Rule 11: Section II applies in sight of one another.

What does COLREGs Rule 11 say?

That the rules of Part B, Section II apply to vessels 'in sight of one another'. That is the whole rule. It sets no duty of its own; it switches the rest of the section on.

Section II is Rules 11 to 18: sailing vessels (Rule 12), overtaking (Rule 13), the head-on situation (Rule 14), the crossing situation (Rule 15), action by the give-way vessel (Rule 16), action by the stand-on vessel (Rule 17), and responsibilities between vessels (Rule 18).

What does 'in sight of one another' mean?

Rule 3(k) defines it: vessels are deemed to be in sight of one another 'only when one can be observed visually from the other'. It is about seeing, not detecting. A radar contact, an AIS target or a voice on the VHF is not a vessel in sight, however clear the picture on the screen. Nor is a vessel whose fog signal you can hear but cannot see.

Why does Rule 11 matter so much?

Because the idea of one vessel keeping out of the way while the other keeps her course and speed belongs to Section II. Rules 12, 13 and 15 say which vessel keeps out of the way (in Rule 14 both alter), Rule 16 says how she does it, Rule 17 tells the other to keep her course and speed, and Rule 18 sets who keeps out of the way of whom between different kinds of vessel. None of that applies unless the vessels are in sight of one another.

Which rules apply in any visibility, and which only in fog?

Part B has three sections. Section I (Rules 4 to 10: look-out, safe speed, risk of collision, action to avoid collision, narrow channels and traffic separation schemes) applies 'in any condition of visibility' under Rule 4. Section II (Rules 11 to 18) applies to vessels in sight of one another. Section III is Rule 19, which applies to vessels not in sight of one another when navigating in or near an area of restricted visibility.

So Section I is always on. When the vessels are in sight of one another, Section II applies as well. When they are not in sight and are in or near an area of restricted visibility, Rule 19 applies instead. Two vessels not in sight of each other in clear weather (a radar contact beyond visual range, say) are under Section I alone until they sight each other.

What applies when you can't see the other vessel in fog?

Rule 19. There is no give-way or stand-on vessel: under Rule 19(d), a vessel that detects another by radar alone must determine whether a close-quarters situation is developing and/or risk of collision exists, and if so take avoiding action in ample time — whichever side the other vessel is on. Rule 19(c) also requires due regard to the restricted visibility when applying the Section I rules.

Can Section II apply in restricted visibility?

Yes. Rule 11 turns on whether the vessels are in sight, not on the weather. In fog, once the other vessel can be observed visually, Section II applies to the two of you, because Rule 19 applies only to vessels not in sight of one another.

In practice that moment often comes late and close, when a vessel you have been watching on radar appears out of the murk. The situation was shaped under Rule 19, but from then on Rules 12 to 18 apply — including Rule 17(b), which requires a vessel that is to keep her course and speed to take 'such action as will best aid to avoid collision' once collision cannot be avoided by the give-way vessel alone.

Do the sound signals change too?

Partly. The manoeuvring signals in Rule 34(a) — one short blast for 'I am altering my course to starboard', two for port, three for operating astern propulsion — are for a power-driven vessel underway when vessels are in sight of one another. The doubt signal in Rule 34(d), at least five short and rapid blasts, is also for vessels in sight of one another. Rule 35 (Sound signals in restricted visibility) works differently: it applies in or near an area of restricted visibility whether or not another vessel is in sight. A vessel in fog keeps sounding her fog signal after the other comes into view, and adds the Rule 34 signals when she manoeuvres.

How might Rule 11 come up in an MCA oral?

It may come up on its own, or as the first decision in a scenario: are these vessels in sight of one another or not? Examples of the kind of question to be ready for:

“You have a vessel on radar fine on your starboard bow in thick fog. Are you the stand-on vessel?”

“What does 'in sight of one another' mean?”

“You can hear a fog signal but can't see the vessel making it. Which rules apply?”

“The fog lifts and you can now see her. Which rules apply now?”

“Which rules apply in any condition of visibility?”

Where do candidates go wrong on Rule 11?

The common slips: applying the crossing rule to a radar contact in fog; treating an AIS target as a vessel in sight; forgetting that Section I still applies alongside Section II; and assuming Rule 19 still governs a vessel that has come into sight in poor visibility.