(4) Application of the Indicator Diagram to Determine the Stresses on Crank-Shafts. Curves of Twisting Moments 483 (B) Effect of the Inertia of the Reciprocating Parts of the MARINE THE STEAM-ENGINE. CHAPTER I. HISTORY AND PROGRESS. THE earliest steam engines were simply reciprocating engines, and for many purposes such engines are still used even at the present day. Until, however, a suitable method of turning reciprocating into rotative motion had been discovered and utilised not any progress was made in adapting the steam-engine to the propulsion of vessels. The adoption of the crank effected this desirable object, enabled the power of the engine to be transmitted to the propeller smoothly and without shock, and was an indispensable step in the progress of steam navigation. The marine steam-engine may justly be considered as a production of the present century. In the latter part of the eighteenth century several attempts were made to adapt the steam-engine for the propulsion of boats, but none of them were quite successful. The first practical steamboat was built on the Clyde, in 1801, by William Symington, for Lord Dundas. She was called the 'Charlotte Dundas,' and was worked for some time with success as a tug on the Forth and Clyde Canal, but was withdrawn from this service in consequence of an apprehension that the banks of the canal would suffer from the wash of the propeller. This boat was fitted with a single paddle-wheel placed near the stern, driven by a horizontal direct-acting engine, with connecting-rod and crank, and the general arrangement of her machinery would be considered creditable even at the present day. The first recorded instance of steam navigation proving commercially successful was in America, where, in 1807, Robert Fulton built a steam vessel called the 'Clermont,' propelled by paddles driven by a Boulton & Watt engine. In 1812 Henry Bell built a vessel called the 'Comet,' which was successfully worked on the Clyde as a passenger steamer between Glasgow and Greenock. The 'Comet' was propelled by two pairs of paddles, each paddle having four floats or blades, somewhat resembling a pair of canoe paddles, crossed at right angles. The paddles were driven by an engine of somewhat peculiar design, which, however, approximated to the side-lever engine of a later day. This small boat was the first passenger steamer in Europe. B From this date the success of steam navigation may be said to have been secured, and the advancement that has been made since has not consisted so much in the discovery of new principles as in the extension of old ones, and the introduction and development of improved mechanism and workmanship, with consequent economy of fuel. The result has been a progressive increase in the size, power, and speed of steamships and in the extent of their voyages; so that at the present day we have ships displacing 19,500 tons, and capable of being driven. at a speed of 22 knots by engines developing more than 30,000 indicated horse-power, while even larger vessels are under construction. Side-lever engine. The propeller used in the earlier steamships was invariably the paddle-wheel, and the type of engine existing and giving satisfaction on land was naturally adapted at first to rotate these paddle-wheels. Almost all these early engines were, therefore, of the beam type. In America the beam was generally placed over the crank, while in this country it was placed below the crank. The latter type of engine was known as the side-lever engine. The general arrangement of the side-lever engine is shown in outline in Fig. 1, and it represents the type usually fitted not only in the first steam vessels, but also for some years after. On the top of the piston-rod is fixed a crosshead with side-rods, s, attached at each end, which, passing down on either side of the cylinder, are connected to the ends, A, of a beam or side-lever, A B, oscillating on a fulcrum or gudgeon at its centre, c. The opposite ends, B, of these side-levers are fitted with journals carrying the crosstail, to the centre of which, one end of the connecting-rod B D is attached, the other end working on the crankpin D. The air-pump E is worked by side-rods from intermediate points in the side-levers, the upper ends of the air-pump side-rods being jointed to the opposite ends of the airpump crosshead, to the centre of which the air-pump rod is secured. The piston-rod crosshead works in vertical guides to insure parallelism, and the parallel-motion rods used in land beam engines are dispensed with. Grasshopper engines. The arrangement of the side-levers was sometimes varied by making them levers of the third order, the gudgeon or fulcrum being at one end and the steam cylinder placed between the gudgeon and connecting-rod. These engines were commonly known as grasshopper engines. The side-lever type of engine, though very heavy and occupying a large space for the power developed, was safe and reliable, securing a sufficient length of connecting-rod, and having its moving parts practically in equilibrium. It consequently continued in general use for a great number of years, but was at length superseded by the direct-acting type, which was lighter and more compact. Introduction of steam war vessels. Steam vessels were introduced into the Royal Navy in the year 1820, when the 'Monkey,' a vessel of 210 tons, was built at Rotherhithe and fitted by Messrs. Boulton & Watt with engines of 80 nominal horse-power. There were two cylinders, about 35 in. diameter and 3 ft. 6 in. stroke, working at 26 revolutions per minute, giving a mean piston speed of 185 ft. per minute. She was followed in 1822 by the Active,' of 80 nominal horse-power, by the same firm, and in 1823 by the 'Lightning,' of 100 horse-power, by Messrs. Maudslay, and some others whose names appeared for the first time in the Official Navy List for March 1828. These early steam vessels were mainly used for towing and general purposes, and could scarcely be classed as war vessels. Between this date and 1840 seventy other steam vessels were added to the Navy, the majority being fitted with flue boilers and slow-moving side-lever engines worked with steam at a pressure of 4 lbs. per square inch above the atmosphere. The Rhadamanthus,' one of these ships, was fitted with side-lever engines and flue boilers by Messrs. Maudslay, Sons, & Field in 1832. The nominal horse-power was 220, but the engines were capable of being worked up to 400 I.H.P., or 1.8 times the nominal power. The load on the safety valves was 4 lbs. per square inch, and the number of revolutions per minute when working at full power 17, giving a mean piston speed of 175 ft. per minute. The total weight of the machinery was 275 tons, or 13.75 cwts. per I.H.P. developed. Between 1840 and 1850 tubular boilers were introduced. In these |