The Efficiency of a Mewis Duct in Waves

Abstract

In this thesis, the efficiency of a Mewis Duct in waves has been investigated with the use of model tests in the large towing tank at MARINTEK in Trondheim. A ?load-varying? self-propulsion method was used, allowing for calculations without the need for results from a resistance test. Still water, regular and irregular wave conditions have been tested. The vessel model used, M3030 A, was originally used to test the Mewis Duct in still water.Results in still water have been compared to the original test results. Deviations from the original tests have been found, which could be due to increased resistance of the model and bias in the tow force and thrust measurements.Results in regular waves show a consistent increase in the effective wake with the Mewis Duct fitted, but the thrust deduction contains a high amount of scatter. This results in scatter in the hull efficiency, and further in the propulsive efficiency.Uncertainty analysis has been carried out and shows that scatter in the tow force are probably the reason for inaccurate results. It indicates the necessity of accurate measurements of the tow force with the load-varying self-propulsion method.