Dimensions (thickness, depth, spacing) of structural members — plating, frames, stiffeners, girders — set by class rules.
Regulatory detail & full definition
Scantlings are the dimensions of a ship's structural members — the thickness of plating and the size and spacing of frames, girders, stiffeners and other steelwork — that together determine the strength of the hull. They are set by the classification society's structural rules, and for bulk carriers and tankers by the IACS Common Structural Rules (CSR), which prescribe the minimum scantlings needed to withstand the design loads over the ship's life. As steel wastes through corrosion in service, class surveyors measure plate thickness against renewal limits, and members that fall below the required scantlings must be renewed.