Emergency signals : Where a navigational emergency is unavoidable, appropriate warnings are given to officers and crew and other vessels and persons who may be affected.
Vessels use a dedicated signal to notify their passengers and crew of emergency. This may be practiced in drills and is commonly:
Additional signals may be used:
Fire on board- Continuous ringing of the fire bell.
Abandon Ship- 1 short and 1 prolonged blast repeated (3 times)
Unsure of your intentions- 5 short blasts
Where radio is not available the International Signals Code Book (Interco) provide for signalling by groups of letters in Morse code by lights or sound, or by code flags.