This article presents a theoretical extension of a semi-empirical method for the determination of squat of ships in shallow water, based on a one-dimensional theory in which the solid bottom is replaced by a higher density fluid layer. It can be shown that, for the evaluation of the effect of the mud layer, a distinction has to be made between three ranges of the ship's speed, separated by two critical values. The first critical value is approximately equal to the maximum velocity of propagation of internal waves at the interface, while the second critical value depends on the blockage factor and on the lower fluid density.Numerical results of theoretical calculations are compared with experimental data obtained in tests carried out at the Hydraulic Research Laboratory in Antwerp-Borgerhout with self-propelled ship models in restricted waters above a solid bottom and above a simulated mud layer
