Module 15 - Restricted Visibility
Precautions in Fog
Active recall
Section 2 of 5
Explain the main idea from precautions in Fog in your own words.
Treat deteriorating visibility as a coordinated response: proceed at a safe speed, have engines ready for immediate manoeuvre, show navigation lights, make the required sound signals, and maintain a proper lookout by sight and hearing. Use radar if fitted and operational, monitor depth and position by all appropriate available means, and obtain and record a position promptly if circumstances allow.
Reduce speed. Under Rule 6, every vessel must proceed at a safe speed adapted to the prevailing visibility. Use a radar reflector where fitted or carried, 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.
- Action
- Fix position
- Why it matters
- Creates a reliable starting point before visual marks disappear
- Rule or principle
- Good navigation practice
- Action
- Switch on navigation lights
- Why it matters
- Makes the vessel easier to identify in restricted visibility
- Rule or principle
- COLREGs lights rules
- Action
- Sound fog signals
- Why it matters
- Warns vessels that may not be visible
- Rule or principle
- Rule 35
- Action
- Reduce speed
- Why it matters
- Allows time to assess risk and avoid collision
- Rule or principle
- Rule 6
- Action
- Use all available means
- Why it matters
- 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 |
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)
- Use radar reflector where fitted or carried
- Put on lifejackets
- Monitor echo sounder continuously
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
Sources and factual review
Reviewed 22 June 2026 - Day Skipper Revision.
Continue studying Restricted Visibility
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