HOW A WARSHIP IS BUILT
When it is decided to build a certain ship, the first thing to be done
is to draw it on paper. The Admiralties of the world, and also the great
shipbuilders, have each their own chief designer installed in a big,
light, quiet office fitted with large strong, flat tables at which work
a number of draughtsmen.
The naval authorities tell the "chief" in general terms what they want
the ship to be capable of, and he determines its size and form. Then the
draughtsmen work out his ideas on paper, themselves deciding upon the
minor details, until they have produced exact representations of the
ship which is to be. Some draughtsmen deal with the actual hull of the
ship, while others design the various fittings and minor details, all
working, of course, under the constant supervision of the chief.
In this connection one may perhaps allude to a matter which the general
public often seems to misunderstand--the work and functions of a
draughtsman. I have heard people say of a boy that he is good at drawing
so they think of making a draughtsman of him. Now the point is that the
actual drawing is perhaps the least important part of a draughtsman's
work. He has to know _what to draw_. He is given just a rough idea of
something and from that he has to produce a perfect design, bearing in
mind that the thing to be made must well fulfil its purpose, must be
easy and cheap to construct, must be strong enough yet not too heavy,
must be made of the most suitable material and so on. He has to possess
a good deal of the knowledge of the skilled workman, he has to be
something of a scientist and a good mathematician in addition to his
ability to make neat and accurate drawings. So, you see, these men whose
minds conceive the details of our great ships are men of long training
and experience, with far greater knowledge and skill than we sometimes
give them credit for.
Anyway, there they stand, each at his own table, bending over his own
drawing-board, each doing his own particular share towards producing the
perfect ship.
But when all is said and done, there are limitations to the cleverness
of the cleverest among us, so the next step, after the draughtsmen have
done their best, is to test what they have done by experiment.
Years ago a certain Mr. William Froude interested himself in the
question of the best shapes for ships, and he found that by making an
exact model of a ship and then drawing that model through water it was
possible to foretell just how that ship would behave. He built himself a
tank for the purpose of these experiments at Torquay, where he lived,
and by its aid he added a very important chapter to the science of
shipbuilding.
Nowadays the Admiralty have a large and well-fitted tank at Portsmouth,
the United States Navy have one at Washington, private shipbuilders have
the use of a national tank at Bushey, near London, while several of the
large firms have tanks of their own.
The national tank at Bushey, by the way, was given to the nation by Mr.
Yarrow, a famous shipbuilder, in memory of Mr. Froude, it being called
the "William Froude Tank" in recognition of the great work done by him.
Now these tanks may be described as rather elongated swimming-baths.
Such a structure is generally a little narrower than the average bath,
but it is longer and much deeper.
At one end there are miniature docks in which the models float when not
in use, while at the other there is a sloping beach upon which the waves
caused by the models expend their energy harmlessly.
Along each side there runs a rail upon which are supported the ends of a
travelling bridge. Driven by electric motors, this bridge can run to and
fro from end to end of the tank, and its purpose is to drag the models
through the water.
Carried upon the bridge is a platform which bears a number of
instruments, chief among which is a self-recording dynamometer.
Now a dynamometer is an instrument for measuring the force of a "pull,"
and when we call it self-recording we mean that it automatically takes a
record of a series of pulls or of a varying pull. In this case there
projects below the bridge a lever, to the end of which the model under
test is attached. As the bridge rushes along it pulls the model through
the water by means of this lever, and the force which is expended in
doing so is recorded in the form of a wavy line upon a sheet of ruled
paper.
If the model slips through the water very easily there is little pull
upon the lever and the line drawn by the pen of the instrument remains
low down upon the chart. If, however, much power is needed and the pull
is a strong one the pen moves and the line rises towards the top of the
paper. Any change, whether increase or decrease, is thus shown by the
rise or fall of the ink line.
One model can be thus tried at various speeds and its behaviour noted
under different conditions. Other matters can be investigated too, such
as whether or not the bow rises in the water or falls when the boat is
in motion, also how much such rise or fall may amount to.
The suitability of a certain shape of vessel, moreover, can to a certain
extent be seen by observing the commotion which it makes in the water.
Everyone has noticed the way in which a ship throws up a wave at its
bows, and that bow-wave, as it is termed, represents so much energy
being wasted. The power of the engines is absorbed to a certain extent
in making that wave. It is impossible to make anything which when forced
through the water will not make some wave, but certain forms cause less
of it than others, and the designer of a ship seeks to find that form
which will make the smallest bow-wave.
In like manner the eddies which a ship leaves in its wake are the
result of wasted energy, and the ship must be so shaped that they too
will be reduced to a minimum.
Shipbuilders find that there are three things which retard a ship's
movement: skin friction, or friction between the water and the sides of
the ship; wave making at the bow and eddy making at the stern. The first
depends largely upon the smoothness of the ship's surface, the second
and third depend upon its shape. If a model behaves badly in the tank
the fault may be either too much wave making or too much eddy making,
and which of these it is the dynamometer does not of course tell. In
many cases the experienced eye of the tank officials furnishes the clue
to the trouble, but in some cases a cinematograph is used to make a
complete series of photographs of the model and the water around it as
it rushes from end to end. These can then be studied in conjunction with
the chart and the cause of the fault discovered.
The real aim, it is obvious, of all these tank experiments is to find
out the lowest horse-power necessary to drive the ship, or the best form
of ship to get the highest speed out of a given horse-power.
The cost of keeping up these large tanks and making the models and
conducting the experiments is very great, for not only are the premises
very large (I know one in which the water alone cost nearly a hundred
pounds) but a highly skilled staff is necessary. The saving effected in
the cost of ships and the superior efficiency of the ships makes it well
worth while however.
There is still one other point about this matter which will possibly be
puzzling the observant reader. What are the models made of and how are
they made? They are made of paraffin wax, and a very important
department of the experimental tank is that where the models are formed.
First of all a rough mould is fashioned by hand in modelling clay and
into this is poured melted wax, the result being a very rough model of
the ship. 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 passes 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 ship, 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 ship 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 passes 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 ships 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 passed out to the works to be translated in terms
of iron, steel and wood.
Perhaps the most important part of a shipyard is the mould loft, a large
apartment on the floor of which the ship 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.
[Illustration: THE TRIPOD MAST.
Here we see one leg of the tripod mast of a warship. 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 ship 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 ship are laid. Upon them are laid other parts, and
upon them others, the joints being made by riveting. Thus the great ship
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 shores 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 mass of the ship 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 ships
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 ship 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
ship 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 ship
by the time it leaves the slip has become a huge magnet, with somewhat
disconcerting effects upon its own compasses, but of that more later on.
Thus the great ship 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 ship 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 ship 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 ship.
Under each side of the ship and upon the launching ways there is built a
timber framework capable of raising the ship bodily off the blocks upon
which until now it has reposed. These two frames, being connected
together by chains passing beneath the keel, constitute what is called
the cradle, the "toboggan" which is to slide down the ways, bearing the
ship upon it.
It is easy to see that being top-heavy something must be done to give
the ship support before the shores on either side can be taken away, and
it is equally clear that these latter must be removed before she can
slide down to the water. Neither would it do to let the vessel slide
upon her own plates, so we see that the cradle fulfils a twofold
purpose, first enabling the ship to reach the water without ripping
holes in her own plates, and secondly giving it the necessary side
support to prevent it from toppling over on the way.
When all is ready, but a short time before the hour appointed for the
launch, a curious operation is performed. Between the main part of the
cradle and the part which actually slides upon the ways wedges are
inserted, hundreds of them, and they are all driven in simultaneously.
Their purpose is to make the cradle slightly higher and so to lift the
ship off the blocks upon which it was built. If they were driven in one
at a time each would only dig its way into the timber and nothing else
would happen, but being driven all together a most powerful lifting
action is produced which actually raises the mighty ship. So hundreds of
men stand, each with his hammer ready to strike a wedge, while the
foreman stands by with a gong. At a stroke on the gong the hundreds of
hammers strike as one, and so the ship is raised off the blocks, which
can then be removed, to facilitate which they too are built of
wedge-shaped pieces which can easily be knocked apart. The shores, too,
have ceased to serve any useful purpose and can be taken away until at
last all shores and all blocks are gone and the vessel rests upon the
cradle only. Meanwhile tons of grease have been put on the ways, and the
ship, urged by its own weight, is straining to get down the greasy slope
into the element for which all along it has been intended. At this stage
the only thing which restrains it is a kind of trigger arrangement on
either side which locks the cradle in its place. In some yards elaborate
mechanical catches controlled by electricity are used for this, but in
many the old device of "dog shores" is still used. These are simply two
stout wood props which fit between a projection on the ways and one on
the cradle, there being one dog shore on either side. Just over each dog
shore there hangs a weight.
The person who performs the ceremony cuts the cord which holds the
weights, the weights fall, the dog shores are knocked away, and the ship
is free. Slowly at first, but gathering speed every moment, she moves
majestically downwards into the water, being ultimately brought to rest
by means of chains.
Whether done by the simple dodge of cutting a cord or by the more
refined method of pressing an electric push, the launching is generally
preceded by the breaking of a bottle of wine against the bows and the
pronouncement of the vessel's name.
Once safely afloat, the vessel is towed away and berthed alongside a
wharf whereon are cranes and other machines which lightly drop on board
of her the massive turbines and boilers which in time will propel her,
and the guns with which she will fight. All the multitudinous little
finishing touches are here put into her until at last she sallies forth
on her trial trips to show what she is capable of, after which follow
trials of her guns, and then she takes her place in the fleet.
Thus, briefly sketched, we see the history of the warship from her
inception in the minds of her designers till she is ready to meet the
foe.