knee-platen.(a) a broad steel plate worn from the 15th to the 17th cent. as a protection for the thigh;(b) Shipbuilding an angled metal plate used as a knee (sense 7a).
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1858 J. GranthamIron Ship-building 217 Bulkheads to be five in number;..to have brackets, or knee plates, riveted horizontally against the ship's side.
1969 Jrnl. Abstr. Brit. Ship. Res. Assoc.24 218 (heading) Determination of the effectiveness of a knee plate by plastic theory.