Which Emergency Beacon?

Confused by all the acronyms?  Read on for a little explanation...


Global alerting and initial location

cospas-sarsatEPIRBs (Emergency Position Indicating Radio Beacons) and PLBs (Personal Locator Beacons) transmit a 406MHz distress alert via the COSPAS-SARSAT satellite network to notify national rescue forces of the identity and initial location of a vessel or person in imminent danger.

In most cases, the alert will be detected within a matter of minutes, but in polar regions or where there is a poor view of the sky, there could be a delay of up to 4 hours for the signal to be picked up by a low level orbiting satellite.

GPS equipped EPIRBs or PLBs can send an accurate location with the alerting signal, so the rescue forces will know the initial location to within about 100 metres.  For EPIRBs or PLBs without GPS (or where the GPS is unable to get a fix due to an obstructed view of the sky), then initial location will be performed by orbiting satellites. This could take up to 4 hours depending on location, and with a typical accuracy of 2-5 km.


Final location

Helicopter and lifeboatA satellite alert will provide a good initial location to search for the survivors, especially if derived from a GPS beacon.  However small targets can still be very hard to find, especially in poor weather.   All EPIRBs and PLBs incorporate additional transmitters operating on 121.5MHz.  SAR helicopters and lifeboats have direction finding (DF) equipment which can home on these signals.   However commercial or leisure vessels which may be quicker on-scene will not have suitable DF equipment.  All EPIRBs also incorporate strobe lights to help in final location.  Many PLBs also have flashing lights for the same purpose.  Additonal locating lights may be fitted to lifejackets and life rafts.

Search and Rescue Transponders (SARTs) are devices specifically designed to help in the location of survival craft.  These have traditionally used radar transponder techniques to "paint" a series of dots on any X-band radar screen.  AIS SARTs are now also available, which transmit an identity and GPS location which can be picked up by most commercial vessels and an increasing number of leisure vessels carrying AIS receivers or transponders.


Man Overboard

Man OverboardIf a crew member should fall overboard, the quickest rescue wil normally be provided by their own vessel - provided the remaining crew are aware of the situation and are able to turn the boat around and effect a rescue.  Various Man Overboard (MOB) alerting and location systems have been marketed in the past, most of which were either of limited effectiveness or based on expensive or proprietary systems, undetectable by other craft in the area.  It is now possible to buy MOB beacons using the AIS SART principle, transmitting a coded signal with GPS location to all AIS receivers within range (typically 2-5nm)  Ideally these should be designed to activate automatically, combined with auto inflation of a lifejacket.  Some models are designed for user retro-fitting to existing automatic lifejackets.  Plotters linked to AIS receivers can be arranged so as to trigger an alarm if one of these AIS beacons is detected.  A test mode is provided to verfify correct operation and allow for crew training.  It should be noted, however, that AIS is not considered a distress alerting system and it cannot be guaranteed that activation of an AIS beacon will trigger an alarm on a nearby vessel.





Emergency Position Indicating Radio Beacons (EPIRBs) are radio distress beacons for use on all types of watercraft.

They operate world-wide using the international COSPAS-SARSAT satellite system which has provided alerts resulting in the rescue of more than 39,000 lives since its inception in 1982 up to the end of 2014.

Early analogue beacons used the aircraft distress frequency of 121.5MHz, but these have been gradually phased out in favour of digital transmissions on the dedicated distress frequency of 406MHz. 121.5MHz satellite processing was switched off in 2009.

All EPIRBs are approved to common standards.

Buyers can opt for EPIRBs with integrated GPS for quicker and more accurate location.  The additional cost is now quite small, so if buying new or replacing an old EPIRB, it's well worth considering.  The point is well made by the Australian video below:


EPIRBs are designed to float in the water when deployed, and have seawater contacts so they will start transmitting automatically once released.

The main decision to make is whether to have a manually deployed EPIRB - which will normally be mounted in a bulkhead bracket or stowed in a grab bag - or an automatic release EPIRB which will float free and activate automatically if the vessel should sink.

Click here for answers to frequently asked questions, or contact us for help in choosing an EPIRB.






GME MT410GPersonal Locator Beacons (PLBs) operate through the same satellite network as EPIRBs, but are designed to be small enough to fit a pocket or even lifejacket.

However they have a shorter operating time, and must be manually activated and held out of the water with a continuous and clear view of the sky.

The big advantage of a PLB is that it can be kept close at hand in case of an emergency.  Sometimes an EPIRB may be unreachable in case of a sudden capsize, or fire in the cabin, for instance.

For man overboard use, it should be borne in mind that PLBs are not permitted to be automatically activated, and their transmissions are aimed at the world-wide rescue system and unlikely to be detectable by commercial or leisure vessels.



Radar SART

SART on radar

Search and Rescue Transponders (SARTs) are short range locating devices, operating either on radar or AIS.  These allow vessels which happen to be in the area of a distress incident to look for survival craft, using their radar or AIS equipment.  These vessels would not normally have the specialist direction finding equipment carried by SAR (Search and Rescue) assets such as lifeboats and helicopters.

Radar SARTs produce a series of dots on nearby radar screens, providing a range and bearing to the liferaft.




AIS SART display


AIS SARTAIS SARTs operate over a similar range (up to 10nm depending on the height of the search vessel's antennas), but will show up on the chart plotter as a special symbol, and may trigger an alarm, depending on the plotter software and settings.







MOB Beacons

Kannad S10 MOB BeaconMan Overboard ( MOB) beacons are designed to assist in retrieval of a crew member falling into the water.  Even if the alert is raised immediately, it can take some time to turn the boat around and, in all but a flat calm, it can be very difficult to spot the casualty.There are now a number of devices on the market, mainly using the AIS SART principle, whereby the beacon transmits the GPS location over AIS, so that all AIS equipped vessels in the area can see the casualty on their electronic charts and can steer a course to locate the casualty.

This video shows the features of the EasyONE beacon which is particularly easy to retrofit to a lifejacket and is fully automatic in operation.





EasyRESCUE_PROOcean Signal MOB1Some MOB beacons are also available with the ability to transmit an alert and location using DSC (Digital Selective Calling).  These are normally programmed to set off an alarm on the mother vessel's VHF DSC radio.  The Weatherdock EasyRESCUE-PRO will automatically send out an "all ships" alert of it does not receive an acknowedgement from the mother vessel, so that other vessels in the area can be alerted.  The Ocean Signal MOB1 can also send an "all ships" alert, but in this case the survivor has to activate the function by pressing a button on the unit.