The Fennica leaving Dutch Harbor for Oregon on Sunday. KUCB/Pipa Escalante photo.

A key ship in Shell Oil's Arctic drilling fleet left Alaska on Sunday afternoon.

The icebreaker Fennica is headed south to Oregon for repairs after a three-foot gash was discovered in its hull.

Two weeks ago, it had to return to port for temporary repairs shortly after leaving Dutch Harbor.

Now, the Fennica is making a week-long journey to Portland, Oregon, for a more permanent fix.

The Fennica reported hitting something as it was leaving Dutch Harbor for Shell’s Arctic Ocean drilling site on July 3. The U.S. Coast Guard is investigating the incident.

The Fennica was sailing between Hog Island and the Dutch Harbor airport on Amaknak Island. National Oceanic and Atmospheric Administration charts show that channel being shallower than the waters around the other side of Hog Island, where Shell kept its oil rigs while they were in Dutch Harbor.

The channel the Fennica sailed, under guidance of a harbor pilot, was even shallower than the area’s 80-year-old charts showed.

Charts still in use in the Aleutians and Arctic Alaska are based on surveys conducted in 1935 with sextants and hand-held lines to plumb the depths.

After the incident, the NOAA ship Fairweather, already in the area on a mission to better map Arctic shipping routes, did a modern, electronic survey and found rocky areas less than 30 feet deep, including one just 22.5 feet deep.

The Fennica sits 27.5 feet deep in the water.

U.S. Coast Guard Lt. Bill Fitzgerald, with the Coast Guard’s Marine Safety Detachment Dutch Harbor, said most of the deeper-draft fishing vessels using Dutch Harbor go around the opposite, deeper side of Hog Island.

“They don’t typically have too deep a draft, at least going between Hog Island and Amaknak,” Fitzgerald said.

Fitzgerald is leading the Coast Guard investigation of the incident. He said he expects to finish a draft in about a month, but it could be several months before internal reviews in Anchorage, Juneau, and Washington, D.C., are completed.

The Coast Guard and NOAA have put out notices to mariners to beware the newly mapped shoals.

Shell spokeswoman Megan Baldino wouldn't say how long repairs at Portland's Vigor shipyard could take. She said Vigor has the time and space to do the repairs.

The Fennica’s voyage to Portland will take 6.5 days, according to Marinetraffic.com.

Shell can only drill during the brief Arctic summer, and it cannot drill for oil without an oil well-capping device on board the Fennica. The Finnish-made icebreaker, owned by Arctia Offshore of Helsinki, is also intended to push large ice floes away if any approach Shell’s drill rigs.

The two rigs, the Polar Pioneer and the Noble Discoverer, are already on their way to the drill site in the Chukchi Sea.

Interior Department officials have not said whether the missing icebreaker will influence their decision on two final permits that Shell needs to begin drilling.