Excessive speed during an advanced harbour-assist manoeuvre led to a tug colliding with a container vessel in the Houston Ship Channel in Texas last year, the US National Transportation Safety Board (NTSB) said recently.
The tug George M and the containership MSC Aquarius collided on April 14, 2022, while the tug was positioning for a ship-assist manoeuvre and the containership was transiting north in the Houston Ship Channel. No injuries were reported.
About 1,000 gallons (3,785 litres) of gear oil were released from the damaged George M's port propulsion unit. Damages to both vessels totaled more than US$900,000.
George M and another tug were performing a harbour-assist operation to dock MSC Aquarius at the terminal. George M was assigned the "centre lead forward" position on the bow of the containership.
To make up to the bow of MSC Aquarius, the tug had to manoeuvre into position ahead of the containership, bow-to-bow.
The mate on George M was operating the tug at the time of the collision. The NTSB said it was the mate's first rotation on board George M's class of vessel.
In manoeuvring George M to the centre forward position, the mate approached the containership as it was transiting at 9.7 knots. While attempting to connect its line to the containership, the tug moved out of centreline.
The mate attempted to manoeuvre the tug back to the centreline, but was unable to regain position. The mate's attempt resulted in two collisions between the vessels.
The mate could have requested the pilot of MSC Aquarius to slow, but the mate did not communicate with the pilot after being assigned to the centre lead forward position. The pilot was unaware of the status of the tug or the need to slow.
The NTSB determined the probable cause of the collision was George M's mate's attempt to make up bow-to-bow while the tug and containership transited at a speed that was excessive for the advanced harbour-assist manoeuvre. Contributing to the collision was the mate's lack of experience operating the tug.
"The risk of a casualty during bow-to-bow harbour-assist operations with azimuthing stern drive (ASD) tugs increases with increasing speed," the report said. "Hydrodynamic forces around an assisted vessel's bow increase exponentially with speed, while the amount of reserve propulsion power available to the tug operator decreases. Owners and operators of ASD tugs that perform bow-to-bow harbour-assist operations should set speed limits for these manoeuvres. These limits may vary for different classes of tug based on design. Tug operators should communicate these pre-determined speed limits to ship masters or pilots in command of the vessels that they are assisting before engaging in these manoeuvres."
Marine Investigation Report 23-15 is available here.
