High efficiency hydrofoil and swim fin designs

Abstract: Methods are disclosed for increasing lift and decreasing drag on hydrofoils and swim fins. Methods are disclosed for providing a hydrofoil with a substantially longitudinal recess or venting system located substantially along the center axis of the hydrofoil. Methods also include providing the attacking surfaces of hydrofoils with an anhedral contour that forms a substantially lengthwise channel with the recess or venting means located along the center axis of this lengthwise channel. Methods are also disclosed for arranging a central recess or venting system to permit water to flow through it toward the lee surfaces in order to reduce the occurrence of outward directed spanwise flow conditions along the attacking surfaces and encourage inward directed spanwise flow conditions to occur along the attacking surfaces. Methods are disclosed for applying lift generating and drag reducing methods to both non-flexible and flexible hydrofoil blades that are used in reciprocating propulsion strokes through a fluid medium. Methods are also provided for controlling and reducing the build up of torsional stress forces within a flexible hydrofoil as it is encouraged to twist to a reduced angle of attack during use.