Mike, do you mean the ceiling inside the cabin? If so our early Mk II has no ash wood in it, everything is teak and there is no wood on the ceiling it is just a dimpled white gelcoat.

The layup schedule that I have that was issued by Catalina in 1997 shows 1/2" balsa core in place of 3/8" plywood that was used in earlier boats I gather. Perhaps someone with a later Mk II could weigh in on what's on their cabin top ceiling?

Or do you mean the strips of wood that run along the hull sides in the cabins where the hull portholes are? That might be ash and on our boat I don't believe there is any plywood behind them from what I can tell they sit right against the inner hull line. Again, it's an early Mk II, post '97s might be different.

technically, the nautical definition of ceiling is as listed below. The thing you call a ceiling in your house, is the 'overhead'.

Term: ceiling (n)
Definition: The lining or inboard sheathing covering the frames of a wooden boat. Usually ceiling is light planking or slats covering the frames in cabin areas to provide insulation, deaden sound, reduce condensation and provide a more finished appearance. (Lubbers beware: the ceiling is located along the inboard sides of a ship, never overhead.)

I've always figured that what's on our boats is probably ash strips with some sort of backing; maybe a thin plywood? But I've never had it off. I guess Catalina would know?

I did individual ash strips on my previous boat, butted up next to each other and screwed onto battens with hundreds of slotted brass screws all lined up. Beautiful, but labor intensive. If I had to do it all over again, perhaps Home Depot beaded board, although the double beads are not quite nautical. For a more nautical appearance, if you have a Dremel/router with a beading bit, you can take plain ash plywood and cut your own single beads, thus simulating individual strips butting up next to each other. Consider using velcro strips on the hull and some on the back of the plywood to attach. Use bits of stiff foam as battens where necessary using contact cement. Ash beaded board and plywood are usually available in 1/8", 3/16" or 1/4" thickness. Get some scrap plywood of those thicknesses and experiment with how much stiffness/flex you need.