Emergency Position Indicating Radio Beacon

An Emergency position indicating radio beacon (EPIRB) is a key part of the Global Maritime Distress and Safety System (GMDSS). All passenger vessels, and all vessels over 300 tons in international commerce, are required, by the Safety of Life at Sea convention, to carry all devices required by GMDSS. Recreational boaters and small fishing craft, are not required to carry an EPIRB, but, if they go out of sight of land, it is very strongly recommended that they do — current EPIRBs can be purchased for less than USD $900. Remember that EPIRB is not the only part of GMDSS; radios equipped with digital selective calling, preferaby connected to GPS, are required for vessels covered by SOLAS and recommended for all.

The system changed frequencies from civilian and military emergency channels to the worldwide dedicated distress beacon frequency of 406 MHz. For maritime use, they are automatically triggered, as when a vessel sinks; they may also have a manual activation switch. After 1 February 2009, the older EPIRBs using 121.5 or 243 MHz will not be detected by search and rescue systems. New EPIRBs are all 406 MHz, but older ones will need to be replaced, removing the batteries from the units being discarded.

Detection

When the beacon is activated, the signal itself will be detected by the COSPAS-SARSAT constellation of satellites, which use direction-finding techniques to locate the beacon. Location will be faster if the EPIRB has a built-in GPS receiver, which will encode the GPS-determined position in the distress message.

Two search and rescue (SAR) satellite systems detect EPIRBs:

• Polar-orbiting COSPAS-SARSAT aboard TIROS weather satellites and other satellites operated by Canada, France, Russia and the United States
• Geosynchronous orbit satellites (GEOSAR) aboard GOES and other satellites

The coverage limitations of the COSPAS-SARSAT orbiters are largely removed by the repeaters, which extend the EPIRB detection area worldwide, except for certain locations between the United Kingdom and Norway, south of the east coast of Australia, and the area surrounding the Sea of Okhotsk near Russia, as well as polar areas.

Neither process is instantaneous. Without GPS, it may take several satellite passes to confirm the location, which can take two hours or more. With GPS, once the position is transmitted to the satellites, the position report is carried quickly, but it must be remembered that a GPS receiver may take several minutes to locate and synchronize with several GPS satellites. GPS and COSPAS/SARSAT are different systems of satellites.

The GPS receiver in a EPIRB faces more difficulty in synchronizing than does a shipboard GPS unit, cabled to a stable antenna. Remember that an EPIRB released from a sinking vessel is bobbing in the water, a much less stable environment for antennas.

While 121.5 MHz, the civilian aviation emergency channel, is no longer monitored worldwide by SAR centers, modern EPIRBs do include a low-power 121.5 MHz beacon that is useful for close-range location of the vessel or people in distress.

GPIRBs do need to be tested regularly, and the vessel operator must be certain that they can always float freely. A recent fatal incident on a fishing vessel was caused by icing, which, as well as causing the boat to capsize, prevented the EPIRB from floating free and activating. While few recreational boaters will venture into icing conditions, nothing must impede the free-floating path of an EPIRB. It is not the place to dry a towel or bathing suit.

EPIRB is only part of GMDSS

EPIRBs complement a different GMDSS function, the DSC-GPS radios. Such radios, VHF near shore and MF further at sea, have distress switches that can be actuated in a situation where a water-activated EPIRB would not, such as medical emergency, fire, or piracy.