1.19 Distress Signals (Rule 37 / Annex IV)

Rule 37 — One Sentence, Entire Annex

Rule 37 is short:

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

That is the whole rule. Everything tested under "distress signals" is Annex IV content plus the misuse prohibition. On ONC06 Q100, you will not write an essay about SAR organization; you will recognize which option is a lawful distress signal and which is an ordinary navigation sound or light.

For a Master LT 100 carrying passengers, Rule 37 is also operational law: when you truly need assistance — flooding, fire beyond control, medical emergency requiring immediate rescue, grounding with hull failure — you must know what to send and, equally, you must never train passengers or crew to "practice Mayday" on a live distress frequency or fire a red flare for fun on July 4th off the swim step.

Annex IV — Signals of Distress (recognition bank)

Annex IV lists signals that indicate distress and need of assistance. Learn them as categories so any exam wording still maps.

Sound and explosive

1. A gun or other explosive signal fired at intervals of about a minute.
2. Continuous sounding with any fog-signaling apparatus (continuous horn/whistle — not the measured one-prolonged-every-two-minutes fog cadence of a healthy vessel making way).

Pyrotechnic and visual

1. Rockets or shells throwing red stars, fired one at a time at short intervals.
2. A rocket parachute flare or a hand flare showing a red light.
3. A smoke signal giving off orange-colored smoke.
4. Flames on the vessel (as from a burning tar barrel, oil barrel, etc.).
5. The signal consisting of a square flag having above or below it a ball or anything resembling a ball.
6. Slowly and repeatedly raising and lowering arms outstretched to each side.

Radio, code, and electronic

1. The signal made by any signaling method consisting of the group ··· ––– ··· (SOS) in the Morse Code.
2. The signal sent by radiotelephony consisting of the spoken word "Mayday."
3. The International Code Signal of distress indicated by N.C.
4. Distress alert by digital selective calling (DSC) transmitted on VHF channel 70, or on MF/HF DSC frequencies as applicable.
5. Ship-to-shore distress alert transmitted by the ship's Inmarsat or other mobile satellite service provider ship earth station.
6. Signals transmitted by emergency position-indicating radio beacons (EPIRBs).
7. Approved signals transmitted by radiocommunication systems, including survival craft radar transponders (SARTs).

Editions and teaching lists sometimes group electronic items under fewer bullets; Q100 cares that you accept Mayday, DSC, EPIRB, SART, SOS, NC, red flare, orange smoke, continuous fog horn, flames, gun, arms outstretched as distress — and reject look-alikes.

What is NOT a Rule 37 / Annex IV distress signal

A continuous fog horn can be distress under Annex IV; a measured prolonged blast on a two-minute cycle is normal restricted-visibility conduct. The exam difference is continuous versus prescribed interval fog signals.

Misuse Prohibited

Annex IV and implementing regulations prohibit the use of international distress signals for any purpose other than indicating distress and need of assistance. Attention must also be paid to signals that may be confused with distress signals — do not invent "party flares," joke Maydays, or continuous horn blasts as docking theatrics.

For Master 100 operations:

• Train with unplugged or training devices, classroom radio simulators, and Coast Guard–approved drill procedures that do not transmit live distress.
• Passenger briefings may show where flares and EPIRBs are stowed and who is authorized to activate them; they must not encourage guests to fire signals.
• False distress wastes SAR resources, is unlawful, and can cost licenses — examiners expect Masters to know misuse is forbidden.

Master Exam Recognition Scenarios

Scenario 1 — Fire on a T-boat. Engine-room fire spreads; extinguishers failing; you need immediate help. Lawful package: Mayday on VHF 16 (and DSC distress if fitted), EPIRB activation if abandoning or as procedure dictates, red hand flares / parachute flares when they will be seen, orange smoke by day, continuous sounding if that helps local craft find you. Not lawful as "distress": five short blasts to a visible vessel when you merely want them to give more room — that is Rule 34 doubt, not Annex IV, though you may still need both tools in a combined emergency.

Scenario 2 — Recognition stem. "Which of the following is a distress signal?" Options include two prolonged blasts, five short rapid, orange smoke, and one short blast. Correct: orange smoke. Two prolonged = fog stopped; five short = danger/doubt in sight; one short = maneuvering.

Scenario 3 — Arms. A person on a disabled skiff slowly and repeatedly raises and lowers outstretched arms. That is a classic Annex IV visual distress signal — do not dismiss it as "waving hello." A Master who sees it treats it as distress until proven otherwise (Rule 2 good seamanship overlays the technical list).

Scenario 4 — Electronic. EPIRB 406 MHz alert to the Cospas-Sarsat system, VHF DSC distress alert on channel 70, and SART presentation on rescue radar are all within the Annex IV electronic family. "Calling the marina on channel 68 to say you will be late" is not.

Scenario 5 — Continuous fog signal. A vessel in distress may sound a fog-signaling appliance continuously. That is different from your own lawful fog cadence while still in command and making way. If you hear a horn that never pauses into the prescribed pattern, consider distress or a malfunction — investigate with lookout, radar, and radio.

How Distress Fits the Rest of Part D

Rule 36 (signals to attract attention) allows light or sound signals that cannot be mistaken for any signal authorized elsewhere — and forbids using signals that may be confused with distress. Together with Rule 37, it closes the loop: get attention without crying wolf.

Exam Framing for Q100 (90%)

Highest-yield Annex IV items on Master banks: Mayday, red flare / red-star rocket, orange smoke, continuous fog horn, flames, outstretched arms, SOS, Code NC, EPIRB/DSC. Highest-yield negatives: ordinary Rule 35 patterns and Rule 34 five shorts are not distress signals by themselves. Misuse is prohibited. When a stem says the vessel is "in distress and requires assistance," the correct option is an Annex IV method — not a creative horn code you invented at the dock.