A gantry crane is a crane built atop a gantry, which is a structure used to straddle an object or workspace. They can range from enormous "full" gantry cranes, capable of lifting some of the heaviest loads in the world, to small shop cranes, used for tasks such as lifting automobile engines out of vehicles. They are also called portal cranes, the "portal" being the empty space straddled by the gantry. The terms gantry crane and overhead crane (or bridge crane) are often used interchangeably, as both types of crane straddle their workload. The distinction most often drawn between the two is that with gantry cranes, the entire structure (including gantry) is usually wheeled (often on rails). By contrast, the supporting structure of an overhead crane is fixed in location, often in the form of the walls or ceiling of a building, to which is attached a movable hoist running overhead along a rail or beam (which may itself move). Further confusing the issue is that gantry cranes may also incorporate a movable beam-mounted hoist in addition to the entire structure being wheeled, and some overhead cranes are suspended from a freestanding gantry. Variants Ship-to-shore gantry crane Ship-to-shore gantry cranes are imposing, multi-story structures prominent at most container terminals, used to load intermodal containers on and off container ships. They operate along two rails (waterside and landside designations) spaced based on the size of crane to be used. Ship-to-shore crane elements Lateral movement system: A combination of two sets of typically ten rail wheels. The lateral movement is controlled by a cabin along the landside wheel. During any lateral movement, lights and sirens operate to ensure safety of the crew operating adjacent to the crane. The wheels are mounted to the bottom of the vertical frame/bracing system. Vertical frame and braces: A structurally designed system of beams assembled to support the boom, cabin, operating machinery, and the cargo being lifted. They display signage describing restrictions, requirements and identifiers. Crane boom: A horizontal beam that runs transversely to the berth. It spans from landside of the landside rail wheels to a length over the edge of the berth. The waterside span is based on the size of ship that it can successfully load/unload. Beams also have the ability to be raised for storage purposes. Hook: Device which moves vertically to raise and lower cargo as well as horizontally along the boom's