The Atlantic Monthly, Volume 05, No. 29, March, 1860

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.[7 - 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.]

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.

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.[8 - 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.] 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 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.

Her dimensions are as follows:—

FT. IN.

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

Displacement. tons. 6050

Diameter of cylinders. 8 2.45

Length of stroke. 5 3.06

Diameter of propeller. (4 bladed) 19 0.70

Pitch " " mean) 37 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,[9 - For debarking a regiment or two of Zouaves on the shores of the Adriatic or upon the coast of Ireland.] 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 cruises 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 steam-power 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 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.