Losing bottom at speed seems to haunt me also. Dang near every boat I had before the present one had the problem. This boat, a G3 V-170T with a Humminbird has never lost bottom. I don't know if I finally got lucky and hit the sweet mounting spot mounting the transducer, or it's the hull design. Sure can be frustrating. I hope you have a transducer mounting board which will allow you to move it around without affecting the boat hull.