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Methods for calculation of design loads for high-speed vessels are investigated. The in uence of operational restrictions on design loads is emphasized. Relevant operational criteria for high-speed displacement vessels are discussed. Procedures and criteria for numerical calculation of operational limits are incomplete and should be further investigated.Operational limits and design loads for a 60 m catamaran are calculated on the basis of linear strip theory. Non-linear eVects on design loads are assessed from calculations in regular waves. Simpli ed formulae commonly used by classi cation societies for prediction of operational limits seem to overpredict the reduction of motions and wave loads at reduced speed. When operational limits typically given by the shipmaster or the operator are used, the design loads found by direct calculations are comparable with design loads given by classi cation societies.For vertical bending moment and torsion, the use of active foils is found to increase the linear loads. Owing to reduced motions, the foils reduce the non-linear loads and hence the total loads. The eVect of non-linear horizontal loads is not investigated but can be important for transverse bending moment.

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