CHAPTER VIII

EXPERIMENTAL IRON SHIPBUILDING The suitability of iron for shipbuilding purposes had been admitted long before the construction of wooden vessels reached its limit as a profitable undertaking. The first experiments with iron were on a small scale, but they demonstrated the theory of displacement, so that observant marine builders had it borne in upon them that flotation depended rather upon the displacement of the floating body than upon the specific gravity of the material for which the floating body was constructed. But the general public was unconvinced, and making deductions from a limited knowledge of the subject, cried: “Put a piece of iron on the water and see if it will float.” With the increase in the size of wooden steamers and sailing vessels there came the demand for stronger, heavier, and thicker timbers for all parts. This meant so much more unremunerative weight of hull to be carried and so much less space available in proportion to the size of the vessel; so that in time the limit of carrying cargo at a profit and of staunchness of construction was bound to be reached. In wooden steam-ships the limit of length was about 275 feet over all; the _Great Eastern_, built in 1858, proved that there was apparently no limit to the length of the iron ship.[78] [78] Mr. John Ward’s Presidential Address to the Institution of Engineers and Shipbuilders in Scotland, 1907. This length has been exceeded by a few American wooden sailing vessels. The largest square-rigged vessel ever built in America, the shipentine _Shenandoah_, was of wood; her dimensions being 299·7 feet, beam 49·1 feet, and depth 19·9 feet; 3407 tons gross and 3154 net. She was built at Bath (Maine) in 1890 for Messrs. A. Sewall and Co., and was acquired a couple of years ago by the United States Government for a hulk at San Francisco, but has since been recommissioned. Though not a clipper in the strict sense of the word, she was a fast sailer and is sometimes called the last of the Yankee wooden clippers. As wooden hulls were made larger they displayed a tendency, especially when they were built to carry propelling engines, to sag or hog, that is to say, to droop amidships or at the ends. This difficulty was ingeniously overcome in America, where wooden steamers were built longer and lighter and shallower than in Great Britain to suit the vast rivers of that country, by Stevens, who introduced his hogging frame, to which fuller reference has been made in Chapter II. But in the steamers of Great Britain, which were entirely for deep sea, this arrangement was impossible, and the solution of the difficulty had to be found in the use of a material other than wood. The only substitute was iron. The change from wood to iron meant a saving in weight of hull of about thirty to forty per cent., while it is asserted that in a few cases there has been an even greater difference. The saving also meant that the difference in weight could be added to the weight of the cargo, without increasing the displacement; while another advantage was that the beams and ribs and stringers were of smaller dimensions, and the space thus gained, added to that obtained by the substitution of thin iron plates for wooden planking several inches thick, also very considerably increased the space available for the stowage of cargo. Practically every part of a ship was of wood until 1810, in which year the scarcity of oak resulting from the extensive felling of trees in the English forests compelled the use of iron for the knees or connections between the deck-houses and the ribs, and for the breast-hooks and pillars of ships. An experimental iron barge was made in 1787 by J. Wilkinson the ironmaster. As early as 1809 it was proposed by Richard Trevithick and Robert Dickenson that ships should be built of iron, but the proposal was received with derision. The _Vulcan_, built in 1818 at Faskine near Glasgow, is, so far as is known, the first iron vessel constructed for commercial purposes, and so well was she built that as recently as 1875 she was engaged in transporting coal on the Forth and Clyde Canal, and looked little the worse for wear. Her builder was one Thomas Wilson. The first iron steamer, however, was the _Aaron Manby_, built in 1821 at the Horseley Iron Works near Birmingham, to the order of Captain Napier, afterwards Admiral Sir Charles Napier, and Mr. Manby. She was put together at Rotherhithe, and in May 1822 at Parliament Stairs took on board a distinguished party of naval officers and engineers, whom she conveyed for a trip of several hours up and down the river between Blackfriars and Battersea. A contemporary newspaper described her as “the most complete specimen of workmanship in the iron way that has ever been witnessed.” This little vessel was 106 feet long and 17 feet broad, and carried a 30-horse-power engine. Her wheels were of the type known as Oldham’s revolving bars. Her only sea voyage was to France under the command of Captain Napier. Upon arrival she was employed on the Seine or Loire. Another iron vessel intended for navigation on the Seine was shortly afterwards made in this country, and the parts sent to France to be put together. Little appears to have been attempted in this country for some years in the way of iron shipbuilding, although in Ireland three or four small iron sailers or steamers were constructed for inland navigation purposes. But in 1828 John Laird of Birkenhead had his attention directed to iron shipbuilding, and completed his first iron vessel there the following year. Other builders followed where he showed the way, and in less than three years there were shipbuilders on the Thames, Clyde, and east coast of Scotland who were launching iron vessels, the great majority of which were sailing ships. The famous yards on the Cheshire side of the Mersey remained for some time the headquarters of the new industry. The first iron vessels for the United States--not the first iron-plated vessels, and this is a distinction which should be noted--were launched there, and so immediate was the recognition of the advantages of iron ships over wooden ones that by 1835 there had been built at Laird’s the first iron vessels for use on the rivers Euphrates, Indus, Nile, Vistula, and Don. They were small compared with the wooden vessels afloat. The _Garry Owen_, built in 1834 by MacGregor, Laird and Co. of iron, was only 125 feet in length, 21 feet 6 inches beam, with two engines totalling 90 horse-power. There were no Lloyd’s rules as to scantlings for iron steamers in those days, and builders put in as much material as they thought necessary for the strength of the vessel, which usually meant a liberal allowance. The _Garry Owen_ was not much to look at, but she was very strongly built, a circumstance which had a great deal to do with the development of iron steam-ship building. She nearly came to grief on her first voyage, for she was overtaken by a violent storm, which drove her and several other vessels ashore. These others were of wood. Some of them were soon pounded to pieces by the heavy seas, and those that escaped total loss were badly damaged; but the _Garry Owen_, though bumped and dented somewhat, was able to get afloat again little the worse and return under her own steam. If a steamer strongly built of iron could survive a storm and stranding which ended the careers of several wooden ships of larger dimensions, it was admitted that there was no valid reason why other iron vessels should not prove equally safe, especially if they were larger. It was considered that iron steamers might find useful employment in short voyages, and several were built. One of the chief of these vessels was the _Rainbow_, launched in 1837 for the London and coastal trade. She was 185 feet long by 25 feet beam, and of 600 tons, with engines of 180 horse-power. The use of iron in construction was not the only factor in the tremendous change which was coming in shipbuilding. A new form of propulsion was necessary, and it was found in the screw propeller. Before considering this, however, the development in the construction of paddle-wheels and of the engines designed for paddle-boats may be noticed. The ordinary paddle-wheel had the floats fixed upon the radial arms, but it was soon found that an improvement could be made by causing the floats to assume a position vertical, or nearly so, at the moment of contact with the surface of the water, and to retain that position until the float had left the water. To effect this the floats are not bolted to the arms but pivoted, and are retained in the required position by means of levers operated by an eccentric pin. By this means a much greater propulsive force was exerted. The old style of paddle-wheel with fixed floats is now very seldom employed. These wheels are now only to be found in vessels in which the expense of construction has to be cut down to a minimum, or in a certain type of steamer plying in shallow rivers, where the wheel is rather large, and the dip of the float slight; but here again economy of construction may count for more with the proprietor of the boat than the increased speed he could obtain with the more expensive feathering wheels. Many of the modern wheeled vessels have floats of steel, but in the great majority of cases wood is employed, elm being largely used for this purpose. The floats are usually about four times as long as they are broad. Various forms are used, some being left square at the corners, others are rounded, others again have the outer edge elliptical in shape, and the experiment has also been tried with a fair measure of success of inclining the floats to the axis of the wheel, instead of having them parallel to it. The advantages claimed for this last method are that the stream of water formed by the rotatory motion of the paddles is driven slightly away from the sides of the vessel, instead of in a direction parallel with her length. Wheels of this type, however, lose much of their effectiveness when the engines are reversed. Radial wheels are sometimes made with the floats adjusted so that they enter the water almost perpendicularly, but they are much more oblique under this arrangement when leaving the water. A difficulty which paddle-vessels have to contend with is that of securing a proper immersion of the floats. For a vessel in smooth water the immersion of the top edge is usually calculated at about one-eighth of the breadth of the float; but for a vessel intended for general sea service, an immersion of not less than half the breadth of the float is allowed, that is to say, the float at its moment of deepest immersion has a height of water above it equal to half its diameter. If the float goes much deeper the efficiency of the wheel becomes impaired. This is a point which has to be taken into consideration in designing paddle-boats, so that the maximum power shall be available when the vessel is fully laden, and shall not be much lessened when the vessel is running light. The earliest steamers suffered greatly in this respect as their designers had not discovered the right size of wheels or floats to suit the hulls. A loaded vessel consequently went very slowly owing to the great depth to which her floats were immersed. To overcome this difficulty an ingenious system of what can best be called reefing was invented. Affixed to the axle of the wheel was a rod with an arrangement of cogs at the end, and these fitted into a series of teeth in rods affixed to the floats, so that it was a simple matter to expand or contract the effective diameter of the wheel by altering the position of the floats as required. The same result has sometimes been obtained by a system of levers, but the toothed wheel business was the older. It was tried on a few of the earlier boats on the Clyde, not always, however, with success. A peculiarity of some of the larger paddle-wheels in use in America is that they are not only of much greater size than those in use in Great Britain in proportion to the size of the boat, but they have a proportionately less immersion and the wheel is constructed in a very different fashion. The floats, instead of being of one piece, as here, are constructed of three narrow fixed strips, two of which are on the same radius but have a space between them equal to the breadth of the third strip, which is placed a few inches behind the vacant space. It is contended that this method disturbs the water less than the broad float and increases the propelling efficiency. Probably the most notable instance is the great wheel of the _Sprague_. Referring now to the construction of the engines of the earliest boats, Symington’s _Charlotte Dundas_ used a horizontal direct-acting engine, and the general arrangement of her machinery would be considered creditable even at the present day.[79] The engine of the _Savannah_ was of the inclined direct-acting type. The type of engine which Newcomen invented has been retained for many years, but the oscillating or walking beam which is such a conspicuous feature of nearly all the American river craft has been placed by engineers in this country below the crank axle instead of above. The type of engine with the beam below the crank axle is known as the side lever. It is a type peculiarly suitable to paddle-wheels, and this being the only method of propulsion adopted on this side of the Atlantic for many years, there was little change for a considerable period in the shape of the engines, which therefore attained to a high stage of perfection until the limit of their profitable employment was reached. When larger engines became necessary, in consequence of the rapidly increasing size of vessels, the great weight of the side-lever engines proved a serious drawback. [79] Sennet and Oram’s “The Marine Steam-Engine,” 1898. Engineers were not long in devising a more compact form of machinery, and direct-acting engines were introduced, these involving the abandonment of the use of the heavy side levers. As the side-lever engines were made larger it became customary to use two beams, one on each side, and a rod from one end of each of these connected with a cross-piece at the top of the piston-rod. The other ends of the double beam were united by a cross-piece which carried from its centre the rod or lever which worked the crank of the paddle-shaft. Where it became necessary to use two engines in one vessel, they were so arranged that while one rod and crank were at their period of least activity, the other pair were exerting their greatest effort. The system of condensation of steam, which it would take too much space to describe in detail, is also a matter of great importance in determining the power of the engine, but the principle upon which the condensation is effected is well known, and the various methods of condensation can easily be ascertained from the numerous handbooks on engineering. [Illustration: MAUDSLAY’S OSCILLATING ENGINE.] Another early form of marine engine was that in which the side levers were arranged as levers of the third order, the fulcrum being at one end and the steam cylinder placed between it and the connecting-rod. The peculiar motion thereby given to the machinery caused this type to be known as the grasshopper engine, from a fancied resemblance to the long legs of a grasshopper. The direct-acting engines were much more compact, more powerful, and lighter than the old side levers. The necessity of providing a connecting-rod of sufficient length was met by Messrs. Maudslay by the provision of two cylinders. The cross-head was not unlike the letter =[T]=, the foot of which passed down between the cylinders, and the lower end of this was fitted with a journal from which the connecting-rod extended to the crank in the axle. A still further improvement was made when the oscillating engines were invented, which form an even more compact and simple type. Messrs. Maudslay fitted a pair of oscillating engines in 1828 into the paddle-steamer _Endeavour_, and subsequently into several ships. This form of engine was improved upon by Mr. John Penn, the famous engineer at Blackwall, and the perfection which he gave it has not been surpassed. The great feature of this method is that the trunnions are hollow, and the steam is admitted to and exhausted from the cylinders through them. The connecting-rod is dispensed with and the upper end of the piston-rod acts directly on the crank pin. This type of engine is the most economical for space and weight that has yet been provided for paddle-wheel engines, the majority of which of late years have been made on this system. Its adaptability for certain classes of work has given the paddle-wheel a long lease of life. Paddles are peculiarly suitable for certain conditions, such as smooth waters and shallow rivers, where speed and light draught combined with considerable carrying power are essential. The Indian rivers, for instance, early demanded suitable steamers, and the paddle-steamers _Lord W. Bentinck_, _Thames_, _Megna_, and _Jumna_ were built of iron in 1832 for the East India Company for the navigation of the Ganges. They were designed and constructed by Maudslay, Sons, and Field, and fitted with oscillating cylinder engines of 30 nominal horse-power. They were flat-bottomed and were shipped to India in pieces. They were 120 feet in length, 22 feet beam, and had a draught of 2 feet. Their tonnage was 275, builders’ measurement. The steamers sent to India, however, from over sea were not the only ones in that country. As far back as 1820 there was launched at Bombay the first steamer built in India; she was intended for service on the River Indus. Her engines were designed by a Parsee. She must have been a familiar object to many hundreds of Anglo-Indians during her long career. She was only broken up as recently as 1880, and her end came not through weakness but through her supersession by more modern and commodious boats. There is a custom peculiar to Bombay, and stated to be of Parsee origin,[80] of driving a silver spike into the stern of a vessel at its launch. This is said to be analogous to the placing of coins under the foundation-stone. The ceremony was observed at the launching of a paddle-steamer at Bombay in 1875, when a nail some seven inches in length and three-quarters of an inch in diameter was used, but whether such a ceremony took place at the launch in 1820 is not recorded. If it is a Parsee ceremony, however, it is quite likely to have been observed, for the East clings faithfully to its traditions. [80] _Notes and Queries._ A paddle-wheel steamer built in 1859 for service on the Indus had a draught of only 20 inches. The hull was a frameless cellular raft, but the walls of the deck cabin were worked into the depth of the vessel, which was thus made a girder 200 feet in length, and by this contrivance the engine and boilers, weighing 150 tons, were supported. A couple of plate girders having a run of 115 feet were included in her middle length. These were 15 feet deep and formed the sides of the cabins, and they also projected under the deck for a distance of 35 feet. The hull of the vessel was practically a long, flat, shallow box; the stern was rounded and the keel was turned up about 2 feet to allow of the water rising easily. The bow was rather fine and designed on the wave-line principle. The engines were of 688 horse-power and the boilers had a pressure of 25 lb. The paddle-wheels were 14¹⁄₄ feet in diameter. Her load displacement was 331 tons and her draught when laden was only 24 inches. The _Ly-ee-moon_, launched in 1860 by the Thames Iron and Shipbuilding Company, resembled in some respects the steam-yacht of the Queen. She was built for Messrs. Dent and Co. for service between Hong-Kong and Shanghai, and was 270 feet in length and 27 feet 3 inches beam with a draught of 12 feet 6 inches. She was of 1003 tons register and 1394 tons displacement; her oscillating engines had cylinders of 70 inches diameter, with a stroke of 5¹⁄₂ feet. She was the first merchant vessel fitted with Lindsay’s apparatus for scaling the boilers with superheated steam. The paddles were 22 feet diameter. She had two masts, the foremast carrying lower yard, topsail yard and topgallant yard, and the trysails reached to the topmast head and gave her a good spread of canvas. She also carried several guns, and the sponsons were so fitted that the guns could be worked on them in case of need. Her speed was from 18 to 19 miles an hour. She afterwards passed into the possession of the Japanese; the story goes that when she was making her first run with Japanese only on board, the Japanese engineers, being unable to stop the engines, put the helm hard over and sat down to wait with true Oriental patience until the steam gave out and she stopped of her own accord. The _Ly-ee-moon_ afterwards passed into Australian ownership and she ran for a long time in the excursion and coastal trade, and was finally wrecked in March 1886, when seventy persons lost their lives. The paddle-steamer _Leinster_ was one of four constructed of iron for the mail service between Holyhead and Kingstown in 1860 by Samuda Bros. She had nine water-tight bulkheads. A vessel intended for this service, on which exceedingly rough weather is at times encountered, through which the vessels are driven at full speed in order to ensure the punctual delivery of the mails, has to be built very strongly to stand the strain of the rough seas. For this purpose the paddle-boxes were formed of iron plates internally, continued from the sides and bulwarks of the vessel together with a strong girder extending from each bow. Two of the four, the _Ulster_ and _Munster_, were withdrawn from the service in 1896-7 and turned into barquentines, their places being taken by larger vessels of the same names. The present bearers of the names are twin-screws and have triple-expansion engines. The engines of the former boats had each two oscillating cylinders, 98 inches in diameter and having a stroke of 78 inches, situated immediately below the paddle-shaft. They had each eight multitubular boilers bearing steam at 20 lb. pressure, arranged in pairs, four before and four abaft the engines, and with their ends backed to the sides of the vessel so as to allow of the stoking of the furnaces from a middle gangway. The paddle-wheels, 32 feet diameter, had fourteen floats 12 feet in length by 5 feet in width. The indicated horse-power was 4751, and the average speed in all weathers was 15¹⁄₂ knots. [Illustration: MODEL OF THE ENGINES OF THE “LEINSTER.”] Messrs. Scott, Russell and Co. launched at Millwall in September 1854, for a Sydney company, the steamer _Pacific_, which was expected to prove one of the fastest vessels afloat. She was 270 feet in length over all, breadth 82 feet, depth 34 feet, and tonnage 1200. She had oscillating engines of 450 horse-power nominal and over 1000 effective, four independent boilers, and her feathering paddle-wheels were of exceptional strength. She was estimated to steam sixteen miles an hour. [Illustration: THE “PACIFIC.”] There was launched in the beginning of 1861 by Messrs. Pearse and Co. of Stockton-on-Tees, for the conveyance of troops on the lower Indus, a vessel which fulfilled the rather unusual requirements of a Government Commission appointed to discover the best means of navigating the Indian rivers which, though broad, are often shallow in places, and abounding in sandbanks. This vessel was 377 feet over all, beam 46 feet, breadth over paddle-boxes 74 feet, depth 5 feet, with a displacement at 2 feet draught of 730 tons. Her tonnage was 3991 under the old system of measurement. Her engines, by Messrs. James Watt and Co., were of 220 nominal horse-power, with horizontal cylinders of 55 inches diameter and 6 feet stroke. The paddle-wheels were 26 feet in diameter. The hull was of steel strengthened longitudinally by four arched girders, two of which carried the paddle-wheels, and the other two extended nearly the full length of the ship. Other girders strengthened her athwartships. She had no rudders in the ordinary sense, but was steered at each end by blades, which were raised from or lowered into the water at the required angle. The vessel had two tiers of cabins, and could accommodate 800 troops and their officers. The paddle-steamer _Athole_, built by Messrs. Barclay, Curle and Co., Ltd., in the year 1866, was the first steamer to be fitted with the saloon above the upper deck. The credit for this improvement rests entirely with the late Mr. John Ferguson, who was then manager of the shipbuilding yard. So impressed were Lloyd’s that they desired Mr. Ferguson to patent his improvement, but this he refused to do as he considered it ought to be given to the shipbuilding world free of royalty. Messrs. A. and J. Inglis were the builders in 1882 of the steel paddle-steamer _Ho-nam_, which has the distinction of being one of the few, and probably the first, English-built vessels constructed on the American plan. She was rigged as a two-master carrying fore and aft sails only. Her paddles were placed very far aft, and she was fitted with a walking beam-engine. She was constructed for the Chinese coastal trade and was of 2364 tons gross register, and was so successful that others of the same type followed. These necessarily brief notices of some of the more remarkable paddle-boats of modern times, together with references in other chapters to paddle-steamers of still more recent years, are sufficient to show that the earlier form of propulsion has never been entirely superseded by the screw. Possibly the earliest definite attempt to apply the screw for propelling purposes was made by David Bushnell in his abortive submarine exploit, an account of which appears in Chapter XII. hereafter;[81] but the propeller seems to have been very primitive. The screw propeller was also proposed in 1752 by the mathematician Daniel Bernoulli. A patent was granted in 1794 to William Lyttleton for a screw propeller which was caused to revolve by an endless rope passing round a wheel at the end of the axle. It was a distinct attempt to solve the problem and nearly succeeded, but it failed because there was too much of it. Had he been contented to use one pair of blades he would have obtained better results than by using two pairs of wide blades and two odd blades, arranged with three blades on either side of the axle so that his propeller became really a long spiral wheel. He also failed from the lack of sufficient power to drive the wheel, as manual labour only was used. Still, a boat fitted with this screw was tried at the Greenwich Dock, London, and a speed of two miles an hour was stated to have been obtained. [81] See p. 376. In 1800 Mr. Shorter, master of the transport _Doncaster_, brought out two plans of propulsion. One was in the form of two duck-foot paddles with an alternate movement; the other was a two-bladed screw propeller. The latter was attached to an inclined shaft carried by a universal joint to the deck of the vessel. One of these methods was said to have moved the _Doncaster_ at a speed of about a mile and a half an hour, the contrivance being driven by eight men running round a capstan. It is difficult to believe from the picture which accompanies his plan, dated 1800, that a transport of the size depicted could have been moved at half that speed with the apparatus shown, although the fact that it was mechanically propelled is attested by credible witnesses. The first really successful screw-propelled boats were those of Colonel John Stevens, which were in operation on the Hudson River from the years 1802 to 1806, and were the first to be used for the effective navigation of the waters of any country. References have already been made to Stevens’ experiment with paddle propulsion in 1796. When he, Chancellor Livingston, Nicholas J. Roosevelt, and Isambard Brunel were making experiments in steam propulsion on the Passaic River, New Jersey, they tried a horizontal centrifugal wheel in a boat of 30 tons, drawing water from the bottom of the boat and discharging it at the stern. This is in its general principles similar to the plan that Mr. Ruthven tried in England on the _Waterwitch_ more than half a century afterwards. They also, unsuccessfully, attempted to use elliptical paddle-wheels. Probably the best description of Colonel Stevens’ propeller is that which he himself contributed to the _Medical and Philosophical Journal_ of New York in January 1812. He refers to the “mischievous effects necessarily resulting from the alternating stroke of the engine of the ordinary construction” which induced him to turn his attention to the rotary principle of steam-engine construction. “For simplicity, lightness, and compactness the engine far exceeded any I have yet seen. A cylinder of brass, about eight inches in diameter and four inches long, was placed horizontally on the bottom of the boat: and by the alternate pressure of the steam on two sliding wings, an axis passing through its centre was made to revolve. On one end of this axis, which passed through the stern of the boat, wings like those on the arms of a windmill were fixed, adjusted to the most advantageous angle for operating on the water. This constituted the whole of the machinery. Working with the elasticity of the steam merely, no condenser, no air-pump was necessary; and as there were no valves, no apparatus was required for opening and shutting them. This simple little steam-engine was, in the summer of 1802, placed on board a flat-bottomed boat I had built for the purpose. This boat was 25 feet long, and about 5 or 6 feet wide. She was occasionally kept going until the cold weather stopped us. When the engine was in the best order, her velocity was about four miles an hour. I found it, however, impracticable, on so contracted a scale, to preserve due tightness in the packing of the wings in the cylinder for any length of time. This defect determined me to revert again to the reciprocating engine.” [Illustration: STEVENS’ 1804 ENGINE, FITTED INTO OPEN BOAT WITH TWIN-SCREW PROPELLERS.] Stevens and his son were crossing the Hudson in this boat on one occasion when the boiler, which was constructed of small tubes, gave way, and the next boiler was constructed with the tubes placed vertically. The engine was kept going for a fortnight or three weeks in the latter part of the summer of 1804, the boat making excursions for two or three miles up and down the river, and for a short distance he could get a speed out of it of seven or eight miles an hour. Stevens’ early experiments with the screw propeller taught him that a vessel driven by only one screw has a tendency to move in a circle. This tendency is displayed in single-screw vessels to the present day. As is well known, a vessel driven by a right-handed screw will deflect slightly to the left, and a vessel driven by a left-handed screw will have a tendency to turn to the right. The explanation given of this peculiarity in the Stevens’ boat by Dr. P. Jones, who was superintendent of the United States Patent Office up to the date of its reorganisation under the law of 1836, in the _Journal of the Franklin Institute_ for 1838, is that this tendency was due to the lessened resistance, as the vanes of the propeller rose towards the surface, in consequence of the greater ease with which the water was removed out of the way. Consequently Stevens overcame this difficulty by using two such wheels placed side by side and revolving in reverse directions. The original screw-engine is still in existence in the Museum of the Stevens Institute at Hoboken, New Jersey. The original boat, of course, has long since disappeared. A replica of it was tried with the old engine on the Hudson in October 1844, and attained a speed of eight miles an hour. One great difficulty which early steamers had to contend with was that of boiler pressure. It should be remembered that the five distinct means Stevens proposed in connection with his screw propeller were: