Author Topic: Mid-Water body search  (Read 8848 times)

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IRC Kevin

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Mid-Water body search
« on: September 22, 2011, 11:36:41 AM »
Can anyone tell me if the fish-finder alert will actually pick up bodies in mid-water, or even on the bottom? We're talking about bodies less than 24 hours in the water by the way) Looks like we may be fitting a 998 to the 18' rescue boat and I need to get a training package together for new users.


Offline ITGEEK

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Re: Mid-Water body search
« Reply #1 on: September 22, 2011, 11:56:38 AM »
I don't think a fishfinder knows the difference between a human body and a dead Carp, or
a submerged log.
I also don't know what fish-finder-alert is?
Do you mean man overboard?

I would think if an object of interest was found, you would have to use the side-imaging
or down-imaging to get a better look, then send divers in.

IRC Kevin

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Re: Mid-Water body search
« Reply #2 on: September 22, 2011, 12:13:08 PM »
Fish finder alert is the bleep with the 'big goldfish' icon in 2D. Wondered if whatever it is that the software uses to differentiate between logs, weed, other debris and fish would treat a recent body as a big fish?

Offline ITGEEK

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Re: Mid-Water body search
« Reply #3 on: September 22, 2011, 12:34:30 PM »
Interesting idea.
I think half of the sonar is from a fish's swim bladder.
Some is from scales and bones.
So, if there was some air in the lungs, then maybe.

Greg would know better.

Offline Del

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Re: Mid-Water body search
« Reply #4 on: September 22, 2011, 01:47:23 PM »
If i understood the device settings correctly then the device is looking for a different size of fish in fresh/saltwater. So saltwater settings might help to give a fish-return on a body i guess.

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Re: Mid-Water body search
« Reply #5 on: September 22, 2011, 02:03:51 PM »
You are right about the percentage of sonar return from the swim bladder of a fish ITG (it’s about 50%) but I don’t know how our Fish ID programming would treat a human body.  Maybe Chuck, Robert or one of the other S&R guys can comment on this.

Greg Walters at Humminbird
gwalters@johnsonoutdoors.com

Offline sonar2000

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Re: Mid-Water body search
« Reply #6 on: September 22, 2011, 03:43:26 PM »
Generally a body does not suspend at midlevels. It is either at the bottom or the top. 
A matter of physics.
However once an object starts to rise due to gas producing "lift" it will continue the ascent unless it hits something and snags it and stop the ascent.
The small amount of time a rising object ascends will not be appreciable with sonar.
Physics--as it ascends it increases in the speed at which it is ascending..So it is not long until on the surface..
This does not say you should disregard looking midlevel or at any level in which you suspect the object is lodged as in a tree or some other subsurface "snag"..
We have seen objects in the top of trees in past submersions..
Kevin, you might be best to concentrate on the bottom returns.  This is especially helped by an external viewer of the recorded scan. Especially with smaller sonar unit screens..
In the 1st 24 hours it is especially to understand depth, temperature, food eaten, liquids consumed. All of this related directly to physics of buoyancy and "when" an object will start to float.
Some deep water submersions may never rise due to "physics". Boyles, Charles and Archimedes . Understanding these laws and principles will describe the rise-float of an object....
This is indeed a science and not an art...
chuck

IRC Kevin

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Re: Mid-Water body search
« Reply #7 on: September 22, 2011, 04:13:12 PM »
Thanks for this folks. I think it's probably worth setting it up, as it doesn't impinge on the side view capability in any way and may just work. Our main methoolgy will be recording grid pattern searches and if possible, using multiple card readers, so a team can be reviewing one run on a laptop with Humviewer, whilst the HB runs another search grid. My main task now will be to get a training pack together for our OPs members who've never even seen a Humminbird yet.

Offline sonar2000

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Re: Mid-Water body search
« Reply #8 on: September 22, 2011, 06:46:18 PM »
Kevin, you can train anyone to run the unit and make a recording. In fact we have done this several times by having fishermen run the scan and then we review the runs.
The most important person you can develop is the one who reads the recordings and determines if there is a target or not.. Usually this is not more than two people on the team. Dedicated to sonar..
Of course they have to begin at the start and learn the unit and its characteristics. Then learn to identify the underwater world as seen by sonar.
Here is another key.  Not one sonar does everything. Each  has strong abilities and each has its limitations. So when you sonar for a target you also have to look at what the unit is capable of doing.
I will add to this that we have 3 types of sonar/manufacture and each has its place and each has its time to stay in the tool bag...

HB is just one too.  So learn it carefully and understand when it is time to call for another brand of sonar.  In a nutshell....you get what you pay for..but that is also a bit misleading as our $35,000.00 (usd) has times when it just wont do the  job. So we fall back to the humminbird.  Also We have use for sector scans.  So now you can see that at least 3 in the tool bag. 

Not trying to be discourging but learn your HB and understand what is can do and what it cant do...

Chuck
« Last Edit: September 23, 2011, 08:48:17 AM by sonar2000 »

Offline Roddy

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Re: Mid-Water body search
« Reply #9 on: September 22, 2011, 08:17:47 PM »
Kevin,

Yes fish alarm will sound if a midwater body is found. SI /DI are best bets midwater and bottom. Fwd Looking Interphase twin scope is good midwater to the top. Any target below 30 feet use a tow fish for a bottom search.

A dead shaved goat makes a real nice tng target (Just tell P.E.T.A. that someone is hunt'n a furry something at the other end of the state.

Roddy
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