888 THE STEAM-ENGINE OF TO-DAY,
power of the engine is four or five times the nominal power.
The boiler is of the form shown in the illustrations of semi-
portable engines, and has a heating-surface, in this case,
of 75 square feet. The boat itself is like that seen on page
386, and is 25 feet long, of 5 feet 8 inches beam, and draws
2 feet of water. These little machines weigh about 150
pounds per nominal horse-power, and the boilers about 300.
Some of these little vessels have attained wonderful
speed. A British steam-yacht, the Miranda, 45 feet in
length, 5 feet wide, and drawing 24 feet of water, with a
total weight of 34 tons, has steamed nearly 18 miles an
hour for short runs. The boat was driven by an engine of
6 inches diameter of cylinder and 8 inches stroke of piston,
making 600 revolutions per minute, driving a two-bladed
screw 2 feet in diameter and of 3 feet pitch. Its ma-
chinery had a total weight of two tons. Another English
yacht, the Firefly, is said to have made 18.94 miles an hour.
A little French yacht, the Hirondelle, has attained a speed
of 16 knots, equal to about 18 miles, an hour. This was,
however, a much larger vessel than the preceding. One of
the most remarkable of these little steamers is a torpedo-
boat built for the United States navy. This vessel is 60
feet long, 6 feet wide, and 5 feet deep; its screw is 38
inches in diameter and of 5 feet pitch, two-bladed, and is
driven, by a very light engine and boiler, 400 revolutions
per minute, the boat attaining a speed of 19 to 20 miles an
hour. Another little vessel, the Vision, made nearly as
great speed, developing 20 horse-power with engine and
boiler weighing but about 400 pounds.
Yachts of high speed require such weight and bulk of engine that but little space is left for cabins, and they are usually exceedingly uncomfortable vessels. In the Miranda. the weight of machinery is more than one-half the total weight of the whole. An illustration of the more com- fortable and more generally liked pleasure-yacht is the Day Dream. The length is 105 feet, and the boat draws 5
