I suspect you'll need to take a pattern of the old base and go do some winch browsing at your nearest suppliers (or on-line). You'll be very lucky to find a match.
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)