# Windlass

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

• 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.[2]
• The rod or stick used to tighten a tourniquet in surgical procedures 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).[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.[4] 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'.[5]

## Differential windlass

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,[6][7][8] 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.

## References

1. ^ "Medieval Builders' Windlass". http://www.bbc.co.uk. Retrieved September 11, 2012.
2. ^ "Engineering the Medieval Achievement-The Crossbow". http://web.mit.edu. Retrieved September 11, 2012.
3. ^ Oleson, John Peter (1984), Greek and Roman Mechanical Water-lifting Devices. The History of a Technology, Dordrecht: D. Reidel, pp. 56f., ISBN 90-277-1693-5
4. ^ "Albert Goldfields Mining Heritage". http://outbacknsw.com.au. Retrieved September 11, 2012.
5. ^ "Searching for Gold". http://www.kidcyber.com.au. Retrieved September 11, 2012.
6. ^ "Chinese". Oxford English Dictionary (3rd ed.). Oxford University Press. September 2005.
7. ^ Morris, Christopher, ed. (1992), Academic Press Dictionary of Science and Technology, Gulf Professional Publishing, p. 416, ISBN 978-0-12-200400-1
8. ^ Knight, Edward H. (1884), The Practical Dictionary of Mechanics, Cassell, Petter, Galpin & Co "Chinese-windlass, a differential windlass in which the cord winds off one part of the barrel and on to the other."