Loss Prevention - Stability

Many different types of vessels are entered in the Club, each possessing their own unique stability requirements.

Generally speaking tankers, bulk carriers and passenger vessels retain more than sufficient stability to ensure compliance with the regulations when fully loaded. Dry cargo ships, container carriers and barges are subject to large reductions in stability when loaded therefore care must be taken to ensure the condition of the vessel complies with the regulations which lay down the minimum stability requirements. If these are not complied with, then the safety of the vessel, her crew and cargo will be compromised.

Over the years the Club has dealt with a number of claims involving general cargo vessels and container ships that have been caused by the vessel having inadequate stability and being allowed to undertake a voyage in that condition. There have also been a large number of similar incidents involving flat top barges loaded with break bulk, containers, scrap metal or combinations of all three. In most cases the lack of sufficient stability has not been made apparent until an external force has acted on the vessel caused by heavy sea conditions, a sharp alteration of course or the pushing of an assisting tug.

Prompted by these claims, the Club has published this booklet on basic stability aimed primarily at Members and crews of dry cargo vessels. The purpose of the booklet is to explain the fundamentals of stability and explanations as to how it can be determined which is not always readily understood by crews and personnel responsible for loading vessels. All to often the GM is taken to be the measure of a vessel’s stability and this is an incorrect assumption.

Appendix 2 contains a number of stability calculation examples and case studies which describe the circumstances leading to actual related claims dealt with by the Club.

Notwithstanding the type of dry cargo vessel or barge, the predominant cause of claims we see is a lack of adequate transverse stability on vessels carrying containers. Although the majority of incidents occurred either on specific container vessels or cargo vessels carrying containers, stability issues are equally important on all types of vessels. Fortuitously most incidents have not resulted in a total loss. This is mainly because, as the vessels listed over, the cargo has fallen overboard and positive stability was been regained, allowing the vessel to return to near upright. In other cases, the vessels developed an angle of loll and upon arrival in port, with the assistance of the authorities, the upper tiers of containers were removed and positive stability was regained by lowering the overall KG. If a vessel were to experience the serious effects of insufficient stability whilst in a heavy sea where dynamic stability is crucial, the results may not be so fortunate with loss of the vessel and life a real possibility.

The Club has also dealt with claims arising from flat barges carrying scrap metal. In each case the vessel capsized but did not sink, but in all probability the cause was inadequate stability compounded by the shifting of cargo.

Causes
We have found it rare that an unsatisfactory situation regarding the vessel’s stability develops though a single cause. In our experience it usually arises through a collection of one or more of the following factors:-

Lack of understanding of the stability criteria
A failure to observe basic principles
Arithmetical errors in calculations

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Stability: Introduction
Many different types of vessels are entered in the Club, each possessing their own unique stability requirements. Generally speaking tankers, bulk carriers and passenger vessels retain more than sufficient stability to ensure compliance with the regulations when fully loaded. Dry cargo ships, container carriers and barges are subject to large reductions in stability when loaded therefore care must be taken to ensure the condition of the vessel complies with the regulations which lay down the minimum stability requirements. If these are not complied with, then the safety of the vessel, her crew and cargo will be compromised. Over the years the Club has dealt with a number of claims involving general cargo vessels and container ships that have been caused by the vessel having inadequate stability and being allowed to undertake a voyage in that condition. There have also been a large number of similar incidents involving flat top barges loaded with break bulk, containers, scrap metal or combinations of all three. In most cases the lack of sufficient stability has not been made apparent until an external force has acted on the vessel caused by heavy sea conditions, a sharp alteration of course or the pushing of an assisting tug. Prompted by these claims, the Club has published this booklet on basic stability aimed primarily at Members and crews of dry cargo vessels. The purpose of the booklet is to explain the fundamentals of stability and explanations as to how it can be determined which is not always readily understood by crews and personnel responsible for loading vessels. All to often the GM is taken to be the measure of a vessel’s stability and this is an incorrect assumption. Appendix 2 contains a number of stability calculation examples and case studies which describe the circumstances leading to actual related claims dealt with by the Club. Notwithstanding the type of dry cargo vessel or barge, the predominant cause of claims we see is a lack of adequate transverse stability on vessels carrying containers. Although the majority of incidents occurred either on specific container vessels or cargo vessels carrying containers, stability issues are equally important on all types of vessels. Fortuitously most incidents have not resulted in a total loss. This is mainly because, as the vessels listed over, the cargo has fallen overboard and positive stability was been regained, allowing the vessel to return to near upright. In other cases, the vessels developed an angle of loll and upon arrival in port, with the assistance of the authorities, the upper tiers of containers were removed and positive stability was regained by lowering the overall KG. If a vessel were to experience the serious effects of insufficient stability whilst in a heavy sea where dynamic stability is crucial, the results may not be so fortunate with loss of the vessel and life a real possibility. The Club has also dealt with claims arising from flat barges carrying scrap metal. In each case the vessel capsized but did not sink, but in all probability the cause was inadequate stability compounded by the shifting of cargo. Causes We have found it rare that an unsatisfactory situation regarding the vessel’s stability develops though a single cause. In our experience it usually arises through a collection of one or more of the following factors:- Lack of understanding of the stability criteria A failure to observe basic principles Arithmetical errors in calculations Top of Page
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Introduction