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35

Sound Signals in Restricted Visibility

Restricted visibility: a power-driven vessel making way gives one prolonged blast; underway but stopped and making no way, two prolonged blasts about two seconds apart. Repeat at intervals no longer than two minutes.

Rule 35 applies in or near an area of restricted visibility, by day or night.

a
A power-driven vessel making way through the water sounds one prolonged blast at intervals of not more than 2 minutes.
b
A power-driven vessel underway but stopped and making no way sounds two prolonged blasts in succession, about 2 seconds apart, at intervals of not more than 2 minutes.
c
NUC, RAM, constrained-by-draught, sailing, fishing and towing/pushing vessels use one prolonged followed by two short blasts instead of (a) or (b), at intervals of not more than 2 minutes.
d
A vessel engaged in fishing at anchor, or a RAM vessel carrying out her work at anchor, uses the (c) signal instead of the ordinary anchor signal.
e
A vessel towed, or the last vessel if several are towed, if manned, sounds one prolonged followed by three short blasts at intervals of not more than 2 minutes. When practicable, sound immediately after the towing vessel's signal.
f
A rigid composite pushing unit is treated as a power-driven vessel and uses (a) or (b).
g
An ordinary anchored vessel rings the bell rapidly for about 5 seconds at intervals of not more than 1 minute. At 100 metres or more the bell is sounded forward, immediately followed by rapid gong sounding for about 5 seconds aft. The vessel may additionally sound one short, one prolonged and one short blast to warn of her position and collision risk.
h
A vessel aground gives the (g) bell and, if required, gong signal, adding three distinct separate bell strokes immediately before and after rapid ringing. She may additionally sound an appropriate whistle signal; the anchor short-prolonged-short pattern is not specifically prescribed for an aground vessel.
i
A vessel from 12 to less than 20 metres need not give the (g)/(h) bell signals; if she does not, she makes another efficient sound signal at intervals of not more than 2 minutes.
j
A vessel below 12 metres need not give the listed signals; if she does not, she makes another efficient sound signal at intervals of not more than 2 minutes.
k
A pilot vessel on pilotage duty may add four short blasts to (a), (b) or (g).
In or near restricted visibility. Rule 35(c) and (d): one prolonged and two short blasts. A manned last vessel of a tow gives one prolonged and three short blasts, if practicable immediately after the towing vessel. Repeat within two minutes. Timing example: short blasts are about 1 s and prolonged blasts 4–6 s; the illustrated 1 s gaps are not prescribed intervals.
In or near restricted visibility. At anchor: rapid bell ringing for about five seconds; from 100 m, rapid gong sounding aft for about five seconds immediately afterwards. Aground: three distinct bell strokes before and after the rapid ringing. Repeat within one minute; smaller-vessel exceptions apply. Fishing vessels engaged in fishing at anchor and restricted-manoeuvrability vessels doing their work at anchor use Rule 35(d) instead.

IMO COLREG 1972Official text

Full wording of the rule, reproduced from the official source below.

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 maneuver, a vessel constrained by her draft, 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 maneuver 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. (g) A vessel at anchor shall at intervals of not more than one minute ring the bell rapidly for about 5 seconds. In a vessel of 100 meters or more in length the bell shall be sounded in the forepart of the vessel and immediately after the ringing of the bell the gong shall be sounded rapidly for about 5 seconds in the after part of the vessel. A vessel at anchor may in addition sound three blasts in succession, namely one short, one prolonged and one short blast, to give warning of her position and of the possibility of collision to an approaching vessel. (h) A vessel aground shall give the bell signal and if required the gong signal prescribed in paragraph (g) of this Rule and shall, in addition, give three separate and distinct strokes on the bell immediately before and after the rapid ringing of the bell. A vessel aground may in addition sound an appropriate whistle signal. (i) A vessel of 12 meters or more but less than 20 meters in length shall not be obliged to give the bell signals prescribed in paragraphs (g) and (h) of this Rule. However, if she does not, she shall make some other efficient sound signal at intervals of not more than 2 minutes. (j) A vessel of less than 12 meters in length shall not be obliged to give the above-mentioned signals but, if she does not, shall make some other efficient sound signal at intervals of not more than 2 minutes. (k) A pilot vessel when engaged on pilotage duty may in addition to the signals prescribed in paragraphs (a), (b) or (g) of this Rule sound an identity signal consisting of four short blasts.
Source:

Signal Workflow

Decide the context first: manoeuvring in sight, restricted visibility, or distress.

The same whistle can mean very different things in a different context.

Check both the pattern and the interval.

For fog signals, the time spacing is part of the rule, not just the blast sequence.

When vessels in sight are approaching and you do not understand the other vessel’s intentions or actions, or doubt its collision-avoiding action, immediately sound at least five short, rapid blasts (Rule 34(d)).

Exam Focus

Three short blasts are astern propulsion, not a fog signal.

Rule 35(a)–(f) signals have a maximum interval of 2 minutes; the anchor and aground signals in (g)–(h) have a maximum interval of 1 minute.

Paragraphs (i)–(j) provide small-vessel alternatives.

Key Takeaways

1

Power-driven making way: 1 prolonged; underway but stopped: 2 prolonged, about 2 seconds apart; intervals ≤ 2 minutes

2

The special-status signal is 1 prolonged plus 2 short; fishing at anchor and RAM working at anchor use it too

3

A manned tow, or the last manned vessel if several are towed, gives 1 prolonged plus 3 short at intervals ≤ 2 minutes

4

Ordinary anchor bell signals recur at intervals ≤ 1 minute, with the specified small-vessel alternatives

5

Aground adds three separate bell strokes before and after rapid ringing; do not substitute an ordinary anchor signal

Common Mistakes

Treating a vessel stopped while underway as anchored

Giving the ordinary anchor bell signal for fishing at anchor or a RAM vessel working at anchor

Teaching the optional anchor short-prolonged-short whistle as a specifically prescribed aground signal

Forgetting the small-vessel alternatives and the maximum intervals

Test Your Knowledge

Practise this topic and review the explanation for each answer.

More rules in this Part

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Frequently asked questions about COLREG Rule 35

In restricted visibility, what does a power-driven vessel making way sound?

One prolonged blast at intervals of not more than 2 minutes (Rule 35(a)). If she is underway but stopped and not making way she sounds two prolonged blasts in succession at the same interval.

What is the sound signal for a vessel aground?

The anchor bell signal, plus three distinct separate bell strokes immediately before and after the rapid ringing, and the gong if required (Rule 35(h)). She may add an appropriate whistle signal; the short-prolonged-short pattern is specifically described for an anchored vessel, not prescribed for an aground vessel. Rules 35(i)–(j) provide small-vessel alternatives.

Which vessels sound one prolonged followed by two short blasts in fog?

NUC, RAM, constrained-by-draught, sailing, fishing and towing/pushing vessels use this signal instead of Rule 35(a) or (b), at intervals of not more than 2 minutes (Rule 35(c)). Fishing at anchor and RAM vessels carrying out their work at anchor also use it instead of the ordinary anchor signal (Rule 35(d)). A rigid composite pushing unit uses the power-driven-vessel signal (Rule 35(f)).

What sound signal does a vessel at anchor give in restricted visibility?

Normally, ring the bell rapidly for about 5 seconds at intervals of no more than one minute (Rule 35(g)). At 100 m or more, sound the bell forward, immediately followed by rapid gong sounding for about 5 seconds aft; an optional short-prolonged-short whistle warns of position and collision risk. Fishing or RAM working at anchor use 35(d); small-vessel alternatives are in 35(i)–(j).