Hydroelastic effects associated with ship slamming are investigated by mean of a decoupled approach. A finite element computation of the ship structural response is performed using the pressure field obtained from a rigid body strip theory. Results show the importance of both, hydoelastic and three dimensional effects for realistic impact situations. A numerical approach is then described and implemented to solve the threedimensional fluid problem. The approach relies on the method of matched asymptotic expansion, associated with a numerical resolution of the simplified problem using finite elements method. Within this approach, the so called "wetted correction" is computed numerically by imposing volume conservation. Preliminary results are given for simple geometries such as wegdes and cones for which analytical solutions are available. Good agreement is reported between numerical and theoretical results.