Ok, I have done a lot of searches and looked through different forums but I'm not finding what I am looking for. Here is my situation, Lowrance HDS Carbons front and rear, 24 v MotorGuide XI3 with Pinpoint GPS. I have 2 12 volt batteries run in parallel for the TM. Then I run 1 HDS off 1 battery and the other HDS of the other battery. The only transducer I have is on the back of the boat (which is a 16' Lund, all aluminum). As you can guess when I run the trolling motor I get interference on the graphs. I have read about using chokes, running a ground from the TM skeg to the battery, twisting power wires, shielding cables and have found some of these work and some don't. Now to my problem, If I take a wire and run it from the ground side of either battery to the hull of the boat, it clears up the interference on both graphs. I have read that this is a bad thing because it produces electrolysis and will destroy an aluminum boat. Is this true or is it ok to do. I don't understand why this simple connection clears up the interference on both graphs. Everything is run in a closed circuit, I'm not using the hull as a path for any of the circuits so I don't understand why hooking this wire from the negative battery to the hull would cause electrolysis. If anyone has any wisdom into this matter please spread the wealth. Thank you.