Quote Originally Posted by jimp View Post
the HB should be hooked up to the cranking batt, this eliminates one source of electrical interference but not all sources. Make sure the HB power wire is not close to the TM power wire as this can cause interference when using the TM. Cross the 2 power wires at 90 degrees if needed, opposite sides of the boat if all possible. You may have the ducer mounted in an area on the transom that gets turbulance from the big motor, I'm thinking that there is a upper speed limit of 8-10mph on DI units before the picture goes fuzzy and inaccurate, but not sure on HB units.
The water depth number is taken from the 2D sonar in the Humminbird units. Sounds like you may be getting electrical interference of some sort as well as air around the transducer at higher boat speeds as jimp stated. Next time out on the water try turning off all other electronics on the boat and see if it shows that clutter again or not. Than start turning each piece of electronic equipment back on again until you see the interference again.

By the way; is the unit wired directly to the cranking battery or is this through a fuse panel/block? It is best to wire it straight back to the cranking battery (using an in-line fuse of course).

For the high speed readings; try lowering the transducer and/or lowering the back end of the transducer slightly. You have to get it into clean air bubble free water to work at faster speeds.