ROLL DAMPING CHARACTERISTICS OF FISHING BOATS WITH AND WITHOUT DRIFT MOTION

Abstract

In the present study, the prediction method of viscous roll damping proposed by Ikeda et al. is modified for applying to a special vessel with round hull form and a long and wide bar keel (deadwood). The modified method is applied to a typical Indonesian fishing vessel, and the prediction results by the method are confirmed to be in fairly good agreement with experimental results. Effects of bilge keels on roll damping of such a vessel are also examined by the prediction method and experiments. Roll motion of such a vessel in regular beam waves is measured to find that strip methods using the modified roll damping prediction method give good results of roll responses in moderate waves but significantly overestimate the roll responses in heavy waves. It is experimentally confirmed that rapid drift motion in heavy waves increases the roll damping and decrease wave exciting roll moment in heavy seas, and that these phenomena causes the discrepancy of roll responses in heavy seas.