The wave excitation force and moment drive the motions of the vessel. For solutions of the coupled heave and pitch equations of motion, only the global force and moment are required; however, for solution of the wave induced shear force and bending moment, the forces must be divided into the sectional Froude-Krilov and diffraction forces. Because several simplifying assumptions may be made, there are three methods available for the evaluation of the Global Wave Excitation Force and Moment, these are:

Arbitrary wave heading; sectional Froude-Krilov and diffraction forces for arbitrary wave angles.

Head seas approximation; sectional Froude-Krilov and diffraction forces for head seas.

Salvesen et al. (1970); approximation for global force and moment in head seas.

Again, the methods follow the work of Salvesen et al. (1970).