Hydrodynamic assessment of stepped planing hulls using experiments

Abstract

This study aims to evaluate the hydrodynamic characteristics of stepped and without step planing hulls by conducting experiments at NIMALA towing tank, Iran. For this accomplishment, total resistance, trim angles and total wetted area are measured for without step hulls, under various deadrise angles (β) and Froude numbers (Fr∇). Moreover, total resistance, trim angles, reattachment length, as well as forebody and aftbody wetted surfaces of one step planing hulls are investigated at different longitudinal distances of the step from transom (Ls) and Froude numbers. According to our lab tests, total resistance, total trim angle, and bottom wetted area of without step planing hulls are increased by an increase in the deadrise angle. The dynamic trim angle of one step planing hull is decreased by an increase in the hull velocity and longitudinal distances of the step from the transom. However, lower resistance is obtained for smaller longitudinal distances of the step from the transom. Moreover, forebody, aftbody, and total wetted areas are increased by an increase in the longitudinal distances of the step from the transom. Based on the comparison between the results obtained from without step and stepped planing hulls, it is found that the total wetted area of stepped planing hulls is significantly smaller than that of without step hull, while, greater total trim angle is achieved for stepped planing hulls compared to the without step hull.