NTSB: Barge Grounded in Prince William Sound After ATB's Lines Parted

 

The National Transportation Safety Board has released the results of its investigation into the loss of the barge Cordova Provider, which ran aground in Prince William Sound and suffered so much damage that it was declared a total loss. 

Cordova Provider began life as an ice-class oil recovery barge, but in 2005 it was modified with a notch to serve as one half of a unique ATB. The other half, the tug Krystal Sea, was built at the Western Towboat yard at the same time. Instead of coupler pins like those found on an Articouple or Intercon system, the Krystal Sea/Cordova Provider fit together with a wedge-and-recess system that had no moving parts. Three wedges on the tug - one on the bow, one to port and one to starboard - would line up with corresponding recesses within the notch at the stern of the barge. Changes in relative draft could be compensated for by backing out of the notch and re-entering at a different set of recesses. 

Instead of a positive mechanical connection, the Krystal Sea was held in the slot by four breast lines (push lines) running from the barge to winches on the stern of the towboat, much like an inland towboat. When Krystal Sea/Cordova Provider were built, the lines and bridles were steel wire rope; the operator later exchanged the wire rope for Dyneema soft lines, which were lighter and safer for the crew to handle over the side. 

Krystal Sea/Cordova Provider operated in this configuration to move breakbulk cargo around Prince William Sound, within sheltered waters. On the morning of January 10, 2025, the ATB got under way from Valdez, headed across the sound for Cordova. The forecast called for winds of 45 knots, consistent with wintertime weather along the coast of the Gulf of Alaska. Six-foot seas were expected in the sound, rising to 10 feet after midnight. 

The ATB's call in Cordova was completed swiftly, and the ATB departed for Whittier at 2110. By 0200 hours the next morning, as Krystal Sea crossed the middle of the sound, seas rose to 4-6 feet, with wind and waves on the port quarter of the tug - typical conditions, according to the crew. 

At 0250, the mate on watch heard a line snap, followed by three more. All four of the Dyneema lines that held the tug and barge together had parted in the middle, and the Cordova Provider was adrift. The master came to the bridge and maneuvered to see if there was a way to regain control of the barge, but the surface conditions made this too dangerous to attempt. 

Instead, the Coast Guard put the master in contact with the operator of the escort tug Latouche, moored nearby. The Latouche arrived on scene at 0550 hours and attempted to retrieve the barge by getting a line onto a bitt on its stern. The crew succeeded, but the line parted shortly after. Latouche was forced to give up the chase as Cordova Provider drifted into dangerous shallows off Axel Lind Island. The barge then ran aground, sustained extensive hull damage on the rocks, and partially sank. It was later refloated, towed offshore and disposed of through sinking in deeper water.

Investigators' focus turned to the lines that connected the two vessels as an ATB unit. The operator had switched to soft shackles and Dyneema pennant lines in 2023-4, and the captain had inspected the rigging about five days before the casualty, finding nothing amiss. After the casualty, a technician from the firm that assembled the lines determined that they were in fair to good condition, with minor abrasion. Three had parted in the middle of the pennant section, and one parted at the soft shackle. All components were rated for a 100,000-pound breaking strength. 

NTSB concluded that the lines likely parted due to shock loading, with cascading failure after the first line parted. As the tug had served in similar conditions before, the reason for the break on this particular trip is unknown.