Thrust Block

Question 1

Describe how the thrust of the propeller is transmitted to the hull of the ship

Answer 1

“Thrust” is transmitted via the propeller shaft and is transferred to the thrust bearing which stops the “thrust” being transferred to the engine, Then the thrust bearing transfers the “thrust” to the trust block where is is then transferred to the hull of the ship.

Propeller –> Thrust Bearing –> Thrust Block –> Ships Hull

Question 2

Describe with the aid of a sketch, how the surfaces within the thrust block, transmitting the thrust are separated by the lubricating oil

Answer 2

INCLUDES SKETCH

The thrust block has several tilting pads arranged around the shaft collar, these pads are free to tilt slightly.
1), As the shaft rotates it drags lubrication oil into the gap between each pad and the collar.
2), the tilting action of the pads creates something called a hydrodynamic wedge.
3), This wedge causes the oil to build up pressure, forming a thin pressurized film that supports the load.
4), This pressurized film separates both surfaces, preventing metal on metal contact.

Question 3

Explain the importance of the oil temperature within the thrust block

Answer 3

WHITE METALS
-Thrust block bearings are made from white metals which are sensitive to heat, they lose tensile strength around 120°C and start melting at 180°C, which is why the thrust block temperature is controlled with the use of cooling systems via water or lube.
LOW TEMPERATURE
- Causes high viscosity which may cause the hydrodynamic wedge to collapse.
HIGH TEMPERATURE
- Causes low viscosity making the oil become to thin which increases the chance of metal on metal contact.

Question 4

Describe the actions that the EOOW should take on finding that the temperature of the thrust block is rising above normal acceptable range

Answer 4

Normal Operating Temperature Range is 55-70°C and if the Temperature were to Reach 90°C the Engine will Shut Down Automatically.

In the event the thrust block temperature rising above normal range…
1), Inform the bridge and Chief Engineer immediately.
2), Request or initiate engine slowdown to prevent further damage.
3), Start the standby generator and auxiliary blower to support systems during slowdown.
4), Ensure the boiler is in auto to maintain steam availability if needed.
5), When safe, stop the engine and allow sufficient cooling time.
6), Inspect the thrust block for signs of damage or lubrication failure once it cools.

Question 5

Explain why the thrust block temperature is critical

Answer 5

WHITE METALS
-Thrust block bearings are made from white metals which are sensitive to heat, they lose tensile strength around 120°C and start melting at 180°C, which is why the thrust block temperature is controlled with the use of cooling systems via water or lube.
LOW TEMPERATURE
- Causes high viscosity which may cause the hydrodynamic wedge to collapse.
HIGH TEMPERATURE
- Causes low viscosity making the oil become to thin which increases the chance of metal on metal contact.