Sea fog can come on suddenly and is dangerous, especially when you are in a busy area. How does fog develop? And what can you do as a sports skipper when it catches you off guard at sea?
We were caught out in Portugal. There was a light wind, the sea was calm, the sun was shining. The mood on board was relaxed. It promised to be a nice, carefree sailing trip. A few hours along the coast, stopping somewhere for a swim, and then back again. That was our plan.
Unfortunately, however, nothing came of it. Because: as soon as we were out at sea, a white-gray wall suddenly appeared in front of us, high and huge, as if out of nowhere. The wall came towards us quickly, and just a minute or two later, visibility was completely gone – the sea fog had enveloped us completely.
From one moment to the next, it had become colder and darker around us, and we could only see things around us for a few meters, just barely making out the bow of our boat. But anything further than ten meters away was simply no longer visible to us, if at all, then only as a vague suggestion.
Fortunately, there was not much activity on the water at the moment, and we were not far from our berth. So, for safety reasons, we decided to turn around on the spot and quickly follow our wake back to the marina. We had a plotter on board, so for safety’s sake we regularly checked our compass heading – until we were able to moor our lines safely back in the marina, where fortunately the fog was not as thick as it was out at sea.
Water droplets are formed by condensation of water in humid and saturated air.
To understand what had just happened, it helps to know what fog. In meteorology, fog is a part of the atmosphere in which water droplets are finely distributed and which is in contact with the ground (they ‘touch’ the ground). The water droplets are formed by condensation of the water in the humid and supersaturated air.
This contact fog (meteorologists also speak of advection fog) occurs when warm humid air from the south flows into the colder areas in the north, thereby stirring up a layer of cold air close to the ground. The warm air is cooled down, which is why condensation and droplet formation occurs. Fog can also be caused by the convergence of ocean currents at different temperatures and by the uplift of air masses.
Lake fog (or coastal fog) is a special case of contact fog
A special case of contact fog is coastal or lake fog. The water surfaces are usually much cooler than the land surfaces, especially in spring. If the warm air masses over the land are then advected, they quickly cool down over the water. The water droplets formed after reaching the dew point then form a thin layer of fog directly over the water surface (cold water fog).
This form of fog is particularly consequential when a warming inland causes a sea breeze during the day. The fog that is actually located over the water is then transported to the coasts. Such an onset of coastal fog is characterized by a significant change in visibility and temperature conditions, and also occurs extremely suddenly. This is exactly what happened to us during our Portugal trip.
In sea fog, you can see much worse – or not at all – but you can hear much better.
What can you do when it catches you out in the open? Well, first of all, you should stay calm and not panic. You should slow down the ship and sail with a reduced sail area (if there is still some wind in the fog), because then you can hear better whether other ships or yachts are nearby. By the way: in sea fog you can see much worse – or not at all – but you can hear much better.
SeaHelp advises:
When foggy, you should definitely turn on the radar, if available. Every 30 seconds, five short beeps (risk of collision) should be emitted when another boat is heard. The driving speed should be reduced to idle. And: the entire crew should be on deck so that no one is locked in the cabin in the event of a possible collision.
Also important: since visibility is lost in fog, it can happen that you quickly lose your bearings. Therefore, you should note the position and time on the nautical chart when the sea fog sets in, the position lights should be switched on, if there are several people on board, one person – or better still two – should keep watch (in all directions).
If you are currently in a fairway, you should leave it quickly. It may be better to move from buoy to buoy on the outside (if possible, note the depth information!).
In summer, fog banks generally dissipate relatively quickly due to the sun or rising winds. This was also the case for us: just hours after the sea fog appeared, it had completely blown away. We set off again in our boat – this time without any further disruptions.
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