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About Sheet Plywood

On July 13, 2012, in Designer Articles, Plywood Construction, by Glen L. Witt
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Plywood is wonderful stuff. It’s lightweight, stiff, strong and readily available in most areas. However, it is limited as to the shape it can be formed.

Sheet plywood requires a developable surface or it won’t bend in place. The designer uses a method often referred to as “conendric” development. This uses a segment of a cone or cylinder to determine the natural bend the plywood will take. As an example, take a sheet of paper and form a cone. Take any continuous segment of the outer surface and it will be one that any sheet material will form to without kinking. Of course there are limitations as to the amount that plywood can be bent based on its thickness. The same thing applies to a cylinder.

Note that the outer surface of the plywood is either straight or convex, it cannot be concave. Prove the fact by bending the sheet of paper in a half-moon shape and attempt to bend it; no go, it kinks.

It is possible to induce a small amount of concavity at the end of a plywood panel, particularly if there is little or no curvature in plan view. This is seen on sheet plywood planked boats that have a clipper shaped bow or stem. The amount of concavity is usually not great and the plywood thickness minimal.

Some use the terminology “tortured” plywood to describe a plywood shape. Our philosophy is that a plywood planked hull should bend in place without splintering or checking. It is bent, often severely, but it is a natural developed bend, not a tortured one. 

We have many designs that have a flare particularly on the sides or bottom toward the bow. However, they aren’t for sheet plywood. They use strips of plywood most often applied diagonally in two or more laminations called “cold-molded” or “double diagonal” planking.

Our designers spend considerable time working out a plywood development. Thus, we frown on the idea some have of altering the sectional contours of a sheet plywood boat. We aren’t being dogmatic, were saving you money and time.

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