Signal · COLREGs Part D

Sound signals

When ships see each other, the whistle announces a turn before it shows. In fog, the whistle tells others what kind of vessel is out there. A short blast lasts about one second; a prolonged blast four to six.

Legend

short blast, about 1 s prolonged blast, 4 to 6 s (5 s here)

Quick: play the rhythm at 40 % of real time

Tap a pattern to hear it. On iPhone, the ringer switch must be on.

Manoeuvring (Rule 34 a)

	I am altering my course to starboard.
	I am altering my course to port.
	I am operating astern propulsion.

Overtaking in a narrow channel (Rule 34 c)

	I intend to overtake you on your starboard side.
	I intend to overtake you on your port side.
	Agreement by the vessel being overtaken.

Doubt and bends (Rule 34 d, e)

	Doubt or warning: I do not understand your intentions or doubt you are taking enough action (at least five short and rapid blasts).
	Approaching a bend or an area where other vessels may be hidden; answered with one prolonged blast.

Restricted visibility (Rule 35), at intervals of not more than 2 minutes

	Power-driven vessel making way through the water.
	Power-driven vessel under way but stopped and making no way (about 2 s between blasts).
	Vessel not under command, restricted in her ability to manoeuvre, constrained by draught, sailing, fishing, or towing or pushing.
	Manned vessel being towed (sounded immediately after the towing vessel’s signal if possible).

Why the patterns are so short

A whistle carries meaning only if it cannot be mistaken. One, two, three short blasts map to right, left and astern; anything longer than five short blasts means doubt. The fog signals add a tempo: the same pattern every two minutes, so the listener can also judge whether the other vessel is approaching.

Source: Convention on the International Regulations for Preventing Collisions at Sea, 1972, Part D (Rules 32 to 37). At anchor and aground ships ring a bell (and a gong if 100 m or more long); those signals are not played here.