Flapping manual propulsion system for personal watercraft

Abstract

A manual propulsion system for a watercraft includes an axle horizontally mounted below a bottom surface of the watercraft in a direction perpendicular to a centerline of the watercraft, an elongated fin rotatable around the axle, the elongated fin being oriented along the centerline of the watercraft, a location of the axle dividing the elongated fin into a forward portion in front of the axle and an aft portion behind the axle in reference to a travel direction of the watercraft, the forward portion being shorter than the aft portion, a first foot pedal linked to the forward portion of the elongated fin, a forward motion by the first foot pedal lifting the forward portion of the elongated fin, and a second foot pedal linked to the aft portion of the elongated fin, a forward motion by the second foot pedal lifting the aft portion of the elongated fin.

What is claimed is: 
     
         1 . A manual propulsion system for a watercraft, the system comprising:
 a first axle horizontally mounted below a bottom surface of the watercraft in a direction perpendicular to a centerline of the watercraft;   a first elongated fin rotatable around the first axle, the first elongated fin being oriented along the centerline of the watercraft, a location of the first axle dividing the first elongated fin into a first forward portion in front of the first axle and a first aft portion behind the first axle in reference to a travel direction of the watercraft, the first forward portion being shorter than the first aft portion;   a first foot pedal linked to the first forward portion of the first elongated fin, a forward motion by the first foot pedal lifting the first forward portion of the first elongated fin; and   a second foot pedal linked to the first aft portion of the first elongated fin, a forward motion by the second foot pedal lifting the first aft portion of the first elongated fin.   
     
     
         2 . The system of  claim 1 , wherein the first aft portion of the first elongated fin is wider than the first forward portion of the first elongated fin. 
     
     
         3 . The system of  claim 1 , wherein at least a portion of the first aft portion of the first elongated fin is flexible. 
     
     
         4 . The system of  claim 1 , wherein at least a portion of the first aft portion of the first elongated fin is detachable. 
     
     
         5 . The system of  claim 1 , wherein the first and second foot pedal are attached to a first and second crank, respectively, both the first and second crank being rotatable around a second axle horizontally mounted to the watercraft in a direction perpendicular to the centerline of the watercraft. 
     
     
         6 . The system of  claim 5 , wherein the first crank is attached to a first curved member linked to the first forward portion of the first elongated fin; and the second crank is attached to a second curved member linked to the apt portion of the first elongated fin. 
     
     
         7 . The system of  claim 6 , further comprising a first cable linking the first curved member to the first forward portion of the first elongated fin and a second cable linking the second curved member to the apt portion of the first elongated fin, wherein the first cable wraps around at least a portion of the first curved member and has a first end attached to the first curved member and a second end attached to the first forward portion of the first elongated fin, and the second cable wraps around at least a portion of the second curved member and has a third end attached to the second curved member and a fourth end attached to the apt portion of the first elongated fin. 
     
     
         8 . The system of  claim 7 , wherein a distance from the first cable on the first forward portion of the first elongated fin to the first axle is equal to a distance from the second cable on the apt portion of the first elongated fin to the first axle. 
     
     
         9 . The system of  claim 7 , wherein a suspended portion of the first cable is of a same length as a suspended portion of the second cable. 
     
     
         10 . The system of  claim 6 , wherein the first curved member has a first circumference in contact with the first cable, the first circumference being a part of a first circle centered in the second axle; and the second curved member has a second circumference in contact with the second cable, the second circumference being a part of a second circle centered in the second axle. 
     
     
         11 . The system of  claim 10 , wherein the first and second circle have a same diameter. 
     
     
         12 . The system of  claim 10 , wherein the first and second circle have a different diameter. 
     
     
         13 . The system of  claim 1 , further comprising a second elongated fin rotatable around the first axle, a location of the first axle dividing the second elongated fin into a second forward portion in front of the first axle and a second aft portion behind the first axle in reference to the travel direction of the watercraft, the second forward portion being shorter than the second aft portion, wherein the first foot pedal is linked to the second aft portion of the second elongated fin and the second foot pedal is linked to the second forward portion of the second elongated fin. 
     
     
         14 . The system of  claim 13 , wherein the first and second foot pedal are attached to a first and second crank, respectively, the first crank being attached to and rotatable along with a first shaft, the first shaft being rotatably mounted to the watercraft in a direction perpendicular to the centerline of the watercraft, the second crank being attached to and rotatable along with a second shaft, wherein the first shaft fits coaxially in a center hole of the second shaft. 
     
     
         15 . The system of  claim 14 , wherein the first crank is attached to a first curved member, the first curved member and a second curved member being attached to and rotatable along with the first shaft, the first curved member being linked to the forward portion of the first elongated fin by a first cable, the second curved member being linked to the aft portion of the second elongated fin by a second cable; and the second crank is attached to a third curved member, the third curved member and a fourth curved member being attached to and rotatable along with the second shaft, the third curved member being linked to the aft portion of the first elongated fin by a third cable, the fourth curved member being linked to the forward portion of the second elongated fin by a fourth cable. 
     
     
         16 . A method for manually propelling a watercraft, the method comprising:
 mounting a first axle horizontally below a bottom surface of the watercraft in a direction perpendicular to a centerline of the watercraft;   engaging a first elongated fin rotatable around the first axle, the first elongated fin being oriented along the centerline of the watercraft, a location of the first axle dividing the first elongated fin into a first forward portion in front of the first axle and a first aft portion behind the first axle in reference to a travel direction of the watercraft, the first forward portion being shorter than the first aft portion;   linking a first foot pedal to the first forward portion of the first elongated fin, a forward motion by the first foot pedal lifting the first forward portion of the first elongated fin; and   linking a second foot pedal to the first aft portion of the first elongated fin, a forward motion by the second foot pedal lifting the first aft portion of the first elongated fin.   
     
     
         17 . The method of  claim 16 , wherein the first and second foot pedal are attached to a first and second crank, respectively, both the first and second crank being rotatable around a second axle mounted horizontally to the watercraft in a direction perpendicular to the centerline of the watercraft. 
     
     
         18 . The method of  claim 17 , wherein the first crank is attached to a first curved member linked to the first forward portion of the first elongated fin by a first cable; and the second crank is attached to a second curved member linked to the apt portion of the first elongated fin by a second cable. 
     
     
         19 . The method of  claim 16 , further comprising engaging a second elongated fin rotatable around the first axle, a location of the first axle dividing the second elongated fin into a second forward portion in front of the first axle and a second aft portion behind the first axle in reference to the travel direction of the watercraft, the second forward portion being shorter than the second aft portion, wherein the first foot pedal is linked to the second aft portion of the second elongated fin and the second foot pedal is linked to the second forward portion of the second elongated fin. 
     
     
         20 . The method of  claim 19 , wherein the first and second foot pedal are attached to a first and second crank, respectively, the first crank being attached to and rotatable along with a first shaft, the first shaft being rotatably mounted to the watercraft in a direction perpendicular to the centerline of the watercraft, and the first crank being also attached to a first curved member, the first curved member and a second curved member being attached to and rotatable along with the first shaft, the first curved member being linked to the forward portion of the first elongated fin by a first cable, the second curved member being linked to the aft portion of the second elongated fin by a second cable, the second crank being attached to and rotatable along with a second shaft, the first shaft being fitted coaxially in a center hole of the second shaft, and the second crank being also attached to a third curved member, the third curved member and a fourth curved member being attached to and rotatable along with the second shaft, the third curved member being linked to the aft portion of the first elongated fin by a third cable, the fourth curved member being linked to the forward portion of the second elongated fin by a fourth cable.