Fog and poor visibility on the water: what to do

Last verified: 14 October 2026

Step by step

1. Fix your position now

   When you see fog coming, note your position straight away on your GPS and on your paper chart.[13]

2. Slow down

   Slow is the only safe speed in fog. Go at a speed that lets you stop or turn in time, and keep the engine ready to manoeuvre at once.[27][6]

3. Lights on, reflector up

   Switch on your navigation lights, even in daytime, and make sure your radar reflector is up.[11][23][14]

4. Sound your fog signal

   Under the COLREGs, a power boat moving through the water sounds one prolonged blast (4–6 seconds) at least every 2 minutes; a sailing boat sounds one prolonged and two short blasts. A boat under 12 m may instead make some other efficient sound signal at least every 2 minutes.[1][2][3][10]

5. Look and listen

   Put extra crew on lookout and check everyone is wearing a lifejacket. Turn off music and keep listening for engines, horns, voices and fog signals.[8][15][18][22]

6. Use radar and AIS, but don't rely on them

   Use radar and AIS if you have them. Remember that small boats may not show up on other vessels' radar, even with a reflector.[14][19][28]

7. Hear a signal ahead? Slow to a crawl

   If you hear another vessel's fog signal ahead of you, slow to the minimum speed that keeps you on course, and stop if you need to, until the danger has passed.[7]

8. Get out of shipping lanes

   At a safe speed and steady course, head for shallower water away from busy shipping lanes, then anchor and wait. If you must cross a traffic lane, cross at right angles to the traffic flow.[16][9]

9. Signal at anchor and listen on channel 16

   At anchor, a vessel rings a bell rapidly for about 5 seconds at least every minute; a boat under 12 m may make another efficient sound signal at least every 2 minutes instead. Keep listening on VHF channel 16.[5][3][20]

10. Call for help if you're in danger

    If you think you are stuck somewhere dangerous, use your VHF radio to call for help.[17]

Don't

• Don't keep your normal speed. Slow is the only safe speed in fog.[27]
• Don't assume ships can see you on radar or AIS.[19][28]
• Don't play the radio or get distracted by conversation; you need your ears.[22]
• Don't cross a shipping lane at an angle; if you must cross, do it at right angles.[9]
• Don't assume the sun will burn the fog off; sea fog can last well into the afternoon.[21]

Before you sail

• Before you sail: fit the best radar reflector that is practical for your boat.[29]
• Before you sail: carry a working sound signal. Boats under 12 m don't need a whistle and bell but must have some other means of making an efficient sound signal.[12]
• Before you sail: learn the horn and bell signals you need to make in fog.[26]
• Before you sail: carry a compass and chart so you can still navigate if your electronics fail.[25]

Frequently asked

Sources

1. IMO COLREGs Rule 35(a), text published by US Coast Guard Navigation Center (2026-10-14): “A power-driven vessel making way through the water shall sound at intervals of not more than 2 minutes one prolonged blast”
2. IMO COLREGs Rule 35(c), text published by US Coast Guard Navigation Center (2026-10-14): “shall, instead of the signals prescribed in Rule 35 (a) or (b), sound at intervals of not more than 2 minutes three blasts in succession, namely one prolonged followed by two short blasts”
3. IMO COLREGs Rule 35(j), text published by US Coast Guard Navigation Center (2026-10-14): “A vessel of less than 12 meters in length shall not be obliged to give the above mentioned signals but, if she does not, shall make some other efficient sound signal at intervals of not more than 2 minutes.”
4. IMO COLREGs Rule 35(b), text published by US Coast Guard Navigation Center (2026-10-14): “A power-driven vessel underway but stopped and making no way through the water shall sound at intervals of no more than 2 minutes two prolonged blasts in succession with an interval of about 2 seconds between them.”
5. IMO COLREGs Rule 35(g), text published by US Coast Guard Navigation Center (2026-10-14): “A vessel at anchor shall at intervals of not more than 1 minute ring the bell rapidly for about 5 seconds.”
6. IMO COLREGs Rule 19(b), text published by US Coast Guard Navigation Center (2026-10-14): “Every vessel shall proceed at a safe speed adapted to the prevailing circumstances and conditions of restricted visibility. A power-driven vessel shall have her engines ready for immediate maneuver.”
7. IMO COLREGs Rule 19(e), text published by US Coast Guard Navigation Center (2026-10-14): “every vessel which hears apparently forward of her beam the fog signal of another vessel, or which cannot avoid a close-quarters situation with another vessel forward of her beam, shall reduce her speed to be the minimum at which she can be kept on her course.”
8. IMO COLREGs Rule 5, text published by US Coast Guard Navigation Center (2026-10-14): “Every vessel shall at all times maintain a proper look-out by sight and hearing as well as by all available means appropriate in the prevailing circumstances and conditions so as to make a full appraisal of the situation and of the risk of collision.”
9. IMO COLREGs Rule 10(c), text published by US Coast Guard Navigation Center (2026-10-14): “A vessel, shall so far as practicable, avoid crossing traffic lanes but if obliged to do so shall cross on a heading as nearly as practicable at right angles to the general direction of traffic flow.”
10. IMO COLREGs Rule 32(c), text published by US Coast Guard Navigation Center (2026-10-14): “The term "prolonged blast" means a blast of from four to six seconds duration.”
11. IMO COLREGs Rule 20(c), text published by US Coast Guard Navigation Center (2026-10-14): “The lights prescribed by these Rules shall, if carried, also be exhibited from sunrise to sunset in restricted visibility”
12. IMO COLREGs Rule 33(b), text published by US Coast Guard Navigation Center (2026-10-14): “A vessel of less than 12 meters in length shall not be obliged to carry the sound signaling appliances prescribed in Rule 33 (a) but if she does not, she shall be provided with some other means of making an efficient signal.”
13. RNLI (2026-10-14): “When you see fog approaching, immediately do a position fix on your GPS and on your paper chart.”
14. RNLI (2026-10-14): “Make yourself visible and help yourself see other vessels – switch on navigation lights, make sure your radar reflector’s up, and use your radar and AIS (Automatic Identification System).”
15. RNLI (2026-10-14): “Nominate extra crew for lookout duty and check all are wearing lifejackets.”
16. RNLI (2026-10-14): “At a safe speed and a steady course, head for shallower water where you won’t be in any busy shipping lanes. There, drop anchor and sit it out.”
17. RNLI (2026-10-14): “If you’re really worried you’re stuck in a dangerous place, use your VHF radio to call for help.”
18. RNLI (2026-10-14): “keep listening out for engine noise, horns, voices and other signs of vessels nearby.”
19. RNLI (2026-10-14): “Very small vessels like dinghies don’t always show up on the radar, so you’ve got to be extra careful.”
20. RNLI (2026-10-14): “Listen on VHF Ch 16 and, in restricted waters, Ch 13.”
21. RNLI (2026-10-14): “It’s a common misconception that fog always gets ‘burned off’ by the sun as the day progresses; sea fog can still linger well into the afternoon.”
22. RNLI (2026-10-14): “Don’t be tempted to stick on the radio while you’re waiting for the fog to clear, or get distracted by conversation”
23. US National Weather Service (NOAA) (2026-10-14): “Turn on all of your running lights, even in daytime.”
24. US National Weather Service (NOAA) (2026-10-14): “If you are unable to get your bearings, stay put until the fog lifts but make sure you are in a safe location.”
25. US National Weather Service (NOAA) (2026-10-14): “Have a compass available. Even if you don't know where you are in the fog, with a compass you can determine the direction you are navigating.”
26. US National Weather Service (NOAA) (2026-10-14): “Be familiar with horn and bell sounds you should produce to warn others around you when in dense fog.”
27. Transport Canada – Safe Boating Guide (TP 511E) (2026-10-14): “Slow is the only safe speed in fog, mist, rain, smoke and darkness”
28. Maritime and Coastguard Agency (MGN 349) (2026-10-14): “There is no guarantee that a small vessel will consistently show on radar screens”
29. Maritime and Coastguard Agency (MGN 349) (2026-10-14): “All small craft should consider fitting, where practicable, the most effective and appropriate radar reflector or radar target enhancer (RTE) for their circumstances; and ensure those comply with international standards.”
30. IMO COLREGs Rule 32(b), text published by US Coast Guard Navigation Center (2026-10-14): “The term "short blast" means a blast of about one seconds duration.”

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