The distinguishing feature of these wheels is that the floats or paddles revolve or vibrate upon radiating arms or axes, so as to enter and leave the water edgewavs, the planes lying parallel to the keel or nearly so, but standing at right angles to it when fully immersed. The following description is abridged from Mr. Dawson's specification, published in the Repository of Arts:-
Fig, 1 represents awheel the paddles of which gradually change their position as they enter and quit the water, which change is effected by affixing on the axis of each paddle two wipers a b crossing each other at right angles and of the form shown in Fig. 2. To the side of the vessel is fixed an immovable plate, on the surface of which are three projecting arcs cde, being portions of circles, as shown in Fig. 3.
One of these arcs is immovable, (describing three parts of a circle;) another, d, draws in and out on guiding rods by a lever acting through the sides of the vessel, the third arc e slides up and down the fixed arc c; the use of this sliding arc e will be particularly pointed out hereafter. For the purpose of effecting the change of position of each paddle gradually and without shock, both the fixed and movable arcs terminate at each end in inclined planes. If these are made long and the wipers in proportion, the motion will be very gradually performed. When the wheel is made to revolve, the point of the wiper a of the paddle entering the water encounters the commencement of the inclined plane of the movable projecting arc d, rolls up it, and the paddle is thereby gradually turned one fourth of a circle on its axis; by which means the position of the paddle is changed from the edge on which it entered the water to full surface, in which position it is retained by the movable arc d, and may be made to act for any determinate space, say from f to g.
The other wiper b then encounters the inclined plane of the immovable arc c, rolls down it, and the paddle is thereby gradually turned another quarter of a circle on its axis, by which means it is turned round to the opposite edge on leaving the water. In this position it is retained by the fixed projecting arc c until it again encounters the water.
Supposing it was required, with the view of obtaining a greater action on the wave, that the paddles of a feathering wheel should exceed three or four feet in breadth, say six or eight feet, it is obvious that the friction and difficulty in effecting the change of position in the paddles would be materially increased, and the number of paddles would be limited. Under these circumstances, instead of making a double feathering wheel, that is, of joining two wheels of three feet together to obtain the breadth required, I prefer constructing a feathering wheel with paddles three feet broad, on each side of which I fix shrouding boards h h, of twenty inches width, at a certain angle; by this means I avoid all increase of friction, check the lateral escape of the fluid from the paddles, and obtain a commensurate surface for the water to act on. Each paddle i and its fixed shrouding boards h h enter the water on their edges; as the wheel revolves, the paddle changes its position and presents its full surface, and thereby closes the open space between the boards, fter a given time it gradually opens as it rises out of the water, and returns to its first position on the edges.
By this arrangement, although the surface of action is increased, the ease of entering and escaping from the water is retained; and, according as the arcs are fixed on one side or the other of the wheel, the water will be thrown off the paddles in or out from the sides of the vessel.
It has been fairly objected to wheels on the above construction, that they are expensive, complicated, and work with much more friction than the wheels commonly employed. To obviate these objections I constructed the wheel shown in Figs. 6 and 7. The paddles of this wheel are formed of two boards posited at a certain angle face to face on their respective axes, leaving only a space sufficient for the free escape of the water between; in this position they are retained by stops from opening any farther. When the wheel revolves, the water acting on the broad surface of the paddles causes them to close as they enter the water, and to remain so until they begin to rise out of it, when the weight of the water lodging on the narrow surface only, causes them to open, and in consequence, the water falls through without being lifted.
Head's Patent Paddle-wheels, (Dec. 18, 1828.) - The principle of this invention is identical with one of those patented by Dawson in 1814, already described. Each paddle consists of two leaves, fixed to radiating and revolving spindles, supported at the outer end by a cross bar attached to the opposite arms of the wheel, and at the other end by a similar bar attached to the two bosses. That part of the paddle shaft which lies within the bosses of the wheel is surrounded by a tube or collar, which passes through one of the bosses, and is fastened to one side of the paddle-box, so that it remains stationary whilst the wheel revolves. Upon this collar are fixed two bosses, in the periphery of each of which is cut a groove composed of portions of two parallel circles, connected by two oblique channels as shown in the diagram; in which a is the grooved boss fixed upon the collar b, and c the paddle-shaft revolving within the collar.
Leeming's Eccentric Sliding Floats, (1835.) - The object of these i provemptits is to diminish the resistance of the back-water; with this view the arms a v of the wheel (which are fixed radially), have grooves extending the greater portion of their length, and in these grooves the paddle boards b b are placed; an eccentric groove c is fixed to the side of the vessel, and a corresponding groove is also fixed to the spring beam of the paddle-box, and a pin in each end of the paddles works in these grooves and regulates the distance of the paddle from the centre of the wheel. The eccentric grooves are so placed as to cause the entering paddles to stand at the extremities of the arms, so as to act with full effect; but after passing the perpendicular the paddles are drawn by the action of the eccentric grooves nearer to the centre of the wheel, so as to lift less back-water as they rise out of the water.
Endless Chain Paddles
With the view of obtaining a direct impulse in the line of the vessel's motion, in lieu of the oblique motion imparted by the ordinary paddle-wheel, trials have been made at various times of floats attached to endless chains, passing over two drums placed at the sides of the vessel at a considerable distance asunder.