Dynamics model is essential and critical for a successful navigation and control system design of an underwater vehicle. The main difficulty in dynamics modelling of an underwater vehicle is due to the hydrodynamics forces, in which added mass coefficients and drag coefficients need to be determined. In this project, two approaches computational fluid dynamics (CFD) approach and experimental approach have been used to find the hydrodynamics coefficients for the RRC ROV II, a remotely operated underwater vehicle. Under the CFD approach, WAMIT and ANSYS CFX have been used to estimate added mass coefficients and drag coefficients respectively. After that, the coefficients were compared with the experimental result obtained from a novel free decay test of a scaled model of ROV II. The results show good agreement in prediction of both added mass and drag coefficients. The usage of experimental method and CFD method in parallel has suggested that the two methods complement each other and one's advantages could be used to mask another's weaknesses. The hydrodynamics coefficients found have been verified through experiments using physical ROV II. Therefore, the combined approach developed in this report could be used to find the added mass and drag coefficients for other underwater vehicles. MASTER OF ENGINEERING (MAE)