Dual propeller drive for ski boat

Abstract

A dual prop drive for a ski boat has a gear box having an input gear that is connected to an engine output shaft. The gear box has two laterally spaced output gears on opposite sides of the input gear, with the output gears being drivingly connected to the input gear. The dual prop dive unit has two propeller shafts, each of which is drivingly connected to one of the output gears. The output gears and propeller shafts desirably rotate in counter-rotating directions. The gear box desirably reduces the rate of rotation of the propeller shafts relative to the engine output shaft. The gear box is lubricated without a pump by a gravity feed splash oil system.

1 . A method for enhancing the pulling power of a single engine recreational motor boat while maintaining desirable top speed performance, wherein the boat comprises an inboard engine that rotates a propeller through a propeller shaft, the method comprising the steps of: 
 disconnecting the main propeller shaft from the engine;    providing a gear box having an input gear adapted to be drivingly connected to the engine output shaft and having two laterally spaced output gears on an opposite sides drivingly connected to the input gear, the gear box being fitted in a boat hull adjacent the output shaft of the engine, with the input gear being mounted on an input shaft that is in driving engagement with the engine output shaft; and    drivingly connecting output gears to laterally spaced propellers positioned on the exterior of a boat, such that the propellers are driven by the output gears through propeller shafts that extend through laterally spaced openings formed in the bottom of the boat.    
   
   
       2 . A method as in  claim 1  wherein a gear box output shafts, on which the output gears are mounted, are drivingly connected to the gear box input shaft in such a way that the gear box causes the output shafts to rotate at substantially the same rotational speed as each other in counter-rotating directions, the gear box reducing the rate of the rotation of the output shafts relative to the rate of rotation of the input shaft, the output shafts being connected to propeller shafts that extend through the bottom of the boat from inner ends that are driven by the gear box to outer ends that are spaced laterally under the boat;  
   
   
       3 . A recreational motor boat having a planing hull wherein the boat has a single engine and a single engine output shaft, the improvement wherein the boat includes a gear box having an input shaft connected to the engine output shaft, the gear box having two spaced output shafts that are driven in counter-rotating directions by the input shaft through gears in the gear box, the output shafts being drivingly connected to spaced propellers mounted on the exterior of the hull, the gear box reducing the rotational speed of the output shafts in comparison with the input shaft.  
   
   
       4 . A boat as in  claim 3  wherein the gear box gear ratios reduce engine output shaft rotation by a factor of 1½ to 1.