hi folks, quick question ...

i've been reading a lot about sacrificial zincs for protecting steel
hulls and i haven't been able to figure out from my reading where they
are mounted. my reading material says how they are mounted, like
welding, or hanging on metal wires, etc, and it says where they are
mounted in relation to each other ... that is, certain distance apart
to protect such-and-such square feet of hull, etc ... but i have more
basic questions like, do they have to be on the outside of the hull or
can they be inside ? and .. do they have to be submerged in seawater
or do they work in the air ? i can't tell if you have to weld them to
the underside of the boat so that they are in the seawater or if you
can just hang them from a wire inside the boat somewhere in the air
where they aren't in the way (while being electrically connected to the
hull of course).

thanks again for the help.