Distress Signals

Rule 37 and the Annex IV list

In short: Read COLREG Structure, Application and Definitions and Manoeuvring, Warning and Fog Signals first. A vessel in distress and needing assistance uses or shows the signals of Annex IV (COLREG Rule 37). There are 15, items (a) to (o), used together or separately.

• Distress = grave and imminent danger, help needed now. A problem that is serious but not life-threatening is urgency, not distress (see the priorities section).
• Easiest way to learn the list: sort it into sound, visual and radio/electronic. Notation: • = short, — = long.

• The radio items (l) to (o) are the modern GMDSS alerts. The current wording comes from IMO A.1004(25), adopted 2007, in force 1 December 2009 (MSN 1781 (M+F) Amd 3, Appendix 2).
• In the UK, COLREG (with Annex IV) is law through the Merchant Shipping (Distress Signals and Prevention of Collisions) Regulations 1996 — MSN 1781 (M+F) Amd 3.
• Annex IV para 3 also points to the International Code of Signals, IAMSAR Vol. III and two signals for aircraft to spot you: an orange canvas with a black square and circle (or another suitable symbol), and a dye marker.
• An upside-down national flag is not an Annex IV signal.

Flags: N C and the square flag with a ball

In short: N over C = “I am in distress and require immediate assistance”. N is a blue and white chequered flag; C has horizontal stripes blue–white–red–white–blue. No code flags on board? A square flag with a ball above or below does the same job (COLREG Annex IV 1(f) and 1(g)).

• November (N): chequered blue and white squares (4 × 4).
• Charlie (C): five horizontal stripes — blue, white, red in the middle, white, blue.
• Hoisted together, N above C, they are the International Code distress signal (COLREG Annex IV 1(f)).
• Memory aid: No Chance — “we can’t cope alone”.
• The square flag + ball is the improvised version: any square flag, with a ball or anything round-looking above or below it (COLREG Annex IV 1(g)).
• Exam trap: flag V = “I require assistance” — a request for help, not a distress signal. Single-letter C alone means “yes” (affirmative).
• Other two-letter code signals asked in the same breath: RY = “You should proceed at slow speed when passing me”; YG = “You appear not to be complying with the traffic separation scheme”.

On the bridge: daylight, no radio

• Your yacht has lost power and the VHF is dead, in sight of another vessel by day. Hoist N over C, fire an orange smoke signal downwind, and make the arms signal from the deck.
• Keep the flags hoisted until help arrives: a flag signal works only while someone is looking.

Pyrotechnics: flares, rockets and smoke

In short: Red = distress (night or day), orange smoke = distress by day. A rocket parachute flare climbs to at least 300 m and burns at least 40 s; a hand flare burns at least 1 min; a buoyant smoke signal at least 3 min (LSA Code 3.1–3.3).

• Rocket parachute flare: at least 300 m altitude, red, at least 30,000 cd, burns at least 40 s (LSA Code 3.1). Best for being seen from far off, by night.
• Hand flare: red, at least 15,000 cd, burns at least 1 min, keeps burning after 10 s under 100 mm of water (LSA Code 3.2). Best for pinpointing you when help is close.
• Buoyant smoke signal: orange smoke for at least 3 min (LSA Code 3.3). Daylight only; good for aircraft and helicopters.
• Ships carry at least 12 rocket parachute flares on or near the bridge (SOLAS III/6.3).
• A liferaft with a SOLAS A pack holds 4 rocket parachute flares, 6 hand flares and 2 buoyant smoke signals (LSA Code 4.1.5.1).
• Pleasure vessels 13.7 m and over (Class XII) going to Category C waters and seaward: a maritime radio (DSC strongly recommended), 4 red hand flares, 2 orange smoke signals and another alerting device such as an EPIRB or PLB. Waving your arms does not count (MIN 542 (M+F) Amd 3).
• Under 13.7 m: no specific carriage rule, but the Annex IV list still applies (MIN 542 (M+F) Amd 3).
• LED “electronic flares” (EVDS): not recognised by COLREG Annex IV or SOLAS; never a substitute for required pyrotechnics. You may carry one in addition (MIN 542 (M+F) Amd 3).
• UK commercial vessels: required flares must carry the Red Ensign mark (MIN 542 (M+F) Amd 3).
• Use: hold hand flares and smoke downwind, over the lee side, away from the liferaft canopy and your face. Fire rockets when a ship or aircraft could see them, not into the empty night.

Radio and electronic distress alerts

In short: Radio distress = DSC alert first (VHF Ch 70), then a MAYDAY voice call on VHF Ch 16 or MF 2182 kHz. Satellite alerts, EPIRB and SART are also Annex IV distress signals (COLREG Annex IV 1(l)–(o)).

• Distress voice frequencies: VHF Ch 16 (156.8 MHz) and MF 2182 kHz.
• DSC alert frequencies: VHF Ch 70; MF/HF 2187.5, 4207.5, 6312, 8414.5, 12577, 16804.5 kHz (COLREG Annex IV 1(l)). Rule of thumb: DSC is data, Ch 16 / 2182 kHz is voice.
• Sending: lift the cover, press and hold the red DISTRESS button until the alert is sent. It carries your MMSI and position (from GNSS, or entered by hand). After a DSC acknowledgement, or after about 15 s, make the voice call on Ch 16 (MCA, GMDSS VHF DSC procedures for small boat users).
• Satellite: Inmarsat (or other approved mobile satellite service) ship earth station alert goes straight to an RCC (COLREG Annex IV 1(m)).
• EPIRB: transmits on 406 MHz via the Cospas-Sarsat satellites to a rescue coordination centre (COLREG Annex IV 1(n)).
• SART: a radar transponder answers an X-band (9 GHz) radar with a line of 12 dots pointing to the survival craft; the AIS-SART shows on AIS. More in Radar in Search and Rescue (COLREG Annex IV 1(o)).
• Make sure the DSC set is connected to the GNSS: without a position, the alert is much less useful.

Message priorities: Mayday, Pan-Pan, Sécurité

In short: Four priorities, highest first: Distress (MAYDAY) → Urgency (PAN-PAN) → Safety (SÉCURITÉ) → Routine. Only MAYDAY is an Annex IV distress signal.

• MAYDAY — grave and imminent danger to a vessel or person, immediate help needed (sinking, fire out of control, abandon ship).
• PAN-PAN — urgent message about the safety of a vessel or person, but no grave and imminent danger yet (engine failure drifting towards a lee shore, a serious medical case — see Emergency Response, Radio Medical Advice and Medical Records).
• SÉCURITÉ — safety message: navigational or weather warnings (a drifting container, a light out of order, a gale warning).
• DSC call categories on a full set: Distress, Distress relay, Urgency, Safety, Individual/Routine, Group, Geographic area, Telephone.
• A small-craft Class D DSC controller (fitted voluntarily on yachts) has only the limited set: Distress, Urgency, Safety and Individual/Routine.

The MAYDAY call and message

• MAYDAY, MAYDAY, MAYDAY
• This is [vessel name ×3], [call sign], [MMSI]
• MAYDAY [vessel name, call sign, MMSI]
• Position (latitude and longitude, or bearing and distance from a known point)
• Nature of distress
• Assistance required
• Number of persons on board
• Any other information (abandoning ship, liferafts, EPIRB activated)
• OVER
• Source: MCA, GMDSS VHF DSC procedures for small boat users. Memory aid: MIPDANIO — Mayday, Identity, Position, Distress, Assistance, Number, Information, Over.

PAN-PAN and SÉCURITÉ calls

• Urgency: send a DSC All Ships Urgency call naming a working channel, then on Ch 16: PAN-PAN ×3, All stations ×3, this is [name ×3, call sign, MMSI], “please go to channel [x]”, Out. Then give the message on the working channel (MCA, GMDSS VHF DSC procedures for small boat users).
• Safety: to pass safety information to HM Coastguard, send an individual DSC call with safety priority to the Coastguard’s MMSI, accept the acknowledgement, and wait on the working channel it gives. No such function? Make a voice call on Ch 16 (same source).

Hearing a distress: acknowledge or relay

In short: Stop transmitting, listen on Ch 16, and log everything. On VHF, give the coast station about 5 minutes to acknowledge; if it doesn’t and you can help, acknowledge by voice. Send a MAYDAY RELAY only when the casualty can’t, or more help is needed.

• Your DSC set sounds an alarm. Stop any transmission that could interfere and keep a listening watch on Ch 16 (MCA, GMDSS VHF DSC procedures for small boat users).
• No DSC acknowledgement after about 5 min and you can help: acknowledge by voice on Ch 16 — “MAYDAY, [casualty name, call sign or MMSI], this is [own name, call sign or MMSI], RECEIVED MAYDAY”, then what help you can give and your ETA, “Over” (same source).
• Don’t acknowledge a DSC alert by DSC yourself: that stops the alert repeating and is the coast station’s job (IAMSAR Vol. III).
• Distress relay (MAYDAY RELAY ×3, All stations ×3, this is …) is sent by a vessel not in distress when: the casualty can’t transmit herself; the master thinks more help is needed; or a Mayday was heard and not acknowledged and you can’t help yourself. Relay to a coast station / RCC by any available means (IAMSAR Vol. III).
• Write it all in the GMDSS radio log and the deck log: time, position, what was heard, what you did.
• Every master must also report dangers to navigation (ice, tropical storms, winds of force 10 or more with no storm warning, sub-freezing air with gale-force winds causing severe ice accretion) to ships nearby and the authorities (SOLAS V/31–32).
• An illustrated table of the life-saving signals (signals between rescue units and survivors) must be available to the OOW (SOLAS V/29).

Duty to assist — and when you may not go

In short: The master must go to help anyone in distress at sea, with all speed (SOLAS V/33.1). You may decide not to go only when it is Unreasonable, Unnecessary or Unsafe — the three U’s — and then you log the reason and tell the SAR service.

• SOLAS V/33.1: a master who receives information from any source that persons are in distress at sea must proceed with all speed to their assistance, if possible telling them or the SAR service that the ship is doing so. It applies to any persons, whatever their nationality, status or circumstances.
• Unable, or in the special circumstances considers it unreasonable or unnecessary to go: enter the reason in the log-book and inform the SAR service (SOLAS V/33.1).
• Unsafe: help is given so far as the master can do so without serious danger to the ship, crew or passengers (UNCLOS Art. 98).
• Unnecessary: the master is released when told that other ships have been requisitioned and are complying (SOLAS V/33.3), or when the persons in distress, the SAR service or a ship that has reached them say help is no longer needed (SOLAS V/33.4).
• Typical “unreasonable”: you are far away and many closer ships are already going; or you are a laden tanker that cannot safely approach a burning vessel.
• The master’s professional judgement on safety cannot be overruled by owner or charterer (SOLAS V/34-1).
• Helping people in distress is not salvage. Salvage is helping a vessel in peril (property); it is neither distress nor towage.

Misuse, false alerts and look-alike signals

In short: Using a distress signal for anything else is prohibited, and so is any signal that could be confused with one (COLREG Annex IV para 2). Sent one by mistake? Cancel it at once, by voice.

• COLREG Annex IV para 2: no distress signal except to show distress and need of assistance; no other signal that could be mistaken for one.
• So: no old flares fired on New Year’s Eve, no “testing” flares at sea, and the doubt signal • • • • • (Rule 34(d)) or attention signals (Rule 36) must never look like distress.
• False DSC alert: switching the set off is not enough. Cancel by voice on the distress frequency (Ch 16 for a VHF alert): “All stations ×3, this is [name, call sign, MMSI], position …, cancel my distress alert of [date, time UTC]” (IMO A.814(19)). A cancelled false alert costs a few minutes; an uncancelled one launches a real search.
• False EPIRB activation: switch it off and tell the nearest RCC / coast station at once.
• Out-of-date flares go back through approved disposal (chandler, Coastguard arrangements) — never fired or dumped at sea.
• A flare seen ashore or at sea that might be distress is treated as distress: report it to the Coastguard.