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Transport, travel and motoring

Manoeuvring and warning signs

Large vessels sound a series of specific signals to indicate their intentions to other vessels in the vicinity. Some of the more common signals are listed below.

Short Blast - about one second duration short blast
Prolonged Blast - four to six seconds duration long blast
I am altering my course to starboard. short blast
One short blast on a horn or similar device.
I am altering my course to port.
Two short blasts on a horn or similar device.
I am operating astern propulsion (Engines in reverse - vessel slowing down, stopping or intends going astern).
Three short blasts on a horn or similar device.
Signal by vessel in doubt as to the intentions of the other vessel.
Five short blasts on a horn or similar device.
Vessel nearing a blind bend in a channel or river. long blast
One long blast on a horn or similar device.


Diver below flag

The signal flag for the letter A shown below is used internationally to indicate: I have a diver below - keep well clear at slow speed.

The flag is coloured white and blue and may be displayed either from a vessel or floating buoy. It is an offence in South Australia to exceed four knots within 50 metres of a vessel or buoy displaying this flag.

diver below flag


More information

On this site
Distress signals
Navigation lights
Giving way
Buoys, beacons and marks


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