Help Me Troubleshoot my Humminbird Transducer Interferance

[VABasser]

I've got a Humminbird 798c SI installed on my 2004 Bass Tracker 185.  My dad installed the whole thing (he's pretty good with that stuff), but from the beginning we've had trouble with the Side Imaging on the left side, particularly in shallow water.  In shallow water (<5 feet), the left side imaging is basically worthless, it's mostly just a black screen on that side.  In water over 5-6ft, there's varying degrees of clarity.  Sometimes it shows a pretty solid picture on par with the right side, other times about half the screen will be black (for instance, say I have SI set to 100feet, the first 50 feet from the boat will be a normal SI picture, but the 2nd 50ft is black or very dim and unclear.  And no I'm not 50 feet from shore).  If I am running the trolling motor and not the outboard, it seems to give a better picture.  All of this leads me to believe I am getting some kind of blockage or interference from the outboard?  But what do I know?  We moved the transducer to see if that would fix it, but its the same, if not slightly worse.  I don't have pictures of what the screen looks like, I keep forgetting to take some.  However I have attached two pictures of where the transducer is.  The triangle of old holes you can see to the right of the transducer is where we first had it installed. I'm at the end of my knowledge, can anyone help me figure out what's going on?   

[Wayne P.]

The transducer needs to be down there where the hull drain is so the motor does not block the left side SI pulse. It can be on either side of the keel as long as it is not behind a hull strake.

No transducer should have been attached where the holes are EVER.

Tracker has done that stupid location from the beginning of the stepped transom until the 2012 models.

Starting in 2012 they finally got it and this is where the factory installation is now:

[VABasser]

That's good to know Wayne, you're the man.  So if I move it down to that first step I should be good to go?  Do you just level it with the main transom area to be sure it's installed straight?  By hull strake do you mean the ridges underneath the hull?  Any tips or good videos for installing the transducer?  My dad doesn't live near me anymore, and I don't know if I trust myself drilling holes in my hull 

[Wayne P.]

The hull strakes are the ridges that go most of length of the hull. Yours are beside the trailer bunks.

You can use the transom step line as a guide to the left to right leveling, not the hull bottom. Bottom line is the transducer should be parallel with the water's surface and low enough to have water contact when on plane. There should be a rubber plug in the gap between the mount arms (it's called a rooster tail plug). If you put it below where it is now, 1/2 of the left side should be lined up with the hull bottom forward of it. That would put more of the right side below the hull since the hull is slanted.

You can download the installation instructions from the Humminbird website or locate the instructions that came in the transducer package. Some add a mount board to the transom for transducer attachment so if they make a mistake with the location, the transducer can be moved without putting more holes in the hull. Do not overtighten the screws as that will fracture the mount base you may loose the transducer. I see that the cable clamps were not used, USE THEM. That way if the mount breaks, the outboard prop won't eat your transducer.