Second Generation Stability Methodology

Abstract

New intact stability criteria are being developed since the re-establishment in 2002 of the Sub-Committee on stability and Load Lines and on Fishing Vessels Safety (SLF) at the International Maritime Organization (IMO) in order to take into account five particular stability failure modes (see Belenky et al., Development of second generation intact stability. Criteria, Naval Surface Warfare Center, US Navy, [1]). These are parametric rolling, pure loss of stability in astern waves, broaching-to, dead ship condition and excessive acceleration. For each failure mode, three levels are defined to assess the ship vulnerability with a gradually increasing level of accuracy in the prediction of ship response. The first level aims to be the more conservative and applicable with simple means such as pocket calculator. The second level could require the use of Excel spreadsheet or coding software while the third one consists of Direct Stability Assessment (DSA) carried out through the use of software implementing state-of-the-art ship dynamics models. We might also observe a rather static analysis at the first level evolving into a totally dynamic analysis at the third level. A ship is required to comply with one of the three criteria for each failure mode. If a vessel is considered as vulnerable according to the first level, then the second level check is carried out. A vessel failing the second level check must be subject to a DSA. In the case of a vessel being still considered vulnerable, operational guidance and/or limitations should be applied. Figure 1 is a summary diagram of the criteria.