NTSB Urges Speed Limits for ASD Tugs During Harbor-Assist Maneuvers

The National Transportation Safety Board is encouraging owners and operators of azimuthing stern drive (ASD) tugs to set speed limits during certain harbor-assist maneuvers following two accidents where excessive speed was a factor.

The NTSB on Thursday released its report into the grounding of the CC Portland in the Corpus Christi Ship Channel last year, revealing that the grounding was caused by excessive speed during a bow-to-bow harbor-assist maneuver.

The CC Portland grounded outside the Corpus Christi Ship Channel while trying to secure a tow line on an LNG carrier, causing $1.3 million in damages but no reported injuries.

ASD tugs are equipped with two azimuth thrusters under the stern and are designed for push-pull, harbour assist and escort towing. ASD tugs perform the majority of towing operations over the bow.

The NTSB determined that the grounding was caused by the mate’s attempt to make up bow-to-bow with an LNG carrier at excessive speed during a harbor-assist maneuver. The lack of a company policy regarding maximum speed for bow-assist maneuvers also contributed to the grounding.

The report noted it was the second marine casualty it investigated in 2022 caused by excessive speed in ASD tugboats while in the center lead forward position.

On April 14, 2022, the tugboat George M and containership MSC Aquarius collided in the Houston Ship Channel. No injuries were reported, but damages to both vessels totaled over $900,000. The NTSB determined that the collision was caused by the George M mate’s attempt to approach bow-to-bow at an excessive speed.

The NTSB continues to encourage owners and operators of ASD tugboats that perform bow-to-bow harbor-assist operations to establish speed limits.

“The risk of a casualty during these operations with ASD tugboats 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 tugboat moves out of position, the operator has less power to regain position as compared to the same maneuver at a lower ship transit speed.”

Marine Investigation Report 23-19 is available on the NTSB website.

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