Ballast planning for accuracy control on offshore floating dock based on stochastic kriging

Abstract

In shipbuilding industry, the capacity of building docks is most important element that determines the productivity of the shipyard. In these days, Korean shipyards strategically move to construct more offshore plants and thus require additional building docks designated for offshore plant and installations. However it is a major and complicated investment decision for shipyard to construct a new building dock onshore, which is almost prohibited by the limited land area in shipyard. The alternative solution that Ship building company chose was to develop and construct Offshore Floating Dock (OFD), which is moored adjacent to block erection platen. Unlike the conventional floating docks for ships, OFD has rectangular deck area suited for offshore plant construction onboard and has matrix arrangement of ballast tanks.During the block erection on a conventional floating dock, ballasting operation is carefully controlled in order to compensate the deflection due to the block weights and to maintain the straightness of the floating dock. Since the floating dock bends only in the longitudinal direction and the ballast tanks are arranged also longitudinally, experienced operators can perform the ballasting operation easily and intuitively. In case of OFD, it deflects longitudinally at the same time transversally due to the non-uniformly distributed blocks thus requires more complicated calculation of ballasting plans to compensate the deflections and to maintain flat-ness of the deck. The other issue in the offshore block erection on OFD is the accuracy control. As the height of the column is over 60~80 meters the minor deflection of OFD deck surface can be magnified at the top of the columns. As the ‘mating’ operation, which erects the topside deck blocks on top of columns of the off-shore installation hull, requires very high accuracy level, the ballasting plan should also consider the control of OFD deck surface shape to help the accuracy control of the mating op...