The International Maritime Organization (IMO) has issued guidelines for direct stability assessment, recognizing pure loss of stability as a failure mode leading to large roll motions or capsizing in large waves. This paper uses the CFD solver STAR-CCM+ to simulate pure loss of stability for ONR Tumblehome in stern-quartering waves. Ship motions with moving rudders were simulated using dynamic grids, with rudder deflection controlled automatically. Two propeller models were used: a fully modelled rotating propeller and a body force model. Simulations at different speeds show consistent trends with experimental data in maximum roll angles. Forces and moments on individual appendages like rudders and propellers were analysed at a specific speed.