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ny Base Has Modern Cranes Electric Operation, Safety Devices and Adequate L tures of Hoisting Units Installed at the United Sta terial at tidewater, the United States army supply base, Boston, js to be equipped with four semiportal bridge-type hoist cranes. The first of the cranes is now in operation while the other three will be installed in the near future. The cranes are a product of the Wellman-Seaver-Morgan Co., Cleveland. This type of crane carries a lifting boom operated from a carriage, which in turn is mounted on a_ semiportal bridge and arranged to rotate about a fixed axis. The bridge runs on two rails, one located near the face of the wharf and the other supported on brackets carried on the side of the wharf shed. The crane has four dis- tinct motions: Bridge travel along the wharf, trolley slewing, boom hoist- ing or luffing and load hoisting. All of these motions are under the con- trol of the operator located in the cab on the rotating carriage. The crane is. designed so that an- other drum can be added and a 2-rope grab bucket operated. The crane is rated to handle 8000 pounds at a dis- tance of 29 feet from the face of the capsill at the rate of 200 feet per minute and 5000 pounds at a distance of 52 feet at 250 feet per minute. It will, however, take care of occasional loads of 8000 pounds at 52 feet from the center of rotation. ' The principal dimensions of the crane are as follows: Horizontal span, center to center of runway rails, 26 feet 5 inches; Fi loading and, unloading ma-_ boom hoisting or luffing, 125 feet per minute; slewing, two rotations per minute with 5000 pounds load at a maximum radius. The bridge travel along the wharf is 200 feet per minute. The mechanism is so arranged that the motion of either hoisting or luffing can be operated simultaneously with both rotating and traveling motions. The semiportal bridge supporting the operating mechanism was designed in accordance with the general speci- fications for steel railway bridges issued in 1910 by the American Rail- way Engineering association, 100 per cent being added to all live loads to allow for impact. In designing this structure, ample allowance had to be made for the swaying of the load. A steel casting is bolted to the deck of the semiportal for supporting the revolving superstructure. This casting has a track plate aad a. cirrcilar rack, which is bolted to the outside for the slewing motion. Concentric with this casting, is a hollow center pivot pin, the lower end of which is securely held by cross framing between the main girders of the semiportal. <A portion of the deck not covered by the casting is covered with steel plate. Hand railings are provided along the sides and outside edges of the deck and a steel ladder is attached to one of the legs to give access from the wharf. Each leg on the wharf side is car- ried on two wheels which are driven through the necessary spur and bevel ifting Capacity are Fea- tes Army Base, Boston gearing by the traveling motor. Each pair of wheels is equalized for the: proper distribution of load. On the shed rail, the frame is supported by -two wheels, one at each corner. These track wheels are double flanged, high carbon, cast steel, of ample size to Carry a maximum load. The flanges of the wheels running on the shed rails are placed to give about a /7-inch tread. Wheels running on the wharf rail have the flanges spaced to allow proper clearance for the head of the rail upon which they run. ° The base frame is made up of rolled steel shapes and plates, braced in all directions. The revolving super- structure is carried on six steel rollers or wheels, four in front where the heaviest load occurs, and two on the back. The front rollers are carried in a pair of steel equalizers. These rollers or wheels are steel. They rotate on roller bearings and are. placed so as to run properly on a cir- cular, track of 5-foot radius about a pivot pin. A babbitted casting, free to rotate about the center pivot pin, is attached to the base frame to hold the crane concentric with the center pivot pin and to transmit longitudinal and overturning loads from the re- volving superstructure to the semi- portal. The center pivot pin is made of a hollow steel casting to permit the threading of conductors through its center to the collector rings on top. The crane is designed so that under normal operating conditions, with a maximum reach of boom from face to capsill, 44 feet; minimum radius of boom, 29 feet. The angle through which boom may be slewed equals 360 degrees while the Concrete counter- Weight required is aP proximately 3 cubic yards. The various motions of the crane have approximately the following speeds under full load: Hoist, 5000 Pounds, 250 feet Per minute; hoist, 8000 pounds, 200 feet per minute ; -SEMIPORTAL WHARF CRANE WIT 5000-pound hook load at the maxi- 479 H BOOM IN LOWEST POSITION--THE SMALL ILLUSTRATION SHOWS THE TYPE OF RAIL CLAMP USED mum _ radius, no appreciable load will be thrown on the center pin. It is, however, de- signed to trans- mit any possible vertical or hori- zontal load from the revolving jib crane to the semi- portal bridge without cramping or binding in any part. The jib and main frame is made of. steel plates and shapes, - stiffened in all directions. The frame is designed