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NTSB: Mooring Buoy Failure Caused Grounding With $4.5M in Damage

NTSB
Image courtesy NTSB

Published Mar 1, 2022 10:24 PM by The Maritime Executive

The fatigue failure of an unrated mooring buoy led to the grounding of a fishing tender during a storm near Bristol Bay, Alaska in 2020, according to the National Transportation Safety Board (NTSB). 

On August 30, 2020, the fishing tender barge SM-3 broke free from its mooring buoy in a storm and went aground. No injuries were reported, but the vessel sustained $4.5 million in damage and left a three-mile-long debris field scattered along the waterfront. 

SM-3 was a converted deck barge originally built in 1966. As an uninspected fishing industry vessel, no trained mariners were required on board, and the vessel's USCG safety oversight was limited to a stability test and a survey of her lifesaving equipment. 

During the Bristol Bay salmon fishing season, SM-3 served as a tender at Nushagak Bay, providing ice, fuel and water to fishing boats. It also took in fresh fish for processing and freezing on board. In season, the barge would house up to 40 workers, including the operating company's chief executive officer (who also served as the person in charge). SM-3 normally moored bow-to-bow with a freezer storage barge, the Riverways-11, with a ramp connecting the two for fork-truck access. 

In mid-August 2020, with the salmon season over, a skeleton crew of eight people stayed aboard to prepare the two barges for winter layup. The SM-3 and Riverways-11 would be towed off to Naknek and Dillingham, respectively, and the mooring system would be recovered. 

On the evening of August 25, the National Weather Service (NWS) forecast the arrival of a storm with potential hurricane-force winds within about five days' time. SM-3's person in charge (PIC) confirmed to NTSB that the staff was aware of the forecast at least 3-4 days out.

With little time before the storm's arrival, the staff decided to have the Riverways-11 towed off to Naknek. There were not enough available towing assets to retrieve both barges in time, so SM-3 stayed at the mooring at Nushagak Bay. 

The crew spent the intervening days preparing for the arrival of the storm. On August 30, as predicted, winds picked up to 30-40 knots, with gusts over 50. The PIC estimated that wave heights were in the range of eight feet. At about 2300 hours, the PIC awoke and detected a "motion change," he told investigators, and he realized that they had gone adrift. He ordered the crew to deploy one of the barge's emergency anchors. It did not hold, so they rigged a second using the barge's crane and released it over the side manually. This did not hold either, and they drifted onto a sandy beach. 

The crew took shelter belowdecks while the surf pounded on the barge's hull. They waited out the dangerous motion until the tide came down, leaving the barge high and dry. The crew disembarked safely onto the beach and were rescued by local good samaritans. No injuries were reported.

Courtesy NTSB

On October 19-20, the badly-damaged barge was towed off the beach and brought to Naknek. Both mooring anchor assemblies were retrieved, and the salvage team found that the mooring buoy was missing the top padeye assembly, which had torn off with a piece of the buoy's steel outer casing. The padeye was found separately, still connected to the barge’s bow by the anchor chain. Investigators were unable to obtain strength rating, manufacturer name or other information about the buoy from the supplier.

"The effect of the storm on the barge resulted in forces that exceeded the capability of the weakest link in the ground tackle system’s components - in this case, the mooring buoy," NTSB concluded. "Mariners must consider the strength of each component of a ground tackle system and should reference marine standards for design. Bending loads can be significantly higher than straight-line pull."