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SECTION I.

On The Application Of Steam Power To Ships Of Wae.

1. It would be foreign to the plan of this work to enter into details respecting the invention of the steam-engine, or to describe the gradual improvements which it has subsequently undergone;" a brief notice only will be given of the several steps by which it has been rendered applicable to the purposes of navigation.b

In the beginning of the eighteenth century the Steam-Engine, or, as it was then called, the Atmospherical Engine, produced its effect solely by the admission of steam into the cylinder at its lower extremity; the steam by its elasticity forced the piston to the upper part of the cylinder, when, a vacuum being caused by a sudden condensation of the steam in consequence of a jet of cold water being introduced, the pressure of the atmosphere on the upper surface of the piston caused this to descend: steam being again admitted below, the piston was forced upwards; and, again, a vacuum being formed as before, the atmosphere caused the piston a second time to descend. This alternate ascent and descent of the piston caused corresponding movements of the pump-rod, by which means water was raised. The steam-engine was long employed for this purpose only.

* For a full explanation of the marine steam-engine in its present improved state, the reader is referred to the treatise on that, important subject by Mr. Thomas J. Main, Mathematical Professor in the Royal Naval College, Portsmouth.

b The author wishes it to be understood that this historical and descriptive notice relating to steam is introduced only for the benefit of the general reader, or of those officers who may not have had the advantage of studying the subject at the Eoyal Naval College.

B

2. The first improvement by Watt consisted in admitting the steam alternately at the bottom and top of the cylinder, so that, when the vacuum was formed below the piston, the pressure of the steam above caused the piston to descend; and the vacuum being then formed above the piston, the pressure of the steam below caused it to ascend. In this manner a reciprocating motion of the piston was maintained; and, as the pressure of the steam could be made to exceed that of the atmosphere, a greater degree of power was obtained; and this augmented power was enabled to act uniformly on the piston. The patent for this great improvement was obtained by Mr. Watt in 1769; and, in 1780, Pickard took out one for converting the reciprocating motion of the pump-rod into a rotatory motion. This was effected simply by means of a crank, and in the following year Mr. Watt invented what he called the sun and planet wheel-work, by which the same end was gained as by the crank; and this rotatory motion was a great step towards the employment of the steam-engine as a means of propelling ships on the water. At length, in 1802, the first boat with paddle-wheels propelled by steam was constructed.

3. It would be improper to dwell on the supposed project of a Spanish captain named Garay, who is said, in 1543, to have exhibited a vessel propelled by poles to which motion was communicated by boiling water, or on the unsuccessful experiments made in France in 1774-5, and in America in 1783, to give motion to a vessel furnished with paddle-wheels, which were made to revolve by means of a small steam-engine; but it deserves to be particularly mentioned that in the years 1788-9 experiments were made at Dalswinton in Scotland on the use of paddle-wheels, at first moved by mechanical means, for the propulsion of vessels on water. These were commenced by a Mr. Millar of that place, and were conducted under his auspices by Messrs. Taylor and Symington; and to the former of these two engineers is ascribed the idea of employing steam-power to give motion to the wheels, which was afterwards put in practice by the latter. Mr. Symington's experiments were carried on under the patronage of Lord Thomas Dundas; and, in 1789, a boat called the ' Charlotte Dundas,' propelled by a double stroke engine (Watt's patent) and paddle-wheels, was tried upon some water in the neighbourhood of Dalswinton; it is said to have been moved at the rate of 5 miles in an hour. Experiments of the same nature continued to be made by the abovenamed gentlemen; and, in 1802, Symington built two steamboats which conveyed goods on the Forth and Clyde canals.

4. The American Chancellor Livingstone had, in 1798, made an unsuccessful attempt to construct a steamboat, to be used on the Hudson; and, in 1803, being in France, he constructed a steam-vessel, in conjunction with Fulton, to be used on the Seine: this also failed, but Fulton afterwards visiting England, was introduced to Symington, and was, by that engineer, allowed to inspect the vessels which he had constructed. Fulton subsequently returned to America; and, in 1807, he completed a vessel with paddle-wheels, moved by a steam-engine which had been executed by Boulton and Watt in England: this vessel, called the 'Clermont,' was the first which was employed as a passage-boat, and its first voyage was made on the Hudson, from New York to Albany.

5. The first steamboat which plied on the Thames is said to have been brought from the Clyde by a Mr. Dawson in 1813: as a speculation the measure failed; but, from the year 1815, steam-vessels have constantly been employed for the conveyance of passengers up and down the river.

6. A Mr. Stevens, junior, of New York, is said to have been the first who took a steamboat to sea; this was about the year 1804, and the vessel is said to have been moved by a machine resembling a smoke-jack: this may consequently be considered as the first application of the Screw Propeller in navigation. The first ship propelled by steam which crossed the Atlantic was the 'Savannah,' a vessel of 350 tons burthen. It was built and equipped at New York, and, in 1819, it proceeded direct to Liverpool; from thence it proceeded to St. Petersburg, and subsequently recrossed the Atlantic, having used steam during the whole voyage. Between the years 1842 and 1845 Her Majesty's steam sloop 'Driver,' commanded by Captains Harmer and Hayes, made the circuit of the earth.

7. It may be interesting to know that as long since as the year 1785 Mr. Bramah obtained a patent for a submerged propeller on the principle, it is said, of a windmill-sail; subsequently patents were obtained by other persons for propellers constructed on similar principles, which being moved by mechanical means, sufficiently demonstrated the efficiency of that construction. In 1836, Captain Erecsson, a native of Sweden, obtained a patent in England for a screw-propeller, and a steam-vessel constructed by that engineer with the screw at the stern was tried on the Thames, in presence of the First Lord of the Admiralty and the Surveyor General of the Navy; the success is said to have been complete, but the new machine failed to gain the approbation of the British Government. The subject being, however, brought to the notice of Captain Stockton, of the United States' Navy, then in London, this officer strongly recommended it to the authorities in America. Under his direction an iron vessel with a screw propeller was constructed in England; and, after crossing the Atlantic, it was employed on the Delaware and Rariton Canal. This vessel afforded the first practical evidence of the success of the screw as a means of propulsion, both for the inland waters of a country and on the high seas.

8. The greatest improvement which has been made in the manner of applying steam as a moving power, with respect to the union of force with economy, has consisted in what is called the expansive principle. It is at present the custom to allow steam whose force of elasticity is expressed by a pressure varying from 25 lbs. to 40 lbs. per square inch, including the pressure of the atmosphere, to enter the cylinder of a steam-engine; and when the piston has moved through a space varying from two-fifths to three-fifths of the whole stroke or range of the piston, to close the steam-slide so that no more steam may enter till the piston is at the end of the stroke, leaving that which has been admitted to complete the stroke by its expansive power.

9. Now, if steam of a given elasticity be allowed to act uniformly on the surface of the piston through the whole length of the stroke, the efficient momentum of the steam would be expressed bjpal; p denoting the pressure of the steam on a square inch of the surface of the piston, a the area of that surface in square inches, and I the length of the stroke also in inches. But if the steam be cut off after the piston has moved through a part of the stroke which is expressed by m I (m being a proper fraction), the efficient momentum of the expanded steam during the remainder of the piston's

a T) Tfh I (L 'V movement will be expressed by the integral of ——

between the limits x=ml and x=l: (the density, elasticity, or pressure of the steam in any part of the cylinder being inversely proportional to the space, or distance of the piston from its place at the time the

steam was cut off.) This integral hap ml hyp. log. —,

which added to apm I, the momentum of the steam previously to being cut off, the sum is the efficient momentum of the steam thus acting expansively. If m = Ts,

the hyp. log. of — is equal (nearly) to 2; and the

whole momentum becomes \ apl nearly. Thus, with T^ths, or less than one-seventh, of the quantity of steam, consequently of the quantity of fuel," a power is obtained equal to one-third of that produced by the whole of the steam if allowed to act unexpansively; it

* Since the pressure on a piston varies with the weight or density of the steam, and the weight of a body of steam is equal to the weight of the water which generates it, it follows that if the quantity of fuel consumed when the steam is employed unexpansively he represented by l, the quantity consumed will be expressed by ) when the steam is used expansively.

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