## 1 Introduction  
In recent years, container vessels have become larger as the amount of seaborne cargo has increased with the development of the world economy. Hydroelasticity has become an important issue in the marine industry with the increase in container vessel size. The hydroelastic response can be classified into springing and whipping. Springing is the vibrational response that occurs when the natural frequency of the hull resonates with a wave encounter. This hull vibrational response is likely to occur in a large ship wherein the natural frequency is generally low. Whipping is a hull vibration caused by the slamming load generated when a ship plunges into the free surface. This hull vibrational response is a temporary response that is likely to occur under severe sea conditions. Considerable research has been conducted on these hydroelastic issues to establish the hull design in terms of safety and other relevant aspects. As an early example of a full-scale measurement campaign of large container ships, [PERSON] et al. [1] performed full-scale measurements of a post-Panamax container ship during the three years from 1999 to 2002. They reported that the presence of whipping stress doubles the fatigue damage. Meanwhile, in 2013, a large container ship broke its back while navigating in the Indian Ocean [2,3]. One of the possible causes of this accident was reported to be the effect of whipping on the longitudinal bending strength of the hull girder, which is still difficult to estimate quantitatively, and necessitates further research. In addition, while the major research activities on whipping have so far focused only on the hull girder vertical bending, the recent increase in the size of container ships has also raised concerns regarding torsional whipping responses. In fact, some recent container ship measurement campaigns have focused on torsional vibratory responses. [PERSON] et al. [4] used the full-scale measurement data of a 14,000 TEU container ship to compare the design values with the extreme values at each moment. Regarding fatigue damage, it was shown that the vibration damage constituted approximately 50% of the total damage for the measured hull stress, or even higher. In addition, it was concluded that the vertical bending mode vibration contributed more to fatigue damage than the torsional mode vibration. [PERSON] et al. [5] compared the fatigue damage of the cases with and without vibration by analyzing full-scale measurements of a 9400 TEU container ship. The fatigue damage increased by approximately 70-85% owing to vibrations, particularly in the vertical bending mode. [PERSON] et al. [6] investigated the effect of torsional vibration on fatigue damage due to the longitudinal stress of a 13,000 TEU container ship. It was found that the effect of vertical bending stress was dominant in the high-frequency fatigue damage, and the effects of the horizontal bending and warping stresses were small. [PERSON] et al. [7] assessed two post-Panamax container ships (8600 and 8400 TEU) with focus on the vibration contribution to fatigue and the extreme loading from torsional vibration. The effect of torsional vibration on fatigue damage ranged from 14% to 16% for an 8600 TEU container ship. In contrast, the effect of torsional vibration on fatigue damage increased to approximately 52% to 55% for an 8400 TEU container ship. The effect of torsional vibration on fatigue damage differs depending on the ship. Therefore, further study is required regarding torsional vibration. Consequently, in this research, we conducted a full-scale measurement of an 8600 TEU container ship for approximately five years, where the hull longitudinal stresses at various locations were measured in combination with ship speed, ship position, ship direction angle, and other conditions. [8; 9]. Wave forecast data corresponding to the ship position were also obtained from the Japan Meteorological Agency.