EPIRB Distances

mjkinch1

mjkinch1

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I am thinking of getting an EPIRB, and quite like the Mcmurdo range.

Quick question, if you have a non GPS version, and set it off, what is the size of the search area (if that makes sense). I gather with a GPS it is down to a couple of meters, so basically they cant miss you.

If its that great why do they still sell the non GPS version.

Any clarification appreciated

Thanks
 
Close enough - the EPIRBS include a homing signal (121.5MHz) to guide SAR to you once they are in the general vicinity.

The big advantage of the GPS version compared to the non-GPS version is that the GPS delivers your position faster than the non-GPS (which relies on Doppler effect of the satelites passing overhead to fix the position). IIRC on average the GPS will lead to your position being fixed 40mins earlier.

In the past there have been doubts cast on the ability of some of the GPS EPIRBS to get a GPS fix in real world conditions.

The truth is that the chance of having to use your EPIRB is very low - the chance of the difference between GPS and non-GPS versions making a difference is even smaller
 
I looked into this a while ago and found quite a bit of info on the web. The satellites are in a low earth orbit and rely on dopler to fix the position accurately. It requires muliple passes to do this.

I can't remember the specifics but as far as I remember, detection of a triggered 406 EPIRB is relatively rapid. However, it can take up to around 45 mins to fix the position. The accuracy of the fix will around 3km. The onboard 121.5 can then guide SAR resources in from 3km provided they get there before it dies.

If the EPIRB has its own GPS then the initial reception will also give an accurate position.

So the advantage of an onboard GPS is not accuracy, although it would help, but time to get an accurate fix.
 
Thanks for that - it makes me think the GPS is probably not worth the extra money, so I will go with a standard model.

Thanks everyone for your help

Martyn
 
Don't forget that if it takes (say) 40 minutes for the non-GPS EPIRB to provide a fix then (presumably) if the non-GPS EPIRB is not transmitting reliably for the whole of that 40 mins then it may never get a usable fix. So it might not be just an issue of delay in rescue, but no rescue at all if for any reason the EPIRB signal fails to reach the satellites for 40 mins.

I am looking to put new batteries into my existing EPIRB or buy new, and having considered this will be staying with a GPS EPIRB because the EPIRB is a core feature of my emergency strategy (which was arrived at after discussions with Falmouth Coastguard and the examiner who took my LRC radio exam, an acknowledged expert in this field).
 
Even GPS EPIRBS do not provide instantaneous alert - IIRC they have to wait for a satelite to come within range so the alert time can still be up to an hour
 
I think I have changed my mind again....Having read the FAQ and comments perhaps I will get a GPS version, after all the difference is cost is not huge and as lemain says, it is going to be my final backup strategy when everything else has failed.
 
the satelitte picks up the 406khz signal, the 121.5mhz is for final homing....in my experiance from sea level on an Arun class lifeboat a 121.5 signal has not been recieved at a distance of 1k, this is greatly improved as the DF reciever is raised i.e. from a helo at 500ft or a nimrod at a greater altitude....in my days at the Oceanic Control Centre (Shanwick) quite often we recieved reports from aircraft flying the atlantic at 35000ft of 121.5 sarbe beacons in mid atlantic.

The MRCC at Kinloss is the recieving centre for all 406khz satelitte hits, these are normally noted then await a second pass and confirmation of the signal before any real action taken.......most 406 hits are also mirror images of where they actually are........not a precise science from what I saw on my last visit!!

Paul.
 
[ QUOTE ]
The MRCC at Kinloss is the recieving centre for all 406khz satelitte hits, these are normally noted then await a second pass and confirmation of the signal before any real action taken.......most 406 hits are also mirror images of where they actually are........not a precise science from what I saw on my last visit!!

[/ QUOTE ]I don't really understand what this means in practice. From your experience, how long would you expect it take before a non-GPS 406 beacon to result in a SAR, and how long for a GPS 406? How recent is your experience and does it conflict with the link posted above (the one that describes how the system works)?
 
I understand only the 406 beacons are recieved by satellite.....from my last visit to MRCC each pass only comes around about every 20 mins or so, it could be 40 though. Therefore it may take well over the hour before any action is really taken due to the mirror images being recieved...these provide most of the false alarms.

I still understand VHF 121.5mhz is used only for final homing of the search aircraft/helicopter from a range dependant upon alltitude of said aircraft!

Paul
 
What about the difference between GPS and non-GPS 406 beacons? I wasn't aware of any 'mirror images' - what are they and do they affect both GPS and non-GPS beacons?

We have already read that the GPS EPIRBs are, in the first instance, received by geostationary satellites which don't require any passes at all because they are geostationary.

So in principle GPS EPIRBS could give an almost instant fix whereas non-GPS EPIRBS cannot possibly give a fix until sufficient doppler information has be received. At least, that's what I understood, is it correct?
 
Sorry if I have confused you as really have been refering to non GPS variants, these do suffer from mirror image hits....not up to speed with the GPS data variant so really cannot help in that respect......previous web site though gives good explanation of the system.

Paul.
 
This is kind of the clincher -
If you are likely to be in area poorly served by Coastguard and other SAR services, or in the middle of the ocean, your quickest rescue is likely to come from a nearby fishing or merchant vessel, diverted to your position by a call from the shorebased rescue services. These vessels will not be able to home on your 121.5MHz transmitter, but if they have your GPS position, they will be able to steer right up to you.

On a seperate point, I assume the general wisdom is to go for an automatic float free, not a manual trigger version.
 
We have a GPS and a non-GPS EPIRB both of which are mounted in brackets that contain a magnet, holding the automatic function off. So if you sink with the EPIRB in the bracket, it will not go off. Presumably that is to reduce false alarms and we have a spare bracket for use when transporting back to the factory for service. We also have a manual GPS Personal Locator Beacon (GPS 406 EPIRB) that you could almost put in a pocket, but wear on a belt. This one is great for the tender and when we are going out in poor conditions, getting back late, or are miles from other boats, we take this with us in the tender (as well as an anchor and the VHF HH and a mobile phone). The 'automatic float free' one has to be manually unhooked or it doesn't float anywhere and you have to tie it onto something so you don't lose it. There is a lanyard for that purpose. You really need to think through the usage and tell everyone how to use it or it could be pretty pointless.
 
[ QUOTE ]
This is kind of the clincher -
[On a seperate point, I assume the general wisdom is to go for an automatic float free, not a manual trigger version.

[/ QUOTE ]
I've only got one - so I've got one that fits in my pocket.

I think I'm far more likely to need one because I've fallen overboard than because the boat has sunk
 
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