ANCHORAGE, Alaska — The failure of a towing vessel’s engine left a Royal Dutch Shell PLC drill ship stalled Friday in rough Gulf of Alaska water 50 miles south of Kodiak Island.

A relief tug plowed through 20-foot waves and winds of 40 mph Friday afternoon to reach the Kulluk, one of two drill ships Shell operated this year in the short Arctic Ocean open water season, and the vessel that had been towing it, the 360-foot Aiviq.

No decision had been made regarding where the vessels would be moved, said Coast Guard spokesman David Mosley in Anchorage.

The Kulluk, a round ship with a 160-foot derrick that resembles a bowling pin in a bowl, has no propulsion system. 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.

In open water, the Kulluk is designed to maintain its location while drilling in storm conditions associated with waves up to 18 feet. It’s designed to withstand waves of 40 feet when disconnected.

Shell Alaska spokesman Curtis Smith said 17 people are on board the drill ship. A crew of 70 can operate it during drilling operations and it has accommodations for more than 100.

The Aiviq is carrying a partial crew of 24 and can accommodate 62. It was built to operate in the Arctic and is owned and operated by Edison Chouest Offshore of Galliano, La.

The drill ship was being towed from Dutch Harbor in the Aleutian Islands to Seattle when problems arose Thursday.

“It was reported that they had lost their tow, so we diverted the (cutter) Alex Haley as a safety precaution,” Mosley said.

The Kodiak-based Alex Haley had been in port for Christmas and had just begun a patrol.

The cutter reached the stricken vessels at 2 a.m. Friday. About two hours later, the Aiviq reported multiple engine failures.

“It’s been reported that they had some bad gas — like water in the fuel — which caused them to lose power to their engines,” Mosley said. That assessment was preliminary, he said.

Coast Guardsmen on the Alex Haley attempted to fix a tow line to the Aiviq, Mosley said, to keep it from drifting. The attempt failed.

“Their tow line parted, and part of the tow line ended up wrapped around one of the propellers on the Alex Haley,” Mosely said. With just one propeller, the cutter had limited maneuverability.

The Aiviq crew was able to restart one engine, and with generators had enough power to maintain its position. The crew also re-established a tow line to the drill ship.

The Coast Guard sent a C-130 aircraft to the ships after daybreak. When it arrived at 11:30 a.m., the Alex Haley was released to address the cable wrapped around its propeller.

Two vessels under contract to Shell left Seward when the trouble began. The tug Guardsman reached the vessels at 2 p.m. The Nanuq, Shell’s principal oil spill response vessel, was expected to arrive early Saturday afternoon.

The Coast Guard Cutter Hickory left Homer on Friday to provide on-scene safety assistance, Mosley said, and should arrive Saturday afternoon.