COLREGS Rule 37 — Distress Signals

Rule Text

What it means on the water

• →Distress signals are defined in Annex IV — 15 recognized signals total.
• →Key signals: SOS by any means, MAYDAY by VHF, continuous fog-signal sounding, red rockets/stars, orange smoke, parachute red flare, flames on vessel, NC code flags, square over/under ball, slowly raising/lowering outstretched arms.
• →Dye marker creates a large colored patch on the water — daytime signal.
• →Rule 37 prohibits use of distress signals (or signals liable to be confused with them) except when genuinely in distress.
• →Pyrotechnic distress signals include: red parachute flares, red hand flares, and orange smoke.

Common exam mistakes

• ✗Confusing the NC flag signal (N over C = distress) with the Code flag signal — NC is the signal to know.
• ✗Missing that orange smoke is a day-only signal while red parachute flares are day/night.
• ✗Thinking the square-over/under-ball signal is a routine navigational signal — it is a distress signal.
• ✗Using a distress signal as an 'attention' signal — Rule 36 covers attention signals; Rule 37 distress signals are reserved for actual distress.

USCG exam questions — Rule 37

These questions are drawn from the same pool used in real USCG licensing exams. Correct answers and explanations are shown.

1. 1. Which of the following is a recognized distress signal listed in Annex IV of the COLREGS?

   • A.Three short blasts on a whistle
   • B.Continuous sounding of a fog signal apparatus✓
   • C.One prolonged blast repeated every 2 minutes
   • D.Four short blasts on a whistle

   Why: The keyed answer is correct: 'a continuous sounding with any fog-signalling apparatus' is a recognized distress signal under Annex IV paragraph 1(b) (not 1(f); 1(f) is the International Code Signal of distress N.C.). Three short blasts is the astern-propulsion signal (Rule 34(a)); one prolonged blast every 2 minutes is the fog signal for a power-driven vessel making way (Rule 35(a)); neither is a distress signal.

2. 2. The International Code Signal of distress consists of which flag combination?

   • A.The 'N' flag flown above the 'C' flag✓
   • B.The 'D' flag flown above the 'K' flag
   • C.The 'M' flag flown above the 'A' flag
   • D.The 'O' flag flown above the 'N' flag

   Why: The correct answer is the 'N' (November) flag flown above the 'C' (Charlie) flag. The International Code Signal of distress is N.C., listed in COLREGS Annex IV paragraph 1(f). The SOS Morse-code distress signal is paragraph 1(d). (The previous explanation incorrectly cited 1(h) — flames on the vessel — for SOS and 1(i) — red rocket/hand flare — for N.C.)

3. 3. An EPIRB (Emergency Position-Indicating Radio Beacon) signal transmitted on 406 MHz or 121.5 MHz is recognized as a distress signal under Annex IV. This is referenced in which paragraph?

   • A.Annex IV, paragraph 1(l)
   • B.Annex IV, paragraph 1(d)
   • C.Annex IV, paragraph 1(n)✓
   • D.Annex IV, paragraph 1(g)

   Why: Annex IV paragraph 1(n) covers 'signals transmitted by emergency position-indicating radio beacons,' encompassing EPIRBs and PLBs on 406 MHz (satellite-detected) and 121.5 MHz (homing). The 1981 amendments added this signal to keep Annex IV aligned with advancing search-and-rescue technology.

4. 4. Rule 37 states that a vessel in distress and requiring assistance shall use or exhibit which signals?

   • A.The signals described in Rule 35
   • B.The signals described in Annex IV✓
   • C.The signals described in Annex II
   • D.The signals described in Rule 34

   Why: Rule 37 is simple: a vessel in distress requiring assistance shall use or exhibit the signals described in Annex IV. Rule 37 itself contains no specific signal descriptions; it delegates entirely to Annex IV, which lists 15+ recognized distress signals.

5. 5. 'Flames on the vessel (as from a burning tar barrel, oil barrel, etc.)' is recognized as which type of signal under Annex IV?

   • A.A fog signal
   • B.A sound signal
   • C.A distress signal✓
   • D.A caution signal

   Why: Annex IV paragraph 1(h) recognizes flames on a vessel — such as from a burning tar barrel or oil barrel — as a distress signal. This keeps the oldest maritime distress indicator (an open fire on deck) officially recognized alongside modern electronic distress alerts. (Paragraph 1(e), by contrast, is the radiotelephony spoken word "Mayday.")

6. 6. Which of the following sequences correctly summarizes all four fog signals for: (1) power-driven vessel making way, (2) power-driven vessel stopped not making way, (3) NUC underway, and (4) vessel at anchor?

   • A.(1) 1 prolonged, (2) 2 prolonged, (3) 1 prolonged + 2 short, (4) rapid bell ringing✓
   • B.(1) 2 prolonged, (2) 1 prolonged, (3) 1 prolonged + 3 short, (4) rapid bell ringing
   • C.(1) 1 prolonged, (2) 1 prolonged + 2 short, (3) 2 prolonged, (4) rapid bell ringing
   • D.(1) 1 prolonged + 2 short, (2) 1 prolonged, (3) 2 prolonged, (4) rapid bell ringing

   Why: Rule 35(a): power-driven making way = 1 prolonged every 2 min. Rule 35(b): power-driven stopped = 2 prolonged every 2 min. Rule 35(c): NUC (and others) = 1 prolonged + 2 short every 2 min. Rule 35(g): at anchor = rapid bell ringing 5 sec every 1 min. This ordering — one, two, one-two, bell — is the essential fog signal matrix for deck exams.

7. 7. Which pyrotechnic device is listed in Annex IV as an approved distress signal?

   • A.A white parachute flare
   • B.A rocket parachute flare or hand flare showing a red light✓
   • C.An orange smoke signal used only at night
   • D.A green star signal fired from a rocket

   Why: COLREGS Annex IV, para 1(i) lists "a rocket parachute flare or a hand flare showing a red light" as an approved distress signal (item (c) is the different signal "rockets or shells, throwing red stars"). Red is the recognized distress color, so the red-light parachute/hand flare is the approved pyrotechnic.

8. 8. The use of Annex IV distress signals is prohibited except:

   • A.When testing equipment in port during daylight hours
   • B.When indicating distress and need of assistance✓
   • C.When conducting Coast Guard-supervised drills
   • D.When entering a port after a long ocean passage

   Why: Annex IV explicitly states that distress signals shall not be used for any purpose other than indicating distress and need of assistance. Misuse can mislead rescuers and divert resources from actual emergencies.

Frequently asked questions

What are the recognized distress signals under COLREGS?

Annex IV to the COLREGS lists 15 distress signals including: SOS by any means (Morse code), MAYDAY by radiotelephone, continuous sounding of fog apparatus, red rockets or shells throwing red stars, a parachute flare showing a red light, flames on the vessel (burning tar barrel), orange smoke, the NC signal flags, a square flag over or under a round object, and slowly raising and lowering outstretched arms. Dye markers and certain radiotelephony signals are also included.

Can you use a distress signal to attract attention even if you are not in distress?

No. Rule 37 and Annex IV prohibit the use of distress signals — or signals that could be confused with distress signals — except when a vessel is genuinely in distress and requires assistance. Using a red flare to attract attention when you are not in danger is a violation of the Rules and may constitute a criminal offense under national law.

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