Thread: Getting The Most From Your Graph (Sonar, Sounder, Fishfinder Thangy, etc.)

Originally Posted by stumpbumpers

Jerry Blake this thread may end up needing to have it's on forum with you as the moderator... :rolleyes: :p :D

Well, I have about 7-hours in it already. I was off today and needed something to do. I have trips scheduled for the next four days, ten trips in the next twelve-days, though so it will have to take care of itself for a while. I'll get some pictures to add and maybe that will help.

Thanks Jerry for this post. It is very informative.

Originally Posted by Jerry Blake

Hey Allen:

Thanks but no thanks - I just wanna go fishin! How's your youngun doing? Is she ready to go fishing yet?

Thanks for asking Jerry. She is getting better everyday. Still having trouble keeping balance and walking. Should be better in a week or two. She has been asking to go, but my two year old is ALL about counting the fish on your website. We do it every night before bedtime. Got to work this weekend, but next weekend, I may try to make a trip over to Cane Creek with them. Maybe run into LA Stumpjumper as well.

Originally Posted by bobberwatcher

Thanks for asking Jerry. She is getting better everyday. Still having trouble keeping balance and walking. Should be better in a week or two. She has been asking to go, but my two year old is ALL about counting the fish on your website. We do it every night before bedtime. Got to work this weekend, but next weekend, I may try to make a trip over to Cane Creek with them. Maybe run into LA Stumpjumper as well.

Sounds like she'll be ready to hit the water soon. I'll be back on Greeson tomorrow and hope to have plenty for your two year old to count!

Originally Posted by Matt Smith

If the air pocket is what reflects back to the transducer, then why does brush and other water-logged structure show up on the sonar?

I've never heard of the air bladder producing the signal. Do you have any articles or web links to support your "impression"?

Second paragraph under the section "Transducer Frequency", in this article:

http://www.boatus.com/boattech/SelectTransducer.htm

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This, from a Furuno Color Depth Sounder article:

The airbladder of fish is what returns the echo to the fish finder. So the larger the fish, the larger the air bladder and thus the larger the target on your screen. Bait fish show up on the screen as a ball, because the echo is being returned on their collective air bladders. The air bladder on a single baitfish is too insignificant to return an echo, but as a school, their air bladders can be picked up by the fish finder. Remember, the denser the target the darker the color will be on your display.
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This, from Pro-Troll.com article about using depth finder to selectively pick out fish species, based on their air bladder size/shape:

" Fish finders cannot read through air. Most fish have air bladders. The locator beam put out by your fish finder passes through water but cannot pass through air. Fish finders read the air bladder of a fish, and the image is bounced back to you."
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And the Vexilar article, "How Sonar Works":
http://www.vexilar.com/help/tips/tip011.html

And, I've read other articles that basically say the same thing.
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I've used depth finders since the first "flashers" came on the market. It has always been "reported", by these fish/depth finder mfg's, that the signal is bounced off of "anything" that's denser than water ... be that rock, weed, wood, etc. They also state that the air, in a fish's body, will interrupt the signal ... and even "warn" users to not place the transducer where "air bubbles" (caused by turbulence) will pass over it, as this will create false signals or signal clutter on your screen (and, essentially block out some of the return signals .... those of the "fish/cover/bottom").

The "ping" doesn't travel thru air very well ..... that's why you can't get a "bottom" reading, on your depth finder, when the boat is on land and the depth finder is still running. It's "sonar" ... not "radar". :D

To answer your question about why we can see "waterlogged structure" -
The "other objects" (brush, trash, thermocline, rocks, etc) are "denser" than the surrounding water ... and they reflect or absorb (change) some of the signal. That's why we get their "picture" imprinted on the screen ... the differences between the strengths of the returning signals are processed by the unit, into the pixel picture which you see on the unit.

............. cp

I would think that the body parts of a fish like muscle, bone or even scales would return a signal better than air in an air bladder. If air "interrupts" the signal rather than reflecting or returning it to the transducer then it wouldn't be possible for the transducer to "see" it.

The transducer sends out a sound wave and has no way of knowing what part of that signal has been interrupted. All it can process is the small fraction of that signal that is reflected or bounced back from an object. I've dumped remains from filleted fish that no longer have any air in the air bladders over the side of the boat and they show up on the graph very much like live fish do.

When I have time to do some experimenting, I'll tie a filleted fish carcass on a line without a hook or jig and suspend it under my graph to see what it looks like.

If a graph can "see" a 1/16-ounce jig I have no doubt it will pick up bones in a fish's body.

It doesn't really matter though what part of a fish returns the signal to the transducer. What is important is having the graph adjusted so it will display fish on the screen and for the operator to understand what they are seeing on the screen.

" Fish finders cannot read through air. Most fish have air bladders. The locator beam put out by your fish finder passes through water but cannot pass through air. Fish finders read the air bladder of a fish, and the image is bounced back to you."
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I believe this. Cut the air bladder out of a fish and dangle it under ur sonar. Hard to see...Fish body bout like ours. Bout 98 to 99 % water. That why higher power sonar units haver better echo return than the lower wattage units. Too much power can be bad as not enough power... catch 22 here.

Kinda sounds like some of yous guys have been sitting in on my sonar classes...ha

Explain this....

We know that the right screen edge is the "real time" echo return and the display is nothing more than a history file. True.
Now, with respect to the cone angle, is what we first visually see on the display: the center of the cone angle, the front of the cone angle or the rear of the cone angle?