Excessive speed during a bow-to-bow harbour-assist manoeuvre led to the grounding of a tug in Texas' Corpus Christi Ship Channel last year, the US National Transportation Safety Board (NTSB) said recently.
It is the second marine casualty the NTSB investigated in 2022 caused by excessive speed in azimuthing stern drive, or ASD, tugs while in the centre lead forward position.
The NTSB continues to encourage owners and operators of ASD tugs that perform bow-to-bow harbour-assist operations to set speed limits.
"The risk of a casualty during these operations with ASD tugs increases with increasing speed," NTSB investigators said in the final report. "Higher speed reduces the amount of reserve propulsion power available to the operator. If the tug moves out of position, the operator has less power to regain position as compared to the same manoeuvre at a lower ship transit speed."
The tug CC Portland (pictured) grounded outside the Corpus Christi Ship Channel on August 7, 2022, while attempting to secure a tow line on the bow of an inbound liquefied natural gas (LNG) carrier.
No injuries were reported. However, the grounding resulted in US$1.3 million in damages to the tug.
The NTSB determined the probable cause of the grounding was the mate's attempt to make up bow-to-bow with an LNG carrier while the tug and LNG carrier transited at a speed that was excessive for the advanced harbour-assist maneuver.
Contributing to the grounding was the lack of a company policy regarding maximum allowable speed for bow-assist maneuvers.
The NTSB noted that an incident involving a tug and another vessel that occurred earlier that same year was also due to excessive speed.
On April 14, 2022, the tug George M and the containership MSC Aquarius collided 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 while damages to both vessels totaled more than US$900,000.
The NTSB determined the probable cause of the collision was the George M mate's attempt to make up bow-to-bow while the tug and the containership transited at an excessive speed.
Marine Investigation Report 23-19 is available here.
