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Keywords

Structural optimisation, Ultimate strength, Full-ship analysis, Weight reduction, Structural safety, Steel catamaran

Document Type

Research Article

Abstract

Hull structures must withstand design loads throughout their expected lifetime. Industry practice often uses a comparative approach, which works for designs similar to proven ships with good service records. However, it can leave some members overly heavy while others barely meet strength criteria, and errors may remain hidden until construction. To prevent such issues at the initial design stage, scantlings should be optimised and reviewed numerically. To address these limitations in the initial design stage, this study aims to develop and demonstrate a practical numerical framework for optimising hull scantlings by integrating a fully automated single-objective optimisation procedure with direct structural analysis. The optimisation is formulated as a single-objective problem in which the longitudinal girder weight is minimised subject to explicit constraints on yielding, buckling and classification-society scantling limits. The framework is applied to a 500-tonne DWT steel catamaran, in which the longitudinal girders are selected as design variables and the structural responses are evaluated by nonlinear finite-element analyses. The procedure is organised into three stages using finite-element models: a full-ship model to determine global wave-induced responses under design waves derived from North Atlantic wave data at transfer-function maxima; a three-hold model in which the longitudinal girder scantlings are optimised under the governing load cases; and a one-slice model to verify the hull-girder ultimate strength of the optimised midship section. The optimisation applied to the three-hold achieves a 4.53% reduction in their weight, which corresponds to a 3.81% reduction in the total hull structural weight, while satisfying the relevant classification rule requirements. The one-slice ultimate strength assessment confirms that the hull-girder strength remains approximately 10.9% and 13.5% above the KR design requirements although the hogging and sagging ultimate bending capacities decrease by about 6.1% and 5.2%, respectively. These results indicate that the proposed optimisation-based framework can be effectively used as a systematic design procedure to refine rule-based scantlings for small and special-purpose vessels without compromising ultimate strength or global longitudinal structural safety. This study is carried out using the commercial finite-element solver MAESTRO. Lee, S. E. (2026). Single-Objective PSA Framework for Longitudinal Girder Scantlings with Full-Ship and Ultimate Strength Verification for a 500-Tonne Catamaran. Seatific, 5(1), 1–20. https://doi.org/10.29187/2792-0771.-D-00026

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