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Ocean-going vessels are under the continuous influence on the effect of the weather, e.g. wind, waves, ocean currents. Since the weather conditions are random in nature, there are situations where the shipmaster changes the ship speed or/and heading of the original sailing path to avoid harsh weather conditions according to his judgment, experience and/or using voyage optimization systems (e.g. weather routing systems). However, ship operators hardly prioritize the ship fatigue routing in their operations. It is preferable to consider the effect of different wave environment due to ship operation in the design process to make a more rational ship design of the structural members. In this study, sailing paths are planned, adopting voyage optimization in order to reduce the probability of encountering severe sea conditions and the minimization of the fatigue accumulation in ship structures. Short-sea sequences are generated by a statistical wave storm model. The storm profiles are determined by using the cumulative frequency of short-seas which are experienced in the different voyages optimized by the algorithm. The influence of the difference in short-seas encountered by the target ship following the optimized voyages on the cumulative damage is demonstrated by a container vessel, which also considers a weather routing system in her operations. Full-scale measurement data for two years’ voyages are considered for the verification. The benefits of using voyages optimization systems focus on reducing fatigue damage to mitigate the risk of structural failure is discussed.

The characteristics of Fatigue Damage Sensors (FDS) that are in use for fatigue life estimation of monitoring structural welding members in ship structures are discussed in order to improve prediction accuracy of estimated fatigue life exposed to random wave loads such as storms under various loading conditions peculiar to ship structures. In our past research, coefficients, which named load effect factors (LEFs) affected by loading histories against constant amplitude loading were introduced for the estimation procedure using FDSs and confirmed by several series of fatigue testing under simplified storm-type loading patterns. In this paper, it is ensured that the abovementioned LEFs are suitable for application to actual random wave load conditions on oceans by numerical simulation using load histories based on a storm model in consideration of variable of sea areas and seasons. Additionally, it is found that the characteristics of FDS under random wave load superimposed whipping vibration show the suitability for the modified Miner rule.