Gale force winds led to liftboat L/B Robert tilt

L/B Robert tilting to port as seen on November 21, 2022, at 09.14. [Source: USCG]

The National Transportation Safety Board has issued its report on a November 2022 incident in which, two days after its crew had evacuated it, the liftboat L/B Robert listed (tilted), incurring damage to the vessel and cargo estimated at $6.9 million.

The NTSB report notes that the 185-foot-long three-legged liftboat as built by Gulf Island Marine Fabricators in Houma, La, in 2012. Acquired by Falcon Global Robert in 2018, it was operated by SEACOR Marine.

On November 20, 2022​, the L/B Robert was reported to be listing (tilting) alongside a stationary oil platform in the Gulf of Mexico about 80 miles southeast of Lake Charles, La. The crew had evacuated two days prior due to forecasted adverse weather in the area, leaving the vessel elevated out of the water and unattended. No injuries or pollution were reported.

The liftboat captain decided to evacuate the vessel on November 17, 2022, because forecasted waves would exceed both the boat’s 8-foot underway and 15-foot jacked up operating limits. Investigators concluded the decision to evacuate rig personnel and liftboat crewmembers from the vessel, rather than attempt a transit to an area of refuge or remain on board, was appropriate for the forecasted conditions and decreased the risk to those on board.

When the crew evacuated the L/B Robert, they left an air gap about 25 feet above the water’s surface in accordance with guidance from shoreside management personnel to stay just at the maximum wave heights predicted by the weather forecasts to maintain the vessel’s greatest resistance to overturning from the combined forces of wind and waves.

The vessel likely experienced waves as high as 30 feet, exceeding the air gap and the forecasts at the time of the captain’s decision to evacuate.

Overturning forces from the wind and waves transferred down the vessel’s legs to the pads, causing the seabed foundation around them to deteriorate. Investigators determined it is likely the deteriorated seabed foundation under the port leg gave way, causing the leg to slide into a can hole and the vessel to tilt to port, submerging its deck edge.

DAMAGE

In addition to the cargo that shifted and was damaged, the L/B Robert sustained multiple stress fractures around the vessel on bulkheads and decking, including in port and starboard Z-drive thruster rooms (one in the starboard thruster room created a hull breach). All three legs showed deflections and several cracks toward their upper sections where they were housed inside the jacking leg towers. The racks that facilitated jacking on all three legs were also damaged, consistent with the leg deflections. Total damage costs were estimated to be $6.9 million.

PROBABLE CAUSE

The National Transportation Safety Board determined that the probable cause
of the tilting of the elevated liftboat L/B Robert was gale-force winds combined with
waves that exceeded the vessel’s air gap, causing vessel movement, which led to a
leg sliding into an adjacent can hole in the seafloor.

• There is, as always, much more in the full NTSB report. Download it HERE