Influence of hull–propeller–rudder interaction on the self-propulsion of wind-assisted ships

Wind-assisted propulsion systems represent one of the most promising technologies for decreasing greenhouse gas emissions in shipping, offering significant potential to reduce fuel consumption. There is a complex interaction between the forces and moments generated by the wind assist device and the hydrodynamic performance of the ship's hull, propeller, and rudder. An experimental investigation was conducted in the 138 m Boldrewood towing tank using a 1/61 scale geosim of a single-screw containership hull. Hull, propeller, and rudder forces were measured through resistance, non-propelled, and self-propelled captive tests at a full-scale representative service speed of 18 knots. Tests covered typical wind assist conditions using four offloaded propeller conditions, simulating partial thrust from wind of 10%, 20%, 30%, and 40%, with leeway (drift) angles ranging from ±5° and rudder angles from –30° to +30° with 10° increments. The study provides physical insight into the relative interactions as well as a benchmark dataset for the effects of leeway and rudder angles on hydrodynamic forces and moments across different propeller loadings available for use in velocity prediction programs and for design. The results indicate that as the physical rudder angle increases, there is a corresponding increase in ship resistance, side force, and rudder-induced yaw moment that is dependent on propeller thrust loading and its flow straightening effect on the effective rudder angle. Analysis of drift-induced resistance provided valuable insights into efficiency tradeoffs in wind-powered ships implementation, including the net resistance penalty of hull leeway and rudder drag on required overall thrust. The relative contribution of rudder side force and yaw moment to the total side force and yaw moment is analyzed. For each tested leeway angle, the study identifies the required rudder angle to balance hydrodynamic-induced yaw moment, demonstrating the significant rudder adjustments necessary for wind-propelled ships and thereby the hull features that would be beneficial for future wind assist ship design.