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.
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.
But, the word "interrupts" was MY interpretation ...... I assume that the air "reflects" a signal back. I was equating both words, to mean the same effect.
And, yes, you are quite correct ...... it doesn't really matter what reflects the signal, or why, in the greater scheme of things. I was just challenging the idea that a catfish won't show a double echo, just because it has skin (and not scales). IF the return signal is, in fact, being reflected by the air in the air bladder (as stated by most sonar mfg's) ... then why would it not show up on fish with skin, in the secondary reading, since those fish do have air bladders ?? I wasn't disputing anyones "beliefs" ... I was seriously wanting to be shown some evidence. .... cp
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?
What you see on your display is somewhere within the view or cone but with a single beam transducer there's no way of knowing what side of the cone it is on. You can get an idea whether an object is moving from the center of the cone to the edge of the cone if the return is getting weaker as it tracks onto and across your screen and visa versa.
Humminbirds's dual beam transducer system is supposed to be able to differentiate between fish in the narrow beam or on the left or right in the wide beam.
If you're seeing fish that are 10-feet deep with a 20-degree transducer they are within about a 3-foot diameter circle so it's not too important where they are in the cone - they are right under your transducer.
When I get over a part of a brushpile that shows fish I'll throw a buoy marker just off to one side and up-wind of that area and then move the boat over and pull our baits to the area using the marker as a reference.
My clients often ask why they don't see any fish on the graph and I explain to them that we can only see what's directly under the boat and not what's in the area we are fishing even though our bait is only 10-feet from the boat.
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?
You know perfectly well, that a "cone" is an elongated, ever expanding circle (for lack of a better explanation) ...... a "dunce's hat" shape, if you will. Therefore, ANY display on the 2D screen is a picture of ANY intrusion into ANY part of that cone, from ANY direction, and at ANY point. The 2D screen scrolls from right to left ... and imprints the return signal, according to strength of return, as a "picture". It would depend on "direction" of the boat, if moving, as to whether you were seeing the "front edge", "back edge", or "side edge" of the cone. If boat is stationary, what comes thru the cone (from any direction) is what you "see" on the screen. The signal is reflected back from the outermost edge of influence of the cone, by anything that intrudes into the cone's "surface" ... regardless of direction.
Case in point: you're running down the lake at 10mph, flat bottom showing on the screen ... then you get a picture on-screen. Chances are, you just passed over that object. But, say the object was a really fast moving fish (going 15mph) ... coming from behind or from the side of the boat ... and it passed thru your "cone" --- it would show up the same. That's the dilemma of using a 2D unit (directional) to show a 3D cone (omnidirectional).
Ok, what grade do I get for this (hope you grade on the curve ... ha) ............ cp
I got one for you then. I use the finder on the consul most when I am running down the lake/river. Setting the speed faster then would be a good thing right. Just slow it down when I am using it for a finder and not for depth only?
Oh by the way thanks for sheding some light on a dark subject. I think you should run for pres. You could get Darrly to be your VP. Just make sure to make crappie fishing a national job or something like that for all us fishermen/women. LOL
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If in doubt, cross their eyes!!
I don't know why people are worried about arches. I have been crappie fishin for 27 years and I am more worried about structure than arches. I fish creek channels, sudden changes in depth, stumps, brush and anything that will hold fish. This holds true for crappie and baitfish. When I see arches or screen clutter this usually means gar or stripes. Mr. Blake is right on his post. This is only complicated if you make it.
I got one for you then. I use the finder on the consul most when I am running down the lake/river. Setting the speed faster then would be a good thing right. Just slow it down when I am using it for a finder and not for depth only?
If you're just using your graph as a depth finder for running down the lake it doesn't really matter. The current depth reading is going to be the same no matter what you have your Scroll Speed or Chart Speed (the speed at which information moves across your display) set on.
If you want to see what the bottom contours are like while your cruising around - keeping an eye out for humps, channels, drop-offs, etc. - then the faster the scroll speed the better. With a slow scroll speed you make look up at your graph and see something of interest but depending on the boat speed it could be several hundred yards or even a mile or more behind you and still be showing up on the screen.
Well Jerry I went to Ky Lake today & tweeked my Humminbirds as I said I would. WOW!!! It made all the difference in the world! I caught 26 NICE keepers & lord knows how many dinks! Turning down the sensitivity & slowing down my scroll speed really cleaned up my display. I was really over doing it! If you're ever around the north end of Ky Lake let me know. I'd like to return the favor. Thanks again.
P.S. I hope you don't mind but I cut & pasted your tips to WORD, and saved them on my computer.
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Teach your kids how to hunt and fish and you'll never have to worry about what they're do'n! Get'rrrr DUN
Sorry Jerry .......
alright, professor .....
(hope you grade on the curve ... ha) ............ cp 
Jerry, You Are The Man!
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