The National Transportation Safety Board (NTSB) has released an investigation report on the flooding and partial sinking of towing vessel Uncle Blue that took place on March 26, 2023.
The incident
On March 26, 2023, about 0500 local time, the towing vessel Uncle Blue was towing one empty barge on the Lower Mississippi River in Ascension Parish, Louisiana, when the vessel began flooding. The six crewmembers aboard attempted to pump out the vessel but were unsuccessful, and they evacuated to the barge. A Good Samaritan vessel pushed the towboat and barge to the right descending bank, where the Uncle Blue partially sank. There were no injuries, and no pollution was reported. Damage to the vessel was estimated at $500,000.
Analysis
While pushing a single barge on the Lower Mississippi River, the Uncle Blue flooded and partially sank near mile 184. The Uncle Blue had been in service for almost 60 years. During salvage, investigators discovered numerous wastage holes in the hull on the port side of the lazarette. They also discovered doubler plates installed on the hull near the wastage holes. Doubler plating can be used as a temporary repair solution; however, because doubler plate repair can lead to increased stress concentrated in the area of the repair, doubler plates are not suitable as a permanent repair for sections of the hull. Given the vessel’s age, the holes found in the hull, and the presence of the doubler plates, the vessel’s hull had not been adequately maintained. Investigators did not identify other potential sources for the flooding; therefore, the wasted steel hull plating in the lazarette was the initial source of the flooding.
Pipe runs (conduits) inside the hull, which had previously been used to allow rods to run the length of the hull, were either corroded or missing where they passed through the voids. These openings allowed water from the lazarette to flood through two voids and, eventually, into the engine room. Thus, the conduits allowed for progressive flooding, which resulted in the partial sinking. The Uncle Blue had only one bilge high-water level sensor, located at the forward end of the engine room. Because the vessel sank by the stern, the float on the sensor would not have lifted until the lazarette and two voids were filled and the aft end of the engine room was inundated with water. Therefore, as it was configured, the bilge high-water level alarm system was ineffective as a means to alert the crew. Had an additional sensor been installed in the lazarette, the crew would have had an earlier indication of the flooding and may have been able to act to address it.
Conclusions
Probable Cause
The National Transportation Safety Board determines that the probable cause of the flooding and partial sinking of the towing vessel Uncle Blue was a lack of
watertight integrity due to the poor condition of the hull, which allowed water to ingress through wastage holes into the lazarette. Contributing to the sinking were unsealed penetrations in transverse bulkheads, which allowed for progressive flooding forward into the engine room, and the lack of a high-water bilge sensor in the lazarette, which prevented early detection of flooding into the space.
Lessons Learned
Inspecting and Repairing Steel Hulls
Steel hulls are susceptible to corrosion, erosion, and damage over time. To avoid flooding or weakening of the hull, it is good marine practice for owners to
conduct regular oversight and maintenance of hulls, including between drydock periods. An effective maintenance and hull inspection program should proactively address potential steel wastage, identify hull and watertight integrity deficiencies, and ensure corrosion issues are repaired in a timely manner by permanent means.
Using Doubler Plates for Hull Repairs
Although doubler plating can be used as a temporary repair solution, it is not generally suitable as a permanent repair for a vessel’s hull. Vessel owners should crop out wasted steel on the hull and replace it by inserting new plating instead of covering it up with doubler plating.
