Abstract: A water jet propulsion unit including an intake section, a pump section having a pair of counter-rotating impellers mounted side by side on parallel driving shafts in separate cylindrical passages through the pump section and a mixing discharge section ending in a discharge nozzle. The mixing/discharge section is adapted to converge the flows of water discharge from the impellers to neutralise non-axial flow components from one impeller by non-axial flow components from the other impeller to maximise axial flow out of the mixing/discharge section. The unit may be operated as a high mass/low pressure unit or low mass/high pressure unit.

Abstract: A water jet propulsion unit for water borne craft including two contra rotating impellers, located in an upstream pump housing and a downstream pump housing respectively, and mounted on coaxial shafts. A pressure control priming device in the form of a spring loaded collapsible skirt is located between the impellers. The pressure in the downstream pump housing can be maintained at atmospheric pressure by the controlled admission of air through air inlets.

Abstract: A water jet propulsion unit suitable for use in outboard or stern-drive configuration in motor boats. The unit has an intake section, a pump section and a drive section within which is incorporated a pressure control device and nozzle. In the pump section there are two counter-rotating impellers on concentric counter-rotating shafts. The impellers are mounted upstream of the drive section. The drive section contains a drive transmission carrier to which is attached the pressure control device both being located in the vortex created in the water flow, downstream of the two impellers. The pressure control device allows the propulsion unit to operate in a low pressure high mass mode while maintaining pump priming. The impellers can be removed without disassembly of the drive transmission carrier.