Stingo
Well-known member
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S&R mission finds the wrong liferaft
- Thread starter Stingo
- Start date
Adios
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"Carotta put out a mayday signal on May 31, but there was just enough power left in his PLB (personal locator beacon) to activate it for a few seconds, several days apart — and that wasn’t long enough for rescue personnel to get an accurate fix on his location."
How does that work? I thought it just uploads GPS coordinates which is surely a tiny data packet. If the device wasn't on long enough to get a GPS fix would it send anything before getting a fix?
"Aaron Carotta had turned on his PLB again — this time long enough for the guardsmen to pick up a complete set of coordinates. They did a flyover to confirm they‘d seen him, and within hours he was picked up by an oil tanker that had been diverted to rescue him.
It’s probably fair to say that the chances of a search party’s accidentally finding a guy in a liferaft, without location info in advance, is about one in a million. Truly serendipitous!"
I'm a bit under awed that they found him "accidentally" with a complete set of coordinates.
How does that work? I thought it just uploads GPS coordinates which is surely a tiny data packet. If the device wasn't on long enough to get a GPS fix would it send anything before getting a fix?
"Aaron Carotta had turned on his PLB again — this time long enough for the guardsmen to pick up a complete set of coordinates. They did a flyover to confirm they‘d seen him, and within hours he was picked up by an oil tanker that had been diverted to rescue him.
It’s probably fair to say that the chances of a search party’s accidentally finding a guy in a liferaft, without location info in advance, is about one in a million. Truly serendipitous!"
I'm a bit under awed that they found him "accidentally" with a complete set of coordinates.
Biggles Wader
Well-known member
Yes but it makes for a much better story if you ignore those inconvenient "details"
Adios
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Yeah I'm terrible to sit next to watching movies too
lustyd
Well-known member
Yes and no. It takes ~30 seconds to get a gps fix from cold start, and it's always a cold start in a PLB. The data is then added to for error checking reasons, and is transmitted at incredibly low data speeds to space, so it might take 30 seconds for the data to get to the satelite, and that's assuming the satellite is in place to receive. It's not a mobile phone and is designed to work in a very specific way. The reason they have the battery life they have is that you are supposed to turn it on and leave it on, don't try to second guess the system.
Adios
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I was curious how all this works in relation to my PLB1 so asked an expert. Here is the reply from Ocean Signal, which clarifies that the PLB unit transmits a distress message with the beacon ID which will be triangulated and only if available ALSO a GPS location.:
Good Afternoon
Although the article does not state it but, because of the picture, there is an implication that the product used was a SPOT X 2-Way Satellite Messenger; this is not the same as a COSPAS/SARSAT PLB.
The SPOT will allow SOS calls to be made but this device is used for other functionality and therefore has a re-chargeable battery – which falls in line with that article statement of “there was just enough power left in his PLB to activate it for a few seconds, several days apart”.
The PLB1 is a COSPAS/SARSAT Personal Locator Beacon.
This means that the battery pack is a primary (non-rechargeable) battery.
The only way that this device would “only have just enough power” would be is the unit had been switched into operating mode (not test mode) previously.
Ocean Signal advise all customers that if the beacon has been previously operated, at any point, or if the battery date has expired, then the battery should be replaced to ensure full operating life time when required.
As long as the beacon conforms to the above then there would be enough power in the unit to turn on for up to an hour a day for 24 days use.
The frequency of the emergency transmission, for a COSPAS/SARTSAT beacon is once every 50 seconds until the unit is switched off.
Assuming that the PLB1 has a clear view of the sky, it should obtain a position fix within 40 seconds (but can take up to 5 minutes depending upon the landscape and conditions).
Once a fix is obtained then the position is encoded into the emergency message – a partial position cannot be used as the system does not allow this – if the position is not valid it is not encoded.
Even if a position cannot be obtained this does not mean that the unit cannot be located.
The COSPAS/SARTSAT system will automatically triangulate a position from the received messages; the encoded position in the message is to give a greater accuracy.
For more information, please visit COSPAS/SARSAT website.
International Cospas-Sarsat Programme - International COSPAS-SARSAT
I hope this helps to answer your question below, if you need any further information or assistance please let me know
Kind Regards
Technical Customer Support
Ocean Signal Ltd.
Good Afternoon
Although the article does not state it but, because of the picture, there is an implication that the product used was a SPOT X 2-Way Satellite Messenger; this is not the same as a COSPAS/SARSAT PLB.
The SPOT will allow SOS calls to be made but this device is used for other functionality and therefore has a re-chargeable battery – which falls in line with that article statement of “there was just enough power left in his PLB to activate it for a few seconds, several days apart”.
The PLB1 is a COSPAS/SARSAT Personal Locator Beacon.
This means that the battery pack is a primary (non-rechargeable) battery.
The only way that this device would “only have just enough power” would be is the unit had been switched into operating mode (not test mode) previously.
Ocean Signal advise all customers that if the beacon has been previously operated, at any point, or if the battery date has expired, then the battery should be replaced to ensure full operating life time when required.
As long as the beacon conforms to the above then there would be enough power in the unit to turn on for up to an hour a day for 24 days use.
The frequency of the emergency transmission, for a COSPAS/SARTSAT beacon is once every 50 seconds until the unit is switched off.
Assuming that the PLB1 has a clear view of the sky, it should obtain a position fix within 40 seconds (but can take up to 5 minutes depending upon the landscape and conditions).
Once a fix is obtained then the position is encoded into the emergency message – a partial position cannot be used as the system does not allow this – if the position is not valid it is not encoded.
Even if a position cannot be obtained this does not mean that the unit cannot be located.
The COSPAS/SARTSAT system will automatically triangulate a position from the received messages; the encoded position in the message is to give a greater accuracy.
For more information, please visit COSPAS/SARSAT website.
International Cospas-Sarsat Programme - International COSPAS-SARSAT
I hope this helps to answer your question below, if you need any further information or assistance please let me know
Kind Regards
Technical Customer Support
Ocean Signal Ltd.
Adios
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I guess mid ocean the smart way to do it might be 10 minutes on, off for an hour then another 10 minutes on to confirm it wasn't an accidental activation then maybe 10 minutes couple of times a day to update, then leave it on full time or at least on more frequently when can hear rescuers, to give the most updated location.
lustyd
Well-known member
I'd say the opposite. Leave it on long enough to be confident the message got through multiple times. Ocean currents are predictable and with a good search area you will probably be found. If you turn it on intermittently it's entirely possible that none of your messages got through and they won't even have a starting point.
Adios
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If it sends a message every 50 seconds they should have 10 or more after 10 minutes. If its got a GPS fix by 1 to 5 minutes at least half will have GPS so they can see the direction and speed of travel. Turn on an hour later for the same and it updates the travel (wind would to some degree effect your position as well as ocean currents even in a liferaft). Repeat a few times a day. If none of the messages get through its broken anyway. I'd rather do that than watch the light go out in just a day. Chances are I'll leave it on full time if i ever use it as I'll be a mile off the south coast of England and this is highly academic anyway. I just like to know how things work.
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lustyd
Well-known member
Again though, it's not a phone. Satelites move about and the info takes a long time to send fully. PLB and EPIRB are designed to run until the battery dies, and the battery is designed to last long enough to ensure the message gets through and ideally give a few updates. It can take 90 minutes for the MRCC to receive your message due to the way the system works. It has been designed to be as foolproof as possible, don't try to out-fool it with crazy antics.
Stingo
Well-known member
What @lustyd says. IIRC, the crew on the Bavaria that lost its keel, mid Atlantic, made the fatal mistake of turning their EPRIB on and off again, repeatedly. We assume to conserve the batteries. All that achieved was making the good folk at MMRC think the EPRIB had a fault, so they ignored it.
I'm sure someone will have a better recollection of this situation than me?
I'm sure someone will have a better recollection of this situation than me?
rogerthebodger
Well-known member
If the EPIRB does not include a GPS location or the EPIRB cannot obtain a GPS signal the satellite must locate it the old way by using Doppler Shift of the transmitted signal . This could take some time as several satellites must receive the signal
On my EPIRB if it in its cradle a magnet disconnects the battery so if its not in the cradle there could be a current drain which is what I think happened wit a lost vessel some years age in the Indian Ocean
On my EPIRB if it in its cradle a magnet disconnects the battery so if its not in the cradle there could be a current drain which is what I think happened wit a lost vessel some years age in the Indian Ocean
ylop
Well-known member
Actually could be significantly longer than that. A PLB is essentially doing a “factory” start as it has no idea where in the world it is or probably the time - so needs 12.5 minutes of uninterrupted view of the sky to get an accurate GPS location. It might be possible with less - but my understanding is that would be a degree of “luck” that the bits of the almanac it downloads first happen to be the useful bits for where you are in the world.
I agreed it would be trivial for the manufacturer to have created a system that instead of transmitting every 50s added increasing gaps between transmissions and went into sleep mode in between - they’ve chosen not to do this (or more likely the GMDSS has been specced not to permit this) because 24 hr of continual data is perceived as more useful than intermittent data. Presumably if the signal stops after a few hours the rescue crews think - shit they’ve sunk/burned out - chance of survivors is less.
Definitetly don’t do 10 on then off for 60 - it’s just about the worst possible way for a GPS to get data. - incomplete almanac for the first fix and then incomplete ephidemeres (sp?) on each subsequent boot. If you need to use a PLB it needs to point to the sky and at sea in the sort of situation where it might be needed that will give you enough interruption without adding your own.
A signal for 24 hrs should give Falmouth the best chance to estimate your future position if they can’t get you help today and they will assume the battery died rather than you did! If you don’t want to rely on that get a proper EPIRB.
capnsensible
Well-known member
Whatever the technical functioning of these devices may be, I found that a Garmin Inreach lost its input several times between the Galapagos Islands and French Polynesia. So perhaps the coverage there isn't Brill. I will leave you techno types to discuss.
By the way,when you get to Nukku Hiva, the only beer they got is tins of Heiniken, so don't go if you are fussy.
By the way,when you get to Nukku Hiva, the only beer they got is tins of Heiniken, so don't go if you are fussy.
lustyd
Well-known member
InReach isn't a proper PLB/EPIRB and it's limitations are well known. While Garmin do offer SOS functionality it's a private organisation that works with MRCCs and not part of normal global rescue services. Not saying it's not competent, but it is a different thing when compared to Cospas sarsat stuff
capnsensible
Well-known member
We. Alled it our ASBO tag, or more often by me, our 'not dead yet box' however it proved a tad unreliable.
lustyd
Well-known member
Don't get me wrong, I love InReach. It is to PLBs what a dinghy is to a liferaft, each have their place.
Adios
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That seems very unlikely.
After a few transmissions the professionals at the receiving end could work out if the signal was stationary in relation to the knowable weather and currents at that location, IE the device wasn't moving more than the current was taking it and it wasn't a dead calm to explain the lack of movement, so they can work out its on a stricken vessel. The fact that it was turning on and off means a human was operating it thereby confirming it was with a conscious casualty. Even more so if the casualty was able to do it at timed regular intervals.
Moreover being in a remote part of the ocean it might reasonably be thought a casualty would expect it to take longer than 24 hours to be rescued and be conserving battery. That Ocean Signal didn't caution on this point when saying "using it one hour a day would make it last 24 days" makes me more sure but I've asked them for clarity in case someone takes the wrong meaning from this thread.
Adios
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That makes no sense, unless by "some time" you mean milliseconds. The satellites are continually listening, they must be as according to the manufacturer the PLBs are giving intermittent signals (every 50 seconds) So it would not take additional time for more than one satellite to receive the signal, they would all receive it at the same time. The time difference when talking about the doppler shift is tiny.
Adios
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The manufacturer believes it is 40 seconds. But then you always sound very sure of yourself. Who should I believe?
The PLB downloads an almanac? Any reference for this info?
The manufacturers have designed these not as full EPIRBS but as wearable beacons with limited functionality most likely to be used somewhere that is well within 24 hours to rescue and any longer and hypothermia will have done for you anyway. This point in question is a "what if" mid ocean and its all you have.
And when it comes on again an hour later, and off again and back on after another interval, what do you presume they will take that to mean?
Hopefully the manufacturer will confirm if that is in any way linked with reality.
And then what? Drift further away from the last position, with every hour fairly rapidly increasing the search radius for your spec on the ocean. No thanks.