Correlation of cavitation : Comparison of full-scale data with results of model tests and computations

Full-scale trials are usually performed to verify the predictions made by means of computations and model tests carried out prior to the building of a ship. The disadvantage of this order is that the circumstances encountered on full scale are never the same as those in the model tests or computations, making comparisons difficult. Early 2003, in the Netherlands, a three-year research project was completed in which correlation of propulsive performance, propeller cavitation and propeller-induced hull-pressure fluctuations were studied by reversing the order. On five different ships, representing three different types of ship, experiments were carried out at full scale first, then followed by model tests and computations in which the circumstances encountered on full scale were approximated as closely as possible. As the focus of the correlation study was on cavitation, the project was named CoCa (Correlation of Cavitation). Some correlation results turned out to be very intriguing. Therefore, a follow-on project was started immediately after CoCa to investigate the cause of these surprising results. In this paper results of both projects are presented. The results show that existing procedures for predicting cavitation and hull-pressure fluctuations either by model tests or computations are not always sufficiently accurate. Development of improved prediction methods is discussed.