Dealing With One of the Most Dangerous Elements of Seamanship

This article was first published online on December 23, 2016. It first appeared in the January/February 2017 issue.

Operating in the fog can be incredibly dangerous and requires dedicated attention and use of both your electronics as well as your personal situational awareness. Whenever you are boating in an area of restricted visibility you should be turning on your navigational lights and sounding the appropriate sound signals. This allows other boats to locate you in the fog before it is too late. To learn more about light and sound signals for both operating in the fog and in the dark check out our Boaters University course, Fundamentals of Seamanship: Navigational Rules.

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We were just a few hours out of London, in the notorious Dover Straits on my first trip to sea at the age of 16, when we collided with another ship in thick fog. It was only a glancing blow so we were able to carry on with our voyage, but it was a lesson about the dangers of fog. At sea, things can happen unexpectedly, and you realize just how your world changes when visibility drops to zero.

That was before the days of electronics. We had no radar, no GPS, and no AIS, so it was a bit like navigating with a stick and we had to rely on listening and locating fog signals. Modern electronics have made a huge difference to navigating in these conditions. They give you confidence to keep going when you can’t see ahead, and you tend to rely on them totally, which is where the danger lies. GPS positioning on the chart plotter can give you a lot of confidence that you know where you are, but radar and AIS have their limitations when it comes to collision avoidance in fog, and cannot be trusted implicitly to detect everything that is around you.


With two displays in the pilothouse—one showing the radar and one the electronic chart—you are likely to be focussing on these screens rather than looking out of the windows. In theory, these two displays show you everything you need to know, so why bother with keeping a visual lookout? The problem is that you cannot be sure that the radar will show everything that is moving on the water, particularly if there is a sea running. That is when the radar will pick up the returns from the waves as well as those from small boats and the small-boat returns can get lost in the sea clutter.

So the visual lookout is vital in fog, not only to reassure yourself that you will see other boats that may be close but also it is a legal requirement under the Colregs. Rule 5 states, “Every vessel shall at all times maintain a proper lookout by sight and hearing as well as all available means.” Hearing implies that you should be listening for fog signals as well. I can’t remember the last time I heard any ship making fog signals and this requirement seems to be studiously ignored these days in fog, because ships and boats rely on their radar alone.

In fog, you need all hands on deck, and the lookout should be outside on the flybridge or deck. There, the lookout will not be distracted by the electronic displays and will have a much clearer view. It can be a real struggle to keep the concentration necessary for a lookout, so you need to change the watch at short intervals. It is best to have one person on visual lookout and one on the radar so that full concentration can be given to both.



1. Autopilot: Operating the boat on autopilot in the fog has advantages. First, it removes the need to have someone steering the boat so they can concentrate on the lookout. Second, it will stabilize the radar pictures and make them much easier to interpret. However, make sure you know where the autopilot disconnect button is so you can quickly take over manual control. If you have MARPA on the radar to show the heading vectors of other vessels, then having the picture stabilized will make these easier to see.

2. SafeSpeeds: Navigating in fog also requires you to proceed at a safe speed, but the actual speed is not defined. In its broadest sense, a safe speed is one that doesn’t contribute to a collision. It also might be defined as a speed that allows you to stop before you hit an oncoming vessel. You may think this means stopping within the visibility range, but adjust for the visibility range with oncoming vessels.


3. Visibility: To enhance safety in fog, make your boat as visible as possible. Switch on your running lights and any other bright lights on deck because they could show up through the fog much better that the boat itself, especially at night. A radar reflector gives you a much better chance of being seen by other vessels’ radar.

4.AIS: Automatic Identification System, or AIS, shows you the course and speed of the targets it sees, and even the name of the ship, so it can help to identify other shipping targets. More important, though, other ships can identify you. Find the best AIS equipment you can afford (Class A being the commercial grade). Class B is acceptable but doesn’t have the priority levels of the Class A units. All ships over 300 tons should have a working AIS, but there are no guarantees that small boats have it: Don’t assume that the AIS targets you see on the screen are the only targets out there. 

5.ShippingLanes: To simplify things, try setting your course to avoid shipping lanes. Not only will big ships possibly be challenged to see you on their radar, they may also choose to ignore you even when they do. Modern ships have tight schedules to keep and rarely seem to slow down in fog, so if you can keep away from the shipping lanes, it is one less thing to worry about.

Ships need deep water so set your course in shallower waters to avoid them. When you are in busy shipping waters that have traffic separation zones you can keep to the inshore zones where the big ships should not go. When I did a cruise from Southampton, England, to Oslo, Norway, we had fog much of the way and it was quite a relief to use the inshore zone when passing through the busy Dover Straits. It took some of the danger away, but you can only use these zones if you are less than 20 metres (66 feet) in length. If you are larger, then the Colregs demand that you mix in with shipping traffic. Pay attention to ship traffic at all times, including ferries that may be crossing the inshore zones in order to come into port.

6. Other Obstacles: Farther into the North Sea on our voyage, we had to cross the shipping lanes in order to make land. Colregs dictate that we traverse shipping lanes at right angles which let us get across as quickly as possible. Then there were oil rigs and platforms that had to be avoided, and these days the North Sea is also littered with offshore wind farms that take up much of the potentially safe navigating area for small craft. These wind farms are coming to U.S. waters and they should be considered serious hazards in fog. We had two people on watch the whole time, but the tension was palpable until we reached clearer waters.

7. AvoidingSmallCraft: Relying on small-boat radar to avoid collisions can be tricky. Have the radar on a head-up display so that the targets are shown relative to your own heading. Put the bearing cursor onto the target and you can then see if the bearing of the target is changing. If it is not changing significantly, then there is a risk of collision and you need to take action according to the Colregs. This sounds relatively easy when you have a single target around you, but when there are multiple targets, this is the time to slow down so that you have more time to determine what each target is doing. Also, it only works when the radar picture is stabilized with autopilot steering. If your radar has a split-screen capability, then use one display to remain on the 6-mile range and one set to a 2-mile range. The former is for early detection of targets and the second is to make collision avoidance manoeuvres.

8. Electronics: These days, with modern electronics, keeping on course is pretty straightforward with GPS positioning and a chart plotter. The accuracy is more than adequate for use in zero visibility. You might want to set the course to pass close to a buoy or two, which could give you the reassurance that the GPS is working and sighting the buoy can also allow you to see just what the range of visibility is. Keeping your depth sounder on is also an extra check, and smart practice.


For navigating in fog, the electronic chart should provide most of the answers, but at some stage you still have to make the transition from the electronic picture to visual navigation as you approach land or you enter harbor. This is where you resort to some of the techniques that were used before electronics came into common use.

When making landfall, set the landfall point to one side of your destination and then you will know which way to turn to find it. Try to choose a point that is easily recognizable so that you know it when you see it. I have seen locals on board who said they knew every inch of the coast. That was fine except they didn’t recognize it in thick fog, and we could not find the harbor entrance. I went back offshore, ran along the coast, and then tried another landfall, but still there was no recognizable point. We could see lights on shore so we landed with the tender and had to ask in a pub where we were.

9. Harbor Approaches: Always approach the land at an angle rather than straight in. That way you will know which way to turn to get out of danger when you sight something and the turn is through perhaps just 90° rather than 180°. Another technique is to use your echo sounder to give early warning of the approach to the shallows, and you may notice a change in the wave patterns as you approach. Of course, try to choose a landfall point where there are no off-lying dangers that can make life difficult.

10. WhenDoesFogHappen: Forecasting fog is not easy because fog comes down when there may be only subtle differences in temperature and moisture content. It can be quite local and it can be patchy or it can cover vast areas. On the East Coast, north of Nantucket, you can get fog for hundreds of miles where the cold Labrador Current meets the Gulf Stream. There are two main types of fog as the table (facing page) shows and knowing which you are experiencing will help you to forecast when it may clear. If you are snug in harbor, you can delay departures until the fog clears, but out at sea you have to cope with what comes along. I hope these tips will assist you in times of pea soup.