Theoretical prediction of running attitude of a semi-displacement round bilge vessel at high speed

Abstract

Running attitudes of semi-displacement vessels are significantly changed at high speed and thus have an effect on resistance performance and stability of the vessel. There have been many theoretical approaches about the prediction of running attitudes of high-speed vessels in calm water. Most of them proposed theoretical formulations for the prismatic hard-chine planing hull. In this paper, running attitudes of a semi-displacement round bilge vessel are theoretically predicted and verified by high-speed model tests. Previous calculation methods for hard-chine planing vessels are extended to be applied to semi-displacement round bilge vessels. Force and moment components acting on the vessel are estimated in the present iteration program. Hydrodynamic forces are calculated by ‘added mass planing theory’, and near-transom correction function is modified to be suitable to a semi-displacement vessel. Next, ‘plate pressure distribution method’ is proposed as a new hydrodynamic force calculation method. Theoretical pressure model of the 2-dimensional flat plate is distributed on the instantaneous waterplane corresponding to the attitude of the vessel, and hydrodynamic force and moment are estimated by integration of those pressures. Calculations by two methods show good agreements with experimental results.