EVALUATION OF CLASSIFICATION RULES FOR DESIGN LOADS AND STRUCTURE RESPONSES IN HIGH-SPEED CRAFT

Abstract: Following the merger of the two classification societies Det Norske Veritas (DNV) and Germanischer Lloyds (GL) in September 2013 the need for a harmonized High Speed Craft (HSC) classification rule set emerged. In this study the respective rules for the bottom structure of HSC where checked against each other. This shone light on the similarities and dissimilarities between the two. The main difference found was the methodology used to determine the craft design acceleration, a concept integral to the hull design process. Further the comparative study showed a need to improve the idealisation of sandwich beams. These two topics where chosen as areas of focus in the latter part of this study. Differences regarding design accelerations led to a review of the source material for DNV’s formulae, the model trials of Fridsma (1971). It was found that the old trials didn’t necessarily capture the worst case scenarios for the model craft in question, due to a limited sea state formulation. It was also found that the exponential distribution is an inadequate assumption for the acceleration peaks of HSC. New trials are hence recommended. As it is today, only the inner skin is considered for calculations of the effective flange width for sandwich beams. It is however well known that both skins contribute to the effective flange width. Consequences are among others that the stresses over the beam are overestimated. It is further demonstrated that the effective flange width for the outer skin is bigger compared to the inner. The study presents important aspects that are recommended to consider in further studies towards a method that considers both skin for the effective flange width of a sandwich.