The present paper employs nonlinear dynamics tools in order to investigate the dynamical characteristics governing the complex coupling of the heave, roll and pitch modes in head seas at some regions of the numerical stability map of a fishing vessel. Bifurcation diagrams and Poincaré mappings are computed and employed to investigate the appearance of multistability and chaos associated with increased values of the selected control parameter, the wave amplitude. The connection between these nonlinear characteristics and the coupled nature of the mathematical model are analyzed. Lyapunov exponents corresponding to the three coupled models are computed. © Springer Science+Business Media B.V. 2011.