In this paper, the possibility of obtaining an efficient description of the roll motion of a ship with liquids with free surface on board is discussed in the case of hig center of gravity of the liquid. An avaulable mathematical model with concentrated parameters is implemented and compared with scale model experiments. The use of a Parameter Identification Technique allows to obtain the best-fit values of the relevant parameters and to discuss the number of parameters to be used. The discussion indicates that the proposed linear model gives a generally good simulation except in the case of very shallow water, where a more sophisticated mathematical model is required.