Static and dynamic stability of planing boats: application cases for an harmonized rule perspective

A comprehensive investigation of recreational small craft characteristics, during the design process, should include also stability assessment of boats underway at high speed. To this aim, in order to gain insight about the transverse dynamic stability of planing boats, a methodology has been considered and implemented, following the approach proposed by Lewandowsky. An application is performed to Series 62 boats and the successive derived hulls tested at Delft University. Two different deadrise values and some other parameters like loading coefficient, longitudinal position of centre of gravity LCG and length on beam ratio are considered in the analysis, with the aim to ascertain the sensitivity of the method and to investigate a wide range of cases. Calculation are performed with and without appendages. Results are presented in terms of the maximum non dimensional KG in relation with volume Froude number. Successively, the ISO12217 stability standards are applied to the investigated cases: besides the zero speed condition, some artificial static conditions are modelled by imposition of proper draft and trim, as identified at different speeds. The max KG curve derived from the basic zero speed criteria, i.e. positive GMT, is also calculated. The resultant maximum KG curves are compared with the values found out during the dynamic investigation, allowing to get an insight in a safety rule perspective.