Windlass

For the tool used to raise paddle gear on canal locks, see Windlass ("lock key")

Turnbridge Windlass Lift road bridge over Huddersfield Broad Canal

File:L-differentialwinde.png

Differential windlass

The windlass is an apparatus for moving heavy weights. Typically, a windlass consists of a horizontal cylinder (barrel), which is rotated by the turn of a crank or belt. A winch is affixed to one or both ends, and a cable or rope is wound around the winch, pulling a weight attached to the opposite end.

Uses

• 'Vitruvius, a military engineer writing about 28 B.C., defined a machine as "a combination of timber fastened together, chiefly efficacious in moving great weights." About a century later, Hero of Alexandria summarized the practice of his day by naming the "five simple machines" for "moving a given weight by a given force" as the lever, windlass, screw for power, wedge, and tackle block (pulley). Until the nearly the end of the nineteenth century it was held that these "five mechanical powers" were the building blocks from which all more complex assemblages were constructed.'

• During the Middle Ages the windlass was used to raise materials the construction of buildings such as in Chesterfield's crooked spire church.

• By the Late Middle Ages most European crossbows employed a windlass as a cocking mechanism, which helped to pull heavier crossbows, but were used in England as early as 1215.

• Windlasses are sometimes used on boats to raise the anchor as an alternative to a vertical capstan (see anchor windlass).

• The rod or stick used to tighten a tourniquet in surgical procedures is called a windlass.

• The handle used to open locks on the UK's inland waterways is called a windlass.

• Windlass can be used to raise water from a well. The oldest description of a well windlass, a rotating wooden rod installed across the mouth of a well, is found in Isidore of Seville's (c. 560–636) Origenes (XX, 15, 1-3).

• Windlass have also been used in gold mining. A windlass would be constructed above a shaft which allowed heavy buckets to be hauled up to the surface. This process would be used until the shaft got below 40 metres deep when the windlass would be replaced by a 'whip' or a 'whim'.

Differential windlass

File:Comparison differential pulley windlass.svg

Comparison of a differential pulley or chain hoist (left) and a differential windlass or Chinese windlass (right). The rope of the windlass is depicted as spirals for clarity, but is more likely helices with axes perpendicular to the image.

In a differential windlass, also called a Chinese windlass, there are two coaxial drums of different radii r and r'. The rope is wound onto one drum while it unwinds from the other, with a movable pulley hanging in the bight between the drums. Since each turn of the crank raises the pulley and attached weight by only $\pi(r - r')$, very large mechanical advantages can be obtained.

See also

• Hoist (device)

External links

• Spanish Windlass

•  (Subscription or UK public library membership required.) (registration required)
• "Chinese-windlass, a differential windlass in which the cord winds off one part of the barrel and on to the other."