Time-domain simulations were performed to investigate the influence of passive and active anti-roll tanks and moving weights on ship motions. A point mass moving across the ship was used to model the non-linear effects of the tank systems in various computer simulation environments. PID control of the mass position was used for the active tank (pump) systems and a vibration absorber was used for the passive tank systems. A single-degree-of-freedom non-linear code was developed to investigate the influence of various coefficients and control strategies. The final active and passive tank system implementations were included in the LAMP code developed by SAIC. Results of the time-domain simulations are shown, which indicate the effectiveness of these types of roll control systems.