semi- submersible vessel has a vertically spaced pair of pontoons with a variable buoyancy. The lower pontoon is held in close proximity in the vertical direction with respect to the upper pontoon while the transport vessel . Lower pontoon is placed ballast in place , the pontoon is lowered to a depth of about 32 meters below the first pontoon initiatives. As a result, the reliability and the motion characteristics of the vessel is significantly improved . The pontoons are connected to each other by pulling the leg .
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