These are typically used for an outdoor application or below an existing overhead bridge crane system. Unlike a bridge crane, a gantry crane does not need to be tied into a building's support structure - eliminating the need for permanent runway beams and support columns. In some cases, this can result in a significant reduction in material costs and can be a more cost-effective solution compared to a similarly specified bridge crane.http://www.mhicrane.com/marine-boat-hoist/shipyard-boat-lift-crane/