Rule 13: the overtaking vessel keeps out of the way.

What does COLREGs Rule 13 say?

Rule 13(a): the vessel that is overtaking keeps out of the way of the one she is overtaking — whatever kind of vessel each of them is.

Rule 13(b): a vessel is overtaking when coming up with another from a direction 'more than 22.5 degrees abaft her beam' — where, at night, she would see only the other's sternlight and neither of her sidelights.

Rule 13(c): a vessel 'in any doubt' whether she is overtaking must assume she is, and act accordingly.

Rule 13(d): no later change in the bearing between the two vessels makes the overtaking vessel a crossing vessel, or relieves her of keeping clear, until she is 'finally past and clear'.

Does Rule 13 override the other steering rules?

Yes. It opens 'Notwithstanding anything contained in the Rules of Part B, Sections I and II', and it applies to any vessel overtaking any other. Rule 18, which sets out who keeps out of the way of whom, itself begins 'Except where Rules 9, 10 and 13 otherwise require'.

So a sailing vessel overtaking a power-driven vessel keeps out of the way, even though Rule 18(a)(iv) would otherwise have the power-driven vessel keep out of the way of her. Two sailing vessels: the overtaking one keeps out of the way, whatever Rule 12 says about their tacks.

What is the 22.5 degrees abaft the beam test?

You are overtaking when you come up with the other vessel from a direction more than 22.5 degrees abaft her beam — measured from her, not from you. The rule ties it to her lights: from there, at night, you would see only her sternlight and neither of her sidelights.

The arcs in Rule 21 match it. Sidelights show from right ahead to 22.5 degrees abaft the beam on their own side; the sternlight shows 67.5 degrees from right aft on each side. The line where her sidelight disappears and her sternlight appears is the overtaking line.

By day there are no lights to check, so you judge it from her heading and your bearing from her: if you are coming up from more than 22.5 degrees abaft her beam, you are overtaking. Near that line, Rule 13(c) settles the doubt against you.

A single white light ahead is not always a sternlight: it may be the all-round white light of a vessel at anchor under 50 metres (Rule 30(b)) or of a power-driven vessel under 12 metres (Rule 23(d)). Keep clear either way, and use bearings and radar to tell which.

What does 'coming up with' mean?

As we read it, closing on her from astern — gaining on her. A vessel astern of you that is not gaining is following, not overtaking, though Rule 7 still applies to deciding whether there is a risk of collision.

What if you're not sure whether you're overtaking?

Rule 13(c) settles it: if you are in any doubt, 'she shall assume that this is the case' — you treat yourself as overtaking and keep out of the way. The doubt is settled against the vessel coming up from astern.

In practice the doubt arises near the 22.5 degree line: at night you may see her sternlight and then a sidelight as one vessel or the other yaws, or by day the aspect is too fine to call. That is exactly the case 13(c) is for.

Who is the stand-on vessel when you are being overtaken?

The vessel being overtaken. Rule 17(a)(i) requires her to keep her course and speed while the overtaking vessel keeps out of the way. She may take action on her own once it becomes apparent the overtaking vessel is not taking appropriate action (Rule 17(a)(ii)), and must act when collision cannot be avoided by the overtaking vessel alone (Rule 17(b)).

What does Rule 13(d) mean?

Once you are overtaking, you stay the vessel that keeps out of the way until you are finally past and clear. As you draw up alongside and ahead, her bearing from you changes and you may end up forward of her beam on a converging course — which, between two power-driven vessels, would look like a crossing situation. Rule 13(d) says it is not: the bearing change does not make you 'a crossing vessel', and it does not take the duty off you.

So the faster vessel that overtakes on the other's starboard side and then angles across her bow is still the vessel that must keep clear.

Which side should you overtake on?

Rule 13 does not say — either side is permitted. Choose the side that gives the room to pass at a safe distance (Rule 8(d)) and keeps clear of hazards and other traffic.

A power-driven vessel underway that alters course to overtake, with the vessels in sight of one another, indicates the alteration on her whistle under Rule 34(a): one short blast for 'I am altering my course to starboard', two for port.

Is overtaking different in a narrow channel?

Where overtaking can only take place if the vessel ahead acts to permit it, Rule 9(e)(i) applies: the overtaking vessel signals her intention under Rule 34(c)(i), and the vessel ahead, if she agrees, answers with the signal in Rule 34(c)(ii) and takes steps to permit safe passing. Rule 9(e)(ii) adds that none of this takes away the overtaking vessel's Rule 13 duty.

Does Rule 13 apply in fog?

Rule 13 is in Section II, so it applies when the vessels are in sight of one another (Rule 11). When they are not, in or near restricted visibility, Rule 19 applies. Rule 19(d)(i) — avoid, so far as possible, altering to port for a vessel forward of the beam — makes an exception for a vessel being overtaken.

How might Rule 13 come up in an MCA oral?

It may come up as a lights picture or as an approach from the quarter. Examples of the kind of question to be ready for:

“At night you see only a white light ahead and you're closing it. What is it, and what do you do?”

“You're closing a vessel from astern at night. You see her sternlight, then her green sidelight, then her sternlight again. Are you overtaking?”

“You're on a sailing yacht overtaking a slow motor cruiser. Who keeps out of the way?”

“You overtook a ship and are now on her starboard bow, converging. Are you now the stand-on vessel?”

“When can the overtaking vessel stop keeping clear?”

Where do candidates go wrong on Rule 13?

The common slips: measuring the 22.5 degrees from their own vessel instead of from the vessel ahead; thinking a sailing vessel overtaking a power-driven vessel is stand-on; treating a later change of bearing as turning an overtake into a crossing; and not knowing that doubt is resolved by assuming you are overtaking.