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Top tips: dealing with fog

Foggy ship There can be few more disorientating scenarios than being out at sea when the fog comes down; a relaxing, tranquil trip can suddenly turn into a hugely challenging test of your seamanship.

In this situation it does, however, help to fully understand your rights of way in fog while correct interpretation of sound signals can make a huge difference and give you a much clearer picture of what is going on.

This excerpt from Tim Bartlett's International Regulations for Preventing Collisions at Sea will hopefully give you a steer:

The third and final section of the Steering and Sailing rules is made up of just one rule: Rule 19. It’s not a particularly long or complicated rule, but when the visibility closes in, it completely replaces all others and means that all the usual stuff about power giving way to sail, overtaking boats keeping clear, giving way to vessels approaching from your starboard side and such like does not apply.

In particular, it is important to appreciate that there is no such thing as a “stand-on” vessel in fog.

Rule 19    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.

The first three paragraphs of the rule seem pretty self-explanatory:- The purpose of paragraph (a) is to make it clear that this Rule applies to vessels that are not in sight of one another because of the visibility.

It does not apply if the only reason you can’t see the other vessel is because there is a headland or harbour wall between you! Paragraphs (b) and (c) effectively highlight the earlier rules concerned with keeping a lookout, maintaining a safe speed, and assessing the risk of collision.

Deciding on a safe speed in fog

Back in 1933, Lord Justice Scrutton came up with a very simple way of deciding upon a safe speed. He said, in effect, that you should be able to stop in half the distance that you can see. More recent court cases have highlighted the fact that Scrutton’s rule is only a rough guide – it is unnecessarily severe, for instance, on very large vessels, and almost frighteningly lax on very fast, manoeuvrable ones – and it says almost nothing about sailing vessels or small power craft.

Deciding on a safe and appropriate speed in a powerboat is even more difficult, and very much depends on the characteristics of the boat itself, as well as on the conditions. Following Scrutton’s “half the limit of visibility” rule could allow a sportsboat to do forty knots in 50 metres visibility – something which is clearly ridiculous.

On the other hand, the strongest asset of most motor boats is their manoeuvrability: there is no point in sacrificing that – and prolonging the agony – by going too slowly.In most “normal” fog and “typical” boats, the answer is likely to lie somewhere towards the lower end of your planing speed range.

Paragraph ‘d’ of Rule 19 is concerned entirely with the use of radar. For a full explanation of this, you will need to pick up a copy of Tim's book

Sound signals in restricted visibility:

   In or near an area of restricted visibility, whether by day or night, the signals prescribed in this Rule shall be used as follows:  
a)  A power-driven vessel making way through the water shall sound at intervals of not more than 2 minutes one prolonged blast.
b) A power-driven vessel underway but stopped and making no way through the water shall sound at intervals of not more than 2 minutes two prolonged blasts in succession with an interval of about 2 seconds between them.
 c) A vessel not under command, a vessel restricted in her ability to manoeuvre, a vessel constrained by her draught, a sailing vessel, a vessel engaged in fishing and a vessel engaged in towing or pushing another vessel shall, instead of the signals prescribed in paragraphs (a) or (b) of this Rule, sound at intervals of not more than 2 minutes three blasts in succession, namely one prolonged followed by two short blasts.
 d) A vessel engaged in fishing, when at anchor, and a vessel restricted in her ability to manoeuvre when carrying out her work at anchor, shall instead of the signals prescribed in paragraph (g) of this Rule sound the signal prescribed in paragraph (c) of this Rule.
 e) A vessel towed or if more than one vessel is towed the last vessel of the tow, if manned, shall at intervals of not more than 2 minutes sound four blasts in succession, namely one prolonged followed by three short blasts. When practicable, this signal shall be made immediately after the signal made by the towing vessel.
 f) When a pushing vessel and a vessel being pushed ahead are rigidly connected in a composite unit they shall be regarded as a power-driven vessel and shall give the signals prescribed in paragraphs (a) or (b) of this Rule.

In terms of definitions of sound, the word “whistle” means any sound signalling appliance capable of producing the prescribed blasts, the term “short blast” means a blast of about one second’s duration. 

The term “prolonged blast” means a blast of from four to six seconds’ duration.

For vessels under way (including those that are “under way but not making way” – i.e. drifting) the basic rules are simple:

Type of vessel   Sound signal required 
Under power One five second blast on the foghorn every two minutes.
Power driven vessel (stopped) Two five second blasts every two minutes.
Everyone else except a vessel being towed (including sailing vessels, fishing vessels, tugs with tows, and vessels constrained by their draught) One five second blast followed by two one second blasts (Letter D in Morse code: think of it as an abbreviation for all the lame Ducks!)
A vessel being towed (or the last vessel in a string) One five second blast followed by three one second blasts (Letter B in Morse code)
Vessels at anchor: What to listen for

If you're at anchor in fog, similar rules apply. Any vessel at anchor must, at intervals of not more than one minute, ring a bell rapidly for about five seconds.

In a vessel of 100 metres in length or more, this bell should be sounded in the forepart of the vessel and immediately after the ringing of the bell, a gong should be sounded in the after part of the ship.

In addition to this, a vessel at anchor may sound three blasts in succession. These should be one short, one long and one short again in succession.

Aground in fog

A vessel aground should give the bell signal as it applies to a vessel at anchor, but in addition, should also give three separate strokes on the bell immediately before or after the rapid ringing of the bell.

Vessels under 20m

Until recently, all vessels over 12 metres in length were required to carry a bell. In reality, and regardless of the rules, relatively few small craft ever did so, so in 2003 the lower limit was extended to 20 metres.

This means that all vessels under 20 metres long are exempt from bell-ringing in fog, but they must make “some other efficient sound signal” instead.

If you want a full rundown of the COLREGS, pick up a copy of Tim Bartletts book from the RYA Webshop. Buy a copy before October 26 and you will receive a 20% discount. 

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