Patent ID: 8162707

Claim:
A propulsion system of displacement or semi-displacement ships, comprising one or more propellers of semi-submerged type, arranged with a partial immersion of bottom blades and with top blades emerged, regardless of craft state of motion and trim, wherein: a) said semi-submerged propellers are arranged at a ship's transom; b) a ratio of diameter (D) or a sum of diameters (Np×D) of the semi-submerged propellers to craft width (L) at a water line is greater than 0.50; c) a ratio of overall blade area (Ab) to propeller area (Ap) is greater than 0.60; d) a ratio of area (Ai) of the propeller immersed, below the water line, to propeller area (Ap) ranges from 0.30 to 0.50; and e) further comprising control means for controlling a height of a stern wave, wherein said means for controlling the height of the stern wave comprises a balancing flap arranged between the semi-submerged propellers and the ship's aft wall.