COLREG sound signals: what the signals communicate
COLREG sound signals are prescribed audible signals used in defined situations. Broadly, a signal tells you one of three things:
- what a vessel is doing;
- what it intends to do;
- what situation or status it is in.
The meaning depends on the pattern, the vessel's situation and the rule that applies. So learn signals in context, not as isolated numbers of blasts.
Start with the context
Before you count blasts, ask: can the vessels see each other?
In sight of one another
Manoeuvring and warning signals, mainly Rule 34. Rule 34(e) separately covers the signal used when nearing a bend or obscured area of a channel or fairway.
Restricted visibility
Fog signals, Rule 35, given in or near an area of restricted visibility, by day or night.
What counts as a short or prolonged blast?
Short blast · Rule 32(b)
Prolonged blast · Rule 32(c)
Whistle means any sound-signalling appliance capable of producing the prescribed blasts and complying with Annex III (Rule 32(a)).
Manoeuvring and warning signals
Most of the manoeuvring and warning signals in Rule 34 concern vessels in sight of one another. Rule 34(e) separately prescribes the signal used when nearing a bend or an area of a channel or fairway where another vessel may be obscured. The Rule 34(a) course and astern signals are given by a power-driven vessel underway when manoeuvring as authorised or required by the Rules.
Course, astern and doubt signals
| Signal | Meaning | Rule |
|---|---|---|
| One short blast | One short = altering to starboard. I am altering my course to starboard. | COLREG Rule 34(a) |
| Two short blasts | Two short = altering to port. I am altering my course to port. | COLREG Rule 34(a) |
| Three short blasts | Think: the engines are being used astern. It does not necessarily mean the vessel is already moving backwards. I am operating astern propulsion. | COLREG Rule 34(a) |
| At least five short and rapid blasts | Remember: the doubt signal. “I don't understand what you're doing”. Doubt whether the other vessel is taking sufficient action to avoid collision, or failure to understand her intentions. | COLREG Rule 34(d) |
Overtaking in a narrow channel or fairway
Pattern cue
| Signal | Meaning | Rule |
|---|---|---|
| Two prolonged, one short | In a narrow channel or fairway: I intend to overtake you on your starboard side. | COLREG Rule 34(c)(i) |
| Two prolonged, two short | In a narrow channel or fairway: I intend to overtake you on your port side. | COLREG Rule 34(c)(i) |
| Prolonged, short, prolonged, short | Vessel about to be overtaken: agreement to the overtaking. | COLREG Rule 34(c)(ii) |
Bends and obstructions
| Signal | Meaning | Rule |
|---|---|---|
| One prolonged blast | Think: “Anyone round the corner?” Nearing a bend or area of a channel or fairway where other vessels may be obscured by an intervening obstruction. Answered by one prolonged blast. | COLREG Rule 34(e) |
- Rule 34(a) signals may be supplemented by light signals: one, two or three flashes of an all-round white light, each about one second (Rule 34(b)).
- The doubt signal may be supplemented by at least five short and rapid flashes (Rule 34(d)).
- Where whistles are fitted more than 100 m apart, only one is used for manoeuvring and warning signals (Rule 34(f)).
Restricted-visibility signals
Rule 35 sets the signals used in or near an area of restricted visibility, by day or night. The signal depends on the vessel's status or activity. Rule 19 sets how vessels not in sight of one another must be conducted; it does not itself define these sound patterns.
See the pattern first
Power-driven vessel
Prolonged blasts
One prolonged = making way. Two prolonged = stopped, no way on.
Special-status vessel
One prolonged + two short
Covers vessels whose status or work limits how they can manoeuvre, and sailing vessels.
Towed vessel
One prolonged + three short
The extra short blast marks the vessel being towed.
At anchor or aground
Bell (and gong) patterns
Rapid ringing = at anchor. Three distinct strokes before and after = aground.
The full detail
| Signal | Meaning | Rule |
|---|---|---|
| One prolonged, at intervals of not more than 2 minutes | Power-driven vessel making way through the water. | COLREG Rule 35(a) |
| Two prolonged in succession (about 2 seconds apart), at intervals of not more than 2 minutes | Power-driven vessel underway but stopped and making no way through the water. | COLREG Rule 35(b) |
| One prolonged followed by two short, at intervals of not more than 2 minutes | Not under command; restricted in her ability to manoeuvre; constrained by her draught; sailing; engaged in fishing; towing or pushing. A vessel engaged in fishing when at anchor, and a vessel restricted in her ability to manoeuvre when carrying out her work at anchor, use this signal instead of the normal anchor signal. (Rule 35(d)) | COLREG Rule 35(c), (d) |
| One prolonged followed by three short, at intervals of not more than 2 minutes | Vessel towed (or the last vessel of the tow), if manned. When practicable, sounded immediately after the towing vessel's signal. | COLREG Rule 35(e) |
| Bell rung rapidly for about 5 seconds, at intervals of not more than 1 minute | Vessel at anchor. 100 m or more: bell in the fore part, then gong rapidly for about 5 seconds in the after part. May additionally sound one short, one prolonged, one short to warn an approaching vessel. | COLREG Rule 35(g) |
| Three separate and distinct strokes on the bell immediately before and after the rapid ringing | Vessel aground, with the anchor bell (and gong if required). May additionally sound an appropriate whistle signal. | COLREG Rule 35(h) |
| Four short blasts (in addition to the normal signal) | Optional identity signal of a pilot vessel on pilotage duty. | COLREG Rule 35(k) |
Exceptions to remember
- A pushing vessel and pushed vessel rigidly connected as a composite unit are treated as a power-driven vessel (Rule 35(f)).
- 12 m or more but under 20 m: not obliged to give the bell signals in Rule 35(g) and (h); if not, another efficient sound signal at intervals of not more than 2 minutes (Rule 35(i)).
- Under 12 m: not obliged to give the Rule 35 signals; if not, another efficient sound signal at intervals of not more than 2 minutes (Rule 35(j)).
Sound-signalling equipment
What a vessel must carry depends on her length (Rule 33).
- 12 m or more
- A whistle.
- 20 m or more
- A whistle and a bell.
- 100 m or more
- Also a gong, whose tone and sound cannot be confused with the bell.
- Under 12 m
- Not obliged to carry these, but if not, must have some other means of making an efficient sound signal.
The bell or gong may be replaced by other equipment with the same sound characteristics, provided manual sounding is always possible. Technical details are in Annex III.
Other signals sit nearby: Rule 36 (signals to attract attention) and Rule 37 with Annex IV (distress signals). They are outside the scope of this page.
How to learn the signals
- Context first: in sight of one another (Rule 34) or restricted visibility (Rule 35)?
- Pattern second: short, prolonged, or bell and gong, and in what order?
- Meaning third: recall what that pattern communicates in that context.
Recall from memory rather than re-reading, and return to weak signals over spaced intervals. StandOn is built around active recall. Sound Signals is launching shortly in StandOn; it is not live yet.
Related: navigation lights and COLREG Rule 19: restricted visibility.
A revision reference, not a substitute for training
This page summarises the main signal categories. It is not a complete statement of the rules and does not replace recognised training, official material, professional instruction or practical experience.
StandOn is an independent sailing revision platform and is not affiliated with or endorsed by the Royal Yachting Association.