A tugboat remains pressed against the starboard bow of the Harbour Feature 24 hours a day as a safety precaution for the tanker that broke free from the New Hampshire State Pier on Monday and hit the Sarah Mildred Long Bridge.

The collision caused $2.5 million worth of damage to the bridge linking Kittery and Portsmouth, N.H., and ripped an 18-inch gash in the side of the ship 15 feet below the water line.

Four hours after the tanker, weighing more than 10,000 tons, broke free in the strong current of an incoming tide in the Piscataqua River, tugboats pushed it back to the dock. The 470-foot ship was moved later to the nearby Granite State Minerals pier.

A nautical engineering firm worked throughout the week to analyze the damage. It will determine whether temporary repairs can be made so the ship can be moved or whether permanent repairs can be made locally, said Coast Guard Lt. Nick Barrow.

The Coast Guard continues to investigate the cause of the accident but indicated that it could be some time before its conclusions are final.

“It’s a matter of looking at the mechanical systems but also conducting interviews, going through logbooks to see how the vessel was moored up and the experience level of those involved in mooring up,” as well as environmental factors like the current, Barrow said.

TB Marine Shipmanagement in Hamburg, Germany, the company that’s responsible for the ship’s management, has said it is working with U.S. authorities to determine what caused the tanker to break away from the pier.

The ship broke free at 1:30 p.m. Monday, during the strongest currents of the day, though the wind was just 10 mph, according to the National Weather Service.

The ship’s mooring mechanisms sustained damage as the ship broke free from its berth, Barrow said. Because of that, the captain has requested the presence of a tug.

“The lines parting and it breaking free had a trickle-down effect,” Barrow said. “Some of the systems that hold the lines in place experienced stress and damage.”

There was little the ship’s crew could do once the vessel broke away from the pier.

Now, Barrow said, “The vessel is secured to the pier by lines, but the tug is there as an extra precaution. … Certainly there’s no imminent danger of it breaking free.”

A ship of that size probably would have had at least 11 lines fastened to bollards on the pier, said Jack Humeniuk, spokesman for the longshoremen in Portland. The lines can be thick nylon rope or, for a tanker, they are often steel cables.

He said a new ship — the Harbour Feature was built in 2011 to carry oil and chemicals — would likely have sensors that detect tension on the lines and pay out some slack before the lines snap.

“Once you snap one line that may have X amount of tension on it,” others will snap, he said. “Generally, one goes, they all go.”

 

David Hench can be contacted at 791-6327 or at:

dhench@pressherald.com