Abstract: A vertical tower and lifting boom are counterbalanced by a separately supported counterweight unit. The counterweight unit is self-propelled and connected to a mobile tower platform by a horizontal stinger. A diagonal tower brace extends between the outer end of the stinger and the upper end of the tower for transmission of rotational forces about the vertical tower axis. A vertical counterweight strut is connected between the counterweight unit and the outer end of a pivoted staymast that extends rearwardly in opposition to the boom.

Abstract: A vertical tower and pivoted upper boom are counterbalanced by a mobile counterweight member mounted on a self-propelled earthborn unit spaced a substantial distance from the tower in diametric opposition to the boom. The tower, which is pivotable about a vertical pivot axis, is connected to the counterweight by a first horizontal rigid spreader link and by a second diagonal rigid spreader link. The two links are respectively connected to the lower and upper ends of the tower. In this manner, rotational torque is transmitted directly to both the lower and upper ends of the tower. Both the tower and the boom can therefore be turned about the vertical pivot axis by operation of the self-propelled counterweight unit without the usual problems of having the tower "winding up" due to the rotational forces applied to it during turning of large loads.