A numerical method for the design of ships with wind-assisted propulsion

• A novel method to compute the thrust allowed by wind assisted propulsion is presented.
• A hydrodynamic model for manoeuvrability is adapted and details are provided.
• The aerodynamic model combines CFD and potential-flow analytical formulations.
• Examples of results show oil saving of the order of 10%.
• The efficiency of the aerodynamic propulsor is found to be critical.

The present paper presents a numerical investigation on the potential of wind-assisted propulsion for merchant ships. In particular, a KVLCC2M hull was equipped with a set of wingsails inspired from those used in the 34th America׳s Cup. The combined thrust due to the propeller and the wingsails required to achieve a given cruising speed was computed by solving the equations of motion. For every wind direction, the wingsail trim was optimised with a genetic algorithm in order to minimise the thrust of the propeller. The aerodynamic forces and moments due to the hull and the wingsails were computed with Reynolds-averaged Navier–Stokes simulations, while the hydrodynamic forces on the hull and rudder were computed by adapting formulations developed for manoeuvrability applications. It was found that the aerodynamic efficiency of the wingsails is critical in order to gain a meaningful thrust contribution. The propeller thrust was decreased by about 10% when sailing crosswind, and the maximum benefit was achieved by sailing at low speed in strong wind conditions. The oil saving was found to be particularly sensitive to the wingsail aspect ratio, suggesting that an efficient wingsail should employ several tall wingsails rather than a few short and larger wingsails.