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The Proof of Humminbird Down Imaging

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A buddy of mine Mike Bucca performed this test. We worked for several days trying to figure out how we could prove the theory of Down Imaging and Fulle Coverage of SI. This test Proves it:

After all the "hoopla" about Down Imaging and questioning whether Down Imagingg scans directly under the boat I thought of an experiment that would prove without a doubt that the the DI IS TRUE Down Imaging.  Let me first go backwards a little bit with some images that have already been posted and then I will move towards my experiment. 

Nobody knows 100% for sure what is inside a SI ducer except for those @ Humminbird and anyone who has personally cut one open. Does it strictly have 2 beams?  Was Humminbird creative enough to have a 3rd beam inside with the intent of doing down imaging?  I don't know the answers to these questions but read further and see if it matters based on the images below.

We started off with this SI image.  This is based on the "theory" that Humminbird uses 2 crystals and creates down imaging from these two crystals to get True Down Imaging? 

If you look at this photo above you can see that I split the trunk of a good sized tree AND it's limbs all the way to the tips which as you know are much much smaller in diameter.  It was also "theorized" that there is a weak signal at the edge of the DI beams.  In this photo there seems to be NO weak signal which is proven based on the crispness of this image above.  If there was a weak signal it would be blurry on the leading edges and you probably wouldn't be able to pick out the seperate limbs...

An argument was also made that this tree was "massive"  So enter exhibit "B".  A smaller tree. 

Again split right down the middle and it's limbs matched by the adjoining red lines. So if in fact there is a gap or weak signal its surely not shown in these side images as the limbs and trunk is again clearly shown.  I got 50 different images of where I have cut tree trunks and limbs in half with Side Imaging so I won't bore you with excessive images.. 

So even with those two images and many others that were presented by Doug and myself I wanted to take it a step further.  So lets take a KNOWN SMALL target and see what we can do with it. 

Here is a balloon.  It was blown up to roughly about the size of a volleyball.  It is approximately 7 inches across.  It is anchored by a milk jug full of rocks with twine and a bouy to above it which marks the spot on the surface.

So all I had to do was run over the bouy to try my hand at SPLITTING a Ballon in half.  I was careful to take the boat out of gear to prevent it tangling in the prop as I heard the bouy slide under the hull. 

The math is 3.5 inches is HALF of 7 inches the width of the ballon.  Can I get 3.5 inches of a balloon on either side of the SI beams AND have it show up on SI, DI and 200khz sonar??  Here is the cross segment of that experiment.

The balloon is approximately 15ft from the bottom and it WAS SPLIT in half by the SI beams (3.5 inches on each side) and it did show up on DI and 200khz (20 degree) sonar.... 

Here is a bigger image of the screen shot.

and just in case you think I got lucky  :wink:

I got plenty more images where the balloon has been split and others with 200hz, 83hz, 200/83 sonar split with DI etc etc..  This one below shows that I had the sensitivity on just 12.  Just a little over half way which means I still got more JUICE to spice up the image. I bet I could have easily gone to 10 and still see the balloon.

Here is proof in the pudding and what it all boils down to..

Having done the test above proves that there is solid coverage below the boat.  Knowing how to get quality images and basic tuning of your machine is part of getting the most out of your unit.  If your unit can't do this simple test call Humminbird customer support @ 1-800-633-1468

Enjoy your FREE TRUE down imaging :).  I know I am :)



Glad to have you over here on the forums.  I have been trying to make this point for months!  Thank you so much for such an intutive post.  This shows without a doubt that the coverage is 100% (or damn near it)!

I look forward to seein more post from you!


Jolly Roger:
Wow Doug,
that is one hell of an article, thanks a ton!
As we say over here "a picture tells more than thousand words", this is truly showing in your post.

I really like the test setup and the results even more. Makes me also a bit jealous seeing some going out on the water, while I have the boat in winter storage.  ;) Can't wait to go out and play with my 981.

Thanks again and greetings from Germany

Great pictures, can't wait for ice out.


Welcome Rezfisher. Glad to see that you have joind us. Hope to see you more often.


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