Experimental investigation of the effect of waves and ventilation in depressurised conditions on a POD-propeller of a cruise liner model

Ventilation is a feared working condition of ship propulsors. Except for rare applications such as surface piercing propeller specially designed for this purpose, traditional propellers could suffer from a noticeable breakdown of thrust and torque once a sufficient amount of air is entrapped by the rotating propeller. 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 has taken into service their Depressurized Wave Basin (DWB). This unique facility is the only in the world that is able to generate waves in a depressurized towing tank. This ensures correct representation of the pressure inside the enclosed ventilation bubbles and vortices, resulting into correct physic behaviour. The EU-funded Streamline project was the first project for which ventilation inception measurements were carried out in the DWB. The tests were carried out with a Podded Cruise liner model, sailing 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. Furthermore one of the recordings and observations will be discussed in a detailed way, providing more insight in the complex phenomena that take place when cavitation and ventilation are originating and vanishing.