But after the tides shifted, one of the anchors of the offshore supply ship Perseverance broke free from the sea floor, swaying the vessel from position.
"It's like anchoring in a river, but the river reverses its flow every six hours. The velocity of the tide is always changing and the direction, too, going in and out every six hours," said Jim Butler, a spokesman for Monarch's owner, Ocean Marine Services of Kirkland, Wash.
Crews pulled the two anchors and released a mooring line attached from the stern to the leg of an oil rig platform operated by Chevron . The 207-foot Perseverance, which had been positioned over the sunken vessel, was taken to a sheltered bay while responders reviewed their options.
Possibilities include dropping more anchors from other sections of the Perseverance, repositioning the ship or using a different one, Butler said.
The Monarch sank Jan. 15 when it was pinned by sea ice to the Granite Point platform during a delivery of supplies. About 3,500 gallons of diesel and hydraulic oil spilled.
The vessel settled upside down on the sea bed near the platform, which is in the northern section of Cook Inlet about 45 miles southwest of Anchorage.
Responders, including state environmental regulators, warned last week about the challenges of working in the inlet. An oil spill response vessel and crew are standing by during the operation, which is expected to take more than a month.
"It is hard to exaggerate the difficulty of this fuel recovery operation," Gary Folley with the Alaska Department of Environmental Conservation said in a statement. "Tidal currents in Cook Inlet are among the highest in the world, visibility for the divers is near zero, and the wreck is upside down."
Butler said Sunday's initial diesel recovery demonstrated that the defueling system works. Once the mooring problem is resolved, divers will go down during slack tides. They'll use a wand attached to a pump on board the Perseverance to drain each of the Monarch's 12 fuel and oil tanks. Beside the diesel, almost 700 gallons of lube oil are on board the Monarch.