It will be evident on a little inspection, that this paddle wheel of Mr. Bucha nan's is, (as he observed himself) liable to the objections stated to exist against the last described apparatus, namely, that of impeding the speed of the boat, by its comparatively o sl w motion on entering and leaving the water. This fault, together with that of great complexity, and consequent liability to breakage, will probably preclude its successful adoption ; although there have been many recent attempts to introduce it.
In the early constructed steam-boats only one steam cylinder was employed, but now it is the invariable custom to use two steam cylinders ; each of which is made to work a crank upon the axle of the paddle wheels. The cranks are at right angles to each so that when one is passing the dead point, the other is exerting its utmost force. In America the engines are usually on the high-pressure plan, and the boilers as well as the principal part of the machinery upon deck. In British steam-vessels the engines are principally constructed on the low-pressure condensing principle, and the machinery all below deck. The latter circumstance renders it indispensable to diminish the height of the en gines, and to transfer the working beams from above the cylinders to beneath them. To reduce the height also, the cylinders are made of greater diameter, in proportion to their length, than in land engines. A tolerably correct idea of the general arrangement of the machinery, as well as the various accommo dations in a steam passage boat, will be afforded by the figures on the oppo site page.
The upper figure represents a longitudinal and vertical section, from stem to stern, of a steam-vessel ; and the lower figure a plan of the same, with the deck removed ; similar letters in each figure refer to the corresponding parts.
a a are two boilers ; to the chimney, leading from the flues of both the fires ; c is the steam-pipe, only partly brought into view in the section, but its course i is better seen in the plan, where it is shown to proceed from both the boilers into a single tube, which conveys it into another cross tube, that connects it to the two cylinders d d, by the intervention of the valve boxes f f. The air-pumps e e, are worked by the main beam, and the eccentric, for giving motion to the valves, is shown at g. The paddle-wheels h h, are usually attached to the main
crank by a coupling-box, or toothed wheels, which enables the engineer to throw off either of the propelling wheels at pleasure; i, one of the paddle-boxes, seen only in the section. j is the fore-cabin, k the after-cabin, o o are staircases ; 1111 the framing of timber which supports a platform or deck (commonly called the gangway,) which nearly surrounds the hull of the vessel.
The American steamers are for the most part fitted up with more extensive and splendid accommodations than our own. The dining-room of The North America is described as being 150 feet in length, and to be capable of dining from 700 to 1000 passengers The floors are covered with the finest carpets ; the curtains of damask silk, and the ornamental work elaborately carved, and richly gilt. The walls are hung with the works of celebrated artists, &c. The fare from New York to Albany, including three meals, is only four dollars. It is usually performed (144 miles,) within twelve hours, including stoppages in the voyage at ten or twelve different places. There being no machinery below, the whole extent of the hull of the vessel is left open for those venous commo dious arrangements, which in reality constitute an American steamer into a grand floating hotel. The British steamers being, on the contrary, built to sus tain the waves of the ocean, are differently constructed. A good example of the construction of steamers in this country is afforded by The United King doss packet, from London to Leith, which is usually performed in from 40 to 50 hours. She measures 148 feet in the keel, and the breadth of her beam is 45 feet. The accommodations for passengers are of the most elegant and con venient description. She is propelled by two engines of 100 horse power each, (constructed by Mr. Napier, of Glasgow,) which are considered as specimens of very superior workmanship. As these sorts of engines very nearly resemble each other, we have selected those of this vessel as illustrations of the made in which steam-boat engines are usually constructed. The boilers to this engine we have already described under that head, pages 214, 215, Vol I.; we shall therefore confine our notice here to the engines only.