Evaluation by a Quantitative Index about Intact Stability Performance in Waves of a Set of Megayacht Units

Intact stability represents one of the most important topics when addressing ship safety, and it is ruled by the IMO Intact Stability code, evaluating ship stability in a calm water scenario. However, the interest in ship stability in waves has increased in recent years and this has led to the formulation of the second generation intact stability criteria (SGISc), finalized at IMO in 2020. In this research, an approach to quantitatively and comprehensively evaluate the ship stability performance in waves has been pursued. A methodology is developed with reference to the SGISc. The intact stability in waves index (ISWI) has been proposed, with the aim to become a complementary tool for designers and shipbuilders in the assessment of stability performance in waves. The ISWI represents a comprehensive stability index, able to capture the stability in waves performance of a vessel. The stability index has been verified on a set of megayacht units and its sensitivity to the wave characteristics has been tested, changing the environmental conditions. The outcomes point to a good agreement between the ISWI and the influence of environmental condition changes on the stability performance.