EPIRB Batteries

[maby]

I think the PLBs were set off some hours apart.

A PLB that won't work if the wearer is in the water is really not much use at all. I am sure they are all waterproof - but the antenna is such that they may not transmit well if not attended

They are all waterproof to a depth of several metres, but they do need to be above the water for the antenna to get a signal out. A full size EPIRB will float upright and continue to work unattended until its battery fails. A PLB is far smaller - many are not buoyant without a buoyancy case and I don't think any are guaranteed to float upright with the antenna clear of the water - a PLB attached to an unconscious person or floating on its own in the water is unlikely to be received.

 

[Buck Turgidson]

Yes, of course they are different satellites, but the two systems could have been designed to provide an integrated system. It would be very easy for the GPS system to accept a data feed from SARSAT that lists PLBs currently being received and forward this on in a reserved timeslot - if the two systems were being designed simultaneously today, I'm sure that they would be cooperating in this way - they were not designed together and they do not interface - which is a pity.

Why interrupt GPS signal with non nav data? The correct network to send receipts would be the SARSAT network but it's nothing more than a warm feeling for the survivors but in reality what does it mean? The rescue currently in the news has been called off. Should you tell the casualties having confirmed receipt?

Sat phones are readily available and serve as 2 way comms. GPS is a navigation system and SARSAT/COSPAS is for search and rescue. How power hungry do you want to make the survival beacon in order to incorporate them all into one?

 

[RobbieW]

On turning EPIRB/PLBs on & off; iirc this is exactly what Bullimore did in the Southern Ocean which alerted the SAR teams that he was still alive, I think he used an SOS pattern of transmissions.

On replacing PLB batteries; my McMurdo Fastfind (now a bit dated) has a users replaceable battery. The current incident makes me reconsider the cost (£200ish)/benefit of carrying one. I've never seen an EPIRB with a user replaceable battery, they are designed for harsher usage & the batteries sealed inside the unit - not the sort of exchange that would be easy in a liferaft.

Yes, of course they are different satellites, but the two systems could have been designed to provide an integrated system. It would be very easy for the GPS system to accept a data feed from SARSAT that lists PLBs currently being received and forward this on in a reserved timeslot - if the two systems were being designed simultaneously today, I'm sure that they would be cooperating in this way - they were not designed together and they do not interface - which is a pity.

Thats certainly true, however the GPS system, and sat transmission protocol was designed in the early 70s - the first operational satellite was in place in 1978. Thats way before satellite SAR systems were being designed and given GPS' military origins I doubt that anything other than targetting was on the designers mind. It would make far more sense to berate the SARSAT designers for not implementing a handshake protocol. This is the only description of the GPS protocol I've found:

GPS satellites transmit two low power radio signals, designated L1 and L2. Civilian GPS uses the L1 frequency of 1575.42 MHz in the UHF band. The signals travel by line of sight, meaning they will pass through clouds, glass and plastic but will not go through most solid objects such as buildings and mountains.
A GPS signal contains three different bits of information — a pseudorandom code, ephemeris data and almanac data. The pseudorandom code is simply an I.D. code that identifies which satellite is transmitting information.
Ephemeris data, which is constantly transmitted by each satellite, contains important information about the status of the satellite (healthy or unhealthy), current date and time. This part of the signal is essential for determining a position.
The almanac data tells the GPS receiver where each GPS satellite should be at any time throughout the day. Each satellite transmits almanac data showing the orbital information for that satellite and for every other satellite in the system.

 

[maby]

Why interrupt GPS signal with non nav data? The correct network to send receipts would be the SARSAT network but it's nothing more than a warm feeling for the survivors but in reality what does it mean? The rescue currently in the news has been called off. Should you tell the casualties having confirmed receipt?

Sat phones are readily available and serve as 2 way comms. GPS is a navigation system and SARSAT/COSPAS is for search and rescue. How power hungry do you want to make the survival beacon in order to incorporate them all into one?

The PLB includes a GPS receiver, so I don't see how putting a handshake down the GPS protocol would make it any more power hungry - in fact quite the contrary - as it stands, the PLB is sending out its ping several times per hour and consuming a lot of battery power - if it were able to get a positive handshake, it could fall back to a battery saving mode and stretch them out a lot longer. Sending the handshake from SARSAT would push up complexity and consumption since it would require an extra receiver in the PLB.

 

[Buck Turgidson]

The PLB includes a GPS receiver, so I don't see how putting a handshake down the GPS protocol would make it any more power hungry - in fact quite the contrary - as it stands, the PLB is sending out its ping several times per hour and consuming a lot of battery power - if it were able to get a positive handshake, it could fall back to a battery saving mode and stretch them out a lot longer. Sending the handshake from SARSAT would push up complexity and consumption since it would require an extra receiver in the PLB.

You do know that GPS is not geostationary?
I think MH370 has sent many people potty!

If you want two way comms there are plenty of available systems. If you want to burden GPS with comms you need to replace the navigation system with a new design. OK for Galileo but a nonstarter for GPS. It's a NAV system not a COMMS system. SARSAT is a 1 way comms system, there are several other 2 way comms systems. They would be suitable for COMMS.

Now if you want to start charging for the service I could put a constellation up that does the lot. Lets say it's a requirement for every vessel traveling outside VHF range of land and my subscription is £3000 a year. I think I would probably show a profit in 5 to 10 years.

 

[maby]

You do know that GPS is not geostationary?
I think MH370 has sent many people potty!

If you want two way comms there are plenty of available systems. If you want to burden GPS with comms you need to replace the navigation system with a new design. OK for Galileo but a nonstarter for GPS. It's a NAV system not a COMMS system. SARSAT is a 1 way comms system, there are several other 2 way comms systems. They would be suitable for COMMS.

Now if you want to start charging for the service I could put a constellation up that does the lot. Lets say it's a requirement for every vessel traveling outside VHF range of land and my subscription is £3000 a year. I think I would probably show a profit in 5 to 10 years.

I know very well how GPS works - I have worked with it for years. I'm commenting on how an integrated solution should have been designed - and accepting that the current solution is not integrated. In addition to the timing signals that each GPS satellite transmits, it also sends out large data blocks which contain the ephemeris and almanac data - it would have been very easy to reserve a sufficient slot in those blocks to positively acknowledge all active SAR beacons being received. If the Americal military had thought of it when they designed it, I'm sure they would have done it - they would have loved to be able to notify a pilot shot down behind enemy lines that they knew where he was and were coming to get him.

 

[Buck Turgidson]

I know very well how GPS works - I have worked with it for years. I'm commenting on how an integrated solution should have been designed - and accepting that the current solution is not integrated. In addition to the timing signals that each GPS satellite transmits, it also sends out large data blocks which contain the ephemeris and almanac data - it would have been very easy to reserve a sufficient slot in those blocks to positively acknowledge all active SAR beacons being received. If the Americal military had thought of it when they designed it, I'm sure they would have done it - they would have loved to be able to notify a pilot shot down behind enemy lines that they knew where he was and were coming to get him.

I happen to know quite a lot about this.

And the ephemeris includes the time signal. Its' PRN, Ephem, Almanac.

 

[lw395]

I know very well how GPS works - I have worked with it for years. I'm commenting on how an integrated solution should have been designed - and accepting that the current solution is not integrated. In addition to the timing signals that each GPS satellite transmits, it also sends out large data blocks which contain the ephemeris and almanac data - it would have been very easy to reserve a sufficient slot in those blocks to positively acknowledge all active SAR beacons being received. If the Americal military had thought of it when they designed it, I'm sure they would have done it - they would have loved to be able to notify a pilot shot down behind enemy lines that they knew where he was and were coming to get him.

They already had that, 243MHz and 168 MHz voice comms were built into military epirbs or ELT's ages ago.

 

[LadyInBed]

My PLB has user replaceable battery.
My thinking when I bought it was to save cost on battery replacement and if I did an ocean crossing I could carry a couple of replacement batteries.

 

[nigelmercier]

They can certainly be turned off - to allow for unintentional activation...

It should be pointed out that there is a procedure to follow in this case, and it doesn't involve just turning it off!

I agree with the OP that something should be done to allow the battery life to be extended. Perhaps software like in a cell phone when searching for cells: they gradually increase the time between pings.

 

[OceanSprint]

I still cannot understand why EPIRBS can not have alternative power supplies. Imagine sitting in a liferaft with a fully functionable satellite beacon, that could work if it had a few volts? We have wind up radios, wind up torches. Why not wind up EPIRBS? Is it that the profit is in selling the sealed battery? If it is beacuse of safety standards,eg RORC, then change them.

 

[sailor211]

Getting a PLB to float with aerial upper most is I think the main problem. More important than battery life. I am sure that I could float and keep my self alive for some time if the water was warm enough. However both our PLB need to be held upright to function. I suspect I would soon tire of holding the thing with aerial up. EPIRB is self operating but big and heavy. It's getting the balance of a device I can keep on me small and light, but will work unattended when operated.

 

[OceanSprint]

Getting a PLB to float with aerial upper most is I think the main problem. More important than battery life. I am sure that I could float and keep my self alive for some time if the water was warm enough. However both our PLB need to be held upright to function. I suspect I would soon tire of holding the thing with aerial up. EPIRB is self operating but big and heavy. It's getting the balance of a device I can keep on me small and light, but will work unattended when operated.

I know this sounds crazy, and I am not joking, but would a velcro patch on top of a lifejacket hood, plus velcro on thePLB work? With a lanyard to stop it being lost if detached?

 

[prv]

I know this sounds crazy, and I am not joking, but would a velcro patch on top of a lifejacket hood, plus velcro on thePLB work? With a lanyard to stop it being lost if detached?

The Kannad AIS SART is physically quite similar to a PLB. It can be mounted on the upper part of a lifejacket bladder and looks like it ought to stay reasonably clear of the water:

(Note the aerial in front of the guy's face; the aerial on, say, a Fastfind 220 sticks up in a very similar way.)

Those who carry PLBs in their lifejackets presumably ought to mount them the same way.

Pete

 

[OceanSprint]

Those who carry PLBs in their lifejackets presumably ought to mount them the same way.

A much more sensible solution, and one I will try and emulate with my PLB.

 

[lw395]

In reality, the life of a PLB battery is pretty much dictated by its size.
There is a lot of commercial pressure to keep PLBs small, indeed many of us are more likely to have one if it's small enough to go into normal LJ packed for normal wear.
That is what a PLB is for, it is not a cheaper smaller EPIRB.

The other point is that the nature of lithium batteries means that they will operate for longer than the minimum quoted when new, and just about fulfll their spec when at maximum shelf life.
So a shiny new PLB might well keep transmitting long after you've expired.

 

[Sybarite]

In reality, the life of a PLB battery is pretty much dictated by its size.
There is a lot of commercial pressure to keep PLBs small, indeed many of us are more likely to have one if it's small enough to go into normal LJ packed for normal wear.
That is what a PLB is for, it is not a cheaper smaller EPIRB.

The other point is that the nature of lithium batteries means that they will operate for longer than the minimum quoted when new, and just about fulfll their spec when at maximum shelf life.
So a shiny new PLB might well keep transmitting long after you've expired.

In addition to electronic devices would it be feasible to have a kite on board a liferaft made of foil with foil trailors?

 

[Gordonmc]

My PLB has user replaceable battery.
My thinking when I bought it was to save cost on battery replacement and if I did an ocean crossing I could carry a couple of replacement batteries.

I recently bought a McMurdo Fastfind Plus specifically because it has a user-replacable battery.
It was new and unregistered but had been sitting on a shelf somewhere and the battery was out of date although the self-test showed it was charged.
I bought a replacement battery and will keep the old one as a reserve power source.

 

[KellysEye]

>My strategy offshore would always be on for 4 hours then off for 2 hours on for 1 until rescue

It can take four hours for a satellite to pick up a signal from an EPIRB, if it took a few minutes more you would be in deep trouble especially if you only then used it for 1 hour at a time. They are designed to stay on for 48 hours which guarantees pick up, never turn it off.

 

[Buck Turgidson]

>My strategy offshore would always be on for 4 hours then off for 2 hours on for 1 until rescue

It can take four hours for a satellite to pick up a signal from an EPIRB, if it took a few minutes more you would be in deep trouble especially if you only then used it for 1 hour at a time. They are designed to stay on for 48 hours which guarantees pick up, never turn it off.

It can take UP TO 4 hours for LEOSAR to triangulate position using Doppler.
GEOSAR will receive the signal immediately.
If your EPIRB/PLB has embedded GPS the position will be received by GOESAR immediately (as soon as the PLB has fixed it's position)

So, for a GPS equipped EPIRB/PLB there is no problem with my strategy which was derived from knowledge rather than guess work.