been started it will work automatically,
providing all the parts are in good running order. Flash steam plants,
however, are difficult to get in the proper adjustment, and once
adjusted they are easily disturbed by minor causes. Owing to the fact
that every square inch of surface in the flash coils is heating surface,
the amount of water supplied to the boiler must be exactly what is
needed. The heat must also be regulated so that the temperature of the
steam will just meet the engine's needs. Many times an increase in heat
causes the steam to reach such a temperature that it will burn up the
lubricating oil before it reaches the cylinder of the engine. This is
liable to cause trouble, because sticking is apt to occur.

Model power boats with speeds as high as thirty-five miles an hour have
been made in America. Such high-speed boats must be assembled with
infinite care, owing to the fact that the mechanism they carry is more
or less erratic in its action, and unless it is well made results cannot
be expected.

[Illustration: FIG. 129]

There are probably few sports more interesting than that of model
power-boat racing. The Central Park Model Yacht Club of New York city is
one of the most progressive clubs in America, and its members not only
have a sail-boat division, but they also have a power-boat division. The
members of the power-boat section have races regularly once a week, and
the most lively competition is shown. It is indeed amusing to watch
these little high-speed boats dash across the pond, their bows high in
the air and their little engines snorting frantically. Owing to the
difficulty of keeping these small racing boats in a straight line, they
are tied to a wire or heavy cord and allowed to race around a pole
anchored in the center of the pond, as illustrated in Fig. 129. The top
of the pole should be provided with a ball-bearing arranged so that the
cord to which the boat is fastened will not wind around the post. In
this way the boats are caused to travel in a circle, and as the cord to
which they are fastened represents the radius of the circle, the
circumference can readily be found by multiplying the radius by 2,
which will give the diameter. The diameter is then multiplied by 3.1416
to obtain the circumference. If the boats were permitted to travel wild
they would run into the bank, a fatal procedure when they are running at
high speed.

Speed boat hulls are usually of the hydroplane or sea-sled