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August, 1919 windlasses and the usual _ chocks, cleats, . fair. leads, ete... The. tomal floating weight of the crane is about 2600 tons. Each .of the 75-tom main -hoist blocks is operated by a hoisting unit consisting of a winding drum con- nected by three cut spur gear reduc- tions, to a 40-horsépower ' series- wound motor. An electrically oper- ated disk brake is attached to the motor pinion shaft, and is so con- netted that it sets - THE MARINE REVIEW design to that of the main hoist units. The 25-ton block is suspended from a movable trolley which travels along the undef side . ef the..jib- ~. The mechanism for moving this trolley is located over the auxiliary hoisting mechanism.- On account of the in- clination of the jib, in its highest position being nearly vertical, the front trolley ropes are required to take practically all of the hook load, and with the boom in its upper po- 373 plate and is controlled in the same manner as the hoisting units. The. jib is luffed by a crosshead moving in vertical guides at the rear of the rotating structure and con- nected by two links to the back~ of the jib. The vertical movement. of the crosshead is controlled by two screws, geared by bevel and_ spur gearing to two 40-horsepower series- motors. The thrust on the screws is car- ~s ried by two con- instantly when the current is cut off the motor. In addition to this, a mechanically operated band brake for gency use only is provided. This brake is attached to the intermedi- ate shaft; This mechanism is sup- ported on a heavy cast bed ' plate. Two 1%-inch steel cables lead from the drum around deflecting sheaves tothe. -75-ton hook blocks. The gearing is prop- erly proportioned to produce .3 hoisting speed of 4 feet per minute. when handling a 75-ton load and 8 feet per minute at half load.. The ~. 25-ton auxiliary hoist block is operated by a hoisting unit lo- cated in the ma- chinery section of the rotating struc-= ture directly above the main hoist units. This mech- anism consists of a drum connected by spur gear reductions to a 40-horsepower series-wound motor. Selective speed gears are introduced into this mechan- ism, which is required to hoist the full load of 25 tons at a speed of 12 feet per minute or 5 tons at 60 feet per minute. The motor operat- ing this mechanism is fitted with an electrically operated disk brake SO arranged as to set instantly when emer= the current is_cut off. _A lever- Operated, mechanical brake is also Provided on the intermediate shaft. This mechanism is also mounted on a heavy cast iron bed plate. The control of the motor is identical in > ANOTHER CRANE OF THE SAME TYPE IN OPERATION AT THE MARE ISLAND NAVY YARD, CAL. | A sition the load is raised as the trolley is moved toward the outer end of the jib. On the other hand very little pull is required in the reverse direction. The mechanism for this motion consists of two drums geared by spur gear reductions to a 40-horsepower series-wound motor. The drums are of different diameters. The ropes from the larger drum lead around deflecting sheaves at the outer end of the jib and connect to the trolley forming a 2-part system. The ropes from the small drum are attached directly to the trolley. The mechan- ism is mounted on a heavy cast bed disk brake. Each motor jackshaft ical rollér bear- mgs, €ach --a which is required to withstand a load, of about .450,000 pounds. The screws are of forged steel, 9% inches in diameter and about 52. feet long, with suff- cient thread to produce a_ cross- head' travel of: about 37. feet. The. entire rotat- ing. structure is supported by a single step. bear-. ing secured, to the--deck "of the. tontoon in the center of the fixed tower. The rotating structure is maintained in a vertical position by a_ horizontal roller bearing ring completely ~ enclosing the pintle section. Sixty cast steel! rollers held in a ciecular. frame comprise this horizontal bearing. circular path surrounding the rollers is secured to the top of the fixed structure about 43 feet above the deck. A bevel-gear ring, 29 feet in diameter, is secured to the fixed structure and meshes with two bevel pinions carried on the rotating struc- ture at diametrically opposite points. The pinions are geared by three reductions of cut spur gearing to separate 40-horsepower series motors, and the gearing is proportioned to produce a complete revolution ir 4 minutes under full load. The mo- tors and the adjacent gearing are mounted on a cast bed plate, and each is fitted with an electrically operated disc brake.