A special form of jib crane, designed to meet a particular purpose, is the “Titan” (fig. 14) largely used in the construction of piers and breakwaters. It contains all the essential elements of the hammer-headed crane, of which it may be considered to be the parent; in fact, the only essential difference is that the Titan is portable and the hammer-head crane fixed. The Titan was the first type of large portable crane in which full use was made of a truly horizontal movement of the load; for the purpose for which the type is designed, viz. setting concrete blocks in courses, this motion is almost a necessity.
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| Fig. 15. | Fig. 16. |
As types of non-revolving cranes, fig. 15 shows an overhead traveller worked by hand, and fig. 16 a somewhat similar machine worked by electric power. The principal component parts of a traveller are the main cross girders forming the Non-revolving cranes. bridge, the two end carriages on which the bridge rests, the running wheels which enable the end carriages to travel on the longitudinal gantry girders or runway, and the crab or jenny, which carries the hoisting mechanism, and moves across the span on rails placed on the bridge girders. There are numerous and important variations of these two types, but the above contain the elements out of which most cranes of the class are built.
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| Fig. 17. | Fig. 18. |
| Fig. 19. |
| Fig. 20. |
One variation is illustrated in fig. 17, and is called a “Goliath” or “Wellington.” It is practically a traveller mounted on high legs, so as to permit of its being travelled on rails placed on the ground level, instead of on an elevated gantry. Of other variations and combinations of types, fig. 18 shows a modern design of crane intended to command the maximum of yard space, and having some of the characteristics both of the Goliath and of the revolving jib crane, and fig. 19 depicts a combination of a traveller and a hanging jib crane.
When the cross traverse motion of a traveller crab is suppressed, and the longitudinal travelling motion is increased in importance we come to a type of crane, the use of which is rapidly increasing; it goes by the name of “transporter.” Transporters can only move the load to any point on a vertical Transporters. surface (generally a plane surface); they have a lifting motion and a movement of translation. They are of two kinds: (1) those in which the motive power and lifting gear are self-contained on the crab; and (2) those in which the motive power is placed in a fixed position. A transporter of the first class is shown in fig. 20. From the lower flange of a suspended runway, made of a single I section, run wheels, from the axles of which the transporter is suspended. The latter consists of a framework carrying the hoisting barrel, with its driving motor and gearing, and a travelling motor, which is geared to the running wheels in such a manner as to be able to propel the whole machine; a seat is provided for the driver who manipulates the controllers. A transporter of this kind, when fitted with a grab, is a very efficient machine for taking coal from barges and depositing it in a coal store.
| Fig. 21. |
In the other class of transporter the load is not usually moved through such long distances. It consists essentially of a jib made of single I-sections, and supported by tie-rods (fig. 21), the load to be lifted being suspended from a small travelling carriage which runs on the lower flange. The lifting gear is located in any convenient fixed position. In order that only one motor may be used, and also that the load may be lifted by a single part of rope, various devices have been invented. The jib is usually inclined, so as to enable the travel to be performed by gravity in one direction, and the object of the transporter mechanism is to ensure that pulling in or slacking out the lifting rope shall perform the cycle of operations in the following order:—Supposing the load is ready to be lifted out of a vessel on to a quay, the pull of the lifting rope raises the load, the travelling jenny being meanwhile locked in position. On arriving at a certain height the lift ceases and the jenny is released, and by the continued pull of the rope, it runs up the jib; on arriving at an adjustable stop, the jenny is again locked, and the load can be lowered out; the hook can then be raised, when the jenny is automatically unlocked, and on paying out the rope the jenny gravitates to its first position, when the load is lowered and the cycle repeated. The jibs of transporters are often made to slide forward, or lift up, so as to be out of the way when not in use. Transporters are largely used for dealing with general cargo between vessels and warehouses, and also for coaling vessels; they have a great advantage in not interfering with the rigging of vessels.
Nearly all recent advances in crane design are the result of the introduction of the electric motor. It is now possible to apply motive power exactly where it is wanted, and to do so economically, so that the crane designer has a perfectly free hand in adding the various motions required by the special circumstances of each case.