EPIRB

What sets this type apart

Other GMDSS distress alerting equipment, such as DSC radios or Inmarsat-C, depends on someone being at a working console to send the alert. An EPIRB is built for the case where nobody can reach the bridge at all: it floats free of a sinking hull automatically, or can be released and thrown clear by hand, and once in the water it starts transmitting on its own. It is the piece of safety equipment specifically designed for the abandonment scenario rather than for routine distress communication while the ship is still under control.

Main components

• Hydrostatic release unit (HRU) - a water-pressure-triggered mechanism holding the beacon in its bracket; it releases the EPIRB automatically at a shallow depth (typically around 1.5 to 4 metres) if the ship sinks without anyone manning it.
• 406 MHz transmitter - sends the coded distress message, including the ship's unique identity, to the Cospas-Sarsat satellite constellation, picked up by both geostationary and low-earth-orbit satellites.
• Integrated GPS receiver - modern EPIRBs encode their own position into the distress message, cutting the time to locate a beacon from hours down to minutes compared with Doppler-only positioning.
• Battery pack - a sealed, non-rechargeable battery sized to power continuous transmission for at least 48 hours, with a marked expiry date.
• Strobe light and whip antenna - visual homing aid and the transmitting antenna, both needing to remain unobstructed once the unit is floating.

Selection and sizing

EPIRB choice on a commercial vessel is largely a matter of category rather than performance tuning: Category I units are float-free with an HRU for automatic release, Category II are manually deployed only. Sea area of operation and ship type determine which is required. Battery and hydrostatic release service life are the two figures that actually vary between products and matter for lifecycle planning.

Regulations and class

Carriage is required under SOLAS chapter IV as part of the GMDSS fit, with the specific requirement (float-free vs manual) depending on ship type and sea area of operation. The battery has a fixed expiry printed on the unit, generally requiring replacement around every five years, and the hydrostatic release unit has its own separate, shorter service life - commonly two years - that is tracked independently of the battery date. Annual testing is required, and beacons must be registered with the relevant national Cospas-Sarsat authority with current ship and contact details, since an unregistered or wrongly registered beacon delays rescue coordination even though the signal itself is received.

Typical faults

• Expired HRU left in service past its date - the unit may fail to release, or release at the wrong depth, defeating the automatic function entirely.
• Registration details not updated after a change of owner, ship name or contact number - satellite alert reaches the rescue authority but with stale information, slowing response.
• Bracket obstructed by later-fitted equipment or lashings - prevents clean float-free release even with a working HRU.
• Battery expired but overlooked because the unit still passes a self-test light - self-test checks circuit function, not remaining battery life against the full 48-hour requirement.

What to look for in a supplier

• Current type approval for the applicable Cospas-Sarsat and flag administration requirements.
• Clear, separately marked expiry dates for battery and HRU, since they are not the same service interval.
• Confirmed GPS integration if the operator wants faster positioning than Doppler-only beacons provide.
• Support for beacon registration and any programming needed to encode the ship's MMSI and identity correctly.

Check the HRU expiry separately from the battery expiry at every inspection - crews that only track one date are the ones who find an EPIRB overdue on the other.