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August, 1909 able surface, the greater resistance be- ing put where the power is greatest, and the heavier buckets placed to bal- ance the irregularities of the power. In side paddle-wheels, where there is an independent engine to each wheel, they are not only weighted, but the buckets are narrowed at the points of least power, so that the wheels are oval shaped. A simple, general, average rule gives one bucket for each foot of the wheel's 'diameter. This makes the buckets a lite over 3 ft... apart, which, in average sizes, works out nearly right. The very large majority of paddle- wheels on our rivers is of the radial type. While feathering paddle-wheels are used most commonly abroad, 1 know of but one instance on the Mis- sissippi river and its tributaries. This is the small U. S. stern-wheel launch Lucia, designed under the direction of Major Mackenzie. Paddle-wheels have a slight advantage over the screw-pro- peller wheel, in that they are more accessible, and their diameter and _ sur- face are easily ingreased or dimin- ished by changing the position and the width or length of the bucket. The buckets are frequently divided in their length, one-half being set one-half a space in advance of the other, giving more even and continuous bearing on the water. A prominent superintendent in the east has put himself on record as stating that paddle-wheels give a more comfortable boat than the screw-wheel. This, however, depends much on _ the depth of the water and the quality of the practice in both cases. One great objection to the paddle- wheel is its great weight. The wheel of the great Sprague, including its shaft, is said to weigh 160 tons, not- withstanding the fact that the shaft has a 2l-in. hole through its center. Hollow shafts in this practice do not seem to be satisfactory. Some boats have had two, with unsatisfactory re- sults, which are now replaced with a solid shaft. Iron ones are still favored by many. Doctors and Heaters. The so-called doctor is, in reality, a walking beam engine, % fitted with two vertical, cold-water, single-acting piston pumps, and two __ hot-water plunger pumps, having pot valves in each case. Above the framing of the engine are carried two _ cylindrical heaters, one for each engine to ex- haust into. The cold-water pump takes water from the river and discharges it, either over a series or perforated Plates, or through a coil into these two heaters. This water, thus par- "'TAE. Marine REVIEW tially heated, is taken by the two hot- water plunger pumps and fed to the boilers. The exhaust steam from the two heaters is conveyed through a long exhaust pipe to the smoke-stack, where it discharges, through reduced nozzles, to increase the chimney draft. This produces a back pressure in the ex- haust pipes and the engines of from 4 to 6 lb. The feed-water pipe is carried through the long exhaust pipe to the boilers and on its way becomes heated to nearly the boiling point. This heater system is about the only enconomizer, and is one of the very good things on the boat. Since the day of direct-acting pumps, - much fun has been poked at the west- ern doctor, but it is a very efficient, though a heavy and clumsy means to an end. It is very singular that while the eastern practice may ridicule the walk- ing-beam doctor, they do not see the much greater beam in their own eye-- the side-wheel-beam engine, which the westerner would not think of using. The doctor, nevertheless, despite its great weight, has its advantages. It is much more economical in the use of steam than a duplex plunger pump. The plungers, being vertical, are suited to pumping water containing mud and sand. The valves are. plain, strong, easily ground, tight and accessible, and the wear and tear is little. Steam Pipes, "Throttle, Etc. The steam pipes, quite long, lead from the steam dome to the engine- room on the center longitudinal line of the boat and are bent downward to the position of the main throttle valve; the latter is mounted on a stand which travels on rollers to and fro, according to the expansion and con- traction of the long steam pipe or the change of line of the hull due to dif- ferent loading or excessive waves. From the throttle valves two branch steam pipes pass, by long and easy bends, up, then overhead and down to the engines. From the position of the throttle, the engineer stops, starts, ships up and unships the cut-off by means of a system of levers, without moving from the throttle. The engines on a stern-wheel boat, being connected to the shaft at right angles, start readily. On side-wheel boats the throttle valve is at each engine, one being operated by the engineer, the other by his assistant, known as striker. When the engines are stopped, the poppet valves of the engines are raised, allowing the steam to blow through the engines; this relieves the boilers 241 and keeps the engines warm, ready to start again. Compound Engines. The accepted compound engine for western river practice is that known as the tandem type, though some build- ers prefer the cross compound. In Europe the latter is more generally used, and when used for stern-wheel- ers is placed in the middle of the aft end of the boat. The wheel shaft is divided with a crank on each inside end. These cranks, at right angles, are connected by a drag link. The engines are set on an inclined bed, one pitman being connected to each crank, The tandem compound lends _ itself to the American system, as it is placed in the same manner as the simple en- gine--on the cylinder beams. The pis- tons of the high and _ low-pressure engine being on the same piston rod, the balancing of the work in each cyl- inder is not important, and the cylinder ratio may be increased to use high- pressure steam--say a ratio of 1 to 5 or 6--with one tandem evompound on each end of the shaft. The work may be varied by throttling, 'each engine doing equal work. In the cross compound, the cylinder ratios should be such as to equally divide the work between both cylinders, and this ratio does not properly admit of very high initial pressure, the largest ratio being about 1 to 4, where- as in the tandem it may be 1 to 6, which gives better results, While the compounding of these . long-stroke engines gives a more economical use of steam, when prop- erly designed and installed they are very: much heavier and: take up valu- able room on the boat and when used in connection with condensers this con- dition becomes more aggravating, The average western river paddle- wheel engines, whether simple, com- pound, or compound-condensing, are many times heavier and more cumber- some than engines of the same class used in connection with screw-wheel propellers. ; The foregoing applies to the several classes of western river steamers, tow- boats, passenger steamers--stern or side-wheelers. All side-wheel boats are passenger steamers. All tow boats are stern-wheelers, but all stern-wheelers are not towboats. In the upper rivers, the stern-wheel boats preponderate, whereas in the lower rivers, where water is more 'abundant, side-wheelers prevail. It is in the larger boats that compounding of the engines is more general. Notwithstanding the admitted econ-