Yachting World

Navigation briefing Advice for sailing safely in fog



Just a few minutes of sailing in dense fog takes most sailors well out of their comfort zones: it’s disorienta­ting and, quite frankly, scary for many. Here are some tips on how to prepare for, and deal with, a ‘pea soup’:

At sea, fog can be summed up as condensed water vapour or just thick cloud on the surface. Sea fog, or advection fog, forms when relatively warm moist air moves over colder water and cools to its dew point temperatur­e, causing the air to saturate.

Unlike land fog, or radiation fog, sea fog can occur at any time of day and still exist with quite strong winds. It only really clears with a change of air mass – usually with the passage of a cold front. Without the passage of a cold front, it can last for days. While radiation fog usually occurs on cold, still winter days, sea fog or advection fog is more prevalent in early summer. June can be a particular­ly bad month in the English Channel, when the water is still relatively cold, with warm moist air coming up from the south-west.

Looking out for the forecasts of fog is important, but one simple trick is to go online and use satellite imagery. Sat24.com is a great website to see the last three hours of visual imagery, where fog often shows as a dull, grey and featureles­s cloud. Next, do a quick comparison with the infra-red satellite imagery and the fog seems to miraculous­ly disappear, whereas other clouds tops still show up. This is due to the fog being approximat­ely the same temperatur­e as the sea, hence giving a neat confirmati­on of the existence of fog on the visual picture. You can then return to the visual imagery and more accurately plot the extent of the fog and potentiall­y take avoiding action.


If you do sail into unexpected fog, first consider whether you need to keep heading further into it? Would it make more sense to do a quick 180° turn and head back out into clearer visibility?

Once in fog, we need to work through a checklist of actions. Note your compass heading. Do we need a more experience­d helmsman? It’s easy to quickly find you’re 30° or 40° off course and not notice. Steering is more exacting and even exhausting. Could it be less stressful to use the autopilot, to allow you to focus on lookout? Just be ready to immediatel­y switch to manual if you need to at a moment’s notice.

Slowing down is certainly good seamanship and the requiremen­t to proceed at a safe speed appropriat­e to the conditions is detailed clearly in the Internatio­nal Regulation­s for the Prevention of Collision at Sea (IRPCS Rule 6 – Safe Speed).

With an increased risk of collision, it’s good practise to ensure everyone is wearing a lifejacket. Maintainin­g a proper lookout is essential. In ‘pea soup’ fog, stationing a person forwards near the bow can help enormously. If motoring, the bow is a good place to escape the noise to allow the lookout crew member to listen for fog signals, or other hazards. On several occasions when I’ve been sailing in thick fog, the lookout at the bow has provided vital informatio­n to avoid a hazard or navigation mark.

In areas of dense shipping, remember to look up as well as straight ahead, I’m sure I am not the only person to have sighted a large vessel from the helm at the angle of the first spreader!

When ‘in or near areas of restricted visibility’ IRPCS states we shall make the prescribed sound signal, which for sailing vessels is one long blast, followed by two short blasts at intervals

not more than two minutes. We need to have a working knowledge of sound signals of other vessels: many don’t appreciate that the fog signal for yachts is the same as vessels involved with fishing, towing, and even vessels ‘constraine­d by draught’ and ‘not under command’.


To help other ships see us, our best chance is to ensure we are clearly seen by the equipment on the bridge, which is radar and AIS (automated informatio­n system). Radar is a great help, but not all yachts have it, and it does take concerted focus and an understand­ing of how best to use it. Nearly all yachts have radar reflectors. Disappoint­ingly tests have shown radar reflectors are not as effective at enhancing our radar signature as many people think. Active radar transponde­rs show up much better.

AIS has been a real step change to aid collision avoidance in fog, though always remember that not all vessels use it and it is only an aid, albeit a very useful one. AIS can give the speed and course of a vessel as well as the closest point of approach (CPA) and time to the CPA: this is really useful data when navigating in fog. AIS also gives the vessel name, call sign, type and size.

Navigation lights are essential in foggy conditions. In a really thick fog the bow navigation lights can reflect back off the fog, leaving you with an eerie red or green glow.

The amount of radio traffic tends to rise in fog, though beware using VHF radio to communicat­e with the watch keeper of another vessel, which can be fraught with problems. There have been at least three occasions in the Dover Straits where watch keepers have opted to use radio to try to negotiate collision avoidance, which has ended unhappily in a collision! These have often come about through misidentif­ication and language difficulti­es, when both watch keepers should have prioritise­d normal rules of the road and not allowed themselves to be distracted in an important close quarters situation.

One tactic for dealing with fog on small vessels is to head away from busy shipping channels and sail to shallow water and anchor. Once tethered to the seabed remember to sound your fog signal (for vessels over 12m, ringing a bell for five seconds every minute). Many sailors may not be familiar with the additional signal of one short, one long, one short blast that can be made after the bell if you are concerned of a risk of collision while you are an anchor.


Racing in fog creates extra challenges. Fog by night can take you by surprise and it is easy to lose hard fought gains, if the helmsperso­n loses awareness. If you have the choice of tacking into fog or not when racing, I would take the clear option every time: humans concentrat­e better when they can see.

The disorienta­tion and confusion that fog can create can easily generate high levels of stress. Mat Sweetman, captain of the J Class Rainbow, suggests: “It is easy to get freaked out in fog, [but] look at is as if it was just a dark night and it gets a whole load less stressful.”

One clue as to the existence of fog at night is an absence of ambient lights and low altitude stars. If you are on the helm and getting close to fog, it is a good idea to start a scan of your yacht instrument­s. Like a pilot flying into cloud, it is imperative to ‘believe in your instrument­s’. A regular scan is most effective but is both tiring and exacting over a long period of time. On top of normal sailing skills such as utilising the feel of your helm, tell tales (if you can still see them) and heel angle, we now need to bring in regular glances at true wind angle, boat speed, and heading. Working out a pattern for your scan is a good discipline in fog.

Sea fog is renowned over the Grand Banks. On the Transatlan­tic Race in 2005, fog prevailed for over six days with sustained wind speeds of 25-30 knots. Visibility was mostly less than 150 metres. Fog for nearly a week is tough going!

 ??  ?? Sailing in fog can be exhausting and disorienta­ting
Sailing in fog can be exhausting and disorienta­ting
 ??  ?? Do you know how to make the prescribed sound signal in restricted visibility?
Do you know how to make the prescribed sound signal in restricted visibility?
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 ??  ?? These Sat24. com website images reveal that what appears to be cloud in the satellite view
(far left), is in fact fog that disappears in the infrared view (left) as shown here in the
Celtic Sea and North Atlantic
These Sat24. com website images reveal that what appears to be cloud in the satellite view (far left), is in fact fog that disappears in the infrared view (left) as shown here in the Celtic Sea and North Atlantic
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