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Old 06-04-2019, 11:28   #1
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PLB Personal Locator Beacon Explained

We have multiple devices onboard to assist Search and Rescue SAR personnel in locating us and/or our boat if there's a Mayday type emergency, so I've taken the time today to try and understand how these various devices work.

Today's project is trying to figure out and then purchase the correct PLB to attach to a pair of Spinlock DeckVest Vito lifejackets I plan to order. I presently own an ACR ResQLink+ and would like to incorporate this into one jacket, since we already own it and it's registered. I'm also looking at adding an Ocean Signal MOB1 to the second lifejacket, which should be easy because both designed are designed to go hand in hand.

So here's a video I found that explains things quite well, but the only issue I'm a little confused about is to whether or not each of the two PLBs will transmit an AIS signal which can be seen immediately on the Raymarine E127 Hybridtouch chart plotters. Or does SAR then broadcast coordinates to find an MOB?

The ACR ResQLink+ was purchased three years ago primarily for my single handed adventures, so having it show up on the chart plotter wasn't a concern or priority, because I couldn't be two places at once. But moving forward, it would be nice to be able to view the location of a MOB on the chart plotter.

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Old 06-04-2019, 11:45   #2
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Re: PLB Personal Locator Beacon Explained

Not sure there is a PLB/AIS combo for lifejackets. There is bigger one for vessels

https://www.orbitalsatcom.com/mcmurd...-g8-epirb-auto
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Old 06-04-2019, 11:52   #3
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Re: PLB Personal Locator Beacon Explained

Which do you think would be the better choice? I’m thinking the Ocean Signal MOB1 is more of a coastal rescue item because the signal just goes out via AIS “up to 5 miles” only to boats in the immediate area, whereas the ACR ResQLink+ Is an offshore and coastal device because the signal is transmitted worldwide to send in all possible SAR to the area to assist with rescue.

I’d prefer to have SAR and the mothership looking for a MOB, rather than just the mothership and someone who might be in the area.
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Old 06-04-2019, 12:10   #4
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Re: PLB Personal Locator Beacon Explained

Read up in the archives about EPIRB response protocol. You will be long dead by the time someone responds to the PLB signal. This is not useful for MOB, at least not in cold water, as the response time is many hours.


I DO carry a ResQLink in my lifejacket, and have for years. But it's not for MOB rescue -- it's in case I get separated from the regular EPIRB in some awful confusion. I would just put it inside the life raft, except that I carry two life rafts.


The MOB1 is what you want to get rescued. It sends out DSC all ships alert, so VHF on all vessels around will be screaming, then shows you on AIS, so they can find you.
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Old 06-04-2019, 12:13   #5
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Re: PLB Personal Locator Beacon Explained

FWIW:
My take is that if the mothership has an EPIRB, you can activate the ship EPIRB to get high/far resources alerted/inbound (even keeping the mothership EPIRB on the mothership). Invariably the mothership should be ~loitering in the vicinity of the MOB.

Next, if if MOB has a PLB even with a limited range...the range will be good enough to guide a local rescue and/or a helicopter that arrives on scene within the 24 hours that the PLB will broadcast.

Next, I sort of figure that the person in the water...if not picked up quickly with the 5 mile range feature (either from local boats or within 24 hours by a helo) that the MOB is in a bad way.

This assumes a witnessed MOB.
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Old 06-04-2019, 12:19   #6
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Re: PLB Personal Locator Beacon Explained

Quote:
Originally Posted by Dockhead View Post
Read up in the archives about EPIRB response protocol. You will be long dead by the time someone responds to the PLB signal. This is not useful for MOB, at least not in cold water, as the response time is many hours.


I DO carry a ResQLink in my lifejacket, and have for years. But it's not for MOB rescue -- it's in case I get separated from the regular EPIRB in some awful confusion. I would just put it inside the life raft, except that I carry two life rafts.


The MOB1 is what you want to get rescued. It sends out DSC all ships alert, so VHF on all vessels around will be screaming, then shows you on AIS, so they can find you.
This time, I’m looking to find what will work best in our situations, where we sail primarily in the warm waters of the Mediterranean and Caribbean with SAR not far away. Cold waters aren’t much of a concern for us, but if we do find ourselves crossing the Atlantic in rough conditions in cold water, there’s no doubt I’ll be wearing one of our Ocean Rodeo Ignite drysuits at the time to provide SAR ample time to locate either if us.

I’m wondering what sort of broadcast is sent out by SAR if the ACR ResQlink is activated?
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Old 06-04-2019, 12:23   #7
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Re: PLB Personal Locator Beacon Explained

Quote:
Originally Posted by Singularity View Post
FWIW:
My take is that if the mothership has an EPIRB, you can activate the ship EPIRB to get high/far resources alerted/inbound (even keeping the mothership EPIRB on the mothership). Invariably the mothership should be ~loitering in the vicinity of the MOB.

Next, if if MOB has a PLB even with a limited range...the range will be good enough to guide a local rescue and/or a helicopter that arrives on scene within the 24 hours that the PLB will broadcast.

Next, I sort of figure that the person in the water...if not picked up quickly with the 5 mile range feature (either from local boats or within 24 hours by a helo) that the MOB is in a bad way.

This assumes a witnessed MOB.
Very good points.

Thanks
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Old 06-04-2019, 12:25   #8
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Re: PLB Personal Locator Beacon Explained

If Iím solo sailing, itís beginning to look like I need both on my vest in case I go over the side.
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Old 06-04-2019, 13:14   #9
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Re: PLB Personal Locator Beacon Explained

Quote:
Originally Posted by Singularity View Post
FWIW:
My take is that if the mothership has an EPIRB, you can activate the ship EPIRB to get high/far resources alerted/inbound (even keeping the mothership EPIRB on the mothership). Invariably the mothership should be ~loitering in the vicinity of the MOB.

Next, if if MOB has a PLB even with a limited range...the range will be good enough to guide a local rescue and/or a helicopter that arrives on scene within the 24 hours that the PLB will broadcast.

Next, I sort of figure that the person in the water...if not picked up quickly with the 5 mile range feature (either from local boats or within 24 hours by a helo) that the MOB is in a bad way.

This assumes a witnessed MOB.

EPIRBs and PLBs emit a 121mhz homing signal.


However, hardly any vessel* has any device which can receive that signal. So it's only after the 406mhz EPIRB/PLB signal has been processed and actioned through the COSPAS/SARSAT system, which takes several hours, and after actual rescue helicopters have been tasked, will that signal get used.




* Yes, you guessed it -- I do have a 121mhz directional receiver on board, but that's not common, so you should not count on "local boats" responding.
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Old 06-04-2019, 13:20   #10
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Re: PLB Personal Locator Beacon Explained

Quote:
Originally Posted by Dockhead View Post
EPIRBs and PLBs emit a 121mhz homing signal.


However, hardly any vessel* has any device which can receive that signal. So it's only after the 406mhz EPIRB/PLB signal has been processed and actioned through the COSPAS/SARSAT system, which takes several hours, and after actual rescue helicopters have been tasked, will that signal get used.




* Yes, you guessed it -- I do have a 121mhz directional receiver on board, but that's not common.
What 121mhz receiving device do you have on your boat and how does it work?
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Old 06-04-2019, 13:21   #11
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Re: PLB Personal Locator Beacon Explained

Quote:
Originally Posted by Kenomac View Post
. . .Iím wondering what sort of broadcast is sent out by [to?] SAR if the ACR ResQlink is activated?

https://en.wikipedia.org/wiki/Intern...rsat_Programme
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Old 06-04-2019, 13:35   #12
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Re: PLB Personal Locator Beacon Explained

Quote:
Originally Posted by Kenomac View Post
What 121mhz receiving device do you have on your boat and how does it work?

It's an old school RDF which came with an ancient MOB system I used to have. It has a directional antenna and emits a sound, which changes in pitch as you point it more towards the transmitter.


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It's still in production: https://www.rhotheta.com/products/rt_100



It cost a fortune, and now I can't sell it. The early adopter always pays
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Old 06-04-2019, 14:28   #13
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Re: PLB Personal Locator Beacon Explained

Quote:
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EPIRBs and PLBs emit a 121mhz homing signal......
I meant to imply that in reality a successful rescue by a boat that is not the mothership would likely result from the PLB's DSC to local AIS receiver function (or just being near a shore with lots of resources).

*but*

In re-reading some of this stuff, it looks like Ken's initial question was not answered. If your PLB can transmit lat/long via DSC VHF (if that's the right way to phrase it) to local AIS receivers....can local AIS receivers be relied upon receive the signal? I thought all AIS receivers could, but apparently not.

As recently as a couple years ago a Panbo article states:
"Iím not aware of any VHF radio with AIS reception that understands AIS MOB beacons yet and, while Iíd love to be corrected, thatís disappointing. {Update: the Standard Horizon Matrix GX2200, and probably other SH VHF/AIS radios, handle AIS MOB beacons well; see comments below.} But Icom has already expressed an interest in updating their AIS rx radios, and itís true that both the M605 and the RS35 passed the AIS MOB test info to all the MFDs above just fine. But wouldnít it be nice, especially on offshore sailboats, if you could leave the MFD off and count on your VHF to help with an AIS MOB?"
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Old 06-04-2019, 14:39   #14
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Re: PLB Personal Locator Beacon Explained

Quote:
Originally Posted by Singularity View Post
I meant to imply that in reality a successful rescue by a boat that is not the mothership would likely result from the PLB's DSC to local AIS receiver function (or just being near a shore with lots of resources).

*but*

In re-reading some of this stuff, it looks like Ken's initial question was not answered. If your PLB can transmit lat/long via DSC VHF (if that's the right way to phrase it) to local AIS receivers....can local AIS receivers be relied upon receive the signal? I thought all AIS receivers could, but apparently not.

As recently as a couple years ago a Panbo article states:
"Iím not aware of any VHF radio with AIS reception that understands AIS MOB beacons yet and, while Iíd love to be corrected, thatís disappointing. {Update: the Standard Horizon Matrix GX2200, and probably other SH VHF/AIS radios, handle AIS MOB beacons well; see comments below.} But Icom has already expressed an interest in updating their AIS rx radios, and itís true that both the M605 and the RS35 passed the AIS MOB test info to all the MFDs above just fine. But wouldnít it be nice, especially on offshore sailboats, if you could leave the MFD off and count on your VHF to help with an AIS MOB?"

PLB's don't transmit anything by DSC. They emit a 440mhz signal to COSPAS-SARTSAT satellites, which go through the SAR services to activate a search and rescue action after the protocols are followed, which takes some hours. They also emit a 121.5mhz homing signal to guide the rescue helicopter or cutter the last mile to your position.


AIS MOB beacons are an entirely different animal. They emit a VHF signal on Channel 70 showing the location of the beacon on local AIS sets, and some of them, the latest ones, will also send out a DSC distress message -- again, to local vessels.


Got it? In a nutshell:


PLB -- via satellite to SAR services after some hours


AIS beacon -- via AIS, and sometimes via VHF DSC distress messages, to LOCAL vessels




One is satellite to SAR -- no local vessels. The other is AIS and sometimes DSC to local vessels only -- no SAR.
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Old 06-04-2019, 14:44   #15
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Re: PLB Personal Locator Beacon Explained

Does the Ocean Signal MOB1 have a test function, so practice MOB situations can be rehearsed using the system? Do you find the Rotheta RT-100 to be a useful tool? Would it be beneficial to have one onboard or have the Ocean Signal MOB1 units replaced the usefulness.
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