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.