PURPOSE: To facilitate the manufacture of a large structure exceeding the width of a dock, by providing a float on lower skids in the dock, placing separable skids on the float, building the structure over the dock and thereafter carrying the structure together with the float out of the dock to launch them.

CONSTITUTION: Lower skids 5 are placed in a dock 2. A float 6 is put on the lower skids 5. Upper skids 8 are separably supported on the float so that the upper skids extend up above the opening 7 of the dock 2. A structure 9 is built on the upper skids 8. After that, the float 6 and the upper skids 8 are sunk in water so that the structure 9 is put thereon. The large structure 9 exceeding the width of the dock 2 is thus efficiently manufactured at low cost.