EPIRB (406 MHz) Category II

What sets Category II apart

A Category II EPIRB is manually activated and manually released from its bracket; it will not float free and self-activate if the ship sinks, unlike a Category I EPIRB, which sits in a hydrostatic release unit and releases automatically. Category II beacons are typically fitted where a Category I is not required by the vessel's SOLAS category, or as a secondary manually-carried beacon in addition to a Category I unit on the same vessel.

Main components

Beacon body and battery

A watertight housing containing the transmitter, GNSS receiver, and a dedicated primary battery sealed for a shelf life typically around five years, after which the battery, and often the whole unit, must be replaced regardless of how little it has been used.

406 MHz distress transmitter

Transmits a digitally coded distress burst on 406 MHz to the Cospas-Sarsat satellite system, encoding the vessel's identity so a rescue coordination centre can trace the ship even before voice contact is made.

Integrated GNSS position

Modern units include a GPS or GNSS receiver that embeds position in the 406 MHz distress message, cutting the time to an accurate fix from the older Doppler-only satellite method, which could take an orbit pass or more, down to the first transmission.

121.5 MHz homing signal

A secondary low-power homing transmission on 121.5 MHz lets search aircraft and vessels close in on the beacon's exact position using a direction-finding receiver once the search area has been narrowed by the 406 MHz alert.

Manual bracket

Category II beacons are stowed in a bracket on the bridge or another accessible position for quick manual release; the crew must physically retrieve and activate the unit, so bracket accessibility and a clear release action matter as much as the beacon itself.

Regulations and class

SOLAS Ch. IV sets carriage requirements for EPIRBs by ship category and area of operation; GMDSS regulations require the beacon to be registered with the national beacon registry so a Cospas-Sarsat alert resolves immediately to vessel identity and an emergency contact. Battery expiry date is checked at annual radio survey, and an expired battery is a deficiency even if the beacon still passes a self-test.

Typical faults

• Battery past expiry date: beacon may still self-test but cannot be relied on for full transmission duration in an actual distress.
• Registration details out of date, such as an old vessel name or contact number: delays rescue coordination even after a valid alert.
• Corroded or seized bracket release mechanism: beacon cannot be freed quickly in an emergency.
• GPS antenna or receiver fault: beacon transmits a distress alert without position, forcing rescuers to rely on satellite Doppler positioning alone.
• Self-test not performed as part of routine checks: a failing beacon is only discovered during an actual emergency.

What to look for in a supplier

• Cospas-Sarsat type approval certificate for the specific model and, where relevant, flag administration acceptance.
• Battery and unit expiry clearly marked, with a straightforward replacement process rather than a full unit return for minor servicing.
• Support for updating registration details when the vessel is sold or reflagged.
• Self-test function that checks transmitter, GPS, and battery condition without triggering an actual satellite alert.

Run the self-test monthly and log it: a Cospas-Sarsat alert that resolves to outdated contact details wastes exactly the minutes a real distress cannot spare.