in vessels, a device for maintaining the vessel on course and for turning the vessel while under way. The rudder is usually a slab (the blade of the rudder), which can rotate about its vertical axis (vertical rudder). When the rudder is turned from the straight position, its surfaces are subjected to hydrodynamic forces that shift the vessel from the trajectory of steady-state motion.
The rudder blade and Rudder Stock bearings must be in line for working absolutly,
Ustun Is Marine Have service for check Rudder Stock Bearings Line, we have service for alignment laser eqipment controls.