MISAPPREHENSION OF THE HIGH COST OF STEAM MARINE PROPULSION: VIEWS OF THE NON-PROFESSIONAL: HIGH SPEED NECESSARY FOR THE DISTANCES IN OUR COUNTRY: WHAT IS THE COST OF HIGH ADEQUATE MAIL SPEED: FAST STEAMERS REQUIRE STRONGER PARTS IN EVERY THING: GREATER OUTLAY IN PRIME COST: MORE FREQUENT AND COSTLY REPAIRS: MORE WATCHFULNESS AND MEN: MORE COSTLY FUEL, ENGINEERS, FIREMEN, AND COAL-PASSERS: GREAT STRENGTH OF HULL REQUIRED: ALSO IN ENGINES, BOILERS, AND PARTS: WHY THE PRIME COST INCREASES: THEORY OF REPAIRS: FRICTION AND BREAKAGES: BOILERS AND FURNACES BURNING OUT: REPAIRS TWELVE TO EIGHTEEN PER CENT: DEPRECIATION: SEVERAL LINES CITED; USES FOR MORE MEN: EXTRA FUEL, AND LESS FREIGHT-ROOM: BRITISH TRADE AND COAL CONSUMPTION:THE NATURAL LAWS OF RESISTANCE, POWER, AND SPEED, WITH TABLE: THE RESISTANCE VARIES AS IS THE SQUARE OF THE VELOCITY: THE POWER, OR FUEL, VARIES AS THE CUBE OF THE VELOCITY: THE RATIONALE: AUTHORITIES CITED IN PROOF OF THE LAW: EXAMPLES, AND THE FORMULÆ: COAL-TABLE; NO. I.: QUANTITY OF FUEL FOR DIFFERENT SPEEDS AND DISPLACEMENTS: DEDUCTIONS FROM THE TABLE: RATES AT WHICH INCREASED SPEED INCREASES THE CONSUMPTION OF FUEL: CONSUMPTION FOR VESSELS OF 2,500, 3,000, AND 6,000 TONS DISPLACEMENT: COAL-TABLE; NO. II.: FREIGHT-TABLE; NO. III.: AS SPEED AND POWER INCREASE FREIGHT AND PASSENGER ROOM DECREASE: FREIGHT AND FARE REDUCED: SPEED OF VARIOUS LINES: FREIGHT-COST: COAL AND CARGO; NO. IV.: MR. ATHERTON'S VIEWS OF FREIGHT TRANSPORT.
MISAPPREHENSION OF THE HIGH COST OF STEAM MARINE PROPULSION: VIEWS OF THE NON-PROFESSIONAL: HIGH SPEED NECESSARY FOR THE DISTANCES IN OUR COUNTRY: WHAT IS THE COST OF HIGH ADEQUATE MAIL SPEED: FAST STEAMERS REQUIRE STRONGER PARTS IN EVERY THING: GREATER OUTLAY IN PRIME COST: MORE FREQUENT AND COSTLY REPAIRS: MORE WATCHFULNESS AND MEN: MORE COSTLY FUEL, ENGINEERS, FIREMEN, AND COAL-PASSERS: GREAT STRENGTH OF HULL REQUIRED: ALSO IN ENGINES, BOILERS, AND PARTS: WHY THE PRIME COST INCREASES: THEORY OF REPAIRS: FRICTION AND BREAKAGES: BOILERS AND FURNACES BURNING OUT: REPAIRS TWELVE TO EIGHTEEN PER CENT: DEPRECIATION: SEVERAL LINES CITED; USES FOR MORE MEN: EXTRA FUEL, AND LESS FREIGHT-ROOM: BRITISH TRADE AND COAL CONSUMPTION:
THE NATURAL LAWS OF RESISTANCE, POWER, AND SPEED, WITH TABLE: THE RESISTANCE VARIES AS IS THE SQUARE OF THE VELOCITY: THE POWER, OR FUEL, VARIES AS THE CUBE OF THE VELOCITY: THE RATIONALE: AUTHORITIES CITED IN PROOF OF THE LAW: EXAMPLES, AND THE FORMULÆ: COAL-TABLE; NO. I.: QUANTITY OF FUEL FOR DIFFERENT SPEEDS AND DISPLACEMENTS: DEDUCTIONS FROM THE TABLE: RATES AT WHICH INCREASED SPEED INCREASES THE CONSUMPTION OF FUEL: CONSUMPTION FOR VESSELS OF 2,500, 3,000, AND 6,000 TONS DISPLACEMENT: COAL-TABLE; NO. II.: FREIGHT-TABLE; NO. III.: AS SPEED AND POWER INCREASE FREIGHT AND PASSENGER ROOM DECREASE: FREIGHT AND FARE REDUCED: SPEED OF VARIOUS LINES: FREIGHT-COST: COAL AND CARGO; NO. IV.: MR. ATHERTON'S VIEWS OF FREIGHT TRANSPORT.
The foregoing arguments bring us to the conclusion thatsteam, however desirable, can not be profitably employed in commerce generally as an agent of transport; and that it is best applicable to the rapid conveyance of the mails, passengers, specie, and costly freights only. That this fact may be presented in a clearer light, and that we may see the almost incredibly high cost of rapid steaming, or the attainment of a speed sufficiently high for the carriage of important mails, it will be necessary to make some critical inquiries concerning the working cost of steam power, under any conditions, as applied to marine propulsion. Much misapprehension prevails on this point among nearly all classes of the people, and even among the rulers of the country whose action controls the destiny and uses of this valuable power. It is hardly to be expected, however, that gentlemen engaged actively in the all-engrossing pursuits of business or of public life, with a thousand different sets of ideas to be matured on a thousand different subjects, such as demand the attention of Congress, and the Departments of the Executive Government, should be practically or even theoretically acquainted with a profession which requires years of close application and study, and a wide field of practical, daily observation and experience. It would be as absurd for unprofessional gentlemen of any class, as well from the walks of statesmanship and the Government as from those of quiet private life, to assume an acquaintance with the theory and practice of navigation, and the cost, embarrassments, and difficulties attending steamship enterprise, as it would for any two or three of them to enter an ocean steamer for the first time of their lives, and essay to work the engines and navigate the ship across the seas. The skill and knowledge requisite for such a task would require years of application; and it can not be reasonably supposed that those entirely unacquainted with the theory and parts of an engine, should know much about its capabilities, or the cost attending its use.
But there are approximate conclusions, readily applicable to practice, at which even the unprofessional can arrive with certainty and security on a proper presentation of the prominent facts and theories concerned; and that these may be given to the public in a reliable and intelligible form, for the removal of the doubts and obscurities which have hung around the subject, is the chief object of this publication. This inquiry becomes the more important as the speed of American steamers is proverbially beyond that of any other steam vessels in the world. From the first conception of fluvial and marine steam propulsion by Fitch and Fulton, the public and the inventors themselves regarded the new application of this power with the more favor as it promised to be a means of shortening the long distances between the different parts of our own large country. And the same object has acted as a stimulus ever since to that increase of speed which has placed localities all over this country, hitherto days apart, now, probably, but as many hours. The slow trip through marshes and rivers, over hills and mountains, and by the meandering roads of the country, between New-York and Albany, once required from four to six days; but the attainment of twenty-five miles per hour in our fast river steamers has at length placed that capital within six hours of the Metropolis. And, as in this instance, so has the effort been throughout our whole country, and upon the ocean, until we have attained, both upon the rivers and the high seas, the highest speed yet known, notwithstanding the important fact that steamship building is a new and not fully developed species of enterprise in this country. We have already seen how imperatively the spirit of the age and the genius of our people demand rapid steam mails by both land and sea, and a rapid conveyance of passengers; and it would be unreasonable to suppose that if we required these for the development of our youth, they would beless necessary for the fruitful uses of manhood and maturity. It is abundantly evident that the American people are by nature and habit a progressive and unusually hurrying people; and it is not to be supposed that they will reverse this constitutional law of their nature in their attempts at ocean navigation.
To answer the question, "What is the cost of high, adequate mail speed?" requires something more than an inquiry into the quantity of fuel consumed; although this is the principal element of its cost. We must consider that the attainment and maintenance of high speed depend upon the exertion of a high power; and that,
I. High speed and power require stronger parts in every thing: in the ship's build, the machinery, the boilers, and all of the working arrangements:
II. High speed and power require a larger outlay in prime cost, in material and building, for the adequate resistance required by such power:
III. High speed and power require more frequent and costly repairs:
IV. High speed and power require more watchfulness, a more prompt action, and consequently more persons:
V. High speed and power require more fuel, more engineers, more firemen, and more coal-stokers.
1. These propositions are nearly all self-evident to every class of mind. That a high speed attained through the exertion of a high power will require stronger parts in every thing that exerts a force or resists one, is as manifest as that a force necessary to remove one ton of weight will have to be doubled to remove two tons. In the prime construction of the hull this is as requisite as in any other part. The resistance to a vessel, or the concussion against the water, at a low rate of speed, will not be very sensibly felt; but if that speed is considerably increased and the concussion made quicker without a corresponding increasein the strength of the frame and hull of the ship generally, we shall find the ship creaking, straining, and yielding to the pressure, until finally it works itself to pieces, and also disconcerts the engines, whose stability, bracing, and keeping proper place and working order depend first and essentially on the permanence and stability of the hull. If the resistance to a vessel in passing through the water increases as the square of the velocity, and if in addition to this outward thrust against the vessel it has to support the greater engine power within it, which has increased as the cube of the velocity, then the strength of the vessel must be adequate to resist without injury these two combined forces against which it has to contend.
The same increased strength is necessary also in the engines and boilers. It is admitted by the ablest engineers, and verified by practice, as will be shown in another part of thisSection, that to increase the speed of a steamer from eight to ten knots per hour, it is necessary to double the power, and so on in the ratio of the cubes of the velocity. Suppose that we wish to gain these two knots advance on eight. It is evident that, if the boilers have to generate, and the engines to use twice the power, and exert twice the force, they must have also twice the strength. The boiler must be twice as strong and heavy; the various working parts of the engine must be twice as strong: the shafts, the cranks, the piston and other rods, the beams, the cylinders, the frame work, whether of wood or iron, and even the iron wheels themselves, with every thing in any way employed to use the power, overcome the resistance, and gain the speed. There is no working arrangement in any way connected with the propulsion of the ship that does not partake of this increase; every pump, every valve, every bolt connected directly or indirectly with the engine economy of the ship.
2. In the second place, seeing that much greater strengthof parts is required to overcome the increased resistance, it is equally evident that this high speed and power thus require a larger outlay in every point of the prime construction of the vessel and engines by which the speed is to be attained. The hull's heavier timbers cost a higher price according to size than the direct proportion of size indicates. Large and choice timbers are difficult to get, and costly. The hull must also be strengthened to a large extra extent by heavy iron strapping and bracing, which, unlike the rest, cost in the ratio of the material used. So with the engines. The shaft, which weighs twice as much, does not cost only twice as much, but frequently three or four or five times as much. This arises not from the weight of the metal, as is evident; but from the difficulty of forging pieces that are so large. The persons engaged in the forging and finishing of the immense shafts, cranks, pistons, etc., used in our first class steamers, frequently consider that the last and largest piece is thechef d'œuvreof the art, and that it will never be transcended, even if equalled again. They have expended all of their skill and ingenuity in the task, and have not succeeded sometimes until they have forged two or three new pieces. When a great work of this kind is done, it may be discovered in the turning, polishing, and fitting up, that it has at last a flaw, and that it will not do for the service intended. As a matter of course, it must be thrown aside and a new piece forged. This was but recently the case with one of the shafts of the "Leviathan," in England. So with the shafts of the new Collins' steamer "Adriatic." They were forged in Reading, Pennsylvania, and in addition to their enormous prime cost had to incur that of shipment from the interior of Pennsylvania to the city of New-York. In all such cases the prime cost increases immensely, and to an extent that would hardly be credited by those not practically familiar with the subject.
3. Again, high or increased power and speed require more frequent and more costly repairs. Friction arises from the pressure of two bodies moving in opposite directions, and pressure results from the exertion of power, and in the ratio of the power applied. The amount of friction, therefore, is in the ratio of the power expended and of the extra weight of parts required for that power. But the effects of friction require a higher ratio when the power is greatly multiplied, as in the case of high speed. An immensely heavy shaft exerting an unusual force is certain to greatly heat the journals and boxes, and thus wear them away far more rapidly. Also a rapid motion of heavy parts of machinery, and the necessarily severe concussions and jarrings can not fail destroying costly working parts in the engine, and necessitating heavy and expensive repairs and substitutions. An ordinary engine working at a slow and easy rate, will not require one tenth the repairs necessary if it were working up to a high power and accomplishing a high speed. With any little derangement the engines can stop and the injury can be repaired before it reaches any magnitude. But with rapid mail packets the engines must run on, and the derangement which at first is small, will amount in the end, when the voyage is completed and the mails are delivered, to a sum probably ten or twenty times as great as in the case of the vessel that stops and makes her repairs as she requires them. The exertion of a high mail power causes many costly parts to burn out from unrelieved pressure and friction, which would not be the case under other conditions. It is also nearly impossible for the best built engines in the world to make fast time without breaking some important part at every trip or two, or so cracking and injuring it from the continued strain, that a wise precaution requires its removal to make the steamer perfectly sea-worthy. Every practical man knows these difficulties, and every steamship ownerestimates their importance according to the immense bills they occasion month by month, or the delays and losses which they cause unless he has expended large amounts of capital in providing other ships to take their place on such occasions of derangement.
Nor is the burning out of heavy brass, and composition, and steel pieces, or the breaking of large and troublesome parts in the engine the only source of repairs on a steamship. The boiler department is particularly fruitful in large bills of repairs, especially if it be necessary to attain a good mail speed. It stands to reason that if the whole ship can not be filled with boiler power, which with reasonably high fires, would give enough steam, then the boilers which are used must be exerted to their highest capacity, or the rapid speed can not be attained. Many suppose that the boilers may generate twice the quantity of steam without any appreciable difference in the wear and tear; but this is a decided error. For high speed, and what I mean by high speed is simply that which gives a sufficiently rapid transit to the mails, the fires must be nurtured up to their highest intensity and every pound of coal must be burned in every corner of the furnaces which will generate even an ounce of steam. This continued heat becomes too powerful for the furnaces and the boilers, and they begin to oxidize, and burn, and melt away, as would never be the case under ordinary heat. When the ship comes into port it is found that her furnaces must be "overhauled," her grate bars renewed, her braces restored, her boilers patched, sometimes all over, several of their plates taken out, thousands of rivets removed and supplied, and probably dozens of tubes also removed and replaced with new ones. But this is not all. The best boilers can not long run in this way. After six to seven years at the utmost, they must be removed from the ship altogether, and new ones must be put into their place. This is also a mostexpensive operation. The boilers constitute a large share of the cost of the engine power. To put a new set of boilers in one of the Collins steamers will cost about one hundred and ten thousand dollars, and this must be done every six years. The boilers of the West-India Royal Mail Steamers, which run very slowly, last on an average, six years.[A]
[A]Statement by Mr. Pitcher, builder, before the Committee of the House of Commons. Murray on theSteam Engine, p. 170, Second Edition.
[A]Statement by Mr. Pitcher, builder, before the Committee of the House of Commons. Murray on theSteam Engine, p. 170, Second Edition.
But this is not all. To restore the boilers, a ship has to be torn literally almost to pieces. All of the decks in that part must be removed and lost; the frame of the ship cut to pieces; large and costly timbers removed, and altogether an expense incurred that is frightful even to the largest companies. To insure perfect safety and to gratify the wish of the public, this is generally done long before it is strictly necessary, and when the boilers are in a perfectly good condition for the working purposes of ordinary speed. But precaution and safety are among the prerequisites of the public service, and must be attained at whatever cost. On slow auxiliary freighting steamers this would be by no means necessary. But the extent and cost of these repairs on steamers far exceed any thing that would be imagined. They are supposed to be twelve per cent. per annum of the prime cost of a vessel of ordinary speed, taking the whole ship's life together at twelve years at the utmost. Atherton in his "Marine Engine Construction and Classification," page 32, says of the repairs of steam vessels doing ordinary service in Great Britain, where all such work is done much cheaper than in this country: "By the Parliamentary evidence of the highest authorities on this point, it appears to have been conclusively established, that the cost of upholding steamship machinery has of late years amounted, on the average, to about £6 per horsepower per annum, being about 12 per cent. per annum, on the prime cost of the machinery, which annual outlay is but one of the grand points of current expense in which steamship proprietors are concerned." Now, if these were the repairs of the slow West-India Royal mail steamers, which ran but 200 days in the year, and that at a very moderate speed, and in the machine shops of England, where at that time (previous to 1852) wages were very low, they can not be less in this country, on rapid mail steamers, where wages and materials are very high, and where marine engineering was then in its infancy.
There are some facts on this subject which prove the positions here taken. The Collins steamers have been running but six years, and yet their repairs have amounted in all to more than the prime cost of the ships, or to about eighteen per cent. per annum. They were as well and as strongly built originally as any ships in the world, as appears from the report which Commodore M. C. Perry made to the Department regarding them, and from the fine condition of their hulls at the present time. Their depreciation with all of these repairs has not been probably above six per cent. per annum. They will, however, probably depreciate ten per cent. during the next six years, and at the age of twelve or fourteen years be unfit for service. The steamers Washington and Hermann, which had strong hulls, have been run eight years, and are now nearly worthless. Their depreciation has been at least ten per cent. The steamers Georgia and Ohio, which Commodore Perry and other superintending navy agents pronounced to be well-built and powerful steamers, (See Report Sec. Navy, 1852,) ran only five years, and were laid aside, and said to be worthless. With all of the repairs put upon these ships, which were admitted to be capable of doing first class war service, as intended, they depreciated probably seventeen per cent.; as it is hardly possible that their oldiron would sell for more than fifteen per cent. of their prime cost. These steamers paid much smaller repair bills than the Collins, and were not so well constructed, or at so high a cost. American steamers do not, upon the average, last above ten years; but if they reach twelve or fourteen, they will pay a sum nearly equal to twice their cost, for repairs and substitutions. Nor is this all. The life of a steamer ends when her adaptation to profitable service ceases. She may not be rotten, but may be so slow, or of so antiquated construction, or may burn so much more fuel than more modern competitors, that she can not stand the test of competition.
4. We thus see that not only are the requisite repairs most extensive and costly, but of such magnitude as to greatly reduce the earnings of any class of steam vessels. But this is not the last costly consequence of mail speed. It requires more cautious watchfulness of the engines, the boilers, the deck, and of every possible department of the navigation, even including pilotage. It requires also more promptness and dispatch in every movement, and hence a much larger aggregate number of men. More men are necessary to keep up high fires; twice as many men are necessary to pass twice as much coal; twice as many engineers as under other circumstances are necessary for the faithful working of the engines, and any accidents and repairs which are indispensable on the ocean; and a larger number of sailors and officers is necessary to all of the prompt movements required of the mail steamer. The Havre mail steamers, the "Arago" and "Fulton," never carry less than six engineers each, although they could be run across the ocean with three under a hard working system. But this number insures the greater safety of the ship under ordinary circumstances, and is absolutely necessary in any case of accident and danger. It is the same case with the firemen. When, in a heavy storm, the firedepartment may be imperfectly manned, the ship has taken one of the first chances for rendering the engines inefficient, and being finally lost. And all of these extra and indispensableemployéesmake an extra drain on the income of the ship, and add to the extreme costliness of a high adequate mail speed.
5. It is clear, then, that an adequate mail speed requires more fuel, more engineers, more firemen, more coal-stokers, and more general expense. The question of fuel is, however, alone the most important of all those affecting the attainment of high speed, and the item whose economy has been most desired and sought, both by those attempting to carry freight, and those who carry the mails and passengers. The principal points of interests concerning it are, the enormous quantity which both theory and practice show to be necessary to fast vessels; the large sum to be paid for it, and the steadily increasing price; and the paying freight room which its necessary carriage occupies. In fast steaming, the supply of coal to the furnaces frequently arrives at a point where many additional tons may be burned and yet produce no useful effect or increase of power. The draft through the furnaces and smoke stacks is so rapid and strong as to take off a vast volume of heat; and this, coupled with a large quantity of heat radiated from the various highly heated parts and surfaces, requires a consumption of fuel truly astonishing. If we reflect that at the twelve principal ports of Great Britain in the year of 1855, the tonnage entered was 6,372,301, and departed 6,426,566, equal to 12,798,867 total, and this during the war, that a large part of this was steam tonnage, and that the total imports and exports of Great Britain for 1856 were 1,600,000,000 dollars, we can somewhat appreciate the present and future uses of coal, and its inevitably large increase in price. The two hundred and seventy steamers in the British Navy, with about 50,000 aggregate horsepower, consumed in 1856, according to a report made to a Committee of the "British Association for the Advancement of Science," this year, by Rear-Admiral Moorsom, 750,000 tons of coal. The difficulty and cost of mining coal, its distance from the sea-shore, and the multifarious new applications in its use among our rapidly increasing population, as well as its almost universal and increasing demand for marine purposes, all conspire to make it more costly from year to year; while, as a propelling agent, it is already beyond the reach of commercial ocean steam navigation. Coal has gone up by a steady march during the last seven years from two and a half to eight dollars per ton, which may now be regarded as a fair average price along our Atlantic seaboard. And that we may see more clearly how essentially the speed and cost of steam marine navigation depend upon the simple question of fuel alone, to say nothing further of the impeding causes heretofore mentioned, I will now present a few inquiries concerning
The resistance to bodies moving through the water increases as the square of the velocity; and the power, or coal, necessary to produce speed varies or increases as the cube of the velocity. This is a law founded in nature, and verified by facts and universal experience. Its enunciation is at first startling to those who have not reflected on the subject, and who as a general thing suppose that, if a vessel will run 8 miles per hour on a given quantity of coal, she ought to run 16 miles per hour on double that quantity. I think that it may be safely asserted that in all cases of high speed, and ordinary dynamic or working efficiency in the ship, the resistance increases more rapidlythan as the squares. Therationaleof the law is this: the power necessary to overcome the resistance of the water at the vessel's bow and the friction increases as the square; again, the power necessary to overcome the natural inertia of the vessel and set it in motion, increases this again as the square of the velocity, and the two together constitute the aggregate resistance which makes it necessary that the power for increasing a vessel's speed shall increase as the cube of the velocity. But whatever therationale, the law itself is an admitted fact by all theoretical engineers, and is proven in practice by all steamships. In evidence of this, I will give the following opinions.
In his treatise on "The Marine Engine," Mr. Robert Murray, who is a member of the Board of Trade in Southampton, England, says in speaking of the "Natural law regulating the speed of a steamer," page 104: "These results chiefly depend upon the natural law thatthe power expended in propelling a steamship through the water varies as the cube of the velocity. This law is modified by the retarding effect of theincreased resisting surface, consequent upon the weight of the engines and fuel, so that the horse power increases in a somewhat higher ratio than that named." It must be understood that when he speaks of power, horse power, etc., it is simply another form of representing the quantity of coal burned; as the power is in the direct ratio of the quantity of fuel.
Bourne, the great Scotch writer upon the Screw Propeller, in his large volume published by Longmans, London, page 145, says, in concluding a sentence on the expensiveness of vessels: "Since it is known that the resistance of vessels increases more rapidly than the square of the velocity in the case of considerable speeds."
Again, at page 236, on "the resistance of bodies moving through the water," he says: "In the case of very sharp vessels, the resistance appears to increase nearly as thesquare of the velocity, but in case of vessels of the ordinary amount of sharpness the resistance increases more rapidly than the square of the velocity."
Again, on page 231, in speaking of the folly of a company attempting to run steamers sufficiently rapidly for the mails at the price paid for them, he says: "At the same time an increased rate of speed has to be maintained, which is, of course, tantamount to a further reduction of the payment. In fact, their position upon the Red Sea line is now this, that they would be better without the mails than with them, as the mere expense of the increased quantity of fuel necessary to realize the increased speed which they have undertaken to maintain, will swallow up the whole of the Government subvention.To increase the speed of a vessel from 8 to 10 knots it is necessary that the engine power should be doubled." This work of Mr. Bourne is now the standard of authority on the subject of which he treats, the world over.
Again, Mr. James R. Napier, of London, known as one of the largest and most skilled engine-builders in Great Britain, in the discussion of the dynamic efficiency of steamships in the proceedings of the "British Association" in 1856, page 436, says: "The power in similar vessels, I here take for granted, at present varies as the cube of the velocity." The power simply represents the coal; in fact, it is the coal.
Mr. Charles Atherton, the able and distinguished Chief Engineer of Her Majesty's Royal Dock Yard, at Woolwich, has published a volume, called "Steamship Capability," a smaller volume on "Marine Engine Classification," and several elaborate papers for the British Association, the Society of Arts, London, the Association of Civil Engineers, and the Artisans' Journal, for the purpose of properly exposing the high cost of steam freight transport as based on the law above noticed, and the ruinous expenseof running certain classes of vessels of an inferior dynamic efficiency. When but a few weeks since in London, I asked the Editor of the "Artisan," if any engineer in England disputed the laws relative to power, on which Mr. Atherton based his arguments. He replied that he had never heard of one who did. I asked Mr. Atherton myself, if in the case of the newest and most improved steamers, with the best possible models for speed, he had ever found any defect in the law of, the resistance as the squares, and the power as the cubes of the velocity. He replied that he had not; and that he regarded the law as founded in nature, and had everywhere seen it verified in practice in the many experiments which it was his duty to conduct with steam vessels in and out of the Royal Navy. I think, therefore, that with all of these high authorities, the doctrine will be admitted as a law of power and speed, and consequently of the consumption of coal and the high cost of running steamers at mail speeds.
It is not my purpose here to discuss this law, or treat generally or specially of the theory of steam navigation. It will suffice that I point out clearly its existence and the prominent methods of its application only, as these are necessary to the general deduction which I propose making, that rapid steamships can not support themselves on their own receipts. The general reader can pass over these formulæ top. 69, and look at their results.
Suppose that a steamer running eight miles per hour consumes forty tons of coal per day: how much coal will she consume per day at nine miles per hour? The calculation is as follows:
83: 93:: 40 : required consumption, which is, 56.95 tons. Here the speed has increased 121/2per cent., while the quantity of fuel consumed increased 421/2per cent.
Suppose, again, that we wish to increase the speed from 8 to 10, and from 8 to 16 miles per hour. The formula stands the same, thus:
Miles.Miles.Tons Coal.Tons Coal.83:103::40:x, =78.183:163::40:x, =320.
Murray has given some convenient formulæ, which I will here adopt. Suppose a vessel of 500 horse power run 12 knots per hour on 40 tons coal per day: what will be the speed if she burn only 30 tons per day? Thus:
40:30::123:V3(or cube of the required velocity,)Or, reduced,4:3::1728:V3,Equation,3 × 1728 = 5184=4V3,Or,5184/4=3√1296= 10.902 knots=V, required velocity.
Thus, we reduce the quantity of coal one fourth, but the speed is reduced but little above one twelfth.
The consumption of fuel on two or more given voyages will vary as the square of the velocity multiplied into the distance travelled. Thus, during a voyage of 1200 miles, average speed 10 knots, the consumption of coal is 150 tons: we wish to know the consumption for 1800 miles at 8 knots. Thus:
150 tons : C required Consumption :: 102knots × 1200 miles : 82knots × 1800 miles.
Then,C × 100 × 1200=150 × 64 × 1800,*Or,C × 120,000=17,280,000Reduced toC =1728/12=144 tons consumption.
Suppose, again, that we wish to know the rate of speed for 1800 miles, if the coals used be the same as on another voyage of 1200 miles, with 150 tons coal, and ten knots speed:
We substitute former consumption, 150 tons for C, as in the equation above, marked *, and V2(square of the required velocity) for 64, and have,
150 × 100 × 1200=150 × V2× 1800,Or,120,000=1800V2,Reduced,1200/18=V2,AndV=√66.66= 8.15 knots.
From the foregoing easily intelligible formulæ we can ascertain with approximate certainty the large quantity of coal necessary to increase speed, the large saving of coal in reducing speed, as well as the means of accommodating the fuel to the voyage, or the voyage to the fuel. It is not necessary here to study very closely the economy of fuel, as this is a question affecting the transport of freight alone. When the mails are to be transported, economy of fuel is not the object desired, but speed; and, consequently, we must submit to extravagance of fuel. This large expenditure of coal is not necessary in the case of freights, as they may be transported slowly, and, consequently, cheaply. But one of the principal reasons for rapid transport of the mails is that they may largely anticipate freights in their time of arrival, and consequently control their movements.
I recently had an excellent opportunity of testing the large quantity of fuel saved on a slight reduction of the speed, and give it as illustrative of the law advanced. We were on the United States Mail steamer "Fulton," Captain Wotton, and running at 13 miles per hour. Some of the tubes became unfit for use in one of the boilers, and the fires were extinguished and the steam and water drawn off from this boiler, leaving the other one, of the same size, to propel the ship. An intelligent gentleman who happened to know that we were using only one boiler, and consequently, but half the power, remarked to me that it was very strange that the ship was still going about eleven miles per hour,without any sail. He said: "It is strange, sir; two boilers of equal size drove us thirteen miles per hour; and here now but one boiler drives us nearly eleven miles, or nearly as fast; when common-sense teaches that the one boiler would drive us only six and a half miles per hour. How is that?" I then explained to him very clearly the natural law relative to power and speed, (SeeRule II., page 68,) which he at once comprehended and admitted, but with the remark: "Indeed, sir, I would have testified that she ought with one boiler to have gone at only half the speed; or that going at six miles with one boiler, she would go twelve with two."
As it will be interesting to the general reader to examine the details of the increased consumption of fuel at increased rates of speed, I present the following elaborate table recently prepared by Mr. Atherton for his new edition of "Steamship Capability," according to the formula above noticed, and the performance of the best type of vessel in the Royal Navy, the steamer "Rattler." Mr. A. found a higher efficiency in this vessel per horse power than any other in the Navy, and consequently based the consumption of coal in the table on the assumption that the mail and passenger vessels generally should be of as good contractive type as "Rattler." I shall present also another table showing a much larger consumption of fuel by an inferior type of vessel. I use these tables because they are thoroughly correct, and quite as perfect as any that I could construct on the same formula; and because they carry with them the weight of probably the highest authority in Great Britain.
Displacement,[B]Speed, and Fuel consumed per Day, for Mail, Passenger, and Freight Steamers, whose locomotive performance is equal to that of the best class of ocean steam vessels; assuming the consumption of fuel to be 41/2lbs. per indicated horse power per hour, equal to 33,000 lbs. raised one foot in one minute. The quantity consumed is expressed in tons per day of 24 hours.
[B]Displacement refers to the number of cubic feet of water displaced by the hull; allowing thirty-five cubic feet to the ton.
[B]Displacement refers to the number of cubic feet of water displaced by the hull; allowing thirty-five cubic feet to the ton.
By the inspection of this table we can see in condensed form the coal-cost of any speed as high as twenty miles per hour, and for any size of vessel from one hundred tons to thirty thousand tons. Let us find in the left hand column a vessel of 2,500 tons displacement. Pursuing the line along to the right we find in the second column 8.89 tons of coal, which a steamer of this displacement would burn in 24 hours, if running, as indicated at the head of the column, 6 Nautical miles per hour.
In the next column, under the head of 7 Nautical miles per hour, we find that she would burn in one day 14.1 tons; or one and a half times as much coal to gain one sixth more speed:
Again, at 8 miles per hour she burns 21.1 tons; nearly three times as much as at six miles:
At 9 miles she burns 30 tons: above twice as much as at 7, and nearly four times as much as at 6, although the speed is but half doubled:
At 10 miles per hour she burns 41.2 tons; about twice as much as at 8 miles, although the speed is increased only one fourth. At 10 she burns 34 per cent. more than at 9, although the increase of speed is only eleven per cent. (Seepages 67and68):
At 11 miles per hour she will burn 54.8 or 55 tons; nearly three times as much as at 8 miles per hour, and six times as much as at 6 miles per hour:
At 12 miles per hour she will burn 71.2; about thirty per cent. more than at eleven miles per hour, although gaining but 9 per cent. in speed; nearly twice as much as at ten miles per hour, three and a half times as much as at 8, five times as much as at 7, and above eight times as much as at 6 miles per hour. It is here seen that to double the speed the consumption of fuel has increased eight-fold, which verifies my statements hitherto made on this subject. We have already seen that to gain two miles ofspeed on any stated speed, it was necessary to double the quantity of fuel used.
At 13 miles per hour she burns 90.5 tons. This is burning two and a fourth times as much coal as if she ran only 10 miles per hour. Now, at this speed, the steamer will reach Southampton or Liverpool in 10 days and 6 hours, which is equivalent to 10 days and 12 hours burning fuel, allowing six hours for heating and starting, and which would make an aggregate consumption of 950 tons of coal for the passage of this steamer of 2,500 displacement or probably 3,000 tons register.
At 14 miles per hour she burns 113 tons. This is nearly three times as much as 10 miles per hour. At this speed the steamer would reach Southampton or Liverpool in 9 days, 12 hours, and 30 minutes, supposing the distance to be 3,200 miles from New-York, or say 9 days 181/2hours coal-burning time, and would consume an aggregate of 1,1041/2tons. As this is but little above the distance from New-York to Southampton, and under that from Panamá to California, and about the tonnage of the steamers running, the time being within eleven days generally, it will be seen how large is the cost of running the steamers of the Pacific Mail Steamship Company, those on the European routes, and also those between New-York and Aspinwall. As the route of the Havre and Bremen steamers is much longer, they are compelled to run slightly slower, or they would be filled up with their own fuel and power. Taking a Collins steamer of 3,000 tons, which we find in the line below, and we see that in running 14 miles per hour as they have frequently done, the consumption would be 128 tons per day, or 1,252 tons for the passage. And yet, one of those steamers could make 12 miles per hour on 80.4 tons per day, or at 11 miles per hour on 61.9, or less than half that used at 14. But pursuing this table we see that,
At 15 miles per hour she would burn 139 tons, or three and a half times as much as at 10 miles.
At 16 miles per hour she would burn 169 tons, or precisely eight times as much as at 8 miles per hour. Here again doubling the speed is found to be an enormous expense.
At 17 miles per hour she burns 202 tons per day.
At 18 miles per hour the consumption is 240 tons per day.
At 19 miles per hour she burns 283 tons coal per day; and
At 20 miles per hour she burns 329 tons per day. At 20 miles per hour she would run 480 miles per day, a thing as yet wholly unheard of, and would consume on the voyage of 6 days and 16 hours, say 6 days and 22 hours, 2,276 tons of coal. It would be clearly impossible for her to carry her own fuel; as the immense boiler and engine power necessary to secure this speed would of itself fill a ship of this size, to say nothing of the fuel which also would nearly fill it. Then, we may never expect any such ship to attain any such speed as seventeen, eighteen, or twenty miles per hour on so long a voyage without recoaling.
Seeing thus the enormous increase in the consumption of fuel for a moderate increase in the speed, we are enabled the better to appreciate the large expense incurred in running ocean steamers sufficiently rapidly for successful mail and passenger purposes. We will further pursue these inquiries by examining in this table the consumption for vessels of 6,000 tons, which would make the displacement of the ship nearly 5,000 tons, such as the "Adriatic," the "Vanderbilt," and the "Niagara." It appears that at 8 miles per hour they would consume 33 tons per day; at 10 miles, 65 tons; at 12 miles, 113 tons; at 13 miles, 144 tons; at 14 miles, 179 tons; at 15 miles, 221 tons; and at 16 miles, 268 tons per day. This is supposing this speed to be maintained on an average across the ocean, in all kindsof weather, which this size of steamer could not do without more engine and boiler power than any of them have. With such additional power the ships noticed would have scarcely any available room for freight or any thing else. One thing is very clear from this table, that when steamers run at very moderately slow rates of speed, their consumption of fuel is very small; and that when they leave this low freighting speed, for that of the necessarily rapid mails and passengers, the consumption increases to an extent and with a rapidity that would seem almost incredible at first view.
The following coal table is constructed in all respects as the preceding, but for a lower type of vessels, or those whose coëfficient of Dynamic performance is inferior to that upon which the previous table is estimated. As a consequence, this style of vessel requires more fuel.
Showing the mutual relation of Displacement, Power, Speed, Consumption of Coal, and capacity for Cargo of vessels of progressively increasing magnitude up to nearly 30,000 tons of Deep-draught Displacement, employed on a passage of 3,250 nautical miles, without recoaling: showing also the prime cost Expenses per ton of Cargo conveyed.
Mr. Atherton gives this table, which shows the following facts:
That, as the various sized vessels named, increase in speed from 8 to 12, or from 8 to 14 miles per hour, their horse power, as well consequently as their coal, increases:
That, as the speed increases, so does the weight of the hull and engines:
That, as the speed increases, with the consequent increased coal and engine weight, the cargo decreases: and
That, as the speed increases, with the other necessary conditions noticed, the expense per ton of cargo also increases in a rapid ratio. In the four cross columns ships of different sizes are considered; of 2,500, 5,000, 10,000, and 20,000 tons. There is also given the working or indicated horse power, and the nominal horse-power, or that of 33,000 lbs. raised a foot in a minute, which is the general basis of making contracts. It is a fact, however, that engines generally work up to three or four times their nominal horse power; so that the word horse power has no positive or useful meaning. Vessels called one hundred nominal horse-power have been known to work up to six hundred.
Let us take a ship of 5,000 tons. We find that at 8 miles per hour the horse power is 436; but at 12 miles it is 1,472, nearly four times as great. At 13 miles, it would be nearly 1800 horse, and at 14 it would be above 2100. So, also, with the weight of engines, boilers, etc. At 8 miles per hour they would weigh 1,109 tons; but at 12 they would have to weigh, to be large and strong enough, 1,368 tons. At 14 miles, they would weigh nearly 1,600 tons.
Now, see the columns "cargo" and "coal," and observe how rapidly that of coal increases, while that of cargo decreases in the inverse ratio of the coal, the engine, the boiler, and the hull weight combined. The cargo has come from 1,209 down to 717 tons; and if the speed were increased to 13 or 14 miles per hour, the cargo would be so reduced as to be unworthy of notice.
The next column shows how much greater the quantity of water displaced as the speed increases. This extra displacement requires extra power.
In the last column it is observable how rapidly the speed enhances the cost price of transporting cargo. At 13 miles per hour the cost would be about six pounds sterling per ton, and at 14 knots speed it would be higher than was ever paid a steamer in the most flush periods of even the best qualities of freights. Freights were about £8 per ton on the Cunard line before the establishment of the Collins; but they soon came down, and are not now £3, or $15, on an average. So with passage. The "Great Western" charged £45, the "British Queen" £50; the Cunarders, until the Collins competition, £40, 19s.The Collins steamers put the price down to £35, and have since reduced it to £30 homeward, and £24 outward. This is but little above half the fare of the Great Western, and something over two thirds of that formerly charged by the Cunard line. The Report to the House of Commons "on Steam Communications with India," No. 372 of 1851, second volume, page 395, says, that the average speed of the Cunard line was 10.443 knots, of the Collins line 11 knots, and of the Havre and Bremen lines 9.875 knots per hour. The Collins line had then just started, and has since made the average passages one and a half days quicker than those of the Cunard line. This being the case, it is easy to estimate the gains of a steamer at such rates, when this column shows us that at 12 miles speed per hour and an average trip of 11 days, the actual prime cost of moving the freight is much above that which is received for it. It is therefore taken in small quantities only to assist in paying the running expenses of the steamer.