FEATHERING PADDLE-WHEELS.          209

in propelling the vessel; in all other positions, it is only the
horizontal component of the pressure which exercises any pro-
pelling effect, and the greater the obliquity of action, the less is
this horizontal component. A large proportion of the power
spent in driving paddle-wheels of this form, is wasted in beating
and churning the water with the floats, when these are in
positions on either side of the vertical line through the centre.
The deeper the immersion of the radial paddle-wheel, and the
smaller its diameter for agiven depth of immersion, the greater
is the obliquity of action, and therefore the greater is the loss of
efficiency.

Radial wheels are sometimes made in such a way that the
floats can be quickly detached and fixed in positions nearer the
centre of the wheel. This is advantageous, when froni an
increased load, the draught of the vessel becomes greater, thus
causing greater immersion of the paddle-wheels, since then the
diameter of the wheel is reduced, and thus by reducing the
immersion of the floats, diminishes the loss from oblique action.
This operation m known as <i>reefing</i> the paddle-wheels.
On account of their small efficiency, radial paddle-wheels are
now rarely used, having given place to the more efficient feather-
ing wheels.

<i>Feathering Paddle-Wheels</i>. - This form of paddle-wheel, as
illustrated, is designed with the object of getting rid of the dis-
advantages which arise from the obliquity of action of the radial
wheel.

The floats are not fixed rigidly to the radial arms, but are
hinged to them, and are provided with levers, G L, so that they
may be turned into any position. These levers are connected
by rods to a boss or eccentric strap, E, which rotates on a central
fixed pin on the sponson beam. This central pin is so placed in
relation to the centre of the wheel, that the floats enter the
water edgewise, and when in the water, are kept by the levers
in a position nearly perpendicular to its surface. The radial
arms of the paddle-wheel, F, are forged with small brackets on
them at right angles to their lengths, so as to receive the round
pins about which the floats hinge.

To find the position of the eccentric pin in order that the
floats may enter the water edgewise, and pass through it nearly
perpendicular to its surface, the following simple construction is
necessary: - Suppose the lower edge, P, of a float to be just
entering the water, then, in order that the float may enter edge-
wise, the resultant of its own velocity of rotation and the
horizontal velocity of the vessel, must lie in the plane of the float.
Let, P A, represent the velocity of the vessel, and, P B, that of

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