Typical design consideration – complete propeller immersion
Design criteria regulated by applicable DNV GL rules cover complete propeller immersion. Design margins also cater for some eccentric propeller loading, for instance, due to an inhomogeneous wake field and/or operation with the propeller blade tips in close vicinity of the water surface.
The shaft alignment philosophy incorporates an acceptable distribution of loading on the shaft bearings while taking into consideration the forces and associated bending moments induced by the propeller during operation. The propeller weight and hydrodynamic forces influences the angular misalignment of the shaft in way of the aft bearing (relative slope) and, subsequently, the shaft-bearing contact area.
Hydrodynamic lubrication conditions are predominantly influenced by the RPM, diameter of the shaft, viscosity of the oil, the net effective contact area of the shaft in way of the bearing and the bearing load. Contact area also regulates the local surface pressure applied on the bearing.
