I was excited when I first heard about Raymarine’s LifeTag wireless man-overboard (MOB) monitoring system. But once I learned what it did, I was somewhat disappointed. It only alerts you that somebody has fallen overboard…it doesn’t tell you where they are! Well, it does set an MOB waypoint as soon as it’s triggered, so that’s something.

But really, I was expecting something that would point the crew toward the MOB, updated from moment to moment. Something that would help show you where they are now, not where they were. Something like this:

The Sea-Marshall SMRS8-LR SOS man-overboard alerting unit (under $300 each) activates automatically when immersed in water, or it can be triggered manually. Once active, it transmits over the 121.5-MHz emergency homing frequency used by Search and Rescue authorities worldwide.

Now, to be clear, this is not a 406-MHz PLB (Personal Locater Beacon). It doesn’t transmit to satellites. There is no GPS onboard the unit. This small unit has limited line-of-sight range, so a receiver must be within range for it to do any good.

In the scenario Sea-Marshall envisions, however, there is a receiver nearby. It’s installed aboard the vessel the MOB just fell from. The original vessel is almost always an MOB’s best chance for rescue, after all: it’s already on the scene!

   
The Sea-Marshall SARFinder 1003 base unit, about $2800, installed aboard your vessel, uses a three-element antenna and direction-finding (DF) radio gear to indicate which direction the victim is relative to the vessel. It has a resolution of 10°.

I got to play with this device at the Pacific Marine Expo, and I was impressed. The fact that the system uses a worldwide standard search-and-rescue frequency means that emergency response personnel may also have equipment capable of locating the victim. It also means that the base station is capable of detecting and direction-finding any manufacturer’s 121.5-MHz PLB or other beacon, if within range.

And about range…well, I’ll just let this diagram do the talking:

With an additional relay unit, which I could not find on the website, the base unit can also initiate a call on your DSC radio, or actuate an engine cut-out switch, or trigger your GPS to create a MOB waypoint (indicating the vessel’s position at the time the alarm first sounded, just like the Raymarine unit).

My understanding is that Sea-Marshall is developing an improved base unit that can be connected directly to your navigation system network without the use of an intermediate device, but it wasn’t clear to me whether this mean NMEA 0183, NMEA 2000, or what, exactly. Sorry I don’t have better information on this. Perhaps the folks at SeaMarshall can clarify.