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.
1984 Fast/Nicholson 345 "FastForward"
".. 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)