Mech theory 2

Question 1

What is the function of the gearbox?

Answer 1

Reverse the direction of the propeller shaft to make the ship go astern
Allow the prime mover to be slowed to a more manageable speed(15000rpm to 250rpm)

Question 2

Types of gear teeth:

Answer 2

Straight cut/spur
Helical
Double helical
Worm and wheel

Question 3

What is double helical

Answer 3

Two helical gears back to back, angle of gear cut opposing directions.
Cancels out thrust and negates any need for thrust bearings.
Can be interchanged with spur gears without any need for additional bearings.

Question 4

How do you change the speed of a gear wheel

Answer 4

Adding a second different sized wheel such as a pinion, depending upon the size of the wheel this will effect the speed and torque.

Question 5

What is the maximum single gear reduction ratio

Answer 5

15/1

Question 6

Double gear reduction

Answer 6

Increase the amount of meshing gears, increases reduction. This reduces overall size of gears and the gearbox.

Question 7

How do you change the speed of a gear wheel

Answer 7

By adding different size gear wheels, different speeds or torques can be produced.

Question 8

What is the driving gear called

Answer 8

Primary pinion

Question 9

What is the driven gear called

Answer 9

Primary wheel

Question 10

Double gear reduction- dual tandem

Answer 10

loading is halved alowing smaller pinions and therefore smaller gear wheels which saves weight

Question 11

What are quill shaft

Answer 11

Maintains alignment of the loading

Acts as a torsional spring

Question 12

What is the purpose of the shaft brake

Answer 12

Used to stop and hold the propeller shaft

Question 13

Shaft brake checks- on application of brake

Answer 13

• Ensure no fire risk exists
• All Brake Pads are APPLIED
• The shaft is stationary

Question 14

Shaft brake checks- on removal of brake

Answer 14

• All Pads are clear/released
• No fire danger exists
• The shaft is turning

Question 15

Thrust block

Answer 15

A large thrust bearing, at the gearbox end of the propeller shaft, designed to absorb the force of the propeller so that the ship moves astern in the water.

Question 16

What is turning gear

Answer 16

Used to slowly rotate the shaft and propeller for docking and maintenance purposes. It uses a worm and wheel-the worm is always the driving gear.

Question 17

Motor driven pump

Answer 17

Used to prime gearbox luboil system
Used to drain oil
Acts as back up to the gear driven pump

Question 18

Gear driven pump

Answer 18

Only works when the gearbox is turning

Question 19

Serckstat

Answer 19

Directs hot oil to the cooler, allows cold oil to bypass the cooler. Sets the oil temperature to an optimum temperature using coolers and exchangers.

Question 20

Tuning valves

Answer 20

Provide boundary lubrication by directing high pressure oil to components that require specific oil pressure

Question 21

Forced lub- cut ins

Answer 21

If oil pressure drops below 18.5PSI the pressure switch will signal the MD pump to take over. Checked and tested every 24 hours.

Question 22

Hazards associated with gearboxes

Answer 22

• Noise
• Heat/Fire hazard
• Rotating Parts – guards must always be in place and secure

Question 23

Purpose of Plummer blocks

Answer 23

used to support the weight of the shaft, within the ship, without absorbing any thrust

Question 24

Components of the Plummer block

Answer 24

A plummers block has bearings, a casing, a dipstick, journal pads and an oil cooler.
Lubricated by dynamic lubrication.

Question 25

Purpose of Bulkhead glands

Answer 25

The purpose of the bulkhead glands is to maintain watertight integrity. Lubricated with grease.

Question 26

Purpose of stern seal

Answer 26

Maintains a water tight seal as the shaft passes through the ships hull, only works when the propeller shaft is stationary.

Question 26

Purpose of Main and Intermediate A Brackets

Answer 26

Support the weight of the propeller shaft | Lubrication of the bearings in the brackets is by sea water using the Hydro-Dynamic principle

Question 27

Purpose of SFK coupling

Answer 27

A hydraulic coupling Designed so that the tail shaft can be separated from the intermediate shaft without leaving a flange. High pressure hydraulic oil is forced between the two sleeves to allow for connection and disconnection between the tail and intermediate shafts. The tail is most likely to sustain damage.

Question 28

What is a fixed blade propeller and what are its benefits and drawbacks

Answer 28

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

Question 29

Controllable pitch propeller

Answer 29

Alter the angle/pitch of the propeller blades using hydraulics to give forward and astern motion.

Question 30

Controllable pitch propeller

Answer 30

alter the angle/pitch of the propeller blades using hydraulics to give forward and astern motion.

Question 31

Methods of embarking fuel

Answer 31

``` Replenishment at sea (RAS) Road bowser/tanker Jetty storage tanks Lighter barge Fixed jetty pipeline ```

Question 32

Displacement tanks/Displaced tanks

Answer 32

A fuel tank that will contain some salt water. Act as fuel storage and ballast for ship stability. Only ever filled to 90%

Question 33

Un-Displaced/Non Displaced Tanks

Answer 33

Only holds fuel (can be dirty) Never filled with water as ballast The fuel then passes through a centrifuge

Question 34

Centrifuge

Answer 34

Separates oil/fuel from water, using centrifugal force. Once the fuel is clean it is stored in a service tank for use.

Question 35

What is fuel tested for

Answer 35

Water Dirt Surfactants MBG

Question 36

Reasons for testing

Answer 36

Good quality fuel is clear and bright Sodium can cause corrosion Water in a tank can encourage MBG MBG is a fungus and is found in most fuels, Moisture and warmth encourage multiplication of the spores. Dirt in the fuel will cause filtration devices to become blocked.

Question 37

Methods of testing fuel

Answer 37

Visual Water reaction test-a mixture of 20ml distilled water and 80 ml, no more than a maximum of 2ml cloudy area Colour test-Darker fuel is older Diesel filtration test kit- shows how quickly a filter will block/clog-must pass 250ml of fuel before pressure reaches 15 PSI

Question 38

Hazards of a fuel system

Answer 38

Fire and explosions toxicity Dermatitis Pollution

Question 39

What is the order of flow from the tanker to ships engines

Answer 39

1. Tanker 2. Filling Trunk 3. Manifold 4. Displaced tanks 5. Centrifuge 6. Undisplaced tanks 7. Fuel Transfer pump 8. Service Tank 9. Fuel Boost Pump 10. Fuel Boost Ringmain

Question 40

What is the filling trunk?

Answer 40

Fuel enters the trunk and fills until it reaches the weir height. The fuel continues to fill until it overfills past the weir height, it then cascades over into the manifold.

Question 41

Order from the gearbox in the propeller shaft

Answer 41

1) Gearbox 2) thrust block 3) plummer block 4) bulkhead gland 5) plummer block 6) stern seal 7) intermediate A-bracket 8) SFK coupling 9) Main A-bracket 10) propeller