This article presents a novel method to compute in an efficient way, the coupled fluid-structure non-linear behaviour of hydrofoil sailing yacht. A parametric model of the pressure exerted by the fluid on the hydrofoil is determined from steady state 3D fluid simulation taking into account free surface and cavitation. The fluid pressure is applied to a calibrated structural model taking into account the local and global structure deformation impacting the local angle of attack and fluid velocity. This tool was used to compute the maximal stress in the linking arm of the Hydroptere when sailing on flat water and in wave conditions. Non-linear and transient behaviour of the structure is found to significantly impact the maximal stress in the structure.