Except for those specials applications where requirements dictate the use of counterrotating propellers, the choice between a single propeller and counterrotating propellers involves a tradeoff related to the higher efficiency of the counterrotating propellers and the greater complexity of the counterrotating machinery. The favorable effect of tangential velocity cancellation achieved by a counterrotating propeller system can be realized without counterrotating machinery by placing upstream of a propeller a stator that generates tangential velocities which are exactly canceled out by the propeller. The results of theoretical calculations show that, using the single propeller as a baseline, the increase in efficiency for SIPUP is 50% of that achieved by counterrotating propellers. The feasibility SIPUP for marine propulsion was demonstrated by the design and at sea testing of a SIPUP propulsor. The comparison of SIPUP’s at sea data and design predictions shows good agreement in both propulsive coefficient and vehicle speed.

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