Thread: Side image distance measurements

I saw this same video the other day. Very informative and well explained I thought. Yes that is my understanding too about how he said it showed. Down then out for total. Sort of confusing.

I thought it was combination of the two beams.


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Originally Posted by lugnutzz

I thought it was combination of the two beams.


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Watch that video. Think it will make it more understandable to you. I stayed confused trying to cypher out distance until I watched it. Now I think I understand it much better.

Originally Posted by Cray

Watch that video. Think it will make it more understandable to you. I stayed confused trying to cypher out distance until I watched it. Now I think I understand it much better.

Next time I get out in my boat I’m going to move out to at least ten ft of water and find a tree and then scan it as I pass by and compare the screen distance with the actual.


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I rely on SI to show me fish, structure etc. I then turn to DI or 2D sonar to confirm the depth of what I have discovered and marked by further examination. SI is a valuable tool, but with out down sonar or down image technology it's almost rendered useless in my opinion.

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It is really simple to me . Some say they can not know exactly where the fish are on the screen . I just run curser over and mark fish as a way point then go investigate . Works for me . lol the distance set in 1/4 increments also set on 40 ft helps .

Originally Posted by RustyJig

I was watching a fellow on YouTube, who seemed very knowable, give a class on side image distance measurements and how to determine where a brush pile, stump, etc. is from your boat and he demonstrated it by placing his boat in a parking lot and towing a cooler out to the side and behind his trailer. He proceeded to show how the fish finder displayed this objects distance from the transducer. Everything was clear to my understanding until he said that if the object showed 25 ft to the side of the boat and that you were in 10 ft of water then the object is physically only 15 ft to the side of the boat. He said the transducer shoots a beam to the bottom and then to the side and you must deduct the depth from the displayed distance displayed.

This would have to be taken into account if you threw a marker bouy for instance. But, he said if you use the “mark” button on the fish finder it would mark the correct spot.

Let’s start by acknowledging that calculating distance to any target in the SI image is not simply “subtract water depth from the SI range to get distance to target”...

It is physically and scientifically impossible for any Sonar beam (sound traveling in water) to travel to point A and then change directions to get to point B (as in the common misconception of measuring from the xducer to the lake bottom and then measuring out from that point) ...

Horizontal Distance to any target in the SI image is a ”slant range CALCULATION using the Pythagorean Theory” ...

Using the OP scenario of 10’ water depth and seeing a target in the SI image 25’ away from the SI image center line ...:


Next we will delve into the HB software engineer’s minds to explain why the HB software engineers designed the SI image layout as they did ...

But 1st I will give space for questions ...

Rickie

I looked at the side image screen shot in the YouTube video and notice that the measurement gradient start at the center of the boat. That would explain why you need to subtract the depth from the total measurement to an object since the screen displays the water column to the bottom before the side image appears.

So here is my conundrum, if you have your helix set to scan 50 ft to the side and you are sitting in 40 ft of water then you are really only scanning 10 ft to the side? Or, are you still scanning 50 ft to the side but only displaying the first 10 ft?

I agree that the helix is probably sending out two beams, one down and one to the side or one beam is rotating from down angle to the side.




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