Rule 12: two sailing vessels.

What does COLREGs Rule 12 say?

When two sailing vessels are approaching one another so as to involve risk of collision, one of them must keep out of the way of the other, decided by Rule 12(a):

(i) Wind on different sides: the vessel with the wind on her port side keeps out of the way.

(ii) Wind on the same side: the vessel to windward keeps out of the way of the vessel to leeward.

(iii) A vessel with the wind on her port side that sees a vessel to windward, and 'cannot determine with certainty' which side that vessel has the wind on, keeps out of the way.

Rule 12(b) then says how the windward side is decided — see below.

When does Rule 12 apply?

Only between two sailing vessels, approaching so as to involve risk of collision, in sight of one another (Rule 11). A sailing vessel is one under sail with any propelling machinery fitted not being used (Rule 3(c)). A sailing yacht with her engine in use — motor-sailing — is a power-driven vessel, and Rule 12 does not apply to her. Rule 25(e) requires a vessel proceeding under sail while also propelled by machinery to show a cone, apex downwards, forward where it can best be seen.

In restricted visibility, with the other vessel not in sight, Rule 19 applies instead and neither vessel is stand-on.

Does Rule 12 apply when one sailing vessel is overtaking another?

No — overtaking comes first. Rule 13(a) says that any vessel overtaking any other keeps out of the way of the vessel being overtaken, notwithstanding anything in Sections I and II. A sailing vessel coming up from more than 22.5 degrees abaft another's beam keeps out of the way whichever side her wind is on.

How is the windward side decided under Rule 12(b)?

By the sails, not by the wind. The windward side is deemed to be 'the side opposite to that on which the mainsail is carried'. For a square-rigged vessel it is the side opposite to that on which her largest fore-and-aft sail is carried.

So a vessel carrying her mainsail on the starboard side has the wind on her port side for Rule 12, and a vessel carrying it to port has the wind on her starboard side.

What about running downwind?

The same test. On a run the wind may be dead astern, or even slightly on the side the boom is out (sailing by the lee), but Rule 12(b) does not ask where the wind is — it asks where the mainsail is carried. A yacht running with her main out to starboard has the wind on her port side for Rule 12, and keeps out of the way of a vessel with the wind on her starboard side.

Which vessel is to windward?

Rule 12(a)(ii) applies only when both have the wind on the same side, and the vessel to windward keeps out of the way of the vessel to leeward. Rule 12(b) defines the windward side for the purposes of Rule 12, so as we read it the same test settles which vessel is to windward: both carry their mainsails on the same side, so both have the same windward side, and the vessel lying on that side of the other is the windward vessel.

What does the 'cannot determine' case in Rule 12(a)(iii) cover?

It applies only when three things are true: you have the wind on your port side; the other vessel is to windward of you; and you cannot determine with certainty whether she has the wind on her port or her starboard side. Then you keep out of the way.

In practice it comes up most at night. A sailing vessel's lights under Rule 25 — sidelights and a sternlight — show which way she is heading, not which side her mainsail is on. If you are on port and cannot be sure, you are the one who keeps out of the way. On starboard, (iii) does not apply to you.

What must each sailing vessel do?

The vessel required to keep out of the way acts under Rule 16: 'early and substantial action to keep well clear', so far as possible. The other is the stand-on vessel under Rule 17(a)(i) and keeps her course and speed. She may act on her own once it becomes apparent the give-way vessel is not taking appropriate action (Rule 17(a)(ii)), and must act when collision cannot be avoided by the give-way vessel alone (Rule 17(b)).

In practice, for a yacht standing on, that means holding the course she is sailing rather than tacking, gybing or luffing — until Rule 17(a)(ii) or (b) comes into play.

What about a sailing vessel and a power-driven vessel?

Rule 12 does not cover it; Rule 18 does. Under Rule 18(a)(iv) a power-driven vessel underway keeps out of the way of a sailing vessel. But Rule 18 opens 'Except where Rules 9, 10 and 13 otherwise require': a sailing vessel that is overtaking keeps out of the way (Rule 13); in a narrow channel she must not impede the passage of a vessel which can safely navigate only within it (Rule 9(b)); and in a traffic separation scheme she must not impede the safe passage of a power-driven vessel following a traffic lane (Rule 10(j)).

Who does a sailing vessel keep out of the way of?

Under Rule 18(b), a sailing vessel underway keeps out of the way of a vessel not under command, a vessel restricted in her ability to manoeuvre, and a vessel engaged in fishing — fishing in the Rule 3(d) sense, with gear that restricts manoeuvrability, not trolling lines. Under Rule 18(d)(i) she must also, if the circumstances of the case admit, avoid impeding the safe passage of a vessel constrained by her draught exhibiting the signals in Rule 28.

How might Rule 12 come up in an MCA oral?

It may come up as a pair of yachts on a chart or model, by day or at night. Examples of the kind of question to be ready for:

“You're on port tack and a yacht is approaching on starboard tack. Who keeps out of the way?”

“Both yachts have the wind on the starboard side. Which one gives way?”

“You're running downwind with the main out to starboard. Which tack are you on for Rule 12?”

“At night you are on port and see a sailing vessel to windward showing a green sidelight. What do you do?”

“You're motor-sailing. Does Rule 12 still apply to you?”

Where do candidates go wrong on Rule 12?

The common slips: deciding the tack from the wind direction rather than the side the mainsail is carried; forgetting that a yacht with her engine in use is power-driven; applying 12(a)(iii) to a vessel on starboard; forgetting that overtaking overrides the tack rules; and saying a sailing vessel always has right of way over a power-driven vessel, without Rules 9, 10 and 13.