ALTHOUGH various propositions for many years were made from time to time to use the screw as an instrument of propulsion, and a great variety of experiments tried in boats and small vessels, yet neither the reasoning of the projectors nor the results of their experiments appear to have carried conviction to the minds of most men that this kind of propeller could be usefully employed, or at all events that it could successfully compete with the paddle-wheel.

The immediate cause of its introduction into the navy was the successful performance round Great Britain and elsewhere of the Archimedes, a vessel of 237 tons, built in the year 1838 by the Screw Propeller Company, with a view of ascertaining the value of the invention. She was first tried against a paddle-wheel vessel in 1840, and the results of the trials are contained in the following report, the first official one made to the Board on the subject of screw propulsion:

In pursuance of the instructions of the Lords Commissioners of the Admiralty, as conveyed to us in your letter dated 25th ultimo, directing us to examine and report upon the principle on which the Archimedes steam vessel is propelled, we beg to state that we have made such experiments as were practicable, and we request that you will be pleased to submit to their lordships the following report.

On our arrival at this place we made arrangements with Commander Boteler, by which the Widgeon Mail Steam Packet was placed at our disposal. The following statement shows the comparative size, power, and immersion of the two vessels :

1.-Our first trial was upon a run of 19 miles upon a W. S. W. course from Dover Roads, with a light breeze aft and smooth water, but without sails. The engine of the Archimedes worked 27 strokes a minute, and the speed of the vessel was 8 knots per hour. The Widgeon performed the whole distance in six minutes less than the Archimedes.

2. In returning the above 19 miles to Dover Roads, against a moderate head wind, without sails, the engine of the Archimedes worked 26 strokes per minute, and her speed was from 7 to 8 knots per hour. The Widgeon performed the distance in 10 minutes less than the Archimedes.

3. The third experiment was. a run of 19 miles, from Dover Roads to Calais Roads, in a perfect calm, with the sea smooth as glass. Archimedes engine worked 27 strokes per minute, and her speed was from 8 to 9 knots per hour. The Widgeon performed the distance in 3 minutes less than

the Archimedes, and the whole time occupied by the latter on this trial was 2 hours 9 minutes.

4. In returning the above 19 miles back to Dover Roads the weather was dead calm, and the sea smooth as before. The French Mail Packet, called La Poste, started at the same moment. Speed of the Archimedes and her engine as before. Widgeon ran the distance in 4 minutes less than Archimedes, and the Archimedes in 25 minutes less than La Poste. The latter has engines of only 50 horses aggregate power.

5.-On this trial there was a fresh breeze at east, and moderate sea. Both vessels set the whole of their sails, the Archimedes carrying much more canvass than the Widgeon. The run was as before, from Dover to Calais, 19 miles close hauled. Archimedes engine from 27 to 28, and her speed from 9 to 9 knots. Archimedes ran the distance in 9 minutes less than the Widgeon.

6. In returning to Dover with a fresh breeze abeam and all sails set, Archimedes engine 28, and speed 10 knots, she performed the distance in 5 minutes less than the Widgeon.

REMARKS.

These trials clearly prove that the speed of the Archimedes is slightly inferior to that of the Widgeon in light airs or calms, and in smooth water; but as the steam power of the former is 10 horses less, and her burthen 75 tons more than the Widgeon, it is evident that in these vessels the propelling power of the screw is equal, if not superior, to that of the ordinary paddle wheel. In this respect, therefore, Mr. Smith's invention may be considered completely successful.

It is also plain, from the second trial, that in the steaming against even a light air of wind, the low masts and snug rig of the Widgeon gave her an advantage over the Achimedes, with loftier masts and heavier rig; and although the prevalence of calms prevented our trying them farther upon this point in blowing weather, we are satisfied that in strong breezes the advantage of the Widgeon's low rig in going head to wind would be still more apparent.

On the last two trials, however, the power of the sails operated strongly in favour of the Archimedes, as she then beat the Widgeon, and made the passages between Dover and Calais in less time than it has ever been performed by any of Her Majesty' mail packets. The Archimedes went upon this occasion from Dover to Calais in 2 hours 1 minute, and returned in 1 hour 53 minu ́es.

There are two points of great practical importance respecting the screw propeller which ought not to pass unnoticed. First, the noise made by the spur-wheels used in giving the necessary velocity to the propeller shaft. Secondly, the liability of those wheels to rapid wear, and to accidental derangement. The noise alone, we conceive, would prevent its being applied to any of Her Majesty's packets in particular. Mr. Smith, however, proposes to obviate this objection by substituting spiral gearing in lieu of the present cogs; and a model of this method will be submitted to their lordships with this report. As it is the intention of Mr. Smith shortly to make trial of this alteration, we abstain from giving any opinion upon its merits at present.

It is, however, in propelling vessels of war that the value of Mr. Smith's invention will probably be experienced. In such cases, the rumbling noise

in the ship made by the spur-wheels is of no great moment, even if it cannot be overcome; for outside the vessel, this noise is not audible to so great a distance as that made by the common paddle-wheel. A ship fitted with the screw propeller may be used either as a sailing or a steaming vessel, or as both, if required; for we ascertained by experiment that the engine can be connected or disconnected with ease, and in any weather, in two or three minutes. In carrying a press of sail, the inclination of the ship does not diminish the propelling power of the screw, nor lessen the ship's way, as with the ordinary paddle-wheel. The getting rid of paddle-boxes also leaves the broadside battery altogether clear of obstruction, and in boarding an enemy's vessel would allow of the ships lying close alongside of each other.

In conclusion, it is proper to state, that the operation of the screw facilitates the steering, and accomplishes the backing of the ship as easily as the common paddle-wheel.

It is obvious that in the Widgeon and Archimedes, which differed materially both in size and form, an exact comparison could not be made between the performance of the screw and that of the paddle; but the result of the trials clearly showed, especially when the peculiar fitness of the screw for war purposes was taken into consideration, the propriety of trying this new instrument in a less equivocal manner.

With this view the Rattler was ordered to be built, and, that the experiment might be conclusive, so far as a trial between two vessels could make it so, she was constructed on the same lines as the Alecto, the after part being lengthened for the insertion of the screw, and fitted with engines of the same power, and on a plan which had been previously tried in paddlewheel vessels.

The river trials of the Rattler lasted from October, 1843, to the beginning of 1845, and from them it was clearly seen that the screw might be advantageously reduced from two half turns to about one-third of this length, an alteration which greatly reduced the weight, facilitated the operation of shipping and unshipping, and appeared to render unnecessary the wounding to so great an extent the after part of the vessel. Before this last point was decided, it not being evident that the good performance of the shorter screw was not attributable to the greater clearance which the reduction of its length had caused, the screw aperture was partly filled up in a temporary manner, so as to leave the shorter screw the same clearance as the longer one originally had. The result of this experiment showed that the screw aperture in future vessels might be constructed of very moderate dimensions without lessening the effect of the propeller.

It was also evident from these trials that the screw, as an instrument of propulsion in smooth water, was not inferior to the paddle-wheel.

In the early part of the year 1845 the Rattler proceeded, in company with the Victoria and Albert, and the Black Eagle, from Portsmouth to Pembroke. When rounding the Land's End, and steaming against a strong head wind, both these vessels, as might be expected, showed a great superiority, their power being much greater than the Rattler's in proportion to their resistance, and their paddle-floats being constructed on the vibrating principle. This comparative failure of the Rattler made an unfavourable impression on the public mind as to the efficiency of the screw against wind and sea in heavy weather, and this impression in some degree still remains, although no conclusive proof of its inferiority in this respect has yet been afforded; for in the subsequent trials of the Rattler with the Alecto at sea, against strong head winds, the only occasion on which the screw has been fairly tried under such circumstances against the paddle-wheel, no decided advantage on either side seems to have obtained, the advocates of the screw and those of the paddle respectively claiming the superiority, while in fine weather the screw is admitted to have had some advantage over the paddle.

The Rattler was next tried against the Vesuvius in a run from the Thames to Leith, and showed in respect of speed a decided superiority over the paddle-wheel vessel, whose power, as compared with her tonnage, was greater than that of her competitor.

Before joining the squadron under the command of Rear Admiral Hyde Parker, in July, 1845, the Rattler was employed to tow the Erebus and Terror to the Orkney Islands, and she appears to have performed this service to the satisfaction of Sir John Franklin.

Before this time, however, the Bee was constructed with both screw and paddle-wheel for the instruction of the officers of the Royal Naval College, the Dwarf purchased, the conditional speed of 12 miles per hour having been realised, and the Fairy built for the use of Her Majesty; but although the results of the experiments made upon the two latter vessels threw some light upon the action of the screw, and satisfactorily showed that by its means a comparatively high rate of speed could be obtained, yet they could scarcely be regarded as proper data on which to proceed in the construction and fitting of larger vessels.

Some private companies also were led to entertain so favourable an opinion of the screw that they ventured to try it; two of them on a large scale. The Great Britain, of 3,000 tons, arrived in the Thames in January, 1845, and the Great Northern, of 1,515 tons, two years previously. Neither of these vessels was successfully worked for any length of time, the former having been wrecked and the other broken up, but the results obtained, as regards the application of the screw, were considered satisfactory.

These results, probably, together with those obtained from the preliminary trials of the Rattler, and, above all, the favourable reports by naval officers of her performance at sea, induced the Board, in 1845, when the steam navy was about to be considerably increased, to determine that the screw should be adopted. They determined at the same time that the engines should be so constructed that every part of the machinery would be below the water line, an important deviation from the practice which had previously existed, and one which must be regarded as a great step towards rendering steam vessels fit for all the purposes of war. The Board likewise ordered the screw and its fitting to be so arranged, that the operation of shipping and unshipping might be easily performed in any weather, thus rendering the vessels, as far as practicable, perfect sailing ships whenever steam power was not required.

It thus became necessary, in order to fulfil the various requirements, to devise new forms of engines and new modes of application, there being at that time no kind of engine which would effectually answer the purpose. All the eminent marine engineers in the country were therefore called on to propose that construction and arrangement of engine which they might severally think the best adapted, the dimensions of the propeller, and the number of revolutions it would be required to make, being furnished for their guidance, and the necessity of keeping the whole of the machinery below the water line being insisted on, Beyond these necessary conditions the manufacturers were left unfettered, and they, as might be expected, seeing a new and wide field open for their excrtions, submitted a great variety of designs, the result of their great experience and mechanical ability.

These designs differed widely from one another; some were with and some without gearing, and many of them appeared to possess great merit. Of these, selections were made, giving to nearly all the most eminent engineers an opportunity of carrying into effect one at least of the plans which they severally proposed, and in no instance giving orders for more than two engines of the same description-a decision which seems to have been judicious, when it is borne in mind that little experience had then been acquired in this novel application of steam power.

In the year 1815 tenders were accepted for fifteen pairs of screw engines for vessels of various dimensions, and, on the suggestion of the Harbour Defence Commission, eight pairs for what were originally termed block ships, four of them being line-of-battle ships and four frigates. The good performance of the former class seems to have altered their original destination from mere floating batteries to sea-going ships, calculated to

serve with advantage in conjunction with a fleet. Of the frigate block ships, one only out of the four has been ordered to be fitted, and with smaller engines than those originally intended for her. She is not yet completed.

In order still further to test the comparative value of the screw, one paddle-wheel vessel, the Basilisk, was ordered to be built on the same lines as the Niger, and to be fitted with engines of the same power. The result of the trials recently made between these two vessels may be shortly stated. In fine weather, when equal engine-power was exerted, there was little difference of speed, and when sail could be used the advantage was in favour of the screw. There was no opportunity of trying the vessel's head to wind in heavy weather, an important point which hitherto remains undecided by actual experiment.

The expenditure of coal was much greater in the Niger than in the Basilisk, but this disadvantage arose from the construction of the boilers and engines, and not from the difference between the propelling instruments. As far as trials have been made of the various kinds of screw engines, success to a greater or less degree may be said to have been the result of all; certainly none of them can be regarded as failures; but the pecuniary loss sustained by most of the manufacturers, and the great anxiety felt by all, can be fully appreciated by themselves alone.

Sufficient experience has not even yet been acquired for the basis of a sound opinion as to the particular form of engine which should be adopted, but the selection may now be confined within comparatively narrow limits, and experience already points out the strong probability that gearing may be altogether dispensed with, thus entirely obviating the noise so much objected to in the first screw vessel, increasing the simplicity of the machi nery and reducing its bulk and weight.

One important fact, however, which during the early trials of the screw most persons doubted, has been incontestibly proved, and has already led and is calculated to lead still further to a very extensive application of the screw as an auxiliary. It has been established beyond all question that it is unnecessary to adopt complex contrivances for altering the angle of the screw, or to use, as was done in some private vessels, differential gearing, to enable the engines to work advantageously under the varying velocity of the vessel, occasioned by using the sails to a greater or less extent in conjunction with steam-power. If, for example, an engine and screw be arranged to drive a vessel at the rate of five knots, the number of strokes given out by the engine will not be inconveniently increased, or the effect of the screw diminished, when by the addition of sail power the rate of the vessel is increased to 10 knots, the simple screw thus becoming a convenient and efficient auxiliary in all classes of ships, and producing, whenever used in conjunction with sail power, a higher rate of speed than could be obtained under the same circumstances by sail alone. This view is confirmed by the successful performances of many private vessels fitted with auxiliary power. The small vessels first built traded to ports at no great distance, but their voyages have already been extended to Constantinople ; and it now seems highly probable, judging by what has been accomplished, that fine sailing vessels fitted with auxiliary screw power will be found able, if not to rival, at least to approach, full-powered and expensive steamships, in respect of their capability of making a long voyage with certainty, and in a reasonably short time.

Another application of the screw, although inferior in importance to its application as a propeller to ordinary ships, is certainly deserving more attention than has hitherto been paid to it, namely, as a manœuvrer to those large ships in which engines of considerable power cannot be placed, or in which it is considered unadvisable to do so. No doubt can be entertained of the efficiency of such an instrument worked by an engine of even 50 horses power. The full extent, however, of its utility cannot, perhaps, be thoroughly appreciated until it shall have been extensively tried in Her Majesty's navy.

The proper form of the run of screw vessels being at the time of their introduction, and for some time after, a matter rather of speculation than a deduction from known principles or facts, a wide difference of opinion on this important point obtained among those who were engaged in designing these vessels; and the Board, in order to ascertain within certain limits the form which ought to be adopted, directed some experiments to be made on the Dwarf. These experiments were carried out by attaching in a temporary manner to the iron plate some pieces of wood, so as to render her afterbody as full as that of any of the vessels then in progress. The great reduction of speed from 9 knots to less than 4 knots caused by this alteration, unequivocally showed the impropriety of adopting such a form; and

all the vessels then in course of construction, except those not sufficiently advanced to render necessary any alteration, were to a greater or less extent improved in the form of their stern immediately before the screw aperture.

The great importance, or rather the necessity, of introducing forms calculated to aid the action of the screw, cannot be questioned in those cases in which a high speed is regarded as indispensable, it being evident that in such cases a proper form is also indispensable, for without it the object of high speed is not attainable; but even when a moderate speed only is required, a suitable form, although not, as in the former case, absolutely necessary for obtaining the required speed, will be seen to be of greater importance than is perhaps commonly supposed, by a consideration of the great waste of power and its attendant evils occasioned by the adoption of the contrary form. If, for example, a ship, which, if of the proper form, would be propelled at 74 knots, is propelled at 6 knots only, about one-half of the engine power is thrown away, thus wasting half the original cost of the engines and boilers, incurring double the current expense of wear and tear, consuming double the quantity of fuel, and losing the advantage of dispensing with half the weight of engines, boilers, and coals, and reducing by one-half the space which they occupy in the ship; or if the weight and space were not calculated to produce serious inconvenience, throwing away the capability of carrying fuel for perhaps three times the number of days. Probably such considerations as these induced the Board to order the afterbodies of so many screw vessels to be improved, with a view of insuring advantages which were neither doubtful nor of small moment, and which appeared to outweigh the expense of making the necessary alterations. Subsequent experience clearly proved the soundness of the views thus

The numbers in the last column of the table, and in the column next but one preceding it, show approximately the relative excellence in respect of speed, of the forms of the various ships, conjointly with the relative efficiency of the propeller, as adapted to each of them.

The formula by which the calculations are made are founded on the assumption that the resistance of a ship varies as the square of her velocity, and therefore that the power required to produce that velocity varies as the cube, and that the useful effect of the engine, that is, the effect which remains after deducting the power absorbed in overcoming friction, working air pumps, &c., bears a constant ratio to the power developed in the cylinder, known by the term "Indicated Horse Power." The resistance is, in the first of these columns, assumed to vary, cæteris paribus, as the area of the midship section, and in the last column as the cube root of the square the displacement.

of

None of these assumptions, however, more especially the last two, are absolutely correct, but probably they are not so far from the truth as to render useless and uninteresting a comparison, of which they are the basis, made between the performances of any two screw ships, while between two vessels which do not materially differ in engines and displacement, or in the area of their midship sections, such a comparison is not only highly interesting, but it may prove of great value in pointing out the forms of ships and proportions of propellers which ought to be adopted. In some striking cases it is scarcely necessary to make any other comparison than that of speed. For example, the Teazer, after her form had been improved, went above a knot an hour faster with 40 horse engines than she had previously gone with engines of 100 horse power. Again, these engines of 100 horse, when transferred to the Rifleman, a vessel approaching to double the tonnage, drove her, after her form had been altered, as fast as she was previously driven by engines of double the power, and nearly 2 knots faster than the same engines drove the smaller vessel before the alteration of her after-body.

Somerset House, May, 1850.