Part 15 (1/2)

First of all a rough mould is fas.h.i.+oned by hand in modelling clay and into this is poured melted wax, the result being a very rough model of the s.h.i.+p. This is then placed in the model-making machine.

Those of my readers who are familiar with an engineer's shop will know what a planing machine is like, and from that they can form an idea of the general structure of this remarkable tool. There is, first of all, a travelling table which, as the machine works, travels to and fro.

Spanning this table is a beam which carries on its under side two revolving cutters, so that as the table pa.s.ses beneath them the cutters can operate upon anything placed upon the table.

Another part of the machine is a board upon which is placed the drawing showing the external shape of the proposed s.h.i.+p, and working over this board is a pointer connected by a system of rods and levers to the cutters just mentioned. The rough block of wax, then, having been placed upon the table and the to and fro motion set going, the attendant guides the pointer along the lines of the drawing, and as he does so the cutters so move as to carve away the soft wax into the precise shape of the model.

A little smoothing by hand is all that is necessary to complete the conversion of the rough piece of wax into a perfect model. It is then placed in the water and ballasted with little bags of shot until it floats at just the correct depth, and finally a light wooden frame is fitted to it for the purpose of making the connection to the lever by which it is pulled along.

Thus, after much thought and experiment, the designs for a new s.h.i.+p are completed. Tracings are then made of them on semi-transparent paper or cloth, which tracings are then used as ”negatives,” from which a number of photographic prints are made, just as the amateur photographer makes prints from his negatives. At least that is how they used to be done, in a huge printing frame, but nowadays a machine is more often employed which pa.s.ses the tracing or negative with a piece of photographic paper behind it slowly past an electric light, thus doing the work more quickly and more conveniently, for the drawings of s.h.i.+ps are often very long and would either require an enormous frame or else would have to be made in pieces and joined together.

The prints are finally pa.s.sed out to the works to be translated in terms of iron, steel and wood.

Perhaps the most important part of a s.h.i.+pyard is the mould loft, a large apartment on the floor of which the s.h.i.+p is drawn out full size. Then from these full-size drawings moulds or templets are made of wood or soft metal, showing the exact size and shape of the various parts. The moulds or templets go thence to the workshops, where the bars and plates of steel are cut to the right shape and perforated with holes, and some of the pieces are there joined together with rivets.

[Ill.u.s.tration: THE TRIPOD MAST.

Here we see one leg of the tripod mast of a wars.h.i.+p. These masts have greater stability and freedom from vibration than others. They are used for observation and range-finding, and have a fighting-top on which guns of small calibre are mounted. Here is shown a sailor carrying a wounded comrade.]

From the workshops the various pieces or parts go to the yard where the slip is on which the vessel is being built. This slip is by the water's edge, conveniently placed with a view to the fact that later on the great structure, weighing possibly thousands of tons, has got to slide down into the water.

Where the keel of the s.h.i.+p is to go a row of timber blocks is placed a few feet apart, and upon these blocks the plates of steel which form the lowest part of the s.h.i.+p are laid. Upon them are laid other parts, and upon them others, the joints being made by riveting. Thus the great s.h.i.+p grows from the keel upwards. As she gets bigger and bigger there comes the danger of her tipping over, and that is provided against by the use of props or sh.o.r.es along both sides.

By the time the hull is ready for launching it is often of great weight, all of which is borne upon the wooden blocks underneath the keel.

Consequently, if the ground be not good, piles have to be driven in or concrete foundations laid to enable the huge ma.s.s of the s.h.i.+p to be supported. For this reason a large vessel cannot be built anywhere but only on a properly prepared ”slip,” and it is the possession of a large number of such places which enables Great Britain to build so many s.h.i.+ps at once.

Along each side of the slip there is usually a row of tall masts with a beam projecting out sideways near the top of each, forming cranes by which the heavier parts can be hoisted into position.

In other yards, again, there is a tall iron structure called a gantry along each side of the slip, while travelling cranes span across from one to the other over where the growing s.h.i.+p lies. These travelling cranes, worked by electricity, permit heavy weights to be handled with ease and safety. Other subsidiary cranes, meanwhile, carry the heavy hydraulic riveting machines by which riveting is done.

Much riveting is done by hand, men working together in squads of four.

Of these one, often quite a boy, heats the rivets in a small furnace, after which he throws them one by one to man number two, who inserts each as he receives it in its proper hole and holds it there with a big heavy hammer or else a tool called a ”dolly.” Number two is called the ”holder-up,” since he holds the rivet up in its place while the remaining two hammer it over with alternate blows of their hammers.

In many cases, however, the two last described men give place to one, who is armed with a tool in shape much like a pistol and operated by compressed air obtained through a flexible tube. When he presses a trigger a little hammer inside the ”pistol” gives a rapid series of blows to the rivet, completing the job more quickly than the two men can do with hand hammers.

A third way of doing this operation so important in the building of a s.h.i.+p is by the hydraulic machine suspended from the cranes. To the casual onlooker this has the notable feature of being silent, whereas riveting by hand and still more by a pistol hammer is terribly noisy.

The reason for this is that the hydraulic riveter does not hammer at all, but, like a huge mechanical hand, it takes the rivet between finger and thumb and just squeezes it down.

One strange result of all this hammering in of rivets is that every s.h.i.+p by the time it leaves the slip has become a huge magnet, with somewhat disconcerting effects upon its own compa.s.ses, but of that more later on.

Thus the great s.h.i.+p grows, being made piece by piece in the workshops to the shapes indicated from the mould loft and put together and riveted on the slip, until finally in due time it is ready to take its first journey.

The launching of a big s.h.i.+p always strikes me as about the boldest and most daring thing which is ever done in the course of industry. For the huge structure, naturally top-heavy, weighing hundreds or thousands of tons, is just allowed to slide at its own sweet will. From the moment it starts until it is well in the water it is in charge of itself, so to speak, and if anything were to go wrong no power on earth could stop it once it had got a start.

That nothing ever does go wrong, or scarcely ever at all events, is due to the care with which all preparations are made before that critical moment when the s.h.i.+p is let loose and to the skill and experience of those in charge.

As the hull reaches that degree of completion when it can safely be put in the water, strong wooden structures termed launching ways are constructed one on each side of her. These really act like huge rails upon which in due course there will slide a gigantic toboggan.

Tremendously solid and strong they have to be, as they have each to carry half the total weight of the s.h.i.+p.