Similar to what others have said... it's a voltage drop because your batteries are up front. Lowrance are the most finicky i've seen for this.

If you make sure you have good clean power to the fish finder, the only other options (besides getting a different FF) are to put the batteries in back or run very large 1/0 or 2/0 battery cables from the batteries to the motor. It's usually the voltage drop on the batteries from starting the motor.... not poor power to the FF.
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