Effect of Forward Speed on Roll Damping of a High-Speed Craft

Abstract

The effects of forward speed on the roll damping of a high speed craft are experimentally investigated. The roll damping is assumed to be divided into five components, which are the wave, the eddy, the lift, the bilge keel and the fin components. In the present analysis the friction component is ignored because it is small enough for such a hard-chine vessel. Measured lift componet of the roll damping linearly increases with forward speed up to Fn=0.4, and over Fn=0.4 increases rapidly due to the increase or the trim by forward motion. The empirical methods to predict the wave and eddy components proposed by Ikeda et. al. for conventional cargo ships are slightly modified, and can predicted the effect of forward speed on the components. The results show that the non-linear eddy component is dominant at Fn=0 and that the linear lift component is dominant at high forward speed if the vessel has no appendage like bilge keels and fins. The effect of forward speed on the bilge keel component is not so significant for normal frequency region of roll resonance. The experimental results suggest that the linear lift forces acting on the bilge keels may be important. A set of fins with the same area as the bilge keels is found to be more effective than bilege keel at high speed region because of its high lift derivatives.