Using a speed optimisation problem variant instance of the US Navy patrol boat SEAFIGHTER, It has been demonstrated in the work reported in this paper that the linear programming formulation yields better results than the nonlinear programming formulation for the ship speed optimisation problem. Furthermore, it is shown that the uniform single speed assumption does not in fact hold unless ship fuel consumption rate is a convex function of ship speed, as assumed in most work on the ship speed optimisation problem19. Therefore, great care must be taken in using the uniform single speed assumption, in view of the complex nature of the functional relation between ship fuel consumption rate and ship speed, as pointed out by Psarftis and Kontovas4.