Manoeuvring and Warning Signals

Large vessels sound various signals to indicate their intentions to other vessels in the vicinity.

Some of the more common signals are given below:

Sound Signals

Short Blast - about 1 second duration
Prolonged Blast - 4 to 6 seconds duration
‘I am altering my course to starboard’
‘I am altering my course to port’
‘I am operating astern propulsion’ (Engines in reverse - vessel slowing down, stopping or intends going astern)
Signal by vessel in doubt as to the intentions of the other vessel
Vessel nearing a blind bend in a channel or river

Flags

'Diver below' Flag

The signal flag for the letter ‘A’, illustrated, 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 offense to exceed 4 knots within 50 metres of a vessel or buoy displaying this flag.