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PLB, AIS or EPIRB? need more acronyms?

If you have that most unfortunate event of falling off your boat, its very very hard to find you again if you don’t have a PLB (Personal Locator Beacon) attached to your lifejacket.

Statistics say you’re dead, basically, if you don’t have one on and fall off the boat at night or in weather. So sounds like a good purchase to have on your body.

But what should you have? An AIS (Automatic Identification System) or COSPAS – SARSAT Epirb style beacon?

There is quite an argument to be had here… so lets look at the two different approaches firstly;


  • Sends a signal via Satellite to emergency services onshore
  • May also transmit on a radio frequency for rescue teams to locate you down to about 100m
  • Chances of a successful notification of rescue services is very high.
  • Chances that they will get to you in a short time period is quite low, depending on your location and distance from shore of course.
  • MOST IMPORTANTLY: your boat is not notified of your falling into the water and has no way of locating you other than a relayed message via sat comms or VHF if they are in range, to the shore-based rescue services.
  • Your location is not tracked dynamically on any vessel until they are within range, and have a device capable of receiving, the 100m radio transmission. Most yachts do not have this equipment.


  • Sends a VHF AIS signal to any boat within the transmission range, activating an alarm and with GPS coordinates of your location.
  • Chance of a successful notification are quite high for boats within range and very high for your own boat.
  • Your own vessel, if you are not a solo sailor, will be notified and an alarm will be activited to wake sleeping crew.
  • Your position will be marked, dynamically, on the Chartplotter to assist with turning around to find you.
  • The range is limited and with wave action probably only a few miles reliably. Another way to put this would be 30mins to a couple of hours reaction time for a sailing boat before you are out of transmission range.
  • Turning around and getting within that transmission range will again pinpoint the location of the beacon to within 10m.
  • Any AIS receiving boat that comes within range will be notified of your status (overboard) and given your location and therefore be in a position to effect a rescue or pass on rescue information.

So which is better? its a fair argument, for instance if you are a solo sailor then an AIS one has limited value, you effectively need another boat to come within range of your transmission. Even if you are with crew, if you’re sailing shorthanded will the alarm wake them before you are out of range? how deeply do they sleep?

The alarm is, in most cases, an escalating volume alarm until it is responded to… so there is a good chance of waking them up.

Whereas the SARSAT device is guaranteed to get a response, its just a matter of is it in time for your survival and can they actually find you. 100M is a big distance in a storm to find a bobbing sailor.

I’ll leave the discussion up to your guys. What does Waiata use? well we use AIS beacons and like to think we will be in a position and the closest to effect a self rescue. Hope we never get to find out!!!

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2 Responses

  1. There are some errors and missing data here.


    The 121.5 MHz local VHF direction finding frequency of a PLB is good for much more than 100m. Just how far depends on line of sight which is more dependent on the antenna location on the SAR platform than the floating PLB. It’s pretty good from an aircraft, less so from a small boat even if you have RDF capability on board and know how to use it. Importantly, the VHF range of an AIS-SART is the same.

    The PLB updates your position as long as the batteries hold out – generally 24 hours.

    Another benefit of a PLB is that the rescue coordination center (RCC) will notify all GMDSS ships in the area so you’ll get more, closer help than you would otherwise.


    Everyone should have a crew overboard (COB) protocol and practice it. If the COB is in eyesight all efforts should be focused on getting the boat back to the COB and the COB on board. In my opinion, if the COB is not in view it is worth the time to drop the MOB mark on the chartplotter, to trigger your EPIRB, and to push the little red DSC button on VHF and HF/SSB. Then start the planned search pattern. The latter is one of many reasons to have ‘track’ activated on your chartplotter.

    My choice: AIS-SART, EPIRB, VHF w/ DSC, HF/SSB/Pactor w/ DSC.

    Everyone on board should be capable of using long range communications on that boat. If you use Iridium GO! (not my favorite), every device on the boat should be connected. There are a number of stories in which the only phone connected to the GO! was in the pocket of the COB.

    1. Hey Dave, Great comments.

      The “Today I learnt’s” are not designed to be full articles but rather discuss a single point that I have learned and this one was that carrying a PLB of some sort is wise, but be aware of the choices you make.

      You’re right that practiced, preparedness, even the simple things is key. The UK and US stats claim you have less than a 25% chance of surviving. But then only 8% were even wearing a lifejacket.

      The important stat with choosing a PLB is, you have between 2 and 4 hours of realistic survival time to be found alive.
      So the real question is what device is going to lead to you being found the fastest in your circumstances. So very much an opinion and also a circumstances driven answer.

      BTW, The 100m effective range was quoted by the manufacturers of one of the biggest selling SARTS, The reason is that VHF Direction finding equipment needs a stronger, reliable signal strength in order to determine, reliably, the direction from which it is being transmitted. It is usually around 1/4 of the maximum VHF data transmission distance (remembering if the data fails 4/5 times, you still get it that 5th time and because of a thing called CRC you know it was exactly the message sent).

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