This paper deals with the estimation of the non-linear wave forces and the subsequent motion response of a tri-hull carrier vessel. The finite element method and the panel method are used for numerical estimation of the forces and motions of the vessel. The numerical results are compared with the pitch and roll motions obtained from physical model tests carried out in a wave flume at the Indian Institute of Technology Madras for regular waves in a head sea and a beam sea for the zero-speed stationary condition. The results show that inclusion of the second-order wave excitation force in the equation of motion for the vessel results in closer prediction of the response amplitude operator to the experimental values in non-linear waves. © Institution of Mechanical Engineers 2011.