Part 7

In 1840 the Britannia, the first of the Cunard steamers, was put on her station. She was a paddle boat, built of wood, and was 207 feet long. Her speed on service was about eight and a half knots, so that she did the passage in 15 days.

Ten years later the now renowned Inman Line commenced with an iron screw steamer named the City of Glasgow, of 1,600 tons burden, and 350 nominal horse-power, a new departure in both ship and propeller.

It was not until 1855 that the Cunard Company built an iron steamer, and they continued to employ paddle boats until 1862, when the celebrated steamship Scotia was completed.

It is interesting to note, in passing, that the average length of voyage in the Cunard Line, in 1856, from Liverpool to New York was 12.676 days, and from New York to Liverpool 11.036 days.

Thirteen years after the Scotia was built the White Star Company placed on the station two vessels that were very great advances on anything then existing; they were marvels of the ship-builder’s and marine engineer’s skill, and even to-day hold their own in many respects with the most modern ships. That these should compete successfully, and eventually drive off the line such a ship as the Scotia is easily seen by reference to contrasted particulars in the table on page 78. The Britannic is a screw vessel 455 feet long; her I. H.-P. on trial trip was 5,400, and at sea is about four thousand nine hundred, or practically the same as that of the Scotia; but the speed on trial was nearly two knots more, and the average of eleven voyages gives a mean of 15.045 knots per hour; while as recently as September, 1890, in her old age, she traversed the Atlantic from New York to Queenstown at an average speed of 16.08 knots. She has compound engines with 4 cylinders, the two high-pressure being each 48 inches diameter, and the two low-pressure each 83 inches diameter, with a stroke of 5 feet. Her consumption of coal will be about one hundred and thirty tons per day, and on leaving port she will have on board, say 1,300 tons of fuel. She can carry a considerable cargo. The weight of her machinery is 1,112 tons. She and her sister ship, the Germanic, were in their day admitted to be all that could be desired; almost as much as was physically possible, and certainly as much as was then possible commercially.

Since then, however, many changes have taken place that will be alluded to later on, so that to-day we have numerous boats running on the Atlantic at an average speed of 19 to 20 knots, with a reputation for being commercial successes as well as triumphs of engineering skill.

The most recent and noteworthy of these are the steamships Teutonic and Majestic, owned by the same enterprising gentlemen, and constructed by the same famed builders as the Britannic and Germanic; and the City of Paris and City of New York, sailing under the same house flag as the steamship City of Berlin, which was a worthy competitor of the Britannic.

The Majestic is a twin-screw steamer of 9,851 tons gross, 565 feet long (or 110 feet more than the Britannic). Each screw is driven by a set of triple-expansion engines. Her consumption of fuel is about two hundred and ninety tons per day, while on leaving port she will have on board about two thousand four hundred tons of coal. Her I. H.-P. on trial trip was 17,000. Her best speed on service is a mean of 20.18, and taking the mean of ten voyages it is 19.72 knots. A picture of the ship, taken while afloat on the Mersey, is shown on page 75.

The City of Paris is 10,499 tons gross register, and is 527 feet long: she also is a twin-screw vessel. It will be observed by comparison with the Majestic [see table, p. 78] that the City of Paris is the larger ship, although she is 38 feet shorter, her extra beam of 5.4 feet giving her this advantage. Her speed with 20,100 I. H.-P. is 21.952 knots, her best run on service being 20.01 knots; and her daily consumption of coal is about three hundred and twenty tons, which necessitates her leaving port with over two thousand seven hundred tons of fuel on board for the trip.

Previous to the advent of these vessels the Cunard Company’s steamships Etruria and Umbria were the fastest boats on the Atlantic, and their performances are highly creditable to all concerned. The best voyage from Queenstown to Sandy Hook by the Etruria was done in 6 days, 5 hours, 3 minutes, and the best from Sandy Hook to Queenstown in 6 days, 7 hours, 32 minutes, and the average in 1886 was about 6 days, 15 hours, as compared with the 11 days, 19 hours of 1856. The average of the Britannic for ten years was 8 days, 9 hours, 36 minutes, Queenstown to New York; and 8 days, 1 hour, 48 minutes, New York to Queenstown.

COMPARATIVE TABLE OF ATLANTIC STEAMSHIPS AND THEIR SPEEDS.

+------+------+--------+--------+--------+---------+------ | | | | | | | | | | Length | | | | |Paddle| | on | | | | | or | When | Water- | | | Horse- | Ton- NAME OF SHIP. |Screw.|Built.| line. |Breadth.| Draft. | power. | nage. ----------------+------+------+--------+--------+--------+---------+------ | | |Ft. Ins.|Ft. Ins.|Ft. Ins.| Nominal.| Sirius |Paddle| 1836 | 170 0 | | | 270 | 700 British Queen | „ | 1839 | 234 0 | 40 4 | 16 0 | 500 | 2,016 Liverpool | „ | 1839 | 210 0 | 36 0 | | 404 | 1,150 Great Western | „ | 1838 | 212 0 | 35 4 | 16 0 | 450 | 1,340 Britannia | „ | 1840 | 206 0 | 34 6 | | 450 | 1,155 Scotia | „ | 1862 | 366 0 | 47 9 | 22 0 | 1,000 | 2,358 City of Richmond|Screw.| 1873 | 440 0 | 43 6 | | 700 | 4,780 City of Berlin | „ | 1874 | 488 6 | 44 2 | | 1,000 | 5,526 | | | | | |Indicated| Germanic | „ | 1874 | 455 0 | 45 2 | 23 7 | 5,400 | 5,008 Britannic | „ | 1874 | 455 0 | 45 2 | 23 7 | 5,400 | 5,004 Arizona | „ | 1879 | 450 0 | 45 1 | 18 9 | 6,300 | 5,164 Servia | „ | 1881 | 515 0 | 52 0 |23 3-1/2| 10,300 | 7,392 City of Rome | „ | 1881 | 542 6 | 52 0 |21 5-1/2| 11,890 | 8,144 Alaska | „ | 1881 | 500 0 | 50 0 | 21 0 | 10,000 | 6,932 America | „ | 1883 | 432 0 | 51 0 | 26 7 | 7,354 | 5,528 Oregon | „ | 1883 | 501 0 | 54 2 | 23 8 | 13,300 | 7,375 Umbria | „ | 1884 | 500 0 | 57 2 | | 14,320 | 8,128 Etruria | „ | 1884 | 500 0 | 57 2 | | 14,320 | 8,120 City of New York| „ | 1888 | 527 0 | 63 0 | | 18,400 |10,500 City of Paris | „ | 1888 | 527 0 | 63 0 | | 20,100 |10,500 Majestic | „ | 1889 | 565 0 | 57 6 | 26 0 | 17,000 | 9,861 Teutonic | „ | 1889 | 565 0 | 57 6 | 26 0 | 17,000 | 9,686 ----------------+------+------+--------+--------+--------+---------+------

+------+--------------------------------+---------+----------- | | CYLINDERS. | | | +------------------------+-------+ | Time | | |Stroke | | occupied |Trial | | in | Working |on Quickest NAME OF SHIP. |Speed.| Diameter in Inches. |Inches.|Pressure.| Passage. ----------------+------+------------------------+-------+---------+----------- |Knots.| | | Lbs. | D. H. M. Sirius | | | | | 18 11 15 British Queen | 8.5 |Two 77-1/2 | 84 | | 13 18 10 Liverpool | |Two 75 | 84 | | 11 18 5 Great Western | |Two 73 | 84 | | 10 10 15 Britannia | |Two 72 | 82 | | Scotia |13.9 |Two 100 | 144 | | 8 4 30 City of Richmond| |68 and 120 | 60 | | 7 18 50 City of Berlin | |41, 65, and 101 | 66 | | 7 14 12 | | | | | Germanic |16.0 |Two 48 and two 83 | 60 | 70 | 7 11 37 Britannic |16.0 |Two 48 and two 83 | 60 | 70 | 7 10 53 Arizona |17.0 |One 62 and two 90 | 66 | 90 | 7 3 30 Servia |16.9 |One 72 and two 100 | 78 | | 6 23 50 City of Rome |18.23 |Three 46 and three 86 | 72 | 90 | 6 21 4 Alaska |18.0 |One 68 and two 100 | 72 | 100 | 6 18 37 America |17.8 |One 63 and two 91 | 66 | | 6 14 18 Oregon |18.3 |One 70 and two 104 | 72 | 110 | 6 9 51 Umbria |19.0 |One 71 and two 105 | 72 | 110 | 6 3 4 Etruria |19.5 |One 71 and two 105 | 72 | 110 | 6 1 50 City of New York|20.13 |Two sets 45, 71, and 113| 60 | 150 | 5 21 19 City of Paris |21.952|Two sets 45, 71, and 113| 60 | 150 | 5 19 18 Majestic |19.87 |Two sets 43, 68, and 110| 60 | 180 | 5 18 8 Teutonic |21.0 |Two sets 43, 68, and 110| 60 | 180 | 5 16 30 ----------------+------+------------------------+-------+---------+-----------

It may well be asked how what seemed to be an impossibility in 1876 has been achieved so successfully in 1890, and it is perhaps less interesting to note the changed conditions than the causes that have produced them. In the very early days of steam navigation the engines were substantially those used for pumping and other purposes on land. Had the genius of Trevithick exerted itself in the direction of improvements in ship propulsion as much as it did in abortive efforts to make the locomotive a success, there is no doubt we should have had fast passenger steamers before we had railway trains; and had not the prejudice of Watt hung over the engineering world as a cloud which obscured the clear light of science, some other engineer would have accomplished the same result. It is disappointing to find that a man of Watt’s genius and reputation should have attempted to damp the ardor of men like Symington and Miller by predicting failure for an engine when applied to marine propulsion, and by threatening the pains and penalties of the law for infringement of patent should those enterprising geniuses disprove his predictions. There can be no doubt that the statement from a man of his position, that Trevithick and others who were experimenting, as well as working, with steam of high pressure deserved hanging for their diabolical inventions, would have great effect on the engineering world, then in its infancy; and the few accidents that in later years occurred on steamboats, through the crass ignorance or the reckless negligence of those placed in charge, recalled to the mind of another generation the words of Watt, and made them doubly impressive as well as deterrent to further progress. Even in our own days the use of steam at such pressures as have enabled the present wonderful monuments of mechanical skill to be commercial successes has been animadverted upon, and prophesied about, and openly denounced, and it is only those who are engaged in this pioneer warfare who know how depressing and discouraging such language is, or who appreciate the great responsibility taken in advancing into the unknown—that is, unknown to the world at large. Moreover, the body of every nation is more or less conservative and slow to comprehend, much less to appreciate, new inventions or new forms of old inventions. Hence, no doubt, it was that an enterprising company like that presided over by Sir Samuel Cunard should refrain from building its ships of the superior material, iron, and adhere to the inferior propeller, the paddle.

The paddle-wheel was obviously the first instrument accepted by the early engineers as a means of propulsion. Long after the experiment of H. B. M. S. Rattler had demonstrated the contrary, the public faith in the visible wheel was greater in reality and more sincere than that in the invisible screw; and it is probable that it was more the question of cost than anything else that gained the victory for the screw for ocean and general service. The paddle engine is in itself heavier and occupies more room than the screw engine; it is as a rule more expensive per I. H.-P.; and in wear and tear—especially of the propeller itself—it far exceeds the screw. It occupies the best part of the ship, and its position is not a matter of choice, as with the screw engine, but is, of necessity, at or near the middle of the ship.[14] It is evident that a paddle steamer must require more room, and that in moving among ships or other obstructions the liability to damage the propeller is greater than with the screw steamer, and in the case of a long voyage the paddle generally worked at a disadvantage, as at the commencement it was too deeply immersed, and at the end not immersed enough for efficient working. If the sails were set so as to steady the vessel, or if set in sufficient quantity to be of any use in quickening the speed, she was inclined until the lee wheel was “buried” and the “weather” wheel doing very little work; besides there was a general tendency on the part of the ship to turn round, which had to be counterbalanced by the rudder. The race of water from the wheels past the ship being at a high velocity, and raised above the normal level, causes a resistance to the ship beyond that due to her passage through the water, as in the case of a screw ship. On the other hand, the paddle boat is more readily got into motion and her speed more rapidly arrested than is the case with the screw steamer; and it is claimed for the paddle-wheel—although the foundation for such a claim is rather nebulous—that when the engines are working at full speed the ship is prevented from the excessive rolling observable with a screw vessel. But against this it must not be forgotten that the paddle engine is far more trying to the structure of the ship, on account of the great weight of the wheels being taken on the sides of the hull, as well as from the effort of the wheels in propelling being applied at the same place. Then there is the additional danger, and that not a remote one, that in case of the shaft breaking and a wheel falling clear of the ship, she would upset. An accident of this kind has occurred more than once, but there is no record of the actual result being so calamitous as just stated, owing to other fortuitous circumstances. That which retains the paddle-wheel in favor to-day, and renders it a necessity in spite of argument or prejudice, is the fact that the screw requires that the draft of the ship shall not be less than its own diameter, whereas in the largest paddle boats a dip of wheel of six feet is generally sufficient. Hence it is that nearly all fast steamers plying on rivers or shallow estuaries, and channel steamers running to ports where there is little water when the tide is low, are of necessity paddle-wheel. By employing two screws (one on each side instead of one amidships) the draft of water can be reduced by at least thirty per cent. Likewise, by increasing the number of revolutions smaller screws will do, and the draft of water may be still less, so that some thirty years ago, on the introduction of twin-screws, there were soon many ships built for services that had hitherto been monopolized by paddle boats;[15] and to-day, when there is a demand for higher speed and more power, and where paddle-wheels are not admissible, three screws are being employed. Ships have also been employed with four screws, viz., two at the bow and two at the stern, and, for the purpose for which they were required, answered very well indeed; but the worst possible place for a propeller is obviously at the bow, and therefore in these ships the bow screws were not very efficient, but they undoubtedly added somewhat to the power of the ship. In the same way some tug-boats have been fitted with a screw at each end.

All attempts at propulsion with internal propellers—that is, by turbine wheels, pulsometers, ejectors, or by pumps—have failed in consequence of the great friction set up by the water in its rapid passage through the pipes from and to the sea; the motion must be rapid owing to the size of the pipes being necessarily restricted. The best experiment with this kind of propeller was made on a costly scale by the British Admiralty in 1866, when they fitted the iron-clad gun-boat Waterwitch, of 1,200 tons displacement, with a Ruthven’s hydraulic propeller, consisting of a horizontal turbine wheel drawing its water through the bottom of the ship and discharging it fore-and-aft-ways at each side, and driven by an engine of 160 nominal horse-power; and although this vessel was only 162 feet long, 32 feet broad, and drew 11 feet 4 inches of water, her speed was only a little over 9 knots, with an indicated horse-power of 801. The speed co-efficients whereby her performances could be compared with that of other ships were most disappointing.

But the achievements of screw steamers are not always satisfactory at first, and time has shown some curious instances where what appeared at first sight a little thing prevented great results. To-day we know somewhat of the screw propeller, but it is very difficult, if not impossible, for the cleverest and most experienced engineer to define his knowledge or to classify his facts so as to deduce any rules from them that shall enable him to lay down fixed laws for the practical guidance of others. In past years more was professed, but still less was actually known, and that which was to be a panacea for the ills of every screw ship proved useless in many instances, and aggravated the evil in others. The patents for propellers are numerous, and some of the specifications interesting and amusing, but of them all there are less than can be counted on the fingers of one hand that have any practical value, or that have influenced the commerce of the world; and we find to-day that the propeller which gives the best results is very simple in form and its working surface a true helix. What is better understood, however, are the proportions, and in them lies the success of the instrument. It is quite true that the blades may be of such a shape and so arranged as to give bad results, but it is very difficult to alter the propeller blade now most generally used and get much improvement thereby.

In 1865 H. B. M. S. Amazon was found to fall short of her designed speed by nearly a knot, although the indicated horse-power was in excess of the requirements. With a four-bladed Mangin propeller, 12 feet 6 inches pitch, it took 1,940 I. H.-P. to drive the vessel 12 knots. A two-bladed Griffith’s screw of 13 feet 9 inches pitch was substituted, when 12.4 knots were obtained with only 1,664 I. H.-P. But the most remarkable case was that of H. B. M. S. Iris, which had been designed for a speed of 17-1/2 knots, but on her first trial trip, although the 7,000 I. H.-P. was exceeded, the speed was only 16.58 knots. A series of trials was then entered upon to find out the cause of this deficiency, with the result that the screws were discovered to be too large; others of 2 feet 3 inches less diameter were substituted, when a speed of 18.57 knots was attained with the same I. H.-P. Similar instances could be adduced, if necessary, to show how comparatively slight changes in the propeller can produce marked improvements in speed.

It has already been shown that the frictional resistance of the skin of the ship is very great, and generally speaking, in fast steamers, is by far the largest portion of the whole resistance. It necessarily follows, therefore, that for high speed it is essential that the submerged portion shall be as smooth as possible; and to that end ships are coated with enamel paints which, when dry, are perfectly smooth and glassy, or remain in a smooth, slimy condition. They do not, however, remain long in this state, as the action of sea-water destroys them, and even the best of these compositions admits, at times, of marine plant growth, and sometimes barnacles. The effect of a coating of weed is very serious indeed; the resistance induced thereby being greater than if the vessel were rough, from the fact that each filament of weed has to be towed through the water, and the total surface thereby exposed may be two or three times that of the ship herself. It is a sound economy in any vessel to keep the bottom perfectly clean and smooth, but in the case of high-speed steamers it is absolutely essential, inasmuch as a very moderate amount of foulness will reduce their speed by 2 or 3 knots.

The introduction of Siemens-Martin steel, about the year 1875, and its continued and extended use since, have however been really the means of rendering possible the construction of steamships of all sizes with high rates of speed now so common, and are undoubtedly the means whereby those ships can be so economically built and worked as to pay as commercial ventures. The construction of their hulls with a material fifty per cent. stronger than iron has rendered it possible to make such appreciable decrease in weight as to admit of fining their lines suitably for high speed without sacrificing carrying capacity. With this same steel, boilers can be constructed for a pressure of 150 pounds per square inch without weighing very much more than iron ones for 75 pounds. By using steel for castings, forgings, etc., the weight of the machinery has been reduced from 5 hundredweight to 2 hundredweight per I. H.-P., and when forced draught is employed it is as low as 1.6 hundredweight per I. H.-P. for large powers, and less still for such engines as are used in torpedo boats and catchers.

It has already been remarked that the consumption of coal, which enters as a most important factor into the question of high speed, both from the weight and cost, had been reduced, by the introduction of the compound engine, from 4 pounds to 2-1/2 pounds per I. H.-P., and latterly, as that engine was improved and higher pressures used, the consumption was further reduced to 2 pounds, and in some cases as low as 1-3/4 pound per I. H.-P. The triple expansion engine, developed within the past eight years, and later the quadruple expansion, have effected a still further saving, until with them and such other means as are now employed, the consumption is under 1-1/2 pound of coal per I. H.-P.