Module 15 - Restricted Visibility
Navigating in Fog
What you will learn
Recognise restricted visibility early and make a route-level delay, divert or continue decision before detection, pilotage and collision-avoidance margins close.
Restricted visibility is not limited to fog and has no universal safe distance. It is any condition in which fog, mist, snow, heavy rain or a similar cause restricts visibility enough to change the navigational decision.
Rule 3 includes fog, mist, falling snow, heavy rainstorms, sandstorms and similar causes. A vessel is 'in sight' of another only when one can be observed visually from the other. Radar or AIS detection does not create an in-sight encounter, and a forecast that omits the word fog does not remove the restricted-visibility duties when the actual view is closing.
There is no single distance at which every yacht must declare restricted visibility. Decide from traffic density and closing speeds, sea room, hazards, pilotage demands, the yacht's manoeuvring and stopping characteristics, crew capacity and the detection limits of equipment that is actually fitted, working and understood. If there is no target against which to judge range and the skipper believes visibility is restricted, MCA guidance says to assume it is and act accordingly.
Put the decision into the passage plan before the route enters the affected area. Name the evidence that triggers delay, diversion or a prepared response; the last point from which the safe alternative remains usable; and the roles needed to sustain lookout, navigation, signals and manoeuvring. A precise electronic position cannot replace the ability to detect traffic, identify a harbour approach or retain a safe escape route.
| Evidence | Command question | Possible decision |
|---|---|---|
| Actual visibility and trend | Can traffic and marks be detected and assessed in time? | Delay, divert or enter only with a defensible margin |
| Traffic and closing speed | How quickly could an unseen close-quarters situation develop? | Create sea room and continuously review safe speed |
| Route and alternatives | When does the checked refuge or safe-water option close? | Act at the decision point rather than after the margin is gone |
| Crew and equipment | Can lookout, navigation, signalling and manoeuvring be sustained together? | Change the plan instead of relying on one person or display |
Use the last useful decision point
A 10-metre yacht is approaching a traffic-used headland. A rain squall is hiding the next visual marks, the radar is intermittent and the refuge astern becomes difficult once the tide turns. The original ETA remains achievable.
1. Classify the condition
Treat the heavy rain as restricted visibility; the trigger is the actual loss of sighting and assessment range, not a weather label.
2. Test the route margin
Compare traffic closure, sea room, pilotage, equipment reliability and crew workload with the time needed to detect, assess and avoid danger.
3. Protect the alternative
Use the checked refuge before the tidal and distance margin closes if the forward route cannot be managed safely.
4. Prepare before entry
Brief the coordinated response while the crew still has visual context and enough room to change the plan calmly.
Sense check: Meeting the ETA is irrelevant if the route has lost the detection, pilotage or escape margin on which that ETA depended.
Common mistake or limitation
- Waiting for dense fog before applying the restricted-visibility framework; heavy rain, mist, snow and similar conditions can create the same legal and practical problem.
- Using one fixed visibility distance without considering closing speed, traffic, sea room, vessel handling and equipment performance.
- Treating an accurate-looking chartplotter position as proof that collision detection and the next visual pilotage task remain manageable.
Recap
- Restricted visibility includes more than fog and has no universal safe-distance threshold.
- Use route, traffic, vessel, crew, equipment and alternatives as one decision.
- Set the trigger and last safe choice before the yacht enters the affected area.
Optional quick check
Section 1 of 8
Heavy rain is hiding traffic and the harbour marks ahead. Which decision uses the correct framework?
Sources and factual review
Reviewed 2 September 2026 - Compass Revision editorial review.
Continue studying Restricted Visibility
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