WHOA BOY ... is that panel shown the rear-most outside transom skin? If so, I believe I can see evidence of chloride precipitate corrosion in the aluminum skin and while you can remove it where you see it on the surface, it can keep corroding internally, as it feeds on itself.Spoondragger said:
BEFORE you start adding a new transom core, you really, rEaLlY, REALLY need to check that transom skin out well! I had a Starcraft, wood non -PT transom, but the wood wasn't sealed with any sealer. It held saltwater, which becomes an electrolyte, especially were stainless steel hardware is used on the boat. My transom skin looked like that and if you see "white" in between the inside and outside layers, you need to grind it all out. Look at the picture attached of my old transom wood, where the boat was under shrink-wrap and hadn't been used for 2-years and when I tore out the wood, it was still weeping a salty, decomposing ooze!
In my case I has BB-sized holes end up being 5/8" diameter. It reached the point where I had to make the decision to fhuggedabout salvaging the original transom skin and put in new ones. That ordeal (will NEVER do it again ... ) is well documented in my signature ...
Check the perimeter of your transom skin, perhaps there's enough usable and good material there to put a new piece inside. Tip - NEVER apply goop, e.g., 5200 or epoxy to an un-primed tin skin and never used silicone on tin as most use an acid base as a curing agent. Wash bare tin with straight white vinegar and scuff with a good scouring pad, then let dry. Then prime with a good zinf-chromate primer. Sandwiching UNprimed/prepped tin between substrates and/or apply products like 5200 WILL cause corrosion to the unprotected tin.
If that hull were mine and usable, I would rivet a new panel of 5052 to the inside, maybe even with a layer of fiberglass in between, then dry fit a piece of 3/4" ply where there were dimples made in the wood to allow for the rivet tails, so that piece can lit perfectly flat to the hull. Then I'd add a layer of glass. Then another 3/4" panel of wood and perhaps an inside tin skin - if needed and if room. All panels would have the edges wet-out a few times with Raka epoxy (https://www.raka.com) 1st, and coated. Messy, but I'd even consider install after another coating and installing everything wet to almost kicked.
Essentially I would be laminating and gluing that new transom together! I'd also put in some large 'L'-shaped brackets to tie the transom skins to the sides of the hull. Grease your SS bolts for fixing things while they cure. For final install, I'd use SS bolts with adhesive-lined heatshrink on the threads, and nylon washers under all boat heads and washers.
And for added safety factor ... please add a Johnson "high water" bilge alarm, only $80.
For your floor, if well supported, I see no need for 3/16" stock, when a panel ~0.100" would do it.
