Thread: Reverse course to find more fish using Humminbird Side Imaging

Great information, thanks and do more

Just a heads up. Part if his issue is also the lower unit of his motor blocking some of the signal. That is why the pic changes so much when he turned. I always trim my motor up some to take care of this issue. Seen this way to many times and 90% of the time is the lower unit cutting part of the signal. Shoot my old unit shows fish even on hard bottom like that, but I have to get the lower unit out of the way.
This shot is hard limestone bottom and rocks, but you can see the fish on both sides of the rocks. I did have the same shot with the lower unit in the way. But can't find it now.

I can understand why a person might think that there is some obstruction that is blocking Side Imaging on one side. However, that is not the case in these screen captures. The reason I know that with 100% certainty is at the end of this note.

In the first image below, I have full coverage to the limits of my displayed range. The right side is pretty dark, but that is because the soft bottom is sloping sharply away from the boat (see the LakeMaster chart on the right for the contour changes). The fish are absent, and I think this is the image where you perceive that I have some blockage on the right side.

However, when the boat is turned around (like in the second image), if there were persistent blockage on the right, then the bright white rocks on the right would be obscured. Quite clearly they are not.

I tend to run at low-moderate levels of SI sensitivity and contrast. Doing so allows me to see very subtle features, and lots of fish, that would otherwise be lost if I ran at high sensitivity and contrast.

To avoid blockage issues, I run two HDSI transducers, one on either side of my outboard. No way to have obstruction from something that is on the inside of the pair transducers.

Hope that helps!

Generally when the lower unit blocks the sonar it also reflects it back to the transducer. This is what often causes the vertical line(s) next to the centerline on the Si sonar Views.

Originally Posted by Humminbird_Greg

Generally when the lower unit blocks the sonar it also reflects it back to the transducer. This is what often causes the vertical line(s) next to the centerline on the Si sonar Views.

So if I have that vertical line next to the centerline, is my SI image being partially blocked, or completely blocked. I do notice when I come around from the other direction I'll get better SI shots.

Ron, it looks to me like Shiloh Red has some blackage on the left side. Jason's look clear on both sides.

Partially blocked Shellback. If it were completely blocked there would be no Si sonar image to that side.

Now, just because there is a line running parallel to the centerline does not mean that the Si sonar is being partially blocked by the lower unit of the motor. It could be getting reflected off of many things like the inside of a jackplate, the aerator intake screen, another transducer,… or even aerated bubbles flowing off the side of the hull. There could also be an issue with the transducer itself that is causing this.

I think you are 100% right there Don G.