Every means available shall be used to determine if risk of collision exists. This could be information from your lookout, radar, or other means. If there is any doubt as to the risk of collision, you should act as if it does exist and take appropriate action.
In determining if risk of collision exists, the following considerations shall be among those taken into account:
- Risk of collision shall be deemed to exist if the compass bearing of an approaching vessel does not appear to change
- Risk may sometimes exist even when an appreciable bearing change is evident, particularly when approaching a very large vessel or a tow, or when approaching a vessel at close range.
- If necessary to avoid collision or allow more time to assess the situation, a vessel shall slacken her speed or take all way off by stopping or reversing her means of propulsion.
- When maneuvering to prevent collision, do so early and make the maneuver large enough to be recognized the other vessel. Small alterations of course and/or speed should be avoided.
When two power driven vessels are in sight of one another and the possibility of collision exists, one vessel is designated by the rules as the stand-on vessel and the other is designated as the give-way vessel. The stand-on vessel should maintain its course and speed. The give-way vessel must take early and substantial action to avoid collision.
If it becomes apparent that the actions taken (or not taken) by the give-way vessel are dangerous or insufficient, the stand-on vessel must act to avoid collision.
So, how do you know a risk of collision exists? An example: your boat and another boat are on a course with a constant bearing but a decreasing range. You are both heading to the same point at the same speed. The risk of collision exists if neither of you alter course and/or speed.
For a graphical view of constant bearing and decreasing range go to: http://boatingbasicsonline.com/content/general/6_2_b1.php