Abstract: The weight of a pivotally mounted boom in a crane is compensated for in part by a counterweight which is suspended from one end of a compensating cable trained over a deflecting pulley at the top of the supporting crane structure. The other end of the cable is connected to a first fastener near the pivot axis of the boom by a rod and to another fastener on the boom remote from the pivot axis by a flexible chain. The rod is shorter than the distance between the first fastener and the deflecting pulley so that the compensating cable and the rod are longitudinally aligned before the boom reaches its steepest position, the boom thereby being relieved from the then unnecessary action of the counterweight.

Abstract: In a crane having two crabs or trolleys on an approximately horizontal beam of the crane, the trolleys are moved along the beam by two cables whose ends are wound on a common, motor-driven drum, and which are trained over pulleys on the beam and on the trolleys in such a manner that both trolleys are moved jointly at one half of the circumferential drum speed or one trolley is moved at the full drum speed when the other trolley is arrested.

Abstract: An improved drive for rotating the boom-carrying portion of a rotary crane on the base portion of the crane about an upright axis employs an electric motor rotating continuously in one direction when energized and operatively connected to a drive element rotatable on one of the crane portions. The drive element engages the other crane portion and thereby rotates the boom-carrying portion. The motion transmitting train which connects the motor to the drive element includes an electromagnetic coupling whose slip may be controlled to vary the torque transmitted from the motor to the drive element.