Posted on May 1, 2024
A Mississippi River dredge crew was not required by their company to regularly check below-deck compartments, an oversight that led to undetected flooding and the eventual capsizing of a dredging vessel last year, the National Transportation Safety Board said Thursday.
The non-propelled 135’x35’ dredging vessel WB Wood capsized on the early morning of Jan. 16, 2023, during dredging operations near mile 85 on the Lower Mississippi River about 10 miles east-southeast of New Orleans. The sole crewmember was rescued by a good Samaritan towing vessel; there were no injuries, according to a summary by NTSB investigators.
An estimated 5,500 gallons of oil were released from the sunken vessel. The WB Wood was salvaged but the vessel, valued at $1.5 million, was declared a total loss.
Before the capsizing, the dredge had been in the same location for nine days, pumping sand from the riverbed to a pit on the west bank.
The WB Wood had two welded-steel, single-skinned, pontoon-type hulls with a deck structure aft. A 165-foot-long open-suction dredge ladder ran between the hulls from the deck structure to forward of the pontoons. The dredge ladder was controlled by an operator (called a leverman) from the lever room atop the deck structure.
The suction pipe ran down the ladder and onto a discharge pipe on the port side of the vessel, aft. The discharge pipe was connected to a submerged pipe, which, in turn, carried material to the bank.
About two hours before the capsizing, the dredge’s leverman noticed the dredge listing abnormally to starboard. The leverman discovered a starboard storage space full of water and began using a portable pump to dewater the space. The onboard portable pump and a second pump later added could not keep up with the rate of flooding and the starboard list continued to increase.
After trying to dewater the space, the night leverman and a deckhand prepared to cut the anchor lines and get the nearby towing vessel Omaha to help push the WB Wood into the river bank.
At 12:42 a.m., “the night leverman asked the night deckhand to go back to the bank to get a torch kit to cut the anchor wires,” according to the NTSB report. “The night leverman told investigators that he could tell the dredge was going to ‘go over’ as everything started ‘creaking really bad.’”
“As the captain of the Omaha approached the WB Wood, he noticed the entire starboard side of the dredge under water. As he maneuvered closer to assist, he saw the lights go out and the WB Wood begin to roll over.”
As the vessel began to roll, the lever man left the lever room, “jumped over the handrails down to the dredge pipe, and from there jumped onto the main deck. By that point, the list had increased so much that he had to climb onto the outboard side of the port pontoon,” the report says. He jumped into the river without a lifejacket and was soon rescued by the towing vessel. The night deckhand had taken a dinghy to get a cutting torch to sever the anchor lines but had not returned before the vessel capsized.
During a post salvage examination, NTSB investigators found a through-hull pipe into the starboard storage space was open and its overboard check valve was missing. Investigators determined the initial starboard list was likely caused by flooding through the unsecured through-hull pipe into the starboard storage space. Progressive flooding through comprised watertight bulkheads within the hull further increased the starboard list and aft trim which led to the capsizing of the vessel.
The overturned hull of the WB Wood with its port pontoon on the left and the starboard pontoon on the right the morning after the capsizing.
Two days before the capsizing, the day shift leverman discovered water in the starboard storage space, but was not able to identify the source of the water. In the time leading up to the capsizing, the crew did not know if any hull compartments had leaks or water in them. The company did not have requirements for regularly checking compartments below deck, which resulted in the undetected flooding.
“Vessel crews should regularly check tanks and voids that are adjacent to the vessel’s hull to identify hull integrity issues,” the NTSB report says. “The presence of water can indicate an issue with watertight integrity or wastage and should be addressed. Vessel operators should ensure crews have procedures for anticipating, preventing, and addressing the potential for water ingress and flooding, including establishing scheduled checks. Bilge alarms set to detect water at a low level in voids and other spaces are another means to ensure early detection.”
