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03-12-2024, 13:22
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#16
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Registered User
Join Date: Mar 2017
Location: Bogue Sound NC
Boat: 1987 Cape Dory MKII 30 Hull #3,
Posts: 1,487
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Re: MOB on ARC.
[QUOTE=PippaB;3954378] For the AIS MOB beacon to give position it has to get a GNSS fix.
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I believe you refer to an EPIRB personal beacon.
My understanding regarding an AIS personal beacon transmits a localized signal to be received by any and all AIS receivers within the range of the transmitting beacon.
The advantage over a personal EPIRB is speed, if the AIS receiver is on and the alarms set;
the person onboard will/should react immediately and start the recovery actions.
And this action is not limited to the vessel the person fell but if lucky and more vessels are in the proximity the odds increase
however, there has been doubts expressed on several posts and that is really unnerving.
The EPIRB as well any of the emergency transmitters units available like InReach will go through the motions you described and time for a person in the water is a matter of life or death.
That is why I carry a personal AIS beacon, BUT if the efficiency is in question we have a problem
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03-12-2024, 13:28
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#17
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Registered User
Join Date: Mar 2017
Location: Bogue Sound NC
Boat: 1987 Cape Dory MKII 30 Hull #3,
Posts: 1,487
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Re: MOB on ARC.
[QUOTE=Shrew;3954419]Is that a question? {I} always have a personal AIS on life jacket....
Or is that a statement? {You should} always have a personal AIS on life jacket....
and........what's a Vesper?
========================
that is a statement of what I do.!
Vesper has been involved in manufacturing and developing AIS units for some time but is now part of Garmin.
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03-12-2024, 13:36
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#18
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Registered User
Join Date: Oct 2021
Posts: 706
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Re: MOB on ARC.
[QUOTE=davil;3954463]
Quote:
Originally Posted by PippaB
For the AIS MOB beacon to give position it has to get a GNSS fix.
=========================================
I believe you refer to an EPIRB personal beacon.
My understanding regarding an AIS personal beacon transmits a localized signal to be received by any and all AIS receivers within the range of the transmitting beacon.
The advantage over a personal EPIRB is speed, if the AIS receiver is on and the alarms set;
the person onboard will/should react immediately and start the recovery actions.
And this action is not limited to the vessel the person fell but if lucky and more vessels are in the proximity the odds increase
however, there has been doubts expressed on several posts and that is really unnerving.
The EPIRB as well any of the emergency transmitters units available like InReach will go through the motions you described and time for a person in the water is a matter of life or death.
That is why I carry a personal AIS beacon, BUT if the efficiency is in question we have a problem
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An AIS MOB beacon transmits two message types; Message 1 (position report) and Message 14 (safety message). The message 14 carries the general "MOB" information, the message 1 carries the current position (once the beacon has a fix). Except for own boat, message 14 is nearly useless to other boats without message 1, it only tells you someone fell overboard within radio range. If all you get is message 14, which way do you turn to assist? Easy enough for the boat you fell off of, but not so much for any other nearby boats.
Quote:
Once activated the position of the AIS MOB device will be displayed as a GPS located target icon on ships in the vicinity with AIS enabled plotter screens. They do this by repeatedly transmitting an AIS message type MSG1 (class A position report) and MSG 14 (safety broadcast message) alternating quickly between both AIS channels AIS1 and AIS2.
A burst of 8 MSG1 messages repeat every 1 minute, with the cycle of messaging repeated many times to overcome wave action and to achieve line-of-sight to a nearby vessel. In a heavy sea with the AIS device close to the sea surface, wave swell can block the transmissions. This is overcome via information being repeated every 2 seconds (over 14 seconds), ensuring some transmissions will coincide with the survivor being on
a wave crest, allowing “line-of–site” path for message relay
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03-12-2024, 13:50
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#19
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Writing Full-Time Since 2014
Join Date: Nov 2008
Location: Deale, MD
Boat: PDQ Altair, 32/34
Posts: 10,283
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Re: MOB on ARC.
Some feel it is rude to surmise in the midst of probable loss of life. That is not the intention, we are truing to learn. Both loss and ocean realities aren't real until they happen.
---
I don't know about the unit in use or much about these beacons, but I read this on that "other" forum.
"Most personal units have to be manually deployed, antenna extended...."
"And mine for one would float upside down if not held or attached to you in some way that the antenna could be held pointing up.
It passes regs to allow me to race, but I consider it near useless if I was in the water ...."
"If my harness inflates, it activates the beacon, including extending the antenna...." [but is it pointing up and clear of the water?]
Watch the video. First, the antenna did not deploy. It is possible that the sailor would not know it should, might be injured and distracted, and it also strikes me that the antenna is practically or is in the water and might not work. I'm very curious if one of these factors might be relevant.
Not knowin', just trying to contribute to the pool of questions and possibilities. Many bits of boating safety kit are tested in the lab but not "in the s__t." Very different from, say, climbing equipment.
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03-12-2024, 13:51
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#20
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Registered User
Join Date: Mar 2017
Location: Bogue Sound NC
Boat: 1987 Cape Dory MKII 30 Hull #3,
Posts: 1,487
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Re: MOB on ARC.
Originally Posted by PippaB View Post
For the AIS MOB beacon to give position it has to get a GNSS fix.
Not my understanding
An AIS signal is transmitted to an AIS receiver system by broadcasting the vessel's data, such as position, speed, and course, over designated VHF radio frequencies (channels 87B and 88B) using a dedicated AIS transponder, which essentially acts like a radio transmitter, sending out the information in a digital format at regular intervals, allowing nearby vessels equipped with AIS receivers to pick up the signal and decode the data.
Key points about AIS transmission:
Frequency:
AIS uses two VHF frequencies: 161.975 MHz (channel 87B) and 162.025 MHz (channel 88B).
Data format:
The information is encoded using a standardized digital protocol called HDLC (High-Level Data Link Control).
Transmission schedule:
Each vessel determines its own transmission slot within a predefined time frame to avoid interference with other nearby vessels.
Antenna:
A VHF antenna is required to transmit and receive AIS signals.
How an AIS receiver works:
Repeating thinwater
Not knowin', just trying to contribute to the pool of questions and possibilities. Many bits of boating safety kit are tested in the lab but not "in the s__t." Very different from, say, climbing equipment.
__________________
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03-12-2024, 13:59
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#21
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Registered User
Join Date: Oct 2021
Posts: 706
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Re: MOB on ARC.
Quote:
Originally Posted by thinwater
... It is possible that the sailor would not know it should, might be injured and distracted, and it also strikes me that the antenna is practically or is in the water and might not work. I'm very curious if one of these factors might be relevant...
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Me too. I can envision all kinds of scenarios where the beacon cannot provide a signal. Between manual deployment (if required) by an unconscious person, being underwater, in the wrong position, etc. I would be interested in seeing some testing that deals with all those factors other than the beacon itself.
Not in any way meant to be demeaning, because there but for the grace of [insert deity] go I, but even with all the newfangled tech Rule 1 is to stay on the boat, because once you are not the odds are not good. I feel deeply for the family and crew, I cannot even begin to imagine what it would be like to give up a search in this scenario.
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03-12-2024, 14:17
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#22
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Registered User
Join Date: Mar 2017
Location: Bogue Sound NC
Boat: 1987 Cape Dory MKII 30 Hull #3,
Posts: 1,487
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Re: MOB on ARC.
on the same tone
I carry both EPIRB and AIS beacons as well my inReach as well as the strobe all interlaced on a loop around my neck.
Decided it was to risky for me dealing with all these gismos afraid my arthritic fingers fumbling them in the cold and panic trying to get them from the life vest pockets/velcro etc.
This ensures they stay with me
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03-12-2024, 14:35
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#23
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Registered User
Join Date: Jul 2018
Location: SF Bay Area
Boat: Other people's boats
Posts: 1,181
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Re: MOB on ARC.
Quote:
Originally Posted by thinwater
Not knowin', just trying to contribute to the pool of questions and possibilities. Many bits of boating safety kit are tested in the lab but not "in the s__t." Very different from, say, climbing equipment.
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The video thumbnail shows a PLB and my assumption, based on the reporting, is that an AIS beacon (example: OceanSignal MOB1) was what was carried. In contrast, PLBs generally require one to manually extend the antenna and activate them.
In contrast, a device like the MOB1 is designed to be attached to the PFD. The unit itself is clipped into a bracket that's in turn clipped to the inflation tube. A tether (for an auto-inflate) connected to both bracket and device is wrapped around the bladder. Tension from inflation on the tether pulls away a bit of plastic resulting in 1) deployment of a spring-loaded antenna and 2) activating the beacon.
There are a number of possible scenarios in play. For example, the device could have been knocked from the clip either by wave action or even accidentally by the MOB (e.g. when trying to pull a spray hood into place). It's also possible the MOB brought a PLB rather than an AIS beacon, or that the PFD itself failed to inflate.
If further information about the specific equipment in play becomes available one might assign probabilities. As the beacon is dependent on the PFD, an old, unmaintained PFD would be more suspect than a recently-purchased model.
The other question I have, to which we have slightly better odds of getting an answer, is the tethering arrangement aboard. Did they run jacklines, or did the boat simply have hardpoints for people to clip to at each station? What was the actual practice aboard, compared to what was "by the book"?
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03-12-2024, 15:17
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#24
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Registered User
Join Date: Aug 2009
Location: between the devil and the deep blue sea
Boat: a sailing boat
Posts: 21,199
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Re: MOB on ARC.
The devices are not guaranteed to work. Especially in the "automatic" mode.
When they work, it is a bonus. But there are many probable scenarios when they will not.
A lifejacket would have an automatic light. Yes/No ?
An automatic jacket light is nearly sure to lit up, unless grossly out of date.
A light on the perch is nearly sure to light up. And the perch will have a big attention catching flag.
The point is to NOT go overboard. To have an automatic lifejacket on. To make sure all crew know how to deploy the perch and how to try and stop the boat IN THE LEAST POSSIBLE TIME.
The MOB device is NOT a problem in this case, but it gets plenty of attention.
I think the problem is that the crew was NOT found.
Maybe he wore a harness but no lifejacket.
Maybe the position did not get marked up immediately.
Maybe the jacket did not open and the sailor was not conscious.
Maybe they failed to stop the boat 'on time'.
maybe maybe maybe
Time will tell, and we will learn. And then many of us will immediately forget.
b.
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03-12-2024, 16:06
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#25
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Registered User
Join Date: Jan 2014
Location: Florida
Posts: 976
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Re: MOB on ARC.
[QUOTE=Montanan;3954361]Technology questions:
How accurate is a personal AIS beacon and what distance will it be able to transmit and be received as worn by a MOB in salt water?
Does the personal AIS signal work similar to a vessel transmitting AIS providing position and drift data?
Are personal AIS beacons rugged devices that can take the wear and abuse of being actively worn and do they go on automatically when submerged or do they need to be manually activated?
An often overlooked set up item some MOB beacons is that you
must enter the the proper info for it to also send out DSC alarm to
the boat you just fell off. None of this stuff is of any use if
nobody knows your overboard for two or three hours.
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03-12-2024, 16:27
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#26
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Registered User
Join Date: Oct 2014
Posts: 7,990
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Re: MOB on ARC.
Quote:
Originally Posted by barnakiel
VOR boats are accident prone. Booms injuring crews and crews washed overboard.
AIS or not, why was the seaman not leashed. I did not ask any questions.
Too bad.
b.
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What do the squiggly lines represent?
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03-12-2024, 16:48
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#27
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Senior Cruiser

Join Date: Jan 2010
Location: PORTUGAL
Posts: 31,297
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Re: MOB on ARC.
Quote:
Originally Posted by Montanan
What do the squiggly lines represent?
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I imagine it's the search pattern on arrival at presumed location.. after the zig zag back into weather.
__________________

You can't oppress a people for so many decades and have them say.. "I Love You.. ".
"It is better to die standing proud, than to live a lifetime on ones knees.."
Self Defence is no excuse for Genocide...
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03-12-2024, 17:12
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#28
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Writing Full-Time Since 2014
Join Date: Nov 2008
Location: Deale, MD
Boat: PDQ Altair, 32/34
Posts: 10,283
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Re: MOB on ARC.
Quote:
Originally Posted by requiem
The video thumbnail shows a PLB and my assumption, based on the reporting, is that an AIS beacon (example: OceanSignal MOB1) was what was carried. In contrast, PLBs generally require one to manually extend the antenna and activate them.
In contrast, a device like the MOB1 is designed to be attached to the PFD. The unit itself is clipped into a bracket that's in turn clipped to the inflation tube. A tether (for an auto-inflate) connected to both bracket and device is wrapped around the bladder. Tension from inflation on the tether pulls away a bit of plastic resulting in 1) deployment of a spring-loaded antenna and 2) activating the beacon.
There are a number of possible scenarios in play. For example, the device could have been knocked from the clip either by wave action or even accidentally by the MOB (e.g. when trying to pull a spray hood into place). It's also possible the MOB brought a PLB rather than an AIS beacon, or that the PFD itself failed to inflate.
If further information about the specific equipment in play becomes available one might assign probabilities. As the beacon is dependent on the PFD, an old, unmaintained PFD would be more suspect than a recently-purchased model.
The other question I have, to which we have slightly better odds of getting an answer, is the tethering arrangement aboard. Did they run jacklines, or did the boat simply have hardpoints for people to clip to at each station? What was the actual practice aboard, compared to what was "by the book"?
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Several incorrect assumptions because you did not watch the video.
- It was attached to the PFD.
- It autodeployed incorrectly. This was sort of the point of watching the video.
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03-12-2024, 17:27
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#29
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Registered User
Join Date: Mar 2007
Location: Santa Cruz
Boat: SAnta Cruz 27
Posts: 7,220
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Re: MOB on ARC.
I have delivered race boats with the MOB AIS gadgets. They are attached to inflating harnesses, and are supposed to turn on when the harness inflates.
One night about 200 miles west of Los Angeles, our AIS transceiver alarmed, indicating there was an active MOB very close to us. I checked all 12 of the boat's PFD's, and found no activations. The MMSI was not the same as the boat's. I woke the crew and asked if anyone had their own MOB AIS. One off-watch guy said yes, and that his was activated. The MMSI matched, and he was able to switch it off, so we reset the alarm and sailed on.
I was within 5 miles of a couple of ships at the time, but there was no indication that either of them had picked anything up. Since we were going about 12 knots, we would have soon been out of range of someone in the water.
I have a couple of questions. Is it possible to test these units without setting off a full scale man hunt? Do they have the range to be picked up by any of the commercial AIS services or Coast Guards?
I remember another Volvo boat had a MOB in the Southern Ocean. The boat's AIS receiver had been damaged in a storm off Auckland, so the MOB AIS system did not work for them, and they lost that crew too.
My own view is that if go MOB, you are going to be very, very lucky to survive.
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03-12-2024, 18:06
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#30
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Registered User
Join Date: Oct 2021
Posts: 706
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Re: MOB on ARC.
Quote:
Originally Posted by donradcliffe
...I have a couple of questions. Is it possible to test these units without setting off a full scale man hunt?...
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I don't know about all units, but for the ACR, yes. You can test that the unit turns on and does a battery check, then you can test a DSC call which sends a DSC Routine call which you should be able to pick up on own ship VHF and compare with MMSI in unit. And lastly AIS test, which sends the MSG1 part of the signal (position report) without the MSG14 (MOB) message.
ACR recommends the active checks at 2-3 times/year to conserve battery life. And we should all be doing them as often as the manual allows, because amongst other things it updates the last GNSS fix in the unit. The further you are in time and/or distance from your last fix the longer it takes to get first fix when you turn it on. So testing the position information as frequently as allowed by the user manual is a good idea.
https://www.acrartex.com/wp-content/...ISLink_MOB.pdf
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