EPIRB and Distress Signals at Sea: A Skipper's Guide
When things go badly wrong at sea, raising the alarm fast and clearly saves lives. This guide covers the full toolkit — the EPIRB and PLB beacons, distress flares, radio Mayday and AIS-SART — and, just as importantly, which one to reach for when.
The layers of distress alerting
No single device is the whole answer. Long-range satellite beacons alert the authorities anywhere on Earth but don't help a nearby ship see you; flares are seen close in but reach no one over the horizon; radio reaches both coast stations and nearby boats but needs power and range. Good practice is to trigger several layers — beacon, radio and visual — so the alarm reaches the widest possible audience.
EPIRB — the satellite beacon
An EPIRB (Emergency Position-Indicating Radio Beacon) is the cornerstone of offshore distress alerting. When activated it transmits a digital 406 MHz signal to the Cospas-Sarsat satellite system, which passes your beacon's unique identity and position to a rescue coordination centre. Key points:
- Built-in GPS in most modern units gives a fast, accurate position.
- A 121.5 MHz homing signal lets search-and-rescue units home in close to.
- Float-free models auto-deploy and activate if the vessel sinks; manual models are released by hand.
- It must be registered with the national authority so rescuers know whose beacon it is and who to contact ashore.
- Battery life is typically several years; check the expiry and self-test periodically.
EPIRB vs PLB
| EPIRB | PLB | |
|---|---|---|
| Registered to | The vessel | A person |
| Size | Larger | Pocket-sized |
| Activation | Manual or float-free | Manual only |
| Battery / transmit time | Longer | Shorter |
| Best for | The boat as a whole | An individual who may be separated from the boat |
Both use the same 406 MHz Cospas-Sarsat network. Many cruisers carry an EPIRB for the vessel and PLBs for crew.
Distress by radio — DSC and Mayday
VHF radio reaches coast stations and nearby boats almost instantly. On a DSC set, press and hold the red distress button for at least five seconds to send a digital alert on Channel 70, then make a voice MAYDAY on Channel 16. We cover both sides of the radio in detail:
- How to send a MAYDAY distress call — the exact wording and order.
- What to do if you hear a MAYDAY — listening, acknowledging and relaying.
Distress flares and pyrotechnics
Flares are line-of-sight signals — use them when there is a realistic chance of being seen:
| Type | Range / use | When |
|---|---|---|
| Red parachute rocket | High, visible up to ~10 NM | To attract attention over the horizon when help may be in the area |
| Red handheld flare | Short range, pinpoints you | To guide in rescuers who are already close, day or night |
| Orange smoke | Daytime, marks position | For aircraft and helicopters, especially in good visibility |
Carry an appropriate flare pack for your area, check the expiry dates, keep them dry and accessible, and know how to fire each type before you need it. Dispose of out-of-date flares responsibly — never just bin them.
AIS-SART and SART
An AIS-SART broadcasts your position over AIS, appearing as a distinctive distress target on nearby vessels' and rescuers' AIS displays and chart plotters — ideal for marking a life raft or a person in the water at close to medium range. A radar SART (Search and Rescue Transponder) shows as a line of blips on rescuers' radar. Both complement the long-range alerting of an EPIRB with close-in homing.
The recognised distress signals
International rules (COLREG Annex IV) list the signals that indicate distress and a need for assistance. Beyond the electronic and pyrotechnic ones above, they include:
- A continuous sounding of a fog-signal apparatus, or a gun/explosive signal at intervals of about a minute.
- The spoken word "MAYDAY" by radiotelephony; the Morse "SOS" by light or sound.
- The International Code signal of distress, flags "NC".
- A square flag with a ball (or anything resembling it) above or below it.
- Flames on the vessel (e.g. from a burning tar barrel); a rocket parachute or hand flare showing red.
- Slowly and repeatedly raising and lowering both arms outstretched to each side.
Frequently asked questions
What is an EPIRB and how does it work?
An EPIRB is a vessel-registered distress beacon. Activated, it sends a 406 MHz signal via Cospas-Sarsat satellites with your identity and position to a rescue centre. Most have built-in GPS and a 121.5 MHz homing signal, can be float-free, and must be registered.
What is the difference between an EPIRB and a PLB?
An EPIRB is registered to the vessel, larger, longer-lasting and can be float-free. A PLB is registered to a person, pocket-sized, manually activated and shorter-lasting. Both use the same 406 MHz system; many crews carry both.
What types of distress flare are there?
Red parachute rockets (high, ~10 NM, to attract attention), red handheld flares (short range, to pinpoint you to nearby rescuers), and orange smoke (daytime, for aircraft). Flares are line-of-sight — use them when you may be seen.
How do I raise the alarm by radio?
Press and hold the DSC distress button for five seconds to alert on Channel 70, then make a voice MAYDAY on Channel 16. See our guides to sending and hearing a MAYDAY for the full procedure.
Related reading
- How to Send a MAYDAY Distress Call — the radio procedure step by step
- What to Do If You Hear a MAYDAY — the other side of the radio
- Free sailing video lessons — safety, VHF, COLREG and more
- Short Range Certificate (SRC) — Complete Guide
Be ready before it matters
SkipperCheck's online VHF/SRC course drills distress procedures — DSC, MAYDAY, beacons and flares — on a realistic simulator, so the right action is automatic when seconds count. Self-paced, online exam, certificate included.
See the VHF/SRC Course →