Anti-collision decision making by course alteration and speed change under COLREGs

Collision between ships is one of the most common types of accident in most navigable waters. A fast and effective anti-collision decision making procedure is significant for the safety of the navigating ships. The ships have to adhere to the International Regulations for Preventing Collisions at Sea (COLREGs) during navigating, which is subjective to a large degree. The paper presents a mathematical model to compute the distance to closest point of approach (DCPA) and calculated the derivative of own ship's course and velocity, based on which the effectiveness of avoiding collision by course alteration and speed change are evaluated in a quantitative way under different encounter situations. The simulation results indicate that in most cases course alteration performs better than changing velocity for the encounter situations with large crossing angle while changing velocity performs better under some encounter situations with small crossing angle. Two case studies are conducted to evaluate the proposed approach.