- For the tool used to raise paddle gear on canal locks, see Windlass ("lock key")
A 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.
Windlasses can also 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). In the Late Middle Ages European crossbows employed a windlass as a cocking mechanism. In the Dark Ages the windlass was also used to raise stones during the construction of cathedrals.
In a differential windlass, also called a Chinese windlass, there are two coaxial drums of different diameters 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 <math>2\pi(r - r')</math>, very large mechanical advantages can be obtained.
- Needham, Joseph (1986), Science and Civilization in China: Volume 4, Physics and Physical Technology, Part 2, Mechanical Engineering. Taipei: Caves Books, Ltd.
- 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
- Morris, Christopher, ed. (1992), Academic Press Dictionary of Science and Technology, Gulf Professional Publishing, p. 416, ISBN 9780122004001
- 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."