plank-sheer

A plank-sheer is the uppermost continuous course of wooden planking that runs horizontally along the hull of a wooden vessel, fastened directly over the exposed heads of the ship's frames. It forms the junction between the hull proper and the rail, taking its name from the sheer, the upward curve of a ship's profile viewed from the side. In traditional wooden shipbuilding, this plank was structural and critical: it had to resist both the longitudinal stresses that tried to hog or sag the hull and the lateral pressure of waves and wind against the rail.

The plank-sheer typically measured 3 to 5 inches thick in merchant vessels and was fashioned from the best available timber, usually oak or elm for ships operating in northern waters. Its width varied by vessel size and design, but usually ran 12 to 18 inches fore to aft. Unlike the planks below it, which were edge-fastened to their neighbors with trenails or nails, the plank-sheer often carried the ship's rail timbers on its upper face and was secured to the frames with large bolts or through-bolts, sometimes supplemented by knees or braces. The plank-sheer also bore the stress concentration where the hull planking met the rail stanchions.

Practical challenges and decay patterns

Because of its position at the waterline region and its exposure to weather, the plank-sheer suffered accelerated decay in service. It was the first course to show rot or worm damage, especially where it sat against iron rail stanchions that could trap moisture. Shipwrights learned that the plank-sheer needed better drainage details and sometimes sacrificial sheathing on its outboard face. In vessels that saw heavy use or poor maintenance, the entire course sometimes had to be replaced while the hull planking below remained sound.

The term is now archaic outside of maritime preservation work, since wooden ship construction has ceased in commercial practice. Modern fiberglass and steel vessels do not use this timber course, and the structural function it served is distributed across different materials and designs. Nonetheless, the plank-sheer remains important to anyone restoring or studying wooden sailing vessels, and understanding its role and typical failure modes is essential for accurate survey and repair work.