Usually just ahead of the keel.... it's usually a flush fitting so may be painted over.. alternatively its mounted in a box or tube inside the hull (or glued on), shooting through a liquid or gel and the hull skin. Then I'd look for it under the Vberth somewhere.
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
1984 Fast/Nicholson 345 "FastForward"