Optimization techniques for the design of crescent-shaped hard sails for wind-assisted ship propulsion

Wind-assisted ship propulsion is one of the most promising technologies to achieve net zero emission in ship operations by 2050 due to its reliance on a fully renewable energy source. Hard sails with crescent profiles have been shown to potentially provide a greater benefit than symmetric sails in recent studies. In order to justify their application, it is necessary to create and adopt a specific design that guarantees a reduction in the engine load over the whole operational range of encounter angles. The current study provides a systematic approach to obtain such a design based on two techniques, one aiming to maximum sail thrust, the other to minimize propeller power. Surrogate models based on validated CFD simulations are adopted for optimization, and the most efficient design is found as an average over all the possible encounter angles. It was shown that the thrust maximized approach increased the average thrust generated by sail up to 12.3%, and the propeller power minimized approach improved the effectiveness of the sails up to 22% in terms of percent power reduction. It was also confirmed that crescent-shaped airfoils generally outperform symmetric airfoils in the considered conditions. • Increasing camber and reducing thickness contributes to reduce propeller power. • A surrogate model coupled with CFD makes the optimization computationally inexpensive. • Minimizing propeller power for shape optimization for sails yields best performance. • The effectiveness of sails increased up to 22% using power minimization approach.