Part D — Sound and light signals
COLREGs Rule 34: Manoeuvring and warning signals
Rule 34 says a power-driven vessel in sight of another signals its manoeuvres: one short blast for 'altering to starboard', two for 'altering to port' and three for 'operating astern propulsion'. Five or more short, rapid blasts mean 'I doubt your intentions'.
What Rule 34 says
- A power-driven vessel manoeuvring as authorised or required, in sight of another: one short blast, altering course to starboard; two short blasts, altering course to port; three short blasts, operating astern propulsion.
- These may be supplemented by matching white light flashes of about one second, at least 10 seconds apart between signals.
- In a narrow channel, overtaking: two prolonged and one short (on your starboard side), two prolonged and two short (on your port side). Agreement: prolonged, short, prolonged, short.
- In doubt about another vessel's intentions or action: at least five short and rapid blasts, which may be supplemented with five short, rapid flashes.
- Approaching a bend or obscured area: one prolonged blast, answered by one prolonged blast from any vessel beyond the bend.
This is a plain-English summary, not the official wording. For the exact text, see the IMO convention. In UK waters the rules are given legal force by the Merchant Shipping (Distress Signals and Prevention of Collisions) Regulations.
What it means on a yacht
The manoeuvring signals are for power-driven vessels, so use them when motoring. Five short blasts from a ship means 'what are you doing?': make your intentions obvious at once.
| Signal | Meaning | When |
|---|---|---|
| Short | I am altering my course to starboard | In sight |
| Short, short | I am altering my course to port | In sight |
| Short, short, short | I am operating astern propulsion | In sight |
| Short, short, short, short, short | I am in doubt of your intentions — danger signal | In sight |
| Prolonged | Approaching a bend or obscured area, or leaving a berth | Any visibility |
| Prolonged, prolonged, short | I intend to overtake you on your starboard side | Narrow channel |
| Prolonged, prolonged, short, short | I intend to overtake you on your port side | Narrow channel |
| Prolonged, short, prolonged, short | Agreement to be overtaken | Narrow channel |
Practise it
Test yourself on who gives way in the free COLREGs trainer, or print the rules of the road cheat sheets for the chart table.
Other rules in Part D
- Rule 32: Definitions of sound signals
- Rule 33: Equipment for sound signals
- Rule 35: Sound signals in restricted visibility
- Rule 36: Signals to attract attention
- Rule 37: Distress signals