Patent ID: 8562382

Claim:
A method of starting a water jet propulsion system for a ship, said propulsion system including a stator shell for mounting to a hull of the ship and having a nozzle ending in an outlet with a cross-sectional outlet area having a diameter of at least 0.3 m, an impeller housing attached to the stator shell and having an upstream inlet, and an impeller rotatably mounted in the impeller housing for receiving water from the inlet and discharging the water through the nozzle of the stator shell so as to create a water jet upon rotation of the impeller, said method comprising activation of at least one air back flow hindering flap adjacent the nozzle during a start up phase of the water jet propulsion system, wherein the hindering flap blocks at least 50% of said outlet area to limit air from entering into said impeller housing via said nozzle, and wherein the hindering flap has an exterior corner comprising a material that has a different flexibility than a hinge portion of the hindering flap.