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Old 08-02-2012, 08:30   #1
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MOB - Ideas for Quick Location

This is an idea that has been in my head for some time and a few recent MOB threads has prompted me to put the following forward again. The post is long but hopefully worth reading!

Although rare, we all realize that a MOB is an extremely serious occurrence. I believe the most difficult aspect is locating and then returning to the person in the water. Sure all the other aspects are serious but unless the person is located and the vessel brought to them, the chances for survival are very very slim. Even if the MOB is witnessed in the moment, keeping them in sight is very difficult, especially when short handed and doing a reverse track search for a MOB event that wasn't noticed in the moment is hardly likely to be successful.

There are a variety of electronic MOB alarm systems available and they have their pros and cons but I have yet to see a off the shelf concept as described below.

This concept relies on the MOB carrying (and activating) a GPS PLB. These are common enough, small enough and cheap(ish). Of course they alert a distant SAR / RCC but they could also alert the parent vessel and provide a GPS position if the following was available.

Consider an onboard 406 MHz receiver that received the PLB transmission, decoded the GPS position and thus both raised the alarm and provided a accurate GPS location of the MOB to say the chart plotter.

Technically it would require an omnidirectional 406 MHz antenna (say a vertical dipole), a receiver (either broadbanded over the several PLB channels or using a fast scanning technique), a decoder for the positional data contained the PLB transmission, convert this to say NMEA position and also a voice readout of the lat. and lon. Perhaps a 121.5 MHz receiver as well for demodulating the audio sweep alarm and connecting that to an audio alarm speaker.

All this technology exists and most of it (if not all) is in the public domain so it just takes someone smarter than me to pt it together in one package. It could be housed in a small waterproof module at the base of the antenna and the only wiring would be power, an audio output to a speaker mounted anywhere and a RS 232 serial bus to the nav instrumentation. It would need to mounted as high as possible. Current draw would be quite low until triggered. Price could kept reasonable if say such receivers were mandated on off shore racing fleets as economies of scale would kick in.

The range would not be great but I would expect it to be better than say 5 nm radius of the antenna. This means that if the MOB is within 5 nm of the antenna, there would be an audile alarm, a voice readout of the lat/lon and a MOB waypoint on the chartplotter. As the 406 transmission is radiated every minute, it would really only need to receive one bust to work and give the location.

This has to be a lot better than a stressed mark 1 eyeball scanning the water from deck height.

Yes it does mean the on deck crew must wear the PLB and be able to use it but that is not a real hardship. Inshore, it is probable the parent vessel would locate the MOB before the local SAR assets could be mobilized and offshore it would allow the parent vessel to be an effective primary independent SAR asset.

Someone will now post a link to an existing similar system
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Old 08-02-2012, 09:17   #2
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Re: MOB, Ideas for Quick Location.

I think it's a cool idea... But... I believe most PLB EPIRBs also transmit continuously on 121.5. So a simpler (and more direct) technology may just be to have a traditional 121.5 directional antenna to home in on the person.

The commercial 121.5 MOB homing antenna kits are of course way over priced. A ham radio nerd could hack together a cheap receiver and directional antenna for ~$100. Ham radio folks also play a 'fox hunt' game where they find a hidden transmitter with directional antennas-- they tend to go far beyond what you'd need to recover a person in the water, but it does mean that there are commercial products, and a good written body of knowledge, to buy and learn from if you want to make your own budget system. Ham radio folks tend to be very generous with their knowledge and someone at the local club may be happy to put a system together -- a complete system may be as simple as a handheld receiver that you clip to the wall, plug into the 12 volt system, and leave locked on 121.5 with the volume turned way up and the squelch maybe halfway up. A transmitting PLB would then break the squelch and you'd hear it through the radio. A neat aspect of this system is that you can easily do MOB recovery drills with a 121.6 transmitter, which is the practice frequency, which you may not be able to do with a system that listens for a 406mhz data stream.

Also, before the EPIRB can transmit a position, it's internal GPS has to do a cold start. Digging into the specification sheets might tell you how long it takes, but it could be as long as a few minutes. So the 121.5 signal would provide more immediate direction finding. I'm not sure if the EPIRB starts transmitting on 406 mhz before it has a GPS fix -- that would be another important detail, because if your hypothetical system is only listening on 406, and there's no transmission until there's a fix, you could sail pretty far away from someone before you know they are gone. I don't know.

There are also AIS and DSC GPS MOB homing beacons. Some of the new ones are currently not FCC approved and only available from European chandleries.

PS-- On another thread someone mentioned that they rigged the MOB in-water-junk (flag pole, light, ring bouy, and smoke canister) to fall in the water when you give a sharp tug on a rope. I think this is a really good idea, and am going to try to make something like this on our boat, if I can figure out exactly how to rig it up. One piece of additional techno-wizardy that could be done is to add a solenoid to this rope, to auto deploy the water junk as soon as someone falls overboard. Many of the commercial MOB products have a relay for an engine kill switch -- on a sailboat this relay could be wired to the solenoid.
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Old 08-02-2012, 09:46   #3
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Re: MOB, Ideas for Quick Location.

as I said earlier, on our harness we have a Lite nylon line running to the ships bell mounted in the nav area of our boat, starts ringing as soon as you go over !!! LOL believe me it will wake ya up if your off duty !!! and it always works!! never runs out of electicity ! LOL and it never wears out or needs fixing (except when worn out ) just an old way ! Bob and Connie
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Old 08-02-2012, 09:52   #4
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Re: MOB, Ideas for Quick Location.

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Originally Posted by bobconnie View Post
as I said earlier, on our harness we have a Lite nylon line running to the ships bell mounted in the nav area of our boat, starts ringing as soon as you go over !!! LOL believe me it will wake ya up if your off duty !!! and it always works!! never runs out of electicity ! LOL and it never wears out or needs fixing (except when worn out ) just an old way ! Bob and Connie
Yes, that also works...

This product is interesting-- it sends a DSC 'MOB Alarm' signal with GPS position and has a computer voice that talks on channel 16 when it get's wet:
Crewsafe V100 - man overboard distress beacon, VHF DSC Maritime Survivor Locating Device | Mobilarm - Man overboard safety systems
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Old 08-02-2012, 10:33   #5
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Re: MOB, Ideas for Quick Location.

i shoot the MOB with a spear gun. sorta like tag and release.

they dont seem to enjoy it very much but it makes for good stories after the fact.

-s
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Old 08-02-2012, 10:40   #6
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Re: MOB, Ideas for Quick Location.

Looks good. Who sells it and costs?
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Old 08-02-2012, 16:04   #7
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Re: MOB, Ideas for Quick Location.

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Originally Posted by s/v Beth View Post
Looks good. Who sells it and costs?
No one that I am aware of; its just an idea still in my head but worth discussion IMO. I might have missed something basic and it might be a silly idea OR it may be a great idea just waiting for someone to run with it.
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Old 08-02-2012, 16:34   #8
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Re: MOB, Ideas for Quick Location.

Quote:
Originally Posted by msponer View Post
I think it's a cool idea... But... I believe most PLB EPIRBs also transmit continuously on 121.5. So a simpler (and more direct) technology may just be to have a traditional 121.5 directional antenna to home in on the person....
Ever tried traditional homing techniques - it ain't easy even for a trained operator - now throw in a pitching boat with a very worried and stressed crew. Plus the directional antennas are more complex to mount and take up real estate etc etc. You have to rely on audio (headpones etc) or have a dedicated display near the helm - it is just too complex.

Quote:
Originally Posted by msponer View Post
Also, before the EPIRB can transmit a position, it's internal GPS has to do a cold start. Digging into the specification sheets might tell you how long it takes, but it could be as long as a few minutes. So the 121.5 signal would provide more immediate direction finding. I'm not sure if the EPIRB starts transmitting on 406 mhz before it has a GPS fix -- that would be another important detail, because if your hypothetical system is only listening on 406, and there's no transmission until there's a fix, you could sail pretty far away from someone before you know they are gone. I don't know.
Here are some facts. PLB's are available with a GPS cold start acquisition time of less than 40 seconds and a hot start of 4 secs. The initial 406 transmission occurs on switch on but is coded slightly differently so the COSPAs system recognizes it as a "test" transmission. The next and subsequent transmissions occur about 1 minute later and are coded as "live" or genuine transmissions. Therefore modern GPS PLB's are transmitting the positional data from the get go.

My proposed receiver could be programmed to consider the initial test transmission as live just like the "real" transmissions. This also allows for testing and practicing MOB drills.

The 121.5 receiver in this system would kick in as soon as the PLB is activated, therefore the alarm is raised on board right away. I agree the positional data might be a minute or two later, but the alarm is instant.

Far better that than trying to visually locate the MOB.

Quote:
Originally Posted by msponer View Post
There are also AIS and DSC GPS MOB homing beacons. Some of the new ones are currently not FCC approved and only available from European chandleries.
The proposed system is a receiver only and therefore simplifies s compliance in most counties.
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Old 08-02-2012, 17:30   #9
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Re: MOB, Ideas for Quick Location.

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Looks good. Who sells it and costs?
I believe that you were asking about the Crewsafe V100 that msponer posted the link to which was developed by Mobilarm who are based in Osborne Park in Western Australia.

This does look like a very good system and seems to tick all the boxes of Wotnames idea. I do not have any personal experience with this unit though but one thing that comes to mind is that as the device is water activated I wonder how it is affected by heavy rain & heavy seas when you can be taking a drenching especially for a racing crew. It is for this very reason that we do not wear water activated lifejackets as they can inflate when you don't want them to. But I would think that Mobilarm have this issue covered but don't know for sure.

They are available in numerous countries throughout the world incl Nth America & Europe but due to local rules in these countries they are either configured as Open Loop (which has full functionality eg Australia, NZ, Bahamas etc ) or Closed Loop (restricted functionaly eg USA etc). Have a good look at the website posted earlier.
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Old 08-02-2012, 17:33   #10
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Re: MOB, Ideas for Quick Location.

Actually I was referring to the mobilarm crewsafe. I would buy a couple of those.
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Old 08-02-2012, 17:35   #11
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Re: MOB, Ideas for Quick Location.

Oh, cool, then yes, I agree -- want. Of course your system is better, I thought you were talking from the perspective of a non-nerd who wanted to kick around ideas for inexpensively hacking something together.

My father in law is an EE (and fellow ham) and showed me one of these inexpensive USB software defined radio dongle things a few weeks ago.

Only $190. If it's fast enough to decode a 406 EPIRB transmission then this could make for a quick prototype and proof of concept. The receiver isn't as sensitive as I'd hoped, but that could easily have been an antenna problem (we were just using pieces of wire to pull in FM radio and WiFi signals). Or make it a plugin to OpenCPN and then anyone can have this system for very little money, and you've made the world better. How many chances are there to do that?

I didn't mean a mounted directional antenna array, but a handheld one, like this or this, but home made.
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Old 08-02-2012, 17:54   #12
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Re: MOB, Ideas for Quick Location.

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Actually I was referring to the mobilarm crewsafe. I would buy a couple of those.
I'm not sure what the import laws are (since they aren't yet FCC approved), but a German chandlery has DSC PLB's for sale online. Budget Marine (in the Caribbean) has the AIS kind for sale.

Is there a functional reason to prefer a DSC PLB over an AIS one? I'm guessing it's more common for people to have AIS integrated with their navigation system.
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Old 08-02-2012, 18:03   #13
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Re: MOB, Ideas for Quick Location.

Further to my earlier post about the Mobilarm Crewsafe V100 I have now had time to read more about this device.

My initial thoughts was that it functioned exactly the same as other GPS equipped PLBs with the additional functionaity that it also calls vessels on VHF to alert them of the MOB situation & provide GPS co ordinates during this VHF call.

It now appears that it only does the VHF calling and does not alert land based rescue authorities like other PLBs.

So, while it has good functionality in it there does not seem to be the best of both worlds.

I posted on another thread that I would like to see the development of a GPS equipped PLB with the inclusion of a waterproof VHF transceiver with digital GPS location readout. Through this device the person in the MOB situation could actually call his own vessel & other vessels in the region to alert them of the MOB & provide his exact Long & Lat so that they could go straight to him while at the same time land based S&R authorities would be alerted to the PLB activation which would be turned off once the MOB had been recovered.

If the vessel involved in the MOB was within VHF range of a land based station they could also advise that a MOB had been recovered which was why the earlier PLB signal had now been switched off.

This sounds like a simple "best of both worlds" solution to me but there are probably rules & regulatory authorities which would throw a spanner in the works.
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Old 08-02-2012, 19:46   #14
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Re: MOB, Ideas for Quick Location.

Ahoy, I cannot actually find anyone to sell me mobilalert crewsafe v100 mob beacon in Australia. I live in West Oz, anyone know a dealer who stocks them, no luck on the mobilalert website. They would be wonderful for my next journey to Sumatra, I currently carry a personal gps/sat beacon and waterproof VHF with my lifejacket and tether whilst on watch, with the cabin /dsc-Vhf always turned on at 16. This device will be a great addition?
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Old 09-02-2012, 02:12   #15
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Re: MOB, Ideas for Quick Location.

Quote:
Originally Posted by Ozbullwinkle View Post
Further to my earlier post about the Mobilarm Crewsafe V100 I have now had time to read more about this device.

My initial thoughts was that it functioned exactly the same as other GPS equipped PLBs with the additional functionaity that it also calls vessels on VHF to alert them of the MOB situation & provide GPS co ordinates during this VHF call.

It now appears that it only does the VHF calling and does not alert land based rescue authorities like other PLBs.

So, while it has good functionality in it there does not seem to be the best of both worlds.

I posted on another thread that I would like to see the development of a GPS equipped PLB with the inclusion of a waterproof VHF transceiver with digital GPS location readout. Through this device the person in the MOB situation could actually call his own vessel & other vessels in the region to alert them of the MOB & provide his exact Long & Lat so that they could go straight to him while at the same time land based S&R authorities would be alerted to the PLB activation which would be turned off once the MOB had been recovered.

If the vessel involved in the MOB was within VHF range of a land based station they could also advise that a MOB had been recovered which was why the earlier PLB signal had now been switched off.

This sounds like a simple "best of both worlds" solution to me but there are probably rules & regulatory authorities which would throw a spanner in the works.
Yes OzBW is correct in that the Mobilarm Crewsafe V1000 is essentially a "specialist VHF" based system and while perhaps suitable on a working boats or off-shore oil & gas platforms etc, it doesn't in my view really answer the needs of the off-shore cruiser and requires "new" equipment for the crew to wear as well significant on-board equipment to do the alerting and tracking. It was a good system but technology (eg GPS PLBs) have already made it somewhat redundant.

My concept is to use already available GPS equiped PLB's for the crew and a "simple" boat mounted receiver. Simple in mechnical construction (combined reciever, decoder and antenna), simple in wiring (one connector for power, serial bus and remote speaker), simple to use (hear the alarm tone from the 121.5 aspects, hear the voice lat./lon. and look at the chartplotter for MOB waypoint).

Even if the on-board receiver fails, the GPS PLB is still activating the COSPAS system completely independently . There is no requirement for the MOB to talk or otherwise communicate, the on board receiver has taken over these functions and is plotting the position direct to the boat's electronic navigation system as well as giving a voice readout.

The only downside that I can foresee is that PLB's are not water activated. The MOB must be conscious and switch the PLB on.

I can't foresee any significant regulatory issues for a system based purely on a receiver.
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