Part 21 (1/2)
After Fulton and Stevens had thus led the way, steam-navigation was introduced very rapidly on both sides of the ocean; and on the Mississippi the number of boats set afloat was soon large enough to fulfill Evans's prediction that the navigation of that river would ultimately be effected by steam-vessels.
The changes and improvements which, during the 20 years succeeding the time of Fulton and of John Stevens, gradually led to the adoption of the now recognized type of ”American river-boat” and its steam-engine, were princ.i.p.ally made by that son of the senior Stevens, who has already been mentioned--ROBERT L. STEVENS--and who became known later as the designer and builder of the first well-planned iron-clad ever constructed, the Stevens Battery. Much of his best work was done during his father's lifetime.
[Ill.u.s.tration: Robert L. Stevens.]
He made many extended and most valuable, as well as interesting, experiments on s.h.i.+p-propulsion, expending much time and large sums of money upon them; and many years before they became generally understood, he had arrived at a knowledge not only of the laws governing the variation of resistance at excessive speeds, but he had determined, and had introduced into his practice, those forms of least resistance and those graceful water-lines which have only recently distinguished the practice of other successful naval architects.
Referring to his invaluable services, President King, who seems to have been the first to thoroughly appreciate the immense amount of original invention and the surprising excellence of the engineering of this family, in a lecture delivered in New York in 1851, gave, for the first time, a connected and probably accurate description of their work, upon which nearly all later accounts have been based.
Young Stevens began working in his father's machine-shop in 1804 or 1805, when a mere boy, and thus acquired at a very early age that familiarity with practical details of work and of business which is essential to perfect success. It was he who introduced the now common ”hollow water-line” in the Ph[oe]nix, and thus antic.i.p.ated the claims of the builders of the once famous ”Baltimore clippers,” and of the inventors of the ”wave-line” form of vessels. In the same vessel he adopted a feathering paddle-wheel and the guard-beam now universally seen in our river steamboats.
As usually constructed, this arrangement of float is as shown in Fig.
87. The rods, _F F_, connect the eccentrically-set collar, _G_, carried on _H_, a pin mounted on the paddle-beam outside the wheel, or an eccentric secured to the vessel, with the short arms, _D D_, by which the paddles are turned upon the pins, _E E_. _A_ is the centre of the paddle-wheel, and _C C_ are arms. Circular hoops, or bands, connect all of the arms, each of which carries a float. They are all thus tied together, forming a very firm and powerful combination to resist external forces.
[Ill.u.s.tration: FIG. 87.--The Feathering Paddle-Wheel.]
The steamboat Philadelphia was built in the year 1813, and the young naval architect took advantage of the opportunity to introduce several new devices, including screw-bolts in place of tree-nails, and diagonal knees of wood and of iron. Two years later he altered the engines of this boat, and arranged them to work steam expansively. A little later he commenced using anthracite coal, which had been discovered in 1791 by Philip Ginter, and introduced at Wilkesbarre, Pa., in the smith-shops, some years before the Revolution. It had been used in a peculiar grate devised by Judge Fell, of that town, in 1808.
Oliver Evans also had used it in stoves even earlier than the latter date, and at about the same time it had been used in the blast-furnace[81] at Kingston. Stevens was the first of whom we have record who was thoroughly successful in using, as a steam-coal, the new and almost unmanageable fuel. He fitted up the boiler of the steamboat Pa.s.saic for it in 1818, and adopted anthracite as a steaming-coal. He used it in a cupola-furnace in the same year, and its use then rapidly became general in the Eastern States.
[81] Bishop.
Stevens continued his work of improving the beam-engine for many years. He designed the now universally-used ”skeleton-beam,” which is one of the characteristic features of the American engine, and placed the first example of this light and elegant, yet strong, construction on the steamer Hoboken in the year 1822. He built the Trenton, which was then considered an extraordinarily powerful, fast, and handsome vessel, two years afterward, and placed the two boilers on the guards--a custom which is still general on the river steamboats of the Eastern States. In this vessel he also adopted the plan of making the paddle-wheel floats in two parts, placing one above the other, and securing the upper half on the forward and the lower half on the after side of the arm, thus obtaining a smoother action of the wheel, and less loss by oblique pressures.
In 1827 he built the North America (Fig. 88), one of his largest and most successful steamers, a vessel fitted with a pair of engines each 44-1/2 inches in diameter of cylinder and 8 feet stroke of piston, making 24 revolutions per minute, driving the boat 15 to 16 miles an hour. Antic.i.p.ating difficulty in keeping the long, light, shallow vessel in shape when irregularly laden, and when steaming at the high speed expected to be obtained when her powerful engine was exerting its maximum effort, he adopted the expedient of stiffening the hull by means of a truss of simple form. This proved thoroughly satisfactory, and the ”hog-frame,” as it has since been inelegantly but universally called, is still one of the peculiar features of every American river-steamer of any considerable size. It was in the North America, also, that he first introduced the artificial blast for forcing the fires, which is still another detail of now usual practice.
[Ill.u.s.tration: FIG. 88.--The North America and Albany, 1827-'30.]
Stevens next turned his attention to the engine again, and adopted spring bearings under the paddle-shaft of the New Philadelphia in 1828, and fitted the steam-cylinder with the ”double-poppet” valve, which is now universally used on beam-engines. This consists of two disk-valves, connected by the valve-spindle. The disks are of unequal sizes, the smaller pa.s.sing through the seat of the larger. When seated, the pressure of the steam is, in the steam-valve, taken on the upper side of the larger and the lower side of the smaller disk, thus producing a partial balancing of the valve, and rendering it easy to work the heaviest engine by the hand-gear. The two valve-seats are formed in the top and the bottom, respectively, of the steam-pa.s.sage leading to the cylinder; and when the valve is raised, the steam enters at the top and the bottom at the same time, and the two currents, uniting, flow together into the steam-cylinder. The same form of valve is used as an exhaust-valve.
At about the same time he built the now standard form of return tubular boilers for moderate pressures. In the figure, _S_ is the steam and _W_ the water s.p.a.ce, and _F_ the furnace. The direction of the currents of smoke and gas are shown by the arrows.
[Ill.u.s.tration: FIG. 89.--Stevens's Return Tubular Boiler, 1832.]
Some years later (1840), Stevens commenced using steam-packed pistons on the Trenton, in which steam was admitted by self-adjusting valves behind the metallic packing-rings, setting them out more effectively than did the steel springs then (and still) usually employed.
His pistons, thus fitted, worked well for many years. A set of the small bra.s.s check-valves used in a piston of this kind, built by Stevens, and preserved in the cabinets of the Stevens Inst.i.tute of Technology, are good evidence of the ingenuity and excellent workmans.h.i.+p which distinguished the machinery constructed under the direction of this great engineer.
[Ill.u.s.tration: FIG. 90.--Stevens's Valve-Motion.]
The now familiar ”Stevens cut-off,” a peculiar device for securing the expansion of steam in the steam-cylinder, was the invention (1841) of Robert L. Stevens and a nephew, who inherited the same constructive talent which distinguished the first of these great men--Mr. Francis B. Stevens. In this form of valve-gear, the steam and exhaust valves are independently worked by separate eccentrics, the latter being set in the usual manner, opening and closing the exhaust-pa.s.sages just before the crank pa.s.ses its centre. The steam-eccentric is so placed that the steam-valve is opened as usual, but closed when but about one-half the stroke has been made. This result is accomplished by giving the eccentric a greater throw than is required by the motion of the valve, and permitting it to move through a portion of its path without moving the valve. Thus, in Fig. 90, if _A B_ be the direction of motion of the eccentric-rod, the valve would ordinarily open the steam-port when the eccentric a.s.sumes the position _O C_, closing when the eccentric has pa.s.sed around to _O D_. With the Stevens valve-gear, the valve is opened when the eccentric reaches _O E_, and closes when it arrives at _O F_. The steam-valve of the opposite end of the cylinder is open while the eccentric is moving from _O M_ to _O K_.
Between _K_ and _E_, and between _F_ and _M_, both valves are seated.
_H B_ is proportional to the lift of the valve, and _O H_ to the motion of the valve-gear when out of contact with the valve-lifters.
While the crank is moving through an arc, _E F_, steam is entering the cylinder; from _F_ to _M_ the steam is expanding. At _M_ the stroke is completed, and the other steam-valve opens. The ratio (E M)/(E L) is the ratio of expansion.
This form of cut-off motion is still a very usual one, and can be seen in nearly all steamers in the United States not using the device of Sickles. It was at about this time, also, that Stevens, having succeeded his father in the business of introducing the steam-engine in land-transportation, as well as on the water, adopted the use of steam expansively on the locomotives of the Camden & Amboy Railroad, which was controlled and built by capital furnished princ.i.p.ally by the Messrs. Stevens. He at the same time constructed eight-wheeled engines for heavy work, and adopted anthracite coal as fuel. In the latter change he was thoroughly successful, and the same improvement was made with engines built for fast traffic in 1848.
The most remarkable of all the applications of steam-power proposed by Robert L. Stevens was that known as the Stevens Steam Iron-Clad Battery. As has already been stated, Colonel John Stevens had proposed, as early as 1812, to build a circular or saucer-shaped iron-clad, like those built 60 years later for the Russian Navy.
Nothing was done, however, although the son revived the idea in a modified form 20 years afterward. In the years 1813-'14, the war with England being then in progress, he invented, after numerous and hazardous experiments, an _elongated sh.e.l.l_, to be fired from ordinary smooth-bored cannon. Having perfected this invention, he sold the secret to the United States, after making experiments to prove their destructiveness so decisive as to leave no doubt of the efficacy of such projectiles.
As early as 1837 he had perfected a plan of an iron-clad war-vessel, and in August, 1841, his brothers, James C. and Edwin A. Stevens, representing Robert L., addressed a letter to the Secretary of the Navy, proposing to build an iron-clad vessel of high speed, with all its machinery below the water-line, and having submerged screw-propellers. The armament was to consist of the most powerful rifled guns, loading at the breech, and provided with elongated shot and sh.e.l.l. In the year 1842, having contracted to build for the United States Government a large war-steamer on this plan, which should be shot and sh.e.l.l proof, Robert L. Stevens built a steamboat at Bordentown, for the sole purpose of experimenting on the forms and curves of propeller-blades, as compared with side-wheels, and continued his experiments for many months. After some delay, during which Mr. Stevens and his brothers were engaged with their experiments and in perfecting their plans, the keel of an iron-clad was laid down in a dry-dock which had been constructed for the purpose at great cost. This vessel was to have been 250 feet long, of 40 feet beam, and 28 feet deep. The machinery was designed to furnish 700 indicated horse-power. The plating was proposed to be 4-1/2 inches thick--the same thickness of armor as was adopted 10 years later by the French for their comparatively rude constructions.
In 1854, such marked progress had been made in the construction of ordnance that Mr. Stevens was no longer willing to proceed with the original plans, fearing that, were the s.h.i.+p completed, it might prove not invulnerable, and might throw some discredit upon its designer, as well as upon the navy of which it was to form a part. The work, which had, in those years of peace, progressed very slowly and intermittently, was therefore stopped entirely, the vessel given up, and in 1854 the keel of a s.h.i.+p of vastly greater size and power was laid down. The new design was 415 feet long, of 45 feet beam, and of something over 5,000 tons displacement. The thickness of armor proposed was 6-3/4 inches--2-1/4 inches thicker than that of the first French and British iron-clads--and the machinery was designed by Mr. Stevens to be of 8,624 indicated horse-power, driving twin-screws, and propelling the vessel 20 miles or more an hour. As with the preceding design, the progress of construction was intermittent and very slow. Government advanced funds, and then refused to continue the work; successive administrations alternately encouraged and discouraged the engineer; and he finally, cutting loose entirely from all official connections, went on with the work at his own expense.