THE PRESSURE SIGNATURE OF A SINGLE HYDROFOIL OF HIGH ASPECT RATIO

The pressure distribution produced by a hydrofoil of high aspect ratio at the bottom of a shallow basin of constant depth is computed. The different character of the solution in the 2 cases of subcritical and supercritical speed is discussed. In the subcritical case, the pressure distribution is approximately sinusoidal, whereas it decreases exponentially with the distance from the foil in the case of supercritical speed. The effect of a hydrofoil upon mines of the pressure-sensitive type is considered. For ordinary operating conditions of a hydrofoil craft, it appears that the duration and amplitude of the pressure signature are of similar orders of magnitude as those of ordinry sea waves. In this case, therefore, the signature of the craft is of a type with respect to which mines are insensitive. However, if a hydrofoil craft is operated close to critical speed, it is possible to produce signatures of longer duration, approaching those resulting from ordinary vessels. A numerical example is calculated and some of the difficulties arising in employing hydrofoils as a mine-sweeping device are pointed out. In general, the discussion is restricted to the case of a single hydrofoil. The case of 2 or more foils, however, can be obtained by superposition of the results derived for a single foil. Equations are given which permit calculation of the load applied by a ship model to false bottoms in towing tank tests.