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.