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Q7 (16 Marks) Propulsion & Shafting
MEKG • Written Exam

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)

Appeared In: Mar 2026

✓ Verified Model Answer (Text Solution)

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Part (a)

The keyless arrangement is most commonly done by fitting in the method of oil injection system. In this arrangement , the propeller bore has a series of axial and circumferential grooves machined into it. The propeller is mounted on the tapered section of the tail shaft and high - pressurised oil is pumped through these groves in between the tapered section of tail-shaft and the propeller. The oil is injected mainly to reduce the friction and for the absorption of heat. Moreover, this is also done at the time of mounting the propeller on the shaft. First, high pressure is built between the two parts and the propeller is pushed up the shaft taper by a hydraulic jacking ring. When the propeller is properly aligned on the shaft, the oil pressure is released and the oil runs back. The release of oil pressure leaves the shaft and propeller fastened together.

Part (b)
  • simple construction
  • No key slot and consequently no concentration of stresses at the edge of key slot unlike the ordinary keyed propeller
  • Uniform distribution of stresses over the internal surface of the propeller boss.
Part (c)

The propeller torque is on taken by friction between propeller and propeller shaft.

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