The paper presents results of unsteady numerical analysis of propeller-rudder system. For the calculations the Ansys Fluent solver was employed. The governing equations are RANSE. The results of computed forces, pathlines and pressure distribution on propeller and rudder are given as a function of rudder deflection angle. Initial investigations point to a number of very interesting effects, e.g. the formation on the rudder for small angle of deflection, the resulting force coincident with the direction of ship speed moving ahead. For that reason the resulting force may be considered as an additional component of the thrust force. Presented analysis may be employed during design of ships which are expected to attain good manoeuvring performance (e.g. LNG carriers) or ships which are designed with diesel-electric propulsion installation where there is a possibility to recover energy from inertia when slowing down