Abstract: A floating offshore wind turbine assembly unit useful for assembling or maintaining wind turbines at an offshore location is disclosed. The floating offshore wind turbine assembly unit may include a first vessel spaced a distance apart from a second vessel, and an extended deck coupled to the first vessel and the second vessel. The extended deck is positioned in the distance between the first vessel and the second vessel, and the extended deck is configured as a dry dock disposed or movable to a height above a sea level. In some embodiments, the extended deck or a portion thereof is movably coupled to the first vessel and the second vessel. For example, the extended deck or a portion thereof is movable between a submerged or near sea level position and a position above a sea level.