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.
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
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.