Oil lubricated stern tubes

In the name of Allah who is the most beneficient and merciful

Progress from sea water to early oil lubricated stern tubes involved exchange of the wood lined bronze carrier
for a while metal lined, cast iron bush. oil retention and exclusion of sea water. necessitated the fitted of an
external face type seal. The stuffing box was returned in many early oil lubricated stern tubes at the inboard end.

the latter designs with an extended length boss built into the stern frame provide better support for the white metal lined
bearing. A minimum bearing length of two times the shaft diameter will ensure that bearing load doesnot exceed 0.8 N/MM2

the tube is fbricated and welded direct to the extension of the stern tube frame boss at the after end and to the aft peak bulkhead at the forward end.

oil contaminated with in simplex type stern tube by lip seal. The elastic lip of each nitrile rubber seal liners at outboard and inboard end of the steel propeller shaft.
The outboard liner additionally protects the steel shaft from sea water contact and corrosion.

Heat produced by the friction will result in hardening and loss of elasticity of the rubber, should temperature of the seal material exceed 110c. cooling
at the outboard end is provided by the sea. Oil circulation aided by convention, is arrranged to maintain low temperature of seals at the inboard end.
connections  are fitted top and bottom between the two inboard seals.

The chrome steel liners act as rubbing surfaces for the rubber lip seals and grooving from fricitional wear has occurred. The problem has been overcome by using a ceramic
filler for the groove or alternately a distance piece to axially displace the seal and ring assembly. Allowance must be made for relative movement of shaft and stern tube due to
differential expansion. New seals are fitted by cutting and vulcanizing in position.

Lip seals will accept misalignment but a floating ring design was introduced by one maker.


WRITTEN BY S/C ZEESHAH AHMED
LECTURE BY: CHIEF ENGR. Tahir jamil
Phone no. 03344011232
EMAIL: ZEETEC4@YAHOO.COM
date: 03.nov.2009