Uhmmm, IMHO I would not use the pictured plywood. I AM a C.O.B, but...In this case I would also recommend using 3/4" NEW plywood laminated for the stringers and 1/2" plywood for the deck.
This might be helpful...Fabricating Decks, Stringers, and Transoms[/URL]
test transom urself with a 1/4 drill bit - drill some test holes and study the wood shavings that come out (or in my case, the wood pulp that comes out).