Fin for oscillating foil propulsion system
A watercraft having propulsion means extending below the water line comprising a pair of flexible fins each adapted to oscillate through an arcurate path in a generally transverse direction across the central longitudinal dimension of the watercraft. As input force is applied, the fins twist to form an angle of attack for providing forward thrust while moving in both directions along the arcurate path. Each of the fins have a generally squared off top and preferably an outer area of harder rubber than the inner area. Each of the fins can be adjusted at the trailing edge to provide adjustable tensioning of the trailing edge.
1. A watercraft having propulsion means extending below the water line comprising a pair of flexible fins each having a leading edge, a trailing edge, a top end and a lower end, said fin being adapted to oscillate through an arcuate path in a generally transverse direction across the central longitudinal dimension of said watercraft, and means operatively associated with said propulsion means comprising foot pedals 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;
wherein each of said fins is firmly restrained along its leading edge and restrained at its lower end near its trailing edge to provide less restraint at said trailing edge, and each said fin is provided with an essentially square top end to provide enhanced fin twist and more efficient propulsion;
wherein the fin has a generally peripheral area which is harder and less flexible than the inner area whereby the cordwise stiffness of the fin itself increases in the direction of the trailing edge.
2. The watercraft of claim 1 having the improvement wherein each of said fins is provided with means at its trailing edge to provide adjustable tensioning of the trailing edge.
3. The watercraft of claim 1 having the further improvement wherein each of said fins is provided with threaded means at its trailing edge to provide adjustable tensioning of the trailing edge.
4. A watercraft having propulsion means extending below the water line comprising a pair of flexible fins each having a leading edge, a trailing edge, a top end and a lower end, said fin being adapted to oscillate through an arcuate path in a generally transverse direction across the central longitudinal dimension of said watercraft, and means operatively associated with said propulsion means comprising foot pedals 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;
wherein each of said fins is firmly restrained along its leading edge and restrained at its lower end near its trailing edge to provide less restraint at said trailing edge, and each said fin is provided with an essentially square top end to provide enhanced fin twist and more efficient propulsion, and
said fins are constructed and arranged such that as input force is applied on said foot pedals, the less restrained lower end of the fins twists to assume a propeller shape and, as the fins oscillate, the fins change pitch or shape as they simultaneously reverse direction of movement at the opposite ends of their arcuate path;
wherein the fin has a generally peripheral area which is harder and less flexible than the inner area whereby the cordwise stiffness of the fin itself increases in the direction of the trailing edge.
5. The watercraft of claim 4 having the improvement wherein each of said fins is provided with means at its trailing edge to provide adjustable tensioning of the trailing edge.
6. The watercraft of claim 4 having the further improvement wherein each of said fins is provided with threaded means at its trailing edge to provide adjustable tensioning of the trailing edge.