John C Harris
Contemporary plywood hulls can be elegant and refined. In order to attain the level of form and finish seen here, a builder must be careful in choosing stock.
"Exterior grade panels are acceptable for plywood boat construction." —Glen L. Witt, Boatbuilding with Plywood, 1962
“AC [exterior plywood] gets my vote because of its competitive price, its wide availability, and its equivalent building strength.” —Harold “Dynamite” Payson, Build the New Instant Boats, 1984
A great deal has changed in the world of plywood since those masters of the medium made the recommendations quoted above. The prospective plywood boatbuilder of 2017 wades into a thicket of unenforced standards, uneven quality, and outright flim-flammery. Lots of great choices remain, but you can’t simply judge marine plywood by its stamp.
I started building boats in the 1980s. The exterior-grade AC fir plywood that Dynamite Payson advocated was already in precipitous decline. Even if you could and a panel not riddled with core voids, it would be warped like a potato chip. Modestly good underlayment-grade lauan plywood could still be had, but the paper thin face veneers and crumbly core that distinguishes lauan today would be the norm by the early 1990s.
Okoume was the stock in trade when I joined the nascent Chesapeake Light Craft in 1994. Strong for its weight and with a pleasing honey-colored grain figure, okoume is a heaven-sent choice for lightweight stitch-and-glue boats. As my purchases grew from a hundred sheets, to multiple pallets, and eventually to entire shipping containers of okoume, I sometimes found myself in the same spot as Patrick Mertaugh at Choptank Boatworks: I could specify internationally recognized standards for my marine plywood, such as the exalted “BS 1088” (see below), yet receive a shipment of plywood not fit for drawer bottoms.
More about that in a moment. First let’s cover thebasics of plywood.
A Marine Plywood Primer
Nearly all marine plywood is made by peeling a giant continuous sheet of veneer off a spinning log, like tissue paper off a roll. Plywood made of such veneers is known as rotary-cut plywood. Plywood with “sliced” veneers has faces assembled from several narrower widths, cut like sliced cheese from one-half of a split log. “Ribbonstripe” plywood uses such sliced veneers, although they’re narrower still, and taken from quarter-sawn logs. Sliced and ribbon-stripe panels are common in marine grades, but are used mainly for decorative joinery.