A campaign of experiments on ship rolling in regular beam sea has been conducted on scale models in the towing tank of the University of Trieste. The research was aimed at studying the features of nonlinear rolling and at obtaining realistic values for the parameters relevant to this motion as damping, excitation and stiffness. The experiments conducted on a 1:50 scale model of destroyer evidenced the presence of a bifurcation in the steady response. A jump from the low or anti-resonant oscillation to the high resonant state has been obtained by means of a schock while maintaining to a fixed value the wave excitation. The analysis of the phase lag between excitation and rolling confirmed the jump due to a bifurcation. The experimental results can be represented with satisfactory agreement by means of a perturbative solution of the nonlinear rolling equation.
