Performance Prediction of High-Speed Planing Craft with Interceptors Using a Variation of the Savitsky Method

A prismatic hull was used to study the effect of interceptors on the performance of planing craft. Interceptors are flat surfaces that are a small geometric projection of the transom plane and cause an interruption in the water flow. This alters the pressure distribution on the hull bottom in a very dramatic manner leading to large variations in drag, running trim and heave. These parameters were measured in a model study using different interceptor penetrations, loads and center of gravity locations. An investigation of the results shows that it is possible to predict the performance parameters using Savitsky’s iteration method after accounting for the pressure induced due to the interceptor, the dynamic drag on the interceptor and variation in center of pressure. A simple approximation to the drag force and an added normal force was derived and used in conjunction with Savitsky’s iteration method. The predictions are fairly consistent with the measurements. Additionally the approximation for the added normal force was used to derive an equation for the non-dimensionalized added pitching moment.