Influence of propeller loading on ship rudder performance

The results of wind tunnel experiments on typical ship rudders and propeller combinations are presented. The experiments simulated the condition of a rudder operating aft of a propeller but without the influence of the hull. Three rudder types were tested, a semi-balanced skeg rudder 'th taper ratio 0.8 and all movable rudders with taper ratios of 0.8 and 1.0. The propeller was modelled on a Wageningen B4.40. The longitudinal separation of rudder and propeller was varied, and by extending the span of the rectangular rudder an insight into the influence of propeller diameter/rudder span was provided. Results are presented for each rudder as lift and drag coefficients and centre of pressure for selected angles of attack and changes in propeller thrust loading. Surface pressure distributions over the rudder were also obtained in order to provide a detailed knowledge of the distribution of forces over the rudder. The results demonstrate the controlling influence of propeller thrust loading on basic rudder forces and on the movement of rudder centre of pressure. The changes in stall characteristics and stall angle due to propeller action were also identified. The results provide force data for use in manoeuvring calculations and detailed data for- the validation of numerical modelling of the interaction problem.