RECENT DEVELOPMENTS IN SHIPYARD PLANTS. 179 



The fixed and rotating cranes involve a great variety of types, which include 

 the hammerhead type, the luffing boom type, both rotating on relatively high towers, 

 the staid type supported on the ground, and derricks placed on towers such as are in 

 general use in building construction. In general, the most suitable field for this class 

 of crane is the slip for smaller ships, involving the handling of small weights, as the 

 handling of relatively heavy weights means the providing of a large capacity for 

 most or all of the cranes. The chief objection to them lies in their relatively small 

 capacity and short reach, necessity for large numbers of operators, and the diffi- 

 culty in delivering and storing material within reach of the crane to be used in plac- 

 ing it on board the vessel. There have been some recent installations in the navy 

 yards of the revolving, hammerhead type of cranes, which for small vessels have 

 proved to be very satisfactory. These have a capacity of 5 tons at 95-foot radius 

 and 10 tons at 50-foot radius, the height of hook being about 95 feet above the 

 ground. The new capital slips being built in the navy yards are all of the bridge 

 crane type with characteristics adopted after many tentative designs which con- 

 sidered capacities from 10 tons to 150 tons. The arrangement as finally adopted pro- 

 vides for two 40-ton cranes, each spanning the entire structure, and permitting a 

 lift of 80 tons, with a double row of cranes above the main cranes, all of them 

 plumbing the center line, and having capacities of 10 tons each. 



In these slips provision has been made for the construction of a maximum 

 vessel of iio-foot beam, or for two merchant vessels abreast or three destroyers 

 abreast. The clear width between the columns of the crane runways is 130 feet, and 

 the columns slope outward so that the hooks of the cranes will plumb the centers of 

 cars on the standard gauge tracks running the length of the slip under the towers 

 on each side. This requires a crane span of 151 feet 9^^ inches. The height of the 

 hooks of the main cranes above the yard level approximates 125 feet. The center to 

 center width of these slips is 164 feet, and as they provide for the construction of 

 ships with iio-foot beam, the ratio of slip to vessel is 1.49. This is a dimension 

 that has a direct bearing on the selection of the type of crane to be used. The 

 ratio of the distance between centers of slip to the beam of vessel becomes in large 

 yards a feature of considerable importance as regulating the total amount of water 

 front required for a given number of ways, and to a certain extent the area of land 

 to be included in the plant. As many factors of cost of plant bear a direct relation 

 to the area, any unnecessary extension involves an undesirable increase in cost. 



STRUCTURAL SHOP. 



The activities of the yard most directly connected with the building of ships are 

 housed in the structural or shipfitters' shop. There has been, in the development of 

 the larger private yards and of the principal navy yards, a tendency to adopt com- 

 mon characteristics, with the result that some of the largest private and government 

 plants have adopted almost identical characteristics, though arrived at independ- 

 ently. In several instances the navy yards are erecting a structural group which in- 



