Capstan (nautical)

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A capstan (also spelt in other forms, or as capstock and cable stock) is a rotating machine used to control or apply force to another element, usually linear, notably used on board ship and on dock walls, for heaving-in or veering cables and hawsers, whether of iron, steel or hemp.

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

A capstan on a sailing ship. The upper portion operates the anchor windlass below in the Forecastle

On the main deck below the capstan shown above is the anchor windlass

It differs from a windlass, which is used for the same purposes, in having the axis on which the rope is wound vertical instead of horizontal.

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 (the conjecture that it came from the Spanish cabra, goat, and estanto, standing, is untenable seems to have come into English (14th century) from French or Spanish shipmen at the time of the Crusades.

The term was first used for the capstan on a ship, which is used to control ropes that are wound around it one or more times, but not stored on it — that arrangement is usually called a winch.

Ships' capstans were traditionally manually operated — consisting of a shaped wooden drum with handles inserted into the rim, at which men could push or pull.

It seems that in Tudor times, when 'kissing the gunner's daughter' was not yet the traditional position for severe corporal punishment on deck, the capstan was a favorite place for sailors to be bound over for a whipping, even for 'petty pilferings'.

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.

The earlier forms were of a comparatively simple character, made of wood with an iron spindle and worked by manual labor with wooden capstan bars. As heavier cables were supplied to ships, difficulty was found, when riding at anchor, in holding, checking and-veering cable. A cable-holder (W. H. Harfields) was tested in H.M.S. Newcastle (wooden frigate) in 1870 and proved effective; its first development in 1876 was the application in the form of a windYass secured to the deck, driven by a messenger chain from the capstan, fitted in H.M.S. Inflexible.

The capstans and engine are shown at A,A,A, and the windlass B is driven by messenger chains C, C. The four cables (dotted line D, D) lead to their respective cable-holders, fitted with a brake, and by these means each cable-holder can be connected to the main. driving shaft, and any cable hove-in or veered independently of the other; by using steam power instead of manual, the previous slow motion was obviated. In H.M.S. Collingwood the windlass:

directly by means of worm gearing; the windlass was divided into two parts, so that the one on the port side could be worked independently of that on the starboard, and vice versa. An independent capstan in both ships, arranged to take either of the cables, could be FIG. 1. worked by hand or steam. In the Collingwoods windlass the cables remained on their holders, and could be hove-in or veered without being touched.

Napier's patent windlass for merchant ships (1906) resembles an appliance fitted in the earlier second-class cruisers of the British navy (1890 to 1900). Two cable wheels or cable-holders are mounted loose on a horizontal axle, one on each side of a worm wheel which is tightly keyed on the middle part of the axle. A vertical steam engine with two cylinders, placed one on each side of the framing, drives a second horizontal axle which is connected by a set of bevel gears to an upright worm shaft, which works the worm wheel. This worm wheel can be connected by means of sliding bolts to one or both of the cable wheels, enabling one or both cables to be hove-in or veered as necessary. A brake, of Napier's self-holding differential type, is fitted to each cable wheel, and is controlled by hand wheels on the aft side of the windlass. For warping purposes, warping drums are fitted (made portable if required). A third central capstan, fitted forward of the windlass, is connected to the upright worm shaft by a horizontal shaft and bevel wheels. It can also be worked by manual labor with capstan bars.

Deep Upper Deck bodied capstans have been superseded by low drum-headed ones, over which the guns may be fired. The three capstans or cableholders of cast steel, capable of taking 2-in. cables, are fitted on vertical spindles, which pass down through the main and armoured decks to the platform one, where the steam engine and gearing are placed. The gearing consists of worm and wheel gears, so arranged that the three capstans can be worked singly or in conjunction, when heaving-in or veering, and the brakes (of the type previously mentioned) are controlled by a portable hand wheel fitted on the aft side of each. The cable-holders can be used for riding at anchor. The middle line capstan E is keyed to vertical spindles and can be coupled up to the capstan engine, by clutch and drop bolts in the capstan engine room; it is fitted with a cable-holder, to take either the port or starboard cables, and in addition is provided with portable whelps, enabling it to be used for warping. It can also be worked by manual labor with capstan bars, a drum-head E, fitted on the spindle on the main deck, enabling additional capstan bars to be used if required.

To avoid carrying steam pipes aft, the after capstan is worked by an electric motor which is kept below the water-line. Napier Brothers capstan (fig. 3) is for warping purposes, for working the stern anchor with wire hawser and for coaling. It is placed on the upper deck, and is fitted with a drum-head for capstan bars, with pawls and pawl rim on the deck plate, the pawls A being lifted and placed on their rests B when working with the motor. The upper portion of the capstan, together with its drum-head, is portable, being fixed to the centre boss with keys and gun-metal screws. The centre boss is keyed to the spindle, which passes through the deck and carries at its lower end a coupling for connecting to the worm wheel gear. For working by motor, the additional security of two drop bolts is provided. The gearing consists of a single worm and worm wheel, working in an oil-bath, the worm shaft being coupled direct to the motor spindle. The motor is of the semi-enclosed type, the working and live parts being protected by a perforated metallic covering; it is worked off a 100-volt circuit, at a speed under full load conditions of 300 revolutions per minute. The motor is of a 4-pole type and compound wound, the shunt winding limiting the speed on - light load to not more than 1000 revolutions per minute.

A frictional break is provided, pulled off by means of a shunt- excited magnet. The controller A is of the reversing drum type, with not less than four steps in either direction, and is fitted I with a magnetic blow-out. The control is effected by a removable hand wheel on a portable pedestal, fitted on top with a circular dial plate and reverses the current as well as graduates the speed in either direction. All capstans of the British navy, after being fitted on board ship, are tested for lifting power and speed; with foremost (steam) capstans, the steam being at 150 lb pressure, the anchor is usually let go in 16 to 25 fathoms water, and the speed ascertained by observing the time taken to heave-in not less than a length of cable, 75 ft.; the length must be hove-in in three minutes, or at the rate of 25 ft. per minute. With the after capstan (motor) of first-class battleships and cruisers, it weight is used instead of an anchor, the test being to lift 9 tons at the rate of 25 feet per minute. Capstans on dock walls in British government dockyards are usually driven by hydraulic or air pressure, conveyed through pipes to small engines underneath the capstans.

[edit] Sources

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• This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain.
• EtymologyOnLine
• CorPun