Even now a casualty during ship berthing or cargo handling operation has being occurring. Furthermore it has been reported in ports exposed to high energy long-period wave conditions that an emergency unberthing operation was repeatedly conducted with mooring line and fender breakage due to the large ship motion. It is important for not only effective workability of cargo handling operation but also safe mooring of ship to measure and monitor the ship motions directly. In this study, we propose

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... a conventional measurement method of moored ship motions by using GPS position data, which is observed at three positions on ship. A field observation has been conducted to confirm the accuracy of the method, and several considerations have been investigated.