How to deal with fog at sea and top tips for navigating in fog

Fog is one of the more challenging issues facing boaters, especially new or inexperienced ones. Jon Mendez shares his top tips for navigating in fog...

On a recent cruise to the Channel Islands, we had to deal with multiple cases of fog, some of which were forecast but others not, and it made me realise afresh just how intimidating it can be. If I was on a boat without radar and fog was forecasted, I’d consider very carefully whether I really needed to leave port.

However, if you are already at sea when fog comes down unexpectedly, I would take the following navigating in fog precautions to keep everyone safe:

  1. Put lifejackets on (if not already being worn)
  2. Double check your boat’s position and write it down
  3. Start making the appropriate sound signals
  4. Slow down to a speed at which you can react to any threat given the available visibility
  5. If it’s really thick fog, head for shallow water and consider anchoring
  6. Keep a good lookout using your ears as well as your eyes – stop occasionally to listen for other vessels.

Thankfully, the boat we were on had a radar, which I had used many times before. It wasn’t the very latest broadband style radar (they are amazing) but it was still a very capable 4ft open array with a 12in MFD screen.

Having used it many times before, I was comfortable that I had the settings correctly adjusted for the sea conditions of a light chop (Rain: off, ITC: on, Gain: about 65%, Sea clutter: on 10%,) so I was confident any targets would show clearly on the display.

I had made those adjustments previously, using a harbour wall and some small boats so I knew I was seeing what was there. It’s good practice to do this every time you go out so it becomes a habit.

I set the radar up in dual-screen mode with one screen showing the chart in North-up and the radar overlay on to confirm my position and the other displaying a single radar screen in Head-up, as I feel that is easiest for the crew to use while keeping a visual looking out for any targets and relating them to the picture on screen.

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We were progressing at 17 knots, about 20mph, in visibility of around 300m. If that sounds quicker than expected, it’s because the boat is really stable at this speed, it holds a good steady course (invaluable for radar) and we were well away from any rocky areas.

I set the radar on a three-mile range with each range ring at ½ a mile. At 17 knots it will take roughly 3½ minutes to cover a mile, so in effect I am looking ten minutes ahead in all directions. One of the hardest tasks when navigating in fog is keeping your heading correct.

Inexperienced skippers wander all over the place as they are used to having a visual point to aim at. For this reason an autopilot can be a big help in fog but if you don’t have one you can use a rolling road on your chartplotter or, as I did, an active waypoint.

This allows you to judge how straight a course you are holding. Even if you just have a basic plotter and no radar, this is still a valuable way to help maintain a heading when navigating in fog.

First published in the October 2023 issue of MBY.