Experimental Studies on Flow around Fin Keel of Sailing Yacht

Abstract

Hull forms of sailing yachts differ considerably from those of general merchant ships. As compared with general merchant ships, sailing yachts are small in L/B and d/B of the main hull and have a fin keel below the surface of the water, that converts the fluid force generated by the sail into thrust. The fin keel and the main hull form a junction, and the flow around the fin keel is a typical juncture flow on a protruded curved surface. It is known that horseshoe vortices are generated around the junction. Since these vortices increase fluid drag, they should be suppressed as much as possible. The fin keel has much effect also on the free surface flow around the sailing yacht. It is recognized that the wavemaking phenomena by the fin keel can not be ignored in the high speed range.In the present paper, experimental studies about the flow field around the fin keel are carried out for the KIT-34 model designed by Masuyannan. Based on these experimental results, possibilities of reducing fluid resistance acting on the sailing yacht are discussed for the condition without yaw angle. In order to suppress horseshoe vortices, a fillet and small bulbs fixed on the junction are tested. For the purpose of reducing wave-making resistance, an inverse taper keel is tested.