Abstract: Pile-driving apparatus comprises a drop hammer for imparting blows; a winch for lifting the drop hammer between successive blows, the winch comprising a winch drive, a winch drum, a clutch for disengageably engaging the winch drive with the winch drum, and a rope or cable connecting the drop hammer to the winch drum; a sensor comprising a mercury containing container mounted on the driven object or the hammer and having electrical terminals, for sensing the delivery of a blow by the drop hammer; and a timer. Upon sensing of the delivery of a blow by the drop hammer, the sensor causes the clutch to engage and the timer to be triggered. Upon engagement of the clutch the winch lifts the drop hammer. At the end of a predetermined time interval, determined by the timer, the clutch disengages again, thereby allowing the drop hammer to fall. This process repeats itself automatically.