What Happened
What Happened
On January 22, 2023, about 1530 local time, the tugboat Mark E Kuebler and the tanker Nisalah collided while the tanker was transiting inbound in the Corpus Christi Ship Channel near Ingleside, Texas. The tugboat’s hull was breached and the tanker’s propeller was damaged in the collision. The captain of the Mark E Kuebler grounded the tugboat to prevent it from sinking, and, while aground, a small sheen of hydraulic oil was observed near the tugboat. The oil was recovered with absorbent pads. No injuries were reported. Damage to the Mark E Kuebler was estimated at $3 million; damage to the Nisalah was estimated at $3.9 million.
What We Found
What We Found
We determined that the probable cause of the collision between the tugboat Mark E Kuebler and the tanker Nisalah was the mate maneuvering the tugboat near the starboard quarter of the tanker, which resulted in the tugboat being drawn in toward the tanker by hydrodynamic forces that the tugboat had insufficient reserve power to counteract due to the transit speed of the vessels.
What We Recommended
Hydrodynamic Forces between Vessels in a Channel
As a large ship moves through a channel, a low-pressure suction is particularly strong on the vessel’s quarters near the inlet side of the propeller, and hydrodynamic forces increase exponentially with the vessel’s speed. Therefore, a small vessel operating near a larger vessel must maintain a safe operating distance or have sufficient reserve power to counteract the hydrodynamic forces to avoid being pulled into the other vessel and risking collision. If a small vessel must operate near a larger vessel—such as a tugboat conducting harbor-assist operations—the operator of the smaller vessel should be aware of the hazards caused by hydrodynamic forces and, if necessary, maintain a safe distance until the larger vessel slows and the hydrodynamic forces are reduced.
Speed During Harbor-Assist Maneuvers
Owners and operators of Z-drive tugboats that perform harbor-assist operations should set speed limits for advanced maneuvers such as stern-first approaches. These limits may vary for different classes of tugboats based on design. Tugboat operators should communicate these limits to ship masters or pilots in command of the vessels that they are assisting before engaging in these maneuvers.
Location Information: Corpus Christi Ship Channel between Port Aransas and Ingleside, Texas (Note: The coordinates may be more useful for map plotting: 27°49.57' N, 97°9.27' W)
