EPIRB

What defines an EPIRB

An Emergency Position Indicating Radio Beacon (EPIRB) is a self-contained satellite distress beacon, carried as required GMDSS and SOLAS life-saving equipment, that transmits on 406 MHz to the Cospas-Sarsat satellite system when activated. It differs from a Search and Rescue Transponder (SART), which is a radar-reflecting device used to guide a rescue unit to a liferaft once search has already narrowed the area, and from an AIS-SART, which broadcasts a position on AIS rather than through satellite. The EPIRB's role is the first alert: getting the vessel's identity and position to a Rescue Coordination Centre as fast as possible after abandon-ship, before any surface search begins.

Main components

406 MHz transmitter

Transmits a digitally coded distress message including the vessel's unique identification (MMSI-derived hex code) to Cospas-Sarsat satellites, repeating at a fixed interval until manually switched off or battery exhaustion.

Integrated GPS receiver

Modern EPIRBs include an internal GPS receiver that encodes position into the 406 MHz message, cutting the time to an accurate fix from the tens of minutes a Doppler-only satellite fix needs down to close to immediate.

121.5 MHz homing signal

A separate low-power homing transmission that search and rescue units use for final approach once in the vicinity, distinct from the 406 MHz distress alert channel.

Float-free bracket (hydrostatic release)

A hydrostatic release unit (HRU) frees the EPIRB automatically at a shallow depth if the vessel sinks with no one able to launch it manually, so the beacon activates and floats clear even in an uncontrolled loss.

Battery

A sealed primary battery with a manufacturer-stated shelf life and a separate, shorter operating life once activated, both marked on the unit and tracked against replacement due dates.

Selection and sizing

Category and mounting depend on vessel type and area of operation: a float-free, automatically activating EPIRB in a hydrostatic release bracket is standard on SOLAS cargo and passenger vessels, while a manually deployed category II unit is more common on smaller craft. Selection points are GPS integration (essentially standard on current models), battery operating life after activation (commonly rated at 48 hours minimum), and coding to the correct vessel identity in the unit's programmed message, which must be re-programmed whenever the vessel's MMSI or call sign changes, such as after a change of flag or owner.

Regulations and class

SOLAS Ch. IV requires an EPIRB as part of the GMDSS fit for the vessel's sea area of operation, and Ch. III requires it as abandon-ship equipment mounted for float-free release where applicable. The beacon must be type approved to Cospas-Sarsat and IMO performance standards, registered with the relevant national beacon registry against the vessel's identity and an emergency contact, and this registration must be kept current — an EPIRB registered to a previous owner or an old contact number materially slows a rescue response. Battery replacement and full functional testing, including hydrostatic release unit replacement, follow manufacturer-set intervals and are checked at every radio and safety equipment survey.

Typical faults

• Expired hydrostatic release unit — an out-of-date HRU may not release the beacon at all, defeating the entire float-free function; this is a frequent survey finding because the date is easy to overlook against the beacon's own battery date.
• Outdated registration — a beacon registered to a previous vessel name, owner or contact number delays a Rescue Coordination Centre's ability to identify the vessel and its emergency contacts.
• Battery expiry — an EPIRB past its battery due date may still self-test as passing but not hold full rated operating life if actually activated.
• Bracket corrosion or fouling — paint overspray, corrosion or a poorly maintained bracket can jam the beacon in its cradle, preventing float-free release even with a valid HRU.

What to look for in a supplier

• Current Cospas-Sarsat type approval and, where relevant, the specific national or flag administration approval required.
• Integrated GPS as standard, since the reduction in time-to-fix is significant for search and rescue response.
• Clear battery and HRU expiry dates and a straightforward replacement/exchange programme through the maker's service network.
• Support for re-registration and re-coding when the vessel's identity changes, not just supply of the physical unit.

Check the registration database entry, not just the beacon itself, at every safety equipment survey: an EPIRB in perfect working order registered to the wrong contact still sends rescuers looking for the wrong vessel.