Current paper addresses planar motion mechanism (PMM) test of planing hulls by taking the advantages of recent progress in modeling of planing hulls motion. A mathematical model based on 2D+T theory is developed for simulating PMM tests of planing hulls when boat is free in heave, pitch and roll directions. Three degrees of freedom have been considered for wedge, and then the hydrodynamic loads on the wedge are obtained. Integrating the forces and angular moment over the entire length of the vessel, the three dimensional forces and moments in vertical, transverse and horizontal planes are computed. Beside, three equations governing on motion of the boat in heave, pitch and roll directions are formulated. Simulations have been performed to find the dynamic response of the boat during pure sway/yaw tests. The results are compared against available data and good agreement between experimental and mathematical results is observed. In the next stage of simulations, hydrodynamic coefficients of a planing hull in horizontal plane are mathematically found. Results of this simulation suggest that amplitude of motion has no remarkable influence on hydrodynamic coefficients. However, small frequencies can affect the added mass in sway and yaw directions, especially at smaller speeds.