GORDON WEST REPLIES
A Maritime Survivor Locating Device (MSLD) is a manually activated digital beacon that sends a local distress message of “man overboard” or “sinking” via the marine VHF AIS channels, which allows all boats with a turned-on AIS receiver in the area to begin their search.
Another type of MSLD could be manually activated to send a distress alert over marine VHF DSC channel 70, similar to a VHF submersible handheld with GPS and the DSC distress red button. In either case you need to hope that the mother ship and any other ships in the area have their marine VHF/AIS turned on.
Note that an MSLD is very different from a personal locator beacon (PLB) that uses the International EPIRB system to uplink, from anywhere in the worldwide, to the COSPAS/SARSAT satellite service. Nor is it an Iridium or SPOT private satellite sender.
Another type of MOB locating system that has been around for some years is a “proximity automatic alert beacon,” a system specifically tied into a man overboard receiver aboard your boat. The water-activated Alert418 beacon, for example, works by transmitting a low-power signal on a non-marine UHF channel back to a dedicated receiver aboard the mother ship. This small 12-volt UHF receiver can then place a mark on the boat’s chartplotter (assuming the two systems have been correctly integrated), disengage the autopilot and/or activate an alarm to alert everyone else on board know that someone fell into the drink.