1 Copyright © 2013 by ASME Proceedings of the ASME 2013 32nd International Conference on Ocean, Offshore and Arctic Engineering OMAE2013 June 9-14, 2013, Nantes, France OMAE2013-10814 EXPERIMENTAL INVESTIGATION OF THE EFFECT OF WAVES, VENTILATION AND CAVITATION IN BOLLARD PULL CONDITIONS G. Hagesteijn ∗ Ships Department MARIN Wageningen, Netherlands g.hagesteijn@marin.nl J. Brouwer Ships Department MARIN Wageningen, Netherlands ABSTRACT * 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. * Address all correspondence to this author INTRODUCTION When ventilation occurs unpredictably and uncontrolled, the propeller starts racing due to the reducing torque in the ventilated regime. This might cause severe damage to traditional Diesel engines with at the same time imposing heavy efficiency losses as at the higher RPM of a racing propeller; the advance coefficient of the propeller is shifted into the unfavourable off-design regime. One of the claimed advantages of electric podded propulsion is that the electrical engines can cope better with the dropping of torque, resulting in less engine damages. On the other hand the loading of the propeller bearings is more difficult to dimension due to the poor knowledge available, in the public domain, on podded propulsors in service or more specific, seakeeping conditions. During higher sea states the propeller loading fluctuates due to the variation in speed and the vertical motions of the vessel, which will result in different cavitation behaviour and inception speeds compared to the calm water conditions. Moreover, based on past experiments in MARIN‘s Seakeeping Basin, it was seen that ventilation can sometimes occur on pods as well, a phenomenon which was observed to greatly affect blade forces and moments, and thus the shaft loading as well. The EU-funded Streamline project aimed at studying these ventilation effects in detail. WAVES IN DEPRESSURISED CONDITIONS Experience [1] showed that the estimation of risk of ventilating propellers in traditional model scale experiments under atmospheric conditions varies from that of depressurized conditions. Moreover, entrapped air pockets are proven to behave differently at different scales [2]. Therefore, better