- Seal is gripping on to the chrome liner.Chrome liner is bolted on to propeller boss(aft)
- Fwd chrome liner is fitted on to a clamp ring . Clamp rings are of 2 halves and have holes.
- Aft sealing assembly consist of 2 main and 1 aux sealing rings.All sealing rings are spring loaded .Fwd sealing ring prevent oil leakage to sea .Lip seals hold oil within Stern tube and accepts small misalignment
- Chrome liner act as rubbing surfaces for lip seals .The chrome liner at the aft end protects the steel shaft from seawater and corrosion .Grooving will not happen on the shaft because of liner, so that the chrome liner can be machined or can be shifted axially by putting spacer.If grooving occurs leak will start.
- As per diagram the space between #2 and #3 is connected to header tank ,#3s is the spare seal
- If water content found on the stern tube that means along with #1 and #2 , then #3 seal is also leaking.Then we have to put #3s seal in use.
Any opening in a pressure vessel is kept to a minimum and for a man entry an elliptical hole is lesser in size than the corresponding circular hole. More over it is prime concern to have a smoothed generous radius at the corners to eliminate stress concentration. Hence other geometrical shapes like rectangle and square are ruled out. To compensate for the loss of material in the shell due to opening, a doubler ring has to be provided around the opening. The thickness of the ring depends on the axis length along the dirrection in which the stresses are maximum and the thickness of the shell. It is important to align the minor axis along the length of the vessel, as the stress in this direction is maximum. Longitudinal stress: Pd/2t where P= pressure inside the vessel, d= diameter of the arc, t= thickness of the shell plating Circumferential stress: Pd/4t More over a considerable material and weight saving is achieved as minor is along the direction of maximum stress.