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Theory 2 > Transmissions > Flashcards

Transmissions Flashcards

1
Q

What is the purpose of the gearbox?

A

Transmit power from the prime mover to the shaft
Allow for variations in speed and power
Allow for changes between ahead and astern thrust

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2
Q

How does the gearbox reduce the speed coming from the gas turbine?

A

The driving gear (pinion) will be smaller and have fewer teeth than the driven gear (wheel).

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3
Q

How does the gearbox increase the speed coming from the gas turbine?

A

The driving gear (pinion) will be larger and have more teeth than the driven gear (wheel).

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4
Q

How is direction changed by a gearbox?

A

Another gear is added.

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5
Q

What are straight spur gears and when are they used?

A

Leading edges are parallel to the shafts their mounted on. Not particularly strong. Used in low speed applications where noise is not a problem.

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6
Q

What is a helical gear and when is it used?

A

Teeth are cut at an angle allowing smoothing meshing of gears. Lubrication must be used as these gears produce a lot of friction. These have axial thrust at high speed therefore thrust bearings are used. Used where high speed and large power transmission is needed ans where noise must be reduced.

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7
Q

What is a double helical gear and when is it used?

A

These solve the issue of helical thrust. Each pair has opposing angles, therefore cancelling out each others axial thrust. Used when high speed and large power transmission is needed.

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8
Q

What are worm wheel gears and when are they used?

A

Used when shafts are 90 degrees to each other. Worm is always the driving gear and wheel is the driven gear. Used when a big torque increase and high control is needed (turning propeller shaft for maintenance.) They will self lock when drive is taken away.

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9
Q

What four types of gears are used?

A

Straight spur
Helical
Double helical
Worm wheel

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10
Q

What is the maximum ratio from a single pair of gears?

A

15:1

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11
Q

What three types of gear reductions are there?

A

Single
Double
Dual tandem

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12
Q

What is a quill shaft?

A

Thin, solid shaft placed so that it carries the same torque as a larger shaft. It acts like a torsional spring. Load can be evenly distributed and any misalignment can be compensated for. They also keep the gears meshed together.

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13
Q

What components are found in a gearbox?

A

Pinions
Wheels
Shafts
Bearings

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14
Q

How often are FL cut ins checked and why?

A

Daily, to check cut in pressure of the motor driven pump.

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15
Q

At what pressure should the MD pump start up in order to assist the GD pump?

A

18.5 psi

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16
Q

What is the purpose of a serkstat?

A

It controls the temperature of the oil by sensing the temperature and sending it through coolers and heaters as needed.

17
Q

What is the purpose of the thrust block?

A

It absorbs the forces from the propeller and transfers it to the ships hull so that the ship moves.

18
Q

What is a bulk head gland?

A

A seal in bulkheads to keep compartments watertight around the shaft. It is lubricated with grease.

19
Q

What is the purpose of the plummer block?

A

It contains bearings and pads which support the weight of the shaft. The pads are sacrificial and can be removed and replaced if they become worn. It will contain lubricating oil that will sit above the bottom pad, coating the oil around the shaft as it rotates. This is a dynamic lubrication method, as once up to speed, the shaft will float on the oil.

20
Q

What is a stern seal?

A

A mechanical seal that keeps a watertight seal around the shaft passes through the ships hull. It also has an emergency inflatable seal in the event that the seal fails.

21
Q

What do A brackets do?

A

Support the weight of the shaft once its out of the ship and underwater.

22
Q

What are the two types of A brackets?

A

Main A bracket

Intermediate A bracket

23
Q

How are A brackets lubricated?

A

The shaft will pull in seawater as it is rotating. Seawater lubricated the bearings. This is hydrodynamic lubrication.

24
Q

What is the purpose of the SFK coupling?

A

It allows the tailshaft to be removed for maintenance. Male/female type taper. Oil is pushed in under pressure to separate the coupling.

25
Q

How is the intermediate shaft connected to the thrust shaft?

A

Bolted flange

26
Q

How is the tail shaft connected to the intermediate shaft?

A

SKF coupling

27
Q

What are the two types of propeller?

A

Fixed blade propeller

Controllable pitch propeller (CPP)

28
Q

What are the characteristics of a fixed blade propeller?

A

The blade angle/pitch cannot be changed
Highly efficient at full power
Loss of efficiency at low power and when moving astern
The gearbox must have a reverse gear

29
Q

What are the characteristics of a controllable pitch propeller?

A

Angle/pitch of propeller blades can be changed using hydraulics
No need for reverse gear in gearbox
Require more maintenance

30
Q

What is the purpose of the shaft brake?

A

To stop and hold the propeller shaft.

31
Q

How is the shaft break applied?

A

By high pressure air between 80-100 bar.

32
Q

What checks are carried out on the shaft break when it is being applied?

A

Ensure no fire risk exists
Ensure all break pads are applied
Check that the shaft is stationary

33
Q

What checks are carried out on removal of the shaft break?

A

Ensure all pads are clear/released
Ensure no fire danger exists
Ensure the shaft is turning

34
Q

What is the purpose of the turning gear, where is it and what does it consist of?

A

Worm and wheel drive that is mounted on top of the gear box. Used to slowly rotate the shaft and propeller for maintenance and docking purposes.

35
Q

What are the hazards associated with a transmission system?

A

Rotating machinery
Noise
Heat/fire

36
Q

What are the main components of a Plummer block?

A 
Bearings 
Casing 
Dipstick 
Journal pads 
Oil cooler
37
Q

What are the three sections of shaft Line?

A

Thrust, intermediate, tail

38
Q

What speed must the shaft be rotating for hydrodynamic lubrication to occur?

A

50 rpm and above

Theory 2 (3 decks)

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