: I know 1/2" ( 12.5mm) marine or exterior grade plywood is
: recommended for Yost's boats sections but I found 1/2 birch ply
: (wbp glued) exactly half price than marine ply.

: I also read the smaller sections can be built using 3/8"
: (10mm) ply, and save some weight there.
: Is it good also using 3/8" birch?

Oh yeah btw, there is some birch plywood, other than baltic birch which is pretty expensive, that seems ok, though it's still heavy, it's the stuff they use normally for underlayment, usually marked with X's on about 6" centers, where the screws go if you're using it for underlayment. I've only though seen it in 1/4" and 3/8", which would be understrength for the frames.

Bill H.