Marine propulsion system

Claim 1

A fluid flow amplifier for a marine propulsion water jet system including the injection of a high velocity principal water flow into a slower velocity secondary water flow to form a water jet, said amplifier comprising: an adjustable orifice through which said principle water flow is injected into said secondary water flow; hydraulically balanced means for automatically adjusting the size of said orifice so as to maintain relatively constant primary water injection velocity; a water jet pod for channeling said a secondary water flow, wherein said hydraulically balanced means includes a compensating annular sleeve mounted in said pod, and said adjustable orifice includes an annular shoulder on the inner surface of said pod and a lip on one end of said annular sleeve interacting with the shoulder, and wherein said hydraulically balanced means also includes a primary annular chamber formed between the end of said sleeve including said lip and said pod for receiving said principal water flow, a secondary annular chamber formed between the other end of said sleeve and said pod, and a constricted water flow channel interconnecting said annular chamber through said sleeve.