Variable area pump discharge system

Abstract

A highly efficient watercraft propulsion system that operates continually submerged and relies on a non-circular variable area pump discharge opening which is configured, positioned and oriented so as to maximize the hydraulic reaction between the high velocity water jet stream and the surrounding body of water and is driven by a positive displacement pump.

1 . A water jet propulsion device for a watercraft, comprising: 
 a positive displacement pump for generating a jet of water; a discharge duct for discharging said jet of water, wherein said duct defines a discharge opening that is positioned under said watercraft so as to be fully submerged at all times; and    a movable element disposed within said discharge duct operative to vary the cross-sectional area of said discharge opening.    
   
   
       2 . The water jet propulsion device of  claim 1 , wherein said watercraft includes a hull and wherein said discharge opening is positioned such that a discharged jet of water flows along a submerged portion of said hull.  
   
   
       3 . The water jet propulsion device of  claim 2 , further comprising a lip that extends from said discharge duct beyond said discharge opening so as to define a surface substantially parallel to said hull along which said discharged jet of water flows.  
   
   
       4 . The water jet propulsion device of  claim 1 , wherein said discharge opening has a cross section defining a generally trapezoidal slope wherein top and bottom sides are parallel and transverse sides may be straight or curved.  
   
   
       5 . The water jet propulsion device of  claim 1 , wherein said movable element is comprised of two flat, parallel surfaces and two opposing surfaces that define a wedge having an apex that is variably extendible from within said discharge duct outwardly through said discharge opening.  
   
   
       6 . The water jet propulsion device of  claim 5 , wherein said movable element is moved toward the aft end of the vessel hull by force generated by a flow of water within said discharge duct impinging directly on said moveable element.  
   
   
       7 . The water jet propulsion device of  claim 6 , wherein said force is resisted by a spring which biases said movable element into a predefined position.  
   
   
       8 . The water jet propulsion device of  claim 7 , wherein said spring is positioned within said moveable element.  
   
   
       9 . The water jet propulsion device of  claim 8 , wherein said spring has a non-linear spring rate.  
   
   
       10 . The water jet propulsion device of  claim 6 , wherein said force is resisted by a hydraulic piston so as to position said movable element into predefined linear positions.  
   
   
       11 . The water jet propulsion device of  claim 1 , wherein one or more additional movable elements are disposed within said discharge duct to vary the cross-sectional area of said discharge opening.  
   
   
       12 . (canceled)  
   
   
       13 . The water jet propulsion system of  claim 1 , wherein said discharge opening is positioned and configured so as to limit upward and downward diffusion of a discharged water jet stream.  
   
   
       14 . (canceled)  
   
   
       15 . A water jet propelled watercraft, comprising: 
 a hull for supporting said watercraft, said hull having an aft end;    a positive displacement pump for generating a water jet;    a discharge duct for directing said water jet rearwardly, said duct having a discharge opening defining a plane, said plane being disposed below said hull and forward of its aft end.    
   
   
       16 . (canceled)  
   
   
       17 . The watercraft of  claim 15 , wherein said discharge duct includes moveable control surfaces configured to vary water jet velocity.  
   
   
       18 . The watercraft of  claim 17 , wherein said moveable surfaces define a wedge that is moveable into said plane defined by said discharge opening.  
   
   
       19 . The watercraft of  claim 17 , wherein said moveable surfaces are parallel and slide in a substantially horizontal orientation.  
   
   
       20 . The watercraft of  claim 15 , wherein said discharge duct includes a surface extending rearwardly beyond the pump discharge plane to limit downward diffusion of a discharge water jet.  
   
   
       21 . The watercraft of  claim 15 , wherein said positive displacement pump comprises a sliding vane pump.  
   
   
       22 . The watercraft of  claim 15 , wherein said positive displacement pump comprises a counter-rotating dual rotor lobe pump.