Lesson 15
Transmission System
Contents
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Introduction
Thrust Bearing
Shaft Bearing
Sterntube Bearing
Shafting
Propeller
Words & Expressions
Introduction
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The transmission system on a ship transmits
power from the engine to the propeller.
It is made up of shafts, bearings, and finally
the propeller itself.
The thrust from the propeller is transferred
to the ship through the transmission system.
Introduction
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The different items in the system include the
thrust shaft, one or more intermediate shafts and
the tail shaft.
These shafts are supported by the thrust block,
intermediate bearings and the stern tube bearing.
A sealing arrangement is provided at either end
of the tail shaft with the propeller and cone
completing the arrangement.
These parts, their location and purpose are
shown in Fig.12.1.
Introduction
Thrust Bearing
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The thrust block transfers the thrust from the
propeller to the hull of the ship.
It must therefore be solidly constructed onto a
rigid seating or framework to perform its task.
It may be an independent unit or an integral
part of the main propulsion engine.
Both ahead and astern thrusts must be catered
for and the construction must be strong enough
to withstand normal and shock loads.
Thrust Bearing
Thrust Bearing
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It can limit crankshaft end play.
Thrust flanges are formed on the main
bearing sides, almost touching the thrust
surfaces machined on the crankshaft.
Absorb axial forces
Thrust Bearing
Ball thrust bearing
Roller thrust bearing
Shaft Bearing
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Shaft bearings are of two types, the aftermost
tunnel bearing and all others.
The aftermost tunnel bearing has a top and
bottom bearing shell because it must
counteract the propeller mass and take a
vertical upward thrust at the forward end of the
tail shaft.
The other shaft bearings only support the shaft
weight and thus have only lower half bearing
shells.
Shaft Bearing
Sterntube Bearing
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The sterntube bearing serves two important
purposes.
It supports the tailshaft and a considerable
proportion of the propeller weight.
It also acts as a gland to prevent the entry of
seawater into the machinery space.
Sterntube Bearing
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Early arrangements used bearing materials
such as lignum vitae (a very dense form of
timber), which were lubricated by seawater.
Most modern designs use an oil lubrication
arrangement for a white metal lined
sterntube bearing.
Sterntube Bearing
Shafting
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There may be one or more sections of
intermediate shafting between the thrust
shaft and the tailshaft, depending upon the
machinery space location.
All shafting is manufactured from solid
forged ingot steel with integral flanged
couplings.
The shafting sections are joined by solid
forged steel fitted bolts.
Shafting
Propeller
Propeller
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The propeller consists of a boss with several
blades of helicoidal form attached to it.
When rotated it ‘screws’ or thrusts its way
through the water by giving momentum to
the column of water passing through it.
The thrust is transmitted along the shafting
to the thrust block and finally to the ship’s
structure.
Propeller
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Most propellers in the marine industry are
made out of aluminum, stainless steel, etc.
There are all sorts of propellers in use today
and each one has its own design, the most
common is the elephant ear blade.
Propeller
Made of hub and blades & creates the thrust
necessary to propel the ship through the water
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Terms:
Pitch: axial
distance advanced
during one
complete
revolution of screw
–Face: the pressure
side
–Back: the suction
side
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Propeller
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Constant vs. Variable Pitch
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Fixed vs. Controllable Pitch
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Variable has the twisted look
Adv: more efficient over wide range of
speeds
In controllable, blades can rotate on hub to
change pitch (change direction)
Right vs. Left Hand Screw
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Viewed from aft of ship
Twin-screw ships have one of each
Propeller
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Cavitation
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Formation and subsequent collapse of
bubbles as propeller turns
Occurs at critical speed
Effects
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Excessive noise
Erosion of blades
Decreased efficiency
Propeller
Pitch of Propeller
Words & Expressions
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cone
rigid
integral
withstand
pivot
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holder
carrier
collar
n.
a.
a.
vt.
v.
n.
n.
n.
n.
螺旋桨轴帽
刚性的
整体的，一体的
承受
转动，滚动
枢轴，支点
轴承座/支架
托架
轴环
Words & Expressions
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counteract
bath
transmit
intermediate
propulsion
gland
tapered
helicoidal
momentum
vt.
n.
vt.
a.
n.
n.
a.
a.
n.
承受，抵消
油槽
传动，传输
中间的
推进，推进力
密封压盖
锥形的
螺旋面
动量
Words & Expressions
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stern tube bearing
intermediate bearing
aftermost tunnel bearing
pad stop
journal bush
thrust shaft
oil scraper
lignum vitae
propeller boss
尾轴管轴承
中间轴轴承
尾轴管轴承
停油板
轴颈衬套
推力轴
刮油器
铁梨木
螺旋桨毂
Assignments
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What does the shafting system consist of?
What is the main function of the transmission
system?
What is provided at the end of the tail shaft?
How many types of shaft bearings are there
used on ships? What are they?
What purposes does the sterntube bearing
serve?
How does propeller drive ships?