EXCAVATING MACHINERY USED IN LAND DRAINAGE. sy 
the spud. All types of spuds must be equipped with a strong locking 
device; they must also be so designed that little time is lost in raising 
or lowering them. A dipper dredge with vertical spuds is illustrated 
in Plate I, Figure 2. 
THE BOOM. 
The boom may be built of either steel or wood. In the former case 
it is made of standard structural sections strongly riveted together. 
Wooden booms are used quite extensively, as they are more flexible 
and will spring back to their original shape if deflected shghtly out 
of line. Of wooden booms several different styles are built. One 
which is spread wide at its foot makes possible the swinging of long 
booms with the revolving deck-swing circle. Long booms (75 feet or 
over) are always of the open or knee build with a solid filler at the 
‘lower end and the chords sprung over posts or cross bulkheads (PI. 
I, Fig. 1). This construction greatly reduces wind pressure when 
swinging. The intermediate lengths differ somewhat in design and 
are of both the solid-filler type and the open type. All booms are 
trussed on the top, bottom, and sides. They are usually suspended at 
an angle of 30° from the horizontal. 
Practice has taught that the length of boom must bear a definite 
relation to the width of the hull. Even on a large dredge it is not 
advisable to have the boom longer than 80 to 90 feet, although manu- 
facturers will build them 100 feet long if desired. Large dredges 
with long booms are much slower in operating. The same number of 
men is required for operation in either case. 
The lower end of the boom is pivoted. The upper and outer end 
is connected to the yoke at the top of the A frame by means of ad- 
justable wire cables. A sheave at the outer end of the boom carries 
the cable leading from the dipper through the fair-lead sheaves at 
the lower end = the boom and thence to the hoisting drum. 
On the early type of dipper dredge, chains were used for hoisting 
and backing. These were hard to fie and would break without 
warning. Steel cable has entirely replaced the chain, since it is less 
expensive, easier to install, clean, and noiseless; also its weakening, 
due to wear, is more readily detected and accidents are therefore less 
likely. 
DIPPER AND DIPPER HANDLE. 
Dipper handles are usually of combined wood and steel construc- 
tion. Those made entirely of steel have not given satisfaction, as a 
sudden stress may throw them permanently out of line. In the com- 
bination type the elasticity of the wood allows some deflection with- 
out permanent injury. The wooden handles are covered with steel 
plates on top and bottom; on the larger sizes all sides are armored. 
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