I'm using this unit on a 13' Boston Whaler. When using the 40 HP Merc there is no problem at all. When using the Electric Trolling Motor, this thing gives false readings of depth and shows tons of fish that are not there. As soon as i shut off the power to the motor, it returns to normal operation. I added a choke in the power line and it did not help. Thanks. Gary gtallmon@comcast.net