- $6.9 Million in Damages After Tug Drawn into Tanker Propeller.
- Hydrodynamic Forces Blamed for Tug-Tanker Collision.
- Tug Mark E Kuebler Grounded to Prevent Sinking After Collision.
On January 22, 2023, around 3:30 PM local time, a collision took place between the tugboat Mark E Kuebler and the tanker Nisalah in the Corpus Christi Ship Channel, close to Ingleside, Texas. This unfortunate incident led to a breach in the hull of the tugboat and some damage to the tanker’s propeller. To prevent the tugboat from sinking, the captain of the Mark E Kuebler decided to ground the vessel. A small sheen of hydraulic oil was spotted near the grounded tugboat, but it was quickly cleaned up using absorbent pads. Fortunately, no injuries were reported. The estimated damages were around $3 million for Mark E. Kuebler and $3.9 million for Nisalah, reports NTSB.
Vessel Transit and Initial Setup
Earlier that same day, at about 2:30 PM, three pilots from Aransas-Corpus Christi boarded the Nisalah near the entrance to Corpus Christi Bay at Aransas Pass. These pilots were in charge of navigating the vessel on its way through the channel to the South Texas Gateway Terminal in Ingleside, Texas, where the tanker was set to load crude oil. At that moment, the Nisalah was in ballast condition, with empty cargo tanks and drafts of 33.8 feet at the front and 35.4 feet at the back. To help with the harbour manoeuvres, five tugboats were sent out. The Mark E Kuebler was positioned at the starboard quarter of the Nisalah when they met. The tug’s mate was at the helm, while the captain was in his stateroom.
Tugboat Manoeuvring and Approach
The Mark E Kuebler had its winch and hawser located on the bow, while the chock on the Nisalah—the spot where the tug’s line would be secured—was situated on a part of the hull that curved inward toward the stern and flared out from the waterline to the deck. To align correctly with this setup, the mate of the Mark E Kuebler decided to reverse the tug’s orientation, aiming to approach the tanker stern-first so that the hawser could lead forward and the tug could rest against the more vertical section of the tanker’s hull.
Hydrodynamic Forces and Collision
As the Nisalah glided through the water, it created a low-pressure zone near its starboard quarter. This effect was amplified by the tanker’s ballast condition, which made the inward curve of the hull more noticeable near the stern. Things got trickier with the hydrodynamic suction near the intake side of the tanker’s propeller. These factors combined to pull the stern of the Mark E Kuebler closer to the hull of the Nisalah.
The mate tried to steer away by adjusting the Z-drives and cranking up the engine power. However, at that moment, the Nisalah was cruising at 9.6 knots, while the Mark E Kuebler was moving at 11.6 knots—just shy of its maximum speed. Most of the tug’s engine power was dedicated to regaining its position, leaving it with not enough thrust to counter the strong hydrodynamic suction. Consequently, the stern of the tugboat was drawn into the tanker, leading to a collision.
Resulting Damage
The tanker’s propeller hit the stern of the Mark E Kuebler, leaving multiple gashes in the hull, warping the stern structure significantly, and damaging the vessel’s fendering system. The impact breached the aft peak tank and the Z-drive machinery room, flooding both compartments up to the waterline and soaking essential equipment. On the Nisalah, all four propeller blades were damaged.
Aftermath and Policy Changes
After the collision, the captain of the Mark E Kuebler quickly grounded the tugboat to prevent further damage or the risk of sinking. A small sheen of hydraulic oil was spotted and was effectively cleaned up with absorbent pads. In the aftermath of the incident, the operating company rolled out a new policy that restricts stern-first landings of tugboats on assisted vessels to speeds of 7 knots or less, aiming to reduce the chances of similar incidents in the future.
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Source: NTSB
