Ships may operate in extreme seas, and partial safety factors are incorporated in the corresponding structural design rules in order to ensure adequate safety levels. However, the impact of so-called freak waves on the global loads is still under intensive investigations as certain vessels may not be able to survive extreme conditions-. This applies especially for unfavorable freeboard conditions. Direct extreme design wave load measurements do not exist or are derived from measurements. Model tests in stochastic irregular seas or deterministic tailored extreme wave conditions are indispensable for a complete understanding. This paper deals with linear hydrodynamic analysis of the vertical bending moment, where a commonly applied assumption for the incoming wave angle is discussed. Model test results for a freak wave event is also conducted in order to analyze the wave—induced vertical bending moment during such an event. For comparison, long-term analyses for an LNG carrier are performed by using hindcast data for the North Sea (i.e. the Statfjord field).
