EPIRB Guide for Bluewater Cruisers: How to Choose, Register, and Use One

An EPIRB is one of maybe four pieces of gear on a bluewater boat where the cheap option will get someone killed and the right option costs less than a single haulout. Yet most owners I talk to bought one, hung it in the bracket, and have never confirmed it is actually registered to them — or that the battery still has juice.

For the 50-foot catamaran we're researching for our circumnavigation, the spec is non-negotiable: a Category 1 (float-free), 406 MHz beacon with GPS at the helm; a PLB clipped to every adult's lifejacket; and an AIS SART per active watch stander as a third layer for in-sight rescue. Here is the reasoning, and the specific gear I'd actually buy with my own money.

What an EPIRB Actually Does (and Doesn't)

Activated, an EPIRB broadcasts a 406 MHz distress packet to the COSPAS-SARSAT satellite constellation. Within roughly 10 to 20 minutes that packet hits a Rescue Coordination Center — the US Coast Guard's JRCC for North American waters, the UK Coastguard for British, CROSS for French waters, and so on around the world. Modern GPS-enabled units narrow your position to about 100 meters. Older non-GPS units narrow it to a few kilometers, which is fine in mid-ocean and useless near a lee shore.

What it is not: a private rescue service. It is a satellite-relayed phone call to the nearest government you happen to be near. Response time and quality depend entirely on where you are. The US Coast Guard 200 miles off Cape Hatteras is fast. The Chilean Armada off Patagonia is slower. Choose your cruising grounds accordingly.

EPIRB, PLB, AIS SART — Three Different Tools

These get confused constantly. They are not substitutes for each other.

EPIRB is the boat's beacon — registered to the vessel, mounted in a float-free bracket so it deploys itself if the boat sinks. 48-hour battery minimum, 72 on newer units. This is the only one that triggers a satellite-relayed government SAR response when the boat is gone.

PLB is your personal beacon — registered to you, worn on your lifejacket, designed for "person in the water and the boat is gone." 24-hour battery. Smaller, cheaper, less powerful, but it goes overboard with you. The Ocean Signal rescueME PLB1 (~$300) and ACR ResQLink View (~$370) are the two units I would actually buy.

AIS SART broadcasts your position to AIS chartplotters within roughly 4 to 7 miles. Excellent for "the boat is still afloat and the crew aboard needs to find me right now." Does not reach satellites. The Ocean Signal rescueME MOB1 (~$300) clips to a lifejacket and self-activates on inflation — that is the unit I would specify for offshore watch standing.

For a family ocean crossing the layered spec is one EPIRB on the boat, one PLB per adult, and an AIS MOB1 per active watch stander. All-in is under $2,500 — under one percent of the safety budget on a 50-foot bluewater catamaran.

How to Actually Choose the EPIRB

Two real decisions: category and homing signal. Skip Category 2 entirely if you are going offshore — it requires you to be conscious to activate it, which is a planning failure. Category 1 deploys itself out of a hydrostatic-release bracket when the boat sinks.

On signal: every modern unit broadcasts 406 MHz to satellite plus a 121.5 MHz analog homing signal. The 121.5 is what the rescue helicopter uses to triangulate the last few hundred meters. Confirm both are present — they usually are, but check.

The two units worth shortlisting for a family offshore boat right now are the ACR GlobalFix V5 (Category 1, GPS, AIS-enabled, ~$700) and the Ocean Signal SafeSea E100G (Category 1, GPS, similar price). Both are 406 MHz with built-in GPS, 48-hour battery, NOAA-approved. Either is the right choice. The ACR has a slightly faster GPS lock; the Ocean Signal weighs less. I would buy the ACR for the lock time and call it done.

Register It Before You Leave the Dock

Registration is where most sailors quietly fail. An unregistered beacon will still trigger a SAR response — but the rescue coordinator gets your beacon ID and nothing else. They burn the first hour figuring out who you are, what kind of vessel they are looking for, and which of your emergency contacts to call. Registered, all of that is on screen the moment the alert arrives.

US owners register at beaconregistration.noaa.gov. You need the 15-character HEX ID printed on the beacon, vessel details (name, type, dimensions, hull color), and at least two emergency contacts. It is free, takes five minutes, and is valid for two years. Re-register whenever you change boats, contacts, or vessel details. Sailing under a non-US flag, register with your flag state's beacon registry — most are online and free.

Install, Test, Replace the Battery

The bracket has to be installed correctly or the float-free feature does not work. The antenna cable has to be torqued properly or the unit will not transmit at full power — a lot of in-the-field EPIRB failures are bad antenna connections. Self-test monthly (instructions vary by unit; usually a long button press that confirms internal state without actually triggering the SAR response).

Batteries get replaced every four to five years regardless of whether the unit has ever activated. It is not a DIY job — you ship the unit to an authorized service center, they replace and reseal the battery and recertify the hydrostatic release. Budget $150 to $250 and two weeks of downtime. Put it on a recurring calendar; if you do not, you will forget.

What Happens When You Press the Button

You raise the antenna and press the button. In the first five minutes the unit acquires GPS and transmits its encoded distress packet. Within 10 to 20 minutes the alert reaches the RCC. Within 30 to 60 minutes the RCC has called your emergency contacts to verify the alert is real (this is the registration payoff). If confirmed, SAR assets dispatch — a Coast Guard cutter, a helicopter, or commercial shipping in the area diverted to assist.

COSPAS-SARSAT has been operational since 1982 and is credited with over 50,000 lives saved. The system works. It only works if your unit is registered, maintained, and able to deploy.

The Spec for Our Family Boat

One ACR GlobalFix V5 at the helm bracket. One Ocean Signal rescueME PLB1 on each adult lifejacket — eventually four, plus child-sized backups once the older kids are big enough to wear one (the youngest two were born in 2024 and 2025, so we have time). One Ocean Signal rescueME MOB1 per night-watch stander, clipped to the lifejacket for self-activation. Total under $2,500. Annual maintenance: monthly self-test, battery service every four years. That is the safety floor for going offshore with four kids — below which no amount of insurance gets you back what you would have lost.

If you are working through your own offshore safety stack as part of buying a bluewater boat, the Bluewater Catamaran Buyer's Worksheet includes the safety-gear line items I am specifying for our circumnavigation, with cost ranges.