ANCHORAGE, Alaska (AP) — The pulling requirement for the tow of a Royal Dutch Shell PLC floating drill rig was revised upward by more than 50 percent after the vessel ran aground in December off a remote Alaska island, a Shell official testified Thursday.

Marine operations manager Jonathan Wilson, speaking by phone from London, told a Coast Guard investigation panel that Shell performed a resistance study from scratch after the Kulluk, a 266-foot diameter drilling barge with no means of propulsion, broke away from its tow vessel Dec. 27 and ran aground four days later on Sitkalidak Island near Kodiak.