An Experimental Study on Roll Damping of A Car Ferry with Twin-Skeg Hull

Abstract

The roll dapming characteristics of a car ferry with split-stern hull (twin skeg hull) are experimentally investigated. The experimental results show that the roll damping is increased by the twin skeg at zero forward speed and at high speed. The increase at zero forward speed is caused by the generation of large eddies at the twin skegs, and that at high speed is caused by the lift force increase due to the skegs. The bilge keel component of the roll damping, however, decreases at high speed over F_n=0.25 because of the low aspect ratio. In order to increase the roll damping, a system of bilge keels and fixed fins of large aspect ratio is designed, and its effect is experimentally investigated. The results show that the roll damping per unit area due to the fixed fins is about 12 times that due to the bilge keels at F_n=0.3 which is the cruising speed of the ship.