Ground to an aluminum hull.

[wiperhunter2]

I can't say every boat is set up that way but it is clear your boat is, so IMO it is normal. What you don't want is the opposite thing to happen, touching your hull and the negative side of your battery and getting power. Because this is an issue with some boats, they will put a ion control switch on their downrigger, to stop it, going down the cable to the ball. There is a way to check that, with an ohm meter, you can look it up online.
[signature]