16 BULLETIN 300, U. S. DEPARTMENT OF AGRICULTURE. 
ber and size of stumps to be encountered is of the highest importance. 
Owing to the expense of knocking down, transporting, and setting 
up a dredge, it is necessary to select or use one of the size that will 
do the most work at one building. This requires an intimate knowl- 
edge of the layout of the proposed work, and of the accessibility of 
the different portions. 
It is the opinion of many contractors that the use of dredges with 
narrow hulls, say less than 18 feet, is to be avoided except where 
the ground is so hard that the bank spuds rest firmly and bear the 
weight of the swinging load; in soft ground it may be cheaper to 
use a wider hull, even though it be necessary to make the ditch wider 
than is specified. 
The various makers of dredges have compiled and made available 
to prospective purchasers tables, giving full descriptions of their ma- 
chines. These tables give for each of the numerous dipper capacities 
such data as the following: Length of boom and dipper handle; dis- 
tances machines will dig below water line and dump above water line ; 
distance from center of hull to center of dump; dimensions of hull 
and amount of lumber required to build; sizes of hoisting and swing- 
ing engines; and daily digging capacity of machine. With the aid 
of these data, and having in mind the ditch specifications and the 
factors enumerated in the preceding paragraph, the proper size of 
dredge for a particular ditch may be determined. 
Where it will be necessary to cope with stumps, this factor will 
often be the ruling one in determining the capacity of machine 
needed. 
When designing a ditch, the engineer should always have in mind 
the type and size of machine to which the work is adapted. So far 
as is consistent with other considerations a ditch system should be 
so designed as to give the contractor the greatest amount of exca- 
vation for a given size of dredge. This point can best be illustrated 
by a practical example. A certain ditch was designed with a bottom 
width varying from 16 to 46 feet, and with a cut of about 7 feet 
throughout the entire length of 15 miles. The ditch as planned was 
too wide at its lower end to be constructed by an ordinary-sized 
dredge, unless equipped with the telescopic or the convertible power 
spuds. By making the cut deeper at the lower end, the width of 
the ditch could have been made considerably less and an ordinary 
dredge could have dug the ditch throughout. The necessity of using 
two dredges of different sizes on such a comparatively small job 
of course tended to increase the unit cost of the work. Conditions 
may, it is true, be such as to make a deeper ditch impracticable, as, 
for instance, scour due to too great a velocity, the lack of a free 
outlet, the presence of rock, and other conditions. 
