Not many of us would happily set sail in fog but sometimes it is unavoidable, and knowing how to avoid collisions is crucial, says Andy du Port

How to avoid collisions in fog

Sir John Harvey-Jones, erstwhile chairman of ICI, once said, ‘Planning is an unnatural process; the nicest thing about not planning is that failure comes as a complete surprise rather than being preceded by a period of worry and doubt.’

When you see the fog rolling towards you, it is too late to start planning.

Not many of us would happily set sail in fog but sometimes it is unavoidable, either out at sea or as we make our way into harbour.

Sailing in poor visibility – fog, heavy rain, even snow – can be disorientating and worrying but some prior thought and basic preparation will help to keep the heart rate near normal and, vitally, you and your crew safe.

With any luck you won’t be in fog for long but while you are, you have two objectives: safe navigation and collision avoidance.

In open waters your attention will be on collision avoidance, but closer inshore you will probably be busy dodging other vessels while at the same time keeping yourself in safe water.

Two people sailng. When planning your cruise think about how you would deal with fog

When planning your cruise think about how you would deal with fog

There is lots of good advice elsewhere about ‘blind’ navigation, so here I will focus on collision avoidance.

This is covered in the Colregs by Rule 19: Conduct of vessels in restricted visibility, which is possibly the most misunderstood rule in the book.

The actions you should take to avoid collision are quite different from those when vessels are in sight of one another: there is no ‘give way’ vessel and no ‘stand on’ vessel.

Even the usual manoeuvring sound signals don’t apply.

In poor visibility your best bet is to avoid all close quarters situations.

In other words, keep the opposition at arm’s length rather than nipping under the stern as you might in clear weather.

One-mile clearance of a big ship in fog is quite close enough for me.

‘A collision at sea can ruin your entire day’ may not have been said by Thucydides, to whom it is often attributed, but whoever actually said it made an indisputable point.

Preparation for fog

You want to be ‘seen’ in fog so invest in a good radar reflector and permanently fit it as high as possible.

A radar reflector is one of the few SOLAS V requirements for small craft.

Which one you choose will depend on the depth of your pocket, but be wary of going for cheap and cheerful.

Knowing how to interpret a radar picture properly will pay dividends in fog

Knowing how to interpret a radar picture properly will pay dividends in fog

You can spend hundreds of pounds on a radar target enhancer, or you can buy a passive reflector for much less.

If you go for a traditional tetrahedral reflector just make sure you hoist it in the ‘rain-catching’ mode, not point up.

AIS does not yet feature in the Colregs but it can be an invaluable anti-collision aid.

Radar on a yacht mast

If you have radar fitted, take time to get to know how to use it and interpret what is shows

Even receive-only sets will make life much safer.

However, AIS is not a radar (whatever some manufacturers may claim), and many small craft are not fitted with it; even larger vessels may not have it set up correctly or even turned on.

Like AIS, the use of VHF is not mentioned in the Colregs, and you should be very wary, even in clear weather, of causing unnecessary confusion by calling another ship to negotiate actions to avoid a close-quarters situation, unless you have both positively identified each other.

This applies in poor visibility when a third vessel may be tempted to take avoiding action based on an overheard conversation.


AIS is no replacement for proper radar equipment

That said, particularly in busy areas, a listening watch will help you to build up a general picture of shipping movements around you.

So, have your set tuned to the relevant channel(s): Ch 16 when offshore as well as the local harbour or VTS channels when appropriate.

If you feel you must check your radio before sailing, try to do so on a working channel and avoid cluttering up Ch 16.

The advantage of radar over AIS is that, when used properly, it will show all other vessels, and not just those fitted with corresponding equipment.

A tetrahedral radar reflector on a yacht

A tetrahedral radar reflector reflector must be mounted in the right orientation

With either AIS or radar, however, the information you are given still needs interpretation.

You should be able to read it and ascertain another vessel’s closest point of approach (CPA), it’s time to CPA (TCPA), and where it will be in relation to your vessel at that time.

If you have radar, it is a requirement of Rule 19 that you make proper use of it in reduced visibility.

Radar reflector on a yacht

Permanently mounting a passive radar reflector is good sense

Therefore, tune it for best reception and know how to get the most out of it.

Unless you are already an experienced operator, book yourself onto a course then practise in clear visibility.

You won’t regret it when your safety depends on it.

Entering fog

You will probably have some warning before being enveloped in fog.

You may see it looming ahead of you but, if you are not keeping a good all-round lookout, it could roll in from astern and catch you by surprise.

When everything starts to look grey take the following actions as soon as possible.

Some of them will need your careful judgement.

1. Lights

Navigation light on a yacht to help navigate in fog

Turn on your navigation lights.

The aim is to be seen at all costs, and dense fog probably justifies bending the rules and showing as many lights as you can – perhaps including an all-round white anchor light at the masthead.

Better, I suggest, to risk a rebuke for showing incorrect lights than be involved in a potentially disastrous collision.

2. Sails

Make yourself visible. If you are motoring, keep the mainsail hoisted and consider having the headsail at least partially unfurled so long as it doesn’t obscure your view.

To keep your options open for rapid manoeuvring, however, lower spinnakers and cruising chutes, avoid poling out headsails and unrig preventers.

3. Speed

Instruments on the cockpit of a Hallberg Rassy

A yacht is unlikely to be able to exceed a ‘safe speed’, but sailing too slowly just prolongs the misery and makes any alterations of course less obvious on another vessel’s radar.

In these conditions, motoring might make sense.

4. Engine

A skipper with his hand on the engine throttle

Have it running or ready for immediate use.

The noise of the engine will reduce your ability to hear other ships, but you may think that instant manoeuvrability is more important in the circumstances.

If you are sailing well and are confident that the engine will start on demand, I would leave it off (but see the point above).

5. Lifejackets and harnesses

Wear a lifejacket when sailing especially in fog and heavy weather

Put on lifejackets. Not only is this a sensible precaution, it also alerts the crew that conditions may become serious.

In calm weather (quite likely in fog), you don’t want to be tethered to the boat in the event of a collision, so probably best not to hook on.

This has to be weighed against the risk of someone falling over the side, as recovering an MOB in fog or rough seas is going to be much more difficult.

6. Liferaft

Prepare a liftraft in case of a collision in fog

Have it ready to deploy. If it is normally stowed in a locker, get it out and secure its painter to a strongpoint.

If you don’t carry a liferaft, a possible alternative is to inflate the dinghy and tow it astern.

It’s also worth having your EPIRB or PLB, and a flare ready to hand if the worst were indeed to happen.

7. Radar

Radar on a yacht

Use your radar, chartplotter, GPS and AIS to build a picture of what is around you, and know how to track vessels’ courses

The rules require that proper use shall be made of radar, if fitted.

This includes plotting and assessing contacts, so give the job to the most experienced operator. As the skipper, this may be you.

At the chart table, you are well placed to build up a picture of what is around you using radar, AIS, VHF and any reports from your team on deck in order to make the right decisions.

8. Sound signals


A skipper blowing a whistle

There is no way your fog horn is going to be heard inside the bridge of a large ship, but it will alert other yachts to your presence.

Anyhow, the rules say it ‘shall be used’.

On our boat, we use a referees’ whistle for making sound signals.

It is just as audible as a canister fog horn, and it doesn’t run out of gas.

9. Lookout

A good lookout, by both sight and hearing (Rule 5), is essential. Brief your crew to report anything they hear or see.

Warn them that direction can be ambiguous in fog, so ‘I think I can hear a big ship’s engines somewhere to port’ is likely to be more use to you than a guess at a precise bearing – which is quite liable to be wrong.

Collision avoidance

Unless you are in confined waters, your main worry will be collision avoidance.

This is where Rule 19 kicks in, and it is absolutely vital that you understand what it says.

The full text is shown below. Rules 11 to 18 deal with the conduct of vessels in sight of one another, but they do not apply in fog.

It doesn’t make any difference whether you are sailing, motoring, fishing or flying your seaplane, no one has a ‘right of way’ (a term, incidentally, which does not feature anywhere in the Colregs, only ‘stand on vessel’), no one is a ‘give way’ vessel, and the usual manoeuvring and warning sound signals (Rule 34) only apply in good visibility.

It is Rule 35 that tells us what sound signals to make in fog.

Rule 19 does not only apply when you are in fog.

You may be in bright sunshine but the actions to avoid collision with a ship you can’t see because she is in a nearby fog bank, a rain squall, or even a snow shower, are dictated by Rule 19.

What this means

Rule 19 says that unless you have determined that a risk of collision or close-quarters situation does not exist, then you must assume that it does and act accordingly.

It goes on to say that if you hear a fog signal ahead of the beam and have not yet determined if it poses a risk, you shall reduce your speed to a minimum.

This is not really applicable to most sailing yachts but the principle stands, and you should not plough on at full speed unless you are quite sure that there is no risk of getting uncomfortably close to the other ship.

A mere reduction in speed (from 6 knots to 3 knots, say) is rarely practicable as it won’t be readily apparent on another vessel’s radar.

Horshoe buoy on the aft of a yacht

Make MOB buoys, liferafts and flares ready for use, as events can unfold quickly

As we have already seen, the steering rules for vessels in sight of one another no longer apply, but Rule 19 rather confusingly only tells us what we should not do.

If you turn this around, it makes more sense.

Put simply: always turn to starboard to avoid a collision or close-quarters situation unless: a) The other vessel is on your starboard quarter (green 90° to right astern), in which case you should alter course to port, or b) You are overtaking, in which case you may alter course whichever way achieves the aim.

Whatever you do, Rule 19 insists that you do it ‘in ample time’.

As always, any actions you take must be ‘positive and readily apparent to the other vessel’.

In other words, act early and don’t faff around with small alterations of course. A turn of 90° or more may be necessary to make your intentions obvious.

Worth the risk

Andy Du Port head shot

Andy Du Port is a Yachtmaster Offshore, and formerly an RN specialist navigating officer and RYA Cruising Instructor

To end on a sobering note, if you do have an incident while underway in fog, you may have to explain to the authorities your decision to sail.

A written passage plan which shows all the factors you have taken into account, and a note of your preparations, would certainly help.

However, while I said at the start that few of us would willingly set sail in fog, there are times when it is foggy close inshore but known to be clear just a few miles out.

The harbourmaster or local VTS may have reports from ships offshore, or you could ask the coastguard or nearby National Coastwatch Institution (NCI) station, available on VHF Channel 65.

In these situations you may justifiably decide to leave the safety of your berth knowing that the gloom won’t last long. Similarly, a forecast for occasional fog patches may be worth the risk.

Rule 19

Diagram showing fog collision avoidance

Conduct of vessels in restricted visibility:

(a) This Rule applies to vessels not in sight of one another when navigating in or near an area of restricted visibility.

(b) Every vessel shall proceed at a safe speed adapted to the prevailing circumstances and conditions of restricted visibility. A power-driven vessel shall have her engines ready for immediate manoeuvre.

(c) Every vessel shall have due regard to the prevailing circumstances and conditions of restricted visibility when complying with the Rules of Section I of this Part.

(d) A vessel which detects by radar alone the presence of another vessel shall determine if a close-quarters situation is developing and/or risk of collision exists.

If so, she shall take avoiding action in ample time, provided that when such action consists of an alteration of course, so far as possible the following shall be avoided:

(i) an alteration of course to port for a vessel forward of the beam, other than for a vessel being overtaken;

(ii) an alteration of course towards a vessel abeam or abaft the beam.

(e) Except where it has been determined that a risk of collision does not exist, every vessel which hears apparently forward of her beam the fog signal of another vessel, or which cannot avoid a close-quarters situation with another vessel forward of her beam, shall reduce her speed to the minimum at which she can be kept on her course.

She shall, if necessary, take all her way off and in any event navigate with extreme caution until danger of collision is over.