The possibility of bifurcations in first order nonlinear motions in stochastic sea is analysed by means of a multiscale perturbation method. The results indicate that this feature can be present in many systems of interest to Naval Architecture and Ocean Engineering, provided that the bandwidth of the excitation is sufficiently small and the centerpeak frequency falls in particular ranges. The possibility of subharmonics is also shown. The results of numerical simulations confirm these conclusions.
