The present paper focuses on the sensitivityand validation of the anti-roll performances of passive U-type ART using CFD. For this, the incompressible Unsteady Reynolds Averaged Navier-Stokes (URANS) code ReFRESCOwas used. The sensitivity on the results for the U-tank is analysed by varying the grid resolution and the numerical time step. The two-dimensional (2D) full-scale and Froude based model-scaleReFRESCO results are compared to 2D and 3D full-scale CFD results of Delaunay (2012)  and Thanyamanta and Molyneux (2012)  and validated with model-scale experimental results ofField and Martin (1975)  and MARIN experimental results by Gunsing et al. (2014) . This paper shows the influence of the convective scheme for capturing the free-surface interface and provides recommendations for a time step and grid resolution to effectively calculate the roll damping of an ART.