The purpose of this paper is to clarify the influence of rail submergence that occurs at the quay on the frictional characteristics of the interface between gantry crane wheels and rails. The characteristics serve as a basis for the dynamic simulation analysis of cranes that run away due to wind and crane designs. An experimental analysis system developed uniquely by the authors was used to carry out this research. Wheel was pressed to submerged rail, then the rail was slid. The friction force generated between the wheel and the rail was measured. This experimental analysis was conducted for contact pressure conditions that the ratios of the maximum Hertzian contact pressure to the yield stress of the material of the rail are approximately 1.76, 2.12 and 2.39. Under these various contact pressures, the ratio of the maximum static friction force under submergence conditions to the same friction force under dry conditions increased slightly. In contrast, when contact pressure conditions were nearly identical, the dynamic friction force under submergence and dry conditions was about same. Finally, the ratio of the dynamic friction coefficient to the static friction coefficient as a reference for designing cranes was shown and discussed.

The Japanese Government’s “Basic Plan on Ocean Policy” (approved by the Cabinet) and “Ocean Energy and Mineral Resources Development Plan” (formulated by the METI [Ministry of Economy. Trade and Industry]) highlight development of seafloor polymetallic sulphides (PMS) as a major initiative Japan intends to promote. After receiving a request from the METI in 2017, the JOGMEC (Japan Oil, Gas and Metals National Corporation) conducted the world's first PMS excavating and ore lifting pilot test under the sea near Okinawa. Before conducting the pilot test, a safety assessment was performed to identify hazards, or risk factors and determine the risk level of the test. To respond to high risk factors, adequate safety measures were developed and reflected in equipment designs and the test plan. This paper describes how the safety assessment was conducted for three years before the test, the results of the test and points that need to be considered for commercial production.