National Transportation Safety Board Marine Accident Brief
The National Transportation Safety Board (NTSB) has issued Marine Accident Brief regarding the breakaway of tanker Harbour Feature from its moorings, resulting in the subsequent allision with the Sarah Mildred Long Bridge.
On April 1, 2013, at 1324 local time, the 473-foot-long tanker Harbour Feature, with 20 persons on board, allided with the Sarah Mildred Long Bridge in Portsmouth, New Hampshire, after the vessel broke free from its moorings at the New Hampshire State Port Authority, Marine Terminal Wharf. No injuries or pollution resulted from the accident. The bridge sustained $2.5 million in damage; the Harbour Feature sustained $1 million in damage.
The 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. The winch brakes are designed to hold 80 percent of the mooring lines minimum breaking load (MBL) but are operationally set to hold 60 percent of the MBL. A satisfactory test of the Harbour Features mooring winch brake holding capacity (BHC) had been conducted on February 26, 2013. 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 manufacturers 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. The heat that resulted from the mooring lines rapidly paying out disintegrated the brake lining, and it could not be determined how thick the brake lining was before the accident.
The National Transportation Safety Board determines that the probable cause of the breakaway of the Harbour Feature from its moorings and subsequent allision with the Sarah Mildred Long Bridge was the inadequate mooring arrangement made by the master and the pilot for the vessels location and the prevailing tidal conditions.
| General Tips for Safe Mooring |
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When mooring a ship at a dock, pay close attention to the following factors:
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Further details may be found by reading the Marine Accident Brief issued by NTSB.
Source: NTSB / Image Credit: U.S. Coast Guard
