Rudder effectiveness and speed correction in practice at tank test

Abstract

The rudder effectiveness and speed correction (RSC) is a control method to ensure the similarity of manoeuvring motion of a free-running model ship to full-scale. RSC tells how to control a model propeller rate of revolution and auxiliary thrust depending on a model ship speed. The rudder effectiveness correction (REC) is a simplified method of RSC, controlling only the auxiliary thrust. This paper presents tank test data that show a clear difference between RSC and REC and confirm how well RSC works in practice. The tank test employed a duct fan type auxiliary thruster for RSC, REC, and the skin friction correction (SFC) for comparison. The ordinary free-running model ship not using the auxiliary thruster or with no correction (NC) are also in the test program. Comparisons are made in turning and zigzag manoeuvres in calm water, and course keeping manoeuvres in regular waves. Numerical simulations verify that RSC compensates for the scale effect with higher precision than REC, and also well explain the difference of tank test data characteristics among RSC, REC, SFC and NC.