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Ships vibrate due to waves, and these wave induced vibrations can not easily be avoided by moderate changes to the hull lines. The waves may cause the whole hull girder to vibrate due to springing (resonance) and whipping (transient response), which increase the fatigue and extreme loading. Recently this has also become an industry concern. Modern hull monitoring systems in combination with model tests are the best tools to answer the key questions: How important is the wave induced vibrations, and does it have to be included in design? This paper addresses the effect of whipping on the extreme loading. Measurements have been carried out on two container vessels operating in the North Atlantic. An elastic model of the larger vessel has also been tested. Results are obtained at quarter lengths and amidships. From the measurements the increase due to whipping is considerable, even though the wave conditions are not extreme. The full scale measurements and model test show that IACS URS11 rule loads may be exceeded in less than extreme sea states, in particularly amidships and in the aft ship. The IACS UR S11 may need revision for container ship design. MAIB’s report based on the investigation of the MSC Napoli incident (vessel broke in two) also recommends increased requirements for container ship design and further research into the effect of whipping.

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This paper deals with time variant overload reliability analysis of a mooring system due to corrosion deterioration. A probabilistic model for uniform corrosion is adopted to predict the strength degradation. A simplified method and nonlinear finite element analysis are used to calculate the breaking strength of the chain link and comparison is made. The strength of one mooring line is modeled by a weakest link system. The effect of correlation in corrosion models for different chain links in one mooring line and the effect of higher corrosion rate in the splash zone are discussed. The annual failure probability of the most loaded mooring line of a semi-submersible is calculated. The first and second order motions of the semi-submersible and the corresponding line tensions are found by a simplified analysis. The time variant reliability analysis is performed by approximating the degraded strength by a piece-wise constant model. The annual failure probability is obtained for different years. It is found that the annual failure probability increases significantly as the chain is corroded.

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.