Design Optimization of America’s Cup AC75 Hydrofoil Sections with Flaps

Abstract Cavitation on foils and appendages is a critical design consideration for sailing yachts like the America’s Cup AC75 monohulls and the SailGP F50 catamarans at their speeds exceeding 50 kn. The growth of vapor cavities beyond onset conditions adversely affects lift and drag. We implement a minimum pressure constraint to control cavitation onset in a shape optimization framework based on a Reynolds-averaged Navier–Stokes solver. We perform multipoint optimizations with the cavitation constraint to optimize hydrofoil sections across ranges of flap angles, lift coefficients, and speeds, starting from established subcavitating baseline sections. The design variables consist of section shape, angle of attack, and trailing edge flap angle. A subsequent comparison against the XFOIL viscous 2D solver demonstrates that the optimizations did not significantly exploit weaknesses in the computational models. The methodology enables effective design of high-performance subcavitating hydrofoils with flaps through expert-guided optimization. Keywords Hydrodynamics, Hydrofoils, Design optimization, Cavitation, Flaps