The National Transportation Safety Board (NTSB) has released an investigation report on the bulk carrier Sirocco which broke away from its moorings and drifted in March 2023.
The incident
On March 27, 2023, about 0208 local time, the bulk carrier Sirocco broke free from its moorings at the Convent Marine Terminal, located at mile 160.9 on the Lower Mississippi River in Convent, Louisiana. The vessel drifted downriver and, at 0249, collided with a barge moored at the Mosaic Uncle Sam dock at mile 160.4. There were no injuries, and no pollution was reported. The Sirocco, the barge, and the Mosaic Uncle Sam dock sustained damage totaling about $5 million.
Analysis
While loading coal, the Sirocco broke free from its moorings at the CMT dock, drifted about half a mile downriver, and collided with barge MEM 5087 at the Mosaic Uncle Sam dock. The NTSB had previously investigated a similar incident on April 6, 2015, involving the bulk carrier Privocean, which broke free from its moorings at CMT during high-water conditions (14.2 feet on the Carrollton gauge). That vessel drifted across the river and collided with the tanker Bravo at the Ergon St. James Terminal. The probable cause was inadequate mooring and insufficient tugs, given the prevailing conditions. Three weeks later, CMT issued a high-water loading plan for vessels moored during high-water operations when the Carrollton gauge exceeded 12 feet.
When the Carrollton gauge dropped below 12 feet, the high-water loading plan was no longer in effect, and CMT did not require hold-in tugs. The Sirocco initially had two tugs holding it, but they were released when the gauge dropped below 12 feet. From 1500 on March 26 to about 0200 on March 27, the crew loaded cargo without incident, keeping the vessel in place by continuously tightening the lines. However, as cargo was added, the vessel’s draft increased. By the time loading began in the forward no. 2 hold at 0050, the draft had increased significantly, causing the bow to sit lower relative to the dock. If not properly heaved, slack in the lines allowed the bow, exposed to the river current, to move off the dock, increasing tension on the lines.
Although crewmembers tended the lines, they did not effectively monitor the bow lines during forward hold loading, allowing the bow to come off the dock. When they attempted to pull the bow back, the winches could not overcome the increased tension. A mooring winch brake provides friction to prevent lines from parting. However, when tension exceeds the brake-rendering load, the lines slip to prevent breaking. During the breakaway, the second officer saw smoke and sparks from the winches, indicating the tension exceeded the winches’ capacity. This caused the Sirocco to break free.
Both anchors were hanging out of their pockets, ready to be deployed, while loading. The master ordered the anchors to be dropped at 0213, but the starboard anchor was not let go until 0220 due to the unsafe situation on the bow. At that time, the water depth was about 70 feet, but only 90 feet of anchor chain was let out, which was insufficient to reach the bottom. The port anchor, released 12 minutes after the breakaway, helped slow the vessel, along with two assist tugs. If both anchors had been let out to an effective length, they may have prevented the collision.
Probable cause
The National Transportation Safety Board determined that the probable cause of the breakaway of the Sirocco was the bow coming off the dock during cargo loading in the forward holds. This exposed more of the vessel’s underwater hull to the strong river current, exceeding the brake-holding capacities of the ship’s mooring winches and causing the lines to pay out, leading to the vessel breaking free and colliding with barge MEM 5087.
Lessons learned
To reduce the risk of vessel breakaways, it is essential for crews to understand the forces acting on a vessel moored in strong currents. Crews should ensure that slack is consistently taken out of the lines as the vessel loads, especially as the forward draft increases and the bow sits lower, exposing more hull to the current. Continuously monitoring and adjusting bow lines during forward hold loading can prevent the bow from coming off the dock. Additionally, developing a breakaway response plan and incorporating safety measures—such as keeping propulsion, thrusters, and steering systems on short standby—can improve preparedness. Masters should also be familiar with how to request tug support on short notice.
