The Assessment of Risk of Collision between Two Ships Avoiding Collision by Altering Course

摘要

Altering course is the most common and effective method employed by ships to avoid collision. Give-way vessels should take early and substantial action to avoid collision, the effectiveness of a course change is influenced by the distance between the two vessels. In some instances involving more than two vessels are present (special cases), the give-way vessel may not be able to alter course as early as possible. In other instances, the stand-on vessel may be required to take action to due to the failure or inability of the give-way vessel to act. In the event of special cases and action by the stand-on vessel, it is important for navigating officers to be able to determine when a course change alone will avert a collision in order to plan for the worst case scenario. Thus, it is advantageous for navigating officers and masters to quickly and simply model the amplitude and effectiveness of course changes up to the distance between the two ships when course changes will no longer avert a collision. By using existing models of ship movement and maneuvering characteristics, a method will be presented to calculate the extent of risk of collision through reasoning process, provide a quantitative explanation of the effectiveness of course changes and identify the point at which course changes are no longer effective in collision avoidance. A worked example will illustrate the need for navigating officers to make early course changes by demonstrating the decreased effectiveness of course changes at small distances between ships.