Had some old plywood getting soft in the center, and decided to re-do
the floor. when we pulled off the old carpet which was weathered
anyhow, we found out that in the times past someone had repaired the
floor by cutting out a center section and replacing it with standard
plywood. Evidently it had held for quite a while but it's days were
numbered. besides it gave us a chance to inspect the stringers and
other bracing etc.

So, after thinking about the re-floor, we decided to not go with
standard ply because it's not weather resistant, or marine due to the
expense, so we settled on "DRYPLY"

http://www.gp.com/build/product.aspx?pid=4882

A weather resistant plywood which has a lot of characteristics of
marine plywood but is more cost effective. Like $23.00 a 3/4 sheet at
Menards, and in stock too.

Regardless. It ought to last way longer than I'll ever have the boat.