## 4 Discussion  
In this study, we demonstrated two major advancements. First, we established a qualitative group decision model to determine the representative risk factors and further used BTA to decide on the causes of ship collision incidents and preventative and mitigation measures. Secondly, through the visualization of the risk factors with a bow-tie diagram, we shed light on the causes of the ship collisions more clearly. Such information can provide a comprehensive assessment for the decision-making departments, which includes public and private department. Considering Taiwan as an example, the public department includes the Ministry of Transportation and Communications, Fisheries Agency and Coast Guard; the private department includes sea freight forwarder and fishing associations. To achieve ship collision risk control more efficiently and reduce the incidence of ship collision incidents, this integrated analysis method can effectively improve the analysis results and risk control of ship collisions. In particular, this study is different from previous studies, which typically focus only on a single behavior and vessel. In fact, it can be used to explore the comprehensive risk assessment of ship collisions with multiple types of ships. This study aimed to explore the representative risk factors of ship collisions, so the prevention and mitigation measures related to ship collision incidents focused mainly on the ship and its management company [22; 47; 48; 74]. In addition, the decision-making group also proposed relevant management policies for each representative risk factor. For example, to prevent ship collision incidents due to the fact of personal carelessness or errors, the automatic ship collision avoidance system was proposed by the decision-making group to reduce the occurrence of ship collisions [75; 76]. They also suggested the revision and strict enforcement of the penalty in the Shipping Law to effectively alert substandard ships. For high-risk vessels, they recommended the inspection of ships to execute Port State Control (PSC), including strict inspections and compulsory punishments [77]. The definition of a substandard ship is a ship whose hull, machinery, equipment, or operational safety is substantially below the standards required by the relevant convention or whose crew is not in conformance with the safe manning document [78]. The conditions for blacklisting ships are different for each country. In Taiwan, the blacklist of ships includes blacklisted ships under the Paris MoU [79] and Tokyo MoU [80], as well as ships engaged in illegal activities. Thus, PSC considers different inspection items for substandard ships and blacklisted ships. Although PSC is used to inspect foreign ships in national ports, if the ships that collide belong to local national ships, especially fishing boats, PSC is not applicable, and the relevant local national laws are enforced instead. The penalty provisions of Law of Ships in Taiwan include prohibition of sailing, with sailing allowed after improvement and payment of fines. The improvement of an early warning system against bad weather conditions was recommended, as well as the establishment of a ship seaworthiness and wave resistance specifications. Seaworthiness means the ship's fitness and preparedness for sailing as well as its essential capability to navigate through various sea conditions while ensuring the safety of the crew and cargo. Its standard extends to all aspects of a ship, including the human element, physical structure, documentation, cargo worthiness, and so on [81]. The wave resistance specification refers to the simulated data based on the ship design data before the ship is built. As a result, both the seaworthiness and wave resistance specifications are crucial to ensure the safety and efficiency of maritime transportation. When the sailing plan may pass through sea areas with bad walrus density or exceeding the seaworthiness rating of the ship, it is necessary to avoid sailing in such sea areas or change the route as soon as possible.