Flow Fin

Abstract

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.

Claims

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 thin sheet of material adapted to wrap around the mast to form the leading edge and having trailing edges that are touching but free to slide relative to each other.

2. The fin of claim 1 which is hollow and the trailing edge has no shear strength.

3. The fin of claim 1 wherein the fin has cord-wise flexibility so that its camber can change.

4. The fin of claim 1 having a constant cord-wise span.

5. The fin of claim 1 wherein the fin has a square tip with rounded smooth corners.

6. 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 fin being supported at its leading edge by a mast, each 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 is made of a thin sheet of material wrapped around said mast to form the leading edge, said each of said fins having trailing edges that are touching but are free to slide relative to each other, said thin sheet of material being bent 90 to at least partially close the 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 fin being supported at its leading edge by a mast, each 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 is made of a thin sheet of material wrapped around said mast to form the 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 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 is made of a thin sheet of material wrapped around said mast to form the leading edge, said each of said fins having trailing edges that are touching but are free to slide relative to each other and having means at the tip of the mast to provide adjustable tensioning of the trailing edge, only one of said trailing edges of each fin being tensioned to enhance deformation, twist and camber of each fin.

9. The watercraft of claim 8 wherein the watercraft is a pedaled kayak or pedaled stand-up watercraft.

Description

THE DRAWINGS

[0030] In the drawings:

[0031] FIG. 1 and FIG. 2 show a side view and a top view of a stand up craft with a drive using the new fin.

[0032] FIG. 3 and FIG. 4 show a side view and a top view of a water craft such as a kayak with a drive using the new fins.

[0033] FIG. 5 and FIG. 6 show a side view and a front view of the drive for the stand up craft. The fins are shown in the deformed or twisted condition.

[0034] FIG. 7 shows a sectional view of the fin assembly.

[0035] FIG. 8 is a sectional view taken at a of FIG. 7.

[0036] FIG. 9 shows an exploded view of the fin assembly.

[0037] FIG. 10 is a plain view of the top end of the fin.

[0038] FIG. 11 is a sectional view taken at a-a of FIG. 10.

[0039] FIG. 12 is a sectional view taken at b of FIG. 11.

[0040] FIG. 12a is a sectional view taken at c-c of FIG. 11.

[0041] FIG. 13 shows cross sectional views of the fin in a relaxed state and in a deformed state.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0042] The fin 1 is essentially a thin sheet of material wrapped around the mast 2. The leading edge 12 is formed where the material is wrapped around the mast 2. The trailing edge 11 is where the two pieces of material meet. The clew 7 is a hole passing through both pieces of material of the fin at the base of the fin near the trailing edge 11. The trailing edge 11 and leading edge 12 of the fin 1 are parallel and the tip end 16 of the fin 1 is parallel to the axis of oscillation 28.

[0043] The fin can be injection molded from a single material such as pure nylon or glass filled nylon.

[0044] The tip end 16 includes inner pocket 15 which receives the mast 2 on which the fin 1 rotates in an oscillating fashion. The mast 2 is secured to sprocket 17 which is driven by a chain. The entire mechanism shown in the drawings of this patent is inserted through the hull of the kayak 22 or the stand up craft 23 and into the water as shown in FIGS. 1 and FIG. 3.

[0045] The clew 7 of the fin 1 are connected to the outhaul block 18 with a clevis pin 8 going through the clew 7. The outhaul 18 is free to rotate around the sprocket 6. The front fairing 5 is rigidly attached to sprocket 6 by two screws 4 and serves to reduce the hydrodynamic drag of the assembly.

[0046] Means for applying input force is provided by pushing on pedals 23 and 24 which are accessible in the water craft 22 and pedals 25 and 26 which are accessible on the stand up craft 23.

[0047] It is to be understood that there is a front fin 1a and rear fin 1b, each with its own sprocket 6, as shown in FIG. 5 and FIG. 6.

[0048] The tip of the mast 13 has a an adjustable length means 10, a #10 socket head screw accessible through a hole 14 from the tip end of the fin 1. The user rotates the screw 10 with an allen wrench through the hole 14 to adjust the mast length. The screw 10 stays in contact with the end of the pocket 15 and increases the tension in the fin 1. The clew hole 7 is bigger than the pin 8 allowing the side of the fin not in tension to slide freely. It will be understood then that as the screw 10 is turned in a counter clockwise direction tension in the fin will be increased and the fin will be stiffer.

[0049] As shown in FIGS. 10, 11 and 12, the structure of the fin 1 is a hollow chamber made of a single material and is only connected along the leading edge 12. As illustrated in FIG. 11, the section profile of the fin 1 can be identified as a NACA0015. Since the fin is basically a thin piece of material wrapped around the mast 2 it has little resistance to twist.

[0050] As shown in FIGS. 11 and 12a at the tip the flat sheet of material makes a 90 degree bend to form projections 27, the edges of which touch but are free to slide relative to each other. The projections 27 extend the full or partial cordwise extent of the tip to close the tip and reduce the hydrodynamic drag.

[0051] The deformation leads to a cambered profile, illustrated in FIG. 13.