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August, 1909 "TAE. Marine REVIEW Mr. Stevenson Taytor, Vice PRESIDENT @F THE Society OF NAvAL ARCHITECTS AND MARINE ENGINEERS. ly well, though there is frequently trouble from this source. They stand forcing--an evaporation of 8 to 10 Ibs. per square ft. of heat- ing surface being common practice. They are not, however, economical in fuel, but furnish the steam when pushed, and they are usually pushed. Owing to the large amount of water they contain, they are steady in car- tying water and have a large heat- Storing capacity, which equalizes ex- tremes of steam supply and demand, yielding its stored energy in emer- gencies, Owing to the large area at- and about the water-line, variations of wa- ter lever are slow and water is con- sequently easily carried. Their great Weight unfits them for light-draught boats, but it comes in useful as a counterbalance to the Jarge paddle- wheel hanging over the stern, and being productive, is much better than the rock in the otherwise empty end of the meal sack. The boilers being situated at one end of the boat and the engines at the other,: a water lével indicator, having a float in the boiler and a dial on the aft end thereof, shows the water-line many feet away. As a further security, a gage cock 1s opened by a lever, to which a cord is atttached from the engine room; on raising. the lever, the engineer knows by the harmonics if water or steam blows. Engines. The earlier engines were of the simplest possible construction, of the slide-valve type and had a stroke of about four times the diameter of the cylinder. The cylinders were cast with:. the parts in one piece, the valves. being by the usual eccentrics and link mo- operated - 239 tion. Owing to the great length of the long-stroke engines, and. the unavoidable distance from the cylin- ders to the crank-shaft, very long ec- centric rods and pitmans were neces- sary. The large surface of the slide valves, with the high steam pressure, made them hard to move, and caused the. eccentric rods to spring. Fhis; together with the limber hull, which changed its line by different loading, caused uncertain valve action, which gave more or less trouble, especially when, as_ frequently occurred, the boilers primed and muddy water was carried over into the valve box, caus- ing the valve to. groan and cut. To correct this difficulty,. another. form of engine, known as the lever-poppet- valve engine, was adopted. It has many desirable features and is well thought of, and in. general. use fo. this day, In its simplest form, the cylinders are made with two nozzles on each end. The steam. passages, or side pipes, as they are frequently called, are cast separate and fitted to: the cylin- ders... The valve. chambers are .im- mediately on the nozzles, one at each. end for the live steam. | and likewise the exhaust, consequently the ports are very short and clearance is reduced to the minimum. | These poppet valves are raised and lowered, each by its respective lever--the lat- ter being operated by a rocker Shaft, which in turn is controlled bya full- stroke cam. The engine is operated 'by changing the hook of the cam rod to the reverse position. A second cam called the cut-off is furnished, and this is designed to cut off the steam at the point desired--usually one-half, five-eighths, or three-fourths of the stroke. Each engine is mount- ed on a pair of beams, always of wood, until recently, when iron or steel beams have gradually come into use. These beams'are generally called cylinder timbers. It is no unusual thing to hear steamboat people speak of iron cylinder timbers. These beams, being in pairs and very long, reach over many of the boat's frames, to which they are se- cured. A system of trussing with numerous bolts connects these beams, the deck beam, and the floor timbers together. | One of these beams ex- tends out beyond the hull to receive the shaft and wheel. On these two beams, the entire engine and wheel: are . carried. Man hath sought out many inven- tions for providing an adjustable cut- off for poppet-valve engines--among the first and more generally used is that known as the California or Cross cut-off. This device is used in connection with the regular levers,