The National Transportation Safety Board (NTSB) has published an investigation into an incident where a dry bulk carrier broke free from its mooring during high winds in the Brownsville Ship Channel in 2024, leading to a collision with a tugboat.
The incident
On January 8, 2024, about 1237 local time, the dry bulk carrier Chang Hang Hui Hai was moored at dock no. 12 in the Brownsville Ship Channel in Brownsville, Texas, when it broke free during high winds (see figure 1 and figure 2). The vessel drifted across the ship channel and struck the tugboat Signet Defender, which was tied up to the tugboat Signet Magic at the Signet Maritime pier along with the tugboat Signet Ranger. There were no injuries, and no pollution was reported. Damage was estimated at $2.5 million.
Analysis
The casualty occurred on the morning of January 8, during rapidly deteriorating weather conditions, with wind speeds increasing and gusts reaching 62 knots within only a few hours. As conditions worsened, the Chang Hang Hui Hai crew increased the initial 10-line mooring arrangement to 16 lines—all lines available, excluding the spares.
As the winds picked up, the higher wind speed increased the wind load (force) acting on the Chang Hang Hui Hai’s lateral surface area above the water (the sail area). The bulker’s freeboard had been increasing as it offloaded, increasing its sail area. This force, acting on the vessel nearly perpendicular to its length, significantly strained the mooring lines holding the ship to dock no. 12.
The force of wind against the ship’s side overcame the breaking strength of several lines forward, causing them to part and the ship’s bow to move away from the pier. This began a cascading failure as the remaining lines took up additional strain. Ten mooring lines and two bollards (with five lines attached) failed, and one line paid out, leading to the ship drifting away from the dock, across an 800-foot-wide section of the Brownsville Ship Channel, where it collided with the Signet Defender.
Neither postcasualty testing of the mooring lines nor an assessment of the mooring bollards’ condition was conducted. However, all the lines were certificated and in good condition, per their last inspection. Nevertheless, without postcasualty tests or an assessment of the condition of the mooring lines and bollards, investigators could not definitively rule out weakened or overloaded mooring lines or overloaded bollards as contributing factors in the casualty.
Probable Cause
The National Transportation Safety Board determines that the probable cause of the breakaway of the dry bulk carrier Chang Hang Hui Hai from a dock and subsequent collision with the tugboat Signet Defender was the force of the wind acting on the exposed freeboard of the Chang Hang Hui Hai, which overcame the breaking strength of several mooring lines.
