A liftboat is a self-propelled, self-elevating vessel with a relatively large open deck capable of carrying equipment and supplies in support of various offshore mineral exploration and production or offshore construction activities. A liftboat also has the capability of rapidly raising its hull clear of the water on its own legs so as to provide a stable platform from which maintenance and construction work may be conducted.
The first liftboat was designed in 1955 by brothers Lynn and Orin Dean in Violet, Louisiana. In 1950 the Dean brothers owned a repair service for automobiles, marine, and farm equipment called Universal Repair Service which is now known as EBI, Elevating Boats LLC. EBI, Elevating Boats LLC, operates 30 liftboats that service the shallow water Oil & Gas industry in the Gulf of Mexico from their liftboat dock in Houma, Louisiana.
If registered to the United States, liftboats structures and their machinery are covered under Title 46 of the Code of Federal Regulations. Liftboats are usually outfitted with at least one crane; marine cranes are usually designed to API specification 2C or the equivalent classification society guidelines.
Liftboats are commonly used to perform maintenance on oil and gas well platforms. The liftboat usually moves on location on a side of the platform where no obstructions or pipelines are observed, lowers its legs and jacks up out of the water. Because the pads of the liftboat are sitting on a muddy, unstable seafloor, most liftboats practice a safety measure called a preload, where the boat jacks-up the absolute minimum to clear hull from the tips of the significant wave heights, fills its holds with water for weight and allows the boat to settle in the mud for several hours before dumping the water and jacking up to work height.
If the mud of the seafloor gives way under the liftboat, it can fall into the water and put the lives of the crew in danger. A complete site survey prior to moving on location is an important safety measure to ensure that all seafloor features (canholes, pipelines, etc.) are known before choosing a final location.
The naval architecture firm A. K. Suda, Ltd. has successfully completed the design of a 450 foot (137.25m) truss-legged liftboat for Teras Offshore. Built by Triyards Marine, Saigon Shipyard in HCMC, Vietnam, this vessel, which is the world’s largest liftboat, was delivered at the end of 2nd Quarter 2014. This state-of-the-art vessel is a 3-legged, self-propelled, self-elevating general service workboat, known as the BH-450, and is suitable for operation in the North Sea. It is an ABS classed with Unrestricted Service, DP-1, Accommodation Service DRC, and carries a Wind Farm Installation Maintenance and Repair Certification. The molded steel hull dimensions are 60m x 54m x 6m. It has two deck cranes, one leg encircling around the starboard jackcase, and the other, a pedestal crane on the port side of the vessel. The quarters arrangement can accommodate 250 persons including crew. With the long legs on this vessel, this Self-Elevating Unit is capable of working in water depths up to 367 feet. A unique feature of this vessel is its easy deployment. Unlike other vessels in this size range, this Mobile Offshore Unit has no rack chocks.
Montco Offshore's MiNO Marine, LLC designed L/B Robert has a working water depth of 270 feet (82 m), 15,400 square feet (1,430 m2) of deck area and a 500-ton crane. The legs are 335' long and it has 3 additional cranes in addition to the main crane. The vessel uses electro-hydraulic jacking systems and cranes all driven from the segregated machinery spaces. 
Liftboats go-by several names in the Marine Industry such as:
- Liftboat – used by USCG & ABS
- MOU (Mobile Offshore Unit) – used by Lloyds Register; but also incorporates other types of vessel like Drill Ships and Semi-Submersible drilling rigs that might not necessarily be Self-Propelled
- SESV (Self-Elevating Support Vessel) – used by owner/operator GMS
- MPSEP (Multi-Purpose Self-Elevating Platform) – used by owner/operator Seafox & shipyard Keppel
- SEWOP (Self-Elevating Work-Over Platform) – used by owner/operator Halliburton & oil company Chevron
- SEP (Self-Elevating Platform) – used by Naval Architect GustoMSC
- Jack-Up Barge – used in the Gulf-of-Mexico prior to USCG regulation as a marine vessel
- Jack-Up - used by UK Renewable (ex. BWEA) but are not necessarily self-propelled
- Wind-Farm Installation Vessel – used generally in the renewables industry but are not necessarily self-propelled