Flapping manual propulsion system for personal watercraft

Abstract

A watercraft propulsion includes an elongated fin disposed below a bottom of the watercraft, the fin having a pivotal spot located closer to a forward end than to an aft end of the watercraft, a hinge attached to the bottom having a slot confining the forward end to a first vertical range of motion, a shaft passing through a hole formed in a hull of the watercraft, the shaft having a lower end below the bottom of the watercraft and an upper spot above a deck of the watercraft, the lower end pivotally engaging the fin at the pivotal spot, a first foot pedal linked to the shaft at the upper spot via a first wheel disposed below the upper spot of the shaft, and a second foot pedal linked to the shaft at the upper spot via a second wheel disposed above the upper spot of the shaft.

What is claimed is: 
     
         1 . A manual propulsion system for a watercraft, the system comprising:
 an elongated fin disposed below a bottom of the watercraft with a fin centerline in an elongated direction of the elongated fin aligned with a centerline of the watercraft, the elongated fin having a forward end, an aft end and a pivotal spot located closer to the forward end than to the aft end;   a hinge attached to the bottom of the watercraft, the hinge having a first slot confining the forward end of the elongated fin to a first vertical range of motion;   a shaft freely passing through a first hole formed in a hull of the watercraft, the shaft having a lower end below the bottom of the watercraft and an upper spot above a deck of the watercraft, the lower end pivotally engaging the elongated fin at the pivotal spot;   a first foot pedal linked to the shaft at the upper spot via a first wheel disposed below the upper spot of the shaft; and   a second foot pedal linked to the shaft at the upper spot via a second wheel disposed above the upper spot of the shaft.   
     
     
         2 . The system of  claim 1 , wherein the elongated fin has an opening at the pivotal spot and a first pin removably inserted through a body of the elongated fin into the opening and a hole formed in the lower end of the shaft for engaging the shaft to the elongated fin, wherein the first pin is positioned perpendicular to the fin centerline. 
     
     
         3 . The system of  claim 1 , wherein the elongated fin has a first and second member protruding vertically from a top surface of the elongated fin at the pivotal spot, wherein the first and second member secure a removable second pin inserted in a hole formed in the lower end of the shaft for engaging the shaft to the elongated fin, wherein the second pin is positioned perpendicular to the fin centerline. 
     
     
         4 . The system of  claim 1 , wherein elongated fin comprises a third pin protruding from the forward end of the elongated fin, wherein the first slot slidably accommodates a first protruding end of the third pin to confine the forward end of the elongated fin to the first vertical range of motion. 
     
     
         5 . The system of  claim 4 , wherein the hinge comprises a second slot symmetrical and parallel to the first slot, wherein the second slot slidably accommodates a second protruding end of the third pin, wherein the third pin is removably inserted through a second hole formed in the forward end and perpendicular to the fin centerline with the first and second protruding end of the third pin protruding from opposite sides, respectively, of the elongated fin. 
     
     
         6 . The system of  claim 5 , wherein the third pin is locked in place in the second hole by a set screw. 
     
     
         7 . The system of  claim 5 , wherein the hinge is a protruding part of the hull. 
     
     
         8 . The system of  claim 1 , wherein the first hole confines the shaft to a vertical motion. 
     
     
         9 . The system of  claim 8 , wherein an upper end of the first hole is above a water line of the watercraft. 
     
     
         10 . The system of  claim 1 , wherein the upper spot of the shaft moves between the first and second wheel with a second vertical range of motion in response to movements of the first and second foot pedal, wherein the second vertical range of motion is larger than the first vertical range of motion. 
     
     
         11 . The system of  claim 1 , further comprising a first and second crank rotatable around an axle mounted on a deck of the watercraft, wherein the first foot pedal is attached to an upper end of the first crank and the second foot pedal is attached to an upper end of the second crank. 
     
     
         12 . The system of  claim 11 , wherein the first foot pedal is linked to the upper spot of the shaft by a first cable with a first end attached to the first crank and a second end attached to the upper spot of the shaft, wherein the first cable loops around a lower part of the first wheel; and the second foot pedal is linked to the upper spot of the shaft by a second cable with a third end attached to the second crank and a fourth end attached to the upper spot of the shaft, wherein the second cable loops around an upper part of the second wheel. 
     
     
         13 . The system of  claim 12 , wherein the upper spot of the shaft has a first and second member protruding from opposite sides of the shaft, wherein the second end of the first cable is attached to the first member and the fourth end of the second cable is attached to the second member. 
     
     
         14 . The system of  claim 12 , wherein the first and second cables are of a same length. 
     
     
         15 . The system of  claim 14 , wherein the length of the first or second cable is adjustable. 
     
     
         16 . The system of  claim 12 , wherein the first and second cable are of one piece of cable looping from one side of the shaft to an opposite side of the shaft. 
     
     
         17 . The system of  claim 12 , further comprising a first and second cover disposed over the first and second wheel, respective, wherein the first cover prevents the first cable from jumping off a first groove of the first wheel; and the second cover prevents the second cable from jumping off a second groove of the second wheel. 
     
     
         18 . The system of  claim 1 , further comprising a frame mounted on a deck of the watercraft, wherein the first wheel is rotatably mounted to a lower end of the frame; and the second wheel is rotatably mounted to an upper end of the frame. 
     
     
         19 . A method for manually propelling a watercraft, the method comprising:
 attaching a hinge to a bottom of the watercraft, the hinge having a first slot confining a forward end of an elongated fin to a vertical range of motion;   freely passing a shaft through a hole formed in a hull of the watercraft, the shaft having a lower end pivotally engaging the elongated fin at a pivotal spot, the pivotal spot being closer to the forward end of the elongated fin than to an aft end of the elongated fin;   linking a first foot pedal to an upper spot of the shaft via a first wheel disposed below the upper spot of the shaft; and   linking a second foot pedal to the upper spot of the shaft via a second wheel disposed above the upper spot of the shaft.   
     
     
         20 . The method of  claim 19 , wherein the hinge comprises a second slot symmetrical and parallel to the first slot, wherein the first slot slidably accommodates a first end of a pin protruding from a first side of the forward end of the elongated fin; and the second slot slidably accommodates a second end of the pin protruding from a second side of the forward end of the elongated fin, the second side being opposite to the first side.