I sure could use some thoughts here on getting my rear mounted Humminbird 170 to work better.

I have a 15ft Alweld semi-v johnboat with ribs on the bottom ( no rivets, all welded), 25hp tiller Yamaha. Its a good little fishing rig, fuel efficient, and all I really need, as I hunt & fish year round with it. First off I know boats like this can be difficult to get good transducer readings with all the turbulance. But at this point I can only get reasonable readings when at the absolute lowest forward rpm or neutral. That's not working well at all. Any thoughts on transducer mounting changes? Hopefully the attached pics will help. I have to say I did adjust the transducer forward tilt a bit to try next time out. And you will note I have two small alum trim/planing tabs on either side of boat, those came built in. On the 2nd pic, I was trying to show how the transducer bottom is fairly parallel with the bottom of the boat and on the inside of that rightside trimtab. And I have the transducer almost centered between two ribs.

I have a HB565 mounted up on the front casting deck with its puck on the trolling motor. Works well, no real issues. But the $500-600 combo DI/SI/gps units are very interesting these days, I have no idea if those would work on my type of transom?
I do the usual bream/crappie fishing, and about to start spider rigging.

Thanks ahead of time for any thoughts or suggestions on all.