Skip to content
RulesAtSea

Listen, identify and respond

Boat sound signals: manoeuvring, warning and fog signals

Learn International COLREG horn blasts, overtaking replies and fog signals by listening to realistic RulesAtSea practice exercises.

Practise: A manoeuvre is announcedRead the guide

Updated Free simulator · No account needed

A manoeuvre is announced: an original RulesAtSea simulator scene.
From the simulatorListen and interpret

The essentials

Start with the situation

Sound signals have to be interpreted in their setting. A whistle blast may announce an alteration, warn around a bend or communicate a vessel’s condition in fog. Count the sounds, distinguish their duration and ask which situation the relevant rule describes.

The simulator plays authored signals and asks you to identify their meaning or choose a reply. Listen to the full sequence before answering. The difference between a familiar rhythm and a correct response is especially useful practice for navigation and oral revision.

This guide covers: International COLREG signals. US Inland manoeuvring and overtaking exchanges differ and are outside these exercises.

Short and prolonged blasts

Rule 32 defines a short blast as about one second and a prolonged blast as four to six seconds. These terms matter: “two blasts” is incomplete unless you know their duration. Bell and gong signals are separate patterns used for particular states in restricted visibility.

Use the simulator audio rather than reading the title and guessing. Describe the sequence aloud, then say whether the vessels are in sight, whether visibility is restricted and whether the situation involves a bend or narrow-channel overtaking. These facts prevent you from applying a remembered sound in the wrong context.

Manoeuvring and doubt when vessels are in sight

Under International Rule 34(a), a power-driven vessel underway manoeuvring with another vessel in sight uses one short blast for an alteration to starboard, two for an alteration to port, and three for operating astern propulsion. Astern propulsion does not necessarily mean the vessel is already moving backwards through the water.

At least five short, rapid blasts express doubt when approaching vessels in sight do not understand intentions or actions, or doubt whether enough action is being taken to avoid collision. It is a warning about the developing encounter. Continue your lookout and assessment rather than treating the sound as a substitute for action.

Put this into practice

Narrow-channel overtaking includes an exchange

When a narrow-channel overtaking passage can take place only if the vessel ahead acts to permit safe passing, International Rules 9(e) and 34(c) describe a proposal and agreement. Two prolonged followed by one short proposes passing on her starboard side; two prolonged followed by two short proposes her port side.

Agreement is one prolonged, one short, one prolonged and one short, in that order. The vessel ahead must also take the steps needed to permit safe passing. The overtaker retains the responsibility to keep clear under Rule 13. In the unsafe-passage exercise, listen to the proposal and inspect the available water before deciding whether agreement is appropriate.

Put this into practice

Fog signals tell you a condition, not an exact track

In or near restricted visibility, Rule 35 generally gives a power-driven vessel making way one prolonged blast, repeated at intervals no longer than two minutes. A power-driven vessel underway but stopped and making no way gives two prolonged blasts. These describe motion through the water, not simply speed over the ground.

One prolonged followed by two short is shared by several categories, including sailing, qualifying fishing, towing, not under command and restricted manoeuvrability. It cannot identify one of them uniquely. A manned tow, or the last vessel of a tow if manned, uses one prolonged followed by three short. The full rule includes anchored, aground, pilot and small-vessel provisions.

Put this into practice

A blind bend requires a warning and reply

A vessel approaching an obscured bend or area of a channel or fairway sounds one prolonged blast. An approaching vessel within hearing around the bend or obstruction replies with one prolonged blast. Particular alertness and caution are still required. The same duration in fog can mean something else, which is why context belongs in every answer.

For revision, alternate recognition with response exercises. Explain what the sound allows you to conclude and what it leaves unknown. Before a voyage, check the signalling equipment and applicable rules for your own vessel; the teaching scenes show selected examples rather than every equipment requirement or local procedure.

Put this into practice

Questions from the watch

Common questions

Do three short blasts mean that a boat is going backwards?

In the International manoeuvring signal they mean operating astern propulsion. A vessel may still have forward motion while her propulsion is working astern.

Does one prolonged and two short mean a sailing boat?

A sailing vessel is one possible source. Several other categories share the fog signal, so use other observations without assuming a unique identification.

Sources and further reading

Use these references for the full rules, official guidance and course requirements.

  1. US Coast Guard · International COLREGs

    International Rules 9(e), 32, 34 and 35 cover the sounds and exchanges described here. Follow the International text rather than Inland alternatives.

  2. IMO · Convention on the International Regulations for Preventing Collisions at Sea

Updated

Keep learning

All guides