17 August 2010

PLB problem and modification

I have been using a Personal Locator Beacon for a few years.
While Australian Maritime laws require that I should carry an EPIRB while paddling offshore (more than two nautical miles from shore in non sheltered waters) I find that for sea kayaking a PLB is possibly a safer unit to have in case of emergency.
I believe that a beacon should be carried on the person and be readily accessible in case of emergency instead of being stored below deck when kayaking.
Current EPIRBs are too bulky to be carried on my PFD.

I have my PLB attached to the back of my life jacket and is exposed to the marine environment, often submerged while rolling or swimming.

While the manufacturer does assure that my PLB (model GME MT 410G) is a waterproof and submersible unit there are several documented cases (that I am aware) of malfunction of the unit by water intrusion.

On a trip to the Whitsunday Islands our group had one GME unit activate by itself without any prompting by the user.
The PLB started to beep suddenly giving the same signal as transmitting an emergency call.
We were able to paddle to shore and had the presence of mind to quickly deactivate the unit by disconnecting the battery.
Here are the steps that we performed to disable the PLB:
To do so, the top cap had to be unscrewed and removed.
unscrewing cap
removing cap

After removal of the cap the plug that connects the battery was separated from the electronics.
removing battery connector
water droplets on battery
salt water present inside the PLB
At close inspection and careful analysis I noticed the small "O" ring under the central screw was deformed.
It appears to be a design flaw.
GME designed the unit to have the "O" ring under the screw under compression but did not create a suitable receptacle for the "O" ring to be housed and prevent lateral expansion.
So, after a while the "O" ring slips away from the screw's head and allows leakage. The faulty unit was returned to GME and repaired under warranty.
I was assured that it was an isolated case but after the recent reports of other GME units malfunctioning I have my doubts.
GME has not recalled the units nor updated the design.

I have therefore decided to address the problem myself and modified the unit to possibly prevent the same problem occur again.
The central screw on the cap is recessed deeply into the shape of the cap.
I simply cleaned the area and applied a liberal amount of polyurethane sealant (not silicone) to the cavity and worked it really well to ensure good adhesion of the sealant.

In a few years time when the battery of the PLB unit will need replacing there might be a bit of a problem reaching that screw but in the meantime I hope that at least my unit will possibly not malfunction there.


  1. Looks like as good a fix as possible without opening the case!

    My GME MT 410G self activated a few months ago - and there were water droplets inside when I opened it to disconnect the battery. It was replaced under warranty so I'll give the polyurethane sealant a go on my new one before I take it out to sea :-) Hopefully this fix will do the trick!



  2. Gnarly Dog,
    I have had the same problem with my GME PLB. It started beeping and I was told to wrap it in Tinfoil and place it in the microwave (without it being on) as they are designed to keep radio wave in. GME replaced the unit. I had purchased the unit off a retiring paddler who had also had a unit replaced so these are not isolated incedences. Thanks for the fix.

  3. Yep, I had exactly the same issue - self-activation due to water ingress into the unit (according to GME, who did replace the unit under warranty) which resulted in full scale SAR response, including rescue helicopter! Interestingly, the beacon only transmitted for 1 minute on 406 Mhz, which was not enough to get a GPS location fix. The chopper was tasked as a result of verbal location information from my registered contacts. Having seen this blog post, I had put silicon over the screw as you suggested. However, GME said that heating/cooling of the unit (hot sun at lunchtime followed by first cold wave on launching?) can result in the air inside the unit contracting, creating a partial vacuum and sucking in moisture.

  4. Guy, thank you for letting us know of your findings and I am concerned that it lead to a full scale unwarranted rescue however I don't buy GME’s story.
    If the unit is supposedly leak proof should there be air "exchange” between the inside of the unit and outside?
    If GME theory is correct then their PLB unit should let some air out by expanding when hot and eventually suck that air back in at some stage.
    That might be OK for kayak hatch where there is a huge volume of air to deal with (and a few drop of water won’t matter too much) but is not OK in an electronic unit that is meant to be totally sealed.
    Do GME's PLB have an air permeable membrane (like Gore-Tex)?
    I though that a truly sealed unit meant just that: sealed.
    Happy to hear a more comprehensive explanation on GME's version of events but I would like it be scientific, not just anecdotal :-)

  5. Thanks Gnarlydog - I should have expanded on the statement from GME, made to me by the Product Manager for the beacon, Matthew Heath, over the phone. I took notes of the conversation, in which he suggested that the rubber seals do perish over a period of time (not specified) which can make them more prone to moisture ingress due to heating/cooling of the unit. He also said that the beacons are manufactured with silicon sachets inside the unit to absorb any moisture that does find its way in - which suggests that the designers have anticipated the problem or are adopting a 'belt and braces' approach. I think this heating/cooling issue is a problem with other supposedly waterproof sealed electronic units: I have had some waterproof cameras (notably Panasonic Lumix) and a radio (Standard Horizon HX850S - IP7 rated) which have suffered from moisture ingress.

  6. My GME MT 410G self activated and turned out to be water in, was sailing a small sit on top cat at the time.. GME replaced it but don't know if i can trust using it on a small boat that you keep getting wet on any more... Any advice as to what would be better to get? Thanks Daniel

    1. I had mine replaced by GME but since I did the modification there has been no issues

  7. Can you tell me if the unit needs to be registered with any particular agency before it is deployed in an emergency at a later date? Cheers.

    1. Mark, I believe that any beacon must be registered with the local National Agency so they know what to look for when a rescue is necessary (in my case they will be looking for kayak, not a large sailing boat or other vehicle). On the other hand I wonder how they go about when one just rents the unit (yes, rental are available); surely the details are not updated every time a different person hires the it....


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