ANCHORAGE, Alaska (AP) -- The pulling requirement for the tow of a Royal Dutch Shell PLC floating drill rig was revised upward by more than 50 percent after the vessel ran aground in December off a remote Alaska island, a Shell official testified Thursday.
Marine operations manager Jonathan Wilson, speaking by phone from London, told a Coast Guard investigation panel that Shell performed a resistance study from scratch after the Kulluk, a 266-foot diameter drilling barge with no means of propulsion, broke away from its tow vessel Dec. 27 and ran aground four days later on Sitkalidak Island near Kodiak.
The pulling requirement, or "bollard pull," had been rated at 200 metric tons as the drill rig was towed south toward Seattle across the Gulf of Alaska.
When Shell — after the grounding in stormy seas— prepared to move the damaged rig back to Dutch Harbor, a resistance study indicated that the new standard for the damaged vessel should be "in excess of 300 metric tons," Wilson said.
Panel members questioned why the rating increased after the grounding.
Wilson attributed the revision to changed conditions. The Kulluk, which has a funnel-shape hull, rode lower in the water after the grounding. It had drafted just less than 11 meters, or about 35 feet. Afterward, the draft was 11.5 meters, or about 38 feet, Wilson said.
Gulf of Alaska seas and winds were also estimated to be higher in February.
"Statistically, the first quarter of year has the worst weather in Alaska," he said. "All those were factors which would drive a higher bollard pull requirement, is my understanding."
Wilson also said towing a damaged vessel could change pulling requirements.
The Kulluk is one of two drill vessels Shell relied on in 2012 for exploratory drilling in oil reserves of the U.S. Arctic off Alaska's northern shores. Federal regulators required both rigs to be available so that in the case of a well blowout, the second rig could drill a relief well. Damage to the Kulluk played a role in Shell's decision to forego Arctic offshore drilling in 2013.
The Coast Guard panel concluded the public hearing Friday with testimony from John Skogland, skipper of the Aiviq, the 360-foot anchor handler built to tow the Kulluk and the vessel moving the rig Dec. 27.
The Aiviq lost power to its four main engines a day after the lines parted. The Aiviq eventually repaired fuel injectors that allowed all four engines to be restored, but the ship and tugs that came to the Kulluk's aid could not maintain tow lines before the grounding.
The Aiviq is rated for pulling 200 metric tons.
Skogland said using a single towing vessel eliminates potential hazards such as crossed tow lines and tow vessel collisions.
The Aiviq on Jan. 6 pulled the Kulluk into deep water and moved it to a sheltered Kodiak Island bay.
In March, three Crowley Marine Services tugs, with a fourth serving as a backup, reached Dutch Harbor with the Kulluk in tow. The Kulluk was later loaded on a lift ship and transported to a Singapore shipyard for repairs.