This paper presents the results and analyses of a combined numerical-experimental study into the performance of three types of rudder to quantify the interactions between propeller, nozzle and rudder at extreme rudder angles. Conventional, flapped and triple rudders are studied numerically as well as experimentally to evaluate the drag, lift and moment generated by the rudders at moderate to extreme rudder angles and at forward propeller shaft speeds and inflow speeds. The experiments were carried out to evaluate the suitability of the three rudder types for a proposed cargo carrier in terms of controllability. The experiments were carried out at the self-propulsion condition of the model equipped with twin stock ducted propellers along with each of the rudder systems. An extensive numerical study was carried out to evaluate the performances of the three rudders in terms of flow velocity, pressure and wake fields. Drag, and lift for different angle of attacks are obtained for complicated propeller-nozzle-rudder arrangements. Investigations are carried out to study the effects of the interaction of the rudder with the propeller-nozzle assembly at extreme rudder angles at high as ±40°. For simplicity, the geometry of the vessel was not modelled in these simulations.

The experimental results are presented along with the computational results for all three rudder cases. The lift and drag measurements are in good agreement with the corresponding predictions for each of the rudder arrangements. The mutual interactions between the rudder and the propulsion system were captured in the simulations and were comparable with the corresponding measurements. The research reveals the nature of the velocity and pressure fields due to the complex interaction between the propeller, nozzle and rudders at extreme rudder angles. It is expected that the current investigation will assist naval architects, at the early design stage, to select the rudder type for their ships such that suitable maneuvering characteristics are obtained and stringent IMO maneuvering criteria are met.

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