Fishfinder/sonar as freediving safety tool

[TheDude]

Anybody have any experience with using a fishfinder or sonar to monitor a freediver during his dive? I asked this as an offtopic question in one spearo thread. Bill mentioned that guys in New Zeland use something like that, also Stavros mentioned it marginally in another thread.

Here are my ideas how it could work:
The device should have continuos measurement with a good refresh rate, be reasonably accurate (but even +/- few meters should be enough) and reliable. The diver could have some small object, which does reflect the waves well, cliped on his belt, taped on wetsuit etc... Any ideas which material could reliably bounce a sonar wave? (maybe a big tuna taped on the divers back to fool the fishfinder )

Other alternative could be to use an active device on the freediver, sending waves (something like a small beacon, maybe integrated in a dive watch), while the surface unit placed some distance away from the dive line could calculate depth by measuring the direction (angle) of the beacon. But this is just a crazy idea, far too unpractical I guess .

Links to the mentioned threads:
http://forums.deeperblue.net/spearo...r-works-only-without-moving-2.html#post646834
http://forums.deeperblue.net/safety/71066-safe-backup.html?highlight=sonar#post642928

 

[Seal]

Be aware that you can't see sharks on it. And so an "empty" sea on the sonar could give a nasty suprise.

We had a colour sonar on our big game boat, and we could never see any sharks on it. And still be getting strikes from tigers up to 4 metres right under the boat.

 

[TheDude]

Thanks for the input. Never met a shark yet, so that is a risk I was not calculating with I'm quite sure the sharks won't find their way to a murky lake where we dive mostly (at least I hope so, otherwise they would scare the shit out of me)

I more ment to be able to use the fishfinder/sonar/whatever to know from the surface what the current depth of the diver is - and thus see if everything is going ok.

 

[Seal]

Thanks for the input. Never met a shark yet, so that is a risk I was not calculating with I'm quite sure the sharks won't find their way to a murky lake where we dive mostly (at least I hope so, otherwise they would scare the shit out of me)

I more ment to be able to use the fishfinder/sonar/whatever to know from the surface what the current depth of the diver is - and thus see if everything is going ok.

Hehe ups sorry didn't see that lake part

 

[Bill McIntyre]

What could you do with the information? It wouldn't allow you to rescue him.

 

[Bill]

Bill the new systems have a retrieval device built in. It can be activated on time or with visual evidence that the diver is outside set parameters. Also it isn't uncommon for one of the safeties to be able to hit the bottom.
Aloha
Bill

 

[Bill McIntyre]

Bill the new systems have a retrieval device built in. It can be activated on time or with visual evidence that the diver is outside set parameters. Also it isn't uncommon for one of the safeties to be able to hit the bottom.
Aloha
Bill

I must not understand what he meant. I thought he was just talking about using a fish finder to get a reading on the diver's depth, but I don't see how a fish finder could incorporate a retrieval device.

 

[TheDude]

I was talking about just the fish finder - just to get the information. It will not help by itself - but the information could trigger some appropriate action - counter ballast, buddy going down etc...

 

[ADR]

Hi Dude,

That was me in NZ last year that got the sounder thing happening on our surface rigs. Mixed results from a couple of diffferent sounders that I have tried.

Here is a link to an article with a pic of the rig.

Australian Freediving Community - Fanatical about Freediving in Australia

 

[TheDude]

Hi Andy,

great site you have there, and good forums as well . But not much info about the sounder except the picture... :hmm Could you post some details on what kind and how you use it and some of your experiences?

Thanks

 

[Bill]

Bill

If my old memory is working OK, using the system that they developed in Nice, on a planned 200 foot dive in 2:10, they start to retrieve the bottom stop at about 1:15. If you stop kicking for any reason, you come up anyway. The retreaval system is activated on every target dive.

Andy
Thanks for jumping in.

Aloha
Bill