208 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1919. 
and cambered top and presenting a useful lifting area of 203 square 
feet. 
The hull is 5 feet 9 inches in diameter and is quite heavily built. 
A system of fore-and-aft stringers are secured to several bulkheads 
and the frame is a continuous spiral wrapped around these. ‘The 
half-inch planking is applied longitudinally and, to resist bending 
and torsional stresses, a number of longitudinal and diagonal steel 
wires are run over the frame. The hull is covered with canvas laid 
spirally in the opposite direction to the framing. Except for the 
cockpit and a fuel tank in the stern. the hull is unused and would 
accommodate a score of people. 
The forward hydrofoil sets, upon which the machine largely de- 
pends for support when under way, are hung on a steel tube 52 inches 
in diameter, which passes through the hull 15 feet from the bow. 
The tail set acts also as a rudder, the struts offering sufficient lateral 
surface for this purpose. It is mounted on a column 6 feet from the 
stern and is operated by tiller lines running to the steering wheel 
in the cockpit. 
The motors are of the low-compression Liberty type, developing 
350 horsepower and weighing 800 pounds each. They are mounted on 
a special form of wooden trussed bed, the horizontal members of 
which are finished in the form of aerofoils, adding a useful lifting 
surface of 83 feet. The function of this surface and that of the deck 
is to provide an air-cushioning effect which acts as a sort of shock ab- 
sorber when the machine is traveling in choppy water. 
The motors are provided with compressed-air starters and all 
controls are led to the cockpit. The fuel is forced from the tank in 
the hull to the level of the carbureters by air pressure maintained by 
a hand pump. 
The center of gravity of the machine is 25 feet from the bow, but 
when she is running at full speed the line of thrust of the air propel- 
lers is 10 feet above the base of support, which brings the virtual 
center of gravity about 23 feet from the bow. 
Now step into the cockpit and we will take a ride, and if you want 
to hear anything for the rest of the day stuff some cotton into your 
ears before the motors are started, for they are not mufiled. - Over 
goes the starboard motor with the crackle of a machine gun and those 
on the dock scurry from the cyclone caused by the whirring propel- 
ler. The mooring lines are cast off and we slip out into the lake at 
about 10 knots. 
Baldwin gives the air to the port motor and the exhaust becomes 
a continuous roar. At 15 knots you feel the machine rising bodily 
out of the water, and once up and clear of the drag, she drives ahead 
with an acceleration that makes you grip your seat to keep from be- 
