>Marine plywood is plane old 3ply plywood except they don't have voyds in the >inside plys like regular construction grades. I beg to differ. I've been building wooden boats for about 9 years now and I can tell you that Marine ply is not plain old plywood. It's made from a variety of Mahogany's mostly from Africa. Construction grade ply is made from pine and Douglas Fir Even the cheaper grades of marine luan is far superior to any regular ply. I've been using Okoume ply exclusively and it is the finest plywood I've ever had the pleasure to work. It comes in a variety of plys from 3-9 layers, free of voids, glued together with resorsenal(sp), is registered and certified by Lloyd's of London. (B.S. 1088 standard) If you want to test it put in boiling water for three hours. Remember, marine ply sits in essentially a 100% moisture environment and stands up for years. I will be using marine plywood in my Fly Baby, saving some money, and not sacrificing strength or quality at all. Anyone of these company's will gladly send you the data sheets and certification requirements fro marine ply. Sources: Harbor Sales 1000 Harbor Ct Sudlersville, MD 21668-1818 1.800.345.1712 M.L. Condon Company 260 Ferris Ave. White Plains, NY 10603 914.949.4111 Boulter Plywood Corp. 24 Broadway Somerville MA 02145 617.666.1340 Edensaw Woods, Ltd. 211 Seton Rd Pot Townsend, Wa 98368 360.385.7878 Also as Dave Williams said contact WoodenBoat Magazine at http://media4.hypernet.com/~WOODENBOAT/wb.htm They have an extensive research library and are more than willing to help. Kevin Riley