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 shiff, 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 paddlewheel, 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 screwfrigate 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, 183 7, 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 6 73 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.1
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 he 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 screwsteamers 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.
Much 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 faroff continents.
In consequence of the success of the Archimedes, the Admiralty ordered the Rattler to be fitted with a screw, ami 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.2
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, bv 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 maybe 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 cautions 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 nauticomilitary science.
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 trunkengine appears to be the favorite, and had performed so well in the Encounter of fourteen guns, the Arrogant of fortysix, 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.3
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 warsteamer 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 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.
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 resists ance of the after stern-post.4 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 manof-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 ?
The best illustration of the effects of a dragging propeller was afforded on the departure of a Russian squadron from Cronstadt, bound to the Amour, in 1857’58, consisting of three sloops of war barkrigged, 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 reportted 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 Iter 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.5
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 : —
|Guns.||Horse Power.||Screw.||Speed.||Days’ Fuel.||Sail Equipment.|
|The Arrogant||46||360||2 Blades||9 knots||8 days||Ship full rig|
|The Dauntless||24||580||"||11 “||11 “||“ light “|
|The Encounter||14||360||"||10 1/2 “||6 “||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-topsad 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 screwships 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 diflicult problem, the construction of a screwman-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 screwpropeller, 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.6
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 distinguisked 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.
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 navylist 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 ot 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 thirtv-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 screwfrigates, 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 readymade.
In considering the auxiliary screwfrigate 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 sailships,— 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 be kept low, and the requisite power and stability combined.
Intimately connected with her sailingpower 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 topmasts, 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 under 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 steamfleet, the United States will not have to encounter tedious and costly experiments, nor to incur the risk of failure.7 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.
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 manof-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-vitæ,— the invention of Mr. Penn, of Greenwich, near London.
The lignum-vitic 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.
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.
Her dimensions are as follows: —
Length extreme. .262 6.40
Length at load-line. 234 0.94
Beam. 53 8.38
Height between decks..... 6 8.72
Height of lower port sill. 7 2.63
Depth of hold. 26 9.34
Deep-load draft. 25 3
Immersed cross section, sq. ft. 1063.48
Diameter of cylinders... 8 2.45
Length of stroke.. 5 3.06
Diameter of propeller... .(4 bladed) 19 0.70
Pitch “ “ .. (mean) 27 11
She has eight boilers, each having five furnaces, consuming, at full speed, (12.14 knots,) 143 tons of coal per day, for which she stows five days' supply. The boilers and engines occupy eighty-two feet in the length of the ship.
The trial of this ship has established the practicability of adapting a propeller to a ship of the largest class, so as to insure great speed, and constitute a most effective man-of-war for certain purposes and in certain situations; but when the great weight of the engines is considered, and the large space they occupy in the vessel,— thereby diminishing the stowage of supplies,— and further, that, after the coal is exhausted, the ninety-gun ship has but the sail of a sixty-gun ship to rely upon, it is not easy to avoid the conclusion, that, however useful such a vessel may be for short passages,8 and in those seas in which her supplies of coal and provisions may be constantly replenished, her sphere of action must be very limited, and she could not be relied upon for the long eruises and various services on which an ordinary line-of-battle ship is employed.
A ship constructed on the plan of the Napoléon, for the sake of gaining a speed of twelve knots per hour for the distance of about two thousand two hundred miles, is compelled to sacrifice a great part of her efficiency in several most important particulars.
In time of war, at short distances from port, for the defence of bays or harbors or the Florida channel, for the speedy transport of troops to an adjacent coast, or to force a blockade, such a vessel would undoubtedly be a most valuable addition to our navy : but her employment must necessarily be confined to such circumstances and such situations ; for should she unluckily fall in with an enemy’s squadron, with her coal expended, or her machinery rendered useless by any of the numerous accidents to which steam-machinery is so constantly exposed, with her comparatively light rig, and want of stability in consequence of losing so great a weight of coals, she would hardly prove a very formidable opponent.
Therefore, while admitting the importance and necessity of providing for special service a small class of fast, full-power steamers, it is submitted that the auxiliary screw-steamer is the description of ship to which the largest and best consideration should be devoted ; for to the nation possessing the most efficient fleet of such vessels must belong the dominion of the sea. And while their cost is counted, let it at the same time be remembered that their value can be estimated only by the character of the service they may render, and that their capacity for aggression abroad makes them the best defence at home.
Having briefly referred to the various views entertained in regard to the steampower with which the navy should be furnished, it will be seen that a difference of opinion on this important subject may most reasonably be entertained.
None can doubt the advantages of celerity to a man-of-war, yet many believe it would be too dearly purchased by the sacrifice of space to such an extent as would require supplies to be often replenished ; as this necessity would in war confine the operations of the navy to our own shores.
On the other hand, it is admitted, that, without high speed, a ship of war cannot exercise many of her most important functions,— that she can neither choose an engagement, protect a convoy, nor enforce a blockade.
The best experience affirms the policy of giving to our cruisers as large steampower as is consistent with a due development of all other warlike qualities ; for what would avail the superior armament of a ship, if the option of fighting or flying remain with her adversary, which must be the case when the latter commands higher speed ? The introduction of improved ordnance, throwing heavy shells with great precision at long ranges, gives increased importance to celerity; for in any future fleet-fight, victory should belong to that flag having at command a steam-squadron of superior speed, which may thereby be concentrated upon any point without having been long under fire.
May not the command of a maximum speed of thirteen knots be obtained from the machinery now employed for a maximum speed of ten knots? It evidently may, and with great economy, too, by the simple introduction of artificial draft, and the use of steam of higher pressure, when requiring the highest speed. At present, in our men-of-war, the boilers are proportioned for natural draft, burning about twelve pounds of coal per square foot of grate per hour, and for a steam-pressure of fifteen pounds per square inch. If, then, the boilers be proportioned to burn at the maximum, with blowers, say twenty-two pounds of coal to the square foot of grate, and to generate steam of forty pounds to the square inch, we shall double the power developed by the machinery, and consequently derive from it the same speed that could be attained without blowers from double the machinery; while the natural draft and the usual pressure of fifteen pounds would give sufficient speed for ordinary service. The inconvenience of the higher pressure with blowers could well be endured for the short and occasional periods during which they would be required.
To create a perfect screw-frigate, a ship with sail-power complete, and efficient for any service that may be required, the endeavor should be made — by getting rid of every dispensable article of weight or bulk, and without reducing supplies below three months’ provisions and six weeks’ water—to find space and displacement for an engine of sufficient force to drive her thirteen knots an hour, together with at least ten days’ full consumption of fuel; and this, it is believed, might be successfully accomplished in ships of the dimensions of the Wabash, beginning with a judicious reduction of spare spars, spare sails, and spare gear, and by the addition of blowers to their present machinery : a subject which should immediately receive the earnest consideration of a commission of the most intelligent officers.
Having fixed upon the proportions of hull and spars, the form of propeller, and the plan of engine, a cautious discrimination should be exercised in multiplying the types of either. Besides economy, many other advantages would flow from a judicious regard to similarity in build; as it would permit us to relieve our ships of many of the spare spars with which they are incumbered, and we should probably not again hear of suspending the operations of a frigate thousands of miles away, until a crank or rod could be sent to her; because, when ships of the same class are cruising together, by a careful distribution of spare spars and machinery among them, it is hardly probable that damage would be sustained, or loss of spars or “ break down ” occur, which might, not be remedied by the resources of the squadron.
On the other hand, this system must not be carried to a Chinese extreme, lest we follow too long a false direction,— thus losing the advantage of improvements constantly being made. For such is the change in all things pertaining to maritime war, that neither model of hull, plan of engine, nor mould of ordnance is best, unless of the latest creation. True progress will be most judiciously sought in not departing too suddenly and widely from the established order.
- For a particular account of the Princeton, by B. F. Isherwood, U. S. N., see Journal of the Franklin Institute for June, 1853.↩
- 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.↩
- “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.↩
- Might not a metallic stern-post, combining strength, lightness, and little resistance, be introduced?↩
- Russian Nautical Magazine, No. XLI., December, 1857.↩
- 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.↩
- The constructors and engineers of the navy arc unsurpassed in professional art or science, and when conjoined with naval officers— who should always determine the warlike 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.↩
- For debarking a regiment or two of Zouaves on the shores of the Adriatic or upon the coast of Ireland.↩