(a) Describe, with the aid of a sketch, a pilgrim nut.(5)
(b) Explain how the pilgrim nut is used to ensure correct fitting of a keyless propeller.(5)
What is a pilgrim nut?
A Pilgrim Nut is a specialized hydraulically-operated nut used primarily in the marine industry for the precise and efficient mounting and removal of heavy components like propellers, rudder stocks, and pintles.
Key Features:
- Hydraulic Operation: The nut uses hydraulic pressure to generate a high axial force, allowing for controlled and accurate tightening or loosening of the component it’s securing. 1. Pilgrim Nuts – Mapeco Products www.mapecoproducts.com
- No Keyway or Key: It eliminates the need for a traditional keyway and key system, simplifying the design and installation process.
- High Load Capacity: It can handle extremely high loads, making it suitable for large propellers and other heavy components. 1. Pilgrim Nuts www.pilgrim-international.co.uk
- Precise Control: The hydraulic pressure can be precisely controlled, ensuring the correct amount of torque is applied during installation or removal. 1. Pilgrim Nuts – Mapeco Products www.mapecoproducts.com
- Compact Design: It’s relatively compact compared to other methods for securing large components, saving space and weight.
How it Works:
- Installation:
- The Pilgrim Nut is screwed onto the threaded shaft until the loading ring is tight against the face of the propeller or other component. 1. Pilgrim Nuts – Mapeco Products www.mapecoproducts.com
- Hydraulic pressure is applied to a piston or bladder within the nut, generating a high axial force. 1. Pilgrim Nuts – Mapeco Products www.mapecoproducts.com
- This force pushes the component onto the shaft taper, achieving the desired interference fit. 1. Pilgrim Nuts – Mapeco Products www.mapecoproducts.com
- The loading ring moves out of the nut body as the component is pushed onto the taper. 1. Pilgrim Nuts – Mapeco Products www.mapecoproducts.com
- Removal:
- The Pilgrim Nut is reversed and fitted with a withdrawal stud and plate. 1. What is Pilgrim Nut?? How do you remove propeller with Pilgrim Nut??|Ramesh SUbramanian|RMETC Videos – YouTube www.youtube.com
- Hydraulic pressure is applied again, this time pushing against the withdrawal stud.
- The axial force generated pulls the component off the taper, allowing for easy removal.
Advantages:
- Precise and Controlled: Provides accurate control over the applied torque and ensures a secure and reliable fit. 1. Pilgrim Nuts – Mapeco Products www.mapecoproducts.com
- Efficient: Reduces installation and removal time compared to traditional methods like heating and hammering.
- Safe: Eliminates the need for heat and heavy hammering, reducing the risk of damage to components and injuries to personnel.
- Cost-Effective: Saves on labor costs and potential damage to expensive components.
Applications:
- Propeller Mounting: Securing propellers to propeller shafts. 1. Pilgrim Nuts www.pilgrim-international.co.uk
- Rudder Stock and Pintle Mounting: Attaching rudder stocks and pintles to the vessel’s structure. 1. Pilgrim Nuts – Mapeco Products www.mapecoproducts.com
- Tapered Shaft Couplings: Connecting shafts with tapered couplings. 1. Pilgrim Nuts – Mapeco Products www.mapecoproducts.com
- Other High-Load Applications: Can be used in other marine applications requiring precise and controlled tightening of large components.
In summary: The Pilgrim Nut is a specialized hydraulic tool that simplifies and improves the process of mounting and removing heavy components in marine applications. Its precision, efficiency, safety, and cost-effectiveness make it a valuable asset in shipyards and onboard vessels.
How is the pilgrim nut used to ensure correct fitting of a keyless propeller.
A keyless propeller, as the name suggests, doesn’t rely on a traditional key and keyway system for attachment to the propeller shaft. Instead, it utilizes a tight interference fit between the propeller bore and the tapered shaft. Achieving this precise fit is crucial to ensure efficient power transmission and prevent slippage or damage. This is where the Pilgrim nut comes in.
1. Keyless fitting of fixed pitch propeller – Wärtsilä
How the Pilgrim Nut Ensures Correct Fitting
- Preparation:
- Tapered Surfaces: Both the propeller bore and the propeller shaft are machined to a precise taper, typically 1:10 or 1:16.
- Surface Finish: The mating surfaces are carefully finished to ensure a smooth and even contact area.
- Cleaning: The surfaces are thoroughly cleaned and degreased to remove any contaminants that could hinder the interference fit.
- Installation with Pilgrim Nut:
- Positioning: The propeller is carefully positioned on the tapered shaft.
- Pilgrim Nut Attachment: The Pilgrim nut, which has a hollow piston and a threaded outer body, is screwed onto the threaded end of the propeller shaft.
- Hydraulic Pressure Application: High-pressure hydraulic oil is pumped into the Pilgrim nut, pushing the piston forward.
- Axial Force Generation: The piston exerts a powerful axial force, pushing the propeller along the tapered shaft.
- Interference Fit Achievement: This force overcomes the friction and forces the propeller to slide up the taper, creating a tight interference fit between the propeller bore and the shaft.
- Confirmation: The movement of a loading ring on the Pilgrim nut indicates when the propeller has reached its final position and the desired interference fit is achieved.
- Removal with Pilgrim Nut:
- Reversal: The Pilgrim nut is reversed and fitted with a withdrawal stud and plate.
- Hydraulic Pressure Application: Hydraulic pressure is again applied, this time pushing against the withdrawal stud.
- Propeller Withdrawal: The resulting axial force pulls the propeller off the taper, allowing for controlled and safe removal.
Benefits of using the Pilgrim Nut:
- Precise Control: The hydraulic pressure can be accurately controlled to achieve the exact required interference fit, ensuring optimal power transmission and preventing slippage.
- No Keyway: Eliminates the need for a keyway, which can be a potential stress concentration point and weaken the shaft.
- Reduced Risk of Damage: Avoids the need for hammering or heating the propeller during installation or removal, reducing the risk of damage to the propeller or shaft.
- Efficiency: The process is faster and more efficient than traditional methods, saving time and labor costs.
In Summary:
The Pilgrim nut, through its hydraulic operation and precise control, plays a critical role in achieving the necessary interference fit between a keyless propeller and the shaft. This ensures the secure and reliable attachment of the propeller, enabling efficient power transmission and safe operation of the vessel’s propulsion system.