C.

CABLE. (_Cable_, Fr.; _Ankertau_, Germ.) A strong rope or chain,

connecting the ship with the anchor for the purpose of mooring it to the

ground. The _sheet anchor_ cable is the strongest, and is used at sea;

the _stream_ cable is more slender, being used chiefly in rivers. A

cable’s length is 120 fathoms. The greatest improvement in mooring

vessels has been the introduction of the chain cable, which, when duly

let out, affords in the weight of its long catenary curve, an elastic

tension and play to the ship under the pressure of wind. The dead strain

upon the anchor is thus greatly reduced, and the sudden pull by which

the flukes or arms are readily snapped is in a great measure obviated.

The best iron cables are chains made of links, bound and braced by rods

across their middle. Experience has taught that the ends of these links

wear out much sooner than the sides. To remedy this evil, Mr. Hawkes,

iron manufacturer, obtained a patent in July, 1828, for constructing

these anchor chains with links considerably stouter at the ends than in

the middle. With this view, he forms the short rods of iron, of which

the links are to be made, with swells or protuberances about one third

of their length from each of their ends, so that when these are welded

together, the slenderer parts are at the sides, and the thicker at the

ends of the elliptic links. Such rods as the above are formed at once by

rolling, swagging, or any other means. When the link is welded, it may

be strengthened, by a brace or stretcher fixed across the middle.

The first avowed proposal to substitute iron cables for cordage in the

sea service, was made by Mr. Slater, surgeon of the navy, who obtained a

patent for the plan in 1808, though he does not seem to have had the

means of carrying it into effect; a very general misfortune with

ingenious projectors. It was Captain Brown of the West India merchant

service who, in 1811, first employed chain cables in the vessel

Penelope, of 400 tons burden, of which he was captain. He made a voyage

in this ship from England to Martinique and Guadaloupe and home again,

in the course of four months, having anchored many times in every

variety of ground without any accident. He multiplied his trials, and

acquired certain proofs that iron might be substituted for hemp in

making cables, not only for mooring vessels, but for the standing

rigging. Since this period chain cables have been universally introduced

into all the ships of the royal navy, but the twisted links employed at

first by Brown, have been replaced by straight ones, stayed in the

middle with a cross rod, the contrivance of Mr. Brunton, which was

secured by patent in this country and in France; but the latter patent

was suffered to fall from not being acted upon within the two years

specified by law.

The first thing to be considered in the manufacture of iron cables is,

to procure a material of the best quality, and, in using it, always to

keep in view the direction of the strain, in order to oppose the maximum

strength of the iron to it. The best form of the links may be deduced

from the following investigation.

[Illustration: 215 216]

Let A B _fig._ 215. be a circular link or ring, of one inch rod iron,

the outer circumference of the ring being 15 inches, and the inner 9. If

equal opposite forces be applied to the two points of the link C D,

pulling C towards E, and D towards F, the result will be, when the

forces are sufficiently intense, that the circular form of the link will

be changed into another form with two round ends and two parallel sides,

as seen in _fig._ 216. The ratio of the exterior to the interior

periphery which was originally as 15 to 9, or 5 to 3, is no longer the

same in _fig._ 216. Hence there will be a derangement in the relative

position of the component particles, and consequently their cohesion

will be progressively impaired, and eventually destroyed. In _fig._ 215.

the segment M N of the outside periphery being equal to 3 inches, the

corresponding inside segment will be 3/5 of it, or 1-4/5 inches. If this

portion of the link, in consequence of the stretching force, comes to be

extended into a straight line, as shown in _fig._ 216., the

corresponding segments, interior and exterior, must both be reduced to

an equal length. The matter contained in the 3 inches of the outside

periphery must therefore be either compressed, that is, condensed into

1-4/5 inch, or the inside periphery, which is only 1-4/5 inch already,

must be extended to 3 inches; that is to say, the exterior condensation

and the interior expansion must take place in a reciprocal proportion.

But, in every case, it is impossible to effect this contraction of one

side of the rod, and extension of the other, without disrupture of the

link.

Let us imagine the outside periphery divided into an infinity of points,

upon each of which equal opposite forces act to straighten the

curvature: they must undoubtedly occasion the rupture of the

corresponding part of the internal periphery. This is not the sole

injury which must result; others will occur, as we shall perceive in

considering what passes in the portion of the link which surrounds C D,

_fig._ 216., whose length is 4-1/2 inches outside, and 2-1/10 inside.

The segments M P and N O, _fig._ 215., are actually reduced to

semi-circumferences, which are inside no more than half an inch, and

outside as before. There is thus contraction in the interior, with a

quicker curvature or one of shorter radius in the exterior. The

derangement of the particles takes place here, in an order inverse to

that of the preceding case, but it no less tends to diminish the

strength of that portion of the link; whence we may certainly conclude

that the circular form of cable links is an extremely faulty one.

[Illustration: 217]

Leaving matters as we have supposed in _fig._ 215., but suppose that G

is a rod introduced into the mail, hindering its two opposite points A B

from approximating. This circumstance makes a remarkable change in the

results. The link pulled as above described, must assume the

quadrilateral form shown in _fig._ 217. It offers more resistance to

deformation than before; but as it may still suffer change of shape, it

will lose strength in so doing, and cannot therefore be recommended for

the construction of cables which are to be exposed to very severe

strains.

Supposing still the link to be circular, if the ends of the stay

comprehended a larger portion of the internal periphery, so as to leave

merely the space necessary for the plan of the next link, there can be

no doubt of its opposing more effectively the change of form, and thus

rendering the chain stronger. But, notwithstanding, the circular

portions which remain between the points of application of the strain

and the stay, would tend always to be straightened, and of consequence

to be destroyed. Besides, though we could construct circular links of

sufficient strength to bear all strains, we ought still to reject them,

because they would consume more materials than links of a more suitable

form, as we shall presently see.

The effect of two opposite forces applied to the links of a chain, is,

as we have seen, to reduce to a straight line or a straight plane every

curved part which is not stayed; whence it is obvious that twisted

links, such as Brown first employed, even with a stay in their middle,

must of necessity be straightened out, because there is no resistance in

the direction opposed to the twist. A cable formed of twisted links, for

a vessel of 400 tons stretches 30 feet, when put to the trial strain,

and draws back only 10 feet. This elongation of 20 feet proceeds

evidently from the straightening of the twist in each link, which can

take place only by impairing the strength of the cable.

From the preceding remarks, it appears that the strongest links are such

as present, in their original form, straight portions between the points

of tension; whence it is clear that links with parallel sides and round

ends, would be preferable to all others, did not a good cable require to

be able to resist a lateral force, as well as one in the direction of

its length.

[Illustration: 218]

Let us suppose that by some accident the link _fig._ 216. should have

its two extremities pulled towards Y and Z, whilst an obstacle X, placed

right opposite to its middle, resisted the effort. The side of the link

which touches X, would be bent inwards; but if as in _fig._ 218., there

is a stay A G B, the two sides would be bent at the same time; the link

would notwithstanding assume a faulty shape.

[Illustration: 219]

In thus rejecting all the vicious forms, we are naturally directed to

that which deserves the preference. It is shown in _fig._ 219. This link

has a cast-iron stay with large ends, it presents in all directions a

great resistance to every change of form; for let it be pulled in the

direction _a b_, against an obstacle _c_, it is evident that the

portions _d e_ and _d f_, which are supported by the parts _g e_ and _g

f_, cannot get deformed or be broken without the whole link giving way.

As the matter composing _g e_ and _g f_ cannot be shortened, or that

which composes _d e_ and _d f_ be lengthened, these four sides will

remain necessarily in their relative positions, by virtue of the

large-ended stay _h_, whose profile is shown in _fig._ 220.

[Illustration: 220 221]

We have examined the strength of a link in every direction, except that

perpendicular to its plane. _Fig._ 221. represents the assemblage of

three links in the above predicament; but we ought to observe, that the

obstacle C, placed between the links A B, must be necessarily very

small, and could not therefore resist the pressure or impact of the two

lateral links.

_Process of manufacturing iron cables._--The implements and operations

are arranged in the following order:--

1. A reverberatory furnace (see IRON), in which a number of rods or

round bars of the best possible wrought-iron, and of proper dimensions,

are heated to bright ignition.

2. The cutting by a machine of these bars, in equal lengths, but with

opposite bevels, to allow of the requisite crossing and splicing of the

ends in the act of welding.

3. The bending of each of these pieces by a machine, so as to form the

links; the last two operations are done rapidly while the iron is

red-hot.

4. The welding of the links at small forge fires, fitted with tools for

this express purpose, and the immediate introduction of the stay, by

means of a compound lever press.

5. Proving the strength of the cables by an hydraulic press, worked by

two men turning a winch furnished with a fly wheel.

The furnace is like those used in the sheet-iron works, but somewhat

larger, and needs no particular description here.

[Illustration: 222 223]

_Figs._ 222. and 223. are a plan and elevation of the shears with which

the rods are cut into equal pieces, for forming each a link. It is moved

at Mr. Brunton’s factory by a small steam engine, but, for the sake of

simplicity, it is here represented worked by four or more labourers, as

it may be in any establishment. These must be relieved however

frequently by others, for I believe each shears’ machine is calculated

to require nearly one horse in steam power. It is portable and must be

placed in the neighbourhood of both the furnace and bending machine.

A and B are the two cast-iron limbs of the shears. The first is fixed

and the second is movable by means of a crank shaft C, driven by a heavy

fly-wheel weighing 7 or 8 cwt.

The cutting jaws G are mounted with pieces of steel which are made fast

by bolts, and may be changed at pleasure.

E, the bar of iron to be cut. It is subjected, immediately upon being

taken out of the fire, to the shears, under a determinate uniform angle,

care being taken not to let it turn round upon its axis, lest the planes

of the successive incisions should become unequal.

F is a stop which serves to determine, for the same kind of chain, the

equality of length in the link pieces.

[Illustration: 224 225 226]

_Figs._ 224, 225, 226. plan and elevations of the machine for bending

the links into an elliptic form. It is represented at the moment when a

link is getting bent upon it.

A is an elliptic mandrel of cast-iron; it is fixed upon the top of a

wooden pillar B, solidly supported in the ground. C is the jaw of the

vice, pressed by a square-headed screw against the mandrel A.

D part of the mandrel comprehended between X and Y, formed as an

inclined plane, so as to preserve an interval equal to the diameter of

the rod between the two surfaces that are to be welded together.

E rectangular slots (shears) passing through the centre of the nut of

the mandrel, in which each of the pins F may be freely slidden.

G horizontal lever of wrought-iron six feet long. It carries at H a

pulley or friction-roller of steel, whose position may be altered

according to the diameter of the links. It is obvious that as many

mandrels are required as there are sizes and shapes of links.

The piece of iron intended to form a link being cut, is carried, while

red-hot, to the bending machine, where it is seized with the jaw of the

vice C, by one of its ends, the slant of the cut being turned upwards;

this piece of iron has now the horizontal direction _m n_; on pushing

the lever G in the line of the arrow, the roller H will force _m n_ to

be applied successively in the elliptic groove of the mandrel; thus

finally the two faces that are to be welded together will be placed

right opposite each other.

The length of the small diameter of the ellipse ought to exceed by a

little the length of the stay-piece, to allow of this being readily

introduced. The difference between the points F, E is equal to the

difference of the _radii vectores_ of the ellipse. Hence it will be

always easy to find the eccentricity of the ellipse.

[Illustration: 227]

_Fig._ 227. is a lever press for squeezing the links upon their stays,

after the links are welded. This machine consists of a strong cast-iron

piece A, in the form of a square, of which one of the branches is laid

horizontally, and fixed to a solid bed by means of bolts; the other

branch, composed of two cheeks, leaving between them a space of two

inches, stands upright. These two cheeks are united at top, and on the

back of their plane by a cross piece B. C, a rectangular staple, placed

to the right and left of the cheeks through which is passed the mandrel

D, which represents and keeps the place of the following link. E, is a

press lever, 6 feet long. F, clamp and counterclamp, between which the

link is pressed at the moment when the stay is properly placed. There

are other clamps, as well as staples C, for changing with each changed

dimension of links.

The links bent, as we have seen, are carried to the forge hearth to be

welded, and to receive their stay; two operations performed at one

heating. Whenever the welding is finished, while the iron is still

red-hot, the link is placed upright between the clamps F; then a workman

introduces into the staple the mandrel D, and now applies the stay with

a pair of tongs or pincers, while another workman strikes down the lever

E forcibly upon it. This mechanical compression first of all joins

perfectly the sides of the link against the concave ends of the stay,

and afterwards the retraction of the iron on cooling increases still

more this compression.

If each link be made with the same care, the cable must be sound

throughout. It is not delivered for use however till it be proved by the

hydraulic press, at a draw-bench made on purpose. The press is an

horizontal one, having the axis of its ram in the middle line of the

draw-bench, which is about 60 feet long, and is secured to the body of

the press by strong bolts.

The portion of chain under trial, being attached at the one end to the

end of the ram of the press, and at the other to a cross-bar at the

extremity of the draw-bench, two men put the press in action, by turning

the winch which works by a triple crank three forcing pumps alternately;

the action being equalized by means of a heavy fly-wheel. As long as the

resistance does not exceed the force of two men, the whole three pumps

are kept in play. After a while one pump is thrown out of geer and next

another, only one being worked towards the conclusion. The velocity of

the ram being retarded first one third and next two thirds, gives the

men a proportional increase of mechanical power.

The strength of two average men thus applied being computed, enables us

to know at every instant the resistance opposed by the chain to the

pressure of the ram. The strain usually applied to the stronger cables

is about 500 tons.

The side beams of the draw-bench are of cast-iron, 6 inches in diameter;

the different pieces composing it are adjusted to each other end-wise by

turned joints. Props also of cast-iron support the beams two feet

asunder, and at the height of 30 inches above the ground. The space

between them is filled with an oak plank on which the trial chain is

laid.