Theoretical prediction of the seakeeping characteristics of two fast displacement catamarans in oblique seas

Abstract

This report employs two different three-dimensional potential flow analyses to evaluate the hydrodynamic coefficients and responses of two high speed displacement catamaran forms. The hullforms are based on the NPL round-bilge series and the Series 64 form. For each hullform two catamaran demihull spacings are considered. These configurations are investigated in regular deep water waves at three different heading angles; namely head seas (? = 180°), ? = 150° and ? = 120°, and for a forward speed corresponding to a Froude number of 0.65.A selection of hydrodynamic coefficients are presented, together with heave, pitch and roll responses for all of the configurations examined. Comparisons with experimental measurements are included and discussed. Differences between the two three-dimensional methods are discussed and the limitations of the current theoretical methods highlighted. Possible ways to improve the theoretical models are outlined with particular reference to: a) the treatment of forward speed effects,b) viscous damping effects around the resonant frequencies,c) the effects of changes in hull attitude with forward speed,d) the modelling of a transom stern, particularly at high forward speeds