For the propulsion of high speed vessels of the semi-displacement or planing type a propulsion system has been designed and tested at model scale which uses partially submerged controllable pitch propellers in semi-ducts for the high speed boost condition. For low speed cruising the same propellers operate fully wetted. The two different operating modes are achieved by adjusting a hinged split flap at the semi-duct inlet ramp. Design and evaluation of the so-called hybrid propulsion system are based on a case study. They comprise the hydrodynamic design of a 6-bladed propeller as well as the mechanical design of the associated controllable pitch propeller hub. Semi-duct and flap design, together with the necessary adaption of the afterbody of a thoroughly tested semi-displacement hull, are also part of the feasibility study. The evaluation of the system at model scale includes comprehensive cavitation tunnel and towing tank tests. As a result, a number of inherent advantages of the system over conventional alternatives can be claimed. In particular, the noncavitating high speed capability must be mentioned in this context. High power density and a low propeller generated noise level are additional features of the system.

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