June 14, 2023

MOB AIS

A safety device, the MOB AIS beacon can be used to rescue a man overboard. Small enough to fit inside an inflatable lifejacket, it activates with it. Having it with you when you’re sailing is a real reassurance. But how do you make sure it’s going to work properly, how do you test it? And what message will it send aboard your own boat?

June 14, 2023

The MOB AIS beacon is a small, personal beacon to be carried on your person, ideally coupled with your lifejacket. Installed in this way, it is designed to activate at the same time as the lifejacket inflates. The signal emitted by this beacon is a man-overboard signal visible on all AIS receivers, but not all!

MOB AIS
A beacon that fits in your hand

By alerting the AIS in the area, there’s a good chance that the crew on board your boat will be immediately alerted, and will come to recover you as quickly as possible. Your boat is always the one closest to you when you fall… The MOB AIS beacon is therefore a highly effective piece of safety equipment.

A callsign beginning with 972

A MOB AIS beacon, MOB for Man Over Board and AIS for Automatic Identification System, sends a VHF signal on the reserved digital channel 70. This signal always starts with 972, followed by 3 digits indicating the beacon manufacturer, then 3 final digits to differentiate the beacons.

When the first AIS receivers were created, MOB AIS, the message beginning with 972, did not exist. Some of the oldest AIS receivers see this coding as a simple AIS signal identical to that of a ship. On this type of receiver, there is therefore no man-overboard alert.

Example of a red cross alarm on a card reader

AIS receiver manufacturers now integrate this information into their devices, and when the receiver receives an AIS 972 MOB, an alarm is triggered. You should therefore refer to the device manual to find out which signal will be emitted in the event of a 972 message.

How to test your tag

Beacon triggered, antenna extended.

MOB AIS beacons have a test function that mainly validates battery status. A flashing LED indicates the battery’s state of charge. The battery is expected to last at least 5 to 7 years before needing to be replaced, by returning it to the product distributor for replacement. This battery test can be repeated many times. Manufacturers recommend carrying it out at least every 2 months. For yachtsmen who sail mainly in summer, it is strongly recommended to test their beacon at least before the start of the season.

A second, more comprehensive test involves testing the GPS and the beacon’s transmission. This test shows whether the beacon is working properly and, above all, whether it is transmitting a signal on its AIS receiver. This message, visible on the AIS receiver, does not trigger an alarm.

In the event of accidental tripping

MOB AIS
Beacon installed in the vest. It will be triggered when the vest inflates.

Sometimes, the beacon can be triggered unintentionally. For example, if your lifejacket inflates due to dampness. In this case, you can interrupt the transmission by manually switching off the beacon. It’s a good idea to notify the 16 of this event. To do this, call the CROSS, indicating the problem and specifying the number of the beacon that has been triggered. This 9-digit number, starting with 972, is marked on the beacon.

No French portal for MOB AIS beacons

In France, a MOB AIS beacon is not attached to a boat or a person. When a beacon is triggered, a search is systematically launched, but the emergency services don’t know who they’re looking for. Some countries, like Spain, maintain a portal on which each beacon is identified with an owner. This is particularly useful when it comes to invoicing an abusive intervention, for example. In France, however, there is no such system, and emergency services are called out every time a beacon is triggered.

ELT tester
AIS Testing BT200
AIS Testing BT200
AIS Testing BT200
AIS Testing BT200
AIS Testing BT200
WST Antenna 420-100
WST Antenna MGAA SMA
WST Antenna 100-GAA-SMA-M
WST Cable 130-029
WST Cable 130-002
WST BT200 screen
WST BT200 screen