Chapter III: DEFENSIVE TORPEDO WARFARE--continued (2)

Immerse the joint in the jointing-bath at 150° to 200° F. and gradually raise the heat so that in half an hour the temperature will be 320° F., at which temperature keep the joint for twenty minutes: then take it out and let it cool in the open air.

_The Formation of a Joint in a Gutta percha Insulated Cable._--Having jointed the conducting wires in the manner described at page 47, clean and dry the joint well and cover the bare conductor with a thin layer of compound. This is best done by heating a small stick of compound to nearly its melting point, and rubbing it over the bare conductor, which has been previously heated with the flame of a spirit-lamp.

Heat the gutta percha covering of both ends gently until it is quite soft, without, however, causing it to bubble or burn. Draw, then, with the fingers, the gutta percha coverings of both ends down, tapering them off until they meet in the middle of the joint; heat them sufficiently to make them adhere together.

Apply a layer of compound on the tapered-off gutta percha in the same manner as described for coating the bare conductor, and cover it with a first coating of gutta percha sheet to about half the thickness necessary to finish the joint. This is done by heating a small sheet of gutta percha, of about one-eighth of an inch in thickness, until it is quite soft, and by pressing it in that state round the joint to the required size; the greatest care to be taken to expel all the air.

The projecting lips are then cut off with a pair of curved scissors. The seam thus produced is to be rubbed with a hot iron until it is completely closed and the joint well rounded off.

Apply another layer of compound and a second layer of gutta percha in exactly the same manner as described for the first layer; care, however, is to be taken to get the seam in this second layer of gutta percha not over, but as nearly as possible right opposite to, the seam in the layer underneath.

The whole to be worked as cylindrical as possible, and to a size not exceeding the original core. The joint, so far finished, is then to be cooled with water until the gutta percha is quite consolidated.

Another, the overlapping gutta percha joint, is made in the following manner:--

Cut off the two ends of the core, so that the gutta percha and the conductor-wire are flush. Warm the gutta percha for a distance of about three inches from each of the ends with the flame of a spirit lamp, and, when sufficiently soft, push it back until it forms an enlargement. The two ends of the conductor are then to be soldered according to instructions for making joint in conductors.

To have a perfectly clean surface of the two gutta percha enlargements, remove all impurities by the way of peeling them with a sharp knife. Warm gently both knobs and the copper joint, and cover the whole length of the bare wire with compound, planing it with a warm smoothing-iron.

Draw then with the fingers one of the warmed and softened knobs carefully up to the other knob or enlargement, leaving on its way a perfect tube of gutta percha upon the wire, decreasing gradually to the thickness of the copper strand towards the other knob. Any superfluous gutta percha is removed. This scarf is finished with a warm smoothing-iron, so as to unite it to the compound on the wire strand, and a thin layer of compound is also put over the scarf in the same manner as before.

The other knob is then warmed and drawn in the same way over the tube already formed, which is at the same time heated sufficiently to make the two adhere.

Apply a layer of compound on the second scarf of gutta percha, covering it in the same manner as described for coating the bare conductor, and cover it with a small sheet of gutta percha in the same manner as described above, so as to make the finished joint to the size of the core as manufactured.

_Rules to be observed in forming Joints._--The following rules must be carefully observed in forming either a temporary or permanent joint:--

1.--In laying bare the conductor, the dielectric should
be warmed and then pulled off, so preventing any chance
of it being damaged, which might be the case were the
dielectric to be cut off.

2.--For a perfect junction, soldering is necessary.

3.--The wires before connection should be carefully
cleaned, and the hands of those performing the work
must be dry.

4.--Gutta percha should not be given too much heat,
for it then becomes oily and will not, in that state,
properly adhere.

5.--Grease and dirt must be scrupulously avoided.

Great care is absolutely necessary in making junctions, as they are the principal sources of defect in the insulation of electrical submarine cables.

_Junction Boxes._--When it is necessary to employ a multiple cable, a junction box is used to facilitate the connection of the several separate wires diverging from the extremities of such a cable. In one angle of such a box the multiple cable is introduced, while the separate cables make their exit on the opposite sides and pass to the different mines. Different views of a junction box are shown at Fig. 41, where _A_ is a plan of the top or lid, _B_ a plan of the bottom, with the lid off, _C_ an elevation, and _D_ a section of the box.

The manner of using the junction box is as follows:--

The multiple cable is put in at _a_, and secured there by means of a nipping hook, shown at Fig. 42, which hook passes through the bottom of the junction and is made secure by means of a nut. The single core cables radiating from the junction box pass through the openings _b_, _b_, _b_ on the sides, and angle opposite to where the multiple cable a enters. Each multiple cable is composed of seven cores, and each of these is connected by means of joints with the mine cables within the junction box, and each of these seven cables is secured by means of a nipper similar to, but smaller than, the one shown at Fig. 42, which are also secured by means of nuts, as in the case of the multiple cable nipping hook. When all the connections are made, the lid _A_ is placed so as to rest on the studs _c_, _c_, _c_, and firmly secured by a bolt _d_, which is made water-tight by means of a washer and nut.

By means of the nipping hooks, which take any strain that may be brought on the cables, the connections within the box are ensured against injury by such a cause.

To enable the whole to be lifted together for the purposes of examination of the cables, &c., a buoyed rope is connected to the eye-bolt _e_. For this service a dummy circuit closer is the best form of buoy, it having great buoyancy and resembling in appearance an active circuit closer.

A junction box should be placed in such a position as to be easily attained, even in the presence of an enemy, and its buoy should, if possible, not be seen. It is also very essential that it should be in a safe and guarded position, for any injury to the junction box or multiple cable would be fatal to the group of mines in connection.

In the following cases, special junction boxes are used:--

1.--A seven cored armoured cable to be connected direct
to another length of the same.

2.--A single armoured cable to be connected as in
foregoing instance.

3.--A T junction box for the branch system of
electrical contact mines.

_Junction Box for Multiple Cables._--At Fig. 43 is represented a plan of lower half of this form of junction box. It consists of a pair of cast iron plates of precisely similar form to the one shown at Fig. 43, and so made as to be capable of being fastened tightly together by means of four bolts and nuts passing through the holes _a_, _a_. The grooves _b_, _b_ at the two extremities are just large enough to grip the armoured cable firmly, when the upper and lower parts are screwed together. A larger space is provided in the hollow for the joint.

_Junction Box for Single Cored Cables._--For this purpose a junction box similar to, but smaller than the one above described is employed.

_T Junction Box._--This form of junction box is employed when the system of electrical contact mines on branches from a single cable is used. This system is dependent on the use of a platinum wire fuze in connection with a platinum wire bridge in each branch close to its junction with the main cable.

This form of junction box, which is shown at Fig. 44 is very similar to the one used for the connection of two multiple cables, only differing in its shape, which is that of a T. _a_ is a disconnector, which will be described further on; _b_, _b_, _b'_ are the armoured electric cables, _b_, _b_ being the main, and _b'_ the branch cable in connection with the forked joint formed within the T junction box; _c_, _c_, _c_ are Turk's heads formed to prevent any strain being brought on the forked joint. This form of Turk's head is made by turning back the wires of the cable armouring, and frapping them round with spun yarn until the necessary size and shape is attained.

_McEvoy's Turk's Head._--Another form of Turk's head, devised by Captain McEvoy, is shown at Fig. 45. It consists of two separate pieces of brass, _a_ and _b_, the former screwing over the latter. The mode of using it is as follows:--

Slip the piece of brass _b_ over the cable _c_, and turn back the wires of the cable _d_, _d_, &c., so that they lie against the shoulder of the brass piece _b_, then slip the other piece of brass _a_ over the cable and screw it on the piece _b_, firmly jamming the turned back wires _d_, _d_, &c. This is a very neat and quick method of forming a Turk's head, and it should be invariably used in preference to the foregoing method, which is clumsy, and which takes some time to form.

The section of a disconnector is shown at Fig. 46. It consists of an iron cover, or dome _a_, which is provided with a screw fitting on to another screw on the ebonite body _b_ of the apparatus. When the dome _a_ is screwed tightly down on the washer _i_, the whole is made perfectly watertight. _c_, _c_ are insulated terminals for connecting the cores of the branch and main cables after their armouring has been removed, as shown at Fig. 44. _d_, _d_ are two copper conducting wires (No. 16 B. W. G.) passing through the centre of the ebonite body _b_, and projecting into the interior of the apparatus. These wires are held in position and insulated by means of a composition formed of a mixture of pitch, tallow, beeswax and gutta percha. This composition is put on whilst hot and allowed to cool gradually, when it becomes hard and durable. Great care is necessary to ensure the cavity within the ebonite body _b_ being completely filled, as otherwise a leakage might occur, owing to the great pressure of water at depths where the disconnection would be generally used. _f_ is a boxwood cover which is slipped on, and fits fairly tight to the ebonite body _b_; _g_ is a piece of thin platinum wire, weighing 1·6 grains to the yard, and being 4/10 inch in length; _h_ is an ebonite pin, which passes through two small holes in the boxwood cover _f_, into which it fits tightly, and in such a position as to be directly beneath the platinum wire bridge _g_, when the boxwood cover _f_ is fixed on. The pin _h_ is pushed through the holes in the cover _f_ from the outside, so as to pass beneath the bridge _g_ after the priming has been inserted, and the cover has been placed on.

When prepared for use, the platinum wire bridge _g_ is surrounded by some loose gun-cotton priming, sufficient in quantity to blow off the boxwood cover _f_, without destroying the dome _a_; the cover _f_ being blown off, carries the ebonite pin _h_ with it, and through the platinum wire bridge _g_, thereby rupturing it, and breaking the continuity of the circuit. The object of so doing is to cut off the connection of an exploded mine, so that the full amount of the firing current is available for the other mines, and not suffered to be wasted by passing through the exposed wire of the broken circuit, which, were the disconnector not employed, would be the case.

When any particular mine of a system is struck, the current passes through the main cable _b_, the disconnector _a_ (which is in connection with that mine), and branch cable _b'_ to the fuze, and so explodes the mine, and destroys the platinum wire bridge _g_ of the disconnector at practically the same instant. The effect of the latter operation would be to cut off and insulate the branch cable of the exploded mine, and so prevent any loss of the electrical current, when another mine of that system is required to be fired.

The platinum wire bridge _g_ is 4/10 inch long, while that of the fuze is 3/10 inch, the object of this difference in length of the bridges being to ensure the former one _g_ being fired, and thus the insulation made doubly sure. Many other forms of disconnectors have been devised, but none have proved in practice so effective as the one just described.

PLATE X]

_Mooring Electrical Submarine Mines._--This is one of the most difficult problems to be solved in connection with a system of submarine mines. The objects to be attained in mooring are as follows:--

1.--The mines should preserve the exact positions in
which they are laid down.

NOTE.--From the comparatively small radius of destructive effect, of even heavily charged submarine mines, it will be understood how absolutely essential, in the case of mines fired by judgment, it is that this object should be attained.

2.--The mooring chains, or ropes, must be so arranged
that no twisting whatever should occur, as otherwise
fracture of the insulated wire would be likely to
happen.

3.--In the case of buoyant mines, their distance from
the bottom must be so adjusted, that at no time shall a
vessel passing over them be out of their vertical range
of destruction, nor shall they be visible.

The difficulties attendant upon the efficient mooring of submarine mines are immense, as will be understood when the action of gales of wind, and strong tides, which latter vary continually in their direction and in their rise and fall, are taken into consideration.

The foregoing remarks apply more particularly to a system of buoyant submarine mines, as those placed on the ground are comparatively easy to moor.

Several modes of mooring buoyant submarine mines have been suggested, the most practicable of which are as follows:--

1.--Ladder moorings.
2.--Fore and aft moorings.
3.--Austrian method of mooring.
4.--Single rope mooring.

_Ladder Mooring._--This is a method of mooring, which in places where it may be necessary to place the anchors far apart will be found useful.

The circuit closer is connected to the mine by two ropes which lead thence to two anchors, the ropes being separated by wooden rounds, or spreaders, 1 to 3 feet long, by which the tendency to twisting is prevented.

The anchors are placed some 12 feet apart.

The only defect of the ladder mooring is the quantity of sea-weed, &c., that is liable to be lodged on the rounds, thus causing the circuit closer to be drawn out of its proper position.

_Fore and aft Mooring._--This mode may be advantageously employed in a tideway where the current runs very strong, that is to say, five knots per hour, or more. It consists simply of two anchors, one of which is moored up, and the other down the stream.

_Austrian Method of Mooring._--This method of mooring, adopted by the Austrians during the war of 1866, is shown at Fig. 47. It consists of a wooden triangular platform on which several heavy weights _a_, _a_, _a_ are placed; the mine is attached to this platform by means of three wire ropes _b_, _b_, _b_, connected to the angles of the latter, and fastened to three chains, which by means of a catch holds the mine at the position required.

This catch consists of a pulley attached to the extremity of the wire rope of the platform, through which the mooring chain of the mine is passed, and fastened by a key at the required depth by means of a self-acting arrangement.

This key, which is of considerable weight, slips down as the mine is being hauled into position, but the moment the chain is slacked, two arms catch into a link of the chain, and so hold the mine in position. The weight of such a key is about 60 lbs. It is fitted with nuts, &c., to enable it to be taken to pieces.

This plan of mooring proved very effective in the harbours of the Adriatic, where there is hardly any tide or current to twist the mooring ropes, or otherwise disturb the mines. The Austrians have lately adopted the mushroom sinker in place of the wooden platform and weights, for their anchor.

_Single Rope Mooring._--This simple method of mooring has after numerous exhaustive experiments been adopted as the most practicable and effective of all others. Whenever possible, a wire instead of hempen cable should be used to connect the mine and its circuit closer to the mooring anchor, as the former is less liable to twist, kink, or wear from friction than the latter.

A ground mine with circuit closer attached is represented at Fig. 48, where _a_ is the wire mooring rope, _b_ the electric cable leading from the mine to the circuit closer, _C_, and _c_ the cable leading from the firing station to the mine; _d_ is the oblong sinker attached to the mine, and _e_ the tripping chain leading to the shore, to which the cable _c_ is attached at intervals, so that by underrunning the electric cable, the tripping chain may be easily picked up, and the mine raised.

PLATE XI]

At Fig. 49 is shown a buoyant mine. The only difference in the mooring of this and the one before described, is that instead of resting on its anchor on the ground, it is moored at a certain distance above its anchor _d_, to which it is secured by a chain _e_.

Fig. 50 represents an electro contact mine. _M_ is the mine with circuit closer enclosed, _a_ the wire mooring rope, _d_ the mushroom anchor, and _b_ the electric cable leading from the mine to the disconnector _D_.

The mushroom sinker or anchor, which is undoubtedly the most effective of all other forms of mooring anchors used for the purposes of anchoring submarine mines, is shown at _e_, Fig. 49; the legs are added for use on rocky or hard bottoms, under which circumstances the weight of the anchor should also be increased.

For ground mines the form of sinker shown at _d_, Fig. 48 is employed; it is of an oblong shape, and hollowed out in the centre to allow of its being lashed close up to the mine.

Large blocks of stones with their bases slightly hollowed are useful as extempore moorings, so also is the one shown at Fig. 51, which consists of a strong heavy wooden shaft _a_, with a number of wooden arms _b_, _b_ attached to its base; this form of extempore sinker was considered very efficient by the American authorities.

The wooden weighted platform, which was described at page 56, is also a very useful form of extempore sinker.

For dead weight moorings, pigs of ballast, heavy stones, &c., may be used.

The weight of the anchor or sinker for mooring submarine mines is a very important consideration. It will depend on the amount of buoyancy of the mine, on the strength of current, and on the nature of the bottom, also whether the mines are to be hauled down to, or moored with the anchor.

Stotherd uses the following formula:

W = [2rt](B^{2} + P^{2})

where B is the excess of the flotation over the weight of the charge of a given submarine mine;

P is the pressure exerted by any given current on the same buoyant mine;

W the weight of sinker necessary to overcome the tendency of the mine to move. In still water P becomes nothing, and therefore W equal to 2 B, that is, in still water double the buoyancy of a mine is a sufficient weight for its anchor.

The value of P may be found from the formula P = 4·085 × V^{2}, where V is the velocity of the current in miles per hour.

From this equation P will be found in terms of pressure in pounds per square foot of flat surface, which is nearly double that on the curved surface of a cylinder.

In regard to the amount of buoyancy of a submarine mine, it has been found by actual practice that in the case of a mine moored in still water it should certainly be not less than the weight of the charge, whilst if subjected to the lateral pressure due to a current, it should be not less than three times the pressure exerted by the current.

It is always necessary to allow an excess of buoyancy over the calculated amount to counteract any leakage, or other disturbing cause which might otherwise materially affect the efficiency of the mine.

There are two modes of placing a mine in position; either by attaching the anchor, with the cable necessary for the depth of water, to the mine, and lowering both together, or by placing the anchor first, and then hauling the mine down to it, and by means of a catch, fastening it at the required depth.

The first mode is exceedingly simple, but except under very favourable circumstances cannot be relied on when firing by observation is the means adopted to explode a system of submarine mines. The second plan is practically easy to carry out, and by it a mine may be placed more accurately. To enable either of the above methods to be properly carried out, specially fitted steamboats, &c., are requisite.

At Fig. 52 is represented a 42 feet launch fitted for laying down a submarine mine by the first of the two modes enumerated above.

PLATE XII.]

_a_ is the mine; _b_ is the electric cable carried from the drum _c_ to the charge, and connected for use; _d_ is the circuit closer, which is attached to the mine by its electric cable and mooring rope; _f_ is the mushroom sinker attached by means of its mooring chain to the mine, it is suspended by a slip rope _g_, which passes over a small crutch fitted with a sheave _h_; _i_ is a hollow iron derrick, and _k_ the tackle and fall for lifting mine into boat; this derrick is formed of an iron tube about 3 inches diameter, 3/8 inch thick, and 10 feet 6 inches long; it is attached to an iron tube mast of similar diameter and thickness to the derrick, but 12 feet 3 inches long, an iron chain 6 feet 6 inches long and 5/8 inch diameter, connects the derrick to the mast; _m_ is a leading sheave to keep the cable clear whilst it is being paid out; _l_ is a crab, for working the tackle _k_, &c., and _c_ is the drum on which the electric cable is wound.

In connection with the defence of a harbour by a system of electrical submarine mines of large size, it will be necessary to employ a service of steamtugs, steamboats, mooring-barges, &c., specially fitted for such work. One of the great advantages of the hauling down method of placing mines in position, is, that the anchors, with the cables connected thereto, may be carefully and accurately got into position during the time of peace, and the mines themselves, which should be kept in store ready fitted for immediate use, need not be placed in position until they are actually required. The drums used for reeling a multiple cable on, are capable of holding half a nautical mile in length. That used for a single core armoured cable is similar to but smaller than the aforesaid drum, and is capable of stowing one nautical mile of such a cable. For transportation wooden drums are ordinarily used.