In this paper, numerical modeling and testing of a complex-shaped remotely-operated vehicle (ROV) are shown. The paper emphasizes on systematic modeling of hydrodynamic added mass using computational fluid dynamic software WAMIT^(TM) on the open frame ROV that is not commonly applied in practice. From initial design and prototype testing, a small-scale test using a free-decaying experiment is used to verify the theoretical models obtained from WAMIT^(TM). Simulation results have shown to coincide with the some of the experimental tests. The proposed method is therefore able to determine most of the hydrodynamic added mass coefficients of the open frame ROV.