In this study, numerical simulations of resistance tests for the KCS ship model are carried out within a commercial software package STAR – CCM+ for computational fluid dynamics. A mathematical model of unsteady three–dimensional viscous flow with a free surface based on Reynolds Averaged Navier – Stokes (RANS) equations and the k – ω SST turbulence model is applied. The volume of fluid (VOF) method is used to track and locate the free surface. Numerical simulations are performed for an even keel and four trim angles for one Froude number in water of limited width and depth. The verification study is carried out using different grid resolutions and time steps, and the numerical uncertainty for the total resistance, sinkage, and trim angle is calculated. The obtained numerical results are compared with the experimental results available in the literature. A detailed analysis of the free surface elevation, wave patterns, distribution of hydrodynamic pressure and wall shear stress, flow around the ship model, and velocity field on the symmetry plane is carried out. A comparison of the obtained values of total resistance for an even keel and all considered trim angles is given. It has been concluded that it is possible to reduce the total resistance of the ship model in constrained and shallow water by adjusting the trim angle to increase the ship energy efficiency in restricted waterways.