The Theoretical Prediction of the Longitudinal Motions of Hydrofoil Craft

Abstract

The nonlinear theory for predicting the longitudinal response of hydrofoil craft in waves due to Weinblum is modified and the results of analog computations based on this theory are presented for comparison with available data. The complete nonlinear equations were used in the computations, and it is shown that the nonlinearities affect the oscillatory amplitudes only slightly, but that they cause large steady components of heave. The steady heave is often comparable with the amplitude of oscillation; it is always downward, tending to cause the craft to crash. The effects of unsteadiness are investigated, and it is shown that the forces are reduced as much as 40 per cent because of unsteadiness, but that there is little net effect on the amplitudes of heave and pitch. From the experimental data, it is concluded that the theory gives good predictions of the amplitudes of heave and probably of pitch.