Liftboat

A liftboat is a self-propelled, self-elevating vessel used in support of various offshore mineral exploration and production or offshore construction activities. A liftboat has a relatively large open deck to accommodate equipment and supplies, and the capability of 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.

For liftboats registered to the United States, structures and machinery are covered under Title 46 of the Code of Federal Regulations.^[1] 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. They have increasingly been used in constructing offshore wind farms in the United States.^[2] 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,^[3] 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 (including canholes, which are the depressions left by the legs of drilling rigs or liftboats, and also pipelines) are known before choosing a final location.