COLREG 1972 · rule 37 of 38
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Rule 37. Distress signals

When in distress and requiring assistance, a vessel uses the signals of Annex IV: rockets and stars, a red parachute flare, orange smoke, continuous sounding of a fog-signalling apparatus, SOS, the spoken word «Mayday», flags N and C, slowly raising and lowering outstretched arms, the DSC alert and the EPIRB signal.

Part of the convention Sound and light signals

When in distress and requiring assistance, a vessel uses the signals of Annex IV: rockets and stars, a red parachute flare, orange smoke, continuous sounding of a fog-signalling apparatus, SOS, the spoken word «Mayday», flags N and C, slowly raising and lowering outstretched arms, the DSC alert and the EPIRB signal.

At sea it looks like this

Five short blasts is not distress, it is doubt under rule 34. Distress is the continuous, unbroken sounding of a fog-signalling apparatus.

The rule says«When a vessel is in distress and requires assistance she shall use or exhibit the signals described in Annex IV to these Regulations».

Sound signals

Sound signals
continuous soundingDistress signal

Check yourself

Which sound signal means distress?

Continuous sounding of any fog-signalling apparatus. Plus the Annex IV signals: red parachute flare, orange smoke, SOS, «Mayday», flags N and C.

Rule 37.

Part of the convention: Sound and light signals