26 BULLETIN 300, U. S. DEPAETMEXT OF AGEICULTUEE. 
the ditch, are used to a considerable extent in drainage work. A 
common form of this type straddles the ditch on cross-beams. The 
straddle ditchers generally work upstream as do all dry-land exca- 
vators. 
A machine of this type often used is illustrated in Plate V, figure 1 . 
It has a 30-foot boom and a 1-yard dipper. The steam power used 
is obtained through a 2-cylinder, 35-horsepower engine and a vertical 
boiler. The machine rests on a platform which is mounted on two 
steel beams, each 29 feet long, that straddle the ditch. It can be 
mounted on either caterpillar tractors or wheeled trucks. In the 
latter case, each end of the two beams is supported on a 2-wheeled 
oscillating truck, the wheels being 2 feet high and 18 inches wide. 
They run on a wooden track 6 inches thick and 3 feet wide, which is 
built in 6 sections each 20 feet long. One section of the track on each 
side is always unoccupied and these are lifted ahead by means of 
cranes operated by power derived from the engines. This track will 
support the machine in the softest ground. The excavator will dig 
12 feet deep and 22 feet wide on firm ground; with an extension to the 
dipper handle it can dig 18 feet deep. It will deposit the dirt on 
either side at a distance of 32 feet from the center of the ditch. The 
dipper will swing over a bank 14 feet high. Where track is used the 
machine is pulled ahead by a cable from the engine which hooks to 
the track on both sides; this is done without interrupting the work 
of excavating. If desired, caterpillar tractors are furnished instead 
of the wheeled trucks. The front tractors are 4 feet wide by 11 feet 
long, and the rear tractors are 4 feet wide by 7 J feet long. This exca- 
vator has been known to dig as high as 1,500 cubic yards in 10 hours 
in especially favorable material. It has dug through 12 inches of 
frost. From 7 to 8 men can set up and take down the machine in 
from 5 to 8 days. 
Another machine of this type is illustrated in Plate V, figure 2. 
The excavator is made in various sizes; that most commonly used has 
a 38-foot boom and a 1-yard dipper. Power is supplied by an internal- 
combustion engine of 25 or 40 horsepower which burns kerosene, 
gasoline, or distillate oil. The machine rests on a platform which is 
mounted on two steel beams, whose standard span is 32 feet. Exten- 
sion axles are provided which permit of a maximum increase of 3 feet 
in the span. The front axle is mounted on a two-wheeled swiveling 
truck with cast-steel double-flange wheels. The rear end is carried 
by two heavy, wide-faced, double-flange steel wheels set loosely on 
the axle. The shipping weight of this size of dredge, including 
engine, dipper, and machinery, is approximately 38,000 pounds. 
Perhaps the cheapest straddle-ditch excavator of the dipper type 
that is in use is a homemade one which has been used to some extent 
