THE EFFECT OF RIBLETS ON SAILS

This paper describes an experimental investigation into the effect of riblets on the aerodynamic forces generated by sails. Riblets are know n to reduce the viscous drag on flat surfaces and on airfoils, but the ir effect on the drag - or on the lift - of a highly three-dimensional , very thin lifting surface such as a sail is unknown. In this work, w e show that riblets have little effect on the drag of a sail, but they increase the lift by about 3%. The result of this increase in lift is to increase the force in the direction of boat motion by up to about 5%. This is significant, because the sails provide the only locomotive force available to a sailboat. In addition, the greatest improvement is found for the case of riblets on both sides of the sail rather than on only the pressure or the suction side. This is, fortunately, the m ost practical arrangement for use on a real sailboat.