The operation of modern marine and railway terminals normally involves the handling and storage of both cargo containers and piggy-back trailers. Large and expensive mobile carriers are used in combination with various types of implements, commonly called grappler spreaders, to transfer the containers or piggy-back trailers between various types of mobile or stationary platforms. The use of front and side loading carriers is becoming quite common in view of their ability to maneuver loads under a variety of difficult situations. In the case of the steerable rubber tired carrier, it is especially desirable to equip the carrier with a grappler spreader in order to eliminate "down" time required for shifting from container handling to trailer handling and vice versa. Moreover, it is desirable that any type of carrier, including straddle carriers, shall be capable of being equipped with a grappler spreader designed for handling loads in all conceivable positions and surroundings. Especially, it is desired that these carriers, in addition to handling piggy-back trailers, be able to stack and unstack containers stacked in very dense arrangement, e.g., in side-by-side rows several containers high with substantially no spacing therebetween. Normally, closely stacked containers can only be handled by a "top lifting" spreader having no grappling arms. The use of a conventional grappler spreader to handle containers at a level below the top row is impossible because of the protrusion of the grappling arms beyond the top outline of a container.
Thus, an important object of the present invention is to provide grappler spreaders of the type adapted for handling containers and piggy-back trailers under the great variety of conditions in which such carriers are expected to perform without the need for switching from one type of load engaging implement to another.
It is also an object to provide a grappler spreader design which lends itself to a multiple part frame construction of a longitudinally expandable grappler spreader adapted for handling various commercially used lengths of containers and trailers.
A more specific object is to provide a grappler spreader which may penetrate the lower levels of closely stacked containers without damage to containers by protruding grappling arm portions.
Another object of the invention is to provide a grappler spreader design adaptable and general to all types of carrier vehicles.