The earliest conception of an auxiliary motive power in navigation
is contemporaneous with the first use of the wind; the name of the
inventor, "unrecorded in the patent-office," is lost in the lapse of
ages. The first motor was, undoubtedly, the hand; next followed the
paddle, the scull, and the oar; sails were an after-thought, introduced
to play the secondary part of an auxiliary.
Scarce was man in possession of this means of _impressing_ the wind, and
resting his weary oar, than, scorning longer confinement to the coast,
he boldly ventured upon the conquest of the main. Under the same
impulse, the tiny skiff, in which he hardly dared to quit the river's
bank, was enlarged, and made fit companion of his distant emprise. These
footprints of the infant steps of navigation may all still be traced
among the maritime tribes of the Pacific.
From that period sails became the chief motor, and the paddle and the
sweep auxiliaries,--which position they still hold to some extent, even
in vessels of considerable burden. But as the proportions of naval
architecture enlarged, these puny instruments were thrown aside;
although the importance and necessity of some such auxiliary in the
ordinary exigencies of marine life have always been felt and it has long
been earnestly sought.
From the first successful application of steam to navigation--by Fulton,
in 1803--it was supposed to be the simplest thing in the world to
provide ships with an auxiliary motor; but the result has shown the
fallacy of this conception.
For more than twenty years steam-navigation has advanced with giant
strides, overstepping several times the limits which science had
assigned it; but the paddle-wheel, by which the agency of steam has
been applied, forms so bad an alliance with canvas, and supplies so
indifferently the requirements of a man-of-war, that it has been
impossible by this intermediary to render steam the efficient coadjutor
of sails; and it is for this reason that steam so speedily took rank
as a primary motor upon the ocean; for, in all the successful marine
applications of steam by means of the paddle, steam is the dominant
power, and sails the accessory, or almost superfluous auxiliary. It is
the screw alone, in some of its modifications, which offers the means of
a successful and economical adaptation of steam to ships of war or of
commerce; for it is susceptible of a more complete protection than, the
paddle, and of an easy and advantageous combination with canvas.
The screw-propeller, in fact, has assumed so important a part in all
naval enterprise, that it may not be without interest to trace briefly
its rise and progress to the consideration it now commands, and
to review, in general terms, the various experiments by which the
screw-frigate has been brought to its present high state of efficiency,
excelling, for purposes of war, all other kinds of vessels.
As early as 1804, John Stevens, of Hoboken, New Jersey, engaged in
experiments to devise some means of driving a vessel through the water
by applying the motive power at the stern, and with a screw-propeller
and a defective boiler attained for short distances a speed of seven
knots; and it is surprising, that, with the genius and determination so
characteristic of his race, he should have abandoned the path on which
he appears to have so fairly entered.
Within the last half-century numerous attempts of a similar character
have been made in Europe and America; but although many of the
contrivances for this purpose were exceedingly ingenious, and the
success of some of the experiments sufficient, one would suppose, to
excite the interest of the public and encourage perseverance in the
undertaking, yet in no instance were they followed by any practical and
useful results until the year 1836, when both Captain Ericsson and
Mr. F. P. Smith so fully demonstrated the speed and safety with which
vessels could be moved by the screw-propeller, as to convince every
intelligent and unprejudiced mind of the importance of their inventions,
and immediately to attract the attention of the principal naval powers
of the world.
Captain Ericsson is a native of Sweden, but for some years previous to
1836 he had resided in England, where he had become known as an engineer
and mechanician of distinguished ability.
In July, 1836, he took out a patent in England for his method of
propelling vessels; and during that year the results of his experiments
with a small boat were so satisfactory, that in the following year he
built a vessel forty-five feet long, with eight feet beam, and drawing
three feet of water, called the Francis B. Ogden, in compliment to the
gentleman then consul of the United States at Liverpool, who was the
first person to appreciate the merits of his invention, and to encourage
him in his efforts to perfect it. This vessel was tried upon the Thames
in April, 1837, and succeeded admirably. She made ten knots an hour, and
towed the American ship Toronto at the rate of four and a half knots an
hour; and in the following summer, Sir Charles Adam, one of the Lords
of the Admiralty, Sir William Symonds, the Surveyor of the Navy, and
several other scientific gentlemen and officers of rank, were towed by
her in the Admiralty barge at the speed of ten miles an hour.
Notwithstanding this demonstration of the powers of his vessel, Captain
Ericsson did not succeed in exciting the interest of any of the persons
who witnessed the performance; and it seems almost incredible that no
one of them had the intelligence to perceive or the magnanimity to admit
the importance of his invention. But, fortunately for Ericsson and the
reputation of our country, he soon after met with Captain Stockton, of
the United States navy, who at once took the deepest interest in
his plans. The result of one experiment with Ericsson's steamer was
sufficient to convince a man of Stockton's sagacity of the immense
advantages which the new motor might confer upon the commerce and upon
the navy of his country, and forthwith he ordered an iron steamer to be
built and fitted with Ericsson's propeller. This vessel was named the
Stockton, and was launched in July, 1838, and, after being thoroughly
tested and her success demonstrated, she was sent under sail to the
United States in April of the next year, and was soon after followed by
Captain Ericsson; when, in consequence of the representations of Captain
Stockton, the government ordered the Princeton to be built under
Ericsson's superintendence, and to be fitted with his propeller.
The Princeton, of 673 tons, was launched in April, 1842, and her
propeller, of six blades, of thirty-five feet pitch, and of fourteen
feet diameter, was driven by a semi-cylinder engine of two hundred and
fifty horse-power, and all her machinery placed _below_ the water-line.
Her smoke-stack was so arranged that the upper parts could be let into
the lower, so as not to be visible above the rail; and as the anthracite
coal which she used evolved no smoke, she could not, at a short
distance, be distinguished from a sailing-ship.
Her best speed under steam alone, _at sea_, was 8.6, and under sail
alone, 10.1 knots; her mean performance under steam and sail, 8.226; and
considering the imperfect form of boiler employed, and the small
amount of fuel consumed, it may be doubted if this has since been much
excelled. She worked and steered well under canvas or steam alone, or
under both combined; was dry and weatherly, but pitched heavily, and was
rather deficient in stability.
[Footnote: For a particular account of the Princeton, by B. F.
Isherwood, U. S. N., see _Journal of the Franklin Institute_ for June,
1853. Taking everything into consideration, the Princeton was a most
successful experiment, and, in her day, the most efficient man-of-war of
her class. By her construction the government of the United States had
placed itself far in advance of all the world in the path of naval
improvement, and it is deeply to be regretted that it did not avail
itself of the advantage thus gained; that it did not immediately order
the construction of other vessels, in which successively the few defects
of the Princeton might have been corrected; that it did not persist in
that path of improvement into which it had fortunately been directed,
instead of suffering our great naval rivals to outstrip us in the race,
and compel us at last to resort to them for instruction in that science
the very rudiments of which they had learned from us.]
The success of the Princeton was followed by the general adoption in
America of the screw-propeller. When Ericsson left England, he confided
his interests to Count Rosen, who, in 1843, placed an Ericsson propeller
in the French frigate Pomone, and soon afterwards the British Admiralty
determined to place it in the Amphion. Not only was the performance of
these vessels highly satisfactory, but they were the first ships in the
navies of Europe in which the great desideratum was secured of placing
the machinery below the load-line. Ericsson's propeller having been the
first introduced into France, it was generally adopted; but afterwards,
in consequence of the accounts of Smith's screw received from England,
it underwent various modifications.
Such was the result of Ericsson's labors; it now remains to relate the
success of Smith. The efforts of either had been sufficient to have
secured to navigation the inestimable advantages of screw-propulsion,
but their rivalry probably hastened the solution of the problem.
In May, 1836, Mr. F. P. Smith, a farmer of Hendon, in England, took out
a patent for his screw-propeller, and exhibited some experiments with it
attached to a model boat, and in the following autumn built a boat of
six tons' burden, of ten horse-power, and fitted with a wooden screw.
This vessel was kept running upon the Thames for nearly a year, and her
performance was so satisfactory, that Mr. Smith determined to try her
qualities at sea; and in the course of the year 1837, he visited in her
several ports on the coast of England, and proved that she worked well
in strong winds and rough water.
These trials attracted much attention, and at last awakened the interest
of the Admiralty, who requested Mr. Smith to try his propeller on a
larger vessel, and the Archimedes, of ninety horse-power and 237 tons,
built for this purpose, was launched in October, 1838, and made her
experimental trip in 1839. It was thought that her performance would be
satisfactory, if she could make four or five knots an hour; but she
made nearly ten! In May, 1839, she went from Gravesend to Portsmouth,
a distance of one hundred and ninety miles, and made the run in twenty
hours.
In April, 1840, Captain Chappel, R. N., and Mr. Lloyd, Chief Engineer of
Woolwich Dockyard, were appointed by the Admiralty to try a series
of experiments with her at Dover. The numerous trials made under the
superintendence of these officers fully proved the efficiency of the new
propeller, and their report was entirely favorable.
The Archimedes next circumnavigated Great Britain under command of
Captain Chappel, visiting all the principal ports: she afterwards
went to Oporto, Antwerp, and other places, and everywhere excited the
admiration of engineers and seamen.
Up to this period, the British engineers were nearly unanimous in the
opinion that the use of the screw involved a great loss of power, and
they had concluded that it could not be adopted; but it was impossible
any longer to resist the impressions made on the public by the
demonstration which had been given both by Smith and Ericsson; and
although the engineers were still unwilling to admit the screw to a
comparison with the paddle, it was evident that their first conclusions
regarding it were erroneous, and thereafter it was viewed by them with
less disdain and spoken of more hopefully. One of the great objections
by engineers to the use of the screw was their inability, at the time of
its introduction, to construct properly a screw engine,--that is to say,
a direct-acting horizontal engine, working at a speed of from sixty to
one hundred revolutions per minute,--all their experience having been in
paddle-wheel engines, working from ten to fifteen revolutions per
minute. The peculiar mechanical details required in the screw engine,
the necessity for accurate counterbalancing, etc., were then unknown,
and had to be learned from a long succession of expensive failures. In
England, the first machines applied to the screw were paddle-wheel
engines, working it by gearing; there were consequently lost all the
advantages of the reduced cost, bulk, and weight of the screw engine
proper, including, for war purposes, the important feature of its being
placed below the water-line. At first, the screw had not only to contend
with physical difficulties, but to struggle against nearly universal
prejudice; many inventors had succumbed to these obstacles, and
therefore too much applause cannot be bestowed upon those who,
unsustained by public sympathy, and in defiance of a prevailing
skepticism, maintained their faith and courage unshaken, and gallantly
persisted in their efforts, until crowned with a world-wide success.
Ericsson, before interesting himself with the screw, was, as has been
seen, an engineer and mechanician of distinguished ability; whereas
Smith, in commencing his new vocation, had all to acquire but his first
conception. Ericsson could rely upon the fertility of his own genius,
was his own draughtsman, and designed his own engines, accommodating
them to the new propeller by dispensing with gearing, and adapting
them to a speed of from thirty to forty revolutions,--a great and bold
advance for an initiative step. Smith, on the contrary, not being an
engineer, had to intrust the execution of his plans to others, whose
knowledge of construction was in the routine of paddle-wheel engines;
and this accounts for the fact, that all the earliest British
screw-steamers were driven by gearing. This want of mechanical resources
on the part of Smith added to the difficulties of his career; but his
resolution and perseverance rose superior to all obstacles, and carried
him to the goal in triumph. Briefly, then, these were the respective
merits of Smith and Ericsson, in the introduction of screw-propulsion;
and it is much to their honor, that, throughout their career, no
narrow-spirited jealousies dimmed the lustre of a noble rivalry.
Such was the origin of the new motor,--the mighty engine by which
armadas are marshalled in battle-array, the burdens of commerce borne to
distant marts, the impatient emigrant transferred to the promised land,
and by which the breathings of affection, the pangs of distress, and the
sighs of love are wafted to far-off continents.
In consequence of the success of the Archimedes, the Admiralty ordered
the Rattler to be fitted with a screw, and it was no small satisfaction
to find that her double-cylinder engines could be easily adapted to the
new propeller. She is of 888 tons, and two hundred horse-power, and was
launched in the spring of 1843, being the first screw-vessel in the
British navy.
In the course of the two succeeding years, she was tried with a great
many different screws, and numerous experiments were made to discover
the length, diameter, pitch, and number of blades of the screw, most
effective in all the various conditions of wind and sea. A screw of two
blades, each equal to one-sixth part of a convolution, and of a uniform
pitch, was, on the whole, found to be the most efficient, and this is
the screw now adopted in most of the ships of all classes in the British
navy.[1]
A propeller of very different construction, which had given great
results in a ship of the Peninsular and Oriental Steamship Company, and
was afterwards exhibited in the docks at Southampton, here claims a
passing notice. This propeller is so constructed as to enable the
engineer to regulate the speed of the piston; for _the pitch of the
screw can be increased or diminished at pleasure_. Thus, with a fair
wind, by increasing the pitch, without increasing the revolutions, the
full power of the engine is effectually exerted in driving the ship,
instead of consuming fuel in driving the engine to no purpose; and with
a headwind, by diminishing the pitch, the engines are made to do their
utmost duty; and when the ship is under canvas only, the blades of the
propeller may be placed in line with the stern-post, and thus offer
little resistance. Another advantage claimed for this propeller (known
as Griffith's) is, that, in the event of breaking a blade, it may be
readily replaced by "tipping the ship"; which method merits careful
consideration by engineers, as does especially every new propeller which
promises a more perfect alliance with canvas.
To resume the narrative,--the speed of the Rattler was afterwards tested
by a trial with the Alecto, a paddle-wheel steamer of equal power,
built from the same moulds; and the result was so favorable, that the
Admiralty ordered the construction or conversion of _twenty-three_
vessels as screw-steamers, and thus was laid the foundation of the
present formidable steam-navy of England.
The superiority which has been asserted for the Princeton was
established during the Mexican War by her performance before Vera Cruz
as a blockading ship of unprecedented efficiency, which, having been
displayed under the admiring observation of a British squadron, tended
more than any other single event to confirm the Admiralty in the
conclusions to be drawn from the experiments just related, and to decide
them in the adoption of the screw as the best auxiliary of sail, the
best mechanical motor upon the ocean. Thus did England, in embracing at
once the practical demonstration of the Princeton, display that forecast
by which she won her ascendency at sea, and the vigilance with which
she maintains it; whilst our own government awaited, in unbecoming
hesitation, the results which England's more extended trials with the
screw might develop.
This cautious policy, rather than the bold and liberal course which the
maritime genius of the country demands, condemned us for long years to
inaction, until, at length, the absolute necessity for the renewal of a
portion of our naval force produced the "Minnesota" class of frigates.
Although they developed little that was absolutely new, they are very
far from being imitations; but in model, capacity, equipment, and above
all in their armament, they have challenged admiration throughout the
world, and called from a distinguished British admiral in command the
significant declaration, that, until he had seen them, he had never
realized his ideal of a perfect man-of-war.
A leading idea in the conception of these ships was to reduce the number
of gun-decks from two and three to a single deck, and, consequently, the
space in which shells could be lodged. This is a consideration which
must, it is believed, sooner or later govern in naval construction;
although France and England, long accustomed to measure the power of
ships by the number of gun-decks, may be more slow in following our lead
in this respect than in imitating the increased calibre of our ordnance.
The new classes of steamers preparing for sea, of which the Hartford and
Iroquois are types, promise to be most efficient ships, and to reflect
much credit upon our naval authorities for their bold, yet judicious
departure from traditions which had long hampered the administration of
this important branch of the public service. Although the reflection is
seldom made, it is nevertheless true, that much of the reputation
enjoyed and of the influence exercised by the United States is due to
the efficiency of her navy; and if these are to remain undiminished,
then it is of the utmost consequence that the national ships should
always represent the highest advancement of nautico-military science.
[Footnote 1: A series of experiments with the screw were made on board
the Dwarf in 1845, and on board the Minx in 1847 and 1848, but the
results did not materially differ from those previously obtained. In the
Rattler, Dwarf, and Minx twenty-nine different propellers were tried.]
The efficiency of the screw having been demonstrated, it was seen that
the next requirement for a war-steamer was to place her machinery below
the waterline; and hence arose a demand for an entirely new description
of engines, which it was clear would make a great change in all the
labors of the engineer and machinist. Such change it was evident would
greatly enhance the risk of failure, and therefore it was determined by
the Admiralty to insure success in this very difficult task by enlisting
all the best talent of the country. Accordingly, for the twenty-three
ships an equal number of screw engines were ordered; and as with the
constructors, so with the engineers, each was required to comply
with certain conditions, yet each was permitted to put forth his own
individuality, and each has illustrated his views of what was required
by a distinct plan of engine.
The wise and liberal action of the British Admiralty, which faltered at
no expense, and made trial of every improvement in machinery that gave
assurance of good performance and promised in any way to increase
the efficiency of the fleet, produced no less than fourteen distinct
varieties of the screw engine. Among them all, Penn's horizontal
trunk-engine appears to be the favorite, and had performed so well
in the Encounter of fourteen guns, the Arrogant of forty-six, the
Impérieuse of fifty, and the Agamemnon of ninety, that two years ago
it had been placed, in about equal proportions of two hundred, four
hundred, six hundred, and eight hundred horse-power, on board of forty
ships and many smaller vessels of the British navy; it had fulfilled all
the promises made for it, without in any instance requiring repairs.
These engines comply with all the conditions reasonably demanded in
the machinery of a man-of-war; they lie very low, and the fewness and
accessibility of their parts leave scarcely anything to be desired;--a
lighter, more compact, or more simple combination has yet to be
conceived.[1]
In all the ships above referred to the connection of the engines is
direct, and many of them are driven at rates varying from fifty to
seventy-five revolutions. This point is dwelt upon because it is
observed that many engineers find difficulty in freeing themselves from
early impressions made by long-stroke engines, express apprehensions at
fifty and sixty revolutions, and stand ready to obviate the difficulty
by gearing,--which it is hoped may not henceforth be adopted in our
national ships. Geared engines are much heavier than those of direct
connection, and occupy more space,--a great consideration in ships where
room for fuel is in such demand, besides making it more difficult to
place them below the waterline,--a consideration which in men-of-war
should be regarded of paramount importance, as the engines of a
war-steamer should be as secure from shot as her magazine. Experience
has shown that the apprehensions entertained from the quick stroke of
direct engines were without foundation; and that, in auxiliary ships,
with a properly modelled propeller, there will be no necessity for a
very high speed of piston.
The form of engine generally adopted with great success in the later
screw-ships.
[Footnote 1: "Its large amount of friction" is an objection often
speciously urged against the trunk-engine, although the friction diagram
shows it to be actually less in this than in most other engines.] of
the United States navy is the "horizontal direct action," with the
connecting-rod returning from a cross-head towards the cylinder;
these engines make from sixty to eighty revolutions per minute.
The steam-valve is a packed slide with but little lap, and the
expansion-valve is an adjustable slide working on the back of the
steam-valve. The boilers are of the vertical water-tube type, with the
tubes above the furnaces, and are supplied with fresh water by tubular
surface-condensers, which, together with the air-pumps, are placed
opposite the cylinders.
While the vessels ordered by the Admiralty were on the stocks, it was
suggested by Mr. Lloyd that the model of their after-bodies was not that
most favorable to speed,--that they were too "full," and that a "finer
run" would be preferable. To settle this question, the Dwarf, a vessel
of fine run, was taken into dock, and her after-body filled out by three
separate layers of planking, so as to give it the form and proportions
of the vessels then building. These layers of planking could be removed
in succession, and the effects of a fuller or finer run upon the speed
of the vessel easily ascertained. A trial was then made, and the result
proved the correctness of Mr. Lloyd's opinion; the removal of the
different layers of planking increasing the speed from 3.75 to 5.75,
to 9, and finally to 11 knots. A trial between the Rifleman and the
Sharpshooter, vessels of four hundred and eighty tons and two hundred
horse-power, and the Minx and Teaser, of three hundred tons and one
hundred horse-power, gave similar results,--the speed in each trial
being twenty-four per cent. in favor of the finer run.
Although great efficiency and economy had now been attained, there was
still an important defect to be remedied, namely, the impediment to
speed and to evolution under sail presented by the dragging propeller;
which was accomplished by the invention of the "trunk" or "well," into
which the propeller can be raised at pleasure; and there is no longer
anything to prevent the construction of a screw-frigate which shall be
fit to accompany, under canvas only, a fleet of fast sailers, with the
assurance that she may arrive at the point of destination in company
with her consorts, having in reserve all her steam-power.
The mechanism by which the emersion of the screw is effected is as
follows:--There are two stern-posts; between these, and connecting them
with each other and with the keel, is a massive metallic frame, in which
rests another frame, or _châssis_, in which the screw is suspended; near
the water-line, the deck and wales are extended to the after stern-post,
and through an opening or trunk in this overhanging stern the frame
suspending the screw is raised by worms, working in a rack secured to
the frame, and operated from the deck, as shown in the accompanying
drawing,--or by a tackle, as is now most common. In the British ship
Agamemnon, of ninety guns, the propeller is raised by a hydrostatic
pump,--a neat arrangement, but liable to get out of order. When it is
desirable to raise the propeller, the blades are first placed in a
vertical position, and the operation of lifting is performed in a few
minutes.
The relative advantages of the propeller fitted to lift, and that which
is permanently fixed, have long been the subject of much discussion.
For merchant steamers, having an established route to perform, on which
the aid of steam is in constant demand, it is generally conceded that
the position of the screw should be permanent. The construction of the
ship is then less costly, while greater strength is preserved; and as
these vessels are out of port but for short intervals, should repairs be
needed, they have access to the docks. But for men-of-war the case is
widely different. Having frequently to keep the sea for long periods,
much under canvas, and often far distant from a dock-yard, they should
be provided with the means of lifting the screw to repair or to clear
it, or to be relieved from the impediment it offers to sailing and to
evolution, and also from the injurious "shake" occasioned by a dragging
propeller.
[Illustration: MODE OF LIFTING SCREW.]
On the other hand, the construction of a trunk or well impairs the
solidity of the stern, renders it much more vulnerable, and weakens its
defences, while it opposes to speed the very considerable resistance of
the after stern-post.[*] Nevertheless, no modern ship of the British
navy is without the means of raising her propeller, and the best opinion
of commanders and engineers of that service, of longest experience in
screw-ships, goes to establish the conviction, that, for men-of-war, the
advantages of being able to lift the propeller far more than outweigh
the objections urged against lifting. In this connection we mention the
fact, that all screw-ships "by the wind" have a strong tendency to
gripe. Would not this be obviated by having a gate or slide to fill out
the dead-wood when the screw is lifted?
[Footnote *: Might not a metallic stern-post, combining strength,
lightness, and little resistance, be introduced?]
The best illustration of the effects of a dragging propeller was
afforded on the departure of a Russian squadron from Cronstadt, bound to
the Amoor, in 1857-'58, consisting of three sloops of war bark-rigged,
and three three-masted schooners, under the flag of Commodore
Kouznetsoff. The vessels of each class were built from the same
moulds, and at the time of the experiment were of the same draft and
displacement. On clearing the land, signal was made to lift screws and
make sail. Soon after, all the squadron reported the execution of the
order, except the Voyerada sloop, which had the misfortune to break a
key in the couplings, and therefore could not lift her screw. Every
effort was tried to get out the key, and meanwhile a very instructive
example was presented to the squadron of the effect of a dragging
propeller on the speed of the vessel. The circumstances were as
follows:--The wind, a gentle breeze, right aft; the Voyerada carrying
all sail but the main course; the other two sloops holding way with
her with their topsails on the cap, and the schooners with their peaks
dropped. Under these conditions, the Voyerada, having her screw-blades
fixed horizontally, could scarcely keep her position, running two and a
half and three knots. The Voyerada next succeeded in getting her screw
vertical, when, without any change in the wind, the speed increased to
four and a half knots. The other sloops then mastheaded their topsails,
and the schooners peaked their gaffs. At length the Voyerada succeeded
in lifting her screw, when immediately all the sloops under the same
canvas continued their course, making six to six and a half knots. A
better example of the obstruction offered by a dragging propeller could
not have been afforded.[1]
The "shake," to which reference has been made, is the tremulous or
vibratory motion communicated to the after-body of the ship, and
particularly to the stern, by the revolution of the propeller, often
opening the seams, and in old ships sometimes starting the butts and
causing dangerous leaks. This movement arises from two causes,--one
inherent in the screw, the other due to its position in the deadwood.
The first cause is the difference in the propelling efficiency of the
upper and lower blades when in any other position than horizontal. The
centre of pressure of the lower blade, being at a greater depth below
the surface than the centre of pressure of the upper blade, acts upon a
medium of greater resistance to displacement, and the differential of
the pressures of the two blades produces inevitably a vibratory motion
in the stern of the vessel. This effect is greatly increased when the
clearance given to the screw in the dead-wood is too small; for the
reduction of the hydrostatic pressure at the stern-post, and the
increase of it at the rudder-post, on each passage of the blades, must
be followed by concussion. Therefore, if the "well," or distance between
the posts, be made sufficiently long in proportion to the screw, the
"shake" due to the latter cause can be almost entirely obviated.
In 1851, the British Admiralty selected three auxiliary screw-ships, of
different classes and qualities, for an experimental cruise, namely:--
[Footnote 1: _Russian Nautical Magazine_, No. XLI., December, 1857.]
---------------------------------------------------------------------
| Guns. | Horse | Screw. | Speed. | Day's | Sail
| | Power. | | | Fuel. | Equipment
---------------------------------------------------------------------
The | | | 2 | 9 | 8 |
Arrogant | 46 | 360 | blades | knots | days | Ship full rig
---------------------------------------------------------------------
The | | | 2 | 11 | 11 |
Dauntless | 24 | 580 | blades | knots | days | Ship light rig
---------------------------------------------------------------------
The | | | 2 | 10-1/2 | 6 |
Encounter | 14 | 360 | blades | knots | days | Barque
---------------------------------------------------------------------
They were ordered to pass round the Azores, each ship holding
her course, and using sail or steam, or both, as was deemed most
advantageous. An officer was sent on board each ship to keep a record of
her performance, and to note the time when and the position where, the
coal being entirely consumed, the contest ended. In this trial, the
Arrogant was found superior to the Dauntless, and both of them far
excelled the Encounter; indeed, no very different result was expected,
the object of the trial being to ascertain their relative as well as
positive value. These ships afterwards formed a part of the experimental
squadron stationed at Lisbon in the same year, which was composed of the
finest ships in the British navy.
It was believed by many officers, that a fast-sailing frigate, in a
reefed-topsail breeze, would be able to get away from any screw-ship;
but in a trial that took place between the Arethusa and the Encounter,
and the Phaëton and Arrogant, under circumstances the most favorable to
the sail-ships, it was found that the screw-ships, using both steam and
sail, had decidedly the superiority,--and that in fresh gales, with one,
two, or three reefs in the topsails, either "by the wind," or "going
free," the Phaëton and the Arethusa, the fastest sail-frigates in
the navy, were always beaten by the Arrogant. This result operated
powerfully in removing the repugnance to steam existing among all
classes of seamen; and the vast superiority of well-organized
screw-ships for the purposes of war is now so apparent, as to render
them the most important and indispensable part of every navy.
While the English were engaged in the trials here related, their rivals
on the opposite coast were not indifferent spectators. The French
were nearly as soon in the field of modern screw experiment as their
neighbors; and did the limits of this paper permit, it would be
instructive, as well as interesting, to trace the ingenious and
persevering steps by which they also approached the solution of that
difficult problem, the construction of a screw-man-of-war.
The first result of their efforts, La Pomone, screw-frigate, was shown
to the world in 1844, and after careful inspection, (in 1853,) it is
affirmed, such was the perfection of her general organization, that she
has hardly been excelled by any of her younger sisters.
The most complete course of experiments ever made, perhaps, with the
new motor, was that carried out by MM. Bourgois and Moll, of the French
navy, in 1847 and '48, which they verified by a second series in 1849.
These experiments were instituted to ascertain the relative efficiency
of all varieties of the screw-propeller, upon vessels of different
models and dimensions, and under all the varying conditions of wind and
sea, in order to determine the propeller best adapted to each particular
description of ship.[*]
Necessarily brief as is the notice of Gallic ingenuity and skill, the
acknowledgment must be made, that, for the invention of the trunk or
well, with its attendant advantages, navigation is indebted to Commander
Labrousse, of the French navy; and for a novel arrangement of the screw-
propeller, which has not attracted all the notice it deserves,
obligations are due to M. Allix, a distinguished engineer of that
service; and the propeller more recently introduced by M. Mangin, of the
same corps, if it performs all that is claimed for it, namely, that it
does away with the "shake," will be of great value.
[Footnote *: For a most interesting and instructive memoir upon these
experiments, the reader is referred to that admirable work, by Captain
E. Paris, of the French navy, _L'Hélice Propulsive_.]
In concluding this recognition of the contributions by France to
screw-propulsion, it is desired to submit a few general observations on
the French navy; for, although upon every sea the tri-color waves
over ships proudly comparing with those under any other flag, it is
nevertheless too commonly believed that the docks of France are crowded
and her navy-list swollen with hulks which are but the mouldering
mementos of the vast armaments hastily created during the Consulate and
the Empire; an illusion most hazardous to our interests abroad and our
security at home.
At the period of _the coup d'état_ of 1851, a Committee of Inquiry,
composed of the most experienced and intelligent officers and
distinguished legislators, had visited all departments of the navy, and
made the most careful investigations into every branch of the service.
Upon the evidence thus obtained, a report was submitted, providing for
the improvement of the condition of the officers and seamen, and the
increase, renewal, and remodelling of the _matériel_,--in fine, for the
correction of every abuse, the remedy of every evil, and the development
of all good existing in the navy. This report, stamped on every page
with patriotism and intelligence, commanded, even in the midst of
revolution, the support of all parties, the adhesion of every faction;
and has since, through all changes in the Ministry of the Marine, formed
the basis of the action of that department.
Under these auspices, France has in the last seven years organized the
means of promptly putting to sea a numerous fleet, composed of the most
modern and most powerful steamers, manned by efficient crews, commanded
by skilful officers; and now worthily maintains a position as a naval
power second only to that of Great Britain. At this moment, whilst
the British fleet includes but thirty-six screw line-of-battle ships,
mounting 3,400 guns, and propelled by 19,759 horse-power, that of France
may boast of forty such ships, mounting 3,700 guns, propelled by 27,500
horse-power; and while England has but thirty-eight screw-frigates,
France has forty-two.
In thus briefly summing up the forces of our ocean rivals, we cannot
avoid making some reflections suggested by the unpreparedness of this
country to meet any sudden burst of hostility. This not only involves
the risk of national humiliation, but paralyzes our diplomacy; since it
deprives us of that influence among the nations, which otherwise--from
the breadth of our territory, the value of our products, the activity
of our industry, the importance of our commerce, and the extent of our
maritime resources--we of right should hold.
No country is more interested than the United States in the maintenance
of peace; yet, even on the principle of economy, we may argue in favor
of a degree of preparation for war; for that calamity may best be
averted by taking from foreign powers the temptation to interfere with
us: all history showing that the justice and friendship of military
states are but slender guaranties for the peace of a nation unprepared
for attack.
It is vain to talk of husbanding financial resources for war, without
other preparation. When once embarked in hostilities, and in a position
to maintain our ground, large finances, judiciously used, will
ultimately command success; but no accumulation of funds can provide a
timely remedy for that weakness which cannot resist the first blow.
The national safety should no longer be left to chance, but be
established on a basis of certainty. A navy cannot be manufactured nor a
fortress built to meet an emergency, but should be kept ready-made.
In considering the auxiliary screw-frigate under the views already
offered, and in determining the canvas with which she should be
supplied, it will be well to refer, as the best guide, to the fastest
sail-ships,--the class which presents the greatest similarity in form to
that demanded in screw-ships. In these ships the great length of deck
offers every facility for the most advantageous spread of canvas;
consequently the centre of effort may he kept low, and the requisite
power and stability combined.
Intimately connected with her sailing-power is another branch of the
equipment of a screw-ship, which requires the most earnest, patient, and
intelligent consideration. Prepared to endure all the wear and tear of a
sail-ship, she should at the same time be ready for transmutation into
a steam-ship; namely, when, for any urgent service, her best powers of
steaming are required, she should be able to divest herself speedily of
yards and top-masts, and, the special service completed, resume all her
perfection as a sail-ship.
It would be out of place here to enter into details of equipment. In
naval affairs nothing is improvised, and a satisfactory conclusion upon
these points can be arrived at only through long experiment, and perhaps
frequent disappointment. Yet it is not doubted that the same ship may
exhibit a handy and efficient rig, develop a high velocity canvas, and,
without great power, a sufficient speed under steam.
In our navy, away from our own coast, sail must of necessity be the
rule, and steam the reserve or special power; and without abandonment of
our anti-colonial policy--with the depots of our rivals upon every sea,
yet not a ton of coal upon which we can rely--we should not dare to send
abroad a single ship which, whenever she gets up her anchor, must needs
also get up her steam.
Fortunately, in the creation of a steam-fleet, the United States will
not have to encounter tedious and costly experiments, nor to incur the
risk of failure.[1] The best form of hull, model of propeller, and plan
of engine are already so well established, that it is not easy to fall
into error; that which is most to be guarded against is the popular
demand, the prevailing mania for high speed,--for which single advantage
there is such a proneness to sacrifice every other warlike quality. That
measure of speed or power which will enable a ship to stem the currents
of rivers, to enter or leave a port in the face of a moderate gale, or
to meet the dangers of a lee-shore, should, it is conceived by many, be
sufficient; and for these exigencies a ship, which, with four months
supplies on board, can in calm weather and smooth water make nine to ten
knots under steam, has ample power. This moderate rate is far below the
popular mark; but, in considering this important question, it should not
be forgotten, that, unlike the paddle, the screw will always coöperate
with sail,--and that, if a ship would go far under steam, she must be
content to go gently. The natural law regulating the speed of a ship
is, that the power requisite to propel her varies as the cube of the
velocity.
[Footnote 1: The constructors and engineers of the navy are unsurpassed
in professional art or science, and when conjoined with naval
officers--who should always determine the war-like essentials of
ships--they are capable of producing a steam-fleet that would meet the
requirements of all reasonable conditions. We venture to say, that
the failures with which they have been charged would be found,
on investigation, to be solely attributable to undue extraneous
influences.]
Let it be distinctly understood what power is here meant. As the power
applied to the propulsion of a vessel is only that which acts upon her
in the direction of the keel,--and as, of the gross indicated power
developed by her engine, one portion is absorbed in working the organs
of its mechanism, another in overcoming the friction of the load, while
still other proportions are expended in the slip of the propeller and
in the friction of its surfaces on the water,--only that portion of
the gross power which remains is applied to propulsion; and it is this
remainder which varies in the ratio of the cube of the speed.
Hence a steamer, that with five hundred horse-power can make eight knots
per hour, will require rather more than one thousand horse-power to
drive her at the speed of ten knots,--the law being thus modified by the
increased resistance consequent upon the greater weight of the large
engines; and thus a limit to speed is imposed, depending upon the weight
of machinery which, relative to her dimensions, a ship can carry. A
ship, that at the rate of ten knots under steam may run twelve hundred
miles, can, at the speed of eight knots, and with the expenditure of
rather less fuel, run the distance of eighteen hundred miles; and
therefore it is, many contend, that a man-of-war for distant service
should not be laden with large engines, whose full power can rarely be
wanted, and which monopolize so great a space and displacement as to
render it impossible to carry fuel for their proper development.
It is true, that, with large power of engine, the vessel may command,
so long as her coals last, the advantage of high speed, and her large
cylinders will enable her, by working the steam very expansively, to use
her fuel with great economy; but there still remains the disadvantage of
the increased first cost of the machinery, and its greater weight and
bulk, to be permanently carried, whether used or not, and which, by
increasing the displacement of the vessel, proportionally diminishes her
speed.
The last great improvement in connection with the screw remains to
be noticed, namely, lining the "bushings" and "bearings" with
lignum-vitae,--the invention of Mr. Penn, of Greenwich, near London.
The lignum-vitae is introduced in the manner shown in the drawing. In
connection therewith, it must be said, that the length and diameter of
bearings has been increased far beyond the proportions of former years.
The "brasses" are bored out about three-sixteenths of an inch larger
than the shaft; then the recesses are slotted out for the reception of
the wooden strips. If care be taken with this part of the operation, any
number of strips can be supplied ready fitted, and to put in a set of
spare strips becomes a short and simple operation.
[Illustration]
Strange as it appears, these wooden bearings are far more durable than
those of metal, and in some ships they have endured for years without
any perceptible wear in those parts which, previously to this invention,
had occasioned so much trouble and expense. But for this important
discovery, it is thought by some of the most competent engineers that
they would have been compelled to abandon the use of the screw in heavy
ships.
The Napoléon, the type of the new steam-ships of the line in the French
navy, is a good illustration of a first-class, full-powered steamer.