That's a "knotty pine" tongue and grove interior.
Popular in the late 1940's and 1950's (and perhaps later), particularly for the interiors of summer cabins, etc., and apparently still available!
That boats shows the difficulty in designing pleasing lines (and in particular compound curves) in wood (and especially in plywood), by home builders.
All carpenters are not necessarily cabinet makers, nor naval architects.
Makes you appreciate the inherent capabilities within fiberglass and the use of molding forms for boats!
Working in aluminum presents some similar challenges and some of its own.
The grace of the C-Dory lines can really be appreciated in the light of these considerations.
Joe. :teeth :thup