Mechanics and operation of Crane (machine)

In contrast to modern cranes, medieval cranes and cranes much like their Greek and Roman counterparts were primarily used for vertical lifting and not for moving loads horizontally over considerable distances.As a result, lifting work was organized differently in the workplace than it is today.For example,in building construction, suppose a crane lifts stones into place directly from the bottom,or from a position opposite the center of the wall to where two teams work at each end of the wall.In addition, the crane supervisor,who usually gives orders to castor workers from outside the crane,is able to steer the movement laterally via small ropes attached to the load.The slewing crane, which allows the load to rotate and is therefore particularly suitable for dock work,appeared as early as 1340.While ashlar blocks were lifted directly by slings,lewis,or devil clamps (Teufelskralle,Germany),other objects were previously placed in containers such as pallets, baskets, wooden boxes, or barrels.It is worth noting that medieval cranes were rarely equipped with ratchets or brakes to prevent the load from running backwards.This strange absence can be explained by the fact that the high friction exerted by medieval tread wheels usually prevented the wheels from accelerating uncontrollably.

Harbour usage 

According to the unknown "state of knowledge" of antiquity,stationary harbor cranes are considered a new development in the Middle Ages.A typical harbor crane is a pivoting structure with twin tread wheels.These cranes are placed quayside for loading and unloading,where they replace or supplement older lifting methods such as see-saws, winches and yards.Two different types of harbor cranes can be identified,which have a different geographical distribution:while gantry cranes rotating on a central vertical axis are common in the Flemish and Dutch coastal regions,German seaports and inland ports are usually characterized by tower.The crane features where the winches and treadwheels are located in a solid tower where only the cantilever and roof rotate.Quayside cranes were not adopted in the Mediterranean and highly developed Italian ports after the Middle Ages,where authorities continued to rely on the labor-intensive method of unloading goods on ramps.Unlike construction cranes,where work speed is dictated by the relatively slow progress of masons,harbor cranes often employ twin tread wheels for faster loading.Two treadwheels,estimated to be 4 m in diameter or greater, are attached to each side of the shaft and rotate together.They have a capacity of 2-3 tons, apparently corresponding to the customary dimensions for sea freight.Today,according to one survey,15 pre-industrial caster harbor cranes still exist throughout Europe.Some harbor cranes were used exclusively for fitting masts to newly built sailing ships,for example in Gdańsk, Cologne and Bremen.In addition to these fixed cranes,the use of floating cranes that can be flexibly deployed throughout the port area began in the 14th century.

Early modern age

Renaissance architect Domenico Fontana used an elevator tower similar to that of the ancient Romans to relocate Rome's 361-ton Vatican obelisk in 1586.It is evident from his report that coordinating lifts between different pulling teams required considerable attention and discipline,as excessive stress on the ropes could cause them to break if force was applied unevenly.Cranes were also used domestically during this period.A chimney or fireplace hoist is used to swing pots and kettles over the fire,and the height is adjusted by a boom.