Fin for oscillating foil propulsion system

Abstract

A watercraft having propulsion means extending below the water line comprising a pair of flexible fins each adapted to oscillate through an arcuate 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 fine 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.

Claims

1. 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 and 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 adjustably restrained at its lower end near its trailing edge to provide less restraint at said trailing edge, said trailing edge being adjustably tensionable and said fin is provided with an essentially square top end to provide enhanced fin twist and more efficient propulsion; 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, and wherein the overall thickness of each of said fins decreases in the direction of its trailing edge, and has a generally peripheral area and an inner area, said peripheral area being a harder, less flexible rubber than said inner area whereby the cordwise stiffness of the fin increases from leading to trailing edge.

2. The watercraft of claim 1 wherein said inner area is of a generally sawtooth configuration.

3. 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.

4. 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.

5. The watercraft of claim 1 wherein said peripheral area has a hardness about 50 to about 90 Shore A Hardness Scale and said inner area has a hardness of about 20 to about 50 Shore A Hardness Scale.

Description

DESCRIPTION OF DRAWINGS

(1) In the drawings:

(2) FIG. 1 is an assembly view in partial cutaway showing a partial view of the fin and its assembly with the fin drive assembly.

(3) FIG. 2 shows the structure of FIG. 1 (encircled and identified by the letter A) as well as the complete fin and drive assembly.

(4) FIG. 3 is a perspective view of one of the fins of this invention.

(5) FIG. 4 is an enlargement of the structure within circle A in FIG. 3.

(6) FIG. 5 is a plan view of one of the fins prior to assembly.

(7) FIG. 6 is an exploded view of the fin showing the stiffer undermolded and soft overmolded areas, separately, and in final assembly.

(8) FIG. 7 is a sectional view taken along line 7-7 in FIG. 5.

(9) FIG. 8 is a side view of a watercraft of the present invention.

(10) FIG. 9 is perspective view of the watercraft of FIG. 8.

(11) FIG. 10 is a perspective view from above of the watercraft shown in FIGS. 8 and 9.

DESCRIPTION OF THE PREFERRED EMBODIMENT

(12) The oscillating fin 10 has a mast 12 on its or in proximity to its leading edge 13. The base is affixed to and carried by base or clew member 14. The top of the fin 10 has two squared off, nearly right angled, corners 16 and 18.

(13) The trailing edge 20 of the fin 10 has an adjustable tensioning means 22 at the base or clew 14 of the fin 10. The tensioning means comprises threaded lead screw 24 rigidly attached to the base 14. A thumb nut 26 is threadably received on lead screw 24.

(14) The lead screw 24 and thumb nut 26 set in cutout 28 in the fin 10. The exposed free face or end 30 of thumb nut 26 and the cutout 28 are such that as the thumb nut 26 is digitally rotated on the lead screw 24, the exposed face or end 30 of thumb nut 26 comes into abutting contact with the exposed edge 31 of the cutout 28 in fin 10. As the thumb nut 26 is then further advanced on the lead screw 24 in the direction of the top of the fin 10, the face 30 of thumb nut 26 exerts increased pressure on the exposed edge 31 of cutout 28. The tension in the trailing edge 20 is thereby increased. It will be understood then that as the thumb nut 26 is turned in the opposite direction so that it no longer applies force or pressure to the edge 31 of the cutout 28, the tension in the trailing edge 20 of fin 10 is lessened so that the trailing edge of fin 10 becomes more flaccid.

(15) The body of the fin 10 presently has two distinct areas. The generally peripheral area is an undermolded area 32 which is pre-formed of a harder, stiffer, less flexible rubber, preferably have a Shore A Hardness Scale of about 50 to about 90 and more preferably about 70. The undermolded area 32 forms the periphery or edges at the top and the leading and trailing edges of the fins. The part forming the undermolded area is then placed in a mold and a composition forming a softer rubber, having a Shore A Hardness Scale of about 30 to about 50, and more preferably about 40, is then overmolded to form the inner sawtooth area 34 to yield a unitary foil, as shown in FIG. 7.

(16) As shown in FIG. 7, the fin is thicker at the leading edge 13 than at the trailing edge 20. However, there is a relatively large area of stiffer peripheral rubber material 32 as the trailing edge 20 is approached. This provides increasing cordwise stiffness in the fin itself in the direction from leading edge to trailing edge even as the fin becomes gradually thinner. Cordwise stiffness can, if desired, be further increased at the trailing edge by advancing thumb nut 26 on lead screw 26.

(17) The sawtooth configuration of the softer rubber material at 34 is preferred. However, other similar shapes of the softer area can be devised by those skilled in the art to provide the same fin characteristics.

(18) The base 14 includes inner member 36 having a through hole for receiving the shaft 38 on which the base carrying the fin 10 rotates in oscillating fashion. Integrally formed at the center of the outer surface of inner member 36 is sprocket 40 over which passes a chain (not shown). The entire mechanism shown in the drawings of this patent is received in the bottom of the lower compartment 45 of a kayak 46 and extends downwardly through the opening in the lower compartment 45 into the water as shown in FIG. 2. The chain drives the base with fin 10. The base has attached thereto fairings 42 and 44.

(19) It is to be understood that there are two fins 10, each with its own base, as shown in FIG. 2.