Re: Aluminum boat electrical field discussion
All my other boats have been glass, and I never worried about it before now. What are the thoughts, opinions you have on an aluminum boat, painted or not creating an electrical field while trolling sending fish running?
I know the problem exists, I'm not however pretending to be any sort of expert on the matter and would like some intelligent/educated input on the issue and how best to avoid it.
OK, simple question can't be answered so simply. I'm not so sure that a problem exists unless you specifically design a "black box" to create it. As I understand electricity, it's a flow of electrons through a pathway from one point to another. The two points must have different charges (picture a bigger pile of electrons on one point than on the other) for there to be a potential for current to flow. With the exception of electrostatic charges, there must be a complete circular return path back to the power supply before a continuous flow of current can exist.
Electrons from your boat's battery post have no desire to flow anywhere but back to the battery's other post. In a properly wired system, electrons have no desire to leave the battery and enter the water. A properly wired system typically has an unavoidable electrical connection between the negative post and an aluminum hull via the engine, be it an outboard or an I/O. Your hull also has an unavoidable connection with the water, paint or no paint. OK, so your boat's negative terminal is connected to the water. If you drop a wire from the positive terminal into the water, electrons will flow through the water between the submerged wire and the aluminum hull in their quest to get back to the battery. They will not only take the shortest path, but every path that they can find to get back to the battery. So the water in the area of the boat will become a wide path for current flow that probably would offend marine life, even at a very low voltage. So, I'm not convinced that positively charging a downrigger as mentioned above is a legitimate way to actually prevent offending fish.
A second concern is hull corrosion. As has been generally advised, using the metal hull as a negative return path (as you would use a metal car body) for various loads such as lights should be avoided. Doing so causes current to flow through the hull's skin to the engine and back to the negative battery terminal. Current flow through the hull can rapidly damage it, particularly at any points of high resistance. It is also a functionally unreliable path. So keep your negative wires from contacting the hull and make sure that they are equivalently sized to the positive wires in the circuit.
Corrosion can also exist through electrolysis where a current flow is established between two dissimilar metals placed in an electrolyte. Two metals having different "nobilities" such as aluminum and brass will establish a current flow that eats away the less noble material (the aluminum). The water surrounding an aluminum hull provides the electrolytic current path, salt water being more effective than fresh water. These conditions exist even without a wiring system on the boat.
Lastly, when shore power is introduced into the equation, the physical rules for electrons are the same, but the pathways for potential current flow are different. 120 volts AC arrives at your boat with a potential to flow to ground (or your aluminum hull in the water). The only reason it has this potential to flow to ground is that back at the voltage source, the transformer, the supply utility has connected one of the transformer terminals to earth, typically via a ground rod as required standard practice. Should the live (ungrounded) wire somehow come in contact with your hull, a short circuit results with current flowing the hull, then through the water, back to the shore and then back though the soil to reach the ground rod and the grounded terminal of the transformer. Again, electrons are not trying to get to the earth; they're using every pathway back to the power source, including the earth. This current flow can exist in the water between two or more vessels and the shore, because of one improperly wired vessel. Damage to aluminum hulls and engines and any submerged fittings can rapidly occur. There are ways to isolate electrical systems and prevent this damage, but this is getting too far off topic. - Grandad
