A single collar thrust bearing is used to absorb the axial thrust generated by the propeller shaft and transmit it safely to the ship's hull.

Construction

• A thrust collar is forged integrally with the propeller shaft.
• Thrust pads (or shoes) lined with white metal are fitted on both sides of the thrust collar.
• The pads are mounted inside a strong bearing casing (housing).
• Each thrust pad is supported by a pivot or fulcrum at its back, allowing it to tilt slightly during operation.
• Lubricating oil is supplied between the rotating thrust collar and the stationary thrust pads.
• The lower part of the bearing housing is securely bolted to the ship's structure so that the propeller thrust is transmitted to the hull.

A single collar thrust bearing operates on the hydrodynamic lubrication principle.

Working Principle

• As the shaft rotates, lubricating oil is drawn between the rotating thrust collar and the stationary thrust pads.
• Due to the tilting action of the pads, a wedge-shaped oil film is formed.
• This oil wedge develops sufficient pressure to support the axial thrust load.
• The rotating collar and stationary pads remain separated by the pressurized oil film, preventing metal-to-metal contact.
• Thus, the propeller thrust is transmitted smoothly with minimum wear.

Thrust Transmission Path

Propeller → Shaft → Thrust Collar → Thrust Pads → Bearing Housing → Ship's Hull

The essential clearances of a thrust bearing are checked mainly by the following methods:

1. Feeler Gauge Method

This is the most common method used to measure the thrust pad clearance.

Procedure

• Remove the stopper.
• Remove all lubricating oil (L.O.) pipes and connections on the forward side.
• Push the thrust pad towards the thrust collar using a small screwdriver or crowbar.
• Insert a feeler gauge into the wear groove provided on the pad (normally 1 mm deep).

Interpretation

• If a 0.1 mm feeler gauge cannot be inserted, it indicates that the pad has worn by 0.9 mm.
• This shows that the thrust pad is excessively worn and should be replaced.

2. Shaft Axial Movement Method

Procedure

• Move the shaft axially using a hydraulic jack.
• Mount a dial gauge on the shaft.
• Continue moving the shaft until the thrust pads make contact with the thrust collar.
• The total movement indicated on the dial gauge represents the thrust clearance.

Significance of Thrust Clearance

• If the clearance is too large:
  • Proper hydrodynamic lubrication cannot be achieved, resulting in poor load carrying capacity.
• If the clearance is too small:
  • Lubricating oil flow becomes restricted.
  • This causes overheating and may lead to wiping of the white metal lining of the thrust pads.