Action in Fog at Sea

Action in fog

Fog is one of the scariest situations at sea. If possible, avoid fog by staying in harbour. Navigating a boat in bad visibility is very stressful and exhausting, you will also find that after a while you start to imagine that you can see things!

I was in the Thames Estuary one day when the visibility was less than 100m, to remain safe we were staying in water that was 3m deep as there was no risk of meeting any shipping in water that shallow. At one point, even though I knew it was not possible, I could see a large ship coming towards us, even when I looked away it was still there when I looked back, I had to get one of the crew to confirm that there was nothing coming out of the fog!

The dangers in fog are:

  • Collision

This is the biggest single danger, especially in open water or near a port entrance.

  • Hitting a hazard

Even though we can use GPS to find our position, poor use of the equipment may mean that we are not able to predict accurately what our future position will be.

  • Getting lost and not being able to find harbour

Less of a problem with GPS now than in the past but there are still harbours I would not enter only on GPS as there are hazards close to the entrance that may be hard to avoid.

The tactics we employ when the fog appears must address these points.

Collision avoidance
  • Sound a fog signal
  • Post lookouts on the bows (change them frequently)
  • Have the engine ready for use (warmed up)
  • Monitor the port control VHF channel (ships call in their position at Pilot reporting point chart symbol.this symbol)
  • Avoid busy waterways and harbours with a lot of shipping
  • Stay in shallow water (too shallow for ships!)
  • Hoist radar reflector
  • Operate your radar if fitted
To avoid hitting a hazard
  • Find shallow water and anchor until the fog clears
  • Change your route or destination to an area with no dangers
  • Monitor the depth constantly
  • Set a clearing depth (a minimum depth)
To avoid getting lost
  • Plot a fix as soon as you realised visibility is reducing
  • Maintain good navigation and records
  • Follow a contour line if possible
  • Aim off to one side of your destination then follow a "handrail" to the harbour (contour lines are usually the best)

Not all these concepts can be used at the same time; you will need to decide on your tactics based on the current situation. On a Coastalskipper or Yachtmaster practical course, you will probably practice fog navigation. It is only by practicing that you begin to believe in your ability to find your way around safely. Try navigating your way around only working from down below, in good visibility, before you have to do it for real!

At the end of the day when you are out at sea in fog it may be safest to get to the shallowest water that is safe and wait for the visibility to improve, just hope the fog is not going to last 2 weeks! is free to use, but if you feel you would like to contribute to the running and development costs you can donate via Paypal:

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