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The cantilever crane, a type much used in the construction of ships and tall buildings, has a horizontal boom that rests upon and can rotate about a vertical mast. The load is suspended from a trolley that can move along a track on the boom. A cantilever crane used in shipyards is depicted in Figure 3. During the erection of a building of many stories, the mast of a cantilever crane may be extended upward repeatedly as the height of the building increases. (See also cantilever.)
A commonly used type of small movable crane is the truck crane, which is a crane mounted on a heavy, modified truck. Such cranes frequently use unsupported telescoping booms; these are made up of collapsible sections that can be extended outward like the sections of an old nautical telescope or spyglass. The extension of the boom is usually managed hydraulically. Truck cranes make up in mobility and ease of transport what they lack in hoisting capacity.