The bridge, on the other hand, is an extremely expensive apparatus, and, being many times heavier than the gantries, cannot be moved back and forth as they are, though it can move with sufficient ease to follow them at intervals and keep the ore trough free for them. By this combination rapidity of unloading is secured without excessive expense for long-span bridges.

The latest developed apparatus for unloading is that brought out by the Wellman-Seaver-Morgan Company, and named for its inventor, Mr. George Hulett, the Hulett unloader. A diagram showing this in conjunction with an ore bridge is shown in Fig. 10. This apparatus is equipped with a grab bucket, a modification of the old clam-shell bucket, but with two important differences from the machines of Brown and Hoover & Mason.

First, the bucket, instead of being suspended by ropes, is carried at the lower end of a rigid leg.

Second, the grab bucket, instead of having both jaws symmetrical, as is the case with the suspended buckets, has one jaw provided with a horizontal traversing motion, so that after it is opened, with the jaws swung up into the vertical position, it can be extended several feet horizontally, and by being lowered into the ore in this position and then drawn in, serves to pull the ore toward the center of the bucket with a motion exactly like that of a gigantic hoe.

The operator rides in a small chamber in the stiff-leg which carries the grab bucket. This is raised and lowered by a walking beam supported on trunnions, which are carried on a truck provided with means for traversing itself back and forth in the plane of the walking beam, that is in a plane at right angles to the dock line. The track on which the truck or trolley moves is carried by a traveling gantry bridge running on a pair of tracks, one close to the face of the dock, the other some distance inshore, as shown, The column, or stiff-leg, which carries the grab bucket, is held in a vertical position by a parallel motion irrespective of the angle of the walking beam.

The grab bucket and part of its load are counter-weighted at the opposite end of the walking beam to reduce as much as possible the amount of power required for raising it and to facilitate its control.

In operation the walking beam is tipped to lower the grab bucket through the hatch, the stiff-leg is then rotated to throw the longer arm of the grab bucket into any desired position, and if only a small quantity of ore remains in the hold at this location, the long arm of the grab is then used to pull several piles of ore together so as to make an approximately complete load for the grab, which it then picks up, so that it always goes up from the hatch loaded to its capacity. This capacity is very large. For a time ten tons was considered to be the limit, but several machines are now in successful operation with fifteen-ton grabs. After the grab is closed it is rotated to coincide with the line of the hatch and raised up through the latter and the truck which carries the walking beam is then traversed inland until the grab comes over to one of two or three alternative points of discharge. Two of these deliver directly to railroad cars on tracks running between the legs of the Hulett. The other is a small retaining hopper running on wheels which travels on the landward cantilever extension of the machine.

Fig. 10. Hulett unloader in connection with ore bridge.

In case stock piling is to be done the grab bucket discharges into this traveling hopper, which then runs out on the cantilever and discharges on the stock pile. If more stock pile room is desired than can be reached by the cantilever, a traveling bridge is brought into play precisely as described for the Hoover & Mason apparatus. The photograph (Fig. 11) on the preceding page shows the hold of a vessel with the grabs of two of these unloaders at work cleaning up its floor. No hand work has been done in this hold, yet it will be seen that the floor is almost as clean as if it had been swept, except for the piles on which the buckets are still operating..

Fig. 12 shows one of these Huletts complete, though not provided with a long cantilever extension, but with a bridge in the background to do the stock piling.

Fig. 13 shows three Huletts working on a vessel with the piles of ore at their landward ends, and the outer end of the bridge, which is making the stock pile, in foreground. Fig. 14 shows four Huletts working on a steamer with stocking bridge behind them.

The absolute control of the mechanism which the operator exercises by having it rigidly supported instead of swung, and by the fact that he himself is immediately above the bucket and can see to control its movements accurately, gives this machine advantages in handling bulk cargoes not enjoyed by any other type of machine. One of these advantages is that this accurate control of the grab bucket enables the operator to avoid striking the bottom of the hold severe blows with the bucket, as frequently happens with older types of apparatus.

In reclaiming the ore from the stock pile for use at the furnace the operation is very similar to that of stock piling. But in this case also it is necessary to provide some more easily moveable means than the bridge itself for carrying the ore from the bridge to the point of consumption. It will be readily understood that there are always several, and often very many varieties of ore in the stock pile, and on account of the great difficulty in keeping these separated, the same kinds of ore are always piled together, so as to make the individual piles as few in number and as large as possible.

When any given kind of ore is desired for the furnace therefore, the ore bridge is moved over this pile and the grab bucket set to work on it. At the furnace or discharging end of the bridge it spans at least one and generally several tracks. Each traverses the tops of the bins from which the immediate supplies of raw materials are drawn. On one or more of these tracks runs a drop-bottom transfer car, generally driven by an electric motor under the control of its operator. Such a car can carry fifty or more tons of material at a trip. The distance from the bridge to the bins where the ore is needed being only a few hundred feet, it can readily run back and forth from bridge to bins, and serve the bridge about as fast as the latter can reclaim the ore.

Many variations of this general plan of operation have been worked out. In some places removed from the Lakes the ore is received in drop-bottom cars, which are dumped from trestles, and the ore then reloaded as needed, either by taking the furnace-filling equipment direct to the stock pile and there loading it by hand, or by reloading the ore with clam-shell buckets, operated by locomotive traveling cranes, loading it into cars on the trestles, taking these to the bins and dumping.

Fig. 14. Four Hulette working on a steamer with the stocking bridge behind them.