| 摘要 |
The vessel comprises a pair of laterally spaced elongated hulls having a plurality of upstanding columns spaced along outboard portions of the hulls. In the preferred form, a central column supports a working platform in spaced relation above the hulls. The hulls buoyantly support the vessel in a low draft condition with the hulls having freeboard. The hulls and outboard columns have ballast compartments for ballasting and deballasting the vessel to respectively submerge the hulls, outboard columns, and a portion of the central column to provide a high draft condition with the mean waterline located intermediate the height of the central column and between the platform and the upper ends of the outboard columns, and return the vessel to a low draft condition. The outboard columns provide stability to the vessel during the initial portion of its transition from the low draft condition to the high draft condition and in the final portion of its transition from the high to the low draft condition. Stability in the high draft condition is predominantly provided by locating the center of gravity below the center of buoyancy. Drilling operations in the high draft condition are effected through the central column which also provides decks for mud handling, storage, etc. |
