Federal investigators determined multiple collisions between a tugboat and containership near a Houston-area terminal stemmed from the vessels’ excessive speed during a challenging towing maneuver and lack of experience from the mate helming the tug.
Crew aboard the 6,772-hp George M were attempting to get a line onto the inbound MSC Aquarius at about 3:45 a.m. on April 14, 2022, as the vessels approached Barbour’s Cut Container Terminal. The tug twice struck its bow and ultimately became stuck in the flare.
The second impact damaged the tug’s portside Schottel z-drive, which leaked about 1,000 gallons of gear oil into the Houston Ship Channel. Nobody on either vessel was hurt. George M required $750,000 in repairs, while damage to MSC Aquarius amounted to more than $183,000.
George M’s mate positioned the tug’s bow very close to MSC Aquarius’ bulbous bow to receive the messenger line – a maneuver known as a ‘stem job.’ According to the National Transportation Safety Board (NTSB), they attempted this maneuver at 9.7 knots, a speed considered too fast given the hydrodynamic forces created by the ship.
“Hydrodynamic forces created by a ship increase exponentially with speed, and therefore an increase of even a few knots will have a significant effect on the forces acting on a tugboat in the center lead position,” the NTSB report said.
“The increased forces acting on a tugboat at higher speed require more reserve power, maneuverability, and operator skill to overcome,” the report continued. “When George M approached MSC Aquarius, the speed of the containership was 2.7 knots above the towing-company-directed limit of 7 knots for the bow-to-bow maneuver.”
Their speed during the maneuver was a full 3.7 knots faster than the 6-knot speed cited by an international group of pilots, tugboat captains, and ship masters surveyed by the International Tug Masters Association/Nautical Institute working group, the report said.
George M was built in 2021 for Bay-Houston Towing Co. and operated by G&H Towing Co. The tug’s captain was on leave, requiring the mate to fulfill those duties temporarily. G&H Towing transferred a mate from different tugboat class to serve that role on George M.
The mate had about 15 years of maritime experience and worked on other G&H tugs since 2018. He performed three towing jobs on George M under the replacement captain’s supervision prior to the incident but otherwise had not worked on George M or any sister tugs. The mate also had not been formally assessed on that series of tugboats, but the replacement captain told investigators he felt confident in the mate’s abilities.
The replacement captain was off watch and sleeping when George M and Mazu, another tug operated by G&H, received orders from dispatch to meet the 984-foot MSC Aquarius heading to Barbour’s Cut. The pilot assigned George M to center lead forward, a position that required the tug to move astern while positioning its bow just forward of the ship’s bulbous bow.
Crew aboard the ship would then secure a hawser line through the ship’s center chock. Once that happened, the tug could stretch its line and create additional space between the vessels. George M had a maximum speed astern of about 11 or 12 knots, leaving limited reserve power while performing the maneuver at 9.7 knots.
Hydrodynamic forces created by the bow pushed the tug out of position while MSC Aquarius crews secured the hawser line. The mate responded by trying to increase power, but he told investigators the tugboat did not respond as he expected.
The mate “continued to add power until the propulsion power suddenly took effect,” the NTSB report said. “When that happened, George M crossed the bow of MSC Aquarius, and the tugboat’s starboard bow struck the starboard bow of the containership.”
The mate tried to regroup and return the tugboat to the appropriate position at the centerline of the bow. Again, the tugboat did not respond as the mate expected and the vessels collided a second time, damaging its portside z-drive thruster.
“With the port z-drive disabled, George M slid aft along the port side of MSC Aquarius until it became lodged in the flare of the containership’s bow,” the report said.
George M broke free after the ship slowed down. The collisions created a 5.6-by-1.6-foot hull breach on MSC Aquarius’ bulbous bow, while George M sustained damage to its mast, railings, port z-drive and hull sections.
Working in the center lead position is challenging for any tugboat operator, particularly when a ship is moving so fast. Hydrodynamic forces increase exponentially with the speed of a ship, the NTSB report said, and these forces are often most pronounced in the area directly in front of the bow.
The mate told investigators he had performed 25 to 50 ‘stem jobs’ before the incident with MSC Aquarius. Speaking with investigators, he acknowledged the speed at the time of the maneuver was “on the high side” and that he preferred to perform the maneuver at speeds closer to 5 knots. •