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37

Distress Signals

Recognised distress signals include a square flag with a ball above or below, red hand flares and orange smoke. They indicate distress and the need for assistance.

Rule 37 states that when a vessel is in distress and requires assistance, she shall use or exhibit the signals described in Annex IV to these Regulations. Recognized distress signals include:

  • a gun or other explosive signal fired at intervals of about a minute
  • a continuous sounding with any fog-signalling apparatus
  • rockets or shells throwing red stars one at a time at short intervals
  • the signal SOS by any signalling method
  • the spoken word "MAYDAY" by radiotelephony
  • the International Code Signal of distress: NC
  • a square flag with a ball or anything resembling a ball above or below it
  • flames on the vessel
  • a rocket parachute flare or hand flare showing a red light
  • orange-coloured smoke
  • slowly and repeatedly raising and lowering arms outstretched to each side
  • a DSC distress alert, a ship-to-shore distress alert through satellite services, an EPIRB alert, or approved radiocommunication distress signals such as survival craft radar transponders
Radio distress alerting includes DSC, 406 MHz EPIRBs and recognised mobile satellite services. VHF DSC uses channel 70; MF DSC uses 2187.5 kHz. SARTs are not shown here.

IMO COLREG 1972Official text

Full wording of the rule, reproduced from the official source below.

When a vessel is in distress and requires assistance she shall use or exhibit the signals described in Annex IV to these Regulations.
Source:

Signal Workflow

Decide the context first: manoeuvring in sight, restricted visibility, or distress.

The same whistle can mean very different things in a different context.

Check both the pattern and the interval.

For fog signals, the time spacing is part of the rule, not just the blast sequence.

When vessels in sight are approaching and you do not understand the other vessel’s intentions or actions, or doubt its collision-avoiding action, immediately sound at least five short, rapid blasts (Rule 34(d)).

Exam Focus

Three short blasts are astern propulsion, not a fog signal.

Rule 35(a)–(f) signals have a maximum interval of 2 minutes; the anchor and aground signals in (g)–(h) have a maximum interval of 1 minute.

Paragraphs (i)–(j) provide small-vessel alternatives.

Key Takeaways

1

Annex IV recognizes both traditional visual signals and modern radio distress alerts

2

MAYDAY is the spoken radiotelephony distress signal and SOS remains a recognized signalling method

3

Red flares and orange smoke are classic visual distress signals

4

Distress signals must only be used when assistance is genuinely required

Common Mistakes

Using a distress signal for urgency or routine communications

Knowing only the flare signals and forgetting the DSC, satellite and EPIRB options

Test Your Knowledge

Practise this topic and review the explanation for each answer.

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Frequently asked questions about COLREG Rule 37

What are the COLREG distress signals?

Rule 37 requires a vessel in distress and requiring assistance to use the signals in Annex IV: red rocket, parachute or hand flares, orange smoke, SOS, the spoken word MAYDAY, the code signal NC, flames on the vessel, a continuous sounding with any fog-signalling apparatus, and DSC, satellite or EPIRB alerts.

Is MAYDAY a COLREG distress signal?

Yes. The spoken word MAYDAY by radiotelephony is one of the Annex IV signals listed under Rule 37, alongside SOS by any signalling method and the International Code Signal of distress NC.

When may a distress signal be used?

Only when a vessel is in distress and genuinely requires assistance (Rule 37). Using a distress signal for urgency or routine communications is a common mistake.