Application of Slender Body Theory to Rolling Motion of a Moving Ship with Bilge Keels

Abstract

A slender body theory for rolling motion of a moving ship with bilge keels is consistently formulated. Under a linear assumption, this theory is in full consideration of both a free surface and free vortex layers. Consequently the three dimensional boundary value problem turns to two dimensional wave making problems considering free vortex layers that flow from the upper stream. Calculated results are presented for two simple uniform bodies with bilge keels and a coastal fishing boat.Furthermore, a comparison between the theory and experiments for the fishing boat is given. Agreements of the comparison are not satisfactory, because the theory ignores non-linear phenomena and changes of running attitudes. The results show how the linear hydrodynamic components due to the hull and bilge keels contribute to the roll damping moment for the ship.