Tests of a Planing Boat Model With Partial Hydrofoil Support, Peter Sherman, Aug 58(0156)
High-speed small craft continue to be used for a variety of military purposes. Possible means of improving the performance of such craft are accordingly of interest. The application of hydrofoils to small craft has been extensively investigated in recent years. It has been found, however, that a boat which is entirely supported by hydrofoils is relatively expensive and complex, both to develop and to build. A possible alternative way of improving the performance of high-speed small craft would be to utilize a planing hull together with hydrofoils which support only part of the weight of the craft. By this approach, it can be presumed that the craft's resistance would be reduced in two ways. First, part of the weight would be supported by hydrofoils operating at a higher lift-drag ratio than the hull alone. Second, the hydrofoil lift could be applied in such a way as to improve the trim angle of the hull. A model of a planing boat was equipped with two horizontal submerged hydrofoils which were designed to carry part of the weight of the craft. Smooth-water resistance tests were made with the foils at various fore-and-aft positions and various angles of attack to determine the optimum arrangement. Tests were also made of the foils alone. It was found that an appreciable scale effect on foil performance existed at Reynolds numbers below about 5 x 105. The data from the tests of the hull with foils, when corrected for scale effect on foil performance, indicated that the resistance of a planing boat can be decreased when such foils are added by as much as 27.5 percent. The best result was attained with the foils located at 28 percent of the hull length aft of the bow, and with the foil chord line at an angle of -3.5 deg. with respect to the hull baseline.