THE MACHINERY OF A SHIP
THE REVERSING ENGINE--MARINE ENGINE SPEED GOVERNORS--THE
STEERING ENGINE--BLOWING AND VENTILATING APPARATUS--PUMPS--FEED
HEATERS--FEED-WATER FILTERS--DISTILLERS--REFRIGERATORS--THE
SEARCH-LIGHT--WIRELESS TELEGRAPHY INSTRUMENTS--SAFETY DEVICES--THE
TRANSMISSION OF POWER ON A SHIP
With many travellers by sea the first impulse, after bunks have been
visited and baggage has been safely stored away, is to saunter off
to the hatches over the engine-room and peer down into the shining
machinery which forms the heart of the vessel. Some engine is sure to
be at work to remind them of the great power stored down there below,
and to give a foretaste of what to expect when the engine-room gong
sounds and the man in charge opens the huge throttle controlling some
thousands of horse-power.
By craning forward over the edge of the ship, a jet of water may be
seen spurting from a hole in the side just above the water-line,
denoting either that a pump is emptying the bilge, or that the
condensers are being cooled ready for the work before them.
Towards the forecastle a busy little donkey engine is lifting bunches
of luggage off the quay by means of a rope passing over a swinging spar
attached to the mast, and lowering it into the nether regions where
stevedores pack it neatly away.
In a small compartment on the upper deck is some mysterious, and not
very important-looking, gear: yet, as it operates the rudder, it claims
a place of honour equalling that of the main engines which turn the
screw.
To the ordinary passenger the very existence of much other
machinery--the reversing engines, the air-pumps, the condensers, the
"feed" heaters, the filters, the evaporators and refrigerators, and
the ventilators--is most probably unsuspected. The electric light he
would, from his experience of things ashore, vaguely connect with an
engine "somewhere." But the apparatus referred to either works so
unobtrusively or is so sequestered from the public eye that one might
travel for weeks without even hearing mention of it.
On a warship the amount of machinery is vastly increased. In fact,
every war vessel, from the first-class battleship to the smallest
"destroyer," is practically a congeries of machines; accommodation for
human beings taking a very secondary place. Big guns must be trained,
fed, and cleaned by machinery; and these processes, simple as they
sound, need most elaborate devices. The difference in respect of
mechanism between the _King Edward VII._ and Nelson's _Victory_ is as
great as that between a motor-car and a farmer's cart. It would not be
too much to say that the mechanical knowledge of any period is very
adequately gauged from its fighting vessels.
[Illustration:
_Photo_]
[_Cribb, Southsea._
A gigantic sheer-legs used for lowering boilers, big guns, turrets,
etc., into men-of-war. The legs rise to a height of 140 feet, and will
handle weights up to 150 tons.]
During the last twenty years marine engines have been enormously
improved. But the advance of auxiliary appliances has been even more
marked. In earlier times the matter considered of primary importance
was the propulsion of the vessel; and engineers turned their attention
to the problem of crowding the greatest possible amount of power
into the least possible amount of space. This was effected mainly by
the "compounding" of engines--using the steam over and over again in
cylinders of increasing size--and by improving the design of boilers.
As soon as this business had been well forwarded, auxiliary machinery,
which, though not absolutely necessary for movement, greatly affected
the ease, comfort, and economy of working a ship, got its share of
notice, with the result that a tour round the "works" of a modern
battleship or liner is a growing wonder and a liberal education in
itself.
This chapter will deal with the auxiliaries to be found in large
vessels designed for peaceful or warlike uses. Many devices are common
to ships of both classes, and some are confined to one type only,
though the "steel wall" certainly has the advantage with regard to
multiplicity.
We may begin with
THE REVERSING ENGINE
All marine engines should be fitted with some apparatus which enables
the engineer to reverse them from full speed ahead to full speed astern
in a few seconds. The effort required to perform the operation of
shifting over the valves is such as to necessitate the help of steam.
Therefore you will find a special device in the engine-room which, when
the engineer moves a small lever either way from the normal position,
lets steam into a cylinder and moves rods reversing the main engine. By
a link action (which could not be explained without a special diagram)
the valves of the auxiliary are closed automatically as soon as the
task has been performed; so that there is no constant pressure on the
one or the other side of its piston. To prevent the reversal being too
sudden, the auxiliary's piston-rod is prolonged, and fitted to a second
piston working in a second cylinder full of glycerine or oil. This
piston is pierced with a small hole, through which the incompressible
liquid passes as the piston moves. Since its passage is gradual, the
engines are reversed deliberately enough to protect their valves from
any severe strains. These reversing engines can, if the steam serving
them fails, be worked by hand.
MARINE ENGINE SPEED GOVERNORS
When a ship is passing through a strong sea and pitches as she crosses
the waves, the screw is from time to time lifted clear of the water,
and the engines which a moment before had been doing their utmost,
suddenly find their load taken off them. The result is "racing" of the
machinery, which makes itself very unpleasantly felt from one end of
the ship to the other. Then the screw, revolving at a speed much above
the normal, suddenly plunges into the water again, and encounters great
resistance to its revolution.
A series of changes from full to no "load," as engineers term it,
must be harmful to any engines, even though the evil effects are not
shown at once. Great strains are set up which shake bolts loose, or
may crack the heavy standards in which the cranks and shaft work,
and even seriously tax the shaft itself and the screw. On land every
stationary engine set to do tasks in which the load varies--which
practically means all stationary engines--are fitted with a governor,
to cut off the steam directly a certain rate of revolution is exceeded.
These engines are the more easily governed because they carry heavy
fly-wheels, which pick up or lose their velocity gradually. A marine
engine, on the other hand, has only the screw to steady it, and this is
extremely light in proportion to the power which drives it; in fact,
has scarcely any controlling influence at all as soon as it leaves the
water.
Marine engineers, therefore, need some mechanical means of restraining
their engines from "running away." The device must be very sensitive
and quick acting, since the engines would increase their rate threefold
in a second if left ungoverned when running "free"; while on the other
hand it must not throttle the steam supply a moment after the work has
begun again when the screw takes the water.
Many mechanisms have been invented to curb the marine engine. Some
have proved fairly successful, others practically useless; and the
fact remains that, owing to the greater difficulty of the task, marine
governing is not so delicate as that of land engines. A great number of
steamships are not fitted with governors, for the simple reason that
the engineers are sceptical about such devices as a class and "would
rather not be bothered with them."
But whatever may have been its record in the past, the marine governor
is at the present time sufficiently developed to form an item in the
engine-rooms of many of our largest ships. We select as one of the
best devices yet produced that known as Andrews' Patent Governor; and
append a short description.
It consists of two main parts--the pumps and the ram closing the
throttle. The pumps, two in number, are worked alternately by some
moving part of the engine, such as the air-pump lever. They inject
water through a small pipe into a cylinder, the piston-rod of which
operates a throttle valve in the main steam supply to the engines. At
the bottom of this cylinder is a by-pass, or artificial leak, through
which the water flows back to the pumps. The size of the flow through
the by-pass is controlled by a screw adjustment.
We will suppose that the governor is set to permit one hundred
revolutions a minute. As long as that rate is not exceeded the by-pass
will let out as much water as the pumps can inject into the cylinder,
and the piston is not moved. But as soon as the engines begin to race,
the pumps send in an excess, and the piston immediately begins to rise,
closing the throttle. As the speed falls, the leak gets the upper hand
again, and the piston is pushed down by a powerful spring, opening the
throttle.
It might be supposed that, when the screw "races," the pumps would
not only close the throttle, but also press so hard on it as to cause
damage to some part of the apparatus before the speed had fallen again.
This is prevented by the presence of a second control valve (or leak)
worked by a connecting-rod rising along with the piston-rod of the
ram. The two rods are held in engagement by a powerful spring which
presses them together, so that a hollow in the first engages with a
projection on the second. Immediately the pressure increases and the
piston rises, the second valve is shut by the lifting of its rod, and
so farther augments the pressure in the cylinder and quickens the
closing of the throttle valve. This pressure increase must, however,
be checked, or the piston would overrun and stop the engines. So when
the piston has nearly finished its stroke the connecting-rod comes into
contact with a stop which disengages it from the piston-rod and allows
the second control valve to be fully opened by the spring pulling on
its rod. The piston at once sinks to such a position as the pressure
allows, and the action is repeated time after time.
The governing is practically instantaneous, though without shock, and
is said to keep the engine within 3 per cent. of the normal rate.
That is, if 100 be the proper number of revolutions, it would not be
allowed to exceed 103 or drop below 97. Such governing is, in technical
language, very "close."
The idea is very ingenious: pumps working against a leak, and as soon
as they have mastered it, being aided by a secondary valve which
reduces the size of the leak so as to render the effect of the pumps
increasingly rapid until the throttle has been closed. Then the
secondary valve is suddenly thrown out of action, gives the leak full
play, and causes the throttle to open quickly so that the steam may be
cut off only for a moment. By the turning of a small milled screw-head
a couple of inches in diameter the pace of 5,000 h.p. engines is as
fully regulated as if a powerful brake were applied the moment they
exceeded "the legal limit."
STEERING ENGINES
The uninitiated may think that the man on the bridge, revolving a
spoked-wheel with apparently small exertion, is directly moving the
rudder to port or to starboard as he wishes. But the helm of a large
vessel, travelling at high speed, could not be so easily deflected were
not some giant at work down below in obedience to the easy motions of
the wheel.
Sometimes in a special little cabin on deck, but more often in the
engine-room, where it can be tended by the staff, there is the steering
engine, usually worked by steam-power. Two little cylinders turn a
worm-screw which revolves a worm-wheel and a train of cogs, the last
of which moves to right or left a quadrant attached to the chains or
cables which work the rudder. All that the steersman has to do with his
wheel is to put the engine in forward, backward, or middle gear. The
steam being admitted to the cylinders quickly moves the helm to the
position required.
A particularly ingenious steam gear is that made by Messrs. Harfield
and Company, of London. Its chief feature is the arrangement whereby
the power to move the rudder into any position remains constant. If
you have ever steered a boat, you will remember that, when a sudden
curve must be made, you have to put far more strength into the tiller
than would suffice for a slight change of direction. Now, if a
steam-engine and gear were so built as to give sufficient pressure on
the helm in all positions, it would, if powerful enough to put the ship
hard-a-port, evidently be overpowered for the gentler movements, and
would waste steam. The Harfield gear has the last of the cog-train--the
one which engages with the rack operating the tiller--mounted
eccentrically. The rack itself is not part of a circle, but almost flat
centrally, and sharply bent at the ends. In short, the curve is such
that the rack teeth engage with the eccentric cog at all points of the
latter's revolution.
When the helm is normal the longest radius of the eccentric is turned
towards the rack. In this position it exerts least power; but least
power is then needed. As the helm goes over, the radius of the cogs
gradually decreases, and its leverage proportionately increases. So
that the engine is taxed uniformly all the time.
Some war vessels, including the ill-fated Russian cruiser _Variag_,
have been fitted with electric steering gear, operated by a motor in
which the direction of the current can be varied at the will of the
helmsman.
All power gears are so arranged that, in case of a breakdown of the
power, a hand-wheel can be quickly brought into play.
BLOWING AND VENTILATING APPARATUS
A railway locomotive sends the exhaust steam up the funnel with
sufficient force to expel all air from the same and to create a
vacuum. The only passage for the air flying to fill this empty space
lies through the fire-box and tubes traversing the boiler from end to
end. Were it not for the "induced draught"--the invention of George
Stephenson--no locomotive would be able to draw a train at a higher
speed than a few miles an hour.
On shipboard the fresh water used in the boilers is far too precious
to be wasted by using it as a fire-exciter. Salt water to make good
the loss would soon corrode the boilers and cause terrible explosions.
Therefore the necessary draught is created by _forcing_ air through the
furnaces instead of by _drawing_ it.
The stoke-hold is entirely separated from the outer air, except for
the ventilators, down which air is forced by centrifugal pumps at
considerable pressure. This draught serves two purposes. It lowers the
temperature of the stoke-hold, which otherwise would be unbearable,
and also feeds the fires with plenty of oxygen. The air forced in can
escape in one way only, viz. by passing through the furnaces. When the
ship is slowed down the "forced draught" is turned off, and then you
see the poor stokers coming up for a breath of fresh air. In the Red
Sea or other tropical latitudes these grimy but useful men have a very
hard time of it. While passengers up above are grumbling at the heat,
the stoker below is almost fainting, although clad in nothing but the
thinnest of trousers.
In the engine-room also things at times become uncomfortably warm. Take
the case of the United States monitor _Amphitrite_, which went into
commission in 1895 for a trial run.
Both stoke-hold and engine-room were very insufficiently ventilated.
The vessel started from Hampton Roads for Brunswick, Georgia. "The trip
of about 500 miles occupied five days in the latter part of July, and,
for sheer suffering, has perhaps seldom been equalled in our naval
history. The fire-room (stoke-hold) temperature was never below 150°,
and often above 170°, while the engine-room ranged closely about 150°.
For the first twenty-four hours the men stood it well, but on the
second day seven succumbed to the heat and were put on the sick list,
one of them nearly dying; before the voyage was ended, twenty-eight
had been driven to seek medical attendance. The gaps thus created were
partially filled with inexperienced men from the deck force, until
there was only a lifeboat's crew left in each watch.... On the evening
of the fourth day out our men had literally fought the fire to a finish
and had been vanquished; the watch on duty broke down one by one, and
the engines, after lumbering along slower and slower, actually stopped
for want of steam.... At daybreak the next morning we got under way and
steamed at a very conservative rate to our destination, fortunately
only about ten miles distant. The scene in the fire-room that morning
was not of this earth, and far beyond description. The heat was almost
destructive to life; steam was blowing from many defective joints and
water columns; tools, ladders, doors, and all fittings were too hot to
touch; and the place was dense with smoke escaping from furnace doors,
for there was absolutely no draught. The men collected to build up the
fires were the best of those remaining fit for duty, but they were worn
out physically, were nervous, apprehensive, and dispirited. Rough Irish
firemen, who would stand in a fair fight till killed in their tracks,
were crying like children, and begging to be allowed to go on deck, so
completely were they unmanned by the cruel ordeal they had endured so
long. 'Hell afloat' is a nautical figure of speech often idly used,
but then we saw it. For a month thereafter the ship was actively
employed on the southern coast, drilling militia at different ports,
and sweltering in the new dock at Port Royal. One trip of twenty-nine
hours broke the record for heat, the fire-room being frequently above
180°. All fire-room temperatures were taken in the actual spaces where
the men had to work, and not from hot corners or overhead pockets."[16]
The ventilators were subsequently altered, and the men enjoyed
comparative comfort. The words quoted will suffice to establish the
importance of a proper current of air where men have to work. One of
the greatest difficulties encountered in deep mining is that, while the
temperature approaches and sometimes passes that of a stoke-hold, the
task of sending down a cool current from above is, with depths of 4,000
ft. and over, a very awkward one to carry out.
On passenger ships the fans ventilating the cabins and saloons are
constantly at work, either sucking out foul air or driving in fresh.
The principle of the fan is very similar to that of the centrifugal
water pump--vanes rotating in a case open at the centre, through which
the air enters, to be flung by the blades against the sides of the
case and driven out of an opening in its circumference. Sometimes an
ordinary screw-shaped fan, such as we often see in public buildings, is
employed.
PUMPS
Every steamship carries several varieties of pump. First, there are the
large pumps, generally of a simple type, for emptying the bilge or
any compartment of the ship which may have sprung a leak. "All hands
to the pumps!" is now seldom heard on a steamer, for the opening of a
steam-cock sets machinery in motion which will successfully fight any
but a very severe breach. It is needless to say that these pumps form
a very important part of a ship's equipment, without which many a fine
vessel would have sunk which has struggled to land.
The pumps for the condensers form another class. These are centrifugal
force pumps; their duty is to circulate cold sea-water round the nests
of tubes through which steam flows after passing through the cylinders.
It is thus converted once more into water, ready for use again in the
boiler. Every atom of the water is evaporated, condensed, and pumped
back into the boiler once in a period ranging from fifteen minutes to
an hour, according to the type of boiler and the size of the supply
tanks.
Some condensers have the cooling water passed through the tubes, and
the steam circulated round these in an air-tight chamber. In any
case, the condenser should be so designed as to offer a large amount
of cold surface to the hot vapour. A breakdown of the condenser
pumps is a serious mishap, since steam would then be wasted, which
represents so much fresh water--hard to replace in the open sea. It
would be comparable to the disarrangement of the circulating pump on a
motor-car, though the effects are different.
We must not forget the feed-pumps for the boilers. On their efficient
action depends the safety of the ship and her passengers. Water must
be maintained at a certain level in the boiler, so that all tube and
other surfaces in direct contact with the furnace gases may be covered.
The disastrous explosions we sometimes hear of are often caused by the
failure of a pump, the burning of a tube or plate, and the inevitable
collapse of the same. The firms of Weir and Worthington are among the
best-known makers of the special high-pressure pumps used for throwing
large quantities of water into the boilers of mercantile and war
vessels.
FEED HEATERS
As the fuel supply of a vessel cannot easily be replenished on the high
seas, economy in coal consumption is very desirable.
If you put a cold spoon into a boiling saucepan ebullition is checked
at once, though only for a moment, while the spoon takes in the
temperature of the water. Similarly, if cold water be fed into a boiler
the steam pressure at once falls. Therefore the hotter the feed water
is the better.
The feed heater is the reverse of the condenser. In the latter, cold
water is used to cool hot steam; in the former, hot steam to heat cold
water. There are many patterns of heaters. One type, largely used,
sprays the cold water through a valve into a chamber through which
steam is passed from the engines. The spray, falling through the hot
vapour, partially condenses it and takes up some of its heat. The
surplus steam travels on to the condensers. A float in the lower part
of the chamber governs a valve admitting steam to the boiler pumps, so
that as soon as a certain amount of water has accumulated the pumps
are started, and the hot liquid is forced into the boiler.
Another type, the Hampson feeder, sends steam through pipes of a wavy
form surrounded by the feed water, there being no actual contact
between liquid and vapour.
An ally of the heater is the
FEED-WATER FILTER,
which removes suspended matter which, if it entered the boiler, would
form a deposit round the tubes, and while decreasing their efficiency,
make them more liable to burning. The most dangerous element caught by
the filters is fatty matter--oil which has entered the cylinders and
been carried off by the exhaust steam.
The filter is either high pressure, _i.e._ situated between the pump
and the boiler; or low pressure, _i.e._ between the pump and the
reservoir from which it draws its water. The second class must have
large areas, so as not to throttle the supply unduly.
Many kinds of filtering media have been tried--fabrics of silk, calico,
cocoanut fibre, towelling, sawdust, cork dust, charcoal, coke; but
the ideal substance, at once cheap, easily obtainable, durable, and
completely effective, yet remains to be found.
A filter should be so constructed that the filtering substance is very
accessible for cleansing or renewal.
DISTILLERS
We now come to a part of a ship's plant very necessary for both
machines and human beings. Many a time have people been in the
position of the Ancient Mariner, who exclaimed:--
"Water, water, everywhere,
But not a drop to drink!"
Water is so weighty that a ship cannot carry more than a very limited
quantity, and that for the immediate needs of her passengers. The
boilers, in spite of their condensers, waste a good deal of steam at
safety valves through leaking joints and packings, and in other ways.
This loss must be made good, for, as already remarked, salt water
spells the speedy ruin of any boiler it enters.
The distiller in its simplest form combines a boiler for changing water
into vapour, with a condenser for reconverting it to liquid. Solids
in impure water do not pass off with the steam, so that the latter,
if condensed in clean vessels, is fit for drinking or for use in the
engine boilers.
A pound of steam will, under this system, give a pound of water. But as
such procedure would be extravagant of fuel, _compound_ condensers are
used, which act in the following manner.
High-pressure steam is passed from the engine boilers into the tubes of
an evaporator, and converts the salt water surrounding it into steam.
The boiler steam then travels into its own condenser or into the feed
water heater, while the steam it generated passes into the coils of a
second evaporator, converts water there into steam, and itself goes to
a condenser. The steam generated in the second evaporator does similar
duty in a third evaporator. So that one pound of high-pressure steam is
directly reconverted to water, and also indirectly produces between two
and three pounds of fresh water.
The condensers used are similar to those already described in
connection with the engines, and need no further comment. About the
evaporators, it may be said that they are so constructed that they can
be cleaned out easily as soon as the accumulation of salt and other
matter renders the operation necessary. Usually one side is hinged, and
provided with a number of bolts all round the edges which are quickly
removed and replaced.
The United States Navy includes a ship, the _Iris_, whose sole duty is
to supply the fleet she attends with plenty of fresh water. She was
built in 1885 by Messrs. R. and W. Hawthorn, of Newcastle-on-Tyne, and
measures 310 feet in length, 38-1/2 feet beam. For her size she has
remarkable bunker capacity, and can accommodate nearly 2,500 tons of
coal. Fore and aft are huge storage tanks to hold between them about
170,000 gallons of fresh water. Her stills can produce a maximum of
60,000 gallons a day. It has been reckoned that each _ton_ of water
distilled costs only 18 cents; or, stated otherwise, that 40 gallons
cost one penny. At many ports fresh water costs three or four times
this figure; and even when procured is of doubtful purity. During the
Spanish-American War the _Iris_ and a sister ship, the _Rainbow_,
proved most useful.
REFRIGERATORS
Of late years the frozen-meat trade has increased by leaps and bounds.
Australia, New Zealand, Argentina, Canada, and the United States send
millions of pounds' worth of mutton and beef across the water every
year to help feed the populations of England and Europe.
In past times the live animals were sent, to be either killed when
disembarked or fatted up for the market. This practice was expensive,
and attended by much suffering of the unfortunate creatures if bad
weather knocked the vessel about.
Refrigerating machinery has altered the traffic most fundamentally.
Not only can more meat be sent at lower rates, but the variety is
increased; and many other substances than flesh are often found in the
cold stores of a ship--butter and fruit being important items.
Certain steamship lines, such as the Shaw, Savill, and Albion--plying
between England and Australasia--include vessels specially built
for the transport of vast numbers of carcases. Upwards of a million
carcases have been packed into the hull of a single ship and kept
perfectly fresh during the long six weeks' voyage across the Equator.
Every passenger-carrying steamer is provided with refrigerating
rooms for the storage of perishable provisions; and as the comfort
of the passengers, not to say their luxury, is bound up with these
compartments, it will be interesting to glance at the method employed
for creating local frost amid surrounding heat.
The big principle underlying the refrigerator is this--that a liquid
when turned into gas _absorbs_ heat (thus, to convert water into steam
you must feed it with heat from a fire), and that as soon as the gas
loses a certain amount of its heat it reverts to liquid form.
Now take ammonia gas. The "spirits of hartshorn" we buy at the
chemist's is water impregnated with this gas. At ordinary living
temperatures the water gives out the gas, as a sniff at the bottle
proves in a most effective manner.
If this gas were cooled to 37·3° below zero it would assume a liquid
state, _i.e._ that temperature marks its boiling point. Similarly
steam, cooled to 212° Fahr., becomes water. Boiling point, therefore,
merely means the temperature at which the change occurs.
Ammonia liquid, when gasifying, absorbs a great amount of heat from its
surroundings--air, water, or whatever they may be. So that if we put a
tumbler full of the liquid into a basin of water it would rob the water
of enough heat to cause the formation of ice.
The refrigerating machine, generally employed on ships, is one which
constantly turns the ammonia liquid into gas, and the gas back into
liquid. The first process produces the cold used in the freezing-rooms.
The apparatus consists of three main parts:--
(1) The _compressor_, for squeezing ammonia gas.
(2) The _condenser_, for liquefying the gas.
(3) The _evaporator_, for gasifying the liquid.
The _compressor_ is a pump. The _condenser_, a tube or series of tubes
outside which cold water is circulated. The _evaporator_, a spiral tube
or tubes passing through a vessel full of brine. Between the condenser
and evaporator is a valve, which allows the liquid to pass from the one
to the other in proper quantities.
We can now watch the cycle of operations. The compressor sucks in a
charge of very cold gas from the evaporator, and squeezes it into a
fraction of its original volume, thereby heating it. The heated gas
now passes into the condenser coils and, as it expands, encounters the
chilling effects of the water circulating outside, which robs it of
heat and causes it to liquefy.
It is next slowly admitted through the expansion valve into the
evaporator. Here it gradually picks up the heat necessary for its
gaseous form: taking it from the brine outside the coils, which has a
very low freezing-point. The brine is circulated by pumps through pipes
lining the walls of the freezing-room, and robs the air there of its
heat until a temperature somewhat below the freezing-point of water is
reached.
The room is well protected by layers of charcoal or silicate cotton,
which are very bad conductors of heat. How the chamber strikes a novice
can be gathered from the following description of a Cunard liner's
refrigerating room. "It is a curious and interesting sight. It may be
a hot day on deck, nearing New York, and everyone is going about in
sun hats and light clothes. We descend a couple of flights of stairs,
turn a key, and here is winter, sparkling in glassy frost upon the pale
carcases of fowls and game, and ruddy joints of meat, crystallising
the yellow apples and black grapes to the likeness of sweetmeats in
a grocer's shop, gathering on the wall-pipes in scintillating coats
of snow nearly an inch deep. You can make a snowball down here, if
you like, and carry it up on deck to astonish the languid loungers
sheltering from the sun under the protection of the promenade-deck
roof. Such is the modern substitute for the old-time salt-beef cask and
bags of dried pease!"
The larder is so near the kitchen that while below decks we may just
peep into the kitchens, where a white-capped _chef_ presides over an
army of assistants. Inside a huge oven are dozens of joints turning
round and round by the agency of an invisible electric-motor. But what
most tickles the imagination is an electrical egg-boiling apparatus,
which ensures the correct amount of cooking to any egg. A row of
metal dippers, with perforated bottoms, is suspended over a trough of
boiling water. Each dipper is marked for a certain time--one minute,
two, three, four, and so on. The dippers, filled with eggs, are pushed
down into the water. No need to worry lest they should be "done to
a bullet," for at the expiry of a minute up springs the one-minute
dipper; and after each succeeding minute the others follow in due
rotation. Where 2,000 eggs or more are devoured daily this ingenious
automatic device plays no mean part.
THE SEARCH-LIGHT
All liners and war vessels now carry apparatus which will enable them
to detect danger at night time, whether rocks or an enemy's fleet,
icebergs or a water-logged derelict. On the bridge, or on some other
commanding part of the vessel's structure, is a circular, glass-fronted
case, backed with a mirror of peculiar shape. Inside are two carbon
points almost touching, across which, at the turn of a handle, leaps a
shower of sparks so continuous as to form a dazzling light. The rays
from the electric arc, as it is called, either pass directly through
the glass lens, or are caught by the parabolic reflector and shot
back through it in an almost parallel pencil of wonderful intensity,
which illumines the darkness like a ray of sunshine slanting through
a crack in the shutter of a room. The search-light draws its current
from special dynamos, which absorb many horse-power in the case of the
powerful apparatus used on warships. At a distance of several miles a
page of print may be easily read by the beams of these scrutinisers of
the night.
The finest search-lights are to be found ashore at naval ports, where,
in case of war, a sharp look-out must be kept for hostile vessels.
Portsmouth boasts a light of over a million candle-power, but even this
is quite eclipsed by a monster light built by the Schuckert Company, of
Nuremberg, Germany, which gives the effect of 816,000,000 candles. An
instrument of such power would be useless on board ship, owing to the
great amount of current it devours, but in a port, connected with the
lighting plant of a large town, it would serve to illumine the country
round for many miles.
In addition to its value as an "eye," the search-light can be utilised
as an "ear." Ernst Ruhmer, a German scientist, has discovered a method
of telephoning along a beam of light from a naval projector. The
amount of current passing into the arc is regulated by the pulsations
of a telephone battery and transmitter. If the beam be caught by
a parabolic reflector, in the focus of which is a selenium cell
connected with a battery and a pair of sensitive telephone receivers,
the effect of these pulsations of light is _heard_. Selenium being a
metal which varies its resistance to an electric circuit in proportion
to the intensity of light shining upon it, any fluctuations of the
search-light's beams cause electric fluctuations of equal rapidity in
the telephone circuit; and since these waves arise from the vibrations
of speech, the electric vibrations they cause in the selenium circuit
are retransformed at the receiver into the sounds of speech. This
German apparatus makes it possible to send messages nine or ten miles
over a powerful projector beam.
In the United States Navy, and in other navies as well, night signals
are flashed by the electric light. The pattern of lamp used in the
United States Navy is divided transversely into two compartments, the
upper having a white, the lower a red, lens. Four of these lamps are
hung one above the other from a mast. A switch-board connected with the
eight incandescent lamps in the series enables the operator to send any
required signal, one letter or figure being flashed at a time. During
the Spanish-American War the United States fleet made great use of this
simple system, which on a clear night is very effective up to distances
of four miles.
Large arc-lamps slung on yards over the deck give great help for
coaling and unloading vessels at night time. The touch of a switch
lights up the deck with the brilliancy of a well-equipped railway
station. The day of the "lantern, dimly burning," has long passed away
from the big liner, cargo boat, and warship.
WIRELESS TELEGRAPHY INSTRUMENTS
Solitude is being rapidly banished from the earth's surface. By
solitude we mean entire separation from news of the world, and the
inability to get into touch with people far away. On the remote ranches
of the United States, in sequestered Norwegian fiords, in the folds of
the eternal hills where the only other living creature is the eagle,
man may still be as conversant with what is going on in China or
Peru as if he were living in the busy streets of a capital town. The
electric wire is the magic news-bringer. Wherever man can go it can go
too, and also into many places besides.
We must make one exception--the surface of the sea. Cables rest on
ocean's bed, but they would be useless if floated on its surface to act
as marine telegraph offices. Winds and waves would soon batter them to
pieces, even if they could be moored, which in a thousand fathoms may
be considered impracticable.
So until a few years back the occupants of a ship were truly isolated
from the time that they left port until they reached land again, except
for the rare occasions when a passing vessel might give them a fragment
of news.
This has all been changed. Stroll into the saloon of one of our large
Atlantic liners and you will see telegram forms lying on the tables.
In the 'nineties they would have been about as useful aboard ships
as a mackintosh coat in the Sahara. A glance, however, at pamphlets
scattered around informs you that the ship carries a Marconi wireless
installation, and that a Marconi telegram, handed in at the ship's
telegraph office, will be despatched on the wings of ether waves to the
land far over the horizon.
Inside the cabin streams of sparks scintillate with a cracking noise,
and your message shoots into space from a wire suspended on insulators
from one of the mast heads. If circumstances favour, you may receive a
reply from the Unseen before the steamer has got out of range of the
coast stations. The immense installations at Poldhu, Cornwall, and in
Newfoundland, could be used to flash the words to a ship at any point
of the transatlantic journey. Owing to lack of space, and consequently
power, the steamer's transmitting apparatus has a limited capacity.
The first shipping company to grasp the possibilities of the commercial
working of the Marconi system was the Nord-Deutscher-Lloyd, whose mail
steamer, _Kaiser Wilhelm der Grosse_, was fitted in March, 1900. At the
present time many of the large Atlantic steamship companies carry a
wireless installation as a matter of course, ranking it among necessary
things. The Cunard, American Atlantic Transport, Allan, Compagnie
Transatlantique, Hamburg-American, and Nord-Deutscher-Lloyd lines make
full use of the system, as the conveniences it gives far outweigh any
expense. A short time since maritime signalling was extremely limited
in its range, being effected by flags, semaphores, lights, and sounds,
which in stormy weather became uncertain agents, and in foggy, useless.
Also the operations of transmitting and receiving were so slow that
many a message had to remain uncompleted.
The following paragraph, which appeared in _The Times_ of December
11th, 1903, is significant of the very practical value of marine
wireless telegraphy. "The American steamer _Kroonland_, from Antwerp
for New York, which, as reported yesterday, disabled her steering
gear when west of the Fastnet, and had to put back, arrived yesterday
morning at Queenstown. The saloon passengers speak in the highest terms
of praise of the utility of the Marconi wireless telegraphy with which
the liner is fitted, and of the facility with which, when the accident
occurred, the passengers were able to communicate with their friends,
in England, Scotland, and the Continent, and even America, and get
replies before the Irish coast was sighted. The accident occurred on
Tuesday about noon, when the liner was 130 miles west of the Fastnet,
and communication was at once made with the Marconi station at
Crookhaven. Captain Doxrud was enabled accordingly to send messages to
the chief agents of the American line, at Antwerp, stating the nature
of the damage to the steering gear of the steamer, and that he would
have to abandon the idea of prosecuting the western voyage. Within an
hour and a half a message was received by the captain from the agents
instructing him what to do, and at once the _Kroonland_ was headed for
Queenstown. Three-fourths of the total number of the saloon passengers
and a goodly number of the second cabin sent messages to their friends
in various parts of the world, and replies were received even from the
Continent before the Fastnet was sighted. Seven or eight passengers
telegraphed to relatives for money, and replies were received in four
instances, authorising the purser to advance the amounts required, and
the money was paid over in each case to the passengers."
The possibility of thus communicating between vessel and land, or
vessel and vessel, removes much of the anxiety attending a sea voyage.
Business men, for whom even a few days' want of touch with the
mercantile markets may be a serious matter, can send long messages in
code or otherwise instructing their agents what to do; while they can
receive information to shape their actions when they reach land. The
"uncommercial traveller" also is pleased and grateful on receiving a
message from home. The feeling of loneliness is eliminated. The ocean
has lost its right to the term bestowed by Horace--_dissociabilis_,
"the separator."
[Illustration:
_Photo_]
[_Cribb, Southsea._
FIXING A BATTLE-RAM
The ram of a battleship being placed in position with the aid of a huge
crane. The size of the ram will be appreciated from the dwarfing effect
it has on that of the man perched near the lifting tackle.]
Steamship companies vie with one another in their efforts to keep
their passengers well posted in the latest news. Bulletins, or
small newspapers, are issued daily during the voyage, which give,
in very condensed form, accounts of events interesting to those on
board. "The amount of fresh news a steamer gathers during a passage
is considerable, and is greatly relished by the passengers, who are
invariably ravenous for signs of the busy life they left behind, more
especially when they have departed on the verge of some important event
taking place; and the bulletins are eagerly sought for when it is
announced that an inward-bound ship is in communication. The shipowners
realise the importance and usefulness of being able to communicate with
their commanders before the huge vessels enter narrow waters, and issue
instructions concerning their movements.
"The stations, which are placed at carefully-selected points at
well-adapted distances around the coast, are connected with either the
land telegraph or telephone line, or are close to a telegraph office.
They are kept open night and day, as the times of the ships passing
are, of course, greatly dependent on the weather encountered during the
voyage. For those on shore who are anxious to greet their friends on
arrival--with good or bad news, as the case may be--this arrangement
enables them to be informed of the exact time of the ship's expected
arrival, and they are left free to their own devices, instead of
enduring long waits on draughty piers and docks--which, on a wet or
windy day, are almost enough to damp the warmest and most enthusiastic
welcome.
"Cases have occurred where a telegram, sent from the American side
to an outlying English land-station two days after a ship has left,
has been transmitted to an outgoing steamer, which in turn has
re-transmitted it to the astonished passenger two days prior to his
arrival off the English coast; and it has now become quite a common
thing for competing teams on vessels many miles apart, and out of
sight of each other, to arrange chess matches with each other, some
of these interesting events taking two or more days to be played to a
finish."[17]
For naval purposes, wireless telegraphy has assumed an importance
which can hardly be overestimated, as the whole efficiency of a fine
fleet may depend upon a single message flashed through space. All
navies are fitting instruments, the British Admiralty being well to
the fore. Even in manoeuvres and during the execution of tactical
formations the apparatus is constantly at work. The admiral gives the
word, and a dozen paper tapes moving jerkily through Morse machines,
pass the message round the fleet. The Japanese naval successes have,
doubtless, been largely due to their up-to-date employment of this
latest development of Western electrical science. No one knows how soon
the time may come when the fate of a nation may depend on the proper
working of a machine covering a few square feet of a cabin table; for,
rapid as has been the growth of wireless telegraphy, it is yet in its
infancy.
SAFETY DEVICES
A ship is usually divided into compartments by cross bulkheads of
steel. In event of a collision or damage by torpedoes or shell, the
water rushing through the break can be prevented from swamping the ship
by closing the bulkhead doors.
Messrs. J. Stone and Company, of Deptford, have patented a system of
hydraulically operated bulkhead doors, which is finding great favour
among shipbuilders on account of its versatility. Each door is closed
by an hydraulic cylinder placed above it. The valves of the cylinder
are opened automatically by a float when the water rises in the
compartment, and every cylinder is also controllable independently from
the bridge and other stations in the ship, and by separate hand levers
alongside the bulkhead.
The doors can therefore be closed collectively or individually. Should
it happen that, when a door has been closed, someone is imprisoned,
the prisoner can open the door by depressing a lever inside the
compartment, and make his escape. But the door is closed behind him by
the action of the float.
THE TRANSMISSION OF POWER ON A SHIP
There are four power agents available on board ship, all derived
directly or indirectly from the steam boilers. They are:--
(1) Steam.
(2) High-pressure water.
(3) Compressed air.
(4) Electricity.
On some ships we may find all four working side by side to drive the
multifarious auxiliaries, since each has its peculiar advantages and
disadvantages. At the same time, marine engineers prefer to reduce
the number as far as possible, since each class of transmission needs
specially trained mechanics, and introduces its special complications.
Let us take the four agents in order and briefly consider their value.
_Steam_ is so largely used in all departments of engineering that its
working is better understood by the bulk of average mechanics than
hydraulic power, compressed air, or electricity. But for marine work
it has very serious drawbacks, especially on a war vessel. Imagine
a ship which contains a network of steam-pipes running from end to
end, and from side to side. The pipes must, on account of the many
obstacles they encounter, twist and turn about in a manner which might
be avoided on land, where room is more available. Every bend means
friction and loss of power. Again, the condensation of steam in long
pipes is notorious. Even if they are well jacketed, a great deal of
heat will radiate from the ducts into the below-deck atmosphere, which
is generally too close and hot to be pleasant without any such further
warming. So that, while power is lost, discomfort increases, with a
decided lowering of human efficiency. We must not forget, either,
the risk attending the presence of a steam-pipe. Were it broken, by
accident or in a naval engagement, a great loss of life might result,
or, at least, the abandonment of all neighbouring machinery.
For these reasons there is, therefore, a tendency to abolish the direct
use of steam in the auxiliary machinery of a modern vessel.
_High-pressure water_ is free from heating and danger troubles, and
consequently is used for much heavy work, such as training guns,
raising ashes and ammunition, and steering. One of its great advantages
is its inelasticity, which prevents the overrunning of gear worked
by it. Water, being incompressible, gives a "positive" drive; thus,
if the pump delivers a pint at each stroke in the engine-room a pint
must pass into the motor, assuming that all joints are tight, and the
work due from the passage of one pint is done. Air and steam--and
electricity too, if not very delicately controlled--are apt to work in
fits and starts when operating against varying resistance, and "run
away" from the engineer.
An objection to hydraulic power is, that all leakage from the system
must be replaced by fresh water manufactured on board, which, as we
have seen, is no easy task.
_Compressed air_, like steam, may cause explosions; but when it escapes
in small quantities only it has a beneficial effect in cooling and
freshening the air below decks. The exhaust from an air-driven motor is
welcome for the same reason, that it aids ventilation. On a fighting
ship it is of the utmost importance that the _personnel_ should be in
good physical condition; and when the battle-hatches have been battened
down for an engagement any supply of fresh oxygen means an increased
"staying power" for officers and crew. Poisoned air brings mental
slackness, and weakening of resolve; so that if the motive power of
heavy machinery can be made to do a second duty, so much the better for
all concerned.
Compressed air also proves useful as a water-excluder. If a vessel
contain, as it should, a number of water-tight compartments, any water
rushing into one of these can be expelled by injecting air until the
pressure inside is equal to that of the draught of water of the vessel
outside.
On land compressed-air installations include reservoirs of large size
in which air can be stored till needed, and which take the place of
the accumulator used with hydraulic power. On shipboard want of space
reduces such reservoirs to minimum dimensions, so that the compressors
must squirt their air almost directly into the cylinders which do
the work. When the load, or work, is constantly varying, this direct
drive proves somewhat of a nuisance, since the compressors, if worked
continuously at their maximum capacity, must waste large quantities of
air, while if run spasmodically, as occasion demands, they require much
more attention. It is therefore considered advisable by some marine
engineers to make compressed air perform as many functions as possible
when it is present on a vessel. The United States monitor _Terror_
is an instance of a warship which depends on this agency for working
her guns and turrets, handling ammunition, and--a somewhat unusual
practice--controlling the helm. The last operation is performed by
two large cylinders placed face to face athwart the ship. They have
a common piston-rod, in the middle of which is a slot for the tiller
to pass through. Air is admitted to the cylinders by a valve which
is controlled by wires passing over a train of wheels from different
stations on the ship. An ingenious device automatically prevents the
tiller from moving over too fast, and also helps to lessen the shocks
given to the rudder by a heavy sea.
We now come to _electricity_, the fourth and most modern form of
transmission. Its chief recommendation is that the wires through which
it flows lend themselves readily to a tortuous course without in any
way throttling the passage of power. And as every ship must carry a
generating plant for lighting purposes, the same staff will serve to
tend a second plant for auxiliary machinery. Electric motors work with
practically no vibration, are light for their power, and can be very
easily controlled from a distance. They therefore enjoy increasing
favour; and are found in deck-winches, anchor-capstans, ammunition
hoists, ventilation blowers, and cranes. They also control the
movements of gun-turrets, having been found most suitable for this work.
If the current were to get loose in a ship it would undoubtedly cause
more damage than an escape of compressed air or water. Electricity,
even when every known means of keeping it within bounds has been tried,
is suspected of causing deterioration to the metalwork of ships. But
these disadvantages are not serious enough to hamper the progress of
electrical science as applied to marine engineering; and the undoubted
economy of the electric motor, its noiselessness, its manageableness,
and comparatively small size will, no doubt, in the future lead to its
much more extensive use on board our floating palaces and floating
forts.
FOOTNOTES:
[16] F. M. Bennett, in the Journal of the American Society of Naval
Engineers.
[17] Charles V. Daly, in _The Magazine of Commerce_.