Low-drag fin and foil system for surfboards

Abstract

The present invention is a Low-Drag Fin and Foil System for Surfboards ( 10 ), particularly including cambered fin foils ( 40; 42 ). The invention ( 10 ) also discloses low-drag, directionally unstable fin positions wherein the lesser of negative angle of attack of a trailing fin ( 50 ), versus the higher or positive angle of attack of a forward fin ( 48 ), makes the board ( 12 ) highly maneuverable by creating a yawing moment that aids the rotation of the board ( 12 ) as it is turned. The system particularly utilizes fins ( 40 ) having foil ( 42 ) shapes in which either the cambered side ( 74 ) or the non-cambered side ( 76 ) is provided with a combination of a convex curvature ( 68 ) and a concave curvature ( 70 ) to result in an oscillating curvature ( 72 ) which has a positive effect on control and acceleration

1 . (canceled) 
     
     
         2 . A fin configured for attachment to an aquatic sports board, the fin comprising:
 a top end;   a bottom end opposite the top end;   a first side surface, the first side surface of the fin having a first degree of curvature;   a second side surface opposite the first side surface, the second side surface of the fin having a second degree of curvature different than the first degree of curvature of the first side surface;   a leading edge;   a trailing edge opposite the leading edge;   a virtual chord defined by a straight line joining a center point on the leading edge of the fin to a center point on the trailing edge of the fin, the virtual chord defining an angle of attack of the fin; and   a camber line extending centrally between the first and second side surfaces from the leading edge to the trailing edge, wherein the camber line is offset relative to the virtual chord to provide the fin with a camber, and the camber line at any longitudinal distance from the bottom end to the top end is offset and cambered toward only one side of the fin, and wherein the curvature of the second side surface is continuously convex, and the curvature of the first side surface has a first convex curvature and a second concave curvature, such that the first side surface has an oscillating curvature similar to a shallow sine wave.   
     
     
         3 . The fin of  claim 2 , wherein the respective curvatures of the first and second side surfaces from approximately mid-chord to the leading edge of the fin are convex and substantially symmetrical, as referenced to the virtual chord of the fin.