Re: marine flooring
The plywood I used for the floor in my 18' Starcraft Holiday restoration was definitely pine. I bought and used enough wood in my day to know woods.
I bought it from a regular lumber yard in Dallas, TX. on Harry Hines Blvd. who just happened to have specialty woods including ash, birch, oak, walnut, mahogany, birdseye maple, teak, and other furniture and trophy constructing woods and oh yes, marine plywood. I used 3/8" which had 5 plies and treated it as I said then covered it with outdoor carpet. Plenty strong for the decking in the boat.
Like I said on this flooring I saw, I never saw it before, at any lumber yard, but it was definitely marketed toward the outdoor user. Now, where you draw the line between outdoor use and marine use is up to you. Like I said, ask questions and if you don't know the answer, ask more questions or look some more.
Mark