Mech Theory 2 Flashcards by Loxley B

What is the function of
the gearbox?

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)

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Types of gear teeth:

Straight cut/spur
Helical
Double helical
Worm and wheel

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What is double helical

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

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How do you change the
speed of a gear wheel

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

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What is the maximum
single gear reduction
ratio

15/1

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Double gear reduction

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

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How do you change the
speed of a gear wheel

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

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What is the driving gear
called

Primary pinion

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What is the driven gear
called

Primary wheel

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Double gear reduction-
dual tandem

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

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What are quill shaft

Maintains alignment of
the loading
Acts as a torsional spring

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What is the purpose of
the shaft brake

Used to stop and hold
the propeller shaft

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Shaft brake checks- on
application of brake

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

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Shaft brake checks- on
removal of brake

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

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Thrust block

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.

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What is turning gear

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

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Motor driven
pump

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

Gear driven pump

Only works when the
gearbox is turning

Serckstat

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

Tuning valves

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

Forced lub- cut ins

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

Hazards associated with
gearboxes

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

Purpose of Plummer
blocks

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

Components of the
Plummer block

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

Purpose of Bulkhead glands

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

Purpose of stern seal

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

Purpose of Main and Intermediate A Brackets

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

Purpose of SFK coupling

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

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

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

Controllable pitch propeller

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

Methods of embarking fuel

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

Displacement tanks/ Displaced tanks

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

Un-Displaced/Non Displaced Tanks

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

Centrifuge

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

What is fuel tested for

Water Dirt Surfactants MBG

Reasons for testing

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

Methods of testing fuel

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

Hazards of a fuel system

Fire and explosions toxicity Dermatitis Pollution

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

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 1 0. Fuel Boost Ringmain

What is the filling trunk?

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.

Order from the gearbox in the propeller shaft

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