Deep manned submersible "SHINKAI 6500" was built in 1989, and has been operated by Japan Agency for Marine-Earth Science and Technology (JAMSTEC). She has capability to dive down to 6500m depth. Currently, she made 1097 dives until the end of July 2008. A round hatch on the top of the pressure hull is designed to constitute a part of the spherical pressure hull, and is very important structure to keep atmospheric pressure and waterproof in the hull. Therefore, we handle a hatch carefully in every operation, and moreover, we remove a hatch from the pressure hull at the time of the annual-maintenance and are doing the careful overhaul which involves the measurement and exchange of components. The number of her diving exceeded 1000 times, and she will reach 20 years old shortly. As consideration for that, an operation team, an engineering division and a ship builder implemented investigation for reconfirmation about soundness and safety of the pressure hull including a hatch. In this report, the result of investigation and evaluation about behavior of a hatch including the pressure hull is described.
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