Module 15 - Restricted Visibility
Navigating in Fog
What you will learn
Recognise restricted visibility before it becomes an emergency and decide whether to delay, divert or continue with enough margin to remain in control.
Restricted visibility is a condition, not just a fog forecast. The COLREG definition includes fog, mist, falling snow, heavy rainstorms, sandstorms and similar causes that restrict what can be seen.
There is no single visibility distance that is safe for every yacht and route. The usable distance depends on traffic, closing speeds, sea room, navigation hazards, the yacht's stopping and turning ability, the available crew and the equipment that can genuinely be used. If there is no target against which to judge visibility and the skipper believes it is restricted, MCA guidance says to assume that it is and act accordingly.
The strongest decision is often made before entering the affected area. Check the forecast and actual observations, the route's traffic and hazards, escape or anchoring options, daylight, crew capacity and whether radar or other aids are fitted and understood. Delay, shorten or divert when the remaining margin does not support safe lookout, navigation and collision avoidance; a planned departure is not a commitment to enter conditions the crew cannot manage.
Restricted visibility should already appear in the passage plan as a trigger, not be invented after the horizon disappears. Name the decision point, a safe alternative and the evidence that will be monitored. A position, depth, radar return or AIS target is one item of evidence, never permission to keep the original speed or route when the wider situation is becoming unsafe.
| Evidence before entry | Question to answer | Possible decision |
|---|---|---|
| Forecast and actual visibility | Will the crew see and assess hazards early enough? | Delay, divert or enter only with a defensible margin |
| Traffic and closing speeds | How quickly could an unseen close-quarters situation develop? | Choose more sea room and continuously review safe speed |
| Route and alternatives | Can the next entrance, refuge or anchorage be reached and used safely? | Use the checked option before its margin closes |
| Crew and equipment | Can lookout, signals, navigation and manoeuvring be sustained together? | Change the plan rather than assume one display will compensate |
Decide before the headland
A 9-metre yacht is approaching a traffic-used headland. Visibility ahead is closing in heavy rain, there is no radar and the next safe harbour entrance needs visual pilotage. The original plan continues around the headland.
1. Name the change
Treat the heavy rain as restricted visibility even though the forecast did not use the word fog.
2. Test the margin
Compare sighting distance, traffic, sea room, crew and equipment with the time and distance needed to detect, assess and avoid danger.
3. Use the planned choice
Turn for the checked refuge or safe water before the headland if the visual entrance and traffic picture cannot be managed safely.
4. Prepare while clear
Brief the crew and ready the restricted-visibility response before useful visual references and manoeuvring room are lost.
Sense check: A chartplotter position can show where the yacht is while still providing no reliable picture of an unreported small craft or the visibility needed for the harbour entrance.
Common mistake or limitation
- Waiting for dense fog before applying restricted-visibility precautions; mist, snow, heavy rain and similar conditions can trigger the same problem.
- Using a fixed distance as the definition of safe visibility without considering closing speed, traffic, sea room, vessel handling and detection limits.
- Treating a good electronic position as evidence that the route and speed remain safe when collision-detection and pilotage margins have already disappeared.
Recap
- Restricted visibility includes more than fog and has no universal safe-distance threshold.
- Decide with the route, traffic, vessel, crew, equipment and available alternatives together.
- Put a visibility trigger and a usable alternative into the passage plan before conditions close in.
Optional quick check
Section 1 of 5
Heavy rain is hiding traffic and the harbour marks ahead. Which response uses the correct decision model?
Sources and factual review
Reviewed 1 September 2026 - Day Skipper Revision.
Continue studying Restricted Visibility
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