Self-tensioning pedal drive mechanism for a human powered boat

A pedal driven aquatic propulsion system of a boat comprising:

• a drive frame with means to support and journal a pedal axle assembly operatively connected to a drive sprocket, a mounting bracket integrally formed with the drive frame to mount the propulsion system to a boat frame;
• a propeller shaft operatively connecting a propeller to a driven sprocket, the driven sprocket located substantially vertically beneath the drive sprocket, wherein the respective axes of rotation of the drive and driven sprockets are skewed relative to each other, and planes of rotation of the drive and driven sprockets are disposed substantially at right angles to one another;
• an endless chain drive operatively connecting the sprockets to transmit power from the drive sprocket to the driven sprocket, the chain drive operating in a twisting three-dimensional orientation as it loops around the sprockets;
• and a pivoting self tensioning means comprising an idler arm is adjustably mounted on the frame, the idler arm further comprising at least one idler sprocket disposed in rotatable contact with the chain drive to maintain the chain under constant tension to compensate for the changing circumference length of the chain caused by at least the reasons related to heat or wear, the at least one idler sprocket having a plane of rotation that is offset from the planes of rotation of the drive and driven sprockets, wherein the self tensioning means is self actuated.