250 HARBOUR CONSTRUCTION. 



Cranes or Setting Machines, The system of constructing 

 vertical-built piers from staging has, to a great extent, been 

 superseded of late years by the use of powerful machines with 

 long overhanging arms. Whether this is desirable in every case 

 is a matter which each engineer must decide for himself. 



Setting machines necessarily vary in design according to the 

 nature of the work they are required to perform. The larger 

 kinds of them are known by fanciful names, such as " Hercules," 

 " Titans/' " Mammoths," and so forth. They all travel upon rails 

 laid on the finished portion of the breakwater, so that they can 

 follow up the work as it advances ; or, when necessary, be run 

 back into a place of safety. 



Some of these machines have longitudinal and transverse 

 motions only, the overhanging portion, or main arm, being pro- 

 vided with a travelling carriage with cross-motion of sufficient 

 scope to admit of its commanding the full width of the breakwater. 



This type of machine was used in constructing the break- 

 waters at Mormugao, Colombo, Kurrachee, and at some other 

 places ; and for facility of setting blocks within its range it is 

 superior to either the " radial " or " all-round " types. Its com- 

 paratively small transverse range is, however, sometimes found 

 to be a drawback, inasmuch as outlying work, such as aprons, 

 etc., cannot be commanded by it. 



One of these machines is represented in Fig. 66. 



In radial machines, the movable arm is pivoted upon the 

 fore-end of the under-carriage, the " tail-end," which carries the 

 engines and balance-load, being supported by rollers running 

 upon a suitable path, fixed at the after-end of the carriage. 



The truck, or "jenny," in these machines has no transverse 

 motion, but merely travels in and out upon rails fixed upon the 

 radial arm. 



The transverse range of these machines is usually sufficient 

 to enable them to place blocks and bag- work in aprons of ordinary 

 width, and, unless something abnormal is required, they afford all 

 necessary facilities. Unless, however, they are constructed to travel 

 with their load which in the larger class of machines is not 

 usual they cannot work so near to the scar-end of a breakwater 

 as " all-round " machines, because room must be left for bringing 

 blocks to the front within range of the "jenny." A portion of 

 their overhang is thus rendered ineffective, a point in which 

 " all-round " machines have a decided advantage. 



