Marathon LeTourneau GranGulf™ Semi Design Offers Economic Construction & Optimum Deck Load

Marathon LeTourneau's new GranGulf™, a large, lighter-weight semisubmersible drilling unit for Gulf of Mexico-type operating conditions, offers construction economies plus optimum deck load for a semi of its size and weight.

Rated for a 4,000-ton deck load when moored in 2,000 feet of water, the GranGulf can be easily upgraded for 2,500 feet of water with only minimal reduction in variable deck load. It also offers the options of propulsion assist and dynamic positioning for drilling in much deeper waters.

The GranGulf's larger diameter, shorter square vertical columns reduce steel weight and offer a number of construction advantages over columns of other configurations.

Marathon expects that the rig will be less costly to build than semis with comparable deck load because the GranGulf requires less steel and less sophisticated fabrication.

The shape of the GranGulf's pontoons is also a major feature of the new design. This configuration gives the rig superior storm response characteristics, less transit resistance and better wave clearance all without loss of normal station-keeping performance while drilling. The pontoon configuration also permits use of the shorter vertical columns without a corresponding loss of airgap.

The GranGulf's pontoon size and shape incorporate principles of SeaTek's patented "B2S" design as well as principles from a pending Marathon patent.

While the GranGulf's pontoons appear larger on the outboard side of the vertical columns, they actually have less displacement than the inboard pontoon sections. This pontoon shape capitalizes on variations in wave phase along the pontoons by reducing the vertical forces waves would exert on these pontoons compared with pontoons of uniform cross section and the same displacement.

The GranGulf's unique pontoon shape also allows for its larger stabilizing columns and larger pontoon sections. These design features let the rig carry its full variable deck load during transit.

Overall length of the GranGulf is 280 feet, overall beam 195 feet, and height to the main deck 96 feet.

Maximum storm conditions are: wave height, 100 feet; wind velocity, 100 knots; and current, 3 knots.

For more information from Marathon LeTourneau, Circle 3 on Reader Service Card

Maritime Reporter Magazine, page 113, Jun 1985

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Maritime Reporter

First published in 1881 Maritime Reporter is the world's largest audited circulation publication serving the global maritime industry.