Transmission Flashcards
What is the function of the main gearbox?
Allow the speed of the prime mover to be reduced to a proportional, more manageable speed for the propeller shaft.
Reverse the direction of rotation of the propeller shaft to allow ahead or astern.
Name 4 gear teeth profiles
Straight cut / Spur
Helical
Double Helical
Worm wheel
Explain how gearwheels change direction
Change of direction can be changed by adding a second gear to the first
Explain how gearwheels change speed
By adding different size gear wheels, different speeds or torques can be produced ie. Gear reduction - Small driving big = more torque, less speed Overdrive - Big driving small = more speed, less torque
What are driving/input gears called
Primary Pinion
What is the driven wheel called?
Primary wheel
What are all driven gears called?
Wheels
Approximately what is the maximum reduction of a single gear reduction and why?
15:1
Due to minimum and maximum size limitations of the pinion and wheel.
Explain double gear reduction
By increasing the amount of meshing gears, we can increase the overall amount of reduction realised across the gear train. Therefore, this reduces the overall size of gear wheels and in turn the gearbox
The gear wheel driven by the primary pinion becomes the secondary pinion, this in turn drives a secondary gear wheel.
What is the purpose of the Quill shaft
Quill shafts maintain alignment of the loading if any misalignment is witnessed. (allows a certain amount of twist/flex to keep gears pushed together) The quill shaft acts as a torsional spring.
Explain double gear reduction - Dual Tandem
Using dual tandem gear trains means the loading will be halved, therefore, smaller pinions can be used giving smaller gear wheels and subsequently a saving in weight
Name all three gear box ancillaries
Shaft brake
Thrust Block
Turning gear
Gearbox Ancilliaries - Explain Shaft brake
The purpose of the shaft brake is to stop and hold the propeller shaft. The shaft brake is applied by HP air (80 – 100 bar).
Shaft Brake Checks: ON APPLICATION OF BRAKE
Ensure no fire risk exists
All Brake Pads are APPLIED
The shaft is stationary
Shaft Brake Checks: ON REMOVAL OF BRAKE
- All Pads are clear/released
- No fire danger exists
- The shaft is turning
Gearbox Ancilliaries: explain thrust block
The thrust block is a large thrust bearing, at the gearbox end of the propeller shaft, designed to absorb the force of the propeller so that the ship as a whole moves ahead/astern in the water and not just the propeller shaft move.
Gearbox Ancilliaries: explain Turning gear
The turning gear is used to slowly rotate the shaft and propeller in a controlled manner for docking and maintenance purposes.
It is mounted on top of the gear case and provides drive onto the upper quill shaft in the gearbox.
The turning gear uses a worm and wheel. the worm is always driving gear. list 3 safety mechanism?
- It will self-lock if power is lost
- It will not work if the wheel/spur gear is powered
- (If drive is attempted the wrong way (wheel driving worm) the whole thing will lock up solid)
What is the purpose of the Serckstat?
Ensure oil temperature is kept at the desire temperature using coolers and heaters.
What is the function of the Turning valves
Provide boundary lubrication by directing high pressure oil to components that require specific oil pressure
What is Forced Lub (FL) Cut-Ins used for?
If oil pressure drops below 18.5PSI the pressure switch will signal the MD pump to take over. FL Cut-Ins are checked/tested every 24hrs
Hazards associated with Gearboxes:
- Noise
- Heat/Fire hazard
- Rotating Parts – guards must always be in place and secure
What is the Plummer blocks used for?
Plummer blocks are used to support the weight of the shaft, within the ship, without absorbing any thrust
How is the Plummer block lubricated?
by dynamic lubrication, using oil from an oil bath.
