ounted in
this way it will be necessary to make the propeller-shaft longer, as is
shown in Fig. 47.

Still another method of driving the propeller is illustrated in Fig. 48.
This method is so simple that the author feels explanation to be
unnecessary.

Clockwork can often be employed for propulsion purposes, but this method
is not very satisfactory. It is also very difficult to obtain suitable
clockworks to install in a boat. Oftentimes it will be possible to
salvage the works of an old alarm-clock, providing the main-spring is
intact. It is a very easy matter to mount the clock-spring and connect
it to the propeller. Any one of the aforementioned methods can be
employed.

Steam propulsion has its advantages; but, on the other hand, the writer
is not inclined to recommend it as strongly as the electric method for
reliability. Of course, steam is a more powerful agency in the
propulsion of small boats and thereby greater speed is attainable by its
use.

[Illustration: FIG. 49]

[Illustration: FIG. 50]

[Illustration: FIG. 51]

Here is a very simple small power plant suitable for driving boats up to
3-1/2 feet in length. The boiler is shown in Figs. 49 and 50. The method
of assembling the boiler is pictured clearly in Fig. 49. A brass or
copper tube about 2-1/2 inches in diameter is used. Two end pieces are
cut to shape and forced into the boiler ends. A hole is drilled in the
center of these pieces before they are put in place. After the end
pieces are forced in place solder is carefully flowed around their
edges. The brass rod is then threaded at each end and placed
concentrically within the boiler, as shown in Fig. 49. A nut is placed
on each end of this rod and tightened. The nut is then soldered in
place. This brass rod, called a stay-rod, prevents the end of the boiler
from blowing out when the steam pressure has reached its maximum value.
Three holes are drilled in the brass tube, as shown. One is to
accommodate the steam feed-pipe that goes to the engine; another is for
the safety-valve, and still another for the filling plug. The
safety-valve and filling plug are both shown in Fig. 51. The little
spring on the safety-valve is adjustable, so that the valve can be
regulated in order to prevent it from blowing off at pressures lower
than that at which the engine operates.

[Illustration: FIG. 52]

A suitable firebox for the boiler is shown clearly in Fig. 52. This is
cut to shape from stovepipe iron an