An inadequate mooring arrangement allowed a tanker to break away from a pier and drift into a bridge in New Hampshire, the National Transportation Safety Board (NTSB) has determined.
The docking setup that did not take into account prevailing tidal conditions was the probable cause of the 2013 breakaway of Harbour Feature. The ship subsequently struck the Sarah Mildred Long Bridge in Portsmouth, N.H., the agency said in November 2014.
The incident occurred at 1327 on April 1 when the 473-foot tanker broke free from its moorings at the New Hampshire State Port Authority’s Marine Terminal Wharf. The accident caused $2.5 million in damage to the bridge, which was closed for six weeks. Harbour Feature sustained $1 million in damage.
The safety board said the river is known for its rapid tidal currents and hazardous crosscurrents. The current was flooding at 3 to 4 knots at the time of the allision.
Harbour Feature had arrived in Portsmouth the previous day. With a local pilot on board, it had docked at the Sprague Energy River Road Terminal Docking Facility about three miles upriver from the accident site and loaded a cargo of tallow.
The NTSB said the pilot had given the master the Portsmouth Pilots’ “Recommendation to Master for Safe Mooring in Piscataqua River,” an information card that warned of “3 to 5 knots of current.” The card recommends “equal tension or equal weight on all ropes at all times [and] mooring winch brakes shall have a holding near the strength of the line.” In addition, the United States Coast Pilot for Portsmouth states that “due to strong ebb and flood tidal currents on the Piscataqua River, a mooring plan will be provided by the Portsmouth Pilots upon boarding for the intended terminal, and masters should be particularly vigilant in minding and tending to their vessel’s moorings.”
The vessel’s Fleet Nautical Handbook warned about mooring winch brake failures and the potential for a vessel to break free from its berth in strong currents. The master put out an extra line, for a total of 11.
With refueling not allowed at the Sprague facility, Harbour Feature had to be moved to the New Hampshire State Port Authority’s Marine Terminal Wharf three miles downriver to take on fuel before departing for the United Kingdom. The shifting of Harbour Feature was timed for slack water at 1153. The captain told investigators that the ship’s tides and current software calculated a maximum tidal current of 2.7 knots during the movement.
At 1115 on April 1, the pilot from the previous day came aboard; the vessel was moved downriver and at 1236 moored starboard-side-to at the Marine Terminal Wharf. The captain had 10 of the ship’s 23 mooring lines deployed: three bow and two spring lines forward, plus three stern and two spring lines aft. Each was 5.5 inches in diameter with a breaking strength of 40 tons.
Harbour Feature draws 29 feet at the stern. The wharf had a depth of only 30 feet at its west end, so the pilot docked the ship farther down the wharf toward the east. That meant the bow extended 30 feet beyond the east end of the wharf and was pointing downriver. The vessel’s stern was 150 feet from the bridge.
The NTSB noted that during flood tide on the Piscataqua, water rushes upriver, deflects off the riverbanks and causes hazardous crosscurrents. Because Harbour Feature’s bow extended beyond the eastern end of the wharf, “the deflecting flood current pushed the bow away from the dock and increased the strain on the vessel’s mooring lines.”
At 1313, an able seaman on gangway watch radioed the bridge that the forward mooring lines were tight. He ran to the bow where he saw a large amount of dust and smoke coming from the brakes on the mooring line drums. The captain tried unsuccessfully to use the bow thrusters to push the vessel back toward the dock. Both of the forward spring lines and one aft spring line attached to a bit on the ship parted. The winch brakes slipped, allowing all of the remaining mooring lines to run free and fall into the river.
By 1324, both anchors were deployed and the master tried to gain control of the ship with the main engine and rudder. While the anchors slowed the drift, Harbour Feature was carried by the current into the bridge, port-side-to, at 1327. The bridge tender notified the Coast Guard and two towing vessels got underway to assist, with the river pilot on the first vessel to arrive.
High water slack was at 1749. At that time, the anchors were raised and the tanker got underway with the assistance of the towing vessels. At 1842, the ship was docked port-side-to at the Marine Terminal Wharf, using 18 mooring lines.
Damage to Harbour Feature included destruction of the freefall lifeboat, flooding of a port wing ballast tank, extensive damage to the frames in several port-side compartments and a hull breach above the waterline into the inert gas generator room. Three structural members were damaged on the bridge. There were no injuries or pollution.
The safety board noted that Harbour Feature was equipped with eight non-auto-tension split mooring winches, four forward and four aft, with the mooring lines on the winch drums set on the brake.
“A satisfactory test of the Harbour Feature’s mooring winch brake holding capacity (BHC) had been conducted on Feb. 26, 2013,” the report said. “During the BHC test, the chief officer had inspected each mooring brake band and noted that about 3 millimeters of the asbestos brake lining remained. The manufacturer’s operations manual stated that the brake lining should be replaced when worn down to 3 millimeters. However, the brake lining had not been replaced when the accident occurred, indicating that the mooring winch BHC may have been less than the operational setting.” Because of disintegration, it was impossible to determine how thick the brake lining was.
The operator of the 3-year-old Portuguese-flagged vessel, TB Marine Shipmanagement GmbH & Co. KG, did not respond to an email seeking comment.