A stern unit of marine craft that comprises a casing, a propeller, a propeller shaft, and at least one rudder actuated by hydraulic pistons is described. The casing is open at the bottom, with its bottom surface having a parabolic shape in cross-section. The casing has an inlet section near to the hull that diverges rearwardly toward an outlet section. The casing provides a housing to the shaft, the propeller, and the rudders, with a gap located above the trace line of the boat bottom where air is sucked above the water surface line such that an air film extends inside the casing along the bottom surface of the casing to an outlet of the casing. The air film reduces frictional resistance between the flowing water and the casing surface to enable additional thrust.
展开▼
