EXCAVATING MACHINERY USED IN LAND DRAINAGE. 15 
plished by swinging the boom. In this case the spuds must be fitted 
with racking. The raising of the spuds and the pinning up of the 
dredge may also be accomplished by means of independent units for 
each spud. The engines for the side spuds are compound-geared 
to grooved drums carrying two lines of cable, one for hoisting the 
spud and the other for pinning up the dredge. After the dredge is 
raised or pinned up the spuds are held in place by brake bands on 
the spud machinery. | 
For lighting equipment on steam-operated machines many contrac- 
tors prefer the steam-driven impulse-type turbine, direct connected 
to the generator. Steam is used from the boiler which supplies the 
engines on the dredge, and thus no extra power equipment is needed 
to drive the generator. A turbine generator.suitable for a steam- 
driven excavating machine will cost approximately $210. 
A FRAME. 
The A frame is a tower composed of timber or steel members se- 
curely anchored on the deck near the front and joined at the top 
by a cast-steel head (see Pl. I). The A frame may have either two 
or four legs. In the latter case the two front, or main, legs are 
set in a vertical plane. If only two legs are used they are inclined 
shghtly forward. The A frame must be strongly guyed and held 
rigidly in position, as the severe stresses from the outer and loaded 
end of the boom are carried by the top of this tower. Failure 
of any part of the A frame may result in serious damage to the 
dredge, and even loss of life. The height is governed by the required 
elevation of the end of the boom, which in turn is determined by the 
depth of excavation and the distance to which the excavated material 
must be placed. On the top of the head block is a large pin on 
which the yoke revolves, this latter being a short beam to the ends 
of which are attached the cables which support the outer end of the 
boom. 
SWINGING DEVICE. 
The swinging device used on the different makes of dredge varies 
greatly. En some cases it consists of a circular double-channel frame, 
firmly anchored to the deck, with several sheaves bolted at intervals 
in the circumference of the frame to carry the cable that travels over 
them in swinging the boom. In this fixed type of swinging device a 
cirele of large diameter can be used. There is also the movable type 
of swinging circle. This generally consists of a solid iron circle 
mounted on a pivot. The heel of the boom is over the point of the 
pivot, and the boom is braced to the circle. This type requires more 
deck room than does the first named. The turntable may be placed 
on deck (PI. I, fig. 1) or overhead, but the deck plan is generally 
used. 
