lowrance transducer on Triton 1680

I cannot get the transducer mounted as to where it reads the depth on plane, I lose it at around 6 MPH. I have a hook2x7HDI splitshot.
I took off a lowrance X515C and mounted the ducer in the same place. Presently the ducer is mounted prolly 1/8 of an inch below the hull
between 2 strakes. I have adjusted up, down and every possible way imaginable, its driving me to a cold beer before 5. Any help would be appreciated.

Mine loses the bottom when I get up on plane. The graphical display gets hinky first then the numerical depth reading starts jumping all over the board as I pick up speed. But in my case that doesn't happen until I'm going a heck of a lot faster than 6 mph. 6 mph seems way to slow for this problem to happen.

You have already tried moving the transducer lower and that didn't work. If this is a brand new unit, make sure you peeled off the protective plastic film from the bottom of the transducer (just sayin . . . ). You can also try wiping off the bottom of the transducer after it is under water. Humminbird says sometimes air bubbles stick to the bottom and interfere with readings. Some kind of capillary adhesion I guess.

Anyway, I think my suggestions are kind of a stretch. Hopefully someone else has encountered this and can offer up a solution. Also, maybe contact Lowrance customer service and get their opinions on what you can try.

Edits: Typos, autocorrect. Sorry about that.