Column-stabilized floating structures with truss pontoons

A method of fabricating, transporting, installing, and operating a floating offshore structure, the structure including an upper hull having a plurality of spaced apart vertical buoyant caissons interconnected together in spaced relation by an open framework of horizontal truss pontoon members and vertical truss column members, each of said caissons having one or more buoyant tanks or chambers enclosed by bulkheads or disposed inside said caissons including ballast control means for selectively adjusting the buoyancy thereof, and one or more keel tanks disposed at a lower end of said truss structures including pump control means for selectively pumping water in and out of said keel tanks to adjust the weight thereof;

• comprising the steps of:
• fabricating the upper hull with a plurality of spaced apart vertical buoyant caissons interconnected together in spaced relation and towing it to a shallow water depth;
• fabricating the open framework of horizontal truss pontoon members and vertical truss columns with keel tanks at a lower end thereof and towing it to the shallow water depth;
• flooding said keel tanks such that the open framework of horizontal truss pontoon members, vertical truss columns, and keel tanks are grounded on the seabed at the shallow water depth;
• lifting the upper hull above said open framework of horizontal truss pontoon members and vertical truss columns and lowering it to engage its spaced apart vertical buoyant caissons on the vertical truss columns;
• securing the spaced apart vertical buoyant caissons of the upper hull to the horizontal truss pontoon members and vertical truss columns;
• pumping water out of said keel tanks to raise the upper hull and framework of horizontal truss pontoon members and vertical truss columns and keel tanks upwardly in relation to the seabed;
• towing the assembled structure to deeper water;
• adjusting the buoyancy of said upper hull to ground the open framework of horizontal truss pontoon members and vertical truss columns and keel tanks on the seabed at the deeper water depth;
• installing a deck platform to the upper end of said plurality of spaced apart vertical buoyant caissons;
• adjusting the buoyancy of said upper hull to raise the deck platform, upper hull, and framework of horizontal truss pontoon members and vertical truss columns and keel tanks upwardly in relation to the seabed to assume a towing draft;
• and
• towing the assembled structure to an operating site.

A method of fabricating, transporting, installing, and operating a floating offshore structure, the structure including an upper hull having a plurality of spaced apart vertical buoyant caissons interconnected together in spaced relation by an open framework of horizontal truss pontoon members and vertical truss columns, each of said caissons having one or more buoyant tanks or chambers enclosed by bulkheads or disposed inside said caissons including ballast control means for selectively adjusting the buoyancy thereof, and one or more keel tanks disposed at a lower end of said horizontal truss pontoon members and vertical truss columns including pump control means for selectively pumping water in and out of said keel tanks to adjust the weight thereof;

• comprising the steps of:
• fabricating, in dry dock, the open framework of horizontal truss pontoon members and vertical truss columns with keel tanks at a lower end thereof, the upper hull with a plurality of spaced apart vertical buoyant caissons interconnected together in spaced relation, and a deck platform to be installed at the upper end of said plurality of spaced apart vertical buoyant caissons;
• transporting the open framework of horizontal truss pontoon members and vertical truss columns with keel tanks, the upper hull, and the deck platform, via towing or barge to a deepwater operating site;
• placing said open framework of horizontal truss pontoon members and vertical truss columns and keel tanks into the water and flooding said keel tanks such that the open framework of horizontal truss pontoon members and vertical truss columns and keel tanks are submerged beneath the water surface and their upper ends are above the water surface;
• lifting the upper hull above the upper ends of said open framework of horizontal truss pontoon members and vertical truss columns and lowering it to engage its spaced apart vertical buoyant caissons on the vertical truss columns;
• securing the spaced apart vertical buoyant caissons of the upper hull to the horizontal truss pontoon members and vertical truss columns;
• adjusting the buoyancy of said upper hull to lower the upper hull and framework of horizontal truss pontoon members and vertical truss columns and keel tanks such that the open framework of horizontal truss pontoon members and vertical truss columns and keel tanks are submerged beneath the water surface and the vertical buoyant caissons of the upper hull are partially submerged;
• lifting the deck platform above the upper ends of the vertical buoyant caissons and lowering it to engage the upper ends of the vertical buoyant caissons;
• securing the deck platform to the upper ends of the spaced apart vertical buoyant caissons;
• and
• adjusting the buoyancy of said upper hull to raise the deck platform, upper hull, and framework of horizontal truss pontoon members and vertical truss columns and keel tanks upwardly to operating draft.