Capstan (nautical)

Tourists turn a capstan. The tensioned portion of the rope would fasten the ship to the quay, hoist aforesail,lift a spar into position on the mast or to transfer cargo to or from a dock orlighter.

Acapstanis a vertical-axledrotating machine developed for use on sailing ships to multiply the pullingforceof seamen when hauling ropes,cables,andhawsers.The principle is similar to that of thewindlass,which has a horizontal axle.

Capstan

Anchor windlass

The capstan and theanchor windlasson the deck below that it drives. On-board the museum sailing shipBalclutha

History

The word, connected with theOld Frenchcapestanorcabestan(t),from Old Provençalcabestan,fromcapestre"pulley cord," from Latincapistrum,-a halter, fromcapere,to take hold of, seems to have come into English (14th century) from Portuguese or Spanish shipmen at the time of the Crusades.Both device and word are considered Spanish inventions.

Early form

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 rudimentaryratchetwas provided to hold the tension. The ropes were always wound in a clockwise direction (seen from above).

Later form

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. On riverine vessels, the capstan was sometimes cranked by steam power.

Diagram of Ruston Proctor Steam Capstan 1883

Hydraulic capstan left after dockland redevelopment in London

Capstan inBelfast,Northern Ireland

Capstan on theUSSCairo

Capstan winches were also important on sailing trawlers (e.g.Brixham trawlers) as a means for fetching in the nets after the trawl. When they became available, steam powered capstan winches offered a great saving in effort. These used a compact combined steam engine and boiler below decks that drove the winch from below via a shaft.Ruston, Proctor and Companyat the UK 1883 Fisheries Exhibition marketed an engine, boiler, shafts and capstan designed specifically for this task.

Messenger

As ships and their anchors grew in size, the anchor cable or chain would be too big to go around the capstan. Also, a wet cable or chain would be difficult to manage. A messenger would then be used as an intermediate device. This was a continuous loop of cable or chain which would go around the capstan. The main anchor cable or chain would then be attached to the messenger for hauling using some temporary connection such as ropes called nippers. These would be attached and detached as the anchor was pulled up onto the ship; (weighed) thus allowing a continuous hoist of the anchor, without any need for stopping or surging.

Modern form

Modern capstans are powered electrically,hydraulically,pneumatically,or via aninternal combustionengine. Typically, agearboxis used which trades reduced speed, relative to theprime mover,for increasedtorque.

Similar machines

• Inyachtingterminology, awinchfunctions 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.
• Mostcassette playersutilize a device called acapstanto draw themagnetic tapefrom thecassetteacross thetape head.It functions similarly to, and was likely named for, the nautical device.

Use on land

See also:Locomotive winch

Hydraulically poweredcapstans were sometimes used inrailway goods yardsforshunting,or shifting railcars short distances. One example wasBroad Street goods stationinLondon.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

• Capstan equation

References

• EtymologyOnLine