In busy and restricted waterways, large vessels use sound signals to notify nearby boats of their intentions. 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. 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 These are a gong, a bell and a whistle that need to comply with the technical details for sound signal appliances set out in Annex III of the COLREGs:
- • 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
- A short blast = a blast of about one second's duration.
- A prolonged blast = a blast of from four to six seconds' duration.
- 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°)".
- 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
port side”
- One prolonged, one short, one prolonged, and one short blast, in that order.
- One prolonged blast = "I am making vessels aware of my presence"
- • 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.
Do not assume a direction for the maritime horn signal as it can be distorted by fog so stop and double-check the direction then proceed with caution.
See also maritime flags and their meaning
Sound signal rules to be followed by vessels in restricted visibility 1
Sound signal rules to be followed by vessels in restricted visibility 2
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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