Since 1994, HDS is a major player in the design of complex composite parts, especiallyfor racing sailing yachts [1]. In this paper, wesuggest to present our approach in the design and finite-element modelling of the rigidwing-sail of the trimaran that won the 33rd America’s Cup, held in February 2010. From thedecision to design the wing-sail to the assembly on the maxi trimaran, we will present thedifferent steps of design and computation: principles and assessment of the aerodynamicloads, structural design and modelling with tools adapted to each problem, massoptimization. Then, we will detail some of the numerical problems that we faced in thisproject.