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.

1 . A method for providing a swim fin comprising providing said swim fin with a foot attachment member and an active portion in front of said foot attachment member, said active portion having opposing surfaces, outer side edges, a root portion near said foot attachment member and a free end portion spaced from said foot attachment portion and said root portion, said active portion having a longitudinal midpoint between said foot attachment member and said free end portion, said active portion having a first half portion between said foot attachment member and said longitudinal midpoint and a second half portion between said midpoint and said free end portion, said first have portion being arranged to pivot around a transverse axis to a significantly reduced angle of attack during reciprocating kicking strokes in an amount sufficient to significantly reduce kicking resistance during said strokes.  
   
   
       2 . The method of  claim 1  wherein said active portion is arranged to bow in a transverse direction between said outer side edges to form a substantially lengthwise channel shaped contour.  
   
   
       3 . The method of  claim 1  wherein said free end portion has a recess sufficient to form two laterally spaced tip portions.  
   
   
       4 . The method of  claim 1  wherein said foot attachment member has a relatively flexible portion made with a relatively flexible thermoplastic material and a relatively harder portion made with a relatively harder thermoplastic material, said active portion having a stiffer portion that is made with a relatively stiffer thermoplastic material that is relatively stiffer than said relatively flexible thermoplastic material of said relatively flexible portion of said foot attachment member, said active portion having a relatively softer portion made with a relatively softer thermoplastic material that is relatively softer than said relatively stiffer portion, said relatively softer thermoplastic material being connected to said relatively stiffer portion with a thermal-chemical bond created during at least one phase of an injection molding process.  
   
   
       5 . The method of  claim 4  wherein said active portion has a longitudinal alignment and said relatively softer portion includes at least one elongated member having an alignment that is at an angle to said longitudinal alignment of said active portion.  
   
   
       6 . The method of  claim 5  wherein said angle is a transverse angle.