Semi-Submersible Drill Barge

1. Field of the Invention

The invention relates generally to drill barges and more particularly to semi-submersible drill barges for operating in an extended range of wave heights and periods.

2. Description of the Prior Art

Heretofore, semi-submersibles have included flat-ended barges or twin hull vessels both requiring external trussing between hulls and work decks, or conventional hulls, all being subject to considerable beam wave effect and short natural heaving periods.

The object of the invention is to provide a barge drill rig with no external trussing and substantially reduced beam wave effect.

Another object of the invention is to provide columnar storage with a resultant low center of gravity.

A further object of the invention is to provide a drill barge with a substantially increased natural heaving period coupled with an added-mass factor.

FIG. 1 is a three dimensional view from the upper left of the invention;

FIG. 1A is a partial three-dimensional view of optional upper-deck side wave deflectors;

FIG. 1B is a partial three-dimensional view of optional upper-deck end wave deflectors;

FIG. 2 is a plan view of the lower hull; and

FIG. 3 is a side elevation of the hull of FIG. 1 omitting upper hull structure.

Referring to FIG. 1, the invention 10 comprises a double-ended, flat-bottomed hull 12 supporting on a pair of free-standing end columns 14 and a pair of free-standing beam columns 16 a work deck 18 without exterior trussing.

Hull 12 is closed and has convex sides 20 and 22 that taper from amidships to oppositely disposed pointed ends 24 and 26. The convex or curved sides substantially reduce a beam effect of water and wind thereon. The ratio of length to width to depth of the hull 12 is of the order of 2 to 1+ to 0.06. Between pairs of columns 14 and 16 deck edges 28 are chamfered for directing water sweeping over and above a low freeboard along the deck 30 of hull 12 to maximize the added-mass effect of the water on the hull. This added-mass effect in addition to the convex sides, both stemming from the length to width to depth ratio, contribute to increasing the natural heaving period by approximately 1/3 more than that of conventional configuration semi-submersibles that is from about 18 to 23 seconds. As a result, hull 12, being so stabilized and less affected by wave direction, height and frequency, can continue drilling when other vessels of equal size have to stop. A center opening 32 is defined in hull 12 for the passage of a drill string therethrough. The center opening is closable at the bottom for fairing purposes when the invention is being towed. The remainder of the hull is subdivided into ballast and storage tanks 33. Optional wave deflectors 34 as illustrated in FIGS. 1A and 1B may be mounted on the tops of end columns 14 and beam columns 16 to help divide and direct high seas.

Referring to FIGS. 2 and 3, end columns 14 are preferably octagonal in cross-section for manufacturing them of flat plate and in identical halves, thus saving costly metal rolling presses and procedures and reducing manufacturing costs by building only halves rather than individual whole columns. Side columns 16 are larger and rectangular except for curved outboard sides that are conformed to and respectively continue convex sides 20 and 22 amidships. Vertical edges 36 of columns 16 are chamfered similarly to deck edges 28 for similar reasons. The respective beam columns are tied together at their upper extremities by means of box girders 38 which also transversly reinforces work deck 18 and provide safe throughways from one side to the other of work deck 18. Both pairs of columns 14 and 16 provide columnar storage and equipment space below the level of the work deck to generally lower the center of gravity of the invention.

Work deck or platform 18 is mounted on the top of columns 14 and 16 and box girders 38, and faired to conform with the columns. A drill aperture 40 is defined therein and in line with center opening 32 but larger to allow for the extended motion of its higher elevation. A drill rig 42 is mounted on work deck 18 over drill aperture 40 for supporting and operating a drill string passing through said aperture. An optional helicopter landing platform is shown as part of upper or working deck structure of FIG. 1.