Mech Theory 2 Flashcards
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)
Types of gear teeth:
Straight cut/spur
Helical
Double helical
Worm and wheel
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
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
What is the maximum
single gear reduction
ratio
15/1
Double gear reduction
Increase the amount of meshing
gears, increases reduction. This
reduces overall size of gears and the
gearbox.
How do you change the
speed of a gear wheel
By adding different size gear wheels
different speeds or torques can be
produced,
What is the driving gear
called
Primary pinion
What is the driven gear
called
Primary wheel
Double gear reduction-
dual tandem
loading is halved alowing smaller
pinions and therefore smaller gear
wheels which saves weight
What are quill shaft
Maintains alignment of
the loading
Acts as a torsional spring
What is the purpose of
the shaft brake
Used to stop and hold
the propeller shaft
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
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.
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
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
- Tanker
- Filling Trunk
- Manifold
- Displaced tanks
- Centrifuge
- Undisplaced tanks
- Fuel Transfer pump
- Service Tank
- 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
