Overtaking.
(a) Notwithstanding anything contained in the Rules of Part B, Sections I and II any vessel overtaking any other shall keep out of the way of the vessel being overtaken.
(b) A vessel shall be deemed to be overtaking when coming up with another vessel from a direction more than 22.5 degrees abaft her beam, that is in such a position, with reference to the vessel she is overtaking, that at night she would be able to see only the sternlight of that vessel but neither of her sidelights.
(c) When a vessel is in any doubt as to whether she is overtaking another, she shall assume that this is the case and act accordingly.
(d) Any subsequent alteration of the bearing between the two vessels shall not make the overtaking vessel a crossing vessel within the meaning of these rules or relieve her of the duty of keeping clear of the overtaken vessel until she is finally past and clear.
This rule is unusual in that it firmly puts the onus on one vessel to take all necessary action, in order that a collision might be avoided.
When approaching another vessel from astern, you are deemed to be responsible for keeping clear of it, if your approach is within the 135 degrees arc of her sternlight. If any doubt exists as to whether you are actually overtaking another vessel, you must assume that you are, and take appropriate action. This is important, as it is obviously not possible to gauge this overtaking sector accurately during daylight hours. To all intents and purposes, if you can see the port and/or starboard quarters at the stern of the vessel you are approaching, it would be safest to assume you are overtaking it and keep well clear.
Although the vessel you are approaching should be keeping a good watch all round, bad practices and/or physical obstructions may mean she is not doing so. Always assume the worst and give plenty of sea room, allowing for sudden course or speed changes from the other vessel that can occur without any warning.
If you are approaching towards the forward extremes of the 135 degrees arc, especially on the starboard side, note that a subsequent alteration of course by the vessel being overtaken does not relieve you of the responsibility to stay well clear.
Whilst Rule 13 does not place specific responsibilities on the vessel being overtaken, other parts of the Regulations are still in force. For instance, failure to notice another vessel’s approach would contravene Rules 5 and 7 and a sudden change of course across the bows of an overtaking vessel certainly takes no account of Rule 2.
Another factor to remember with regard to this particular Rule, is that it does not matter, what type of vessel the overtaking vessel actually is – “Any vessel overtaking any other vessel shall keep out of the way of the vessel being overtaken”. If you are on a large slow moving power-driven vessel and a yacht or windsurfer is going faster than you, then they are the overtaking vessel and should keep clear of you, irrespective of what Rule 18 says about power-driven vessels keeping clear of sailing vessels. However, a vessel Restricted in its Ability to Manoeuvre (RAM) and/or a vessel Not Under Command (NUC) overtaking you, by their very definitions, are unable to manoeuvre and therefore keep out of the way. This is an example of when Rule 2 would apply with regards to the ordinary practice of seamen or by the special circumstances of the case and you would therefore, keep clear of them.
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