An actuating device intended for spacially moving a mobile part in relation to a fixed point, characterized in that it includes a motor (1) driving, around its shaft (2), a winding element (4) pulling a mobile lifting element (9) connected to a fixed point (22) used as anchoring point for the flexible element (4) and sliding, perpendicularly to the axis of the thus constituted pulley block mechanism, in a tube-shaped guide (15) inside which it is housed and compressing a return spring (10) ensuring the return in extension of the mobile element (9), in such a way that this device works in traction and without any buckling stresses.

A gantry crane including a lifting grappler is provided with a hoist locking mechanism to prevent undesired downward drifting of the grappler, especially during periods when the crane is parked and not in operation. The hoist locking device can selectively secure the grappler in a raised position, maintaining a maximum clearance under the raised grappler. The crane includes a hoist line, such as a chain or cable, that suspendably supports the weight of the grappler, and a hoist actuator for moving the hoist line, thereby lifting or lowering the grappler. In an embodiment, the hoist locking device is selectively operable to secure the hoist line in a predetermined position, preventing the grappler from lowering. For example, an embodiment of the hoist locking device includes a hook-shaped latch member movably mounted to the frame for engagement with a catch member fixed relative to the hoist line. The catch member may, for example, be a projection from a clevis mounted to the hoist actuator. A latching actuator is provided for driving the hook between engaged and disengaged positions.