In-depth | SUPERYACHTS Keeping it steady
Te Superyacht Builders Association (SYBAss) has observer status at the IMO, enabling it to monitor and advise in the development of new regulations that may affect the large yacht industry. Chris van Hooren, technical and environmental director of SYBAss explains the latest developments
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ignificant changes in the design and operation of ships have occurred over recent decades. Tese changes,
and their impact on the intact stability performance of ships, have motivated the development of the so-called second generation intact stability criteria by the IMO Subcommittee on Stability and Load Lines and Fishing Vessel Safety (SLF). The new criteria addresses failure modes not appropriately considered in existing intact stability criteria. Consolidation and testing of various proposed second generation intact stability criteria is now underway with a targeted completion date of 2014. Several SLF delegations have applied proposed requirements to a variety of ship types. All results are being evaluated by an Intersessional SLF Corresponding Group (ISCG) and the way forward will be discussed during the 55th SLF Subcommittee Meeting in February 2013. This article introduces the agreed
structure of the second generation intact stability requirements and briefly describes the vulnerability criteria as proposed at this time. Results of the application of the Level 1 criteria for Pure Loss of Stability and Parametric Roll on a sample of large motoryachts are presented and discussed. It shall be noted that this article reflects a
state of affairs in June 2012. Te presented information may change as a result of ongoing developments.
Structure of second generation intact stability criteria Figure 1 describes the current view of the multi-tiered approach to the second generation intact stability criteria. In this process, the current criteria
contained in the International Code on Intact Stability 2008 (2008 IS Code) are applied to all ships covered under IMO instruments. Ships built aſter 1 July 2010 that also receive SOLAS or International Load Line certificates must
The Naval Architect September 2012
Figure 1: Structure of 2nd generation intact stability requirements, excessive stability not included (Courtesy SLF Delegation of the USA)
meet criteria contained in part A of the 2008 IS Code. In addition, each ship is also checked
for vulnerability to pure loss of stability, parametricroll, surf-riding / broaching and excessive stability, using Level 1 vulnerability criteria (L1). If a possible vulnerability is detected, then the Level 2 criteria (L2) are used, followed by a direct stability assessment (DA), if necessary. For the most part, the Level 1 vulnerability criteria would merely identify ships that might be vulnerable because of hull form, speed, and/or loading condition characteristics. Te Level 2 criteria would be more rigorous. If the direct stability assessment (DA)
shows an elevated level of risk for the respective mode of stability failure, then ship specific operational guidance (OG) may be developed, which is
subject to the requirements of the flag administration (ADM). When no vulnerability is detected to
any mode of stability failure, or the risk of stability failure is not considered excessive, no additional requirements need be satisfied. The process is repeated for all stability failure modes.
Dead ship condition Te stability hazard posed to a ship when it loses power in heavy seas is referred to as dead ship condition. Tis was the first mode of stability failure addressed with a physically-based criterion, also known as the weather criterion. A more detailed description of the weather
criterion can be found in section 2.3 of the 2008 IS Code. Te SLF Subcommittee has noted, however, that the weather criterion
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