The National Transportation Safety Board (NTSB) cited speed as a leading cause of an August 2022 tugboat grounding near Ingleside, Texas, that sheared off the vessel’s starboard z-drive unit.
The 4,500-hp CC Portland grounded outside the Corpus Christi Ship Channel at about 4:25 p.m. on August 7. The incident occurred while the crew tried to get a tow line aboard the inbound liquefied natural gas carrier LNG Fukurokuju.
According to the NTSB, the mate helming the tug lost control while moving astern in the center lead forward position near the ship’s bulbous bow. The maneuver occurred at about 8.5 knots – a speed faster than many seasoned local tug captains considered optimal.
“The probable cause of the grounding of CC Portland was the mate’s attempt to make up bow to bow with a liquefied natural gas carrier while the tugboat and liquefied natural gas carrier transited at a speed that was excessive for the advanced harbor-assist maneuver,” according to the NTSB report, which concluded that the lack of a companywide speed limit for conducting bow assist towing maneuvers contributed to the incident.
At the time, Edison Chouest Offshore (ECO) operated CC Portland. The unidentified mate helming the vessel at the time of the incident had joined the company about six months earlier. Investigators said he previously worked as a captain for river cruise boats and salvage vessels. He was enrolled in an ECO training program for aspiring captains.
The NTSB investigation determined ECO training captains had reservations about the mate’s abilities, particularly when performing the difficult bow assist maneuver. They also raised the possibility that he misrepresented training he had already completed as part of the ECO program.
“All six interviewed training masters raised concerns that many of the initials on the mate’s sign-off sheet either did not match their own handwriting or that the initials were for training elements, positions, or maneuvers that they never completed with the mate,” according to the report.
On the afternoon of the grounding, CC Portland joined three sister tugs to assist the 961-foot Bahamas-flagged LNG Fukurokuju into its terminal berth. The ship was in ballast as it prepared to load LNG for export.
CC Portland met the inbound carrier at about 4:18 p.m., with the mate helming the tug and the training captain seated nearby in the wheelhouse. CC Portland moved astern at 8.5 knots, roughly the same as the inbound ship, and took position on the starboard side of its bulbous bow to secure a tow line.
The mate began to lose control of the tug about five minutes later as the ship’s crew hauled in the heaving line connected to the towing line. “The mate began increasing the tugboat’s speed astern, pulling ahead of the LNG carrier’s bow to reposition the tugboat in line with the centerline Panama chock,” the report said.
“While pulling ahead of LNG Fukurokuju,” it continued, “CC Portland reached 10.2 knots and the mate stated that the tugboat ‘zigzagged’ and did ‘a couple of fishtails,’ moving the tugboat out of position to the port side of the LNG carrier.”
The tugboat lost speed as the mate attempted to regain control and retake its position along the ship’s centerline. Ultimately, the heaving line snapped, fell into the water, and fouled CC Portland’s portside z-drive unit. The tug grounded outside the channel soon afterward.
The grounding sheared off the tug’s starboard z-drive unit, leaving it without propulsion. Three starboard keel coolers were also damaged, as was a support bracket for a keel cooler that broke free from the hull, opening a 12-square-inch hole in a day fuel tank. Total damage to the tug amounted to $1.3 million.
About five gallons of diesel escaped into the waterway with crews deploying a spill kit to prevent additional pollution, the report said.
CC Portland was towed to a dock for temporary repairs and subsequently underwent permanent repairs in Louisiana.
The incident involving CC Portland is the second NTSB casualty investigation released in recent months highlighting vessel speed during complex towing maneuvers. The other involved an April 2022 collision in the Houston Ship Channel involving the Bay-Houston Towing tug George M. and the containership MSC Aquarius.
Details about that incident were reported in the October/November 2023 issue of Professional Mariner.
In both cases, the NTSB highlighted hydrodynamic forces that act on the tugboat when operating near the ship’s bow. The ship’s speed increases the high-pressure area near the bow, further complicating the towing maneuvers, the agency explained.
“The pressure increases with decreasing distance to the bow,” the report said. “Therefore, the hydrodynamic forces are greatest when a tugboat is very close to the ship’s bow while making up the hawser.”
Several ECO training captains interviewed by the NTSB agreed that operating in the center lead forward position is one of the most challenging maneuvers for a tugboat captain. At least one acknowledged feeling nervous working in that area despite years of experience.
Although there was no ECO company policy around speed when working in the center lead forward position, most training captains said they prefer to conduct these tows at speeds between 5 and 7 knots. Any faster, they said, leaves the tug with limited reserve power.
“You never want to max out,” an unidentified captain told NTSB investigators, “because you don’t have any power to get out, and you’re using the rest, 15-20 percent just to do what needs to be done on the job.”
ECO did not respond to an inquiry regarding the NTSB findings.