A capstan is essentially a very large, vertically-oriented winch, used mainly in nautical settings. The design dates back centuries, as a way to raise and lower very heavy things, like anchors. Throughout history capstans have been used for numerous other applications as well, most notoriously as a setting from which to administer floggings.
An easy way to visualize a capstan is to think of its diminutive cousin, the garden hose reel. By cranking the reel one way or the other, the hose can be let out or taken in with minimal effort. Pictured turned on its side so the crank is on top — and replacing the hose with something like an anchor, and multiplying its size by roughly one hundred — it becomes a basic capstan.
The capstan is generally considered to be a Spanish invention, dating to around the 14th century. The first capstans were merely logs placed vertically through the body of a ship. The top of the log, exposed on deck, was ringed with holes. Into these holes, sailors would place smaller pieces of wood or metal, known as bars, that they could push to rotate the log in either direction. A thick rope wrapped around the log would, in turn, wind in or out.
This fundamental design has changed little throughout history, though innovations, such as metal construction and the addition of gears, have been made to improve functionality and efficiency. Capstans are still a common sight in modern seafaring vessels. Since the Industrial Revolution however, manpower has given way to steam and fossil-fuel powered operation. Most new ships built in the 21st century feature capstans that are pneumatic or hydraulically-driven, with transmissions that allow for multiple speeds.
The benefits of using a capstan compared to directly pulling an anchor, or even using a pulley system, are numerous. Firstly, utilizing the mechanical advantage present with a reel system greatly reduces the raw manpower needed to move heavy objects, which is a great benefit on a ship. The fewer men needed, the fewer berths, and less food and water required — all valuable commodities at sea. In addition, the horizontal operation of a capstan eliminates the effective opposition of gravity that is encountered when lifting directly, or using pulleys.
Another historic benefit to the capstan, though likely unintended by its original designers, was that it made a good place to mete out punishments. Before corporal punishment was outlawed in most navies, strict discipline and the constant threat of severe punishment was the main way that order was maintained at sea. The British Navy, for much of its history, famously adhered to the Articles of War, a book of rules and punishments that served as final word in shipboard discipline. One of the most common punishments for a variety of offenses, ranging from theft to insubordination, was to be given a public flogging. The severity of the crime dictated the number of lashes an offender would receive, and made the capstan itself a symbol to be both respected and feared on deck.