Rule 19 — Restricted visibility
The rule behind the classic fog-and-radar scenario, and the one where the instinct from the crossing rules leads you wrong. When it applies, what it asks, and the alterations it tells you to avoid.
To vessels not in sight of one another when navigating in or near an area of restricted visibility. Both parts matter: the vessels must not be in sight of each other, and you need only be in or near the restricted visibility — clear weather alongside a fog bank still counts.
Once the other vessel is in sight, Section II (Rules 11 to 18: overtaking, head-on, crossing, give-way and stand-on) applies instead.
Rule 3 defines it as any condition in which visibility is restricted by fog, mist, falling snow, heavy rainstorms, sandstorms or any other similar causes. The rules give no distance.
No. The give-way and stand-on rules are in Section II, which applies only to vessels in sight of one another. In Rule 19 every vessel that detects a developing close-quarters situation or risk of collision must act. Treating yourself as stand-on in fog is the classic Rule 19 mistake.
Every vessel must proceed at a safe speed adapted to the restricted visibility, and a power-driven vessel must have her engines ready for immediate manoeuvre. Every vessel must also apply the rules of Section I — look-out, safe speed, risk of collision, action to avoid collision, narrow channels and traffic separation schemes — with due regard to the restricted visibility.
A vessel that detects another by radar alone must determine whether a close-quarters situation is developing and/or risk of collision exists. If so, she must take avoiding action in ample time. Where that action is an alteration of course, so far as possible she must avoid:
(i) an alteration of course to port for a vessel forward of the beam, other than for a vessel being overtaken; and
(ii) an alteration of course towards a vessel abeam or abaft the beam.
Working from the two things 19(d) says to avoid: for a vessel forward of the beam — on either bow — the alteration to avoid is to port, so an alteration is normally to starboard (unless you are overtaking her). For a vessel abeam or abaft the beam, the alteration to avoid is towards her, so you alter away from her side. Reducing speed, or taking all way off, is avoiding action too, and often the better one.
The rule says 'so far as possible' — the circumstances can make another action right, and you need to be able to say why.
Unless it has been determined that a risk of collision does not exist, a vessel that hears the fog signal of another vessel apparently forward of her beam, or cannot avoid a close-quarters situation with a vessel forward of her beam, must reduce her speed to the minimum at which she can be kept on her course. If necessary she must take all her way off, and in any event navigate with extreme caution until danger of collision is over.
Rule 35 sets the sound signals in restricted visibility, and Rule 20(c) requires the lights, if carried, to be shown from sunrise to sunset in restricted visibility as well as at night. Rule 6 lists the factors for a safe speed, including the extra ones for vessels with operational radar.
It may come up as a radar scenario. Examples of the kind of question to be ready for:
“You're in fog. A radar contact on the starboard bow is closing with a small CPA. What do you do, and why?”
“Same again, but the contact is on your port quarter.”
“You hear a fog signal apparently forward of the beam. What does the rule require?”
“What sound signal do you make, underway in fog, making way?”
The common slips: applying the crossing rule and 'standing on' in fog; altering to port for a vessel on the port bow; forgetting that slowing down is an action; and not knowing that 'close-quarters' has no figure in the rules — you must say what you would consider close for your vessel and the conditions.
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