Thomas W. Clapp
Engineering at Dracaena Ct, Houston, TX

6371697, Apr 16, 2002

Apr 30, 1999

09/303078

Edward Huang - Houston TX
Bambang A. Sarwono - Katy TX
Thomas W. Clapp - Houston TX

ABB Lummus Global, Inc. - Houston TX

B63B 3544

4052242, 405200, 4052231, 114264

An exemplary floatable vessel is described having an upper tower section with a reduced diameter or width and an affixed lower base section having an enlarged diameter or width. The lower section contains weighted ballast distributed upon its lower floor. The lower section also includes flotation tanks which can be filled with air to raise the vessel in the water such that portions of the lower section are raised above the water line. Alternatively, the flotation tanks can be flooded to dispose the lower section and a portion of the upper section below the water level. The upper tower section of the vessel supports a deck structure upon which rig components can be constructed or secured. The tower section includes flotation tanks as well. In preferred embodiments, these tanks are variable tanks that can be partially filled with air and partially flooded with water. The vessel defines a central chamber within which drilling risers are contained and suspended from the deck structure of the vessel downward toward the sea floor.