Numerical and Experimental Study on Ventilation for Azimuth Thrusters and Cycloidal Propellers

On ships in rough water, the propellers can be subject to ventilation if the propulsors approach or break the water surface. The entrapped air results in large force and torque fluctuations which may lead to the power transmission system failing. Additionally, a ship with ventilating propellers will encounter thrust losses that will limit the maneuverability in rough seas. Whereas many investigations into the ventilation behavior of azimuth thrusters were carried out in the past, no publications are known to the authors where cycloidal propellers, such as the Voith Schneider Propeller, have been examined in that regard. With the help of scale model testing, the study on hand compares the ventilation characteristics of a rudder propeller to those of a Voith Schneider Propeller. The tests are supported by CFD calculations that reveal details of the flow mechanisms involved in propeller ventilation.