Is GPS on an EPIRB/PLB Worth the Extra Cost?

[Tranona]

Faith purchase Tranona! Consequence purchase maybe. Rational, not at all. Who knows what the statistics are but they may prove that one does not need to buy any safety gear based on a rational conclusion.

No. Its "faith". You have to believe that you are going to need it, and that it is going to work when you do. Regrettably there is little hard evidence to support either, so what else can it be but faith? What you are describing is passive "safety" rather than "active" which is a very different thing.

When have you ever seen an advert for these things that says "X lives saved last year because they had our MK9 gizmo - Y died because they did not. Buy now before its your turn".

Instead all you get is "our Mk9 can do all sorts of wonderful things" and the implication that somehow you are failing yourself, your loved ones and society in general if you don't have one - trust us, we know.

 

[maxi77]

Certainly the mobile pnone is not always a good backup to ones VHF, we have so far sailed from the Forth to the Solent and on several occasions we have lost phone coverage. I suspect that at least once and possibly more often we would have been well outside handheld VHF range of a CG antennae. Also several times we were also outside likely parachute rocket range. As a reslt we have a gps plb in the grab bag.

Now the legs we do tend to be planned to be less than 10 hours where possible and never planned to be more than 18 hours, so we are not adventurous offshore sailors but the benefits in terms of potential improvement of rescue response times then the small extra for the gps version of the plb was well worth it.

 

[grumpy_o_g]

So what would be really good is a hand-held VHF with a built GPS and DSC to alert local shipping and the coastguard in busy inshore waters (as is available in the US)?

What a shame our idiot administrators don't agree. The same sets have to have the DSC function disabled to get EU certification. They seem to think DSC is much better employed warning us we're about to hear the weather forecast.

 

[BrendanS]

don't think it's anything to do with idiot administrators. Icom had a handheld with DSC which was discontinued due to lack of sales. We used to have a very good Icom guy on here, who used to explain all this sort of stuff to us. Unfortunately, he left Icom.

 

[dt4134]

... but the benefits in terms of potential improvement of rescue response times then the small extra for the gps version of the plb was well worth it.

That's the bit I'm trying to get at.

I started off assuming GPS was better but then I wondered if the non-GPS ones were a waste of space why were they still on sale? Why weren't the RNLI/RYA/MAIB etc insisting on GPS over non-GPS.

So when I looked into it, it seems the only difference is that with the non-GPS SAR resources they don't quite get as close before they have to use the 121MHz homing signal. OK, alan_d pointed out that non-SAR resources don't have the homing beacon but that seems a small factor.

In general there seems to be no reason to believe there will be a difference in response times between the GPS & non-GPS versions of 406MHz EPIRBs/PLBs(this wasn't true for the old 121MHz EPIRBs but they're obsolete now).

Most other answers can be paraphrased (toungue in cheek of course) as 'spending more money on safety equipment makes you feel better'.

Yes the difference for a PLB isn't that big, but the difference for an EPIRB is much more so. You could pretty much get both a non-GPS EPIRB and PLB for the price of a GPS EPIRB.

So far no one seems to be telling me my research is wrong or that there are major factors I haven't considered.

Incidentally the MAIB report on the Aquila would back up your concerns about gaps in the VHF coverage in Scotland (I maybe shouldn't mention the bit about the EPIRB getting trapped in the superstructure).

 

[bedouin]

last time I looked this up the official line was that it can take over an hour for the emergency services to get a fix - something to do with satellites in range and the the number of passes required to fix your location. So in theory going for the GPS equipped version could mean you get help an hour earlier.

So the question is whether you can envisage a situation where that difference of one hour would make a significant difference to the outcome.

However these days the price difference between the GPS and non-GPS versions is only about £30-40 so if I were buying one now I would probably go for the GPS version.

 

[pvb]

So what would be really good is a hand-held VHF with a built GPS and DSC to alert local shipping and the coastguard in busy inshore waters (as is available in the US)?

What a shame our idiot administrators don't agree. The same sets have to have the DSC function disabled to get EU certification. They seem to think DSC is much better employed warning us we're about to hear the weather forecast.

Not true! See the Standard Horizon HX851E - yours for around £230. DSC handheld, GPS, Li-Ion battery, waterproof, floats face up, makes tea, etc, etc.

 

[maxi77]

That's the bit I'm trying to get at.

I started off assuming GPS was better but then I wondered if the non-GPS ones were a waste of space why were they still on sale? Why weren't the RNLI/RYA/MAIB etc insisting on GPS over non-GPS.

So when I looked into it, it seems the only difference is that with the non-GPS SAR resources they don't quite get as close before they have to use the 121MHz homing signal. OK, alan_d pointed out that non-SAR resources don't have the homing beacon but that seems a small factor.

In general there seems to be no reason to believe there will be a difference in response times between the GPS & non-GPS versions of 406MHz EPIRBs/PLBs(this wasn't true for the old 121MHz EPIRBs but they're obsolete now).

Most other answers can be paraphrased (toungue in cheek of course) as 'spending more money on safety equipment makes you feel better'.

Yes the difference for a PLB isn't that big, but the difference for an EPIRB is much more so. You could pretty much get both a non-GPS EPIRB and PLB for the price of a GPS EPIRB.

So far no one seems to be telling me my research is wrong or that there are major factors I haven't considered.

Incidentally the MAIB report on the Aquila would back up your concerns about gaps in the VHF coverage in Scotland (I maybe shouldn't mention the bit about the EPIRB getting trapped in the superstructure).

At the end of the day it is time to rescue that is affected. Now with no GPS they need to first fix your position rather than just read it of the screen, then there is also the potential for additional delays in finding you because the non gps derived position has a cep of kms rather than metres. Another useful reality of a gps derived position is that another receiver will end up in almost exactly the same position irrespective of the cep error in the gps position, a fact that makes geocacheing practical.

My fear with VHF is not lack of coverage but failure of my VHF for some reason. I have been in a boat that suffered total power failure leaving only handhelds with limited life.

I do think than in my position being reached say an hour earlier was well worth the extra cash because it seriously enhances my chance of survival.

 

[pteron]

According to ACR, the average fix time for the non GPS versions is 46 minutes. If I'm floating in my lifejacket in frigid waters, that additional 46 minutes could be the difference between life and death.

My PLB has GPS.

 

[Tintin]

The way I look at it is that it is immersion time that kills, not the initial immersion,unless you are unconscious and not wearing an auto lifejacket - oops, didn't mean to light that fire ;-)

I like the idea of being found quickly and am prepared to pay an extra £40 for that pleasure - the cost of a meal out somewhere or just over a half tank of fuel in my passat.

If I ever have to use it in anger I would rather say, "dammit the cost of that meal was well used" to the rescuers, rather than be swimming around for an hour or so longer remembering all the research I did to convince myself I had saved myself the money.

Buy with GPS.

 

[dt4134]

I've been doing a little bit more research myself.

Distress signals are picked up by GEO & LEO satellites (GEO= Geostationary Earth Orbit & LEO = Low Earth Orbit). The GEO satellites only cover between 70deg N & S but that's irrelevent for sailing around Britain & Ireland.

Only LEO staellites can work out a position using doppler techniques. They cover the poles as well.

A single position is considered ambiguous, so a GPS position has to be backed up by a doppler position to be considered resolved. Without GPS, two doppler positions are required to resolve the ambiguity.

There's a flow chart on it which you can see on P22 of this doc: http://www.cospas-sarsat.org/images/stories/SystemDocs/Current/A1OCT29.09CompleteDoc.pdf


What I don't yet understand is what the practical impacts are when the Coastguard are dealing with an alert which has an unresolved positional ambiguity and what impact that might have on response times, especially when you consider the other steps in the process, such as checking with contacts, and the time taken for a lifeboat or helicopter to reach that position.


I realise a lot of forumites believe a GPS EPIRB will get them rescued quicker but I still haven't found the solid basis for that belief.

 

[maxi77]

I've been doing a little bit more research myself.

Distress signals are picked up by GEO & LEO satellites (GEO= Geostationary Earth Orbit & LEO = Low Earth Orbit). The GEO satellites only cover between 70deg N & S but that's irrelevent for sailing around Britain & Ireland.

Only LEO staellites can work out a position using doppler techniques. They cover the poles as well.

A single position is considered ambiguous, so a GPS position has to be backed up by a doppler position to be considered resolved. Without GPS, two doppler positions are required to resolve the ambiguity.

There's a flow chart on it which you can see on P22 of this doc: http://www.cospas-sarsat.org/images/stories/SystemDocs/Current/A1OCT29.09CompleteDoc.pdf


What I don't yet understand is what the practical impacts are when the Coastguard are dealing with an alert which has an unresolved positional ambiguity and what impact that might have on response times, especially when you consider the other steps in the process, such as checking with contacts, and the time taken for a lifeboat or helicopter to reach that position.


I realise a lot of forumites believe a GPS EPIRB will get them rescued quicker but I still haven't found the solid basis for that belief.

Well you have just explained why GPS may improve the response time, they need two positions LEO positions take up to one hour so two takes 2 hours, whilst GP is instant through the GEO sattelites, there being 2 covering our local waters.

 

[dt4134]

Well you have just explained why GPS may improve the response time, they need two positions LEO positions take up to one hour so two takes 2 hours, whilst GP is instant through the GEO sattelites, there being 2 covering our local waters.

I don't believe two LEO positions take anywhere near that long. It is variable though as it depends quite on where the satellites are at the time.

Interestingly, GPS positions are considered as only one position no matter how many satellites receive the broadcast, so you still need a LEO position.

However, I don't yet understand the practical implications on the response of having only one position (an unresolved ambiguity as they say in the documentation). Presumably they'd start to act on the first report identifying the EPIRB, even if it is only calling the contact numbers given in the registration.

Still, it seems certain that VHF & flares would give a faster response than either type of EPIRB, providing you're in coastal or busy waters and have time to use them (however I'm not sure I really want to trigger that discussion).

 

[Tranona]

I realise a lot of forumites believe a GPS EPIRB will get them rescued quicker but I still haven't found the solid basis for that belief.

Like you I am surprised there is no firm data available. Given that EPIRB and PLB are monitored through one source it should not be difficult to provide information on simple facts like the number of times activated (for real), response times (by class of beacon) and outcomes.

Either somebody is hiding something, or more likely, the number of "real" emergencies is so low that there are no meaningful statistics.

You have obviously read the MAIB reports and seen how few real emergencies (life lost or near life lost) ther have been that involve pleasure craft. Within those very few mention EPIRB usage. One would think that a situation so severe as to warrant an EPIRB deployment would justify at least a preliminary MAIB investigation - where are they?

 

[maxi77]

I don't believe two LEO positions take anywhere near that long. It is variable though as it depends quite on where the satellites are at the time.

Interestingly, GPS positions are considered as only one position no matter how many satellites receive the broadcast, so you still need a LEO position.

However, I don't yet understand the practical implications on the response of having only one position (an unresolved ambiguity as they say in the documentation). Presumably they'd start to act on the first report identifying the EPIRB, even if it is only calling the contact numbers given in the registration.

Still, it seems certain that VHF & flares would give a faster response than either type of EPIRB, providing you're in coastal or busy waters and have time to use them (however I'm not sure I really want to trigger that discussion).

It is certainly difficult to find exact details of almost any part of the system, but I found a comment that indicated the typical time for an LEO pass was one hour. In reality though unless it is in very rapid interval you have to wait double the time to validate your position because you need two passes.

I don't dispute that for most of us most of the time flares or VHF will generate the fastest response, but we do find ourselves out of flare range from time to time and various failures can deprive you of your VHF, even when like me you carry a spare set and more than one handheld.

For my present situation where I am sailing in what for me are unknown waters the addition of a GPS PLB gives myself and the mrs just a little extra comfort despite my intention to avoid at almost any cost the need to use it.

 

[dt4134]

Either somebody is hiding something, or more likely, the number of "real" emergencies is so low that there are no meaningful statistics.

I think the most likely explanation is I haven't worked out where to look for them. Or that they're not on the internet.

I do agree with you that the number of real emergencies amongst pleasure craft is low, but for the GPS Vs non-GPS EPIRB question they should be able to take data from all types of craft, so meaningful statistics should be available, and probably are somewhere.

There's certainly statistics on the false alarm rate and the number of false alarms that are resolved by telephone.

Perhaps it could be an interesting subject for a bit of investigative journalism from YM or PBO. Or maybe I'll just keep looking myself.

 

[Tranona]

I only raise it because I have looked. Nothing from Coastguard, nothing from RNLI, nothing in summary from MAIB reports (and as you know little in detailed report).

When you consider the millions spent on these devices (and liferafts) each year, the lack of information on their effectiveness in performing their primary function is appalling.

As in this thread the debate is always about theoretical benefits rather than sharing of empirical evidence.