Basic avoidance rules between vessels are stipulated by the Maritime Collision Prevention Act (Act No. 63 of 2003). However, the law lacks clear provisions regarding avoidance rules between a vessel underway and a drifting vessel. In Japan, the proportion of liability in vessel collisions is proportional to the proportion of negligence at the time of the collision. The existence and magnitude of negligence at the time of the collision will be determined in accordance with the duty of avoidance rules under the law. In past precedents, the ratio of a vessel underway to a vessel drifting at sea was often determined at around 7:3. Recent a precedent have shown that the ratio of a vessel underway to a drifting vessel is 10:0, but is this really appropriate? Based on past precedents, laws, and the results of a questionnaire of maritime personnel, this paper presents the basic concept when considering the percentage of negligence in collisions between vessels underway and drifting vessels.
