SEATTLE -- Shell Oil's efforts to bring an Arctic drill rig to a Seattle shipyard involved a winter tow through the Gulf of Alaska, where powerful storms brew treacherous seas.
Even under the best circumstances, the buoy-shaped Kulluk rig, with derricks towering 230 feet above the ocean's surface, is a slow tow. In the final week of December, conditions were anything but ideal as huge waves and strong winds defeated multiple efforts to maintain secure lines and prevent the Monday evening grounding of the rig off Alaska's Sitkalikdak Island.
Shell officials say the rig's journey south from Dutch Harbor in the Aleutian Islands to Seattle was expected to take three to four weeks, and that the tow plan was "positively reviewed" by the Coast Guard.
Others question the decision to move the rig through the Gulf of Alaska in winter.
"You got notoriously big storms this time of year in the Gulf," said Dan Magone, president of Dutch Harbor-based Magone Marine, which has been involved in salvage work in Alaska for more than 30 years. "To tow it down (to Seattle) at this time of year, it was unwise. They didn't realize what they were getting involved with, or overestimated their abilities to handle a tow like that."
Magone said the rig's rounded shape, height and weight make it a difficult tow. During heavy seas, tremendous strain may be put on tow lines, connecting shackles and other elements of the tow system, he said.
Curtis Smith, a Shell Alaska spokesman, said the Kulluk had survived previous tows through rough seas without mishap, and that the weather forecast before leaving Dutch Harbor indicated a favorable two-week window. He said the grounding was the result of unpredictable events that included multiple engine failures on the Aiviq, the vessel that attempted to tow the Kulluk through the Gulf of Alaska.
The oil rig does not have its own propulsion system.
"Over time, an investigation will tell us more about this marine incident but it's clear that a sequence of unlikely events compounded over a short period time," Smith said in a written statement. "We intend to use lessons from that review to strengthen our maritime fleet operation
On Wednesday, a five-person team was lowered from a helicopter to board the Kulluk to assess the rig. The effort to free the vessel will be led by Netherlands-based Smit Salvage, according to a statement released by a unified command of state, federal and industry officials formed in the aftermath of the grounding.
Coast Guard Capt. Paul Mehler, who made a helicopter overflight, said Wednesday evening that it was too early to speculate on a timeline to try to recover the rig.
"We going to do this smart. We are going to be as careful as we can," Mehler said.
The grounded rig holds about 143,000 gallons of diesel and some 12,000 gallons of lubricants. So far, there are no signs of any leaks.
The Kulluk is one of two mobile drilling rigs that Shell has refurbished to prospect for oil off Alaska's North Slope, and its grounding is a major setback in an exploration effort to develop new crude reserves in the Beaufort and Chukchi seas.
Vigor Marine in Seattle last June completed a major overhaul of the drilling rig that included installation of new diesel engines, and the rig was scheduled to return for winter maintenance, according to Brian Mannion, a Vigor spokesman.
Vigor officials have hoped that Shell's 2012 exploration effort would kick off a decade of offshore Arctic oil drilling that would be a boon to Seattle's maritime industry.
The exploration has been opposed by environmental organizations, which in lawsuits have cited the risk of an offshore oil spill in the Arctic, and faulted federal oversight of Shell.
The Kulluk's troubles began last Thursday as a tow line severed. Coast Guard and industry crews struggled over the weekend to secure the Kulluk. But problems continued Monday even after the Aiviq, with its engines restarted, as well as a second, smaller tug, the Alert, had the oil rig under tow.
As a storm raged through the Gulf, with seas some 40 feet high, the Aiviq lost its tow line to the Kulluk. That left the second tug, the Alert, with a tow line still attached.
But at around 8:15 p.m. Monday, the MV Alert disconnected its tow line to protect the safety of its crew. The Kulluk drifted aground about 9 p.m. Monday.
"The Alert wasn't able to successfully continue to tow the Kulluk away from the beach, so they decided to release it," said Jason Moore, a spokesman for the Unified Command.
The Kulluk is believed to rest on a stretch of sand and graveled shoreline, where aerial photos showed waves breaking against its sides.
"There is surf there all the time. I've never seen it calm there," said Edward Pestrikoff, a salmon fisherman from the Kodiak Island village of Old Harbor located about 10.5 miles from the Kulluk's resting place.
Authorities said the Kulluk appears intact and stable.
Though the hull is fortified to deal with Arctic ice, the pounding surf could still cause damage, said Magone, the salvage industry official.
Another risk is that water could break over the deck, and cause flooding that could damage engines and other equipment, he said.
"This is likely not going to be simple," he said.