In this manuscript a mathematical model to study the forced motions on planing boats is developed, the hydrodynamic coefficients in the six degrees of freedom are computed, the formulation is based on flow potential theory and slender body theory and it allows to evaluate the pressure distribution and the forces in the six degrees of freedom. Virtual towing tank tests of the oscillatory forced motions in the vertical, horizontal, and transverse planes were carried out; the results of the simulations are compared with CFD runs and experimental data by other authors with good agreement, the current solution requires low computational resources in comparison with CFD simulations. The time series of forces in the forced test of heave, pitch and roll motions are high non-linear while the time series of forces in the tests of sway and yawing are linear.