Underwater robots have garnered more attention in recent years for various uses including deep sea exploration. As these robots operate underwater, they experience various forces and moments from the surrounding fluid. Researches have to be conducted on these forces and moments so that ways to better improve the robots can be discovered. One such model of the underwater robots is the OpenROV. It is a type of remotely operated vehicle, which means that it requires a user to control its operations underwater. As it is still a new model, not much analysis had been done on the model. In this research paper, it was discovered that the robot experienced instability in its forward motion. The vehicle was shown to tilt slight downwards in forwards motion through water. To improve the motion of the robot, hydrodynamic analysis was conducted to determine the cause behind the instability. There are various ways to conduct hydrodynamic analysis and CFD was chosen as the method in this research paper. After conducting hydrodynamic analysis, it was determined that the cause of the instability was due to the Centre of Mass (COM) and Centre of Pressure (COP) not aligning. The concentrated pressure at the frontal area of the robot caused the vehicle to tilt downwards. To increase the stability of the vehicle, a modification was added to the model in the form of a fin attached to the rear end of the model. It was shown by the addition of the fin that the pressure distribution was even out between the frontal area and rear end. A study to determine the optimum length for the fin was conducted and the optimum length was determined to be 0.0053m or 5.3 mm. This result was validated by running the simulation of the forwards motion. The motion of the model without and with fin was captured by frames and compared. It was concluded that with the addition of the fin modification, the model will tilt slightly upwards when starting from rest and tilting back down as the motion continues. However, the tilt downwards was shown to be less than the situation prior to modification. Therefore, the modification improved the stability of the model slightly.