Description of the Great Britain Iron Steam Ship, with Screw Propeller; with an Account of the Trial Voyages

Description of the Great Britain Iron Steam Ship, with Screw Propeller; with an Account of the Trial Voyages

From The Journal of the Franklin Institute. Third Series. Vol. XI. Page 79.

By Thomas Richard Guppy, Esq., C.E.
(From the Proceedings of the Institution of Civil Engineers.)
Continued from page 11.

Mr. F. P. Smith repeated, that in his opinion, the screw was preferable to paddle-wheels under all circumstances; but it was in a rough sea, in combination with sails, that its merits were most apparent.

In going down the river with the Archimedes, he had repeatedly been passed by merchant steamers; but by the time he had reached Dungeness, the Archimedes had fetched up the loss, and was some distance ahead of the other steamers.

With a propeller of two arms, he had found, that if, instead of disengaging the screw and letting it run loose, the arms were fixed vertically with the stern-post, the Archimedes would make, under sail, from 9 to 9½ knots per hour.

The propeller formerly used on board the Rattler was 10 feet in diameter, with two blades one-eighth part of the disk, and that now used was of the same diameter with the blades of two-sixths of a disk.

The speed was ascertained by the common and by Massey’s Patent log, carefully thrown, and attended to by the officers.

Mr. J. G. C. Curtis remarked, that it was necessary to be extremely cautious in using the results of the ordinary log ; for although very useful for the common purposes of navigation, he did not think they ought to be allowed to enter into the computation of a vessel’s velocity, where the ‘slip of the screw’ was to be determined.

Mr. Curtis, having been employed under Sir Edward Belcher, in his surveys in the Pacific, when the distance run by the vessel had to be determined with the greatest precision, might, perhaps, be permitted to make a few remarks on this subject.

The velocity of a ship being determined with the ordinary log, by ascertaining how much of the line, attached to the log, ran out in a given time, it was essential that both the time and the distance should be correctly measured ; but that was seldom the case, as the sand in the sand-glass, which measured the time, was affected by every change in the atmosphere, and the line which measured the distance was alternately wet and dry, and being stretched unequally, at different parts, it was impossible that the marks, or knots, could remain at the distances which they were intended to indicate. These difficulties, when the vessel was going less than eight or nine miles an hour, might be partially surmounted, by counting the requisite number of beats of a good watch, instead of using the sand-glass, and by actually measuring the quantity of line which ran out, instead of counting the distance by the knots

But in heaving the log at higher rates, it was difficult to prevent the log from being dragged after the ship by the friction of the reel; and whether the line was “taken off’ or “paid out,” there was always a degree of doubt whether the correct length had been allowed to go off the reel.

was a so nearly un possi He to nieasn re the lime to he requisite degree of accuracy, by the 11 seconds sand-glass, which was gene rally used at lugh rates.
For instance, if a vessel were going 14 knots, the quantity of line represciitiiig one mile passed through the hand of the observer in one second of time ; and hence, in order to obtain the speed to the eighth part of a mile, it would be necessary to measure the interval to time eighth part of a second. In like manner, to obtain a vessel’s speed to the eighth part of a mile, when she was going 10 knots, it would be necessary to measure the interval to the sixth part of a second.

As these small portions of time could not possibly be measured by a sand-glass, persons unacquainted with the subject would not be surprised to learn, that Mr. Curtis had heard it expressed as an opinion, by most naval officers, and had found by his own practice, that the rate of a ship going more than 10 knots could scarcely be obtained within a mile, under favorable circumstances.

As Mr. Curtis was convinced that the difficulty of accurately measuring the speed was one of the greatest causes of the discrepancies which existed in the accounts of the trials of vessels, he ventured to suggest an expedient “for determining a vessel’s velocity at any given instant,” which he thought would be more accurate than the common log. He proposed that the time which a vessel took in passing through her own length should be measured; from which her velocity per hour could be easily ascertained by proportion.

For thus purpose he would fit, in convenient places, at a short distance from either end of a vessel, two rods, one vertical and the other horizontal, so that each pair, when seen in coincidence, should point in a line perpendicular to the direction of the vessel’s keel. He would also have a buoy painted white and black, or any colors that would show well when in the water; to this he would attach a line considerably exceeding the length of the vessel.

This buoy should be passed forward, with plenty of spare line, to the bowsprit end, the end of the line being made fast abaft, ready to haul it in when done with.

When these preparations were complete, he would stand at the foremost pair of rods, with an assistant at the after pair; he would then direct the buoy to be hove overboard, as far out from the vessel as possible ; as it passed his own rods, he would commence counting the beats of a good watch, until his assistant, by holding up his hand, or giving some other signal, indicated that it had passed the after rods; and then the calculation was easy. The number of beats counted was to the number of beats in an hour as the distance between the rods way to the velocity per hour.

In a vessel like the Great Britain, where the length was one-nineteenth of a nautical mile, the method proposed would possess great advantages over the common log, particularly at high velocities; and in practice the method would he very easy, as a table might be made of the velocity, corresponding to a given number of beats, and in smooth water, a good-sized chip, or a bottle, might be thrown overboard, and would save the trouble of hauling in the buoy.

Captain Hosken could not agree with Mr. Curtis as to the general incorrectness of observations by the log. He was convinced that with a correct glass, and a log properly “hove” by an experienced seaman, the distance would be given to one-eighth of a mile. Under all circumstances, he thought the common log was the best known means of ascertaining the speed at sea. “Massey’s” log was, perhaps, the best of all the other instruments he had seen and tried. When a vessel was going less than 5 knots, it did not indicate sufficient distance; between 5 knots and 8 knots it was very correct; but above that speed, it again gave insufficient distance. He had “ Massey’s” log overboard from the Great Western all the way from New York to Bristol, when the distance shown was about 200 miles less than the ship had actually run. The average speed on that occasion was about 10 knots per hour. He, however, thought that Massey’s
log was an excellent guide for running channel distances in the night, or in thick weather.

Sir John Rennie, President, directed attention to a remark made by Sir Charles Napier, as to the relative powers of vessels with screw propellers, and with paddle-wheels, for clawing off a lee shore.

Mr. F. P. Smith was of opinion, that if a vessel with a screw used her canvas, as well as the propeller, she would claw off quite as well, if not better, than a paddle-wheel steamer, as, from the heeling of the vessel, the lee paddle would thereby lose much of its power.

Captain Hosken thought that a screw would make less lee-way than paddle-wheels, and would be quite as effective in clawing off. The American steamers had their paddle-wheels driven by separate engines, and had of course the advantage of being able to turn ahead on one side, and astern on the other. Even that, however, was not very effective; and of course was not applicable to a sea-going steamer, in which disconnected engines and wheels would be, practically, very dangerous.

Mr. F. Braithwaite said, that Captain Hosken’s remarks on American steamers induced him to ask, whether there was any proviso on board the Great Britain for disconnecting the engines from the screw, and in how short a time it could be done? Some very good methods of disconnecting had been designed and put in practice by Messrs. Maudslay and Field, and by Messrs. Seaward; and he understood that the system had been advantageously applied on board some French steamers. Two steamers recently on their passage from France to Algiers, with a fair wind, afforded a good example. One of them, being able to disconnect the paddles, and use the sails, saved half the fuel, and arrived within a few hours of the other that had steamed the whole distance. He believed that only about half a minute was occupied in disconnecting.

Mr. Guppy explained that, on board the Great Britain the means of disconnencting the screw was by taking out four screw-bolts, and drawing back a coupling-box, which occupied about a quarter of an hour, during which time the engines must be stopped He considered it hazardous, with such powerful engines, to have any means of disconnecting which might be used while the machinery was in motion.

Mr. F. Braithwaite must contend that, under certain circumstances, it was very advantageous to have the power of disconnecting rapidly. The Phoenix, a vessel built by Messrs. Scott and Sinclair, (Greenock) struck, and sprung a serious leak; and when it was found that the hand-pumps could not gain upon the leak, the paddles were disconnected, arid all the power of the engines being applied to pumping, she was kept afloat arid was saved.

Mr. J Scott Russell corroborated the statement as to the Phoenix. The coupling alluded to was very efficient and safe.
With respect to the value of the lee paddle, he thought it of little use, even if the windward paddle could he disconnected. In some experiments on the subject, he found that a vessel using her power upon both wheels could be brought round in two minutes, and when using only one wheel, three minutes were occupied in bringing her round; proving that the diminution of speed by the loss of one wheel was more than equal to the effect of the disconnected wheel. There were instances of vessels having one wheel disabled, and finishing their voyage with the remaining wheel, without much inconvenience in steering.

An instance was recorded of a steamer, commanded by a good seaman, though but little accustomed to steam navigation, getting his vessel into the trough of the sea, in very heavy weather, and being entirely unable to bring her head to windward until the mate suggested reversing the engines; by which means she was easily brought and afterwards made her passage safely.

Captain Hosken stated, in reply to a question from the President, that he thought the Great Britain would not be more liable than other ships to “broach to’’ when scudding. His opinion was founded upon experience in the Great Western. The same question had been put to him by old seamen, before the first voyage of that vessel, when, from that ship’s great length, it was thought there would be more than usual difficulty in steering her: Captain Hosken differed from the general opinion; and time had clearly show that he was right, as she scudded and steered as well as any, and better than most other ships. The Great Western was as great an increase in size when she was built as the Great Britain is now; and he felt confident that ship would prove as triumphant a specimen of naval architecture.

Scudding well was a point of great importance, and was entirely a seaman’s question. No point required more judicious management and correct judgment than as to when a ship could not scud longer with safety, and ought to be ‘‘hove to.’’

He had very often, in the Great Western, been scudding past very fine ships of from 500 tons to 1000 tons, not very deep in the water, laying to,’’ because they could not scud with safety.

There were now several steamers longer than the Great Western, and he ha never heard that any difficulty had been experienced with them on this important point.

So far as he had the opportunity of trying, he would say most decidedly the Great Britain steered easier and better than the Great Western; and he was sure he could not find a better ship to compare with, either in the naval or mercantile service.

Mr. Pim mentioned an advantageous application of the combined power of tire screw and sails, which had been practiced by his relations, Messrs. Pim, of Hull. They had adapted to two fine trading schooners screw propellers, driven by small engine power. The result of this experiment had proved that, in cases where extreme speed was not an object, but in which regularity was essential, this plan might be advantageously adopted; especially for commercial purposes, in which it was requisite to combine economy and a certain amount of dispatch.

The vessels he alluded to were very sea-worthy boats; and on one occasion, when on a voyage to Dublin, the Shannon, a large merchant steamer, had been obliged to run for shelter, one these vessels had ridden out the gale, and made her passage. He believed that they were propelled by Mr. Smith’s screw, and that he could give all particulars of their construction.

Mr. F. P. Smith said the vessels alluded to were the Margaret and the Senator, trading from Hull. They were fine four-masted schooners, of 242 tons burthen; each vessel had on board two engines, severally of 14 horse power, placed as close as possible to the screw propeller, which was driven by gearing. The total weight of the engines, screw, and tubular boilers with their water, was 15 tons, and they worked under a pressure of 8 lbs. to 10 lbs of steam.

In a trial between one of these vessels and the Shannon steamer, it was found that, between Dublin and London, the Shannon consumed 90 tons of fuel, while the schooner, with 300 tons of cargo on board, only used 18 tons of coal, and arrived in London within 10 hours after the Shannon. In an experiment with the Senator, with 172 tons of cargo on board, when steaming only, the rate through the water by the log was 6 knots; and with sails and steam the rate was 9½ knots to 10 knots. It was remarkable that this increase of speed did not appear to augment the consumption of fuel; whereas with paddle-wheels and sails the consumption of fuel increased in proportion to the rate of the vessel through the water.

Captain Hosken could not permit the discussion to terminate with out stating that in his opinion, as a naval officer, one of the great merits of the screw as a propeller, was its capability of being adapted to a full-rigged ship, using at times her canvas as usual. The British seamen would thus be fully as much employed as heretofore, and they would retain that superiority which had so largely contributed to the high position held by Great Britain in the scale of nations.

To be Continued.

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