Investigation of asymmetric twin-rudder load behaviour through free-running model tests

During tight manoeuvres, twin-screw ships equipped with two rudders located in the propeller slip stream experience a fairly large imbalance in the hydrodynamic loads on the propeller and rudders. To investigate the phenomenon of rudder asymmetric load in some depth, manoeuvring experiments based on a free-running model were set up in which the kinematics of the model, the forces on the rudder and the stock moment were recorded. In parallel, with the aim of obtaining an exact estimation of free-stream characteristics of the rudder blade, corresponding wind tunnel experiments were also performed. Based on the results of this investigation, an analysis of the interaction effects within the hull-propeller-rudder system was performed and some conclusions were drawn.