Theoretical prediction of the seakeeping characteristics of fast displacement catamarans

Abstract

The increase in the number of high speed craft of all types operating throughout the world that has been seen over the last decade is continuing. With this likely to remain so for the foreseeable future, there is considerable interest in being able to predict the motions of such vessels in a seaway with accuracy.This report employs both two-dimensional and three-dimensional potential flow analyses to evaluate the hydrodynamic coefficients and responses of high speed displacement catamaran forms. The hullform is based on the NPL round-bilge series, and is considered in three configurations; as a monohull and two catamaran demihull spacings. These hull configurations were investigated in regular head waves at three different forward speeds, corresponding to Froude numbers of 0.2, 0.53 and 0.8.Hydrodynamic coefficients and heave and pitch responses are presented for all of the configurations examined. Comparisons with experimental data are included and discussed. For one of the catamaran configurations comparisons of pressure measurements at points around the hull are also presented.The limitations of the theoretical models used are discussed with reference to: a) their treatment of forward speed effects,b) viscous damping effects around the resonant responses,c) the effects of changes in hull attitude with forward speed,d) the modelling of a transom stern, particularly at higher speeds