Regarding surge force predictions, the four models give similar results for the medium to large depth ratios, however with a tendency for overestimation by Newman’s approximation and the Hooft based method and a slight overestimation by the no free surface model, as compared to the complete second order solution. For small depth ratios, Newman’s approximation largely underestimates the forces. Hooft’s approximation compares very well with the complete second order and no free surface solutions for small depth ratios.