Patent ID: 8435089

Claim:
A marine propulsion assembly operable as a screw pump that is mountable to a support strut which has fore and aft ends and extends downward from below the hull of a ship, said assembly comprising: a- a pod shaped housing with fore and aft ends and a central longitudinal axis X, said hull having a lower side, said pod being pivotally mounted to said lower side of said hull about a pivot axis Y that extends upward from said pod through said hull and extends generally transverse of said central longitudinal axis X, b- a motor mounted within said housing, said motor having a transmission shaft extending in said aft end direction, said transmission shaft having an aft end, c- a propeller situated at the aft end of said housing and coupled to said aft end of said transmission shaft, said propeller having a hub part and at least two blades each having a near end fixed to said hub part each blade extending radially and having a remote tip edge, d- at least three flow-directing fins extending generally radially outward from said housing and terminating in an outer tip edge, each of said fins having fore and aft edges, said fins spaced apart circumferentially around said housing, said outer tip edges of said fins (i) defining a ring zone of axial length Zx, (ii) having a central longitudinal axis coaxial with said longitudinal axis X, and (iii) being situated axially between said support strut and said propeller, and e- a nozzle through which a water flow is forced by said propeller, said nozzle formed as a ring generally coaxial with said housing and having a fore part fixed to said outer tip edges of said flow-directing fins and an aft part extending axially in the aft direction where it surrounds and is adjacent said remote tip edges of said propeller blades, said propulsion assembly having no fins situated aft of said propeller and fixed to said nozzle or housing, whereby said propeller constitutes the rotor of a screw pump, where said propeller imparts a rotational torque to said water flow and said flow-directing fins impart to said water flow a rotational torque substantially equal but opposite to said rotational torque imparted by said propeller such that the flow of water is free of rotation energy at the outlet of the propeller.