hullgirder

Hullgirder, more commonly referred to as the hull girder, is the main longitudinal structural element of a ship’s hull. It is the portion of the hull that behaves as a single bending beam, carrying the longitudinal bending moments produced by buoyancy, the ship’s weight distribution, and wave loading. In naval architecture, the hull is designed and analyzed as a girder formed by the combination of deck and bottom plating, connected by longitudinal stiffeners and frames, with transverse bulkheads providing cross-sectional integrity.

The hull girder derives stiffness from the arrangement of its longitudinal members—such as deck stringers, bottom stringers, and large girders—together with the transverse framing that ties the structure together. Longitudinal framing schemes emphasize continuity along the length to improve bending resistance, while transverse frames primarily resist local buckling and maintain shape. The location of the neutral axis and the section modulus of the hull girder determine its capacity to resist hogging (upward bending) and sagging (downward bending). Materials are typically steel or aluminum, and scantlings (thicknesses of plating and size of stiffeners) are chosen to meet required strength while controlling weight.

Design and analysis of the hull girder involve evaluating the maximum design bending moment under service loads and ensuring the allowable stress in the girder is not exceeded. Methods range from simplified, rules-of-thumb approaches used in early design to detailed linear elastic or plastic analyses and finite element models used by classification societies. Modern practice also considers double-hulled configurations, which alter stiffness and load paths.

See also: ship structural analysis, longitudinal framing, scantling, hull integrity.