval and for ship operation. It further provides instructions and guidance for determination of light ship parameters, of effects of free surfaces of liquids in tanks, considerations for watertight integrity (recapitulation of relevant SOLAS and ILLC Regulations) and general provisions against capsizing and information for the master. However, the typical mechanisms of capsizing of ships are not specified in the Code. There is, for example, no particular clause, which limits the applicability of the stability criteria to situations where cargo and other masses on board do not shift, except for the crowding of passengers. There is also no clear definition of the "stability accident" in the Code. But such a definition is necessary for the identification of hazards within a Formal Safety Assessment (FSA) on the legal status of IMO Intact Stability criteria. For the purpose of this study, a "stability accident" shall be understood as an incident, where • a ship capsizes, or • a ship suffers a large heeling angle, or • a ship suffers heavy rolling. There are many causes for stability accidents, like • neglecting minimum stability criteria (design and operation), • faulty assessment of stability, • excessive stability (design and operation), • heavy weather (wind and waves), • ingress of water (leakage, fire fighting), • increase of top masses (water soaking, icing), • grounding, docking, • towing operation, • changing course at high speed, • transverse shifting of masses (cargo etc.). While the first nine causes can be referred to as primary causes, the transverse shifting of masses is mainly a result of one of those, but often has the deciding impact. The consequences of a stability accident under the above definition are in line with the risks to be minimised according to paragraph 1.1 of the Code, namely • threat to persons (health or life), • damage to or loss of cargo, • damage to or loss of the ship, • damage to the environment.


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Figure 1.1: Stability accident in port

• Stability accidents (case studies) In this chapter a number of cases are presented for demonstrating the variety of influences, which contribute to a stability accident, and the consequences, which such accidents may have.

• "Lime Bay" 1 On Saturday, 8th February 1997, at about 04.00 hours, the Antigua and Barbuda flag container feeder vessel "Lime Bay" (Loa = 85 m) was about to enter the port of Alexandria in Egypt with a full cargo of containers. Last loading port was Damietta, Egypt. The weather was fine and the sea smooth. A few minutes after the pilot had boarded the vessel and the speed was brought to about 5 knots again, a sudden list of 15° developed without any external reason. The pilot prohibited to enter the port in this condition and left the ship. At about 05.00 hours two tug boats took the vessel in tow and she berthed at about 08.30 with her starboard side alongside a jetty. The port list had grown in the mean time. The master, uncertain about the reasons of the list, decided to order a careful counter-flooding by means of the starboard side tank. The vessel righted up after some minutes, but then fell over to the starboard side with a list greater than before. Containers of the top tier on deck came to rest on the jetty. Further flooding was not stopped because the chief engineer had already left the engine room. The master, the chief officer, the chief engineer and the other three crew members jumped ashore at this time. Port authorities assumed the responsibility for initiating the salvage operation. But before any measures had been effected the vessel sank to the bottom of the harbour due to water ingress through various vent pipes and other small apertures. Later the vessel was unloaded, refloated, and taken to the Netherlands for repair by end of September 1997. An investigation of this accident was carried out in Egypt and later in Emden, Germany, because the master and the chief officer were holding German Certificates of Competence. The following findings were reported:

• The ship was equipped with an approved loading and stability computer. The software was, however, not compatible with the planning computer of the charterer's agents in Damietta. Thus, a precise pre-calculation of stability for the departure condition had to be left until the ship had arrived in Damietta and was actually loading.

1 Report by Seeamt Emden, Germany, 17.12.1997 – DI 13/97 E

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• The amount of cargo to be loaded, according to the stowage plan issued by the charterer's agents, was 2545 t. The chief officer calculated the stability, trim and draught and informed the master that all were within acceptable limits.

• After leaving the port of Damietta at about 10.00 hours on Friday, 7th February, the chief officer informed the master that his final draught reading indicated that about 120 t excess cargo were on board. The master was concerned and informed the charterer. However, there were no signs of difficulties with the behaviour of the ship and the master decided to continue heading for Alexandria.

• A re-calculation of stability, carried out by a British consulting company on behalf of the charterer, revealed a GMC = 0.15 m for departure using the cargo data as supplied in the stowage plan. This GMC-figure was insufficient to satisfy the IMO Intact Stability criteria.

• Another calculation by the same company, using identical stowage positions but the weight figures from the cargo manifest, which was not available to the charterer's agent at the time of cargo planning, revealed a GMC = − 0.00 m for departure with 2801 t of cargo.

• Later, a further re-calculation was carried out by an expert from Germanischer Lloyd with updated cargo weights and a reasonable assumption of the somewhat lower centre of gravity of containers. The result was GM = 0.08 m with 2813 t of cargo, yielding a GZ30° of 0.02 m. This condition was assumed to be the closest approximation to the actual condition at departure from Damietta.

Figure 1.2: Accident of "Lime Bay"

It appears, that this accident was caused by wrong cargo weight figures in the first place. But there was also a lack of diligence within counter-checking the cargo intake by draught readings, not to mention the possibility of checking the actual stability by an in-service measurement at a reasonable time prior to completion of loading. It remains further unclear, whether the chief officer and the master were fully aware of the interpretation and application of the IMO Intact Stability criteria. Finally the measures of controlling the initial list to port were obviously not taken in a proper way.


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• "Sun Breeze" On Saturday, 21st August 1999, at 18.00 hours, the Panamanian flag general cargo vessel "Sun Breeze" left the West Australian port of Bunbury with a full cargo of packed sawn timber. The weather was fine with a gentle north-east wind of Beaufort 2. After the harbour master had disembarked the engine revolutions were increased to sea speed and the 3rd mate changed from manual steering to auto pilot. Due to some disorder the vessel started turning to starboard and the 3rd mate changed back to manual steering. In his attempt to bring the vessel back on course a list developed, first to port and then to starboard. The master, who had left the bridge immediately before this incident, returned and found a list of about 15° to 20°. He stopped the engine while the list increased to 30° and settled at about 25°. Nine packs of timber stowed on deck were lost overboard from hatch No. 1 at this time. A distress message was sent at about 18.48 hours and the anchor let go at about 19.00 hours. The master ordered all personnel to muster at the life boat deck with lifejackets. After an initial check for damage the master decided to ballast Nos. 3 and 4 side tanks for correcting the list back to 5° starboard and lowering the ship's centre of gravity. During the late evening some crew members were taken off the vessel and the harbour master, who had returned to the scene, investigated together with the master how to handle the case. The owners of "Sun Breeze" arranged for a surveyor to board the vessel next day. After a thorough establishment of the ship's stability by the surveyor appointed by the owner's P&I Club the vessel was permitted to re-enter the port of Bunbury, where the cargo was restowed, existing gaps filled and chocked off, in holds as well as on the hatch tops. The vessel eventually sailed on 25th August and arrived on 10th September at the port of destination in China without further incident.

Figure 1.3: "Sun Breeze"; Loa = 109.3 m, B = 19.8 m

The Australian Transport and Safety Bureau investigated the case2 and found the following facts from ship's documents and interviews with the master, the mate and the 2nd and 3rd mates: • The master's voyage instruction were to load a minimum of 10,000 m3 of timber with a

stowage factor of 1.6 m3/t. The cargo description indicated that there were in total 2,140 packs with 14,354 m3 net to load. Loading cargo on the hatch top appeared necessary.

2 Report No. 150 of the Australian Transport Safety Bureau, June 2001

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• The packages of timber were not marked with their weights as required by Australian law. The gross stowage factor turned out to be about 2.35 m3/t, partly due to lost or broken stowage under deck.

• The master had asked the mate to calculate the stability for departure. He required to maintain a GM of 0.50 m as a minimum. The calculation had to be carried out manually. A righting lever curve had not been plotted and hence not been checked against the IMO Intact Stability criteria.

• Prior to completion of loading a rolling test was carried out with the result of 19-20 seconds, indicating a GM of about 0.50 m. It is unclear how much cargo was loaded after that, but it appears that some was loaded on the hatch top.

• The harbour master, being concerned about the vessel's stability, contacted the master in the afternoon of 21st August, the day of the initial sailing, and was given a stability calculation showing a GMC of 0.47 m, corrected for free surfaces.

• The cargo in the holds and tween decks had not been stowed perfectly tight. Gaps between cargo blocks had not been stuffed or chocked. The cargo on deck was not adequately secured. The ship's Cargo Securing Manual did not contain instructions on securing a timber cargo. The master did not have a copy of the IMO Timber Deck Cargoes Code on board.

• The ship's stability documents had several deficiencies. It was found out that the initial inclining test at the building ship yard had been conducted with a heeling angle of about 0.365° only. The test condition included a total mass of liquids on board of 52.6 % of the light ship mass. Thus the obtained position of centre of light ship mass KG in the stability booklet appears doubtful. Furthermore, the tabulated imax of No. 1 fuel tank was given with 439 m4, but it was found that the correct figure was greater than 1,300 m4. This discrepancy caused a specific error in the stability calculations carried out before departure of about 0.07 m difference in GM.

• The chief officer's stability calculations did not allow for free surfaces in a number of tanks, which were assumed by him as full but in fact were slack.

The conclusions were, that the vessel actually sailed on 21st August 1999 with a GM close to zero. This and the insufficient securing of cargo brought the ship and the crew to the brink of a disaster. It remains unclear whether the master was fully aware of the interpretation and application of the IMO Intact Stability criteria.

• "Dongedijk" On Tuesday, 15th August 2000, at about 04.00 hours, the Dutch flag container feeder vessel "Dongedijk" capsized shortly after departure from Port Said in Egypt on an intended voyage to Lattakia in Syria. The crew of 12 were rescued by pilot boats and fishing vessels. The ship in fact took the ground when heeling over. This apparently prevented her from fully turning over and drowning at least some of the people on board. One year later the case was investigated by the Dutch "Raad vor de Scheepvaart" with the following findings3:

3 CESMA Newsletter


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• During the initial loading planning it had already become apparent that the vessel was overbooked, indicated by calculated insufficient stability and excess draught. For this reason the master had already cancelled 12 containers from the loading plan. The ship was equipped with an approved loading and stability computer.

• In order to reach an acceptable loading condition regarding load line requirements, all double bottom tanks except No. 2 had to be emptied. The stability in this condition complied with the IMO Intact Stability criteria indicated in chapter 3.1 of the IS-Code but not with the weather criterion in chapter 3.2. However, this outcome was obviously accepted by the master.

• The final draught readings on departure revealed that excess cargo had been loaded. But this indication was obviously not properly comprehended by the ship's command.

• After the ship had been recovered and brought alongside in Port Said the actual weights of the containers were traced and found to exceed the planning figures by 180 t.

Figure 1.4: The accident of "Dongedijk"

This case clearly shows, that the safety of this ship was put at risk almost deliberately. One main reason is again the supply of uncertain and actually wrong weight figures of a considerable number of containers. The other reason is the readiness of the master to accept a departure condition where the recommended IMO Intact Stability criteria were only partly satisfied. • "X" (anonymous report) This report was earlier presented in the IMO document SLF 43/9/1. A feeder container vessel, partly loaded, was bound to load another 350 containers with about 5000 tonnes in a small modern container terminal in the Mediterranean area for another port in the region. Cargo planning was carried out on board in advance by booking lists received from charterer's agents via satellite. The onboard computer revealed that the vessel would be loaded down to her marks. The stability would be at the limit using all the appropriate low ballast capacity. Care had to be taken because experience gave reason to suspect the booking figures.


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During loading the planned container positions were strictly followed, draught readings were taken and roll periods were observed at regular intervals. At about 02.00 hours in the morning the chief officer stopped the loading because the summer draught was reached and the rolling period was at the limit. There was no chance for de-ballasting. Unfortunately there were still about 40 containers to load. The agent appeared and tried to convince the master to load the rest of the containers with the argument that the batches with common B/Ls (Bill of Ladings) could not be separated. The proposal of the chief officer to unload broken batches and complete others had to be dropped because the agent was not in the possession of copies of the B/Ls which had been forwarded from Far East directly to the final port of destination. The vessel departed without the rest of the cargo with marginal stability. In the port of unloading the receipt of the broken batches was denied. The containers had to be re-loaded with uncertain commercial consequences. At this occasion the master could take a look into the shipping documents where it quickly turned out that the booking lists did not reflect the tare weight of the containers and above that there was a difference in weight of 120 tonnes, needless to mention inconsistencies in the declaration of IMDG containers. The following claim of consignees reproached the ship's command with wrong stability calculation, wrong ballasting and such things. This case did not end with an accident like a similar case described in the document SLF 42/INF.6. But it makes clear that masters of certain vessels, not low in number, are in need of tools to assess the stability of their ships in a fast and accurate manner, which is also accepted by other commercial parties. This assessment should be independent from any booking documents or remote tank gauging device readings. These masters are also in need of support by mandatory intact stability criteria.

• "Rautz" On Monday, 13th July 1998, at about 01.00 hours, the Austrian flag multi purpose vessel "Rautz" capsized and sunk west of Gibraltar straits with a cargo of about 2950 t copper ore concentrate on her way from a North African port to Poland. Six of the ten persons on board survived in a life raft, including the master, and were rescued by a fishing vessel about two days later. The fishing vessel had been directed to the survivors by an SAR-plane within the search action triggered by the EPIRB of "Rautz". An investigation of the accident, initiated by the Austrian Maritime Authorities, revealed the following facts:

• The master had accepted the cargo for loading without having received the demanded certificate from the shippers, indicating the moisture content of the fine-grained material. He had assured himself by close inspection of the cargo and different tests, that it were safe for carriage, also considering his past experience with such cargoes. The cargo was loaded and the ship sailed close to midnight on 11th July.

• There were no signs of lack of seaworthiness of the vessel. Ship and company had been certified according to ISO and ISM-Code. The weather during voyage prior to the accident was fine with moderate wind and swell. There was no significant rolling or pitching of the vessel.


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• When the first list of the vessel of about 5° was discovered in the evening of the 12th July, an immediate inspection of the two cargo holds showed that a small portion of the cargo in the after parts of both cargo holds had liquefied in the form of slurry. The majority of the cargo appeared firm and dry.

• Course and speed of the ship were adapted to reduce ship motions and to a head for a port of refuge at the Portuguese coast. The crew was alerted and assembled. Some ballast was taken in to reduce the list. Inspections were repeated at about hourly intervals. The situation appeared to remain stable.

• At about 01.00 hours the list increased again fairly rapidly and then the ship turned over to 90° within about one minute. Eight of the crew managed to assemble on the side of the vessel and six of them emerged after the vessel had disappeared a few minutes later. They manned one of the two life rafts released from the sunken ship.

• A certificate approving the suitability of the cargo for sea transport was issued in the loading port on 13th July, the day when the vessel had capsized at 01.00 hours. The investigation proved that not only the visibly liquefied part of the cargo had shifted. Also the apparently dry part shifted on a "wet foot", where compression had caused saturation with water.

This stability accident has a completely different character compared to the previous cases. Minimum stability criteria did not play a role at all. Instead, there were deficiencies in information exchange and in the appreciation of the critical nature of the cargo leading to a fatal result in the end. The master had virtually no chance to avert the capsize of his vessel once the liquefaction of the cargo had started.

• Present status of the IMO Intact Stability criteria

• Relation to SOLAS and other Conventions The Code on Intact Stability for all Types of Ships Covered by IMO Instruments comprises the annex to Resolution A.749(18). In this resolution the IMO Assembly recognises the need for development of an internationally agreed code on intact stability and invites Governments concerned to use the provisions of the Code as a basis for relevant safety standards, unless their national stability requirements provide at least an equivalent degree of safety. This recognition and invitation present a high level of importance given to the Code. However, in its Preamble the Code is clearly denoted as providing recommended provisions and the criteria being based on the best "state of art". SOLAS, Regulation II-1/22 on Stability Information for Passenger Ships and Cargo Ships requires to provide a stability booklet on board to enable the master to determine the ship's stability and also to have an initial inclining test carried out to establish the necessary light ship particulars. The Code on Intact Stability is addressed to in a footnote only, together with the MSC/Circulars 456, 706 and 707. SOLAS, Regulation II-1/25-8 repeats, in the context of damage stability for cargo ships built after 1992 and after 1998, the requirement of having sufficient documents for the assessment of stability on board, in particular curves or tables of minimum metacentric height or maximum KG, according to applicable intact and damage stability criteria. However, the intact stability criteria themselves are neither described, nor a reference is given to the IMO Code on Intact Stability. This particular SOLAS Regulation is remarkable insofar as it prescribes the provision of limiting curves or tables based on relevant intact stability requirements and the requirements of


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regulations 25-1 to 25-6, i.e. on intact stability criteria acceptable to the flag state and on mandatory damage stability requirements laid down in the Convention. In many cases the requirements from damage stability supersede those of the intact stability, depending on the individual design and sub-division of the vessel, and the actual draught and trim. The International Load Line Convention contains in Annex I, Chapter I the principal provision that the rules under this Convention imply sufficient stability and the observation of all internationally applicable regulations on stability. Thus, a ship may be considered being over-loaded in a legal sense, if there is deficient stability, although it remains unclear, which "yardstick" shall be used to define the borderline between sufficient and deficient stability. Another similarly vague reference to the provision of sufficient stability documents to the master can be found in Regulation 10 of the Annex. MARPOL, Regulation I/25A contains mandatory intact stability criteria for oil tankers of 5000 tdw and above, built after 1999/2002. These criteria are identical with those stipulated in Chapter 3.1 of the Code on Intact Stability. In addition, Regulation I/25A requires for these tankers a minimum GM, corrected for free surfaces, of 0.15 m during stay in port. Another important reference to the IMO Code on Intact Stability is found in MSC/Circ.707, containing Guidance to the Master for Avoiding Dangerous Situations in Following and Quartering Seas. The applicability of this guidance for operating a vessel at sea is connected to the condition that IMO stability criteria are satisfied. Altogether, with the exception of MARPOL Regulation I/25A, and the very successful "Grain Code" (Resolution MSC.23(59)), the legal weight of the IMO Intact Stability criteria appears to be very low. There is, indeed, no explicit recommendation on their use, neither in the SOLAS Convention nor in the Load Line Convention or any other mandatory Codes. There is just a reference by a footnote in SOLAS, which legally is not part of the Convention. • Status perceived by ship owners and mariners Ship owners or ship managers and ship masters are obliged, since 2002 latest, to run their ships under the regime of the ISM-Code. This Code requires to perform so-called key shipboard operations in accordance with prepared plans and instructions issued by the Company. A limited survey among shipping companies has revealed that the instructions regarding the onboard management of stability simply refer to the approved loading and stability manual without reference to specific intact stability criteria. Thus the application of the IMO Intact Stability criteria depends on the flag the vessel flies. However, in all cases of the limited company survey, covering different flag registers, it were the IMO Intact Stability criteria which were practically used, and in some cases the interviewed persons were even unaware of the recommendatory status of these criteria. They considered them as mandatory. This applies to many ship masters and officers as well. • Status perceived by carriers (charterers) and shippers Carriers, often today charterers of tonnage, and their clients the shippers, feel mainly bound to the freight contract based on private law. Although the safety of the vessel and the safe performance of the voyage plays an important role in these contracts there is no mentioning of technical details of stability in them. As the responsibility for the safe conduct of the voyage remains with the master who represents the owner, he has to defend the vessel against undue


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expectations of the carrier, e.g. regarding the amount of deck cargo affecting the stability, and against the implications of incorrect cargo information supplied by the shipper. It remains unclear whether both, carriers and shippers, are generally aware of the presently recommendatory status of the IMO Intact Stability criteria. However, there is a vague impression that both, carriers and shippers, perceive limits of ship's stability as a negotiable issue. • Status perceived by flag State authorities The perception of the IMO Intact Stability criteria by flag state authorities differs largely. It appears that most traditional flag states have adopted the IMO Intact Stability criteria to a great extent but use national modifications. A limited survey has shown that the criteria listed in chapter 3.1 of the IS-Code are generally applied while certain types of ships are exempted from the application of the weather criterion in Chapter 3.2, and a selective use is made of the special criteria in chapter 4 of the IS-Code. These modifications appear to provide an at least equivalent level of safety against capsizing and are generally laid down in national legislation. There are some other flag states who have adopted the IMO Intact Stability criteria without modification as national law or apply them without legal approval, mainly by commissioning a classification society with the technical approval of vessels applying to fly their flag. • Status perceived by port State authorities Port state authorities are generally bound to international mandatory legal instruments as basis for their inspection and detention regimes. The non-mandatory status of the IMO Intact Stability criteria presently prevents the implementation of "stability inspection campaigns" beyond the control of documents that must be on board under SOLAS regulations. This restriction does not apply to the inspection of "grain stability" where the mandatory Grain Code provides the necessary legal instrument for substantial controlling by port states. • Status perceived by classification societies and underwriters Classification of ships is a private law issue introduced in the 19th century as a tool of risk assessment for hull and machinery underwriters. Sufficient stability is an indispensable safety parameter. Therefore all IACS-classification societies and most other classification societies apply the IMO Intact Stability criteria or equivalent criteria of the particular flag state for the classification of ships. It should be noted that in many cases classification societies also act on behalf of the flag state when stability documents of a new or converted vessel are assessed and approved. • Status perceived by naval architects The Code on Intact Stability and the stability criteria therein play an important role within the practical design process of a ship, in particular of containers ships, where stability limits are the prevailing parameters for the cargo carrying capacity. Since the charterer may change several times during the life-time of a vessel, most owners are interested in a common yard-stick for her stability and agree on the application of IMO criteria in the building contract, unless the intended flag state requires a modification.


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This becomes quite obvious for design bureau's and software producers who are prepared to offer all national variations of the IMO criteria to their customers on demand. Another more critical issue among naval architects is the suitability of the IMO Intact Stability criteria for new types of vessels, e.g. large passenger cruising vessels and fast ferries. An ongoing scientific discussion questions the applicability of the existing criteria for vessels other than those for which these criteria have been developed. In particular the "statistical" criteria in chapter 3.1 of the IS-Code are prone to being "misused" in design optimisation [1]. This, however, addresses the challenge of developing new criteria, providing an equivalent level of safety and adapted to the needs of new ship types and their desired performance. The worthiness and value of the existing criteria for more conventional ships remains unquestioned among ship designers and approving authorities. • National stability criteria This chapter is intended to give a short insight into the nature of some national applications and modifications of the IMO Intact Stability criteria, selected by availability. It can be seen that the development of national intact stability criteria in traditional shipping countries has an own history in most cases but has common grounds with IMO criteria, the research work by Rahola in the early 20th century. • Australia Australia4 gives mandatory effect to the criteria of chapter 3.1 of the IS-Code, contained in Appendix 2 to Marine Orders Part 12. Australia gives mandatory effect to the weather criterion of chapter 3.2 of the IS-Code in relation to passenger ships only, but may also require it to be applied to fishing vessels of 45 m in length and above and to high-sided cargo ships, e.g. car carriers. With regard to chapter 4 of the IS-Code effect is given to various sub-chapters as follows: • Mobile offshore drilling units must comply with the criteria specified in sub-chapter 4.6

of the IS-Code. • Pontoons must comply with the criteria specified in sub-chapter 4.7 of the IS-Code. • Dynamically Supported Craft (DSC) must comply with the criteria specified in

sub-chapter 4.8 of the IS-Code. • Offshore supply vessels, which cannot comply with specified national criteria, may

comply with requirements reflecting sub-chapter 4.5.6.2 of the IS-Code. • Ships carrying timber on deck may be permitted to comply with the criteria specified in

sub-chapter 4.1 of the IS-Code in place of specified national criteria. • Container ships of a length greater than 100 m may be permitted to comply with the

criteria specified in sub-chapter 4.9 of the IS-Code. • Germany Germany had used national criteria until 31st March 2001. After that date the IMO Intact Stability criteria have been made mandatory for new ships with the keel laid on 1st April 2001 or later. The 4 http:/ / www.amsa.gov.au/sd/mo/MO_main/MO12.pdf


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main features of the previous national criteria, which are still applicable for existing ships under German flag, are: General criteria: − GZ30 ≥ 0.20 m for L ≤ 100 m, − GZ30 ≥ 0.002⋅L for 100 < L ≤ 200 m, − GZ30 ≥ 0.40 m for L > 200 m, − GMC ≥ 0.15 m, − A30 ≥ 0.055 m⋅rad, − A40 ≥ 0.090 m⋅rad, − A30-40 ≥ 0.03 m⋅rad, − Range of positive GZ values ≥ 50°, − GZ30 to be increased by 1 cm for each degree of range less than 60°. Ships with large windage area, except passenger vessels: − Consideration of wind pressure 0.3 kN/m2 in coastal voyages, 0.6 kN/m2 in short range

voyages, and 1.0 kN/m2 in medium and long distance voyages; heel less than 18° or less than an angle producing 10% residual freeboard on the low side.

Container vessels with mass of deck cargo exceeding 10% of cargo in holds: − Wind heel criterion as above, and − GMC ≥ 0.30 m for L ≤ 100 m, − GMC ≥ 0.005⋅L – 0.2 for 100 < L ≤ 120 m, − GMC ≥ 0.40 m for L > 120 m. There are special additional criteria for tankers, pontoons, tugs, passenger vessels, hopper dredgers, offshore supply vessels, vessels carrying timber on deck, vessels carrying crushed coke on deck, and ships handling heavy lift units with own gear. As mentioned above, these criteria have been replaced by the IMO Intact Stability criteria for new ships from 1st April 2001. • Japan Japan applies chapters 3.1, 3.2 and 4.1 (only) of the IMO Code on Intact Stability for cargo ships as mandatory criteria. However, for passenger ships and for fishing vessels national criteria apply5. These national criteria provide, according to a sample calculation carried out in 1995, almost the same limiting GM-values as those by the IMO IS-Code. Critical GM-values found by the IMO weather criterion are slightly smaller than those by the Japanese weather criterion. In this way Japan applies the IMO Intact Stability criteria in general, with modifications for certain ships. These modifications are at least equivalent to IMO criteria standards.

5 described in: Yamagata, M., Standard of Stability Adopted in Japan, Transaction of RINA, Vol. 101, 1959


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• Sweden Sweden applies chapter 3.1 of the IMO Code on Intact Stability for cargo ships as mandatory criteria with one exception, that is, the maximum righting arm shall occur at a heeling angle of at least 30° instead of 25°, and one additional requirement for a range of positive stability of at least 60°. Both modifications can be considered as more demanding for ships with low freeboard. The weather criterion according to chapter 3.2 of the IMO Code on Intact Stability is not used. The IMO special criteria in chapter 4 of the IS-Code are applied for ships carrying grain in bulk, for supply vessels and for mobile offshore drilling units. Sweden has additional criteria as follows: − Ships with a length of less than 24 m shall have a righting arm GZ at 60° heel of at least

0.2 – L/120. − Ships with certain design parameters may be permitted a range of positive stability

(φvanish) of less than 60° and a maximum GZ at an angle of less than 30°, but not less than 15°, if compensated by an area under the righting arm curve of at least 0.055 + 0.001 ⋅ (30° − φ) m⋅rad counted to an angle φ, which is the smaller of φGZmax and 0.5⋅φvanish.

There are criteria deviating from IMO criteria, but presumably equivalent, for − passenger vessels, road ferries and unmanned barges in coastal trade, − passenger vessels in unlimited trade, − tugs, − fishing vessels, − sailing vessels, − ships with timber on deck, and − ships carrying solid bulk cargoes. • USA The Code of Federal Regulations contains in Subchapter "S" on Subdivision and Stability within the Parts 170 to 174 a number of regulations with regard to intact stability criteria. Section 170.170 describes a weather criterion that is applicable for all ships, unless superseded or replaced by special requirements. This weather criterion is in fact a wind criterion with wind pressures modified according to trade areas and aiming at limiting heeling angles to 14° or less to immerse not more than one half of the freeboard of the vessel. The result is a minimum GM, which increases with reduced freeboard. Section 170.173 contains criteria for vessels of unusual properties and form up to 100 m length. These criteria are in fact identical to those of chapter 3.1 of the IMO Code on Intact Stability, but they present a modification for ships with a maximum GZ at a heeling angle of less than 25°. Section 171.050 contains special criteria for passenger vessels, section 171.055 for monohull sailing vessels.


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There are further sections for special ship types as follows: − barges carrying hazardous liquid substances (section 172.090), − gas tankers during cargo transfer (section 172.165), − vessels engaged in lifting operations (section 173.020), − vessels engaged in lifting operations, counter-ballasted (section 173.025), − deck cargo barges (section 174.015), − mobile offshore drilling units (section 174.045), − tugboats, towboats (section 174.145), − offshore supply vessels (section 174.185). It should be noted that all the above criteria apply to ships approved according to the Code of Federal Regulations. However, the majority of US cargo vessels obtain SOLAS certificates and must therefore comply with the criteria of the IMO Code on Intact Stability. • Common practice of ship stability management • Ships with critical operational stability The operational stability of a ship may become critical, either by the way she is loaded with cargo or by the way she behaves or is handled in rough seas. Ships designed to carry a considerable proportion of their cargo on deck, are more frequently operated close to their stability limits. These are typical modern container vessels, in particular the smaller container feeder vessels, ships carrying timber on deck and in some cases also ro/ro-vessels. These ships require regular and close attention to statutory stability limits during cargo operations. Another cargo related threat to stability is introduced by cargoes that are liable to shift. These are bulk cargoes in general with specific emphasis on grain and on minerals liable to liquefaction, and non-bulk cargoes with difficult stowage and securing like vehicles, steel coils and other break bulk cargoes. In this context it is important to note that shifting of cargo is often triggered by excessive stability in a seaway that is not necessarily exceptional. Proper stowage and securing is the most important means of controlling stability in these ships. In certain cases also liquid bulk cargoes, in particular mineral oils, can cause stability problems during loading or unloading, if carried on so-called "Single Tank Across Design" (STA) tankers or on Ore-Bulk-Oil (OBO) carriers. These "tankers" do not possess an overall transverse subdivision that excludes negative initial stability in any possible intermediate stage of loading and ballasting. Therefore the observation of approved loading and ballasting sequences is imperative in these ships.


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Figure 1.5: Typical low freeboard feeder vessel of about 700 TEU

The behaviour of ships in rough seas depends a lot on their under water hull form, their windage area and their speed capacity. In particular the under water hull form of modern container ships, ro/ro-vessels and passenger vessels shows a pronounced bow and stern flare with otherwise fine lines. This creates periodic fluctuations of stability in large head or stern seas and bears the risk of parametric resonance. A large windage area, although providing a considerable roll damping in strong winds, may create a dangerous heel, unless counteracted by large initial stability. However, large initial stability may be a drawback with regard to harmonic resonance. Speed capacity, if used recklessly, can be another threat to stability, in particular in stern or stern quartering seas, causing pure loss of stability on a wave crest or surf riding and broaching to. • The role of the owner, the charterer and the shipper Safe transport of goods by sea, in particular in the container trade, is today markedly characterised by the splitting of interests between the charterer and the owner. The owner, or managing owner – in the ISM-Code addressed to as the Company – is responsible for the safe operation of the ship. He will have to identify potential risks and to establish procedures for the safe conduct of so-called key shipboard operations. Monitoring and managing ship's stability is certainly a key issue on a container vessel. Great effort can therefore be expected from the master of the vessel in keeping cargo distribution, ballast management and cargo handling operations under control. The charterer of the vessel is in principle interested in the optimal use of the vessel's cargo carrying capacity and speed potential. The time or voyage charter party of course contains the necessary restrictions to the use of the vessel for protecting the interest of the owner regarding safety and integrity. However, the non-mandatory status of the IMO Intact Stability criteria may weaken the implementation and observation of strict stability limits under the gentle pressure exerted to the master by the charterer's super cargo, even if the flag state of the vessel has adopted these criteria or appropriate national criteria in a mandatory regulation. The third important partner is the shipper. His contract with the charterer is governed by the freight contract, laid down in the Bill of Lading. In this document the gross weight of the goods to be transported has to be declared by the shipper. The clauses attached to a Bill of Lading usually contain a provision reading: "The Shipper warrants to the Carrier that all details given


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by him to the Carrier ... are correct." It is consistent that another clause reads: "The Shipper shall indemnify the Carrier against all losses, damage, fines and expenses, arising from any breach of any of the warranties." In that way the carrier, i.e. the charterer, protects himself against liability for damages and losses caused by incorrect declaration of cargo weights. But this does neither protect the owner's interest nor the lives of his people on board. This is left to public legislation and thereby without consequences, unless inconsistencies are denounced to authorities or an accident has happened. SOLAS, Regulation VI/2 requires: "The shipper shall provide the master or his representative with appropriate information on the cargo sufficiently in advance of loading to enable the precautions which may be necessary for proper stowage and safe carriage of the cargo to be put into effect. Such information shall be confirmed in writing and by appropriate documents prior to loading the cargo on the ship. The cargo information shall include, in the case of general cargo, and of cargo carried in cargo units, a general description of the cargo, the gross mass of the cargo or of the cargo units, and any relevant special properties of the cargo. For the purpose of this regulation the cargo information required in sub-chapter 1.9 of the Code of Safe Practice for Cargo Stowage and Securing, adopted by the Organization by resolution A.714(17), as may be amended, shall be provided. Prior to loading cargo units on board ships, the shipper shall ensure that the gross mass of such units is in accordance with the gross mass declared on the shipping documents." This regulation is clear and well understood by all parties concerned. But obviously, there are a number of mechanisms, which by intent or unintended cause a notorious misinformation on cargo weights, in particular within the complicated network of long distance carriers and sub-contractors, who operate feeder vessels. • On-board stability monitoring and assessment The typical procedure of on-board stability monitoring and assessment has been demonstrated in the above case studies. The usual procedure for container feeder vessels and other dry cargo ships, where stability may become the critical parameter during down loading, is: • There is a cargo booking process well in advance of the arrival of the ship. This task is

carried out by the carrier's agents in the loading port or, in certain cases, in a regional planning centre of the carrier. Along with this booking the agents have to take care that the vessel will not be overbooked in terms of dead weight and in terms of stability. In some cases this task is solved by the preparation of a complete stowage plan and associated computer based stability and draught calculation. In other cases only a rough estimation on the suitability of the booking is made.

• The cargo information used in this booking process originally comes from the Bill of

Lading, which has been issued by the principal carrier, who is often responsible for the full distance of a multi modal transport. Extracts of these data are assembled in cargo manifests. However, it seems not unusual that a sub-contracting carrier's agent will not be supplied with these manifests, for commercial reasons, but will receive only a simple cargo list.


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• The booking list and/or the prepared stowage plan is presented to the master of the vessel on arrival in the loading port. Somehow, the master has to approve this plan or advise alterations in a very short time, generally in less than half an hour. This process is assisted by the chief officer who generally uses the ship's approved loading and stability computer to check the proposal against stability criteria, load line requirements, sight line requirements and commercial parameters. Cargo operations are started in the mean time and any alterations to the plan must be advised to the stevedores and the terminal operators as soon as possible. Particular attention must be paid to the commercial procedure of feeder vessel operators who declare "open booking end" to their customers, allowing the latter to bring cargo alongside until the vessel is bound to sail.

• It should be noted that this process takes place immediately after the ship has arrived

from a more or less strenuous sea passage, port entry and mooring procedure, with port entry clearance administration people sitting in the ship's office, charterer's agents and stevedores advising or waiting for orders. In short, the important decision on cargo distribution has to be made under time-pressure in an atmosphere of stress and under the possible effects of fatigue. This situation will repeat in short intervals, in particular in the container feeder trade.

• During cargo operations, consisting of simultaneous unloading and loading in general, a

close supervision must be exercised by the ship's staff with regard to:

− Complying with the stowage plan as approved by the master. − Deciding on suitable deviations from the stowage plan, if late changes of the

booking list are advised. − Monitoring the correct stowage of dangerous goods according to the approved

plan. − Carrying out appropriate ballast operations following a pre-arranged plan,

controlling list and trim. − Checking cargo intake by draught readings at suitable intervals, associated with

simultaneous tally checks. − Checking stability by observation of rolling motions from crane operations or

in-service inclining test if available. − Considering commercial parameters (avoiding re-stow, care for reefer containers). − Care for and supervision of cargo securing according to approved plan in the

Cargo Securing Manual.

• Although the pre-planned cargo stowage and distribution of ballast should guarantee a safe passage, there must be a final assessment of sea-worthiness, including the checking of the water-tight closing of hatches and other openings, the careful pressing up of all ballast tanks intended to be in a full state, the confirmation of the intended fuel consumption and transfer modalities from bunker tanks to settling tanks, and the appropriate documentation within the company's Safety Management System.

However, it appears from accident reports, that in many cases the necessary skill and carefulness with these tasks of ship masters and cargo officers suffer from lack of education, experience, or simply lack of motivation, superimposed by fatigue. Thus it may happen that ships sail with insufficient stability, although these cases are not too frequent in number.


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There is, in particular, the occasional observation of incorrect interpretation of intact stability criteria. The use of KG-limits or GM-limits, given on board in the form of curves or tables according to SOLAS Regulation II-1/25-8, should rule out any doubt about the required minimum stability. But the awareness of certain easy to retain specific criteria like the minimum GM of 0.15 m has been found to create serious mistakes. If, e.g., a GM of 0.30 m is actually obtained in an assessment, while the minimum table requires 0.60 m, the responsible officer or master may still be satisfied by the conception that the limiting table is not complied with but the minimum GM still exceeded by 100% and the ship may sail safely. Another simple "trick" is to trim the vessel by the stern and thereby increase the KM-value. In this way KG can be further increased, without violating GM-minimum requirements. The outcome of this procedure is often deficient stability with regard to righting levers beyond 20° heel. • Practical consequences of deficient departure stability When considering the practical consequences of deficient departure stability, it appears useful to distinguish unknown deficient stability, suspected deficient stability, and tolerated deficient stability. Unknown deficient departure stability, as being a possible result from unknown errors in light ship data or other ship's parameters, but mainly from incorrect cargo figures, unreliable ballast management or wrong interpretation of stability criteria, is obviously the most dangerous option. Minor additional effects on stability, like fuel oil transfer, trim corrections by ballast, crane operations, tug assistance, hard rudder, and even moderate wind and seaway can trigger the disaster, often accompanied by a shift of cargo in the late stage of the accident. Unknown deficient stability is often also the source of unsuitable counter-measures against an unexpected heeling of the ship. Most stability accidents can be considered as resulting from unknown deficient departure stability. Suspected deficient departure stability, which is sometimes a permanent burden of masters and mates on container feeder vessels, is much less dangerous. The awareness of the possible deficiency leads to an increased care-taking with regard to all of the above mentioned effects on stability. It can further cause the master to attempt an additional assessment by an in-service stability measurement. However, the consequences of a measuring result, which might reveal deficient stability, are not easily accepted and appreciated by charterers, terminal operators, and shippers. Masters, who have refused further loading after having proved deficient departure stability, have been "sacked" in some cases and replaced by another more daring, not to say foolhardy individual. Thus, it is not unusual, that masters choose the "silent" solution that is ballasting after de-berthing to improve the stability, without respecting the Plimsoll mark. Tolerated deficient departure stability, with regard to IMO Intact Stability criteria or other equivalent criteria, presents a legal situation that is open for a wide discussion as long as no accident happens, i.e. the ship arrives safely at the destination. There are only rare cases where authorities detect deficient departure stability prior to sailing of the vessel. In a case where the flag State has adopted the IMO Intact Stability criteria or other equivalent criteria as national mandatory regulation, authorities in a port of the flag State will be entitled to detain the vessel until the criteria are complied with. The same will not necessarily work in a foreign port by local port state authorities.


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If neither the IMO Intact Stability criteria nor other equivalent criteria are adopted as national law there is generally no legal means to detain the vessel in any port, unless the deficiency of stability appears as an obvious or immediate threat to the port environment and the people on board. However, the discussion following a detention on how far the stability must be improved until the vessel can be released, suffers considerably from the presently non-mandatory status of the IMO Intact Stability criteria. The legal situation appears more simple considering private law. A tolerated deficient departure stability is not made public by the owner or charterer. It does not come to the knowledge of the designated classification society or the underwriters. The validity of the classification certificate is not affected. Nothing will happen as long as no accident occurs. However, there will be severe legal consequences regarding loss of insurance protection of the owner and also regarding the right of limiting liability of the charterer, if an accident has happened resulting from such deficient stability. In this case, there may also be a public prosecution of the master for neglecting principal obligations resulting from the International Load Line Convention and for disregarding recommended standards, if the accident can be attributed to ignoring IMO Intact Stability criteria. The practical consequence of tolerated deficient departure stability will be an extremely careful master in avoiding additional threats to stability, like turning the ship with hard rudder at high speed or tank adjustments with undue free surfaces. Additionally, the tolerated margin below the criteria level will be kept limited, contrary to a situation with unknown deficient stability, where GM and other relevant stability parameters have been found close to zero in some cases. Summary of hazard identification This Formal Safety Assessment is directed to the consequences of making the presently recommendatory IMO Intact Stability criteria mandatory. This task requires a specific investigation of the hazards, which can be avoided or minimised by a mandatory status of these criteria. The following definition of a stability accident of a vessel, either in port or at sea, has been proposed for the purpose of this study: • a ship capsizes, or • a ship suffers a large heeling angle, or • a ship suffers heavy rolling. A close investigation of the mechanisms, which can lead to such accidents, has shown that the classical threat, heavy weather with severe wind and waves, is not the dominating influence. Instead, there are a number of other more trivial but nonetheless stochastic parameters, in particular inadequate loading control procedures, which may lead to either • unknown deficient departure stability, • suspected deficient departure stability, • tolerated deficient departure stability. These situations, if combined with other usual effects and threats to stability including heavy weather, can lead to a stability accident.


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From the underlying mechanisms it appears that a limited scope of ship types is affected and should be given priority with regard to legal measures of protection against stability accidents. These are in particular container feeder vessels, break bulk vessels carrying timber or other cargo on deck and in some cases also ro/ro-vessels, because stability criteria determine the operation and profit of these vessels. Stability accidents according to the above definition can also be the result of excessive stability, in combination with shifting of cargo. However, this situation has not been included into the risk assessment within this study, because excessive stability is not addressed by the present IMO Intact Stability criteria, and will therefore not be controlled by a mandatory status. The IMO Intact Stability criteria, although not being mandatory, are already widely applied in ship design, ship approval and ship classification. An obviously large number of flag states have them in place as national regulation, often with modifications, which provide an at least equivalent level of safety, measurable by the mandatory GM- or KG-limiting curve for a particular ship. Port state control authorities, however, are not readily in a position to expand their inspection regime to stability matters beyond document control, due to the lack of a legal instrument, i.e. mandatory criteria. • Risk assessment • Methodology The principal methodology to be applied in an FSA on the present task is the determination of the absolute risk of capsizing of representative types of seagoing vessels during their life-time. Within this determination the influence of the non-mandatory status of the IMO Intact Stability criteria on that risk must be established. In a second step the change of risk due to making these criteria mandatory must be identified. This change of risk should appear as a reduction, which can then be compared with the effort, cost and other consequences of making the criteria mandatory. To make it perfectly clear, it is not the suitability of the present IMO Intact Stability criteria that shall be investigated, as discussed in [1], but their application dependant on their legal status. These criteria are applied within two main areas, that is ship design and ship operation. The ship types being considered are those where the use of stability criteria during operation is considered important and a change of risk can be expected from a change of the legal status of those criteria. These ships are: • Container vessels, • Ro/ro-vessels, • Multi purpose (break bulk) vessels.

This selection excludes bulk carriers and tankers. Bulk carriers in fact suffer from stability accidents at times due to shifting of cargo, but not due to insufficient observation of stability criteria. Tankers, in particular those with critical design parameters (STA-design or OBO-carriers), are obliged to satisfy mandatory criteria as set out in MARPOL, Regulation I/25A. Also passenger vessels are excluded, because there are no distinguished mechanisms of compromising stability by the non-mandatory status of the IMO Intact Stability criteria.


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• Hazard and Operability Study (HAZOP) A Hazard and Operability Study is a basic analysis of procedures, events and possible deviations, which can cause accidents. It is carried out generally without considering the probability of events and critical deviations in the first place, but with the aim to generate the basis for a quantified risk assessment. The deciding parameters leading to a ship departure with deficient stability measured against intact stability criteria are external sources, mainly: − ship design and approval below IMO Code on Intact Stability standards, − errors in light ship data as documented for onboard use, − errors in cargo information supplied to ship planners and/or to the master of the vessel, and lack of ship staff competence, leading to: − errors in the assessment of stability, including errors in tank management, − misinterpretation of applied intact stability criteria, and − neglecting intact stability criteria. Another frequent event, excessive departure stability, can be attributed to both, external sources and lack of operational competence, and may also result in a stability accident via the mechanisms of poor ship behaviour in waves and subsequent cargo shifting. But this cannot be easily related to the influence of the legal status of intact stability criteria. After a ship has departed with deficient stability, a number of further events are usually necessary for triggering a stability accident. These are mainly: − operational events, like turning at high speed, normal towing operations, dry-docking,

additional free surfaces, usual tank adjustment and operational increase of top masses, − heavy weather or extremely heavy weather, combined with unsuitable course and speed, − consequences of heavy weather, like shifting of cargo and/or ingress of water, and − wrong counter measures in an early state of the accident.


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Figure 2.1 shows the result of a relevant Hazard and Operability Study.

External sources:

Ship design and approvalbelow standards

Errors in light ship datadocuments

Errors in cargo information

Lack of ship staff competence:

Faulty assessment of stability

Misinterpretation of stability criteria

Neglecting stability criteriaintentionally

Excessive departure stability

Unknown deficient stabilityat departure

Known deficient stability atdeparture

Excessive stability atdeparture

Additional events:

Usual turning at highspeed

Normal towing assistance

Usual dry-docking

Usual tank adjustments

Operational increase oftop masses

Perils of the sea:

Heavy weather

Unsuitable course

Shifting of cargo

Ingress of water

Perils of the sea:

Extremely heavyweather

Unsuitable shiphandling

Inappropriate countermeasures

Inappropriate countermeasures

Stability accident

Figure 2.1: Procedures and events leading to a stability accident

• Event Tree Analysis of stability accidents (ETA) An event tree analysis combines possible pre-conditions, events and counter-measures, which in combination may lead to a stability accident. The pre-conditions, events, and counter-measures are given individual probabilities, derived from statistical analysis and/or expert opinion. A mathematical processing of these individual probabilities, reflecting the appropriate logical connection (AND, OR, EXOR), will lead to the final probability of a stability accident. Calibration of this final result by means of casualty statistics increases the reliability of the model.


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The following parameters are of importance, related to critical types of ships, which may lead to unknown and to known deficient departure stability. The category known comprises of suspected and tolerated deficient stability, having the common feature of raised awareness.

Number of ship departures per year at stability limits = dp Proportion of those ships with incorrect light ship data = p1 Proportion of severely wrong cargo information at these departures = p2 Proportion of severe errors within stability assessment at these departures = p3 Proportion of misinterpreted stability criteria at these departures = p4 Proportion intentionally neglected stability criteria at these departures = p5

The event "ship design and approval below IMO Code on Intact Stability standards" has not been included into the above list of parameters, because it seems that the vast majority of shipyards and classification societies keeps design and at least class approval within these standards. The in fact important issue of departures with excessive stability has been left out as well, because there is no direct relation to the legal status of the IMO Intact Stability criteria. Deficient departure stability must be combined with additional events to create a stability accident. There are a number of events of normal routine ship operation, which can happen in AND/OR-combinations. They may cause an accident if AND-combined with unknown deficient stability only, because it can be assumed that these events are avoided if the deficient stability is known to the master. The relevant probabilities are:

Probability of usual turning with hard rudder at high speed = p6 Probability of severe transverse pull during towing assistance = p7 Probability of a critical situation during dry docking = p8 Probability of usual tank adjustment including free surface effects = p9 Probability of temporary additional top masses during operation = p10

Another event, which cannot be avoided in general, is heavy weather and extremely heavy weather. These two issues are distinguished by the assumption that extremely heavy weather will cause an immediate capsize if deficient stability is present and wrong ship-handling is applied by the master, while normal heavy weather tends to require additional events like cargo shifting and/or water ingress for that outcome. The relevant probabilities are:

Probability of meeting heavy weather = p11 Probability of steering an unfavourable course = p12 Probability of a severe cargo shifting or asymmetrical loss of deck cargo = p13 Probability of severe water ingress = p14 Probability of unsuitable remedial measures in case of heavy list = p15 Probability of meeting extremely heavy weather = p16 Probability of improper ship handling in an extremely heavy weather = p17


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The above probabilities have been calibrated in such a way that their appropriate combination just produces one stability accident, i.e. a situation where the ship capsizes or suffers a heavy list or dangerous rolling. Figure 2.2 shows the arrangement of the Event Tree Analysis.

Number of departures per shipand year at stability limits

Incorrect light ship dataAND/OR

Severely wrong cargo informationAND/OR

Severe errors within stability assessmentAND/OR

Misinterpretation of stability criteria

Intentionally neglected stability criteria

AND AND

Number of departures with unknowndeficient stability

Number of departures with knowndeficient stability

Usual turning with hardrudder at high speed

AND/ORSevere transverse pull

during towing assistanceAND/OR

Critical situation during drydockingAND/OR

Usual tank adjustmentincluding free surface effects

AND/ORTemporary additional topmasses during operation

Heavy weatherAND

Steering an unfavourablecourse

Extremely heavy weather

Severe cargo shifting orasymmetrical loss of deck

cargoAND/OR

Severe water ingress

Unsuitable measures incase of heavy list

Unsuitable measures incase of heavy list

AND AND ANDAND AND

AND

AND

AND

Improper ship handling inextremely heavy weather

AND

Number of accidents type 1per ship and year



Figure 2.2: Event Tree Analysis


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Accident type 1 is generally not a capsize, but will often end in a severe list (refer to the case "Sun Breeze"). Cargo shifting can be involved as well, but this is not shown in the ETA above, because it should not be considered as deciding. Accident type 2 can also end with a large heeling angle. Cargo shifting is more important here, because a heavy seaway will cause repeated heavy rolling motions with an increased probability of cargo shifting. Accident type 3 is the pure capsize in extremely heavy weather, although cargo shifting may accelerate the process. The numbers of the three accident types per sensible ship and year is calculated as follows: Number of departures with unknown deficient stability:

uds = dp ⋅ (1 – (1– p1) ⋅ (1– p2) ⋅ (1–p3) ⋅ (1– p4))

Number of departures with known deficient stability: kds = dp ⋅ p5

Number of accidents type 1: acc1 = uds ⋅ (1 – (1– p6) ⋅ (1– p7) ⋅ (1–p8) ⋅ (1– p9) ⋅ (1– p10)) ⋅ p15

Number of accidents type 2: acc2 = (uds + kds) ⋅ p11 ⋅ p12 ⋅ (1 – (1– p13) ⋅ (1– p14)) ⋅ p15

Number of accidents type 3: acc3 = (uds + kds) ⋅ p16 ⋅ p17

A sensible estimation of the influencing parameters by experts and a calibration of the results by means of casualty statistics has provided the following figures:

Entry parameters Results dp = 10 p5 = 0.10 p10 = 0.02 p15 = 0.10 uds = 1.2449 p1 = 0.01 p6 = 0.10 p11 = 0.15 p16 = 0.01 kds = 1.0000 p2 = 0.06 p7 = 0.02 p12 = 0.20 p17 = 0.03 acc1 = 0.0196 p3 = 0.02 p8 = 0.005 p13 = 0.15 acc2 = 0.0012 p4 = 0.04 p9 = 0.02 p14 = 0.03 acc3 = 0.0007

Within the determination of the important influence p2, i.e. the proportion of severely wrong cargo information, the usual distrust of masters and cargo officers against these data has been taken into account. Otherwise the figure of p2 would have been much greater.

The total number of accidents per ship and year will then be 0.0215 or one accident in 46.5 years. With an estimated number of 6000 sensible ships this is 129 accidents per year. A minimum of four of these 129 accidents will be pure capsizes in extremely heavy weather. But there will be some additional capsizes under less extreme conditions (refer to the case "Lime Bay").

• Average cost of stability accidents and monetary risk A stability accident, as defined for the purpose of this study (see chapter 1.1), has a wide variation in cost. The most severe option, the capsize, would easily be attributed to a total loss,


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the cost of which would exceed the value of the ship and the cargo by the amount of usually noninsurable cost of loss of business related to the lost cargo. Additionally, there may be the cost of wreck removal and loss of business of other parties, if the wreck, e.g. blocks a jetty or port entrance or river for a certain time. Most remarkable, however, in the case of a capsize, is the high probability of loss of life. Even if the process of capsizing is slow or foreseeable there is a high risk that not all persons manage to clear from the vessel in time and to be rescued. The less severe options, large heeling, either in port or under way, or heavy rolling with cargo damage, causes less cost in all aspects and also bears less probability of injury or loss of life, if there is a chance to get the ship and the possibly shifted cargo under control. The lightest case would probably cause only some delay to the voyage and the nerves of the master. Unfortunately, there are no specific statistics available, which distinguish precisely between causes of stability accidents, as defined above, in particular in the light of deficient stability. It should be noted that a considerable number of accidents at sea with heavy rolling, subsequent cargo shifting and potentially ending in a capsize can be attributed to excessive stability, apart from improper stowage and securing. Therefore estimates gathered from experts, mainly hull and cargo underwriters must be used to get figures for the costs involved. These estimates give the following figures, covering the critical ships: • Three percent of the stability accidents are total losses accountable for 30 Million Euro

per case. • Sixty-seven percent or two thirds of the stability accidents are moderate cases with

consequences accountable for 400,000 Euro in average per case. • Thirty percent of the stability accidents are light cases with negligible costs. These estimates give an average figure of 1.168 Million Euro per case. This figure is combined with the probability of one stability accident per ship and year of 0.0215 resulting in a monetary risk of about 25000 Euro per ship and year. This risk can be compared to the average insurance cost of a 1000 TEU container vessel of about 500000 Euro per year6, including hull and machinery, liability (P&I) and cargo. The figure of 25000 Euro appears plausible, bearing in mind that probably only two thirds of the cost included in this risk figure are covered by underwriters, and the figure of 25000 Euro applies to ships, which are sensible with regard to operational stability. • Estimated consequences of mandatory IMO Intact Stability criteria • Indirect influence of mandatory criteria Mandatory intact stability criteria would obviously not have a direct influence on the operational performance of ships, because the present recommendatory status is widely applied through class rules and/or distinguished flag state requirements. Moreover, in case of an accident due to deficient stability the recommendatory stability criteria will generally be treated as standards or

6 Figure obtained also in the Formal Safety Assessment on the proposed expansion of mandatory Emergency Towing Systems in merchant vessels.


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rules of good seamanship, and any offend against them used as prima facie proof of neglecting the necessary care, in private as well as in public jurisdiction. However, there may be a number of indirect influences from a mandatory status of the IMO Intact Stability criteria. A mandatory status could be used to create a greater awareness of safety margins among charterers and shippers with a certain improvement of the reliability of cargo information. The mandatory status could also lead to a certain amount of port state control activity directed to departure stability of critical ships and hence improve the performance of onboard stability assessment and interpretation of the criteria themselves. Finally, a remarkable reduction of cases with intentionally neglected stability criteria can be expected for the same reasons. A careful estimation of these indirect influences can be used for re-calculating the risk of a stability accident. • Reduction of calculated risk The parameters liable to change by mandatory IMO Intact Stability criteria are, as mentioned above, the following four with their attached probabilities:

Proportion of severely wrong cargo information at critical departures = p2 Proportion of severe errors within stability assessment at critical departures = p3 Proportion of misinterpreted stability criteria at critical departures = p4 Proportion intentionally neglected stability criteria at critical departures = p5

The estimated potential changes of these probabilities are indicated in the following table, together with the changed results:

Entry parameters Results dp = 10 p5 = 0.10→ 0.05 p10 = 0.02 p15 = 0.10 uds = 1.2439→ 0.5881p1 = 0.01 p6 = 0.10 p11 = 0.15 p16 = 0.01 kds = 1.0000→ 0.5000p2 = 0.06→ 0.03 p7 = 0.02 p12 = 0.20 p17 = 0.03 acc1 = 0.0196→ 0.0092p3 = 0.02→ 0.01 p8 = 0.005 p13 = 0.15 acc2 = 0.0012→ 0.0006p4 = 0.04→ 0.01 p9 = 0.02 p14 = 0.03 acc3 = 0.0007→ 0.0003

The total number of accidents per ship and year will then be reduced from 0.0215 to 0.0101 or to one accident in 99.0 years instead of 46.5 years. With an estimated number of 6000 sensible ships the number of accidents is reduced from 129 to 61 per year with a minimum of two pure capsizes in extremely heavy weather. The monetary risk is reduced to about 12000 Euro per ship and year. This result is based on expert opinion only, but indicates that the risk of failure related to the control of operational stability would be considerably reduced by common mandatory stability criteria. • Summary of risk assessment The risk assessment has been restricted to ship types where the legal status of the IMO Intact Stability criteria has a distinguishable influence on the operation of these ships. These are:


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• Container vessels, • Ro/ro-vessels. • Multi purpose (break bulk) vessels. A Hazard and Operability Study has revealed why ships occasionally depart with deficient stability and which additional operational events may lead to a stability accident. This complex scenario was simplified into an Event Tree Analysis with distinguished probabilities of all influencing events. The identification of these particular probabilities has been solely based on expert opinion because statistical material on stability accidents is rare in the first place and does hardly contain any information on events and parameters. However, the results have been counter-checked by statistical summary figures and adjusted to meet the global picture. Again, expert opinion, mainly from underwriters, was used to judge the plausibility of the results. This also applies to the estimation of the cost of stability accidents. The results obtained as a consequence of deficient stability at departure are in summary: The total number of accidents per ship and year will be 0.0215 or one accident in 46.5 years. With an estimated number of 6000 sensible ships this is 129 accidents per year. A minimum of four of these 129 will be pure capsizes in extremely heavy weather. The probability of a stability accident, multiplied with the average cost of such an accident, is the risk. The resulting figure is 1.17 Million Euro per case. This figure, combined with the probability of one stability accident per ship and year of 0.0215 results in a monetary risk of about 25000 Euro per ship and year. This risk figure includes damage to ship and cargo and cannot, of course, account for loss of health and life. The figures of those probabilities of events, which can be influenced by a mandatory status of the IMO Intact Stability criteria, have then been reduced. This reduces the number of accidents per ship and year to 0.0101 or to one accident in 99.0 years. With an estimated number of 6000 sensible ships then number of accidents is reduced 61 per year with a minimum of two pure capsizes in extremely heavy weather. The monetary risk is reduced to about 12000 Euro per ship and year. Risk control options Although the risk assessment in chapter 2 of this study has already shown that common mandatory intact stability criteria would have a remarkable benefit for reducing the risk of stability accidents, some light shall be shed on other possible risk control options with the view of a feasible implementation through IMO initiative. • Improvement of ship design and equipment • Ship design The main commercial goals of ship design are to meet the contracted cargo or passenger carrying capacity, the contracted speed with minimum fuel consumption, and a low light ship mass for


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meeting the budget of the customer. Compliance with class rules and flag state requirements is indispensable in most cases for reasons of public and private law. In this context, the recommendatory status of the IMO Intact Stability criteria does not appear to be a noticeable hindrance for proper ship design, because the majority of classification societies apply these criteria in principle. Considering the sensitivity of certain types of ships, e.g. ferries and passenger vessels, against combined wind and sea effects to stability, a revision of the criteria can be expected. However, such a revision will not noticeably change the situation for the critical ships in the sense of this study, i.e. small container vessels, ro/ro-vessels and multi purpose vessels with heavy deck cargo. Therefore, improvement of ship design, within the framework of the present intact stability criteria, will not readily reduce the risks associated with the control of operational stability, notwithstanding the considerable progress in ship design through IMO initiatives with regard to survival in damaged condition. • Equipment for control of stability The risk assessment in chapter 2 of this study has shown a considerable influence from incorrect cargo information, in particular wrong mass statements of containers in cargo documents, and of errors in onboard stability assessment to the risk of a stability accident. This influence is attributed to the procedure of loading planning and stability assessment by means of a "desk top" exercise, i.e. a calculation, which completely relies on the entered figures collected by the operator. Apart from the uncertain cargo masses there are also quite often errors in the onboard tank management. A possible solution of this particular problem would be the onboard measurement of stability by means of an in-service inclining test. Extensive studies on the feasibility and suitability of this option have been carried out in the past 15 years with the result that a limited number of container vessels and ro/ro-vessels have been fitted with such equipment and approved by flag state authorities. This has been brought to the attention of the SLF Sub-Committee. There is, however, a general reluctance of the shipping industry to apply this measure of safety in a broad scale due to several reasons, which include cost of installation, delay of cargo operations and a pretended lack of competence of onboard personnel. IMO has not been prepared to recommend the in-service inclining test or relevant equipment. Other suitable equipment, e.g. on-line monitoring of displacement through automated draught measurement and on-line monitoring of the filling state of ballast and bunker tanks, has been developed and installed at a limited scope. The effect of this equipment with regard to prevention of stability accidents is not so clearly determinable, although it allows a closer control of loading parameters. Misinterpretation and intentional neglecting of stability criteria cannot be directly prevented by such advanced equipment. Another equipment option for preventing stability accidents in heavy weather would consist of a monitoring and warning system for avoiding course and speed combinations, which could lead to harmonic and parametric resonance, prolonged loss of stability on a wave crest and the risk of surf riding and broaching to. The MSC/Circ.707 is a first step into that direction. Advanced computer based systems are presently under development. However, such systems may prove helpless and ineffective, if the ship's departure stability is deficient in the first place. Such equipment can therefore take a supportive role only.


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• Improvement of ship operation • Enforcement of SOLAS Regulation VI/2 (information from the shipper) An effective enforcement of SOLAS Regulation VI/2, in particular regarding the correct gross weight declaration and marking required in paragraph 2.1, would be quite helpful to eliminate a substantial source of uncertainty to ships' departure stability assessments. Quite often the proposal has been raised to prescribe a mandatory weighing of export containers at their arrival in a terminal or after their packing in that terminal. But apart from the undue delay through this procedure and the associated cost, the established weight would be available far too late because ship loading planning takes place well in advance of the physical availability of the containers, either ashore or/and aboard ship. The enforcement of SOLAS Regulation VI/2, however, should be worth to consider and should address the individual shipper or packer of the container, possibly in the context with other associated declaration requirements regarding maritime security measures. A mandatory status of the IMO Intact Stability criteria would certainly support any effort into that direction. • Review of loading and stowage procedures A review of loading and stowage procedures appears not very promising with regard to improving the control of departure stability of ships. Cargo operations in ports have undergone drastic processes of rationalisation, including the respond to multi modal transport chains and productive warehousing, since the introduction of the container and other "fast" modes of cargo handling. Commercial competition between ports and regions have brought all relevant cargo operations to a high degree of perfection, including the care for ship safety, so that it seems hard to imagine how substantial changes could be initiated by IMO. What is needed, is simply a refinement with regard to the reliability of cargo data, as discussed under 3.2.1. Stability accidents are quite often related to cargo shifting, with a focus on ro/ro-vessels. This includes departures with excess stability. In that area IMO has produced appropriate tools (CSS-Code, Cargo Securing Manual), which have the potential to be effective and sufficient in the long term, but certainly depend on sustained training and qualification of personnel, ashore as well as on board. • Review of education and training of masters and deck officers The revision of the STCW-Convention of 1978 and the specification of mandatory competencies of masters and deck officers in the Tables A-II/1 and A-II/2 of the STCW-Code in 1995 is certainly a great step forward to providing common grounds for the performance of merchant shipping and safety at sea. However, the overall profile of nautical competence in these tables appears somewhat one-sided in favour of "Navigation". Of course, collision, grounding and stranding contribute the majority of marine accidents and deserve the greater attention in maritime education and training. But this should not permit the underscoring of the remaining areas cargo handling and ship management. In the late 1960s, when the standard container was introduced in shipping, rumours appeared that very soon the importance of the cargo officer would vanish. He would become superfluous in the


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end, because care for cargo operations would completely be taken over by shore based organisations under the responsibility of the carrier. This did not come true for mainly two reasons, the higher cost of effective shore based cargo care, and the undeniable responsibility of the master and his officers for the safety of the ship. Today we can observe a quiet revival of the role of the cargo officer on board, together with an increasing lack of care-taking ashore. This affects the management of stability as well. Therefore it seems worth to carefully investigate the future role of mariners in cargo operations, taking into account their responsibilities stipulated by the ISM-Code, and to review the above mentioned STCW-Code competence tables with particular attention to the competencies: • Plan and ensure safe loading, stowage and securing, care during the voyage and

unloading of cargoes; • Control trim, stability and stress. In this context, a mandatory status of the IMO Intact Stability criteria would prove very supportive by providing a clear and unambiguous reference for the specific training objectives of shipboard stability management. Although, as mentioned above, the function "Navigation" in the nautical competence tables has been given an abundant share and details, in particular for the competence "Manoeuvre and handle a ship in all conditions", there appears a certain weakness in the formulation of the competence for ship handling in heavy weather. The appropriate text under the column "Knowledge, understanding and proficiency" reads: .12 management and handling of ships in heavy weather, including assisting a ship or aircraft in distress; towing operations; means of keeping an unmanageable ship out of trough of the sea, lessening drift and use of oil. This text needs, of course, the interpretation by a professional maritime course designer or lecturer like all the other descriptions in the STCW competence tables. But the inclusion of important keywords like avoidance of resonance, surf riding, loss of stability on a wave crest, or the direct reference to the MSC/Circ.707 would be helpful to support the intended common standard of competencies, notwithstanding the need to replace the doubtful phrasing "means of keeping an unmanageable ship out of trough of the sea". • Enhancement of administrative supervision • Flag state control The means of a flag state to enhance the avoidance of stability accidents beyond the presently attained level appear to be very limited. The mechanisms described in chapter 1 of this study, which are responsible for a stability accident, cannot be influenced directly by a flag state. Indirect measures, like approval of the ship and stability documents, appropriate manning with competent officers and regular preventive inspection is all what can be done and has been done for a long time. A more stringent requirement for keeping records on stability assessments, e.g. through the ISM inspection regime, could improve the performance in an indirect manner. However, this would


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imply a mandatory status of relevant intact stability criteria in the first place, addressing either the IMO criteria or equivalent national criteria. Some shipping companies already have these controls included in their approved Safety Management System and require a consistent recording of loading and stability parameters. • Port state control (PSC) Port state control organisations, like the Paris MOU, are based on IMO and ILO Conventions for justifying their inspections of ships. Therefore, the means of port state control organisations to enhance the avoidance of stability accidents are very limited, although port state authorities are generally much closer to the scene of relevant events than flag state authorities. Port state control officers are virtually present in the actual loading ports and can decide on the spot to inspect a critical vessel with obviously heavy deck load. The main hindrance to do this is the simple lack of a "legal instrument" in the case of cargoes other than grain. The mandatory "grain rules" have, in fact, established a long and successful tradition of shore based inspection and controls in major grain exporting countries, which always have included the assessment of grain stability. This situation may radically change to an expansion of inspections to other critical cargoes like containers, ro/ro-vehicles and timber on deck, if the presently recommendatory stability criteria for those ships would become mandatory. According to the opinion of a distinguished PSC representative, a mandatory status of the IMO Intact Stability criteria would immediately lead to the development of guidelines for the common approach to checking certain aspects of the onboard management of ship's stability. In this way a pro-active approach for the prevention of stability accidents would become feasible and certainly appreciated by many ship masters seeing themselves under constant commercial pressure. • Revision of the IMO Code on Intact Stability Having noted above that in a number of risk control options, like • better enforcement of SOLAS Regulation VI/2, • review of education and training of masters and deck officers, • enhanced flag state control, • enhanced port state control (PSC), the lack of internationally agreed mandatory stability criteria appears as a "missing link", the making mandatory of the IMO Intact Stability criteria shall be given a closer look. • Re-structuring the IS-Code The present lay-out of the IS-Code appears as a historically grown conglomerate of instructions, provisions and technical standards. There is general advice for the layout of stability booklets, general precautions against capsizing, advice for ship handling in heavy weather, stability criteria for various types of ships and certain cargoes, instructions to naval architects regarding the preparation of stability information, icing considerations directed to masters and naval architects, consideration for watertight integrity directed to naval architects and detailed standards and instructions for the determination of light-ship displacement and centre of gravity. It seems impossible to transfer the Code in the present composition into a mandatory status. Therefore Germany has proposed within the Intact Stability Correspondence Group a restructuring of the IS-Code into three parts as follows:


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• Part A shall contain intact stability criteria applicable to all types of ships, • Part B shall contain recommendatory provisions for all types of ships, • Part C shall contain explanatory notes useful for compliance with Parts A and B. A preliminary overview shall provide the relation between the existing contents of the IS-Code and the proposed new structure.

Proposed new structure of the IS-Code Contents related to existing Code

Part A – Criteria for All Types of Ships Chapter 1 – General 1.1 Purpose identical to 1.1 1.2 Application identical to 1.2 1.3 Definitions identical to 1.3 Chapter 2 – Design criteria applicable to all ships 2.1 Static intact stability criteria identical to 3.1 2.2 Dynamic intact stability criteria to be developed with reference to 3.2 Chapter 3 – Special criteria for certain types of ships 3.1 Cargo ships carrying timber deck cargoes identical to 4.1 3.2 Fishing vessels identical to 4.2 3.3 Special purpose ships identical to 4.3 3.4 Cargo ships carrying grain in bulk identical to 4.1 3.5 Offshore supply vessels identical to 4.2 3.6 Mobile offshore drilling units (MODUs) identical to 4.3 3.7 Pontoons identical to 4.1 3.8 Dynamically supported craft (DSC) identical to 4.2 3.9 Containerships greater than 100 m identical to 4.3 Part B – Recommendations for All Types of Ships Chapter 4 – Stability information 4.1 Effect of free surfaces of liquids in tanks identical to 3.3 4.2 Assessment of compliance with stability criteria identical to 3.4 4.3 Standard loading conditions to be examined identical to 3.5 and including 2.4 4.3 Calculation of stability curves identical to 3.6 4.4 Stability booklet identical to 2.1 4.5 Operating booklets for certain ships identical to 2.2 Chapter 5 – Operational provisions against capsizing 5.1 General precautions identical to 2.3 and expanded as appropriate 5.2 Ship handling in heavy weather identical to 2.5 and expanded as appropriate 5.3 Measures in special cases and in emergencies to be developed Chapter 6 – Icing considerations identical to Chapter 5 Chapter 7 – Considerations for watertight integrity identical to Chapter 6 Chapter 8 – Determination of lightship parameters identical to Chapter 7 Annex 1 – Detailed guidance for the conduct of an ... identical to Annex 1 Annex 2 – Recommendations for skippers of ... identical to Annex 2 Annex 3 – Determination of ship's stability by ... identical to Annex 3 Part C – Explanatory notes Chapter 9 etc. as appropriate to be developed


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It appears from this overview that the majority of the contents of the existing Code may remain unchanged. A major task will be the re-development of the "weather criterion" of the present IS-Code. Further expansion and development may be desirable in a new Chapter 5, Operational Provisions Against Capsizing, which would contain comprehensive advice for the master. Finally, development will be needed for the proposed Part C of the new IS-Code.

• Mandatory status of the stability criteria The above overview provides the opportunity to declare Part A as mandatory in general. This shall mean that the criteria mentioned therein would be obligatorily applied for ship design and approval as well as a common yardstick in ship operation. This does, however, not affect the mandatory application of relevant damage stability criteria, which may be more stringent for certain ship designs or certain loading conditions. It should further be noted, that a mandatory status of intact stability criteria as a risk control option will not be a perfect warranty for the avoidance of stability accidents, although this status would be beneficial in several ways by influencing positively the enforcement of SOLAS Regulation VI/2, the education and training of mariners, and enhanced flag state and port state control. As mentioned earlier, stability accidents can also be the result of excessive stability, improper cargo securing and of poor ship handling in heavy weather. However, a mandatory status of the IMO Intact Stability criteria will be perceived as an indispensable corner stone of the overall safety concept of shipping, best proved by the surprise of many mariners and shipping operators when confronted with the "news" that the well known IMO-criteria were only recommendatory at this time. • Summary of risk control options A number of risk control options has been investigated and presented above with the following results: • Improvement of the situation by alternative ship design appears not feasible without

severe reduction of the profitableness of the ships involved. • A certain progress of making departure stability assessment more reliable would be

expected from the use of advanced equipment for onboard stability management. • An important step towards the avoidance of ship departures with deficient stability would

be achieved by more realistic cargo figures through a legal enforcement of SOLAS Regulation VI/2. However, this would necessarily imply to make the IMO Intact Stability criteria mandatory.

• A review of usual procedures of loading cargo vessels, e.g. by weighing containers,

appears neither useful nor feasible. • A review of the STCW-based competence's of masters and deck officers with regard to

stability management, cargo handling and manoeuvring in heavy weather appears suitable, but would also benefit from mandatory IMO Intact Stability criteria.


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It appears that making the IMO Intact Stability criteria mandatory is not the only possible and successful measure, but all other suitable measures are less effective without such mandatory criteria.

Cost-benefit assessment In this chapter only the option "mandatory intact stability criteria" is considered and discussed with regard to cost-benefit relation, although some of the other options will benefit indirectly from mandatory criteria. • Benefit of mandatory intact stability criteria The possible benefit of mandatory intact stability criteria has been numerically estimated in Chapter 2.2 of this study and can be addressed as "considerable", not only in terms of financial savings but also in terms of preservation of life and health. This benefit can be identified by the following estimated effects: − The proportion of severely wrong cargo information, which remains undetected by

suspicious masters and cargo officers, can be reduced under the assumption that mandatory intact stability criteria create a greater public awareness of the importance of correct data for the safety of shipping. This effect may be further supported by more effective prosecution of offences against the requirements of SOLAS Regulation VI/2.

− The proportion of severe errors within stability assessment at critical departures can be

reduced under the assumption of improved training and education of mariners and enhanced port state control activities on stability management, both produced and favoured by mandatory stability criteria. Also advanced onboard equipment for stability management may be promoted in this way.

− The proportion of misinterpreted stability criteria at critical departures can be reduced

under the assumption of improved training and education of mariners and enhanced instructions in the Safety Management Manual of the company, both favoured by mandatory stability criteria.

− The proportion of intentionally neglected stability criteria can be reduced taking into

account that mandatory stability criteria may reduce the pressure from the charterer on masters and/or strengthen the back of masters with regard to respecting the limits of downloading the vessel.

The numerical effect of this reduction of negative influences, estimated in chapter 2.2 in a conservative manner, is a potential reduction of the risk of stability accidents to about 50% of the existing level.


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• Regulatory consequences • Revision of the IMO Intact Stability Code The anticipated revision of the IMO Code on Intact Stability, in particular with regard to developing "performance based criteria" for types of ships where the traditional "statistic based criteria" appear no longer applicable, is a task that will take a huge effort of research and debate, to find solutions which provide an at least equivalent level of safety. The proposed re-structuring of the Code into a mandatory Part A and two recommendatory Parts B and C is a comparably easy task. Bearing in mind the possible benefit for the indicated "critical" types of ships, i.e. small container vessels, ro/ro-vessels and similar multi purpose vessels, a preliminary restriction of the mandatory status to those types of vessels would make this task even easier. There are no specific costs related to this task, in particular no direct costs for the shipping industry. It should be borne in mind, that the majority of cargo ships already apply the IMO Intact Stability criteria in practice as if they were mandatory. • Revision of SOLAS Chapter II-1 A mandatory status of the anticipated Part A of the IMO Code on Intact Stability must be laid down and confirmed in the SOLAS Convention. This can be done by a simple re-wording of Regulation II-1/25-8, Stability information, in sub-paragraph 1. The existing text reads: 1 The master of the ship shall be supplied with such reliable information as is necessary to enable him by rapid and simple means to obtain accurate guidance as to the stability of the ship under varying conditions of service. The information shall include:

.1 a curve of minimum operational metacentric height (GM) versus draught which assures compliance with the relevant intact stability requirements and the requirements of regulations 25-1 to 25-6, alternatively a corresponding curve of the maximum allowable vertical centre of gravity (KG) versus draught, or with the equivalents of either of these curves.

The proposed amendment would consist in a change of the words "relevant intact stability requirements" into the words "applicable criteria laid down in the International Code on Intact Stability, Part A,". The new text would read in full: 1 The master of the ship shall be supplied with such reliable information as is necessary to enable him by rapid and simple means to obtain accurate guidance as to the stability of the ship under varying conditions of service. The information shall include:

.1 a curve of minimum operational metacentric height (GM) versus draught which assures compliance with the applicable criteria laid down in the International Code on Intact Stability, Part A, and the requirements of regulations 25-1 to 25-6, alternatively a


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corresponding curve of the maximum allowable vertical centre of gravity (KG) versus draught, or with the equivalents of either of these curves.

It should be noted that the appended formulation "or with the equivalents of either of these curves" contains the optional application of national criteria, which are at least equivalent to the IMO criteria with regard to the information "minimum GM" or "maximum KG" for the distinguished draught of the vessel. The cost of this particular amendment for Administrations will be shared with other SOLAS-amendments introduced at the same SOLAS Conference. There are no direct costs for the shipping industry. • Revision of national regulations A revision of national regulations would only be necessary if existing national criteria would fall below the standard set by the IMO criteria. This can be identified by comparing the GM- or KG-limit curves of the particular ship. From the survey of IS-Code application by flag states it appears that this will rarely be the case. Therefore the cost for Member Governments will be negligible. • Consequences for ship design and classification Since classification societies under IACS and many other societies have already adopted the IMO Intact Stability criteria as mandatory requirement for the allocation of a class certificate there will be no change of procedures and consequently no extra costs. The present concern among scientists in ship theory and naval architecture about the appropriateness of the existing IMO Intact Stability criteria may be seen as prohibiting a mandatory status at this time. However, any attempt to develop criteria, which would substantially improve safety against capsizing by in-built features, appears infeasible [12]. It is therefore preferable to uniformly apply the existing criteria, at least for critical ships in the context of this study. A mandatory status of the IMO Intact Stability criteria will strengthen the common basis for fair competition among ship builders and national economy interests, at least from a technical point of view. • Consequences for ship operation • Strengthening of legal demands on shippers and carriers An indirect positive effect of mandatory stability criteria can be expected on the correct supply of cargo information by shippers and on easing the pressure to ship masters from carriers (charterers) with regard to down loading the vessel. This will, of course, imply a certain effort to be taken for generating and forwarding correct cargo figures and on thorough assessment of operational stability. This indirect effect can be established and controlled by enhanced public attention, e.g. by prosecution of offences against regulations, and/or by private effort of the industry. The cost of this additional effort must be borne by the customers of sea transport service in general.


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If the maritime community succeeds to raise the level of reliability of cargo information and of thorough stability management evenly throughout the world, no imbalance of competition will arise and the additional cost will pay back in the long term by a reduction of delays and accidents, possibly also by a reduction of insurance premiums. • Standardisation of key shipboard operations regarding stability management A mandatory status of the IMO Intact Stability criteria may promote the existing sound practice of shipboard stability management within many major shipping companies to become standard among all companies, thereby providing fair competition on a higher level of safety. The training and education of deck officers and masters will harmonise regarding stability management, and progress of development of technical tools for stability management and their implementation into shipping practice will be encouraged. The costs of these measures are either negligible or, in the case of specific technical tools, will pay back by more reliable service and customer orientation. • Optional supervision by port state authorities Port State Control regimes will obtain the necessary legal instrument and the justification to formally check the assessment of ship's stability before departure and detain a vessel where necessary. Such expansion of PSC-activities is certainly not cost-neutral, but beneficial and justified with respect to tax-payers if carried out proportional to the needs. • Summary of cost-benefit assessment The benefit of mandatory IMO Intact Stability criteria for the safety of shipping can be judged as considerable, while there are no direct cost for the industry for the legal implementation. The public cost for the legal implementation are negligible. Ship design and classification will not be affected, because the presently recommended criteria are already widely applied by naval architects and classification societies. There is a certain additional private effort to be expected if the mandatory status of the criteria would lead to an enhancement of legal demands on shippers, regarding more realistic cargo information, and on carriers, regarding the consequences of an improved assessment of departure stability. Another cost related consequence would be the expansion of onboard equipment for stability management, to be borne by the owners. But these additional cost can be expected to pay back in medium to long term by improved safety and reliability.

Expansion of PSC-programs towards operational stability will cause public costs, but this would be justified by necessity and controlled by public interest. In summary, there is no reason to be seen why the IMO Intact Stability criteria should not become mandatory.


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• Recommendations for decision making The above Formal Safety Assessment has shown that the presently non-mandatory status of the IMO Intact Stability criteria, although widely used by ship yards, classification societies, flag states and ship operators, bears a distinguished potential of creating hazardous situations which may lead to stability accidents. There is, in particular for certain types of ships, a compelling need to eliminate the "grey zone of negotiability" of this important safety margin and to reverse the trend towards compromising safety of life, the marine environment and property in shipping. A conversion into a mandatory status would substantially improve the situation through several mechanism. The costs of this measure are comparably small and largely controllable by the shipping industry itself. If a mandatory status of the existing IMO Intact Stability criteria would create difficulties for the design and approval of certain types of ships this mandatory status could be provisionally limited to the critical types of ships as identified in this study. It is therefore recommended to make the IMO Intact Stability criteria mandatory. The following steps of action are suggested from the outcome of this study, notwithstanding the formal application for inclusion of this proposal into the work program of the Maritime Safety Committee and relevant subsidiary bodies: 1. Discussion of and agreement on a structural revision of the existing Code on Intact

Stability in the sprit of the draft presented in chapter 3.4.1 of this study. 2. Discussion of and agreement on a revision of certain provisions of the existing Code on

Intact Stability taking relevant submissions of Member Governments into account. 3. Discussion of and agreement on a possible temporary exemption of certain ship types

from the mandatory application of the criteria taking relevant submissions of Member Governments into account.

4. Discussion of and agreement on an amendment to SOLAS Regulation II-1/25-8 in the

sprit of the draft presented in chapter 4.2.2 of this study. Relevant subsidiary bodies would be: − SLF Sub-Committee for the revision of the IS-Code and the amendment to SOLAS

Regulation II-1/25-8, as proposed above, − STW Sub-Committee for the revision of the STCW-Code with regard to on-board

stability management, if considered appropriate, − DE Sub-Committee to consider equipment for stability management if requested by the

SLF Sub-Committee.


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Literature [1] Francescutto, A.: Intact Ship Stability – The Way Ahead; Proceedings of the

6th International Ship Stability Workshop, Webb Institute, 2002 [2] Kobylinski, Dr. L. K.: Performance Oriented Intact Stability Criteria; Comments by

Poland to the Intersessional Correspondence Group on Intact Stability; March 2003 [3] Bruinsma, W.A.: Safe Transportation of Containers by Sea and Safe Unloading and

Loading of Container Vessels; The Hague, 2001 [4] Kaps, H., Kastner, Dr. S. and Knickmann, A: Pilotstudie Ladungssicherheit Seeverkehr,

Fe-Nr. 40099/84; Hochschule Bremen, 1985 [5] Kaps, H. and Kastner, Dr. S.: Beurteilung der Stabilität von Schiffen in der Praxis; Fe-Nr.

40199/87, Hochschule Bremen 1989 [6] Kaps, H. e.a.: Stabilität Seeschiffe; Fe-Nr. 40301/93, Hochschule Bremen, 1994 [7] Institut für Seeverkehrswirtschaft und Logistik (ISL): Shipping Statistics Yearbook 2002,

Bremen, December 2002 [8] Institut für Seeverkehrswirtschaft und Logistik (ISL): Shipping Statistics and Market

Review; World Merchant Fleet, Bremen, January/February 2003 [9] Institut für Seeverkehrswirtschaft und Logistik (ISL): Shipping Statistics and Market

Review; World Shipbuilding, Maritime Casualties, Bremen, August/September 2002 [10] Institut für Seeverkehrswirtschaft und Logistik (ISL): Shipping Statistics and Market

Review; General Cargo and Container Shipping, Bremen, June 2002 [11] International Maritime Organization: SOLAS, Consolidated Edition, London, 2001 [12] Kobylinski, Dr. L. K.: Stability Standards – Future Outlook; Proceedings of 7th

International Conference on Stability of Ships and Ocean Vehicles; Lauceston, Tasmania, 2000

[13] International Maritime Organization: MSC/Circ. 931; MEPC/Circ.366; 1999

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