Pre-Erection Method in Shipbuilding

Abstract

The Shipyard lay-out and facilities have been modernized in line with the adoption of the block construction process. In these days the most modernized shipyards have been newly constructed both in Japan and abroad to cope with the increased demand of super-large type ships.In the first stage of these new shipyards simply a single building dock each was constructed in view of the then prospect of newship tonnage to be built and the cost of the dock construction.After that due to the ever increasing demand for super large ships, it became necessary either to lengthen the dock or to add another new dock in which the after block of the hull containing the machinery space to be pre-erected. Even in this case, it was necessary to float and shift the pre-erected after-ship block, and this process was not so easy due to the problems for the adjusting of its draft and trim.As the next stage the pre-erection process of the aft part of the ship including machinery space and some oil tanks was adopted. But even in this process it was necessary to float and shift the portion, and though the draft problem was solved, the labour manhour balancing problem remained unsettled.To solve this problem new shipyards with dual entrance dock or two building docks have emerged. In these docks, the pre-erected hull portion are constructed without shifting. At the same time, in some docks the pre-erected hull portions are shifted mechanically in lieu of the floating procedure.In this essay, the authors intend to explain these aforesaid various construction methods. At first the theoretical explanation of the construction process is made and then calculation of the length of the necessary pre-erection dock to peak-shaving the labour manhours is shown.As a result, it is concluded that the mechanical shifting of the pre-erected portion from the pre-erection dock with a suitable length shall be very advantageous to solve the problems. Finally the authors describe the fundamental design of the mechanical moving system.