Numerical Evaluation of Rudder Performance Behind a Propeller in Bollard Pull Condition

Correct evaluation of rudder performance is a key issue in assessing ship maneuverability. This paper presents a simplified approach based on a viscous flow solver to address propeller and rudder interactions. Viscous flow solvers have been applied to this type of problems, but the large computational requests limit (or even prevent) their application at a preliminary ship design stage. Based on this idea, a simplified approach to include the propeller effect in front of the rudder is considered to speed up the solution. Based on the concept of body forces, this approach enables sufficiently fast computation for a preliminary ship design stage, thereby maintaining its reliability. To define the limitations of the proposed procedure, an extensive analysis of the simplified method is performed and the results are compared with experimental data presented in the literature. Initially, the reported results show the capability of the body-force approach to represent the inflow field to the rudder without the full description of the propeller, also with regard to the complex bollard pull condition. Consequently, the rudder forces are satisfactorily predicted at least with regard to the lift force. However, the drag force evaluation is more problematic and causes higher discrepancies. Nevertheless, these discrepancies may be accepted due to their lower influence on the overall ship maneuverability performance.