Sound & Fog Signals

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Navigation Rules

Sound & Fog Signals

Maneuvering and warning signals (COLREG Rule 34) and fog signals for restricted visibility (Rule 35). A short blast is ~1 second; a prolonged blast is 4–6 seconds.

Blast Pattern Legend

~1sShort blast (~1 second)
4–6sProlonged blast (4–6 seconds)

Maneuvering & Warning Signals

Rule 34

Used when vessels are in sight of one another and maneuvering or warning is needed. Signals must be made on the whistle. Light signals may accompany sound signals (same pattern, visible flash).

~1s

I am altering my course to starboard

Rule 34(a)
~1s~1s

I am altering my course to port

Rule 34(a)
~1s~1s~1s

I am operating astern propulsion

Rule 34(a)
~1s4–6s~1s4–6s~1s

I intend to overtake on your starboard side

Rule 34(c)
~1s4–6s~1s4–6s~1s~1s

I intend to overtake on your port side

Rule 34(c)
4–6s~1s4–6s~1s

Agreement / I understand — overtake

Rule 34(d)
4–6s

Warning / I am unsure of your intentions

Rule 34(d)
4–6s4–6s

Warning — approaching a bend or blind bend

Rule 34(e)

Fog Signals — Restricted Visibility

Rule 35

In or near restricted visibility (fog, mist, heavy rain, snow), all vessels must sound signals at intervals of not more than 2 minutes. A vessel under 12m is not obliged to make these signals but must make an efficient sound signal every 2 minutes.

Vessel StatusSignal PatternDetails
Power-driven — making way through waterrapid, >2/minOne prolonged blast every 2 minutes
Power-driven — underway but stopped, no wayrapid, >2/minTwo prolonged blasts every 2 minutes
Sailing vessel — underwayrapid, >2/minOne prolonged + two short blasts every 2 min
Fishing / trawling — underwayrapid, >2/minOne prolonged + two short blasts every 2 min
Vessel constrained by draftrapid, >2/minOne prolonged + two short blasts every 2 min
Vessel at anchor — <100mrapid, >2/minRapid bell ringing for 5 seconds every minute
Vessel at anchor — ≥100mrapid, >2/minBell forward + gong aft for 5 sec every min
Vessel aground — same as at anchor + 3 distinctrapid, >2/minBell 5 sec + 3 separate strokes before & after
Pilot vessel — underway or at anchorrapid, >2/min4 short blasts in addition to fog signal

Warning Signal (Rule 34(d))

If you do not understand another vessel's intentions, or doubt whether they are taking sufficient action to avoid collision, sound at least five short and rapid blasts on the whistle. This may be supplemented by a light signal of at least five short and rapid flashes.

Guidelines Only — Operator Responsibility. These signal patterns are general reference for COLREGs Rules 34–35. Vessels under 12m, pilot vessels, and vessels at anchor have additional or simplified requirements. Always carry and consult the full COLREGs. The operator is solely responsible for safety of the vessel and crew.