On all but very small pieces of work the cars should be provided with hinged drop sideboards, [Fig. 79], using either of the arrangements shown in [Figs. 80] and [81], which will enable them to carry 12 to 14 cu. yds. instead of 6 or 7. The side boards are made in two pieces on each side of the car, [Fig. 79]. Those shown in [Fig. 80] are used for both center and side plows; they can be quickly dropped by a man walking along the train, after arriving at the unloading place and striking the hook A an upward blow with a light hammer. The boards are hooked up again after the cars have been returned to the steam shovel pit. The side boards shown in [Fig. 81] are used where the side plow only is used. Here the board on one side only (the unloading side) is hinged (or chained), and dropped by pulling out the pin B, thus leaving that side of the car entirely unobstructed for unloading the material; the board on the other side of the car is bolted to the stake pocket and is not moved.
Fig. 80.
Fig. 81.
The cars should also be provided with sheet iron aprons, [Figs. 82] and [83], extending from the end of one car onto the floor of the next, to prevent the material from falling on the track between the cars as the plow is drawn over them, and delaying the departure of the train until it can be shoveled out. These aprons are made either in two pieces, [Fig. 82], or in one piece only, [Fig. 83]. The former are more easily handled, and permit access to the coupling of the cars without lifting the apron. Very little material drops on the track when the aprons and the center plow are used. The single apron is used mostly in connection with the side plow.
The number of cars and engines required for each steam shovel to keep it in nearly constant operation depends upon the nature of the material excavated, the length of haul, and the density of other traffic upon the main line. This number must be determined by accompanying circumstances in each case; ordinarily, however, it averages about as given in Table III.:
TABLE III.