A three-dimensional panel method developed for the prediction of the seakeeping properties of conventional ships has been extended to predict the motions and added resistance of IACC Yachts. The method solves the three dimensional unsteady potential flow around the yacht in monochromatic oblique waves. Predicted quantities include the heave and pitch motion amplitudes and phases and added resistance over a broad range of wave frequencies yacht speeds. Computations have been carried out for a series of IACC hull shapes studied by PACT (Partnership for America's Cup Technology) and correlations with experimental measurements are found to be very satisfactory. The same method was also used to study the added-resistance properties of hull shapes supplied by the America3 Foundation. A sensitivity analysis was carried out of the added resistance on the principal yacht hull shape parameters, including the slenderness, displacement, LCBLCF separation and pitch radius of gyration.