The objective of this thesis is aimed at develop a functional and practical decision support system for the human navigators operating surface ships. The system developed has to be tested in real-life by using a full-scale maritime simulator. If this system works flawlessly within the simulated environment, then it proves that this can be deployed in a real surface vessel. The proposed decision support system must adhere to the COLREGs rules and aid the human operator in tackling complex marine traffic encounter situations. In this thesis, we suggest that such a system can increase the situational awareness capabilities of the human operator (Navigator). This decision support system is proposed and developed through the understanding gained from previous research conducted by many researchers worldwide.The main step in the decision support mechanism is to identify the threats. This is achieved by conducting a risk analysis by calculation of the Collision Risk Index or CRI. Once we have identified the threats we can evaluate the encounter situation combined COLREGs rules to develop an action plan. To make this a little further we can utilize a collision avoidance algorithm such as velocity obstacle (VO) to generate a collision-free path, that can assist the human operator to choose the right decision faster.For the development of any system, it is important to choose the right software, we have chosen Python as the primary development platform for this research. As this system is supposed to be used by ordinary navigators, there should a user-friendly interface, for this there should be a custom Graphical User Interface (GUI). The GUI should convey useful information in real-time to the operator controlling the vessel.