A Royal Dutch Shell PLC drill ship and the vessel towing it are awaiting relief off the coast of Alaska's Kodiak Island after the tow ship experienced engine problems.

The Coast Guard said Friday the Aiviq, an anchor handler, experienced multiple engine failures about 50 miles south of the island but was able to restart one engine.

The vessel lost power to its main propulsion, said Shell Alaska spokesman Curtis Smith. It was towing the Kulluk, which drilled in the Beaufort Sea over the summer.

"We're using power generators on the Aiviq to avoid significant drift to both vessels," Smith said.

Two vessels under contract to Shell are on their way to assist the idled vessels.

The tugboat Guardsman left Thursday from Seward and was expected to reach the stricken vessels Friday afternoon. A second vessel, the Nanuq, Shell's principal oil spill response vessel, was expected to arrive late Friday or early Saturday.

The Coast Guard cutter Alex Haley was on scene and monitoring the vessels, Capt. Paul Mehler III said in an agency announcement.

"Our primary concern is ensuring the safety of the personnel aboard the Aiviq and Kulluk," Mehler said.

The Coast Guard reported winds of 40 mph in the Gulf of Alaska and 20-foot seas.

Smith said 24 people were aboard the Aiviq, a 360.6-foot ice-class anchor handler owned and operated by Edison Chouest Offshore of Galliano, La.

The vessel can accommodate 62 and was partially staffed for the trip from Dutch Harbor, a port in the Aleutian Islands, to Seattle, where the Kulluk was headed for maintenance. The Aiviq was built to operate in the Arctic and is under long-term contract to Shell, Smith said.

The Kulluk has no propulsion system and is towed to its destinations. It was built in 1983 for a Canadian company and purchased by Shell in 2005.

The ship was designed for extended drilling in Arctic waters has an ice-reinforced, funnel-shape hull 266 feet in diameter. The conical shape is designed to deflect moving ice downward and break it into small pieces.

The centerpiece of the vessel is a 160-foot derrick.

In open water, the Kulluk is designed to maintain its location in storm conditions associated with waves up to 18 feet while drilling and 40 feet while disconnected.

A crew of 70 can run the drill ship but it has accommodations for more than 100.