Short and prolonged blasts
Under Rule 32, a short blast lasts about one second and a prolonged blast four to six seconds. Below, · is a short blast and — a prolonged one.
Manoeuvring and warning signals (Rule 34)
These are for vessels in sight of one another. A power-driven vessel must sound the first three when she manoeuvres as the rules allow or require. They may be backed up by the same number of light flashes.
| Signal | Meaning |
|---|---|
| · | I am altering my course to starboard |
| · · | I am altering my course to port |
| · · · | I am operating astern propulsion |
| · · · · · | Five or more short and rapid: I doubt you are taking enough action to avoid collision |
| — | Approaching a bend or obscured part of a channel (answered with one prolonged) |
| — — · | Narrow channel: I intend to overtake you on your starboard side |
| — — · · | Narrow channel: I intend to overtake you on your port side |
| — · — · | Narrow channel: agreement from the vessel being overtaken |
Signals in restricted visibility (Rule 35)
These apply in or near restricted visibility, by day or night. Notice the pattern: power-driven vessels sound only prolonged blasts; every vessel with restricted manoeuvrability, or under sail, sounds a prolonged and two shorts.
| Vessel | Signal |
|---|---|
| Power-driven, making way | — every 2 minutes or less |
| Power-driven, underway but stopped | — — every 2 minutes or less |
| Sailing, not under command, restricted in ability to manoeuvre, constrained by draught, fishing, towing or pushing | — · · every 2 minutes or less |
| Last vessel of a tow, if manned | — · · · immediately after the towing vessel's signal |
| At anchor | Bell rung rapidly for about 5 seconds every minute (plus a gong aft if 100m or more). May add · — · to warn an approaching vessel |
| Aground | The anchor bell, with three separate, distinct strokes before and after |
| Pilot vessel on duty | May add four short blasts · · · · to identify herself |
A vessel under 12m doesn't have to give these signals, but if she doesn't, she must make some other efficient sound signal at intervals of not more than two minutes. See Rule 19 for how to manoeuvre in fog.
Equipment (Rule 33)
- 12m or more: a whistle.
- 20m or more: a whistle and a bell.
- 100m or more: a whistle, a bell and a gong.
- Under 12m: not required to carry these, but must have some other means of making an efficient sound signal.
Distress
A continuous sounding with any fog-signalling apparatus is one of the distress signals in Annex IV of the COLREGS. On a yacht today, a DSC alert and a Mayday on VHF come first.