The Computational Fluid Dynamics analysis of the hydrodynamic performance of two America's Cup design candidates is presented. Two fully appended hulls were tested in a free to sink and trim condition. The experimental data of one of the two hulls was known a priori and was used to investigate several computational parameters, which are discussed in the present paper. The validated numerical model was used to predict the performance of the second hull, whose experimental data were unknown a priori. The a posteriori numerical/experimental comparison showed that the numerical model was able to predict the performance of the two hulls with a level of accuracy of the same order of magnitude of the experimental test.