PLBs and AIS man-overboard beacons
Safety beacons
Two different personal beacons. A PLB is a pocket-sized 406 MHz satellite beacon, like a personal EPIRB, that alerts rescue authorities almost anywhere. An AIS man-overboard (MOB) beacon alerts your own boat and nearby boats, so the crew can turn back and find you quickly.
How it works
A PLB uses the same Cospas-Sarsat satellites as an EPIRB, is switched on by hand only, and must transmit for at least 24 hours; its hex ID is registered with NOAA. A MOB beacon is short-range: it appears as a special AIS target, with an MMSI starting 972, on nearby plotters, and many also set off a DSC alarm on your own VHF. One maker quotes up to about 5 miles. The Coast Guard doesn't monitor AIS MOB signals as distress alerts.
Using it
- Wear it. A beacon in a drawer can't help someone in the water. MOB beacons are designed to fit inside an inflatable life jacket and switch on automatically when it inflates.
- To use a PLB, raise the antenna, press ON, and keep the antenna pointing at the sky with nothing covering the GPS window. One maker says its PLB must be held above the water to work. Leave it on until rescued.
- Program your boat's DSC MMSI into a DSC-capable MOB beacon so it rings your own radio. Some can be reprogrammed if you change boats.
- Check that your plotter and VHF actually show MOB alerts; one maker warns that older equipment may not.
- Brief the crew: a MOB alarm on the radio or plotter means someone is in the water. Mark the position and start the recovery at once, because your own boat is usually the fastest rescue.
- PLB registration (FCC, 47 CFR 95.2905): each PLB owner must register it with NOAA and report any change of owner or details. Registration is free at beaconregistration.noaa.gov; NOAA asks for renewal every two years.
- PLBs may be used only for distress and safety-of-life communications (47 CFR 95.2931, 95.2933).
- AIS MOB beacons are 'maritime survivor locating devices' under FCC rules (47 CFR Part 95, Subpart K). They're licensed by rule, so no individual licence, but the device must be FCC-certified, and use on land isn't allowed.
- MOB beacons aren't registered with NOAA; they carry a factory-set MMSI beginning 972 that the owner can't change (USCG NAVCEN; maker).
- Since January 17, 2020, PLBs that don't meet the current RTCM 11010 standard can't be made, imported or sold in the US (47 CFR 95.2991).
Looking after it
- Self-test as the manual says; one PLB maker recommends monthly, or at least two weeks before a trip, and limits the number of tests over the battery's life.
- For a MOB beacon with several test modes, follow the maker's limits. One maker: basic test monthly, DSC test no more than twice a year, AIS/GPS test no more than three times a year, done with a clear view of the sky.
- Replace the battery by the date on the label, and after any real activation.
- Each season, check the MOB beacon is still correctly fitted in the life jacket and its lanyard is attached, and have the life jacket serviced as its maker advises.
- Keep the PLB's NOAA registration current.
Troubleshooting
PLB self-test fails
- Repeat the test exactly as the manual describes.
- Check the battery expiry date.
- If it fails again, send it to the maker or an authorised service centre.
MOB beacon's AIS test doesn't appear on the plotter
- Run the test outdoors with a clear view of the sky; one maker's beacon won't transmit AIS without a valid GPS position.
- Check the plotter is receiving AIS and shows MOB/SART targets.
- Check the AIS receiver or transponder and its antenna are working.
MOB beacon's DSC test doesn't ring your radio
- Check the beacon is programmed with your boat's MMSI.
- Check your radio has an MMSI programmed and DSC is working (Test Call to 003669999).
- Check with the radio maker whether that model accepts the individual distress relay call MOB beacons send.
PLB set off by accident
- Switch it off as the manual describes.
- NOAA says to call the US Air Force Rescue Coordination Center at 1-800-851-3051 for a PLB (the Coast Guard at 1-855-406-8724 for an EPIRB).
- Have the battery checked or replaced.
Buying a boat that has one
- Check the battery expiry date on every beacon.
- A used PLB must be marked sold in NOAA's database by the previous owner before you can register it, and it must be coded for the US.
- For a MOB beacon, check which DSC MMSI is programmed; it should be your boat's.
- A 121.5 MHz-only personal beacon can't alert the satellites, which stopped listening for 121.5 MHz in 2009; it only helps a searcher nearby who is listening on that frequency.
Sources (11)
sarsat.noaa.gov · sarsat.noaa.gov · sarsat.noaa.gov · ecfr.gov · fcc.gov · navcen.uscg.gov · navcen.uscg.gov · navcen.uscg.gov · oceansignal.com · acrartex.com · acrartex.com
General guidance for recreational boaters, researched from the sources listed and written in our own words. Your equipment manuals, local knowledge, the Navigation Rules and a qualified instructor come first.