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Why can longitudinal framing reduce the weight of a ship’s hull?

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naval architecture A cargo ship passing the Golden Gate Bridge, near San Francisco.

In naval architecture, longitudinal framing reduces the weight of a ship’s hull primarily by enhancing the structure's ability to resist longitudinal bending.12

Unlike traditional transverse framing, where frames run at right angles to the ship's axis and contribute little to longitudinal strength, longitudinal frames run parallel to the principal axis of the ship. This orientation allows the metal in these fore-and-aft stiffeners to actively supplement the shell plating and the uppermost decks in two critical ways:12

Resisting Bending Moments: The stiffeners assist the shell and deck in resisting tensile loads caused by the hull's bending moments.2
Preventing Buckling: They provide necessary support to the shell plating, helping it resist buckling when subjected to compressive loads.2

Because the longitudinal stiffeners contribute directly to the overall structural integrity of the hull as a beam, the thickness of the shell plating can be reduced. While this system requires internal transverse support from bulkheads and web frames, the overall weight savings remain significant enough to make it a preferred choice in many modern designs.12