Module 15 - Restricted Visibility
Rule 19 — Conduct in Restricted Visibility
What you will learn
Apply Rule 19 to radar-only and sound-signal encounters without importing the in-sight stand-on framework or turning its cautions into an automatic starboard manoeuvre.
Rule 19 applies to vessels not in sight of one another when navigating in or near restricted visibility. Rules 4–10 still apply, so lookout, safe speed, collision-risk assessment, positive action and routeing duties remain active.
A radar or AIS target is not 'in sight' unless the vessel can be observed visually. The normal Section II encounter pairs in Rules 11–18 therefore do not govern a radar-only contact. Rule 19 does not erase the rest of the Rules: Rules 4–10 apply in any visibility, and relevant not-to-impede duties can continue. There is no stand-on vessel under a Rule 19 close-quarters situation, so expect the other vessel may also manoeuvre.
For a vessel detected by radar alone, use systematic observations to determine whether a close-quarters situation is developing or collision risk exists. If so, take avoiding action in ample time. When that action is an alteration of course, so far as possible avoid altering to port for a vessel forward of the beam except when overtaking, and avoid altering towards a vessel abeam or abaft the beam. These are cautions, not a command that every starboard turn is safe.
Except where collision risk has been determined not to exist, if a fog signal is heard apparently forward of the beam, or a close-quarters situation with a vessel forward of the beam cannot be avoided, 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 is over. Sound direction can be deceptive and an unseen small vessel may not appear on radar.
Worked example
Repeated radar observations of one forward contact are 3.0 M at relative bearing 020°, 2.4 M at 021° three minutes later and 1.8 M at 021° after another three minutes.
- 1The range closes 0.6 M in each three-minute interval.
- 2Three minutes is 0.05 hours, so relative closing speed is 0.6 ÷ 0.05 = 12 kn.
- 3The bearing changes only about 1° while range decreases, so collision risk must be treated as existing rather than dismissed.
- 4At 1.8 M and 12 kn relative closure, zero range would be about nine minutes away if neither vessel changed movement; act in ample time and continue plotting.
Sense check: The nine-minute figure is a time-compression warning, not a predicted collision point. Own or target manoeuvres, measurement error and another contact can change the solution.
| Situation | Rule 19 response | Boundary |
|---|---|---|
| Radar-only contact | Determine close quarters or collision risk systematically | One observation or scant information is insufficient |
| Contact forward of beam | So far as possible avoid port alteration | Exception when overtaking; starboard is not automatically safe |
| Contact abeam or abaft | So far as possible avoid altering towards it | Check all targets and safe water |
| Fog signal apparently forward | Minimum speed to keep course; all way off if necessary; extreme caution | Unless collision risk has been determined not to exist |
Command a two-contact radar picture
The closing contact lies forward of the port beam. A second radar-only target is abaft the starboard beam, and a channel edge limits sea room to starboard.
1. Keep the layers clear
Apply Rules 4–10 and Rule 19; do not invent a stand-on right from the forward contact's apparent crossing aspect.
2. Respect both cautions
Avoid a port alteration for the forward contact so far as possible, but do not turn towards the abaft target or through the channel edge.
3. Use speed deliberately
Create time with an effective speed change when appropriate and be ready for the other vessels to manoeuvre too.
4. Verify the result
Continue systematic observations until every target is finally past and clear and the route remains safe.
Sense check: A starboard alteration can satisfy one remembered phrase and still turn towards another vessel or out of safe water.
Common mistake or limitation
- Saying Rule 19 replaces every other rule; Rules 4–10 and relevant not-to-impede duties remain part of the decision.
- Assigning stand-on and give-way roles to vessels that are not visually in sight of one another.
- Treating 'avoid port' as 'always turn starboard' without checking other targets, sea room and the effect of the action.
- Assuming a fog signal's apparent bearing is precise enough to support an immediate course alteration.
Recap
- Rule 19 governs vessels not in sight in or near restricted visibility while Rules 4–10 remain active.
- Its course-alteration cautions are conditional and do not prescribe one automatic turn.
- A forward fog signal or unavoidable close quarters requires the complete speed-and-caution response.
Optional quick check
Section 5 of 8
A radar-only contact is forward of the beam. Does Rule 19 automatically require a starboard alteration?
Sources and factual review
Reviewed 2 September 2026 - Compass Revision editorial review.
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