- Volume 19 Issue 2
In the Steering and Sailing Rules of International Regulations for Preventing Collicions at Sea, 1972, any relative distance between two vessels necessary for taking action to avoid collision in head-on situation is not referred. In this paper, the author analyzed the ship's collision avoiding actions from a viewpoint of ship motions and worked out mathematical formulas to calculate the relative distances necessary for collision avoiding actions. Figuring out the values of maneuvering indices through experiments of actual ships, the author applied these values to the calculationg formulas and calculated the minimum safe relative distances. On the assumption that two vessels same in size and condition are approaching each other in head-on situation, the minimum safe relative distance was calculated as 5.0 times, sufficient safe relative one as 10.0 times their own length.