Two main functions of the ships gearbox
- Change the speed of prime mover
- allow for forwards and backwards
Types of teeth profiles
Spur
Helical
Double helical
Worm and wheel
What would spur teeth be used for
Low speed
Low torque
They are loud aswell
Positives and negatives of helical teeth
- There cut at an angle so more surface area in contact
- however the angle forces the gears away from eachother
Describe the double helical
Two helical gears in opposing direction, cancelling out the dice pushing a single gear away.
Explain the worm and wheel
They are not parallel to each other, they form a 90degree
Due to this it allows motion to change directions.
Very large gear reduction is possible
What is the maximum single gear reduction in the Royal Navy
15:1
What is a dual tandem
Double gear reduction
What is the purpose of a dual tandem
It shared the load across two gears
What is the input gear called
Primary pinion
What is the driven gear called
Primary wheel
Want so quill shafts do
Maintain alignment
Made out of spring steel
So acts as a torsion bar so flexes to keep gears pushed together
What are the gearbox ancillaries
Shaft breaks
Thrust block
Turning gear
What does the shaft break consist of
Break disk on shaft
3 break callipers
2 pads in each calliper
How is the shaft break applied
HP air 80-100 bar
Shaft break checks (on application of break)
- Ensure no fire risk
- All break pads are being applied
- the shaft is stationary not vibrating
Shaft break tests (break not applied)
- All pads are cleans and released
- no fire danger exists
- the shaft is turning
What is the thrust block
- Large thrust bearing
- At the gearbox end of the shaft
- absorbs force of the propeller
What does the thrust block consist of
- A machined collar on both sides
- White metal pads
- lubricated by “Michelle” principle
What is the purpose of the turning gear
Used to slowly rotate the propeller when going into dry dock
What type of gear teeth will be used on the turning gear
- Worm and wheel (worm is always the driving gear)
- mounted on top of gear box case, drives the upper quill shaft
Benefits of the turning gear
It will self Lock if power is lost, so it’s easy to turn the propeller to the exact point needed
Parts of a forced oil lub system
Motor driven pump Gear driven pump Serckstat Turning valves Forced lub cut ins
What is the use of a motor driven pump in a forced lub oil system
- Used to prime the gearbox lub oil system
- can drain the oil
- can be used as a back up of gear driven pump fails
