The National Transportation Safety Board (NTSB) has published an investigation into an incident where the towing vessel Kitty while pushing two loaded tank barges through the Algiers Lock on the Lower Mississippi River, had the lead barge strike a lock gate.
The incident
On July 4, 2023, about 1808 local time, the towing vessel Kitty was pushing two loaded tank barges through the Algiers Lock near mile 88.4 on the Lower Mississippi River in New Orleans, Louisiana, when the lead barge, EMS 317, struck one of the lock gates. There were no injuries, and no pollution was reported. Damage to the barge was negligible, while damage to the lock gate was about $2 million.
Analysis
While the Kitty tow was maneuvering into the Algiers Lock towards the Gulf Intracoastal Waterway during low water conditions on the Mississippi River, surging waters within the lock chamber affected the tow, and, at 1808, the lead barge, EMS 317, struck Algiers Lock Gate D. The captain of the Kitty told investigators there were no problems with the vessel’s propulsion and steering control, navigation, or communication systems.
Based on onboard image recorder system video footage of the vessel’s propeller wash, investigators found no evidence of an erroneous or inadvertent movement of a steering or propulsion control lever. Mississippi River water gauge heights were reported to be “extremely low” at the time of the casualty near the lock entrance from the river (the gage at Algiers Lock was at 1.7 feet at the time of the strike).
The Coast Guard had issued a safety advisory of the low water conditions and the need for river pilots to maintain safe speeds when transiting in the vicinity of docks, fleeting areas, and other vessels to minimize wake. Wakes from ships can travel for miles and their waves can be hazardous to other vessels and infrastructure along shorelines. There were no speed restrictions for vessels transiting the Mississippi River near the Algiers Lock at the time of the casualty.
The pilot of the southbound loaded tanker Garden State told investigators that vessels commonly transit that area at full ahead. The size of a wake caused by a vessel and the volume of water displaced is proportional to the vessel’s speed, displacement, draft, trim, beam, and hull form, as well as the water’s depth and the width of the area the vessel is moving through. Prior to the casualty, three loaded ships (587 feet long and 820 feet long, moving southbound at about 13–14 knots; and 580 feet long, moving northbound at about 10 knots) had transited near the lock within about 10 minutes’ time.
The size, speed, and frequency (each within about 5 minutes of each other) of the three loaded ships transiting near the lock would have produced wakes that affected the forebay and lock chamber. The effects of water displacement from a deep-draft vessel’s wake can increase when that water pushes into and recedes from narrow and/or smaller water bodies, such as shallow areas and lock chambers.
With the river, and therefore forebay water level, at a much lower level than normal, the size (volume of water) and surface area in the forebay would have been reduced. The forebay narrowed to the lock chamber, and surges in the lock had been witnessed before (although only about a foot). The crew of the Kitty described the variance of water in the lock chamber during the casualty as 3–6 feet, and the video study found the lower limit of the actual water level variations (minimum change in the lock chamber water level) to be 3.4 feet.
The captain of the Kitty described that the tow was pulled out of the lock, which is consistent with the movement of receding water. Following that, the tow was pushed back into the lock chamber, consistent with rising water. Neither of these conditions occurred when there were no ships transiting in the river nearby. Thus, it is likely that wake effects from deep-draft ships, transiting the Mississippi River adjacent to the Algiers Lock forebay during extremely low water conditions, moved water in and out of the forebay and lock chamber, causing the vessels in those areas to surge.
Probable Cause
The National Transportation Safety Board determined that the probable cause of the contact of the barge EMS 317 with Algiers Lock Gate D was surging water within the lock chamber, which was likely caused by the wakes from three deep-draft ships passing the lock forebay in quick succession during extreme low water conditions on the Mississippi River.
