propeller.
The National Transportation Safety Board says speed and hydrodynamic forces played a major role in a collision between a tugboat and a tanker in the Corpus Christi Ship Channel last year.
The collision took place on Jan. 22, 2023, when the tugboat Mark E Kuebler collided with the tanker Nisalah near Ingleside, Texas. Fortunately, there were no reported injuries.
The agency’s report revealed that the smaller tug was drawn in by the hydrodynamic forces of the larger tanker, stressing that “small vessels operating near larger ones must ensure a safe distance or have enough reserve power to counteract hydrodynamic forces and avoid being pulled towards the larger vessel.This is particularly important for tugboats conducting harbor-assist operations.”
Mark E Kuebler was, at the time, one of the five tugboats assigned to assist the Nisalah’s arrival. The tugboat’s position was at the tanker’s starboard quarter.
As the tanker moved at nearly 10 knots, the tugboat’s mate attempted to turn around and transit backwards to their assigned position.
However, during the turn, the tugboat was pulled towards the tanker and the two vessels collided. The NTSB found that the tug “lacked enough reserve power to counteract hydrodynamic forces due to the speed of the transit” and that water poured into Mark E Kuebler’s Z-drive machinery room.
Because of the danger of sinking due to the flooding, the tug’s captain intentionally grounded the tugboat in the bank outside of the Corpus Christi Ship Channel.
The Nisalah pilots and crew saw no indications of damage to their vessel and the tanker proceeded to the terminal, mooring without further incident.
The NTSB report recommended that owners and operators of Z-drive tugboats “establish speed limits for advanced maneuvers such as stern-first approaches.”
These limits, it stated, “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.”
In response to the incident, G & H Towing, the towboat’s operator, implemented a new policy that limits stern-first landings of tugboats on assisted vessels to speeds of 7 knots or less.
The collision resulted in nearly $7 million in damages between the two vessels including an estimated $4 million in salvage and repair costs for Mark E. Kuebler alone.