Inadequate water transfer monitoring caused flooding on moored towboat, NTSB report finds

The National Transportation Safety Board (NTSB) has published a marine accident brief in relation to the flooding incident on the 25-metre towing vessel Alton St Amant in the Harvey Canal in New Orleans on May 17, 2020.

Background

On April 1, the 2009-built Alton St Amant, owned by Blessey Marine Services, arrived at the Bollinger Quick Repair shipyard in Harvey Canal to be drydocked and to complete major maintenance that also included work to bring the vessel into compliance with towing vessel regulations (46 Code of Federal Regulations (CFR) Subchapter M).

Maintenance items consisted of inspecting all the overboard fittings; blasting and painting the hull; replacing anodes; surveying and reconditioning, where necessary, all the running gear (propellers, shafts, bearings, etc.); and overhauling the bilge alarm system and associated pumps. Additionally, maintenance was scheduled on the main engines, generators, and gear sets, along with some small steel repairs. The vessel-monitoring and closed-circuit television (CCTV) systems were also to be upgraded.

During this maintenance period, there were no crewmembers aboard the vessel. A Blessey port engineer was assigned to the project and communicated directly with the shipyard project manager.

Several shipyard workers and equipment specialists — such as welders, pipefitters, and painters — performed specific tasks aboard the vessel while it was in the shipyard.

Upon completion of the maintenance, a sea trial was scheduled for May 18. The crew was expected to return to Alton St Amant the day after the sea trial.

On May 9, after spending about six weeks at the Bollinger Quick Repair shipyard, Alton St Amant was shifted from drydock to a wet berth to complete outstanding maintenance items. Among the remaining work, two bilge pumps, which had been removed from the vessel for overhaul, were to be reinstalled; the sealing rings on several of the vessel’s tank access hatches were to be replaced; and the sealing surfaces of the hatches were to be cleaned.

On May 15, about 90,000 litres of fuel were loaded onto the vessel. The flush hatches to the vessel’s two potable water tanks located on the main deck in the rudder room had been opened for maintenance, but the covers were not reinstalled at the end of the day.

That same day, the port engineer requested that the shipyard workers fill the two potable water tanks. A pipefitter, who had worked for Bollinger Quick Repair about eight years, returned to the shipyard the following morning on May 16 and began reinstalling the bilge pumps with three other shipyard workers at about 05:00 local time.

At about 10:00, after completing the pump installation, the pipefitter started filling the potable water tanks from a shoreside water manifold that was connected to the vessel’s potable water fill pipe via a two-inch hose through the open exterior engine room doors. He opened the supply (fill) valve at the shoreside manifold, and began filling the two tanks, which had a combined capacity of around 50,000 litres.

Unaware that the potable water tank access hatches were open in the rudder room, the pipefitter left the shipyard about 10:30 with plans to return the next day. He intended to fill the tanks and then allow them to overflow onto the exterior main deck through their vents to flush out any residual debris inside before turning off the water supply.

Throughout the remainder of the day and throughout the night, the two potable water tanks continued to fill with fresh water on the unmanned Alton St Amant. After the pipefitter left, no other shipyard workers boarded the vessel to check the water tank levels.

At about 06:30 on May 17, a shipyard worker walking past Alton St Amant noticed that the vessel was sitting low in the water and called the shipyard general manager.

Upon arrival, the general manager found Alton St Amant partially submerged and resting on the bottom of the canal alongside the pier. The engine room was flooded, and the main deck was partially submerged.

The US Coast Guard, Blessey personnel, and a local salvage company were notified.

While observing Alton St Amant, the general manager noticed the potable water hose connected to the vessel was charged; he then closed the potable water supply valve on the pier manifold.

Pollution mitigation and recovery efforts began that morning. By 16:30, Alton St Amant was lifted by crane from the bottom of the canal and refloated.

No hull damage was found when the vessel was inspected.

When Alton St Amant was then shifted to the drydock and placed on blocks by 21:00, shipyard and Blessey personnel walked around the vessel and found that no water was leaking or seeping from the hull in the areas of the flooded spaces.

The following morning, shipyard workers who were disconnecting electrical power cables from the recovered vessel found the potable water hose still connected to the fill pipe on the Alton St Amant. They also discovered that the access hatches for the potable water tanks in the rudder room were open.

The pipefitter told investigators after the accident he was unaware that the access hatches were open. Although a pre-work safety meeting was conducted each day, the status of these hatches was not communicated to the pipefitter.

Approximately 3.7 litres of diesel fuel were released into the water, and damage to the vessel was estimated at US$1.5 million. No injuries were reported.

Additional information

After the sinking of Alton St Amant, Bollinger Quick Repair conducted an internal investigation and implemented procedures for conducting water transfers. These procedures were intended to ensure communication reached the shipyard’s management and staff; project managers obtained approval from the facility superintendent; and a pre-inspection of tanks, valves, piping, and other components of the vessel’s water system be conducted.

Additionally, water transfers were to be monitored for the duration of the filling process.

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 vessel, the access hatches to the potable water tanks in the rudder room were found to be open and the two-inch hose supplying water to the vessel was still connected to the vessel’s fill pipe for these tanks.

Fresh water 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.

Probable cause

The NTSB has determined that the probable cause of the flooding of 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.

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.