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Mech Theory 2 Transmissions and Fuel systems > Transmissions > Flashcards

Transmissions Flashcards

1
Q

What is the main purpose of the gearbox?

A

To reduce the speed of the prime mover to a more manageable speed for the propeller shaft.

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2
Q

What is the secondary purpose of a gearbox?

A

To reverse the direction of rotation of the propeller shaft to allow ahead or astern thrust.

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3
Q

What are the 4 types of gear teeth profiles used within the RN?

A
  1. Straight cut/spur
  2. Helical
  3. Double helical
  4. Worm and wheel
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4
Q

When is it suitable to use a straight cut/spur gear wheel?

A

It is suitable for low speed/low torque applications where noise generation is not important.

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5
Q

What is the advantage of helical gears compared to straight cut?

A

Because the teeth are cut at an angle there is more tooth contact which makes these gears stronger and quieter.

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6
Q

What are the 3 disadvantages of helical gears?

A
  1. Because of the angle of the teeth (axial) thrust is created which means thrust bearings and collars are required to prevent shafts pushing apart.
  2. Extreme pressure gear oil is required.
  3. They are more expensive to produce than straight cut/spur gears.
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7
Q

What is a double helical gear?

A

Essentially 2 helical gears back to back. with the angle of gear cut in opposing directions.

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8
Q

What is the advantage of a double helical gear over a helical gear?

A

Due to the fact that the angle of the gears are cut in opposite directions. Axial thrust is negated and thrust bearings and collars are not required.

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9
Q

Which 2 gears can be interchanged without the need for additional bearings?

A

Straight cut/spur and double helical.

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10
Q

What gear is this?

A

Straight cut/spur

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11
Q

What gear is this?

A

Helical

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12
Q

What gear is this?

A

Double helical or herringbone.

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13
Q

What gear is this?

A

Worm and wheel

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14
Q

When is a worm and wheel gear used?

A

On a non parallel axis.

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15
Q

In a worm and wheel gear setup which gear is driving and which gear is driven?

A
  1. The worm is always the driving gear

2. The wheel is always a driven gear.

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16
Q

What is possible in a worm and wheel gear setup?

A

Large gear reductions are possible giving very low rpm but very high torque output.

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17
Q

How can change of direction be achieved in a gear setup?

A

By adding a second gear to the first.

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18
Q

How can you achieve a change of speed in a gear setup?

A

By adding different size gear wheels.

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19
Q

What is the name of the driving/input gear?

A

Primary pinion

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20
Q

What is the name of the driven gear?

A

Primary wheel

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21
Q

What’s the maximum gear reduction allowed in a single gear reduction?

A

15:1

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22
Q

What are the 4 components of a gearbox?

A
  1. Pinions
  2. Wheels
  3. Shafts
  4. Bearings
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23
Q

What are quill shafts made of? And why?

A
  1. They are made of spring steel.

2. Spring steel can twist to absorb energy and keep gears pushed together.

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24
Q

Which component acts as a torsional spring?

A

Quill shafts.

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25
Q

What is this?

A

Single gear reduction.

26
Q

What is this?

A

Double gear reduction

27
Q

What sort of gear reduction can you expect in a worm and wheel

A

30-50:1

28
Q

What is the purpose of the shaft brake?

A

To stop and hold the propeller shaft.

29
Q

what components make up the shaft brake?

A
  1. Brake disc
  2. Three evenly spaced callipers.
  3. 2 brake pads in each calliper.
30
Q

What medium is used to apply the shaft brake?

A

High pressure air (80-100 bar)

31
Q

What are the 3 checks carried out on application of the shaft brake?

A
  1. Ensure no fire risks exist
  2. All brake pads are applied
  3. The shaft is stationary
32
Q

What are the 3 checks carried out on removal of the shaft brake?

A
  1. All pads are clear/released
  2. No fire danger exists
  3. The shaft is turning
33
Q

What is the purpose of a thrust block?

A

Transfers axial thrust to the ships hull so the whole ship can move ahead/astern rather than just the propeller shaft.

34
Q

What principle is used to lubricate the thrust block?

A

Michelle principle.

35
Q

What is turning gear used for?

A

To slowly rotate the shaft and propeller in a controlled manner for docking and maintenance purposes.

36
Q

What gear setup is used for the turning gear?

A

Worm and wheel.

37
Q

What is the purpose of the MD (motor driven) pump within the forced lubrication system?

A

The MD pump is driven by an electric motor and therefore doesn’t rely on the gearbox to be operated.
It is used to fill the gearbox with oil before starting.

38
Q

What is the purpose of the serckstat?

A

It works in conjunction with the heater/cooler to keep the gearbox oil at optimal temperature.

39
Q

What is the purpose of the tuning valves?

A

To adjust oil pressure for different parts of the gearbox.

40
Q

How often are forced lub (FL) cut ins tested?

A

Every 24 hours

41
Q

If pressure drops below …… the pressure switch will signal the MD pump to take over.

A

18.5 PSI

42
Q

What are the 3 hazards associated with gearboxes?

A
  1. Noise
  2. Heat/fire hazard
  3. Rotating parts
43
Q

What is the purpose of a plummer block?

A

Plummer blocks support the shafts weight without absorbing any thrust.

44
Q

What are the the 5 components of a plummer block?

A
  1. Bearings
  2. A casing
  3. A dipstick
  4. Journal pads
  5. An oil cooler
45
Q

How is the plummer block lubricated?

A

Using dynamic lubrication with oil from an oil bath.

46
Q

What is the purpose of the gear driven (GD) pump?

A

To provide oil to the gearbox once it is up to speed. as soon as the GD pump is being used the MD pump can be switched off.

47
Q

What is the purpose of bulkhead glands?

A

To maintain watertight integrity as the shaft passes through compartments, without absorbing any thrust.

48
Q

How is the Bulkhead gland lubricated?

A

It is lubricated with grease forced in via grease nipples.

49
Q

What is the purpose of the stern seal?

A

To maintain a watertight seal as the shaft passes through the ships hull.

50
Q

What kind of seal is a stern seal?

A

Mechanical seal.

51
Q

What do the main and intermediate A brackets do?

A

Support the weight of the tail shaft section of the propeller shaft.

52
Q

What medium is used to lubricate the A brackets?

A

Sea water

53
Q

What principle is used to lubricate the A brackets?

A

Hydro-dynamic lubrication.

54
Q

Which parts of the shaft does an SKF coupling join?

A

Tail shaft section and intermediate shaft section.

55
Q

What is the benefit of a fixed blade propeller?

A

Highly efficient at full speed

56
Q

What are the drawbacks of a fixed blade propeller?

A
  1. The blade angle/pitch can’t be changed.
  2. Loss of efficiency at low power and when moving astern.
  3. The gearbox must have a reverse gear.
57
Q

How are the intermediate and thrust shaft connected?

A

Bolted flanges

58
Q

Why does a ship with a controllable pitch propeller (CPP) not need a reverse gear?

A

A CPP propeller can alter its pitch and angle using hydraulics to give forward or astern motion. This negates the need for a reverse gear.

59
Q

What are the 3 shaft brake application checks?

A
  1. Ensure no risks exist
  2. All brake pads are applied
  3. The shaft is stationary
60
Q

What are the 3 shaft brake release checks?

A
  1. Ensure all brake pads have released
  2. No fire danger exists
  3. The shaft is turning

Mech Theory 2 Transmissions and Fuel systems (2 decks)

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