Not ever using a "BlackBox" and reading all of this stuff makes me curious...... Of course, we all know about the sensitive lateral line of fish, and common sense would say that current in the water (too much) would turn fish away... My thoughts are that current travels in water by way of electrolytes (salt, magnesium, calcium, etc.) and being as the sound is laden with these electrolytes I cannot see any current as small as what you folks talk about (.06volt) traveling very far without dispersing and thus the voltage dwindling to nothing.....
Freshwater may be a different story altogether, since there are no (or very little) electrolytes in it the current would not travel very far, if at all..... If one has plenty of zinc nodes on their boat, would that cause more voltage to spread behind and below your boat, or less??
Also, someone said fiberglass boats were worse than aluminum.... How? If my DR is mounted to a fiberglass gunnel, since fiberglass is not a conductor of electricity, how can "bad" electrical charge travel down the DR cable???

Can a volt/ohmmeter be used to see how much abherrent electricity is leaking from my aluminum boat???

Boy, so many questions!!

MC