Similarity of Rudder Effectiveness and Speed Response of a Free-Running Model Ship

Abstract

The authors had proposed a method, rudder effectiveness correction, to realize full-scale equivalent manoeuvring motion using scale models with the auxiliary thruster. In the method they introduced the rudder effectiveness correction factor to make the effective inflow velocity to rudder defined in a steady straight course similar to a corresponding full-scale ship. The method assumes the factor constant during manoeuvring motion for a model ship running at a constant propeller rate of revolution. In this report the authors propose by a numerical approach a detailed method ensuring more precisely the similarity of manoeuvring motion than the former one. The detailed method takes into account the similarities both of the speed response and rudder effectiveness. The time-varying control both of the propeller rate of revolution and rudder effectiveness correction factor, based on the new method, enables scale model ships to realize the similar manoeuvring motion to full-scale ships more accurately. Simulation calculations using the modular mathematical model of manoeuvring motion clarifies how well the detailed method raise the precision of the full-scale equivalent manoeuvring motion in free-running model ship testing comparing with the former method.