The bulkhead is the "wall" between "rooms" on a boat and is many times structural holding up the "roof" (deck) and many times the chainplats are bolted or fiberglassed to it. If the chainplate is not sealed ten water gets in and rots the wood so it is bolted to mush. Your repair
depends on extent of rotten wood (if any) and if your chainplate is bolted to it. Sometimes the chainplates are bolted to a solid fiberglass hull and the only thing needed is to fix the leak.