EPIRB stands for Emergency Position Indicating Radio Beacon.
It is a portable unit that runs on its own long life battery (usually a sealed lithium one). Once activated, it broadcasts its position via the Cospas - Sarsat polar orbiting satellite system and/or ground stations located around the Earth. It can take up to 45 minutes for a position fix dependent on the location of the satellites in orbit. Once identified, the system can usually determine the position of an EPIRB to within 3 nautical miles, although GPS-enabled EPIRBs now have the ability to pinpoint an EPIRB’s position to within 50 metres or less within 3 minutes of activation.
The EPIRB is registered by its owner with an emergency coordination centre. In the case of UK boat owners and UK registered vessels this would be the The Maritime & Coastguard Agency’s Emergency Coordination Centre in Falmouth.
The beacon transmits a coded radio distress signal on 406 MHz which, once received, will usually instigate a search and rescue operation. This is usually co-ordinated and run by the centre where the EPIRB is registered but if you are sailing the World, the rescue itself might be co-ordinated by SAR (Search & Rescue) organizations operating under the jurisdiction of another country.
Some EPIRBs have a secondary distress beacon which transmits on 121.5 MHz. This is used for ‘homing’ purposes once SAR teams are within a few miles of the indicated position. Sometimes vessels will carry a separate transmitter for this purpose known as a SART (Search And Rescue Transmitter). Both items also have a bright LED light which flashes once activated.
Nowadays, EPIRBs come in varying sizes. Original EPIRBS were the size of an average-sized travel kettle and were used by vessels. Smaller PLBs (personal locator beacons) are now used by individual crew although their usefulness in the case of a man overboard situation is questionable. The more recent AIS-based PLB is now considered more beneficial in such circumstances as it broadcasts locally on VHF to the casualty vessel and any surrounding vessels, as long as they have an AIS receiver.