Since the amplitude and frequency of irregular waves change with time, great difficulties are brought for solving ship load responses in random waves. To take the effect of various frequencies of irregular waves into consideration in load responses of hull, the wave memory effect is necessary. A semi-analytical method is introduced for the time-domain retardation functions, and then a nonlinear hydroelastic method considering memory effect for ships in irregular waves is proposed. Segmented self-propelling model experiments of a container ship were carried out in a towing tank, a ship motion measuring device for self-propelling model test was designed. Whipping responses of the ship in regular and irregular waves are analyzed. Finally, the calculation results are compared with those measured by segmented model experiments, and the result indicates that the memory effect has little effect on load responses of ship in regular waves, but pronounced effect on results in irregular waves. Moreover, the presented method is reasonable for the prediction of ship load responses in irregular waves.