A compact computational method for predicting forces on a rudder in a propeller slipstream

A modified lifting line theory is presented which models ship rudder load characteristics when operating downstream of a propeller. The effects of the propeller upstream are modelled using blade element-momentum theory and are incorporated in the lifting line analysis as changes in the spanwise input velocity and incidence distributions. An outline of the theoretical analysis is given, together with detailed comparisons with experimental data. It is demonstrated that satisfactory predictions of the form of the spanwise loadings for different propeller thrust loadings and rudder-propellor separations can be made. The theoretical model provides a very useful design tool and examples are presented of parametric studies which use the theory to investigate variations in rudder and propeller particulars. The theoretical method is sufficiently rapid and compact that it should be suitable for incorporation directly within a manoeuvring simulation model.