HB Helix 7 with transducer at the back of the boat. Slow speeds, everything works as expected. High speeds, I get false information (depth is way too high, and screen shows false echos). I've tried all the tricks that the manual suggests - not in line with ribs, change depth, change angle. I just can't get it to work. My boat is a 1998 Alumicraft Super Bandit with a Merc 75 hp if that info is needed. Appreciate any advice!!