Q7
With reference to a keyless propeller designed for hydraulic
(wet) fit and withdrawal:
(a) Describe, with the aid of a sketch, how the propeller is fitted to the tail shaft;
(10)
(b) State two advantages compared to a dry fit.
(3)
(c) Explain how the thrust is transmitted without the use of a key and keyway.
(3)
Reference Answer
### (a) Procedure for Hydraulic (Wet) Fitting of a Keyless Propeller The hydraulic or 'wet' fitting method for a keyless propeller relies on creating a high-pressure oil film between the tapered surfaces of the propeller boss and the tail shaft. This film acts as a lubricant and slightly expands the propeller bore, allowing it to be pushed axially onto the shaft with a controlled force to achieve a precise interference fit. **Pre-fitting Preparations:** 1. **Surface Inspection:** The tapered section of the tail shaft and the internal bore of the propeller are meticulously cleaned, degreased, and inspected for any damage, burrs, or scoring. Any imperfections must be polished out.
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