Inadequate preload procedure probable cause of liftboat overturning: NTSB

The US National Transportation Safety Board (NTSB) said that an inadequate preload procedure was the probable cause of the overturning of US-flagged, liftboat Kristin Faye in the Gulf of Mexico on September 8th 2019. The NTSB issued its analysis in Marine Accident Brief 20/36.

The Kristin Faye had been working in the Main Pass lease area of the Gulf of Mexico, servicing various platforms for 37 days, when the accident occurred. Those operations had included the September 3rd removal and transfer of a 17,000-pound tank from the offshore Platform AQ to a supply boat, which brought it ashore for repair. When the Kristin Faye arrived near Platform AQ during the morning of September 8th 2019 the captain manoeuvred the liftboat to a position about three metres closer to Platform AQ than it had been a few days earlier. This was done so that the liftboat would be close enough to the platform to put out a walkway between them. The captain said he was confident that the bottom survey used for the Kristin Faye’s operations at the platform five days earlier still verified the sea bottom clear of hazards or obstructions.

However, during the operation on September 8th the Kristin Faye began tilting to port. The captain left the crane control station and ran to the wheelhouse, where he attempted to level the hull by retracting the starboard and aft legs to match the height of the falling port corner at the bow. However, although he began moving the starboard and after legs upward, the vessel continued to fall to port. The captain estimated that it took less than one minute from the time he first felt the liftboat tilting until the port side was in the water.

Unable to get to the bow of the liftboat with the other crewmembers, the captain initiated emergency calls, donned his lifejacket, jumped into the water, and swam to the safety of a supply vessel about 50 to 100 yards away. The two other crewmembers held onto the starboard rail until they were rescued from the Kristin Faye’s bow with a personnel basket from Platform AQ.

Within five hours the Kristin Faye was resting on the seafloor, nearly submerged, with just a small part of the starboard bow protruding out of the water.

On September 12th a contractor began salvage operations. Salvage divers reported that the port leg had penetrated roughly 40ft down into the mud, and the port side of the vessel was completely embedded in the mud. Although salvage operations continued daily, the challenging weather conditions impeded a successful salvage. On September 13th the vessel’s owner declared the Kristin Faye a total constructive loss, at an estimated cost of $750,000. The salvage company was eventually able to right the Kristin Faye and transport it to a scrapyard in Belle Chase, Louisiana, where it arrived on October 7th 2019.

One crewmember was injured evacuating the vessel. The accident resulted in the discharge of about 120 gallons of diesel fuel.

Because the Kristin Faye overturned in less than a minute, the NTSB said that it was likely that the seabed below the port leg became unstable, causing the leg to settle very quickly in what was known in the industry as a “punch through”.

The Kristin Faye and other small liftboats that lack preload tanks operating in the Gulf of Mexico typically conduct a preload test using only the weight (displacement) of the vessel, including any cargo or equipment. This was a simple concept used to conclude that the vessel would remain stable while jacked up in an area of the Gulf where silt deposits, mud ledges, and “can holes” were prevalent. If the vessel does not shift an hour after planting its pads on the seafloor, the procedure assumes the vessel will remain stable.

After waiting for an hour at the elevated level, the captain raised the boom. Once the port crane boom was moved from its cradle to the vertical position, the 22,500- pound boom’s centre of gravity shifted about 17 feet toward the port crane pedestal at the forward port corner of the liftboat. With this shift, the weight supported by the port forward leg pad increased due to the boom’s weight shift toward it. The weight supported on the forward port pad increased until the pad suddenly punched through the bottom, resulting in the vessel overturning.

The NTSB said that a preload test should account for the most extreme loading conditions the liftboat will experience at the elevated level. In anticipation of lifting a 17,000-pound pressure vessel onto the platform, the preload test for the Kristin Faye, a liftboat without preload tanks, should have included sufficient weights, appropriately placed to replicate the load on each of the pads.

Many alternatives are available to test the sea bottom before commencing elevated operations. These testing methods include:

  • measuring the resistance of the soil in PSI as an indication of how compacted the soil is;
  • seabed sampling; laboratory tests;
  • remote operated vehicle, sonar, or diving surveys;
  • replicating loads and weight shifts in the preload test;
  • and, as mentioned by the Kristin Faye owner, using liftboats fitted with preload tanks specifically constructed to add weight to the vessel during the preload test.

The NTSB determined that the probable cause of the overturning of the liftboat Kristin Faye was the company’s inadequate preload procedure that did not account for crane movements or the planned loads (weights) to be lifted. It was this that resulted in the punch through of one of the vessel’s three legs.

  • Owner/operator Mitchell Liftboats, LLC
  • Year built 1973
  • Official number (US) 548383
  • Length 62.6 ft (19.1 m)
  • Beam/width 31.9 ft (9.8 m)
  • Tonnage 97 GT
  • Persons on board 3

https://www.ntsb.gov/investigations/AccidentReports/Reports/MAB2036.pdf