Flow fin
A human propelled watercraft having a pair of flexible fins supported by a mast extending into the water each adapted to oscillate through an arcuate path in a generally transverse direction with respect to the central longitudinal dimension of said watercraft. Pedals are provided for applying input force whereby as input force is applied, the flexible fins can twist to form an angle of attack for providing forward thrust with respect to the longitudinal dimension of the watercraft while moving in both directions along the arcuate path. Each of the fins preferably is composed of a layer of stiff and durable material that is wrapped around the mast. The two layers of material touch at the trailing edge and they are free to slide relative to each other. Preferably, each of the fins is provided with adjustable tensioning at the tip of the mast.
1. A fin for providing propulsion force to a watercraft having a mast carrying a fin which oscillates through an arcuate path in a generally transverse direction with respect to the central longitudinal dimension of the watercraft, said fin comprising:
a leading edge and a trailing edge, said fin further comprising a sheet of material wrapped around said mast at said leading edge and said sheet of material forming trailing edges that are touching but free to slide relative to each other.
2. The fin of claim 1 which is hollow and has chord-wise flexibility so that said trailing edge has no shear strength.
3. The fin of claim 1 wherein said fin has chord-wise flexibility so that its camber can change.
4. The fin of claim 1 having a constant chord-wise span.
5. The fin of claim 1 wherein said fin has a square tip with rounded corners.
6. A watercraft comprising propulsion means extending below the water line comprising a pair of flexible fins each having a leading edge, a trailing edge and a tip end, each fin being supported at its leading edge by a mast, each said fin being adapted to oscillate through an arcuate path in a generally transverse direction with respect to the central longitudinal dimension of said watercraft, and means operatively associated with said propulsion means for applying input force to said propulsion means whereby as input force is applied said flexible fins can twist to form an angle of attack for providing forward thrust with respect to the longitudinal dimension of the watercraft while moving in both directions along said arcuate path;
the improvement wherein each of said fins comprises a sheet of material wrapped around said mast at said leading edge, said each of said fins having trailing edges that are touching but are free to slide relative to each other, said sheet of material being bent approximately 90° to at least partially close said tip end to form a hollow chamber.
7. A watercraft comprising propulsion means extending below the water line comprising a pair of flexible fins each having a leading edge and a trailing edge, each said fin being supported at its leading edge by a mast, each said fin being adapted to oscillate through an arcuate path in a generally transverse direction with respect to the central longitudinal dimension of said watercraft, and means operatively associated with said propulsion means for applying input force to said propulsion means whereby as input force is applied said flexible fins can twist to form an angle of attack for providing forward thrust with respect to the longitudinal dimension of the watercraft while moving in both directions along said arcuate path;
the improvement wherein each of said fins comprises a sheet of material wrapped around said mast at said leading edge, said each of said fins having trailing edges that are touching but are free to slide relative to each other and having a thick airfoil section profile conforming to NACA0015 to provide more efficient propulsion.
8. A watercraft having propulsion means extending below the water line comprising a pair of flexible fins each having a leading edge and a trailing edge, each fin being supported at its leading edge by a mast, each said fin being adapted to oscillate through an arcuate path in a generally transverse direction with respect to the central longitudinal dimension of said watercraft, and means operatively associated with said propulsion means for applying input force to said propulsion means whereby as input force is applied said flexible fins can twist to form an angle of attack for providing forward thrust with respect to the longitudinal dimension of the watercraft while moving in both directions along said arcuate path;
the improvement wherein each of said fins comprises a sheet of material wrapped around said mast at said leading edge, said each of said fins having trailing edges that are touching but are free to slide relative to each other and said trailing edge being adjustably tensionable, only one of said trailing edges of each said fin being tensioned to enhance deformation, twist and camber of each said fin.
9. The watercraft of claim 8 wherein said watercraft is a pedaled kayak or pedaled stand-up watercraft.