Okinotorishima is the Japanese southernmost tropical island and has the exclusive economic zone (EEZ) of about 430,000km2 area. It is located approximately 1,700km away from Tokyo and 1,100km away from Okinawa and consists of a coral reef of 7.6km2 area and two islands within the reef. In the waters of Okinotorishima, sea bottom mineral resources such as manganese nodule and cobalt rich manganese crust, biological resources such as fish and renewable energy resources such as ocean thermal energy conversion (OTEC), wind force and solar power are promising.

The objective of this research is to propose an OCEAN CITY Planning to administrate and utilize Okinotorishima and its surrounding waters (EEZ) and to report the development of mechanical connector, which is a key technology to construct the OCEAN CITY in its waters. In the OCEAN CITY, economic activity, research and development (R&D) activity and sightseeing/leisure activity are performed based on the resources mentioned above. The proposed OCEAN CITY consists of a semisubmersible floating ring structure and a semisubmersible floating rectangular runway. The ring structure and the runway are constructed with mechanically connected multiple floating units of about 300m length each. Both semisubmersible structures are also connected by mechanical connectors. In this paper, it is shown that the OCEAN CITY can produce electricity, water and food for the use in the city and for the sale outside the city. It is also shown that the mechanical connector, which is indispensable for very large floating structures such as the proposed OCEAN CITY used in open seas, has been promisingly developed.

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