PADDLE-WHEEL. An appliance in steam vessels be whirl the power of the engine is made to act upon the water and produce locomotion. It consists of a skeleton wheel of iron. on the outer portion of whose spokes flat boards, called floats or paddles, are fixed, which beat upon the water, and produce, continuously, the same effect as is given, in an intermittent manner, by the blades of oars. The use of paddle-wheels in eon junction with steam as a motive power dates from about the commencement of the nineteenth century. but the employment of the paddle-wheel itself is as ancient as the time of the Egyptians. A specimen is also known to have been tried in Spain in the sixteenth century.
In the usual form of paddle-wheel. called the radial, the floats are fixed, and it will he seen that a certain loss of power is involved, as the full force of the engine on the water is experi enced only when the float is vertical, since when the floats enter or leave the water the power is mainly employed in depressing or lifting the particles of water. This resistance has great force at the moment of starting, or when progress is very slow, as is illustrated by the small power a paddle-steanier evinces when trying to tug a stranded vessel off a sandbank; but when in full progress. the action is less impeded by this cir cumstance, the water in front of the wheel being depressed. and that abaft being thrown into the
form of a wave. The extent of the immersion much influences the economy of power, as will be readily understood if the consequences of immersion up to the centre of the wheel be imagined. An immersion somewhat over the top of the lowest float is about the most ad vantageous, and, in order that the floats may be as nearly as possible vertical when they strike the water. it is advisable to give the wheel as large a diameter as possible, and to place the axis at the highest available point in the vessel.
To overcome the drawbacks to the radial wheel, there was devised early in the nineteenth century the fcatheriny paddle-irhcrl, in which the floats are mounted on axes, and are connected by rods with a common centre, which revolves upon a pin placed eccentrically to the axis of the paddle wheel. By this method the floats are kept. while immersed, at right angles to the surface of the water. So long as the water is smooth the gain is great, consequently feathered floats are much used in river-steamers. Paddle-wheels have been almost entirely superseded by screw propellers (see SCREW PROPELLER) on all vessels except river and lake boats. See STEAM NAVIGATION.