Estimating shallow water resistance for a vessel is an issue of primary importance for inland water navigation, not only for determining the total power absorbed by the propulsors but also for predicting the far-field wave pattern necessary to assess the wake-washing effect on the shores. Once it is not possible performing model tests for a specific water depth or it is not possible to execute complex CFD simulations, it is necessary to estimate the shallow water effect and add it to the deepwater results. Traditional empirical methods usually refer to the subcritical regime for shallow water; however, for several applications, also critical and supercritical regimes require attention. The present work analyses the shallow water effect adopting a linearised theory for wave resistance prediction using the thin ship approximation and an empirical formulation for the viscous resistance. Such a methodology allows for determining a procedure for estimating shallow water effects for slender semi-displacement ships operating also in critical and supercritical regimes. The novel resulting process is tested on a reference semi-displacement hull designed for navigation in lagoons. The results are compared with conventional empirical methods and RANS calculations in shallow water, highlighting the agreement of the proposed method with the CFD calculations for the critical and supercritical regimes.