Resumen
Collision-risk measurements are crucial for ships, as they are necessary for collision avoidance decision making. However, collision risks between ships have not been quantified in unified standards. In this study, a critical collision index is proposed to describe the critical degree of collision risks between ships. Based on the field theory, a collision-risk field was introduced to build a field strength model based on the collision index. The model synthetically considers the influences of distance at closest point of approach, time to closest point of approach, and the relative bearing of coming ships. Moreover, the real time to the closest point of approach was used for describing the collision risk between ships. In addition, encounter situations and collision risks in the field were simulated using the field strength model and isorisk lines. The results are in agreement with the real collision-risk perceptions of Officers on Watch. It was shown that the proposed ship critical collision index can play an important role in ship collision avoidance and early warning systems.