Capstan
CAPSTAN (also spelt in other forms, or as "capstock" and "cable stock," connected with the O. Fr. capestan or cabestan, from Lat. capistrum, a halter, capere, to take hold of; the conjecture that it came from the Span. cabra, goat, and estanto, standing, is untenable), an appliance used on board ship and on dock walls, for heaving-in or veering cables and hawsers, whether of iron, steel or hemp. 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 seems to have come into English (14th century) from French or Spanish shipmen at the time of the Crusades. The earlier forms were of a comparatively simple character, made of wood with an iron spindle and worked by manual labour 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. Harfield's) 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 windlass secured to the deck, driven by a messenger chain from the capstan, fitted in H.M.S. "Inflexible" (fig. 1).
Fig. 1.
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" steam power was used to work 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 worked by hand or steam. In the "Collingwood's" 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 labour with capstan bars. Fig. 2 represents the arrangement of the capstans on the forecastle of a battleship, fitted by Napier Brothers. Deep-bodied capstans have been superseded by low drum-headed ones, over which the guns may be fired. The three capstans or cable-holders of cast steel, capable of taking 211/16 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 (see Cable). 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 labour with capstan bars, a drum-head E', fitted on the spindle on the main deck, enabling additional capstan bars to be used if required.
Fig. 2. - Elevation looking aft.
Fig. 3. - Napier Brothers' capstan.
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 is of the reversing drum type, with not less than four steps in either direction, and is fitted 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 indicating pointer; the hand wheel 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, a weight is used instead of an anchor, the test being to lift 9 tons at the rate of 25 ft. 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.
(J. W. D.)
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)
