Experimental Investigation of the Effect of Waves, Ventilation and Cavitation in Bollard Pull Conditions

Ventilation is a feared working condition of ship propulsors, especially in Dynamic Positioning operation, since it leads to the lost of thrust of the propeller resulting into an uncontrollable ship. Experience showed that the risk of ventilating propellers was negligently underestimated in traditional towing tank experiments but better predicted in depressurised towing tanks, where the ambient pressure is scaled down according to Froude similarity.
In 2012 MARIN's Depressurized Wave Basin (DWB) has taken into service. This unique facility is the only one in the world that is able to generate waves in a large depressurized towing tank. This ensures correct representation of the pressure inside the enclosed ventilation bubbles and vortices, resulting into a correct physic behaviour. The EU-funded Streamline project was the first project for which ventilation inception measurements were carried out in the DWB. Tests were carried out with a fully instrumented podded ship model, sailing and in bollard pull condition, in waves and depressurised conditions.
In order to acquire detailed load measurements, MARIN used their in house developed 6 component and 5 component transducers. The 6 component transducer was used for measuring the omnidirectional propeller loads, while the 5 component transducer was used for measuring 2 blade forces and 3 blade moments. At the same time synchronised high speed video recordings were made to acquire insight in the occurring phenomena. In the present paper a description of the test set up will be presented briefly, followed by a discussion of the recordings and the observations that were made for bollard pull condition in waves.