The behavior of fast and relatively small ships in large following seas has been a serious concern for the operators for a long time now due to the possible occurrence of “broaching”. Due to the relatively low encounter frequency of these fast boats with respect to the large and high following and stern quartering seas an intensive coupling between surge, roll and yaw may occur which may finally lead to a capsize of the boat. The applied (and necessary) rudder control using the conventional rudder layout to prevent the excessive yaw motion may even further aggravate the situation.
In an extensive research project the Delft Ship hydromechanics Laboratory of the Delft University of Technology has constipated, developed, tested and evaluated the application of a “bow rudder” to control this situation much better. In conjunction with the conventional rudders (or waterjets) at the stern the application of such a bow rudder yielded a significant (up to 50%) reduction of the both the yaw and the roll motion in these conditions. Comparative studies of models with and without such a “bow rudder” in the towing tank showed no tendency to broaching of the boat with bow rudder at all any more. In a later design evolution this bow rudder has evolved into the development of a “retractable bow rotor”, using the well-known Magnus effect as the lift (steering) force generator. This made it possible to retract the rotor when it’s application was not asked for and thereby eliminating any possible negative effect on the resistance of the boat.
The results of earlier studies will be shown in this publication together with the obtained results of various towing tank test campaigns carried out to develop the rotor and also some different design concepts. Based on these tests an actual rotor has been build and placed on board a real ship, a DAMEN Stan Pilot 2205, a pilot boat of circa 22 meters long and capable of attaining a maximum speed of 25 knots. Herewith full scale measurement have been carried out at the North Sea and these results will also be presented here. In addition the results of tests specially of interest for a typical Pilot Boat operation will be shown.
