Twisting power wires is primarily about reducing fields around the wires and decreasing the effects of fields that exist near the wires by constantly changing the direction of the wires, which effectively causes the fields to cancel out. It is most effective when there is no mechanical electrical connection between the circuits.

The main cause of interference from trolling motors is the rapid current surges caused by the pulsing of the PWM controller that allows for variable speed trolling motors. When they share a battery, the input power of the depthfinder is going to rapidly change voltage at the same rate as the trolling motor speed control, and it can be very difficult to filter such noise out of the analog circuits in the sonar. It would be much like trying to write smoothly while someone is dropping a bowling ball on your desk constantly.