Longitudinal Stiffener

Long, slender flat-bar, bulb-flat, or rolled-angle section running fore-and-aft and welded to plating to resist buckling under bending compression. Longitudinals are the primary load-carrying members of a longitudinally framed hull (the standard for tankers and bulkers under IACS CSR), and their spacing — typically 700–900 mm — together with web-frame spacing fixes the panel aspect ratio. Class rules size each longitudinal by section modulus including effective plate breadth, and require continuity through web frames via cut-outs or lugs that satisfy fatigue criteria.