Experimental Investigation of the Effect of Waves and Ventilation on Thruster Loadings

In order to obtain insight into the effect of waves and ventilation (air drawing) on propeller loading and dynamic fluctuations, tests of a model open pushing thruster were performed at different immersion ratios in different regular waves at different advance speeds. A high sampling frequency was employed for measurements, and wireless transmission was used to minimise data transfer noise. The objective of the study was to help to understand the dynamics of forces which in turn can improve the design of mechanical components for realistic loads. In additions results of the study provide knowledge for improved dimensioning of the thruster and more robust thrust allocation algorithms for dynamic positioning mode. The test set up is described briefly. Measurements of the total thrust from the thruster and propeller thrust and torque, together with underwater photographs of ventilated propeller at different submersion positions, are presented and discussed. Findings in this paper are – to some extent – also valid for podded propulsion units.