The effect of cavitation on the rotating cylinder rudder

Tests have been carried out in the water tunnel to measure the side force produced by a model of the rotating cylinder rudder for a range of cavitation numbers in uniform flow.

It was found that at atmospheric pressure the maximum side force coefficient obtained was 1.46 at a rudder angle of 50° compared with 0.65 at an angle of 20° when the rudder was being used in the conventional way, i.e., without the cylinder rotating. The highest useful ratio of cylinder speed to flow speed was found to be 3.0.

Under cavitation conditions it was found that the maximum side force coefficient which could be obtained was decreased as the cavitation number was reduced, thereby affecting the beneficial effects of the rotating cylinder. At the lowest cavitation number ( σ = 0.5 ) the side force coefficient developed, with the cylinder rotating at its normal optimum speed ratio of 3.0, was little greater than when the cylinder was not rotating.