Propulsive factors in waves: A comparative experimental study for an open and a ducted propeller

Abstract

The estimation of propulsive factors in waves is essential to understand the propulsion characteristics for a ship in actual sea conditions. While the propulsion factors of open propellers in waves have been established by significant experimental work, similar study for the ducted propulsion case couldn’t be found. The propeller–duct interaction has a considerable influence on the propulsive factors for a ducted propeller, and hence demands a separate study for understanding the effect of waves. This paper presents the results of model propulsion tests with a 120m cargo vessel at two Froude numbers under different propeller loadings for a series of head sea conditions, carried out with both a ducted and an open propeller. Comparison of propulsive factors in waves shows that, there are differences in both magnitude and in some cases—also trend between an open and a ducted propeller, most notably in the effective wake fraction, where the ducted propeller shows a stronger influence of the waves. The thrust deduction fraction is found to be independent of propeller loading in a broad range of loadings. The propeller efficiency doesn’t seem to be much influenced by the waves, except for the effect of change of propulsion point.