The National Transportation Safety Board (NTSB) has published an investigation report on the flooding of the towing vessel ‘Alton St Amant’ while moored in the Harvey Canal in New Orleans. The incident resulted in an oil discharge into the water. The investigation identified lack of pre-inspection and monitoring procedures for water transfer as a key cause of the incident.
On May 17, 2020, about 0530 local time, a shipyard worker reported that the towing vessel Alton St Amant was partially submerged while moored at a shipyard in the Harvey Canal in New Orleans, Louisiana. There were no crew members or shipyard workers aboard the vessel. Approximately five gallons of diesel fuel were released into the water. Damage to the vessel was estimated at $1.5 million. No injuries were reported.
Probable cause
NTSB has determined that the probable cause of the flooding of the towing vessel Alton St Amant was the absence of shipyard pre-inspection and monitoring procedures for water transfer, which resulted in potable water tanks overflowing through their open access hatches during an unmonitored transfer.
Analysis
After shipyard managers reported to the shipyard on the morning of the sinking, the potable water supply valve at the manifold ashore was found in the open position.
Later that day, during the post-salvage inspection of the Alton St Amant, the access hatches to the potable water tanks in the rudder room were found to be open and the 2-inch hose supplying water to the vessel was still connected to the vessel’s fill pipe for these tanks.
According to NTSB, freshwater had been filling the potable water tanks for over 20 hours. The pipefitter was not aware of the open access hatches when he began filling the tanks. After he departed the vessel, no other persons came aboard to monitor the status of the tank levels, and there was no shipyard policy for monitoring the filling process.
Having been filled for several hours, the potable water tanks reached capacity, resulting in an overflow through the open hatches in the rudder room (rather than the tank vents as planned). After the rudder room flooded, the water spilled over the open doorsill onto the main deck of the engine room and began flooding down into that space.
With the bilge system inoperable due to planned maintenance during the shipyard period and no one aboard the vessel to monitor the water transfer, the potable water continued to fill the aft spaces undetected and submerged the vessel until it came to rest on the bottom of the canal.
Lessons learned
Precautions for Tank Filling
Crew and shipyard personnel designated to conduct liquid transfers must be aware of the status of a vessel’s tanks, including their access hatches and associated piping systems, whether ashore or at sea.
When filling a tank, open access hatches create a risk of unintended flooding. Pre-inspection and monitoring of transfers provide the opportunity to identify and remedy any issues in order to ensure they are safely completed.
Download the investigation report: NTSB - Flooding of Towing Vesse Alton St Amant
Read another NTSB report: Engine failure caused fire on another towing vessel says NTSB report
