Abstract: RANSE solvers are being increasingly applied to test solutions to ship hydrodynamic problems and one such application is the modelling for the performance of the bilge keel, considering the viscous effects. This includes the drag on the hull form as it rolls and the flow separation from the bilge and keel where subsequent vortex formation accounts for a large amount of the roll damping. This study presents a numerical modelling effort to estimate the oscillations of a ship subjected to beam waves. Using CFD tool, the model defines transient boundary conditions that simulate waves on the free surface. The wave model generates a number of field functions based on wave parameters and these field functions are used as initial and boundary conditions. It generates a linear wave given by a first order approximation from the Stokes wave theory with regular periodic sinusoidal profile. The solver calculates the resultant force and moment acting on the model due to the pressure and shear forces exerted by the fluid and by solving the governing equations, finds the new position of the model. As a validation effort, model scale experiments were carried out on a 500t displacement ship hull with and without bilge keels in beam sea conditions. Numerical and experimental roll decay tests are also simulated for comparison to bring out the modelling efficiency of the bilge keel. The flow around the bilge keel is presented showing the velocity vectors and vorticity contours around the hull.