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SOLAS 2009 takes ro-ro’s to new limits In-depth | DAmAge STAbILITy


Te Stockholm Agreement added more stringent stability requirements to SOLAS 90 for ro-pax vessels following the loss of Estonia in 1994. Daria Cabaj, a naval architect with Burness Corlett Tree Quays (BCTQ), asks will the generation of new SOLAS 2009-compliant ro-pax ships be safer?


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OLAS 2009 is considered to be a major step forward in the rationalisation and harmonisation


of the damage stability rules. In general, SOLAS 2009 is perceived to achieve a higher overall level of safety and passenger ships must also comply with requirements to cover local vulnerabilities to flooding. However, there are certain designs such as ro-pax ships with long lower holds (LLH) that can be susceptible to critical damage. Although a ship can be shown to


comply with SOLAS 2009 there may be certain moderate damage scenarios that are not covered by the present regulatory framework. Recent research shows that some commercially attractive ro-ro ships with wider LLH configurations meet the current standards but are particularly vulnerable to the consequences of lower hold flooding. Although the number of such damage scenarios may be small (otherwise the required survivability index would not be met), it introduces some controversy as to whether SOLAS 2009 brought about an improvement. In fact, some recent research leads us to


the conclusion that SOLAS 2009 is a slightly higher standard than SOLAS90 but not quite as high as SOLAS90 plus the Stockholm Agreement. Maritime authorities are further examining the adequacy of requirements currently set out in SOLAS 2009 for ro-pax ships. The question as to whether or not


SOLAS 2009 offers a higher standard is difficult to answer because level of safety can be interpreted in different ways. Tis has led to a general lack of confidence in SOLAS 2009 for ro-pax ships and, as a result, the European Union (EU) has decided not to rescind the Stockholm Agreement (directive 2003/25/EC) for new ro-pax ships but to retain it in addition to the SOLAS 2009 requirements. The


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Naval architect Daria Cabaj receives RINA-Lloyds Trust safety award in 2009 from the former RINA president Stephen Payne.


EU is awaiting clarification and further direction from the International Maritime Organization (IMO) before concluding this matter.


How to define the level of safety? With a probabilistic approach to damage stability, the overall level of safety is defined by the capability of a ship surviving all possible damage scenarios (attained index, A). Tis capability must be greater, than the


stipulated level of survivability (required index, R). For passenger ships additional factors, such as protection against local vulnerabilities to flooding, must also be considered when defining the level of safety.


What makes ro-ro ships so particular? Te main characteristic of ro-pax ships is wide open decks to facilitate efficient loading and unloading. In the event of


The Naval Architect September 2010


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