Optimization of Bow Thruster Openings for Improved Hydrodynamic Performance

Bow thrusters are a common feature of ships nowadays and come with the undesired effect of creating relatively large openings at the bow of the ship, increasing the resistance of the hull. The most common solution for mitigating the increase in hull resistance, and at the same time protecting the thruster from ingestion of large objects, is to use grids which are generally placed perpendicular to the local flow. Until the advent of Computational Fluid Dynamics (CFD), the effect of the grids on resistance could not be properly assessed due to the difficulty (or rather impossibility) of scaling their contribution in the towing tank, on the one hand, and the perceived negligible influence, on the other hand. Since their effects are mainly viscous, it is understandable why towing tank testing will not provide the actual picture. In the present paper, CFD is used to study several ships with bow thruster openings, at operating speed. Optimization solutions are presented and the effect of the grids as built is assessed against alternative solutions. The simulations are carried out in full scale, in three steps: the hull with completely closed tunnels; hull “as built”; hull with optimized bow thruster opening grids. The results indicate that in all studied cases, the grids are detrimental to resistance and savings can be obtained by using other solutions or different placement or orientation.