Actually, the current your boat puts out is from the different metals in the water interacting with each other, not from the hull at all. Aluminum outdrive, zincs, steel cable, stainless steel, all act with water at differnt rates, which creates a charge. Add salt water, and it is worse yet. If you look at a dry cell battery, it is just two different metals in contact with each other creating an electrical charge as they dissolve each other, so to speak. Therefore, every boat will have a small electrical charge around it, even without downriggers from the interaction of the water on the metals present. If you have a ground problem on your electrical system, or all of these metals are connected physically, you have even more of a problem. The hull material doesn't matter, you still have the same metals in the water. Now drop a couple of steel cables a couple of hundred feet down with bare lead balls on the end and you have just extended a couple of antennas to take this electrical charge down in the water to your bait. I thought my glass boat was fine until I checked it out. I now have a black box I will install next week.