Studies on the Lateral Force on a Hull Induced by Rudder Deflection

Abstract

Rudder deflection produces a lateral force on a hull in addition to a normal force on the rudder. It is known that the lateral force can reach as much as 30 percent of the normal force on the rudder, and cannot be neglected even for a single-screw ship with a propeller aperture. This paper treats a method of theoretical evaluation of this force with a good agreement to experimental results for a 4.5m merchant ship model. Two kinds of hydrodynamic theories are used for the analysis, i.e. one is the lifting surface and the other the slender body theory, Assumptions used are ; 1) the water surface is regarded as a solid boundary (neglecting wave formation), 2) a ship hull is replaced by a rectangular plane, 3) a rudder is represented by a pair of semi-infinite horse-shoe vortices extending downstream along uniform stream line, 4) the boundary condition is assumed to be satisfied only along the center line of the rectangular plane.