A container crane (also container handling gantry crane or ship-to-shore crane) is a type of large dockside gantry crane found at container terminals for loading and unloading intermodal containers from container ships. Container cranes consist of a supporting framework that can traverse the length of a quay or yard on a rail track. Instead of a hook, they are equipped with a specialized handling tool called a spreader. The spreader can be lowered on top of a container and locks onto the container's four locking points ("corner castings") using a twistlock mechanism. Cranes normally transport a single container at once, but some newer cranes have the capability to pick up two to four 20-foot containers at once. Types There are two common types of container handling gantry crane: high profile, where the boom is hinged at the waterside of the crane structure and lifted in the air to clear the ships for navigation, and low profile, where the boom is shuttled toward and over the ship to allow the trolley to load and discharge containers. Low-profile cranes are used where they may be in the flight path of aircraft, such as where a container terminal is located close to an airport. The type of crane selected in container terminal design process is determined by the design vessel and local environment. Sizes Container cranes are generally classified by their lifting capacity and the size of the container ships they can load and unload. Smaller sizes Smaller container cranes, such as straddle carriers, are used at railway sidings to transfer containers from flatcars and well cars to semi-trailers or vice versa. Both the rolling stock and the trailers may pass under the base. Smaller container cranes are also used at break-of-gauge transloading facilities. Panamax A Panamax crane can fully load and unload containers from a panamax class container ship capable of passing through the Panama Canal. Post-Panamax A "post-Panamax" crane can load and unload containers from a container ship too large (too wide) to pass through the Panama Canal. Super-post-Panamax The largest modern container cranes are classified as "super-post-Panamax". A modern container crane capable of lifting two long containers at once (end to end) under the telescopic spreader will generally have a rated lifting capacity of 65 tonnes. Some new cranes have a 120-tonne load capacity, enabling them to lift up to four or two containers. Cranes capable of lifting six 20-foot