Capstan (nautical)

From Ship Mechanics
Jump to: navigation, search
File:CapstanCrewModel.jpg
A portion of a model depicting a manual capstan in use. The sailors would coordinate the rhythm of their movements by singing a particular type of sea shanty as they walked around the capstan. The tensioned portion of the rope here would hoist a foresail and could also be used to lift a heavy spar into position on the mast or to transfer cargo to or from a dock or lighter (barge).

A capstan is a vertical-axled rotating machine developed for use on sailing ships to apply force to ropes, cables, and hawsers. The principle is similar to that of the windlass, which has a horizontal axle.

History[edit]

The word, connected with the Old French capestan or cabestan(t), from Old Provençal cabestan, from capestre "pulley cord," from Latin capistrum, -a halter, from capere, to take hold of, seems to have come into English (14th century) from Portuguese or Spanish shipmen at the time of the Crusades.[1] Both device and word are considered Spanish inventions.[2]

Early form[edit]

File:Capstan-nautical.jpg
A capstan on a sailing ship. The upper portion is operated by the anchor windlass below in the Forecastle
File:AnchorWindlass.jpg
Below the capstan shown above is the anchor windlass

In its earliest form, the capstan consisted of a timber mounted vertically through a vessel's structure which was free to rotate. Levers, known as bars, were inserted through holes at the top of the timber and used to turn the capstan. A rope wrapped several turns around the drum was thus hauled upon. A rudimentary ratchet was provided to hold the tension. The ropes were always wound in a clockwise direction (seen from above).

Later form[edit]

Capstans evolved to consist of a wooden drum or barrel mounted on an iron axle. Two barrels on a common axle were used frequently to allow men on two decks to apply force to the bars. Later capstans were made entirely of iron, with gearing in the head providing a mechanical advantage when the bars were pushed counterclockwise. One form of capstan was connected by a shaft and gears to an anchor windlass on the deck below.

Modern form[edit]

Modern capstans are powered electrically, hydraulically, pneumatically, or via an internal combustion engine. Typically, a gearbox is used which trades reduced speed, relative to the prime mover, for increased torque.

Similar machines[edit]

In yachting terminology, a winch functions on the same principle as a capstan. However, in industrial applications, the term "winch" generally implies a machine which stores the rope on a drum.

Use on land[edit]

Hydraulically powered capstans were sometimes used in railway goods yards for shunting, or shifting railcars short distances. One example was Broad Street goods station in London. The yard was on a deck above some warehouses, and the deck was not strong enough to carry a locomotive, so ropes and capstans were used instead.

See Also[edit]

Notes[edit]

  1. Society for the Diffusion of Useful Knowledge (Great Britain): Penny cyclopaedia of the Society for the Diffusion of Useful Knowledge, Volume 27. C. Knight, 1843, page 444
  2. "The sailor's 'capstan' is of Spanish invention and christening (cabestran, rope-winder)". Lummis F. Charles (1909). Flowers of our Loast Romance. BiblioBazaar, LLC, 2009, page 202. ISBN 1115547461

References[edit]