A Personal Locator Beacon (PLB) is an electronic device designed to be used by individual crew members in order to Mark their position in the event that they go overboard, especially when untethered.
PLBs are continually getting smaller and smaller as battery technology, Electonic components and LED lights become more efficient. They generally fall into three types. These are VHF DSC / AIS, EPIRB and smartphone app-based solutions.
The original PLB was a battery powered Personal locator based around EPIRB technology. These PLBs had a GPS transmitter which transmitted on 406 MHz to a network of geostationary satellites positioned in orbit around the planet. When activated, the PLB would locate itself using GPS technology and then transmit the casualty's position. This position would then be relayed to a ground station, perhaps thousands of miles from the casualty’s location.
The AIS/DSC PLBs and the smartphone app based systems work more locally.
The AIS/DSC PLB works by combining a GPS locator with a VHF based DSC transmitter. Because the transmitter relies upon VHF, range is limited, especially in a larger sea where waves will reduce range. At first glance this might seem to be a significant drawback but in reality, the fact that the Personal Locator Beacon is transmitting the casualty’s signal on VHF means that any vessel in the immediate vicinity (say between 1 - 2 miles) will also see the casualty’s position.
Many AIS based systems will activate an alarm on the vessel’s chart plotter and may also speak to the vessel’s own main VHF set, requesting it to send out a DSC distress alert.
Both the AIS and EPIRB based systems usually include an LED or strobe light and can be fitted inside suitably designed life jackets, enabling them to be automatically activated when the lifejacket inflates.
The last type of individual safety transmitter is smartphone based. Whilst not yet as effective as the EPIRB or AIS based systems, these systems, usually based on WiFi or Bluetooth technology can be a good low cost interim solution, especially when short handed. The system does not yet offer location transmission, but instead works when a smartphone connected into the daisy chain of other devices held by the crew members does not detect the device. It then sets off an alarm to notify the crew that they may have a man overboard.
In our opinion, an AIS based system is currently by far the best option given that in a man overboard situation, time is of the essence and local assistance will have immediate information on the casualty's location. EPIRB based systems are probably more useful when a vessel needs to broadcast a distress message and location or when the casualty is in a liferaft.
Of course, when sailing in coastal waters in your country of registration, it could be argued that some of the drawbacks of the EPIRB (namely time to respond) will be much reduced, making the EPIRB option effective in MOB situations also.