Liftboats explained
In 1955 two brothers who ran a repair shop in Violet, Louisiana, built a boat that could stand up on its own legs. Lynn and Orin Dean repaired cars, farm machinery and marine equipment under the name Universal Repair Service. Their invention, the liftboat, became a fixture of the shallow Gulf of Mexico, and the business they started was still running liftboats out of Houma, Louisiana, as Elevating Boats LLC in 2018, with a fleet of 30.
Bennett Offshore spent its last years designing these vessels and their larger cousins. This page explains what a liftboat is and how it works, so that the restored design pages, from the V-703 wind farm support vessel to the ORCA series, read more easily.
A boat that becomes a platform
A liftboat is a self-propelled, self-elevating vessel. It has a large open deck for equipment and supplies, at least one crane, and legs that let it lift its hull clear of the water to make a steady work base. Two things separate it from a drilling jack-up: it moves under its own power instead of behind tugs, and its deck exists to carry equipment for work on other structures. In the United States the Coast Guard treats it as a vessel, with structures and machinery covered under Title 46 of the Code of Federal Regulations. Marine cranes on liftboats are usually designed to API Specification 2C or to an equivalent classification society standard.
The type has collected a lot of names. The Coast Guard and the American Bureau of Shipping say liftboat. Lloyd's Register uses Mobile Offshore Unit. Operators and yards have used Self-Elevating Support Vessel, Multi-Purpose Self-Elevating Platform and Self-Elevating Work-Over Platform. Bennett Offshore, like the Dutch designer GustoMSC, preferred Self-Elevating Platform, or SEP, which is why the restored menu reads "SEP designs".
What liftboats do
The classic job is maintenance on fixed oil and gas platforms. A liftboat pulls up beside the platform on a side clear of obstructions and pipelines, lowers its legs, jacks up and puts its crane and deck within reach of the wells. Crews use liftboats for well intervention, plug and abandonment, coiled tubing work and construction support. Larger units add accommodation for work crews. The ORCA range, according to the Wikipedia summary of the series, could be configured for construction support, light drilling, well intervention, plug and abandonment, coiled tubing operations, wind farm installation, gas compression and accommodation.
Starting in the early 2000s, US liftboats took contracts in Brazil, China, Nigeria and the United Kingdom. Offshore wind gave the type a second market; the Wikipedia article on liftboats notes their growing use in building US offshore wind farms. Bennett's V-703 was drawn as a wind farm support vessel, and the later ORCA 3500-WIND and 4500-WIND pages show the same idea at a larger scale.
The preload routine
The pads of a liftboat sit on soft, uneven seabed, so most operators follow a preload routine before raising the hull to working height. The boat jacks up only far enough to clear its hull from the tips of the largest waves. The crew fills the holds with seawater for extra weight and lets the legs settle into the mud for several hours. Then they dump the water and jack up to work height. If the soil is going to give way, the preload is the moment it should happen, with the hull a short drop from the sea.
A survey of the site comes before any of that. The crew needs to know where the pipelines run and where earlier rigs and liftboats left canholes, the depressions their legs pressed into the seabed. A pad that lands on the edge of a canhole can slide into it.
Three accidents and what investigators found
The record of US Gulf accidents shows why designers and operators fuss about soil and preload.
On 18 November 2018 the liftboat Ram XVIII, a 215-foot vessel built in 2015, overturned about 15 nautical miles south-southeast of Grand Isle, Louisiana. All fifteen people aboard abandoned ship and were rescued. The National Transportation Safety Board found that the port leg had become unstable and named, as the probable cause, the industry's failure to give liftboat operators enough information about the seafloor. Investigators could not say whether the seabed had washed away, the leg had punched through, or the edge of a nearby canhole had collapsed.
On 8 September 2019 the Kristin Faye capsized while servicing a platform about 18 nautical miles east of Venice, Louisiana, after workers extended one of its two bow cranes. Divers later found that the port leg had pushed about 40 feet into the seabed in a punch-through. The NTSB blamed preload procedures that did not account for shifting and loading the crane.
The worst case came on 13 April 2021. The 234-foot Seacor Power capsized about 8 nautical miles south of Port Fourchon, Louisiana, when an unnamed storm brought winds of 70 to 80 mph and rough seas. Six crew were rescued that day. The captain died at his post, and the Wikipedia account records the body of a second crew member recovered on 16 April with eleven people still missing.
None of these units was a Bennett design. They appear here because the restored engineering pages, especially naval architecture and marine operating manuals, deal with exactly these questions: stability afloat, leg strength in the elevated condition, and written procedures that tell a crew what the vessel can and cannot do.
How big liftboats got
The early Dean boats were small. Montco Offshore's L/B Robert, designed by MiNO Marine, works in up to 270 feet of water with 335-foot legs, about 15,400 square feet of deck and a 500-ton main crane plus three auxiliaries. The SUDA 450-L3T designed by A. K. Suda for Teras Offshore, delivered in 2014 from Triyards Marine at Saigon Shipyard, was described at delivery as the world's largest liftboat: a 60 by 54 by 6 metre hull, truss legs, a working depth up to 367 feet and quarters for 250 people.
Bennett's range spanned much of that scale. The ORCA units ran from small platforms meant for the Gulf of Mexico up to the 115-metre ORCA 10000, which could install turbines and foundations heavier than 800 tonnes. The first ORCA 2500, customised for the Middle East and North Africa, went to a Qatari operator in February 2016; the archived news story about Al Safliya covers that delivery.
Reading a liftboat spec sheet
Each restored ORCA and V-series page carries a particulars table; the V-887 workover liftboat, with 90-metre legs and quarters for 114, is a typical example. A few lines matter more than the rest when you compare designs. Leg length, including the pads, sets the deepest water the boat can stand in once you subtract penetration and air gap. Pad area tells you how much the boat spreads its weight on soft soil. Crane rating and outreach set the jobs it can take. Accommodation numbers decide how long a work crew can stay without shuttling. Design speed and thruster layout decide how fast it can hop between platforms. The jack-up page explains the jacking system behind the leg numbers, and the glossary decodes the abbreviations.
Questions readers ask
How is a liftboat different from a drilling jack-up?
A liftboat moves under its own power instead of behind tugs, and its open deck and crane exist to support work on other structures, such as fixed platforms or wind turbines.
Why do liftboat accidents so often involve the seabed?
The pads stand on soft, uneven soil. In the Ram XVIII and Kristin Faye cases the NTSB pointed to seabed information and preload procedures, and in the Kristin Faye case divers found a leg that had punched about 40 feet into the seabed.
What does SEP mean on the Bennett pages?
Self-Elevating Platform. Bennett, like the Dutch designer GustoMSC, used that term for its liftboat designs, which is why the old menu reads SEP designs.
Sources
Next in the archive: Semi-submersible platforms explained · Legs, spudcans and preload · Restored page: Key personnel