The paper describes the validation of a time domain method to simulate the behaviour of a fast patrol boat operating in stern-quartering seas. First, the simulation method is described. Subsequently results of validation based on motion statistics are presented, showing that the statistical uncertainty in predicting horizontal plane motions is large. Finally, to overcome this, a method is described to reconstruct experimental wave trains and the results of deterministic validation are presented showing satisfactory agreement between computed and measured time traces. Results suggest that the method can be used to investigate dynamic stability and course keeping in stern quartering seas.