COLREGs · Rule 37 · 33 CFR §83.37
Distress Signals
Annex IV lists the distress signals: SOS, MAYDAY voice, NC flag hoist, square-flag-and-ball, continuous fog horn, gun fired at one-minute intervals, red star rockets, parachute red flare, hand red flare, orange smoke, slow-and-repeated arm raise/lower, EPIRB, DSC alert.
What does Rule 37 actually say?#
Source
Practice this rule#
One real exam question on this rule, cited to source. No sign-up.
Under the Inland Navigation Rules, when a vessel is in distress and requires assistance, she shall use or exhibit the signals described in which regulation?
Does Inland Rule 37 change anything?#
Inland Rule 37 is 33 CFR §83.37, reproduced above, and carries no exam-relevant divergence from COLREGs Rule 37. One answer serves both the International and the Inland version of a Rules of the Road question on this rule — which is worth knowing precisely because several neighbouring rules do not work that way.
21 of 38 rules differ somewhere; the five the exam leans on are Rule 9, Rule 10, Rule 24, Rule 28 and Rule 34, side by side on Inland vs International Rules.
Why it shows up on the exam#
Rule 37 itself is one sentence and points at Annex IV — the exam questions are really Annex IV questions, so learn the signal list rather than the rule.
What does the exam actually test here?#
The rule
Points to Annex IV
When a vessel is in distress and requires assistance she shall use or exhibit the signals described in Annex IV to the Rules, 33 CFR part 87.
Where the content lives
33 CFR part 87
Annex IV carries the list itself — among them a gun or other explosive signal at about one-minute intervals, continuous sounding of any fog-signalling apparatus, rockets or shells throwing red stars, SOS by any signalling method, the spoken word 'Mayday', the N-over-C flag signal, a square flag with a ball above or below it, flames on the vessel, a red parachute or hand flare, orange smoke, slowly raising and lowering outstretched arms, and the EPIRB.
The constraint
Distress signals mean distress
The signals are for indicating distress and need of assistance. Using or exhibiting any of them for another purpose, or using anything that may be confused with them, is prohibited.
Rule 37 — common exam questions#
What does Rule 37 require?
When a vessel is in distress and requires assistance she shall use or exhibit the signals described in Annex IV to the Rules, at 33 CFR part 87 (33 CFR §83.37).
Where is the list of distress signals?
In Annex IV, 33 CFR part 87 — Rule 37 is a one-sentence pointer rather than the list itself.
Can distress signals be used for anything else?
No. They are for indicating distress and need of assistance, and using or exhibiting them for any other purpose — or using any signal that may be confused with them — is prohibited.
Authoritative source#
- 33 CFR §83.37 — this section with its neighbours. 33 CFR Part 83 is public domain; checked 2026-05-16.
- COLREGs Rule 37 is published by the IMO and is authoritative internationally.
Practise this rule against the real exam.
Real exam questions. No signup, no card.
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