Glomar Explorer Converted for Deep-Water Drilling

After twenty years in lay-up/ready reserve, the Glomar Explorer is being revived as a civilian ship.

With the decks stripped of 25.5 million lbs (11.5 million kg) of superstructure, the 619-foot (188.7 m) Glomar Explorer was lifted this February in Dry Dock 4 at the Portland Shipyard for a unique conversion project. Today with oil wells being discovered at ever-greater depths, the Glomar Explorer has found a new mission as a deep-water drill ship. It has been chartered by its original builders, Global Marine Drilling of Houston, TX. Cascade General, the company which took over sole control of the Portland Shipyard in 1995, was selected to reconfigure the vessel.

The contract, valued in excess of $18 million, requires the addition of some 4,500,000 lbs (2,041,155 kg) of steel to fill the "moon pool", an open area occupying the central third of the hull to create interior machinery spaces. "The Glomar Explorer conversion is the largest, most complex project in the history of this yard," said Cascade General Executive Vice President Andrew Rowe. "It is enabling us to demonstrate the full potential of the Portland Shipyard and Cascade General as a major player in the US conversion market."

The primary challenge was to replace the retractable, 200-foot (60.7 m) gates under the moon pool with prefabricated double-bottom sections, leaving a 74-x 42-foot (22.5 x 12.8 m) drilling well. After making a thorough survey in San Francisco, Cascade General's production engineering staff established a tight schedule to complete the work by July 1997. Design and pre-fabrication began immediately.

When the ship arrived in Portland, it was lifted in the 982-foot (299.3 m) Dry Dock 4 and blocked at the bilges with a 12-foot (3.7 m) clearance. In a carefully orchestrated sequence, the gate fittings were cut away, the gates lowered and the dock partially submerged. In a delicate operation using winches then tugs, the moon pool gates were hauled free between the bilge blocks.

The new double-bottom modules were then moved by barge onto Dry Dock 3, floated off, maneuvered under the Glomar Explorer and into the aperture. Their close fit allowed fast attachment to temporary suspension brackets in the main hold. The ship was lifted again, this time on standard 6-foot (1.8 m) blocking. On the dry dock, floor welders quickly began connecting the new bottoms to the original 1.75-inch (4.4cm) plate. Only when this stage was structurally complete could the interior construction begin.

Two bulkheads were erected fore and aft of the drilling well, creating new decked holds. The fore space will carry 40,000 feet (12,192 m) of riser pipe and related handling equipment. The aft now contains ten 40- x 15-foot (12.2 x 4.6 m) mud tanks and 4 each 7,500 psi mud pumps. The largest fitting in the well is the 25-ton (22.7 m ton) vertical rack which guides the blow-out preventer through the moon pool.

Integral to its new role of deep water oil prospecting, the Glomar Explorer will have the ability to hold position of +10 feet (+3 m) over a drill site up to 7,500 feet (2,286 m) deep. Cascade General crews overhauled the existing array of 2,000 HP shaft-driven thrusters - three in the bow and two in the stern - and added four, 3,000 HP, azimuthing units operating in 50 X 12.5-foot (15.2 x 3.8 m) vertical tubes. These electric thrusters can be raised and inspected at deck level via a vertical rail system - the entire installation calling for machine-level tolerances.

The total power of the nine thrusters, 22,000 HP, is now greater than the ship's twin-screw propulsion system. All eleven screws will be connected to the vessel's new dynamic-positioning system which will utilize GPS satellites and a hydrophone system below water. The acoustic signals will be received by six receptors which will operate in tubes projecting below the hull. The largest thru-hull structure is a 16 X 19-foot (4.9 x 5.8 m) moon pool designed specifically for Remote Operated Vehicle (ROV) deployment. The ROV will have the ability to inspect the wellhead at great depths and will have its own service facilities and stowage area.

To meet the increased power demands, four EMD 645 16-cylinder AC generators have been installed forward of the old engine room. The ship's original diesel-electric system comprising five Nordberg 16-cylinder AC generators and six 2,200 HP DC shaft motors has been re-built and activated after 16 years in layup.

"We found the ship was well preserved," reported Cascade General's Ship Superintendent Jim Mattix. "Our goal is to restore full operational readiness. We are overhauling all systems -- including electrical, piping, ventilation, shafts and steering. When she departs, the entire vessel will be in first-class voyage condition."

When dry dock work is complete, the ship will be berthed dockside for a second critical maneuver. The last remnant of the Glomar Explorer's original, 17,000,000-pound (7,711,030 kg) lifting capacity is a pair of trusses which supported the derrick. At 150 tons (136 m tons) each, these beams are beyond the dockside capacity of any other US West Coast repair facility and will require the coordinated efforts of two of Cascade General's largest Whirley cranes.

This heavy lift will clear the way for construction of new deck levels, on-deck pipe racks and a new drilling substructure. The pedestals for two Seatrax cranes, with boom lengths of 90-110 feet (27.4 - 33.5 m) will then be built over the original side decks.

Coincidentally, the Glomar Explorer was drydocked when mothballed in Portland in 1980. When it leaves this summer, it will be delivered under its own power to the Gulf Coast around South America, where it will be fitted out with the rest of its state-of-the-art drilling equipment and commence work under a five-year, exploration contract in early 1998.

According to Jeff Shepard, Global Marine Construction Manager, "The work accomplished in Portland has been a critical milestone in the process of creating a state-of-the-art, deep-water drill ship. Our company has made a significant investment to stay on the leading edge of exploration technology. Reflecting on the conversion work, he added, "Taking on a conversion of this size and complexity is a challenge for any shipyard. Cascade General has the unique features, manpower and expertise required to perform this kind of conversion, and they are responsive to the needs of the owners."

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Glomar Explorer
(Project Profile)

Cascade General operates Portland Shipyard, the largest and most complete ship repair and industrial facility on the West Coast of the United States. We provide full-service repairs and conversions for tankers, cruise ships, bulk carriers, container ships, government vessels, tugs, barges and workboats. Cascade General's Portland facility includes a 60-acre (24.2 ha) yard, 550,000 square feet (51,096 square meters) of craft shops, more than 7,600 ft. (2,326 meters) of full-service repair berths, and two floating dry docks.