sny

A sny is an upward bow or curve that appears along the length of a wooden plank, typically in shipbuilding and boat construction. It differs from intentional shaping: a plank that should lie flat develops a gentle hump, running from end to end or across part of its length. The curve is almost always a defect, though a minor sny can sometimes be worked into the hull without replacing the timber.

Snies occur most often in planks that have dried unevenly or been stored poorly. Moisture loss is the main culprit: if the outer surfaces of a thick plank dry faster than the interior, shrinkage stresses build up and the plank cups or bows upward. Sapwood dries much quicker than heartwood, so a plank with uneven grain distribution across its thickness is at high risk. Exposure to direct sun or heat during storage accelerates the problem.

Detecting a sny requires stretching a line along the plank or laying it against a straightedge. Even a gentle curve of half an inch over a 12 foot length will cause problems: it prevents proper fitting against the hull frame, opens seams as fasteners are driven, and weakens the overall structure. A pronounced sny makes the plank unusable for critical parts of the hull; it may only serve in less demanding areas or be broken down for repairs.

The term appears in English shipwright and maritime timber vocabulary, particularly in the North Atlantic traditions of British and Scandinavian boatbuilding. The origin is uncertain, though it may derive from Old Norse or similar roots in maritime languages. It belongs to a family of defect terms that includes cup, warp, and check, each describing a different failure mode in wood under stress.

Prevention relies on slow, even seasoning: stacking planks with spacers to allow air circulation, storing them under cover away from direct weather and sun, and selecting timber with straight grain and balanced sapwood-to-heartwood ratio. In modern boatbuilding, steamed or laminated planks reduce snies, but traditional wooden boats still encounter them, and recognition of the fault is essential before fairing the hull or caulking seams.