first power boat I owned had the 'bilge' under the sole with a small well for draining aft. when I repowered the old enging slipped off the hoist and came crashing down onto the sole and messed up the ply. First plan was to just repair the damage by inserting a section large enough to catch the stringers, but as soon as I started cutting I found mold and crap, found that everything in there was plywood, and nothing was sealed in any way, roughly half the stringers were tabbed in, the rest were screwed to those,or the 'backbone' and the sole was just screwed to the stringers and caulked at the perimeter. Everything was soft enough that you could delaminate it with your fingernails.
Boat at the time was about 6 years old.
I ended up spnding a month on that boat making everything from the sole down out of marine ply, and encapsulating it and tabbing everything together on the subassembly. Totally changed the behavior of the boat, and reduced maintenance a bit because a lot of things that used to work loose and get wobbly stayed solid,
seats, engine cover and so on, figure the 'loose' floor system allowed everything to shift and wobble, when I redid it it acted as a single unit.
My Ariel has a couple 'open' pywood panels under the cockpit, and an unsealed area above the bilge, but I'm willing to leave it sit, as at 43 the plywood still looks as good as new.
Ken.