Patent ID: 7448926
Filing Date: 2008-11-11
Classification: B63H,F04D

Abstract:
1. A water propulsion unit including an upstream impeller and a downstream impeller, a pump housing, a water inlet to communicate with the upstream impeller; and an outlet to directly communicate with the downstream impeller, the said impellers being mounted on and, in use, driven by shafts so as to be co-axial with each other, within the pump housing; said impellers are spaced apart and are adapted to be rotated within the pump housing in opposite directions, and wherein each impeller includes a series of impeller blades extending radially from a central boss, and the blades of the upstream are of opposite pitch to the blades of the downstream impeller; characterized in that, the water jet propulsion unit is a low pressure high mass device; one of the impellers is arranged to impart less energy to the water than the other impeller; wherein means are provided to vary the cross sectional area of the interior of the pump housing between the upstream and the downstream impellers; and wherein the cross-sectional area of the outlet is such that in use it presents minimal impedance to the flow of water therethrough.