Restricted Visibility (Rule 19)
Conduct of vessels in or near restricted visibility. Rule 19 applies when vessels are NOT in sight of one another — it is a distinct decision framework from the clear-visibility give-way rules.
Rule 19 Decision Flow
Procedure — Step by Step
Detect restricted visibility
Visibility drops below ~5 nautical miles due to fog, heavy rain, snow, or mist. Rule 19 applies to all vessels not in sight of one another.
Reduce speed to a safe minimum
Proceed at a speed appropriate to prevailing circumstances — slow enough to take proper and effective action to avoid collision, and to stop within a distance appropriate to the conditions.
Post a dedicated lookout
In addition to the helm, station a crew member as a dedicated visual and auditory lookout. Maintain a proper lookout by all available means (Rule 5).
Switch on navigation lights
Turn on sidelights, stern light, and (if ≥50m) masthead light. If making way, show steaming light; if underway but not making way, show appropriate lights per vessel type.
Sound fog signals
Begin sounding the correct signal for your vessel type and activity every ≤2 minutes (see Sound & Fog Signals page).
Use radar and ARPA if fitted
Switch on radar and plot targets. Use long-range scale first to detect, then short-range for precision. Plot bearings and ranges over time to determine CPA/TCPA.
Assess risk of collision
Use radar plotting, compass bearings, and AIS. If risk of collision exists, or you are unsure — take avoiding action early and substantially.
Take avoiding action
Follow the Rule 19(d) constraints below. Avoid: turns to port for a vessel forward of the beam, and turns toward a vessel abeam or astern.
Stop if you cannot assess risk
If you cannot determine if risk of collision exists, reduce speed to minimum or stop — navigate with extreme caution until danger is past.
Avoiding Action Constraints
If a risk of collision exists (or you cannot rule it out), take avoiding action early and substantially. Rule 19(d) places two hard constraints on your manoeuvre:
Do NOT alter to port
For a vessel forward of your beam
Never turn to port for a vessel detected forward of the beam, especially if a close-quarters or collision risk is developing.
Rule 19(d)(i)Do NOT turn toward
For a vessel abeam or astern
Do not alter course toward a vessel on your beam or abaft your beam if a collision risk exists.
Rule 19(d)(ii)Fog Readiness Checklist
Key Differences from Clear-Visibility Rules
- •No stand-on / give-way vessel distinction. In restricted visibility, every vessel is a give-way vessel — there is no "stand-on" obligation to hold course and speed.
- •No "port-to-port" assumption. You cannot assume the other vessel will alter to starboard — there is no mutual visibility.
- •Action must be early and substantial. Small, late course changes are dangerous — they may not be detected on the other vessel's radar in time.
- •Stop if uncertain. If you cannot determine if risk of collision exists, you must reduce to minimum speed or stop — this is mandatory under Rule 19(e).
Guidelines Only — Operator Responsibility. This is a general reference for COLREG Rule 19. Radar plotting, target tracking, and safe speed determination require professional training and vessel-specific knowledge. Always maintain a proper lookout by all available means. The operator is solely responsible for safety of the vessel and crew.