A study on high-lift rudder performance in adverse weather based on model tests under high propeller load

High-lift rudder performance is studied on the basis of model test results with regard to the requirement of interim guidelines of International Maritime Organization for minimum propulsion power to maintain the manoeuvrability in adverse weather. Model tests of two types of high-lift rudder in flow behind highly loaded propeller in a cavitation tunnel have clarified their performance comparing with a conventional mariner rudder. The analysis of the test data presented here proposes a procedure to deduce the equivalent rudder areas to conventional rudders for estimating minimum propulsion power of ships equipped with high-lift rudders in adverse weather. The authors estimated the required minimum speed and the minimum propulsion power of ships equipped with the high lift rudders according to the interim guidelines using the equivalent rudder areas quantified by the model tests. The test data, the analysis method, and the estimates for the guidelines reveal how the high-lift rudders perform and contribute well to reduce the required minimum propulsion power.