Same coefficients than those given in [7] have been used to non-dimensionnalise excitation forces in Fig. 3 and hydrodynamics coefficients in Figs. 4 and 5, and excellent correlation is found. Also parameters are shown for the case where the radius of the column is half of the radius of the buoy that corresponds to case-study no.2. Looking at added mass and radiation damping, we note that only the amplitude of the coefficients changes with the increase and decrease of the wet body surface but not the behaviour. Now, if we look at the excitation forces on the buoy, the presence of the column does not seem to have an effect on it. However, we notice that for the platform, the behaviour is totaly different at low frequency and we can observe a rebound which varies with the radius of the plate except for relatively big sizes. Then, it seems that a radius ratio between the plate and column exists for which the column no longer influences the behaviour of the wave excitation force on the platform