Thread: SI fish in water column?

Originally Posted by brettw

Ok
I have a question about what I'm actually seeing in the water column, the black portions of my SI.
If I'm in 25ft of water, i know I'm seeing 25 ft of water straight down, but is it also showing 25ft to the side of the boat?
In other words, using SI in 25ft of water would i be able to see fish 25ft to the side of the boat in the black areas on my screen ?

Hope this makes sense. Never heard it discussed.


Thanks




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So I’m no pro but let me try at this with what I know. So if u set the range at 100 feet on both sides and your in 25 foot of water, your only scanning 75 foot out the sides. The 25 foot down is part of the range. The black column on the SI screen is below the boat/straight down. Hope this helps and I think this is what your asking. Again I’m no pro on this!

Thanks
Reason I'm asking is i was scanning for crappie under docks. 1st time I ever really did that.
Didn't see much , poles shadows.
A friend told me to get close to the docks and i could see fish in the water column under the docks.
I couldn't pick them out of the orange humminbird background but a black background would be easy.

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Here's a 'bird screen shot of a huge school of crappie under a floating dock. Below is a dock with no fish.


Sonar only shows range to object. Depth is straight down, or one side of a right triangle, and range shown on screen is the hypotenuse of the right triangle *. It is not linear. If your depth is 10 feet, and fish is at 30 foot range mark, the distance out from side of boat (assuming fish on bottom) is 28.3 feet per Pythagoras theorem: z**2 = x**2 + y**2. X is depth, and z is range shown on screen. Solve for y.

*: assumes flat bottom. if bottom isn't flat, it gets way more complicated. Google "sonar slant range". HTH

No, I don't keep a calculator in the boat. I do have an app on my phone. I just make a SWAG and cast!

You can learn a good bit when bream are bedded. This year I started throwing out markers when it first comes on screen and when it goes off. Then circling around it several times shows me how the screen Vs real world relates to one another.


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The dark water column represents everything within a semi circle equal to (or less than) the water depth ...



The bottom detail (left and right) in the SI image is actually touching under the boat. The SI software engineers simply “scooted” these 2 sections outward in the SI image to make room on the display for the water column ...
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Targets in the water column that are the same distance from the xducer will be painted in the SI image as the same distance from the SI image centerline (regardless of where those targets are in the water column).



Then use the target shadow to help the “mind’s eye” visualize how high that target is off the bottom ...

Rickie

Rickie,
Thanks for the information. Very help.
And difference in the semi circle between 455. 800, or mega frequencies?

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455kHz and MEGA cover 180°

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800kHz covers 130°


Rickie