Six personal AIS rescue beacons compared

six man-overboard AIS locator beacons to see how they perform against each other

Emergency Position Indicating Rescue Beacons (EPIRBS) and Personal Location Beacons (PLBS) are vital pieces of equipment for cruising offshore, but if you fall off a coastalbased motor boat, they lack one key function – they don’t communicate your position to the boat you’ve just fallen from. A Search and Rescue Transponder (AIS SART) shows your position, speed and course over the ground on the chartplotter in front of your remaining crew, and any other vessel or station able to receive AIS within the SART’S range.

HOW DOES AN AIS SART WORK?

Instead of sending a worldwide distress alert via the GMDSS satellite constellation like an EPIRB or PLB, an AIS SART is simply an AIS transmitter that sends out an MOB alert message on the standard AIS VHF frequencies (161.975/162.025MHZ). This will be displayed by any Class-a or Class-b AIS receiver within range, usually as an X inside a circle. Owing to the proximity of the SART’S antenna to the water, in an MOB situation, its range will be around 4-6nm, less than the 8-24nm expected from a ship’s AIS transponder. An AIS SART does not need to be registered to the owner or a vessel but does come with its own unique MMSI number programmed in so that the rescue services can identify it more easily.

Some AIS SARTS also include a DSC function that will send out an MOB Distress Alert message to your radio (provided you’ve programmed in the MMSI of your boat’s DSC/VHF radio). With some SARTS, this is done simultaneously with the AIS transmission. Others send the DSC message initially, only following on with an AIS alert if it isn’t cancelled within a certain time period. This handy function allows the crew to rescue the MOB and cancel the alert before all nearby Ais-carrying vessels receive an MOB alert message.

HOW WE TESTED THEM

We took six of the most popular AIS SARTS into the Solent on a quiet weekday to try them out. Clearly we couldn’t activate them fully without causing mayhem in the busy Solent but, with the full knowledge and permission of the local Coastguard, we were able to put each one through its full test procedure to see if they functioned properly and to see if we could receive the ‘Test’ AIS message on our Garmin AIS receiver and multifunction display.

We also assessed how easy they would be to arm and activate manually, as even the simplest procedure can become a challenge when you’re cold, wet and frightened.