Abstract: A high mass/low pressure liquid propulsion device which includes:—two counter-rotating impellers mounted inside a housing;—an inlet which in use allows inflow of liquid into the housing on a first side of said impellers; an outlet which in use allows outflow of liquid from the housing on a second side of said impellers opposite to said first side;—means for driving said impellers;—wherein the improvement comprises the provision of means for reversing the drive to said impellers, such that the direction of flow of liquid through the device is reversed and liquid enters the device through said outlet, passes through said impellers, and leaves the device through said inlet.

Abstract: A water propulsion unit having an intake housing, a pump housing and an outlet with two spaced apart counter rotating impellers being located in the pump housing. The impeller blades on one impeller have an opposite pitch to the blades of the second impeller. The impellers are configured so that one of the impellers will impart less energy to the water as it passes the blades of the impeller than the second impeller.

Abstract: A propulsion or pumping device which includes two counter-rotating shafts (3, 4) each carrying at least one impeller (7, 8), wherein each impeller (7, 8) can deflect by a predetermined amount in directions substantially perpendicular t to the longitudinal axis of the shaft (3, 4) on which the impeller (7, 8) is mounted.

Abstract: A water propulsion unit having an intake housing, a pump housing and an outlet with two spaced apart counter rotating impellers being located in the pump housing. The impeller blades on one impeller have an opposite pitch to the blades of the second impeller. The impellers are configured so that one of the impellers will impart less energy to the water as it passes the blades of the impeller than the second impeller.

Abstract: A water propulsion unit having an intake housing, a pump housing and an outlet with two spaced apart counter rotating impellers being located in the pump housing. The impeller blades on one impeller have an opposite pitch to the blades of the second impeller. The impellers are configured so that one of the impellers will impart less energy to the water as it passes the blades of the impeller than the second impeller.

Abstract: A water propulsion unit having an intake housing, a pump housing and an outlet with two spaced apart counter rotating impellers being located in the pump housing. The impeller blades on one impeller have an opposite pitch to the blades of the second impeller. The impellers are configured so that one of the impellers will impart less energy to the water as it passes the blades of the impeller than the second impeller.