Module 15 - Restricted Visibility
Precautions in Fog
Fix your position immediately while you can still see landmarks. Switch on navigation lights. Start sounding fog signals (one prolonged blast every two minutes for a power vessel, one prolonged + two short blasts for a sailing vessel). Post extra look-outs — use eyes AND ears.
Reduce speed. Under Rule 6, every vessel must proceed at a safe speed adapted to the prevailing visibility. Have your radar reflector hoisted, and use radar or AIS if available. Put on lifejackets and consider clipping on harnesses.
Plot your position regularly using GPS. Monitor depth — your echo sounder is now a critical navigation tool. Consider anchoring if you are near shallow water and uncertain of your position.
Key points
- Fix position while you still can see marks
- Navigation lights ON
- Sound fog signals (Rule 35)
- Post extra look-outs (sight AND hearing)
- Reduce speed to safe speed (Rule 6)
- Hoist radar reflector
- Put on lifejackets
- Monitor echo sounder continuously
Creates a reliable starting point before visual marks disappear
Rule or principle: Good navigation practice
Makes the vessel easier to identify in restricted visibility
Rule or principle: COLREGs lights rules
Warns vessels that may not be visible
Rule or principle: Rule 35
Allows time to assess risk and avoid collision
Rule or principle: Rule 6
Sight, hearing, radar, AIS, depth and GPS all contribute
Rule or principle: Rules 5, 7 and 19
| Action | Why it matters | Rule or principle |
|---|---|---|
| Fix position | Creates a reliable starting point before visual marks disappear | Good navigation practice |
| Switch on navigation lights | Makes the vessel easier to identify in restricted visibility | COLREGs lights rules |
| Sound fog signals | Warns vessels that may not be visible | Rule 35 |
| Reduce speed | Allows time to assess risk and avoid collision | Rule 6 |
| Use all available means | Sight, hearing, radar, AIS, depth and GPS all contribute | Rules 5, 7 and 19 |
Common questions
What is the first thing to do if fog descends?
Fix your position while visual references are still available, then slow down, switch on navigation lights and start the correct sound signals.
Do normal give-way rules apply in fog?
When vessels are not in sight of one another, Rule 19 applies rather than the normal in-sight give-way rules.
Should a yacht use navigation lights in daytime fog?
Yes. Navigation lights should be shown in restricted visibility even during the day.
Keep revising this topic
Last reviewed: 22 June 2026 by Day Skipper Revision
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