Direct stability assessment: pragmatic solutions

ABSTRACT The second-generation intact stability criteria developed at IMO consist of three alternative assessments: level 1, level 2 and a direct stability assessment (DSA). In a probabilistic DSA, the probability of stability failure is used as a criterion, which requires some form of counting of stability failure events and therefore, requires very long simulation time. The paper studies several possibilities to simplify DSA and thus enables its use in practical design approval: extrapolation of the average time to stability failure over wave height, reduction of the number of assessment cases to few selected design situations, and use of non-probabilistic safety criteria. The results show that the extrapolation leads to sufficiently accurate results; however, outliers may require manual control; the design situations’ method provides sufficiently accurate results while significantly reducing the number of required simulations; non-probabilistic assessment significantly reduces simulation time but leads to a significant scatter of the assessment results.