Question

With reference to sleeved keyless propeller assemblies:

(a) (i) State, with reasons, the metals used in the manufacture of the sleeve and tail end shaft

(ii) State the type and thickness of material used to bond the sleeve to the propeller boss.

(b) When removing the propeller from the tail end shaft, state why the following procedures are not recommended:

(i) Application of push off force by means of wedges or jacks and draw off force by strong back

(ii) Expansion of propeller boss by concentrated local heating with gas torches.

(c) State the correct procedure for removal of the propeller from the tail end shaft

Answer 1

Part (a)

With a coefficient of friction of 0.28, it minimizes the likelihood of propeller slippage.
Its expansion rates are similar to those of steel, reducing the risk of misalignment or loosening during temperature variations.
Pearlitic cast iron exhibits excellent resistance to fretting, which is important for prolonged and reliable operation.

Tail End Shaft: Forged Mild Steel

Forged mild steel provides the necessary mechanical strength and durability for withstanding high torsional forces.
Easy to fabricate and repair during maintenance.
Suitable for marine environments when properly treated.

(ii) Material Used to Bond Sleeve to Propeller and Thickness of Bonding Material:

High-strength epoxy Araldite filling is used to bond the sleeve to the propeller securely.
The bonding material is applied with a thickness of approximately 1 mm, ensuring adequate adhesion and durability.

Part (b)

Can put the shaft in tension, leading to potential damage to the thrust block or propeller boss.
May cause elongation or damage to coupling bolts, especially due to the high stress concentration.
Excessive force on the screw threads can result in cracks or permanent deformation.

(ii) Local Heating with Gas Torches is Not Recommended due to:

Concentrated heating causes uneven expansion, which can lead to cracks or other structural damage during service.
High temperatures can weaken or destroy the epoxy layer bonding the sleeve to the propeller
Prolonged heating can alter the material properties of the sleeve or boss\

Part (c)

Remove the Propeller Cone and Locking Plate to expose the shaft-end fitting.
Slack the Pilgrim Nut by the amount equivalent to the push-up distance
Insert a wooden piece between the pilgrim nut and the boss face to absorb the impact during disconnection.
Connect a hydraulic oil pump and inject hydraulic oil into the fitting to expand the boss.
Operate the pump and maintain a pressure of 100–150 kg/cm² until the propeller disengages.
The propeller releases safely and rests on the wooden block, ready for removal.

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