Complete reference index
Read each signal’s meaning, context and limitations. Use the interactive cards above for visual or listening practice.
Altering course to starboard
“I am altering my course to starboard.”
Short. A power-driven vessel underway manoeuvres with vessels in sight of one another. One short blast, about 1 second. The turn is relative to the signalling vessel’s bow. This is not an instruction to your helm or an overtaking agreement.
Source: 34(a)
Altering course to port
“I am altering my course to port.”
Short · short. A power-driven vessel underway manoeuvres with vessels in sight of one another. Two short blasts, about 1 second each. Do not confuse two short blasts with two prolonged blasts: the latter report stopped/no way in restricted visibility.
Source: 34(a)
Operating astern propulsion
“I am operating astern propulsion.”
Short · short · short. A power-driven vessel underway operates astern propulsion with vessels in sight of one another. Three short blasts, about 1 second each. The vessel may still be moving forward while braking. The signal does not prove sternway or give permission to pass behind it.
Source: 34(a)
Overtake on your starboard side
“I intend to overtake you on your starboard side.”
Prolonged · prolonged · short. Vessels are in sight in a narrow channel or fairway, where overtaking requires the other vessel to take action to permit safe passing. Two prolonged blasts followed by one short. The side belongs to the vessel being overtaken. This is a proposal, not automatic permission to pass.
Source: 34(c)(i) and 9(e)(i)
Overtake on your port side
“I intend to overtake you on your port side.”
Prolonged · prolonged · short · short. Vessels are in sight in a narrow channel or fairway, where overtaking requires the other vessel to take action to permit safe passing. Two prolonged blasts followed by two short. Hear the complete sequence. Its final two short blasts are not a standalone port-turn announcement.
Source: 34(c)(i) and 9(e)(i)
Agreement to an overtake
The vessel being overtaken agrees to the proposed passing arrangement.
Prolonged · short · prolonged · short. The vessel ahead can permit the proposed narrow-channel/fairway overtake safely and agrees to cooperate. One prolonged, one short, one prolonged, one short, in that order. Agreement does not release the overtaking vessel from keeping clear until finally past and clear.
Source: 34(c)(ii), 9(e)(i) and 13
Power-driven, making way
A power-driven vessel is making way through the water.
Prolonged. In or near restricted visibility, by day or night. One prolonged blast, repeated at intervals of no more than 2 minutes. Making way through the water is not the same as making progress over the ground. The sound gives no exact heading or range.
Source: 35(a)
Power-driven, stopped / no way
A power-driven vessel is underway but stopped and making no way through the water.
Prolonged · prolonged. In or near restricted visibility, by day or night. Two prolonged blasts with about 2 seconds between them; repeat at intervals of no more than 2 minutes. Underway is not the same as moving. This vessel is not anchored, made fast or aground, and may drift with the current.
Source: 35(b)
Sailing, fishing, towing & other statuses
A vessel is sailing, engaged in fishing, towing/pushing, not under command, restricted in ability to manoeuvre, or constrained by draught.
Prolonged · short · short. In or near restricted visibility. Also used by a fishing vessel at anchor and a vessel restricted in ability to manoeuvre while carrying out its work at anchor. One prolonged followed by two short blasts; repeat at intervals of no more than 2 minutes. The sound alone cannot distinguish these categories. A rigidly connected pushing composite unit instead uses the ordinary power-driven making-way/no-way signal.
Source: 35(c), (d) and (f)
Manned vessel being towed
A manned vessel being towed—or the last vessel of a multiple tow, if manned—is sounding its signal.
Prolonged · short · short · short. In or near restricted visibility. One prolonged followed by three short; repeat at intervals of no more than 2 minutes. When practicable, sound immediately after the towing vessel’s signal. Do not confuse the three-short ending with the towing vessel’s two-short ending. It does not establish the tow’s length or a safe gap.
Source: 35(e)
Pilot vessel identification
A pilot vessel identifies itself while engaged on pilotage duty.
Short · short · short · short. A pilot vessel may add this identity signal to its normal making-way, stopped/no-way or anchor signal in restricted visibility. Four short blasts as an additional identity signal. It supplements the applicable status signal; it does not replace it or confer priority over other traffic.
Source: 35(k)
At anchor: rapid bell
An ordinary vessel is at anchor.
Rapid bell ringing. In or near restricted visibility; this is the bell pattern for a vessel under 100 m, subject to the small-vessel exemptions below. Ring the bell rapidly for about 5 seconds, at intervals of no more than 1 minute. Fishing vessels at anchor and vessels restricted in ability to manoeuvre while working at anchor use the one-prolonged/two-short whistle instead.
Source: 35(g), (d), (i) and (j)
At anchor: bell then gong
An anchored vessel of 100 m or more gives its fore-and-aft sound signal.
Rapid bell → rapid gong. An ordinary anchored vessel of 100 m or more is in or near restricted visibility. Rapid bell for about 5 seconds forward, immediately followed by rapid gong for about 5 seconds aft; repeat at intervals of no more than 1 minute. The gong is an addition to the bell, not a second vessel or an overtaking reply. Sound alone still does not provide exact dimensions or a safe passing distance.
Source: 35(g)
Aground: distinct bell strokes
The vessel is aground.
3 separate bell strokes → rapid bell → 3 separate bell strokes. In or near restricted visibility, subject to the small-vessel exemptions below. Three separate, distinct strokes immediately before and after about 5 seconds of rapid bell ringing; repeat at intervals of no more than 1 minute. The separate strokes distinguish this from ordinary anchoring. An appropriate whistle warning may also be given.
Source: 35(h), (g), (i) and (j)
Aground: bell strokes and gong
An aground vessel of 100 m or more gives both the aground bell pattern and the required gong.
3 strokes → rapid bell → 3 strokes → rapid gong. A vessel of 100 m or more is aground in or near restricted visibility. Use the aground bell pattern, then rapid gong for about 5 seconds aft; repeat at intervals of no more than 1 minute. Listen for the separate bell strokes as well as the gong. An anchored large vessel also uses a gong but does not add the aground strokes.
Source: 35(h) and (g)
Anchored vessel collision warning
An anchored vessel warns an approaching vessel of its position and the possibility of collision.
Short · prolonged · short. May be given in addition to the ordinary anchor signal in restricted visibility. One short, one prolonged, one short, in succession. This is a supplementary warning, not the normal anchor bell or an overtaking-agreement sequence.
Source: 35(g)
Doubt or danger warning
“I do not understand your intentions/actions, or doubt that you are taking sufficient action to avoid collision.”
At least 5 short, rapid blasts. Approaching vessels are in sight and one vessel has this doubt. Immediately give at least five short and rapid blasts. This example plays five. It does not command a particular helm direction and is not, by itself, a distress declaration.
Source: 34(d)
Approaching a blind bend
A vessel warns of its approach near an obscured bend or reach.
Prolonged. Nearing a bend or an area of a channel or fairway where an obstruction may hide other vessels—even in clear weather. One prolonged blast. An approaching vessel within hearing around the bend or obstruction answers with one prolonged blast. The same sound means power-driven making way in fog. The setting changes the meaning; it is not permission to enter the hidden reach.
Source: 34(e)
Continuous distress sounding
Distress and need of assistance.
Continuous sounding. A vessel is in distress and requires assistance; continuous sounding with any fog-signalling apparatus is an Annex IV distress signal. Continuous rather than a short/prolonged status sequence. Playback is an 8-second illustration, not a prescribed duration. Use distress signals only for actual distress. Do not confuse this with a five-short-blast doubt warning.
Source: 37 and Annex IV 1(b), 2
SOS in Morse code
Distress and need of assistance.
··· ——— ··· (SOS). A vessel in distress may signal the SOS group by any signalling method, including sound. Three dots, three dashes, three dots. A Morse dash is three dot units; this is not the COLREG short/prolonged-blast timing. Reserved for distress, not an attention or manoeuvring signal. Use appropriate radio distress procedures as well when available.
Source: 37 and Annex IV 1(d), 2