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The "hammerhead", or giant cantilever, crane is a fixed-jib crane consisting of a steel-braced tower on which revolves a large, horizontal, double cantilever; the forward part of this cantilever or jib carries the lifting trolley, the jib is extended backwards in order to form a support for the machinery and counterbalancing weight. In addition ...
Diagram 3 shows three rope parts supporting the load W, which means the tension in the rope is W/3. Thus, the mechanical advantage is three-to-one. By adding a pulley to the fixed block of a gun tackle the direction of the pulling force is reversed though the mechanical advantage remains the same, Diagram 3a. This is an example of the Luff tackle.
An overhead crane, commonly called a bridge crane, is a type of crane found in industrial environments. An overhead crane consists of two parallel rails seated on longitudinal I-beams attached to opposite steel columns by means of brackets. The traveling bridge spans the gap. A hoist, the lifting component of a crane, travels along the bridge.
Disadvantages of this crane type are the higher power demand and increased maintenance requirement due to the increased number of moving parts. Knuckle boom crane arms are much lighter than boom truck cranes, and they are designed to allow for more payloads to be carried on the back of the truck that it is mounted on.
A level-luffing crane is a crane mechanism where the hook remains at the same level while luffing: moving the jib up and down, so as to move the hook inwards and outwards relative to the base. [ 1 ] Usually the description is only applied to those with a luffing jib that have some additional mechanism applied to keep the hook level when luffing.
Some new cranes have a 120-tonne load capacity, enabling them to lift up to four 20-foot (6.1 m) or two 40-foot (12 m) containers. Cranes capable of lifting six 20-foot containers have also been designed. Post-Panamax cranes weigh approximately 800–900 tonnes, while the newer-generation super-post-Panamax cranes can weigh 1,600–2,000 tonnes.
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Taisun, the world's strongest gantry crane, at Yantai Raffles Shipyard, Yantai, China. Full gantry cranes (where the load remains beneath the gantry structure, supported from a beam) are well suited to lifting massive objects such as ships' engines, as the entire structure can resist the torque created by the load, and counterweights are generally not required.