This paper aims at developing a model based on theoretical first principles involving nonlinear equations for the coupled heave and pitch dynamics of surface vehicles that is suitable for evaluating planar motion control strategies. The model developed uses a novel approach of representing the ship dynamics in the frequency domain that provides greater insight to the surface vehicle’s behavior over a wider operating range than the traditional time domain models. The theoretical model was validated by experimental data that was obtained from tow tank experiments. The theoretical model results compared well with the experimental data.