I'm pretty sure that Denise is correct and that the 87 H31 is an iron keel. (Many of the Hunter series used iron keels) That said, the post repairs should not be a big deal unless the support in the hull, or the structure of the deck in that area is damaged.
Either way, though, I'd guess the stick's gotta come off to make the proper repair.
".. 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"