The recent use of large aspect ratio and highly loaded composite hydrofoils on sailing boats illustrates the limit of the assumption of rigid body. When flying, the hydrofoil presents large deformations which impact significantly the hydrodynamic loads expected. The present work focuses on an experimental campaign performed on a trapezoidal hydrofoil, made of polyacetate material, in the hydrodynamic tunnel at the Research Institute of French Naval Academy. Large deformations up to 4.5% of the span on the hydrofoil’s tip are measured at angle of incidence 10° for Re=0:7 x 10 6 calculated at mean chord. Vibration analysis performed on this foil, highlights an increase of its resonance frequencies with bending loading. A coupled approach between the Vortex Lattice Method (VLM) potential flow code, AVL, for inviscid calculations, corrected to consider the viscous component and, an in-house structural code based on beam theory by Finite Element Method (FEM) is developed for this application. The comparisons of simulations show good agreements with experiments in a large range of angles of incidence and flow velocities.