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COLREG

Rule 19: Conduct of Vessels in Restricted Visibility

Under COLREG, without vessels in sight in or near an area of restricted visibility, proceed safely; if power-driven, keep engines ready for immediate manoeuvre.

Rule 19 of 41

Decide

Decision 1 of 2

It is foggy. You hear this signal, apparently forward of your beam, and cannot see the vessel. What do you do?

The rule in plain words

  1. When does it apply and how do you proceed?When vessels are not in sight of one another in or near restricted visibility. Adapt speed to conditions; if power-driven, keep engines ready for immediate manoeuvre.
  2. What if radar alone detects the other vessel?Determine whether a close-quarters situation is developing or a risk of collision exists. If so, take avoiding action in ample time.
  3. Which course alterations do you avoid?If the action is an alteration of course, avoid altering to port for a vessel forward of the beam, except for a vessel being overtaken; and altering towards a vessel abeam or abaft the beam.
  4. Do you hear another vessel's fog signal apparently forward of your beam?Unless it has been determined that no risk of collision exists, reduce to the minimum speed at which you can keep on course; if necessary, take all your way off and navigate with extreme caution until danger of collision is over.
Radar-only contact ahead of the beam in restricted visibility; the vessels are not in sight. If avoiding action requires a course alteration, avoid turning to port so far as possible, except for a vessel being overtaken. The amber arc is a conditional caution, not a recommended manoeuvre.

Before you read on: what would you do?

Question 1/1

When does Rule 19 apply?

Frequent mistakes

  • Wrong: "If I see it on radar, the normal crossing rules apply."

    Right: Radar alone requires assessing close-quarters or collision risk and taking action in ample time.

  • Wrong: "I can alter to port for any vessel forward of the beam."

    Right: Avoid it, except for a vessel being overtaken.

  • Wrong: "When I hear fog, reducing a little is enough."

    Right: Reduce to minimum course-keeping speed; take all way off if necessary and use extreme caution.

Exam keys & interpretation

  1. "No risk exists" is the exception: without that determination, a fog signal triggers Rule 19's response.
  2. In fog, do not automatically classify stand-on or give-way: apply COLREG's specific restricted-visibility conduct first.
  3. "Forward of the beam" is not every direction: avoid port, except overtaking; avoid altering towards abeam or abaft.

How to read it

Use the actual visibility conditions: do not wait for visual contact before adapting speed, engines and manoeuvre.

Read "so far as possible" and "if necessary" as conditions on action, not permission to delay or ignore danger.

Key points

  • Restricted visibility + vessels out of sight → safe speed.
  • Power-driven vessel → engines ready for immediate manoeuvre.
  • Radar alone → assess close-quarters situation and collision risk.
  • Fog signal forward of beam → minimum speed to keep on course, extreme caution.

Test your knowledge

3 questions to check it. Pick an answer to see why.

Question 1/3

Radar alone detects another vessel. What must you determine?

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Official text

IMO COLREG 1972 U.S. Coast Guard — International Navigation Rules (2024)

Full wording of the rule, reproduced from the official source below.

(a) This Rule applies to vessels not in sight of one another when navigating in or near an area of restricted visibility. (b) Every vessel shall proceed at a safe speed adapted to the prevailing circumstances and conditions of restricted visibility. A power-driven vessel shall have her engines ready for immediate maneuver. (c) Every vessel shall have due regard to the prevailing circumstances and conditions of restricted visibility when complying with the Rules of Section I of this part. (d) A vessel which detects by radar alone the presence of another vessel shall determine if a close-quarters situation is developing and/or risk of collision exists. If so, she shall take avoiding action in ample time, provided that when such action consists of an alteration of course, so far as possible the following shall be avoided: (i) an alteration of course to port for a vessel forward of the beam, other than for a vessel being overtaken; (ii) an alteration of course towards a vessel abeam or abaft the beam. (e) Except where it has been determined that a risk of collision does not exist, every vessel which hears apparently forward of her beam the fog signal of another vessel, or which cannot avoid a close-quarters situation with another vessel forward of her beam, shall reduce her speed to the minimum at which she can be kept on course. She shall if necessary take all her way off and in any event navigate with extreme caution until danger of collision is over.
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Reviewed by Ramon Curto, Nautical teacher at IECNPC · Last reviewed:

Frequently asked questions about COLREG Rule 19

When does COLREG Rule 19 apply?

Rule 19 applies to vessels not in sight of one another when navigating in or near an area of restricted visibility. There is no stand-on vessel under Rule 19: every ship must assess the situation and manoeuvre prudently.

What speed should a vessel keep in restricted visibility?

Every vessel shall proceed at a safe speed adapted to the prevailing circumstances and conditions of restricted visibility, and a power-driven vessel shall have her engines ready for immediate manoeuvre.

Which course alterations should be avoided in restricted visibility?

So far as possible, avoid an alteration of course to port for a vessel forward of the beam other than for a vessel being overtaken, and avoid an alteration of course towards a vessel abeam or abaft the beam (Rule 19(d)).

What must you do when you hear a fog signal forward of the beam?

Unless risk of collision has been determined not to exist, reduce to the minimum speed for keeping course and, if necessary, take all way off, then navigate with extreme caution until danger of collision is over (Rule 19(e)). The same applies when a close-quarters situation with a vessel forward of the beam cannot be avoided.