Measurement of Hydrodynamic Coefficients on a Planing Hull Using Forced Roll Oscillations

Abstract

For planing hulls, dynamic lift reduces the submergence of the hull, allowing small motions to result in large changes in hydrodynamic forces and moments. This article explores various modeling assumptions associated with transverse plane dynamics in roll and the hydrodynamic forces in the planing regime. The significance of nonlinearities in the roll hydrodynamic forces for planing hulls was investigated with regard to roll amplitude, model speed, model displacement, and roll oscillation frequency. A wooden 20° deadrise prismatic planing hull was tested at steady roll angles and in dynamic roll at various roll amplitudes and frequencies. Two displacements, three model speeds, three roll amplitudes, and four roll oscillation frequencies were tested. The measured wetted lengths, roll-restoring coefficient, roll-added inertia coefficient, and roll-damping coefficient are presented. The roll-restoring moment is found to be nonlinear with roll amplitude, the added inertia coefficient shows some dependence on model speed, and the roll-damping coefficient shows some amplitude dependence.