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skipping one hatch between two holds being loaded or un- loaded would be an_uneco- nomical procedure. It is far better to have but one crane working on each hatch in- stead, but even then overlap- ping of the circles described by the jib heads will scarcely ever be entirely obviated. Further difficulties will more- over be encountered when slewing long jibs above sea- going vessels, because of the many obstacles to be nego- tiated in the shape of deck superstructures, masts, and rigging. These considerations led to the addition of sup- plementary motion—luffing the jib—to the two previous ones, i. e. the slewing motion, and the traveling motion parallel with the wharf-edge or the traveling motion of the crane on a bridge. The work- ing cycle of a crane with the supplementary motion there- fore now proceeds as follows: After attaching the load to the hook in the hold, the first motion to be performed is hoisting, by which the load is brought to some_ point above the level of the hatch. At this stage luffing is ap- plied, the jib carrying the load there- by being drawn back towards the eenter of slewing. This is succeeded by the slewing motion itself which takes place over a very small radius, and finally the jib is run out again to the required new radius. Fig. 2—Comparison: Unloading a sea-going ship with four slewing cranes (at the top) having jibs of 55 ft. 19 in. fixed radius, or with eight luffing cranes (at the bottom) reducing their jib radius from 55 ft. 10 in. to 19 ft. 9 in. Fig. 3—Field covered by a luffing crane (on the left) and that of a crane with jib of fixed radius, the maximum radius being the same Cranes with jibs that could’ be lengthened or shortened when loaded, were first evolved in Great Britain. Local conditions were responsible for this invention. Most British ports, especially the port of London, are so hard up for room that cranes with jibs of fixed radius can scarcely be used at all. If the warehouses are situated close to. the wharf-edge, as is frequently the case, making the distance from the ware- house wall to the center of the slewing circle shorter than the distance from the latter to the center-line of the ship, a luffing jib obviously becomes an imperative neces- sity. Such cranes with luf- fing jibs are able to deposit or receive their load at any desired point between the wharf-edge and the warehouse wall, despite the lack of space around them. Compared with eranes having jibs of fixed radius, luffing cranes as in Fig. 1, show the following advantages: As the jib must always be withdrawn suffi- ciently to prevent interfer- ence with neighboring cranes before beginning to slew, more cranes can now be em- ployed on one vessel simulta- neously than when using other cranes. Careful exami- nation of the hatch plans of numerous’ sea-going ships showed that in most cases twice aS many cranes could be applied to a ship at the same time, and without hampering each other, if luffing cranes were used for the purpose (Fig. 2). Owing to their adaptability in point of motion, luffing cranes can avoid such obstacles as masts, rigging, or deck superstructures far more quick- Li Yash IT peared > hl My HU Hy SAN a A\ TAN ANWR RUA WRWWAWA «5973-66-00 Fig.5 5 AT LEFT—FIG. 4—TRANSSHIPPING FROM SEAGOING SHIP TO LIGHTER BY MEANS OF FLOATING CRANE WITH LUFFING JIB. AT RIGHT—FIG. 5—DIAGRAMMATIC SKETCH OF A LUFFING CRANE WITH CURVED GUIDES FOR BALANCING THE ROPES MARINE REVIEW—June, 1928 43