It can be tricky to fit an entire one piece replacement bulkhead, but it would certainly make for the best possible
repair. The problem with through-deck chainplates secured to a bulkhead is that there is often
water intrusion, and this is bad news for
plywood. So, whether you do the entire bulkhead or just a piece, I suggest a layer of mat and one of cloth, and
cheap polyester resin over the piece, especially the edges. When securing a bolt through the piece to attach the
chain plate, drill the hole way oversize, fill with resin and some wadded up scrap of matting, and then drill through this
fiberglass potting. Oversize replacement chainplate and backing plate, with extra bolt holes, is a good thing. Also take a good look at where the chainplate passes through the
deck, and do what you can to prevent
water intrusion. I should say, moisture intrusion. It usually isn't a steady dribble... more like a seep.
You might also consider moving the chainplate to the
hull itself, with proper reinforcement and backing. I have done this a time or two. Sometimes it is the best way out of a dilemna.
While you are messing with this
project, carefully inspect your chainplate for crevice
corrosion. These things do fail, sometimes.