Sunday, April 19, 2020

Pilgrim nut

  • The pilgrim nut provides a predetermined grip between the propeller and its shaft.  
  • The propeller boss is fitted with a S.G cast iron internally tapered sleeve, which is secured (fixed firmly in position) into the boss. This sleeve is bedded to the shaft cone before mounting in the  boss so that better fit is achieved which, combined with the pilgrim nut push up, ensure a good  friction grip. No key is required.  
  • The pilgrim nut is a threaded hydraulic jack, which screwed on to the tailshaft. A steel ring  receives thrust from a hydraulically pressurised nitrile rubber tyre. This thrust is applied to the  propeller to force it onto the taper sleeve.  
  • Propeller removal is achieved by reversing the pilgrim nut and using a withdrawal plate, which is fastened to the propeller boss by studs. When the tyre is pressurised the propeller is drawn off the taper.  

Advantages
1. The sleeve has a similar thermal expansion to the steel shaft, thus reducing the risk of
slackness in hot water.
2. An extension to 5 years survey period is allowed by classification societies.
3. The boss stress are reduced.
4. The cast iron/ steel contact has a higher friction coefficient than bronze/ steel.

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