What is the issue?In busy and restricted waterways, large vessels use sound signals to notify nearby boats of their intentions.
Why address this?Sound signals are used to signal intentions on the waterways like an automobile's turn light indicators on the highways. All boaters should know proper sound signals, especially those boaters operating near commercial vessel traffic. If you are unaware of the signal communications it may become problematic and place your vessel and surrounding craft in jeopardy.
How to address this?The following regulations are for vessels operating in the British Isles and covered by the The Merchant Shipping (Distress Signals and Prevention of Collisions) Regulations 1996 November 2003 - see Rules 34/35 extract . These are the same ones agreed to internationally and used on the high seas.
Unfortunately some countries may have different inland water regulations, for example in the United States of America for instance, they reverse the port and starboard signals and have different overtaking signals. These are noted by dashed magenta lines found on many charts and labelled COLREGS DEMARCATION LINES which are the boundaries of restricted-navigation zones. To seaward of these lines, or where the lines do not exist, a skipper must follow the International rules - more formally known as the 1972 International Regulations for Preventing Collisions at Sea (72 COLREGS). Where these lines exist, and inshore of them, a skipper must use the specific Inland Waterway Rules.
Rule 33, equipment for sound signals, specify three devices used for sound signalling.
Photo: Courtesy of Lauzas
- • A vessel of 12 metres or more in length shall be provided with a whistle
- • A vessel of 20 metres or more in length shall, in addition, be provided with a bell
- • A vessel of 100 metres or more in length shall, in addition, be provided with a gong
The rules do not oblige a vessel of less than 12 metres in length to carry a specially prescribed sound-signalling appliance. It states that it must have the means to produce some type of sound.
The prudent mariner should subscribe to the rules and carry an appropriate horn, even if it's only a portable air horn priced under £10.
In a little more detail, marine regulations specify that a vessel of twelve metres or more in length must have sound signalling capabilities. A vessel of less than twelve metres is not obliged to carry sound signalling equipment as long as they are enabled with some other means of signalling.
Sound signals are of two kinds, a short blast or a prolonged blast:
- A short blast = a blast of about one second's duration.
- A prolonged blast = a blast of from four to six seconds' duration.
These are used to define the type of manoeuvre summarised in the image below which would be good to have printed and to hand when in busy waterways.
The following sound signals are used when vessels are in sight of one another and meeting or crossing within half a mile of each other:
- One short blast = "I intend to leave you on my port side"
- Two short blasts = "I intend to leave you on my starboard side"
- Three short blasts = "I am operating astern propulsion"
- Five short and rapid blasts = "Danger signal, I do not understand your intentions"
- Four short blasts, a short interval and one short blast = "I intend to turn about to Starboard (turn vessel through more than 135°)"
- Four short blasts, a short interval and two short blasts = "I intend to turn about to Port (turn vessel through more than 135°)".
It is important to observe that the operating astern signal refers to the shaft and propeller, not to the actual motion of the vessel which can be either forward or astern.
The following sound signals are used when vessels are in sight of one another in a narrow channel or fairway:
- Two prolonged blasts followed by one short blast = “I intend to overtake you on your starboard side”
- Two prolonged blasts followed by two short blasts = “I intend to overtake you on your
If in agreement with these manoeuvres you should acknowledge by the following signal:
- One prolonged, one short, one prolonged, and one short blast, in that order.
Conversely, if the vessel being overtaken is in doubt about the safety of the proposed manoeuvre, or you doubt whether sufficient action is being taken to avoid a collision, you should signal the above five short and rapid blasts of the danger signal to indicate that their intentions are unclear.
Lights have the same sequence with the duration of each flash at about one second. The light should be an all-round white or yellow that is visible for about two miles synchronized with a sound signal.
The other times that a vessel is likely to use a sound signal is when they are nearing a bend or an area of a channel or fairway where other vessels may be obscured from their view. At these times they sound a single prolonged blast. This signal should be answered with a prolonged blast to indicate your presence. When a power-driven vessel is leaving a dock or berth they also sound one prolonged blast.
- One prolonged blast = "I am making vessels aware of my presence"
Sounds on the water are many and varied. Bells, gongs, fog horns, boat whistles all combine to produce a confusing cacophony. The above Rule 33 objective, the different types and variety of devices used by the various classes of vessel, is to enable mariners to detect the scale of the vessel by the sound it makes when heard through the dark of a foggy night.
A vessel underway must give one prolonged foghorn horn blast every two minutes. If motoring, you may have to turn off the engine at regular intervals to listen to hear the echo. You should also be listening for the sound signal of other vessels or navigation aids.
Sound signals are either prolonged, four to six seconds; or short, one second. A bell can be sounded as a single ring or as a rapid ringing for five seconds, and a gong is rung rapidly. The meaning of the signals for boating are as follows:
- • Under sail (and some other vessels): One prolonged foghorn horn blast and two short blasts every two minutes
- • Making way under power: One prolonged blast every two minutes.
- • Under way but stopped: Two long blasts with an interval of about 2 seconds between them at two-minute intervals.
- • Aground - under 100m (328ft): Three bells, rapid ringing, three bells, at one-minute intervals.
- • Aground - over 100m (328ft): Three bells, rapid ringing, three bells, a gong sounded aft, every minute.
- • At anchor - under 100m (328ft): Rapid ringing of bell in the forepart of the boat for 5 seconds, at one-minute intervals.
- • At anchor - over 100m (328ft): Rapid ringing of bell in the forepart of the boat for 5 seconds, at one-minute intervals 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.
- • Pilot boat on duty: Four short blasts (after underway or making way) every two minutes.
Navigational aids, such as buoys and lighthouses, are also fitted with maritime sound signal apparatus so that they can be identified.
See also maritime flags and their meaning .
With thanks to:Michael Harpur, Yacht Obsession.
Sound signal rules to be followed by vessels in restricted visibility 1
Sound signal rules to be followed by vessels in restricted visibility 2
Add your review or comment:
Matt Reid wrote this review on Dec 31st 2013:
The signals outlined above are not quiet correct. One short blast means "I am altering course to starboard" Two short blasts means "I am altering course to port" When overtaking these signals are preceded by two long blasts to indicate the intention to overtake as shown in rule 34. Rule 34 (c) When in sight of one another in a narrow channel or fairway: (i) a vessel intending to overtake another shall in compliance with Rule 9(e)(i) indicate her intention by the following signals on her whistle: • two prolonged blasts followed by one short blast to mean “I intend to overtake you on your starboard side”; • two prolonged blasts followed by two short blasts to mean “I intend to overtake you on your port side”. (ii) the vessel about to be overtaken when acting in accordance with Rule 9(e)(i) shall indicate her agreement by the following signal on her whistle: • one prolonged, one short, one prolonged and one short blast, in that order. (d) When vessels in sight of one another are approaching each other and from any cause either vessel fails to understand the intentions or actions of the other, or is in doubt whether sufficient action is being taken by the other to avoid collision, the vessel in doubt shall immediately indicate such doubt by giving at least five short and rapid blasts on the whistle. Such signal may be supplemented by a light signal of at least five short and rapid flashes.
Michael Harpur wrote this review on Jan 26th 2018:
Thank you Matt. I have now edited this to the letter of the law and also added links back to 'The Merchant Shipping (Distress Signals and Prevention of Collisions) Regulations 1996'. Any further suggestions please do not hesitate.
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