Module 15 - Restricted Visibility
Rule 19 — Conduct in Restricted Visibility
What you will learn
Apply Rule 19 without importing the in-sight stand-on/give-way framework, while retaining Rules 4–10, continuing not-to-impede duties and the exact radar and fog-signal cautions.
Rule 19 applies to vessels not in sight of one another when navigating in or near restricted visibility. It is a risk-assessment and action framework, not a simple instruction always to turn to starboard.
Rules 11–18 form the section for vessels in sight of one another. When the other vessel is not visually in sight in or near restricted visibility, Rule 19 applies and there is no Section II stand-on vessel. Rules 4–10 still apply, including proper lookout, safe speed, risk assessment and effective avoiding action. Obligations not to impede another vessel under Rules 9, 10 and 8(f) can also continue in restricted visibility.
When another vessel is detected by radar alone, determine whether a close-quarters situation or risk of collision is developing from systematic observations. If so, take avoiding action in ample time. When that action is an alteration of course, Rule 19 says that so far as possible avoid an alteration to port for a vessel forward of the beam, except when overtaking, and avoid an alteration towards a vessel abeam or abaft the beam. Those cautions do not make every starboard turn safe: check the full plot, sea room, other targets and the effect of the action.
Except where risk has been determined not to exist, if a fog signal is heard apparently forward of the beam, or a close-quarters situation cannot be avoided with another vessel forward of the beam, reduce to the minimum speed at which the vessel can be kept on course. If necessary, take all way off and in every case navigate with extreme caution until the danger of collision is over. Sound direction can be deceptive, and small craft may not be detected by radar, so absence of a plotted target is not proof that the danger is absent.
| Situation | Rule 19 decision | Boundary to retain |
|---|---|---|
| Radar-only vessel forward of beam | Assess risk; act in ample time; so far as possible avoid port | Except when overtaking; check the whole plot and sea room |
| Radar-only vessel abeam or abaft | So far as possible avoid altering towards it | Another direction is not automatically safe |
| Fog signal apparently forward | Unless risk is ruled out, reduce to minimum speed to keep course | Take all way off if necessary and use extreme caution |
| Close quarters unavoidable forward | Apply the same minimum-speed and caution response | Continue until danger of collision is over |
Work a radar-only encounter
In fog, repeated radar observations show a contact fine on the port bow with little bearing change and decreasing range. Another target is abaft the starboard beam. Neither vessel is visually in sight.
1. Establish the rule
Apply Rules 4–10 and Rule 19; do not label either unseen vessel as the Section II stand-on vessel.
2. Establish the risk
Use systematic observations, not one echo or AIS label, and assume risk exists if doubt remains.
3. Test the action
Act in ample time and, so far as possible, avoid port for the forward target and avoid turning towards the target abaft the beam.
4. Use speed
Consider reducing speed or taking all way off to create assessment time and avoid building a second close-quarters situation.
5. Verify
Continue systematic observations until the action's effect and both targets are safely resolved.
Sense check: A starboard alteration that turns towards the starboard-quarter contact or removes sea room is not made safe merely by being to starboard.
Common mistake or limitation
- Saying Rule 19 replaces every other steering and sailing rule; Rules 4–10 still apply and some not-to-impede obligations continue.
- Assigning stand-on and give-way status to vessels that are not visually in sight under Rule 19.
- Turning automatically to starboard without a systematic plot, sea-room check or assessment of other targets.
- Shortening Rule 19(e) to 'slow down if worried'; its trigger and minimum-speed, all-way-off and extreme-caution requirements are specific.
Recap
- Rule 19 governs vessels not in sight in or near restricted visibility; Rules 4–10 and relevant not-to-impede duties remain.
- Radar-only alteration cautions are 'so far as possible' and depend on a systematic assessment of the whole situation.
- A forward fog signal or unavoidable forward close quarters triggers the specific minimum-speed, all-way-off-if-needed and extreme-caution response.
Optional quick check
Section 5 of 5
A radar contact forward of the beam creates collision risk. Is a turn to starboard automatically the correct Rule 19 action?
Sources and factual review
Reviewed 1 September 2026 - Day Skipper Revision.
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