Moving to the location is called "slewing".
Further the mast is attached to the slewing unit (gear and motor) that allows the crane to rotate.
On top of the slewing unit there are three main parts which are: the long horizontal jib (working arm), shorter counter-jib, and the operator's cab.
The main difference between a swing yarder and a tower yarder is that the upperworks is mounted on a large slewing bearing.
Slewing bearings resemble oversize aircraft control surface bearings.
Slewing bearings often use two rows of rolling elements.
However, there is a damping moment (proportional to roll "rate") created by the slewing-about of long wings.
Slewing cranes which allowed a rotation of the load and were thus particularly suited for dockside work appeared as early as 1340.
