The Coast Guard said the drilling rig broke loose from a Shell-contracted ship, the tow vessel Aiviq, Monday afternoon, the Anchorage Daily News reported Tuesday.
The rig had been secured to a second tow vessel but when grounding was imminent, the second vessel was directed to abandon its tow line to avoid endangering the crew, the crisis command team said.
No one was hurt, the Coast Guard said.
When the Kulluk was removed from its final towline, it was 4 miles from land, a command team said late Monday. The 250-member command team includes members of the Coast Guard, representatives from the state and contractors.
The grounding was the latest development in the crisis that began Thursday when the $290 million, 266-foot-diameter Kulluk rig lost a towline after a mechanical failure in the shackle used to connect it to the Aiviq, the Daily News said.
The Coast Guard evacuated the Kulluk's 18-person crew on Saturday for safety reasons as the floating rig rose and fell in giant swells in the Gulf of Alaska. Once the crew was evacuated, there was no way for the Kulluk to drop anchor and avoid grounding, Coast Guard Commander Shane Montoya said.