BÀI GIẢNG TRANG TRÍ ĐỘNG lực (MARINE PROPULSION PLANT)

CHAPTER I: NOTIONS AND CLASSIFICATION OF
MARINE PROPULSION PLANT.
(Total: 08 periods, Theory: 08 periods, practical: 00 periods)

1.1 Notions of Marine propulsion plant.
Marine propulsion plant (MPP) is a group that consists of main propulsion plant equipment and other
auxiliary propulsion plant equipment to take on the action ability of ship and the life of crews on ship in
every sea condition.
Depending on the ability of working, that group can be divided as follows:
1.1.1. Main propulsion plant equipment.
Main propulsion plant equipment is a system of equipment that undertake speed and direction of ship.
They consist of following parts:
a. Main engine:
Main engine generates mechanical energy to turn a ship's propeller. In the marine propulsion plant,
kinds of following main engine can be used: Steam engine, steam turbine, gas turbine, diesel engine, and
“generator – motor”. In fact, a diesel engine propulsion plant is mostly used nowadays. Besides this, on
modern ships newly manufactured with large power, the steam turbine propulsion plants are being
developed. In the marine propulsion plant, one or more main engine can be used.
b. Propulsion equipment
Propulsion equipment transforms mechanical energy of the main engine into thrust force when
maneuvering. The oldest type of mechanical propulsion for ships is Jet propulsion. The Jet propulsion is based
on jet principal of water line ejected strongly and fast in a contrary direction of ship. It usually consists of an
impeller or pump installed inside the hull, which draws water from outside, imposes on it an acceleration,
and discharges it astern as a jet at a high velocity. This kind of propulsion was used on ships from 1782. In
1801 the first steam ship driven by paddle wheel was appeared, with paddle wheels installed both sides of
ship. Paddle wheel was used on steamers until about 1850. Two kinds of propulsion equipment above have
disadvantages of unwieldy and low efficiency. With paddle steamers, the immersion varied with ship
displacement, the wheels came out of the water when the ship rolled, so the course will be changed and they
were easily damaged due to rough seas. The idea to use a screw propeller on ship appears in 1680, but until
1836 the first screw propeller was applied. The screw propeller has many advantages over paddle wheel.
Nowadays, screw propeller was used on all ship with advantage of high efficiency and safe working. There

are two kinds of screw propeller used in the marine propulsion plant, they are: Non controllable - pitch
propeller and controllable - pitch propeller. There may be one or more propellers are used in the propulsion
plant according to type of ship and the installation of the propulsion plant.
c. Driving equipment
It is intermediate equipment to transmit power from a main engine to a screw propeller. Driving
equipment consists of: Shafting, flanges, split muff coupling, clutch, and reduction gear.
d. Main boiler
Its duty is to supply steam (with high pressure and temperature) to steam engine, steam turbine and
other auxiliary machinery. Main boiler is used only on steam ship.
e. Conveyance equipment
They are used to convey working substance to a main engine. They consist of steam tube, gas tube.
1.1.2. Auxiliary equipment of MPP

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It supports the main propulsion plant equipment and other operations of a ship. Auxiliary equipment
consists of:
a. Generator
Its duty is to supply electric energy for the ship to serve many different objects, such as: illuminating,
loading and unloading cargoes and all other electric equipment. Remember that, there must be at least two
generators in the marine propulsion plant.
Generators can be driven by diesel engines like in the diesel engine propulsion plant. In the other
hand, in the steam propulsion plant, the generators can be driven by steam engines or steam turbines.
Besides this, in large power diesel engine propulsion plant, a waste recovery steam turbine can be used to drive
the generator.
b. Compressed air system
Compressed air system generates and stores compressed air with high pressure for starting and
reversing the main engines, starting generator engines, cleaning parts of the engine. Besides this, compressed
air is also used in remote control and automatic control systems. Compressed air system consists of

compressors, reservoirs (air tank), non-reversible valves, relief valves, and compressed air pipes...
c. Auxiliary boiler
Auxiliary boiler supplyes steam to heat fuel, water, diesel engine (before starting) and cabins. In
addition, it also serves steam machineries and equipment (such as cargo pumps on tanker ships).
1.1.3. Safety equipment of MPP.
To undertake the safe operations of the ship in every condition to limit damages due to trouble. Safety
equipment consists of:
a. Bilge system
Its duty is to suck dryly shaft tunnel, cargo holds and engine room. Because bilge water is mixture of
water, oil, sludge ... so it is required to provide with the oily - water separator in the system to separate oil
from water before pumping out to sea.
b. Ballast system
Its duty is to adjust the balance of the ship.
c. Fire protection system
It is easy to happen damages due to fire on the ship especially in the engine room, so protection firing
should be specially concerned. Fire protection system consists of: Personal fire extinguishings, carbon
dioxide cylinders, foam cylinders, water fire extinguishing system, carbon dioxide fire extinguishing system,
foam fire extinguishing system.
d. Repairing equipment, store and spare parts for replacing.
1.1.4. Equipment for serving the domestic requirement.
They are equipment to undertake the living requirements of all ship's crews. They consist of light
system, ventilation and air conditioner system, provision refrigerator system, fresh water system, washing
water sytem and so on...
1.1.5. Deck's equipment
They consist of steering gear, mooring winches, cargo winches, life equipment (life boats, life rafts an
so on...).

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1.2 Classification of Marine Propulsion Plant
Depending on the kind of working substance used in the main engine, the marine propulsion plant can
be classified by two main types. They are steam propulsion plant and diesel propulsion plant. Besides these,
nuclear propulsion plant can also be used.
To combine main kinds of propulsion plant with driving modes, we have many different kinds of
propulsion plant.
1.2.1 Steam propulsion plant.
It is a kind of propulsion plant in which, generating process of mechanical power is the process of
using heat energy when burning fuel to generate steam in a main boiler, and then steam expands and
generates power in a steam engine or a steam turbine. In the steam propulsion plant, the main propulsion
plant equipment is group of boiler and steam engine or boiler and steam turbine.
In 1807, the first time the steam ship Klecmong with power of 18 horses - power appeared on a river
of South America. Although the ship had small power and low speed but this event had a great significance
in the ship building industry. With improvement of science and technology, ship building industry
manufactured many steam engines with power up to thousand horses - power. In the whole of 19 century, all
of ships used the direct driving steam engine propulsion plant.
Nevertheless, steam engine has still many disadvantages. This type of engine has small power, low
efficiency, weight and dimension is big, so cannot satisfy the high requirements of sea transport.
In about years of 80 of 19 century, a Swedish engineer Guntavdo Laval made a first steam turbine
with power of 5 horses - power, speed of 25000 rpm. But until 1896 steam turbine applied to drive screw
propeller and the steam turbine propulsion plant came.
In this period, all of steam turbines were used to drive directly screw propellers, so working
conditions of turbine and propeller were contradicted each other. If revolution of turbine is high then its
power is large, efficiency is high and weight, dimension can be reduced. In the othe hand, if turbine and
propeller working together then thrust efficiency of propeller is decreased because revolution of turbine is
excessively higher than optimum working revolution of propeller. Therefore, in direct driving steam turbine
propulsion plant, turbine has large dimension and low efficiency.
To operate effectively power of steam turbine, it is required to provide intermediate equipment to
reduce revolution of turbine to optimum revolution range of propeller. From 1910, multi - stages mechanical
gears box was applied on board and the indirect driving steam turbine propulsion plant was appeared.

Besides this, turbine was also used to drive screw propeller in the electric driving steam turbine propulsion
plant.
In beginning period of 20 century, because steam engine was still used, the combinative steam engine
- steam turbine propulsion plant was used to decrease a loss of heat due to unperfected expansion of steam in
steam engine.
1.2.2. Diesel engine propulsion plant.
In 1903, the first diesel engine vessel was used in the world. It is named "Vandan" and made in
Russia. Although came latter, the diesel engine propulsion plant had fast improved and popularly applied
because it has many advantages. Diesel engines have high heat efficiency, low specific fuel consumption,
their dimension and weight are smaller than steam engines, and range of power is large. Up to now, diesel
engines were used on board by three kinds of: Direct driving diesel engine propulsion plant, indirect driving
diesel engine propulsion plant and special driving diesel engine propulsion plant. In the direct driving diesel
engine propulsion plant, direction and revolution of propeller are the same with main engine. This kind of
propulsion plant is generally applied on tanker ships, general cargo ship... Main engine is kind of low - speed

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diesel engine, direct reversing. The most common is low - speed diesel engine, two - stroke with cross head
and used heavy fuel oil.
The direct driving diesel engine propulsion plants have disadvantages that their weight and dimension
are large so they are not suitable for ships with small displacement, limited height of engine room. In that
case, it is necessary to provide with indirect driving diesel engine propulsion plant to drive propeller. In the
indirect driving diesel engine propulsion plant, a main engine is generally kind of high and medium speed
diesel engine, non- - reversible. Its revolution is much higher than propeller. In this kind of propulsion plant,
two or more main engines can be installed together to drive propeller. In the other hand, only one main
engine can be used to drive two or more propellers in some cases. Besides of shafting, clutch and gears box
should be provided between main engine and propeller. The indirect driving diesel engine propulsion plants
are commonly used on passenger ships, container ships, and naval ships. In comparison with the direct
driving diesel engine propulsion plant, this kind of propulsion plan is more complex and lower transmission

efficiency.
Special driving diesel engine propulsion plants are electric driving diesel engine propulsion plant
and diesel engine propulsion plant with controllable - pitch propeller. The same as the indirect driving
diesel engine propulsion plant, a main engine is kind of high and medium speed diesel engine, nonreversible. Advantage of the special driving diesel engine propulsion plant is very flexible. However, it has
disadvantages: system is complex, transmission efficiency is low. So it commonly used for flexible ships
such as: workshop ships, naval ships, passenger ships, fishing ships, rescue ships and so on.
1.2.3. Other types.
Besides the main types of marine propulsion plant as mentioned above, some others are known as gas
turbine propulsion plant and nuclear propulsion plant.
Gas turbines differ from steam turbines in that gas rather steams is used to turn shaft. These have also
become more suitable for use in ships. Many naval ships are powered by gas turbine and several container
ships are also fitted with them.
Nuclear propulsion plant is commonly used on naval ships, especially submarines. But this form of
power will be used more in merchant ships when oil fuels become rarely. Nuclear propulsion plant uses the
energy released by the decay of radioactive fuel to generate steam, and the steam is used to turn a shaft via a
turbine in the conventional way.

1.3 Technical characteristics of Marine propulsion plant
In a marine propulsion plant, the characteristics of the main engine have a direct effect on technique
of operation, methods of design and installation systems and equipment in the engine room. According to the
type of main engines, nowadays there are two main types of propulsion plant, they are diesel engine
propulsion plant and steam propulsion plant (with main engine is steam turbine).
1.3.1. Technical characteristics of diesel engine propulsion plant.
- In the diesel engine propulsion plant, working substance is combustion product of air - fuel mixing
formed in engine combustion chamber.
- Thermal efficiency is high while specific fuel consumption is low.
- Output is not continuously generated. It should be provided with air and gas distributors suitable for
suction and exhaust cycles of the main engine.
- When working, diesel engines generate reciprocating forces and inertia moments. These inertia
forces and moments vibrate body of engine and ship's hull. The balance of a diesel engine is depended on

weight of the engine moving parts, number of cylinders and suitable arrangement of cranks.

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- Engine parts withstand also the forces that vary cyclically. These characteristics limit an increase in
power and revolution of main engine.
- Immediate pressures and tempretures in the engine combustion chamber are very high; the engine
parts have to work in high temperature and friction condition so the longevity of diesel engines are reduced.
- Moving rule of the pistons independ on direction of crank shaft so rotation direction of diesel
engines can be easily reversed by change work order of starting mechanism. In the diesel engine propulsion
plant, reversing equipment can be installed on the engine to reverse directly rotation of the engine or installed
on shafting to reverse direction of propeller shaft.
- In light load conditions, diesel engines are not working economically and stably.
- It is flexible because of short time for starting.
- Heat energy, which goes out of engine with gas together, is high; if waste heat recovery equipment
is used in the diesel engine propulsion plant then its efficiency is raised.
1.3.2. Technical characteristics of steam turbine propulsion plant.
- Working substance is high-pressure steam generated in main boiler.
- Output is continuous: it is the most important advantage of turbines. It permits raise revolution of
turbines, therefore can increase power, efficiency and reduce weight, dimension of turbines. Nowadays, the
modern turbines have revolution up to 15000 (rpm) or more.
- Working substance flows continuously through the turbine so rotating moment, heat and mechanical
load in the parts of engine are stable. Therefore, turbine has a high longevity.
- All moving parts of turbine are installed on a rotor, rotated with the same certain direction and
speed. It permits to reduce mechanical losses, raise efficiency of turbine. When working, turbine doesn't
generate inertia forces.
- Output of turbine depends on only parameters and amount of steam that flow through turbine. So
turbine can generate a large power.
- Turbine direction is determined by direction of steam, which acts on blades wheel of turbine. With a

certain blade wheel, turbine cannot reverse its self. To reverse direction of ship, it should be provided with
astern turbine. So it increases power loss of system. Nowadays, that problem has been solved with using
intermediate driving or controllable - pitch propeller.
- Turbine's revolution is much higher than optimum range of propeller's revolution, so turbine cannot
directly drive propeller. Therefore, it should be provided with reducing gears in the system. In fact, the steam
turbine propulsion plant is only installed on ships with a big displacement.
- Gas temperature in boiler combustion chamber is limited by heat durability of material. Cycle
temperature is low; boiler and transmission pipes have heat losses so efficiency of propulsion plant is low.
Nowadays, efficiency of the steam turbine propulsion plant is about 22 ÷ 26% while it is about 35 ÷ 40%
with the diesel propulsion plant.
- Boiler has been burning continuously, its temperature and pressure is very high. High pressure and
temperature steam flows continuously inside transmission pipes. It may cause danger to operators when
emergency happens.
- It requires having a high quality of water in the system.
- It takes a long time to prepare for starting the system, so it is not flexible.

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1.4 Interaction between Hull and Propeller.
1.4.1 Resistance of ship.
When sailing, all resistance act on the ships and affect to the ships’ movement are determined as
follow:
R = RN + RK

(KG)

Where:
- RN (KG): Resistance of water acts on ship's hull.
- RK (KG): Resistance of air affects on floatage of ship.

a. Resistance of water.
Resistance, which is generated when a ship moves on water surface, depends on ship's speed,
roughness of wetted surface, form and structure of ship's hull. Resistance of water is performed by:
R N = RS + R H + R M

(KG)

Where:
- RS : Wave - making resistance.
- RH : Form resistance.
- RM : Frictional resistance.
* Wave - making resistance is made due to wave when a ship moves on water surface.
RS = C S

ρV 2 Ω
2

(KG)

With:
- CS : Wave - making resistance coefficient.
- ρ: Kinetic viscosity of water.

(KGs2/m4)

Seawater: ρ = 104.8
Fresh water: ρ = 102
- V: Ship's speed.

(m/s)

- Ω: Area of wetted surface

(m2)

* Form resistance is generated due to form and outside structure of ship's hull when a ship moves on
water surface:

ρV 2 Ω
RH = C H
2

(KG)

CH: Form resistance coefficient:
* Frictional resistance.
Frictional resistance is generated due to roughness of ship's hull. It is determined by:
RM = C M

ρV 2 Ω
2

(KG)

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CM is frictional resistance coefficient. Reynolds calculated it:
CM = 0.455 lgRe

(Re Reynolds number)

b. Resistance of air.
Besides the resistance of water, air also generates resistance when a ship moves. Resistance of air is
generated by air affecting on ship's floatage. Resistance of air depends on form and section area of ship's
floatage, ship's speed, direction and speed of the wind.
Resistance of air is performed by:

ρ K VG 2 FC
RK = C K
2

(KG)

Where:
- CK: Air resistance coefficient, it depends on floatage structure form of a ship:
All of ship's floatage have a form of a pyramid: CK = 0.4 ÷ 0.5
A part of ship's floatage have a form of a pyramid:

CK = 0.6 ÷ 0.7

Ship’s floatage have a form of a arc:

CK = 0.7 ÷ 0.8

Ship’s floatage have a flat form:

CK = 0.8 ÷ 1.0

- ρK: Density of air, ρK = 0.125 (KGs2/m4).

- FC: Transverse projected area of floatage

(m2).

- VG: Relative speed of the wind

(m/s).

VG = V 2 + W 2 + 2V .W cos α

(m/s).

V- Ship's speed

(m/s).

W- Absolute speed of the wind

(m/s).

α - Angle is formed by direction of the ship and the wind.
1.4.2. Relationship between main engine power and resistance of ship's hull.
We consider that effective thrust force (generated by propeller when a ship moves) is T (KG), in
balance moving condition, we have:
T=R

(KG)

To maintain ship's speed at V (m/s) with resistance R (KG), necessary power can be determined:
NK =

TV
75

or

NK =

RV
75

(hp).

In fact, ship's hull has an effect on thrust force of propeller. That effect can be performed as hull
efficiency ηH :

ηH =

NK
NP

Where:
- NK : Necessary power to maintain ship's speed at V (m/s), with resistance R (KG).
- NP : Thrust power of propeller. It is performed:

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NP =

TP V P
75

(hp).

VP - Advance speed of propeller

(m/s).

TP - Thrust force of propeller

(KG)

In fact, the propeller is now working in water, which has been disturbed by the passage of the hull,
and in general the water around the stern has acquired a forward motion in the same direction as the ship.
This forward-moving water is called the wake, and one of the results of the wake influence is that the
propeller's speed is not the same with speed of the ship. The difference between ship and propeller's speed is
called wake speed VW.
VW = V − V P

(m/s).

According to Froude expression, wake coefficient w is defined as a ratio between wake speed and
propeller's speed:
w=

VW
VP

or

w=

V − VP
VP

However, Froude expression is used only in older published data, particularly British.
According to Taylor definition, wake coefficient w is the ratio between wake speed and ship's speed:
w=

VW
V

or

w=

V − VP
V

- For one propeller-ship:

w = 0.5 δ - 0.1

- For two propellers-ship:

w = 0.5 δ - 0.16

(δ: Fat coefficient of the ship).
Then, propeller's speed is that:

VP = V(1-w)

(m/s).

When a ship's hull is towed, there is an area of high pressure over the stern, which has a resultant
forward component reducing the total resistance. However, with a self- propeller hull, the pressure over some
of this area is reduced by the action of the propeller in accelerating the water flowing into it, the forward
component is reduced, the resistance is increased and so also the necessary thrust force to propel the ship.
Therefore, when propeller working to propel the ship only T (KG) overcome resistance R of ship and
component (TP - T)(KG) overcome augment of resistance when accelerating the water.
TP − T
= t is called thrust-deduction fraction. The thrust-deduction fraction t is determined
TP
by practical formula of Kenvil:
Ratio:

t = C1w.
C1: coefficient depends on rudder structure characteristic. C1 = 0.5 ÷ 1.05.
We can perform:
TP (1 − t ) = T

(KG).

Then:

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TP =

T
1− t

or

TP =

R
1− t

(KG).

Now, use determined values on formula of hull efficiency:
TV
NK
TV
RV
ηH =
= 75 =
=
.
R
N P T PV P T PV P
V (1 − W )
1− t
75
And:

ηH =

1− t
.
1− w

Thrust power of propeller:
NP =

NK
ηH

or

NP =

RV
75η H

(hp)

Then, power on propeller hub:
N CV =

NP
ηP

(hp).

With ηP is efficiency of propeller, for:
- Non-controllable pitch propeller:

ηP = 0.6 ÷ 0.75.

- Controllable - pitch propeller:

ηP = 0.58 ÷ 0.65.

When driving propeller, a part power output of a main engine is lost to overcome friction resistance
on shaft bearings, clutch, and reducing gears box... So the power of a main engine depends on also shafting
efficiency ηtr :
Ne =

N CV
RV
=
η tr
75η H η Pη tr

(hp).

Shafting efficiency depends on characteristics of propulsion plant:
- Direct driving propulsion plant: ηtr = 0.95 ÷ 0.98.
- For indirect driving propulsion plant, shafting efficiency ηtr still depends on efficiency of clutch and
reducing gears box and its value is about 0.86 ÷ 0.96.
In fact, the power of a main engine Ne determined above equals to only 85% its designed power.

1.5 Requirements of Marine Propulsion Plant.
To operate the ship safely and economically, a marine propulsion plant has to satisfy the general
requirements as follow:
- The transformation of energy is optimum.
- Equipment are simple.

- It is safe and trustful.
- Dimension and weight are small.
- Longevity is high.
- Cost must be low.

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In fact, to meet all these requirements together is very difficult. To simplify it, we study the following
requirements;
1.5.1 Requirement about the power of marine propulsion plant according to propeller and hull
characteristics.
Suppose NK (hp) is the necessary power to maintain ship's speed at V (m/s), with total resistance R
(m/s), then;
RV
75

NK =

(hp).

According to result of 1.4, thrust power of propeller is that:
NP =

NK
ηH

(hp).

The power on propeller hub:

NP
RV
=
η P 75η H η P

N CV =

(hp).

Power of the main engine:
Ne =

N CV
RV
=
η tr
75η H η Pη tr

(hp).

Power of the main engine depends on type, functions and displacement of the ship. If the ships have
the same displacement, but functions and types are different then their powers are also different. Therefore,
definition "relative power" is used:

α=

Ne
D

(hp/T - displacement).

With D: Displacement of ship(T).
Or:

α=

N CV
η tr D

(hp/T - displacement).

The power on the propeller hub NCV is determined according to 1.4. However, to simplify the power
on the propeller hub can be calculated by Naval formula:
N CV =

3

V D
Cw

2
3

(hp).

Where:
- V: Ship's speed

(knot/h).

- D: Displacement

(T).

- Cw: Naval coefficient.
Finally:

α=

1
V3
⋅3
C wη tr
D

(hp/T - displacement).

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This result shows that at the same displacement, the higher the speed, the larger power is.
1.5.2. Requirement about economical norm of marine propulsion plant.
The economical norm in operating of marine propulsion plant is estimated by amount of fuel
consumption of a main engine on one knot of itinerary:
gM =

B
V .t

(kg/knot).

Where:
- V: Speed of the ship

(knot/h).

- t: Working time of propulsion plant

(h)

- B: The fuel consumption of main engine in the working time t (h). It can be determined:
B = g e .N e .t

(kg).

With ge: Specific fuel consumption of main engine. (kg/hp.h).
And then:
gM =

g e .N e .t g e .N e
=
V .t
V

(kg/knot)

1.5.3. Requirements of propulsion plant for independent working ability of the ship.
a. Requirement about the weight of propulsion plant.
Total weight or displacement of the ship consists of four main components:
- Weight of hull.

- Weight of propulsion plant.
- Weight of needments (fuel, lubricating oil, water, provision, stores and spares).
- Weight of cargoes.
With a certain ship, one of the weights increases, then other component has to reduce. If the weight of
propulsion plant is increased then the cargoes transportation and the independent working ability of the ship
is reduced. So application methods to reduce the weight of propulsion plant are necessary.
In fact, the ships have the same displacement but speed and power are varied, so then the weight of
propulsion plant is varied. In the other hand, with the same power but the weight of propulsion plant is also
varied when type of propulsion plant is different. Therefore, the definition of "relative weight" is used:
K1 =

W
D

With W is total weight of propulsion plant

(kg/T - displacement).
(kg).

b. Requirement about dimension of the engine room.
Almost machinery is installed in the engine room. So, the dimension of the engine room has to suit to
all of the machinery and the equipment installed in to it. Besides, it must be convenient for maintaining,
repairing and safe for operating the machinery of the propulsion plant. To satisfy these requirements, the
engine room is as large as possible. In the other hand, if the engine room is too large, cargo holds space is
reduced and it reduces the cargo transportation ability of the ship. Therefore, the dimension of the engine
room should be calculated to satisfy the both requirements. To perform the requirement about dimension of
the engine room, the definitions "saturated coefficient" are used:

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- Area saturated coefficient of the engine room: The number of horsepower (hp) of the propulsion
plant on unit of the engine room area.
KS =

∑N

e

(hp/m2).

S

- Volume saturated coefficient of the engine room: The number of horsepower of the propulsion plant
in unit of the engine room space.
KV =

∑N

e

(hp/m3).

V

Where:
- ∑Ne: Total power of the propulsion plant.

(hp).

- S: Total area of the engine room floors.

(m2).

- V: Total volume of the engine room space.

(m3).

c. Requirement about the needments of the propulsion plant.
Needments stored on the ship to permit her running in a certain time. For the marine propulsion plant,
main needment is fuel. The more amount of fuel stored on the ship, the higher the independent working
ability is. However, weight of the fuel stored is also component of the displacement, if the fuel stored is too
much then transportation ability of the ship will be reduced. So the fuel stored should be calculated suitably
with power, specific fuel consumption of the propulsion plant, the times on voyage, operation area of the ship
to raise the transportation ability.
The fuel stored can be calculated according to the fuel consumption in all times of an independent
voyage:

∑B = ∑N

e

.g tb .t

(kg).

Where:
- ∑B: Amount of the fuel consumption in all times of the voyage (kg)
- ∑Ne: Total power of the propulsion plant.
- gtb: Average specific fuel consumption of the propulsion plant

- t: The times of the independent voyage.

(hp)
(kg/hp.h)
(h)

d. Requirement of the propulsion plant according to sea condition.
- All of the machinery should normally work when the ship heeling or rolling.
- All of the service system (fuel oil sys., lubricating oil sys., cooling sys.,...) should normally work in
every condition.
- The starting, reverse and adjustment the main engine is easy in every condition. The main engine
has to work stably even when the ship is reversing.
- It is necessary to provide the main engine with over speed protector.
- The main engine can be overloaded to overcome augment resistance in some special cases.
- It is easy to operate, maintain, and repair.

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CHAPTER 2: SHAFTING AND ITS COMPONENTS
(Total: 14.5 periods, Theory: 10.5 periods, Practice: 4.0 periods)

2.1 Arrangement of shafting.
2.1.1. Arrangement of the single shafting
Description of single shafting is illustrated in Figure 2.1

1
3
5

4

6

8

7

M/e

9
2
Figure 2.1: Shafting arrangement
1- E/R bulkhead
2- Stern tube
3- Water tank
4- Propeller shaft
5- Intermediate shaft

6- Intermediate bearing
7- Thrust shaft
8- Thrust bearing
9- Double bottom tank

2.1.2. Installation principle of the shafting.
There is one or more shaft line depending on kind of ships. In almost cargo ships, the shafting has
only one propeller and one shaft line is used. Normally, a shaft line is placed parallelly with the keel of the
ship; in some case the shaft line is placed unparallelly with the keel. It makes with basic line an angle α, α ≤
5o (α- angle is formed by the shaft line and the keel of the ship in vertical section).

α
β
β
β
β

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In a propulsion plant with two shaft lines, they are normally installed symmetrically and parallelly to
the vertical keel section of the ship. In some cases, they make with the vertical keel section angles β (β- angle
is formed by the shaft line and the ship vertical keel section), β ≤ 3o. If α > 5o, β > 3o then thrust force of
propeller will be decreased. However, in some special cases α is permitted till 15o.
To reduce cost and total weight of the propulsion plant; to economize on metal and increase
transmission efficiency, the shafting should be shortened.
2.1.3. Position of shaft bearings.
Shaft bearings are usually positioned near bulkhead or keel of the ship where ship's hull structure is
strongest. Position of the shaft bearings relates to vibration of the shafting.
According to the rule of Russia Register:
12D < L < 22D
Where: D - Diameter of a shaft
L - Distance between shaft bearings.
If D < 100 mm, L is calculated:
Lmax = 91 3 D 2

2.2 Propeller shaft (Tail shaft)
Propeller shaft works in hard condition such as contacting with seawater and heavy load, wearing by
friction so, it is required a high quality material and structure.
Traditionally, a non-controllable pitch propeller is fitted to the propeller shaft with key and taper. On
the other hand, a controllable pitch propeller is normally fitted to a flanged propeller shaft because the

operating mechanism is housed in the propeller boss. Of course, a non-controllable pitch propeller could be
flange-mounted, however the propeller shaft cannot be drawn into the ship for inspecting and result in a
larger boss diameter of the propeller.
Key

Taper
Shaft

Figure 2.2: Structure of the propeller shaft and the propeller boss.

17


The propeller is pushed tightly to taper by hydraulic jack, after that the propeller is secured to the
propeller shaft by key and nut together with interference fit method.
The propeller shaft is connected to the intermediate shaft by flange or coupling. This flange may be
cast either integral with the shaft or separately and secured to the shaft by key and nut.
In some cases, especially the propeller shaft lubricated by water, to increase longevity of the shaft, a
brass sleeve is inserted to the shaft. The thickness of a brass sleeve is calculated as the following formula:
t=

d p + 235

(mm)

32

And the length of this sleeve: l ≥ 4dp. Where: dp is diameter of the propeller shaft.

2.3 Stern tube

There are many differences in structure of stern tube depending on individual ship and kinds of stern
bearing. Its function is to place bearing for supporting of propeller and propeller shaft. With heavy load, so
its structure must be strong enough to withstand the acting forces. At the aft end of stern tube is provided
with lock nut to secure stern tube to stern frame. The fore end of stern tube is secured to bulkhead by bolts
and nuts.

11
6
7
5

12

2

9

8
4

3

1
10

Figure 2.3: Stern tube
1- Propeller shaft
4, 5- Stern bearing
8- Retaining ring
11- Aft peak bulkhead

2- Stern tube
6- Stern frame
9- Gland cover
12- Water pipe

3- Metal bush
7- Stern tube nut
10- Packing

18


2.4 Stern bearings
The propeller shaft is supported by stern bearings. There is one or more bearing for each of the
propeller shaft depending on the structure of the ship and length of the propeller shaft. Stern bearings
withstand too heavy working conditions; it is very difficult to inspect and repair (unless on dry dock). So its
structure must be strong enough to ensure safe operation of the ship.
There are some kinds of materials for making stern bearings such as:
- Special wood (lignum vitae).
- Synthetic rubber.
- White metal.
Special wood and synthetic rubber bearings are lubricated and cooled by water while lubricating oil
(L.O) is used for white metal bearings.
2.4.1. Special wood bearing (lignum vitae bearing).
a. Structure.
The traditional propeller shaft or stern bearing is lubricated by water. It consists of a number of
lignum vitae staves located in longitudinal grooves in a metal bush. Lignum vita is a kind of hard wood with
very good wear characteristics and it is compatible with water.
The staves with against the grain are used in lower part of the bearing. They have a higher longevity

than staves with the grain. These staves are closely placed and secured by brass plate. The length of secured
plate is equal to length of the staves and thickness of this plate is about 60% of the staves. Two or three brass
plates can be used to secure the staves. When the bearing is working with water-cooling, the staves will
expand boundary and create pressing force to each other.
The metal bushes in which the staves are mounted are pressed into cast iron stern tube. At the after
end of the metal bush is provided with a shoulder and it is secured by a lock nut on the stern tube. Generally,
two staves bush are fitted in the stern tube. The aftermost bush has a length about 4 times the diameter of the
shaft and it is the main bearing unit. The forward bush is short and acts mainly as a guide. The center
(unbushed part) of the stern tube is connected to a seawater service line, which, together with ingress of
water between the shaft and aft bush, provides lubrication.
To increase longevity of the propeller shaft, the brass sleeves must be fitted.
Clearance of fitting: D1 = 1.003D + 1.0

(mm)

Where D1 is inside diameter of the bearing, D is outside diameter of the shaft (including brass sleeve).

4

3

1
2

19


Figure 2.4: Lignum vitae bearing
1- Metal bush
2- Lignum vitae

3- Secured plate
4- Screw

b. Advantages of lignum vitae bearing.
- This kind of bearing is very suitable for propeller shaft, which has a big diameter and low speed.
- It is safe in operation.
- Absorb vibration of the propeller shaft.
- Maintain clearance between shaft and bearing if optimum cooling and lubricating.
- Longevity is high (about 10 years)
c. Disadvantages
- Lignum vitae are an uncommon material. It is very expensive.
- It is difficult in manufacturing.
- Bearing is excessively worn if the ship is sailing in shallow and dirty water, especially when
sand comes into clearance of the bearing.
2.4.2. Synthetic rubber bearing (Rein forced rubber).
a. Structure.

2

1

Soft rubber

5

Hard rubber

4

3

Figure 2.5: Synthetic rubber bearing
1- Stern tube 3- Rein forced rubber stave
2- Metal bush 4- Brass sleeve
5- Propeller shaft

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There are some differences in structure of synthetic rubber bearings but basically, the rubber staves
are positioned in a metal bush. A groove is made between two staves to let water flow in for lubricating. The
metal bush is fixed to the stern tube by screws (metal bush must not rotate). The same with special wood,
brass sleeves must be inserted to propeller shaft in case of rubber bearing. The friction coefficient between
rubber bearing and brass sleeves in water is about 0.02 ÷ 0.007 depends on kinds and shapes of rubber
bearing.
b. Advantage of rubber bearing.
- When working in water, friction coefficient is decreased.
- Abrasion resistance ability is high even in dirty water with much sludge and sand
- Noise and vibration is reduced. When rotating propeller shaft can center it self.
- It is cheaper than lignum vitae material.
- This kind of bearing is suitable for propeller shaft with medium and high speed.
c. Disadvantages.
- Heat exchange coefficient is low, so working temperature of the bearing is limited under 65 oC. If
temperature is excessive the limit value about 20 0 C, rubber may be deformed and if temperature is too low
(about - 40oC), it will be hardened.
- Sulfur in rubber will corrode the brass sleeve of the shaft. Because of this when the ship staying in
port for a long time, sometimes the shaft must be turned.
- Oil must be away from bearing if not, bearing will be worn very fast.
2.4.3. White metal bearing.

a. Structure.
A typical analysis of white metal is 3% copper, 7.5% antimony the remain is tin. The thickness
depends on requirement of registry. Lloyd’s register recommends the thickness of 3.8 mm for shaft 300
diameters, up to 7.4 mm for shaft 900 diameters. The bearing clearance can be calculated:
5

4
3

1

2
Figure 2.6: White metal bearing

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1- Propeller shaft
2- Stern tube

3- White metal

5- Oil groov

4- White metal liners
D1 = 1.001D + 0.5 (mm)
Where: D1 - Inside diameter of the bearing, D - Outside diameter of the shaft.
White metal liner must be fixed to the stern tube otherwise it will be turned together with shaft and be
soon damaged. The white metal bearing must be lubricated by lubricating oil.
b. Advantages of white metal bearing

- Propeller shaft without brass sleeve can be used.
- It can withstand heavy load with vibration and changing direction of the shaft.
- Corrosion of the shaft is prevented because seawater does not contact with the shaft.
- Wear of the shaft is very small. If it is properly lubricated, longevity of the bearing may last 7- 8
years.
- Because there are many good features, so nowadays almost big ships use white- metal bearing.
c. Disadvantages
- Replacing and making is complex.
- Sealing and lubricating system for propeller shaft is complex.
- Longevity of bearing depends on operating condition, installation standards and especially the
sealing.

2.5 Stern tube sealing:
Its function is to prevent leakage of seawater through, or loss of oil from, the stern bearings. Shaft
seals are very important during operation of the shafting; they maintain good condition of the stern bearings
and protecting marine pollution.
Nowadays, there are two common types of shaft seal are used widely on board ships. They are gland
packing and simplex shaft seal types.
2.5.1. Gland packing seal type.
Gland packing seal almost used on small ships. Its structure consists of simple stuffing boxes filled
with packing material; usually rove cotton imbrued with tallow or graphite as a lubricant. In the case of high
duty packing the material may be white metal clad. Figure 2.7 below illustrates structure of a gland packing
seal. Gland packing can be lubricated by water or lubricating oil. Gland packings are adjusted by tightening
or loosening gland cover (4).

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3

4

2

1
5
Figure 2.7: Structure of gland packing seal
1- Propeller shaft
2- Stern tube
3- Gland packings

4- Gland cover
5- Metal bush

2.5.2. Simplex shaft seal:
a. Aft seal
Figure 2.8 is an illustration of aft simplex shaft seal. The aft seal is composed of the casing fixed to
the hull and the liner, which is fixed to the propeller boss and rotates with the propeller shaft together. The
casing consists of three kinds of metal rings (flange ring, intermediate rings and cover ring), which are
separately tightened with bolts. Individually assembled between these rings, four sealing rings are composed
the leading edge (lips) touching the liner. These lips are pressed hard against the rotating liner by the water
and oil pressure, elasticity of the rubber material and the tightening force of the springs to maintain sealing
effect.
The four sealing rings are numbered by No.1, No.2, No.3, and No.3S from the seawater side. Seawater
penetration is tightly protected by No.1 and No.2 sealing rings.
No.1 sealing ring, in particular, has an additional function to protect the inside of the stern tube from
extraneous substances in seawater.
The oil pressure in the chamber between two (No.3 and No.3S) sealing rings located at forward is
usually adjusted to be the same pressure as stern tube pressure, which is 0.2 - 0.3 kg/cm 2 higher than sea
water pressure. Therefore, there is no pressure loaded on No.3S sealing ring on the above conditions.

Normally, lubricating oil in the stern tube is sealed by No.3 sealing ring.
However, if much oil leakage from No.3 and No.3S chamber would be found, No.3S sealing ring
could be used to protect the above leakage instead of No.3 sealing ring by the easy valve operation handle
inboard.

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8
5

4

1

Propeller boss

2

3

No.1

No. 2

6

7

10

9

No.3

No.3S

Propeller shaft

Figure 2.8: Aft simplex seal
1- Cover ring
2- Sealing ring (No.1, 2, 3, 3S)
3- Inter mediate rings
4- Oil inlet
5- Flange ring

6- Packing
7- Stern tube
8- Stern frame
9- “O” ring
10- Aft chrome steel liner

b. Forward seal
The forward seal is of a construction almost similar to the aft seal, except that it is composed of two
sealing rings.
The sealing rings are numbered No.4 and No.5 from the side of stern tube
No.4 sealing ring seals tight the lubricating oil inside the stern tube while No.5 sealing ring seals tight
the lubricating oil in the oil chamber between No.4 and No.5 sealing rings. The forward liner is tightened
with bolts to the split - type clamp ring mounted to the propeller shaft

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10

9
8
7
6

5

4

2

1

3

No.4

No.5

Propeller shaft

Figure 2.9: Forward simplex seal
1- Clamp ring
2- Forward chrome steel liner
3- “O” ring

4- Cover ring
5- Sealing ring (No.4, 5)

6- Intermediate ring
7- Flange ring
8- Packing
9- Stern tube
10- Aft bulkhead

2.6 Requirements for cooling and lubricating stern bearing.
To lubricate and cool the stern bearings, lubricating oil or water can be used. If the bearings are
lacked lubricating, dry friction will be created and the shaft and the bearings will be damaged soon.
- For the bearings made from white metal, ball bearing, lubricating oil is used to lubricate.
- Lignum vitae, rubber used water for lubricating.
2.6.1. For the bearings lubricated and cooled by water.
Lignum vitae, synthetic rubber bearing uses water for lubricating and cooling. Seawater outside the
ship or water pumped from engine room can be used for these purposes.
These kinds of the bearings need enough capacity of water for lubricating and cooling. If lack of
water, the bearings temperature increases then the bearings and shaft sleeve will be damaged. The best
temperature for lignum vitae bearing is smaller than 50oC.
For synthetic rubber bearing, when lack of water the friction coefficient of the bearing increases then
bearing temperature will be fast increased and both shaft and bearing will be stuck to each other.
The best water for lubricating and cooling is the pressured water pumped from the engine room after
cleaned by a strainer. The flow of pressured water will clean sand and dirt from working surface of bearings
when the ship sailing at shallow and dirty water area.

25


The water lines must be provided with pressure gauges, sight glasses, thermometer to monitor the

lubricating and cooling condition of the bearings. Water pressure ≤ 2.5 Kg/cm2, temperature ≥ 20oC.
Cooling and lubricating water for the bearings must be supplied before trying the main engine.
2.6.2. For the bearings lubricated and cooled by lubricating oil.
Oil for lubricating of this type can be supplied by a pump or a gravity tank. After lubricating the
bearing, the oil must be cooled by water in a cooler. Pressure gauges, sight glasses, thermometer must be
provided to monitor the lubricating condition.
If the gravity tank is used for lubricating, they must be installed above the highest water level of the
ship. Level gauge and low-level alarm must be fixed to this tank.
For this type of the lubricating, the sealing condition is very important if the after sealing ring
damaged, oil may be leaked or seawater may come into lubricating oil, so attention must be paid when
operating. The best way is to follow instruction of the maker.
Figure 2.10 illustrates a stern tube lubricating oil system.

26


Gravity tank high
Venting pipe

Stern tube cooling tank
Gravity tank low

T

P

Three-way cock

Needle
valve

Transfer line

Figure 2.10: Stern bearing lubricating oil system
2.7 Intermediate shaft and bearing:
Depending on arrangement of engine room, marine propulsion plant may have intermediate shaft or
not. If engine room is arranged in midship, the shaft line may have two or more intermediate shaft, but
almost ship engine room is placed at the aft of the ship and there is only one intermediate shaft. Steel is
material to make the intermediate shaft.
- Flanges are arranged at the both ends of the shaft to connect the intermediate shaft to the propeller
shaft and the thrust shaft.
- Normally, each intermediate shaft has one bearing. Figure 2.12 illustrates structure of the
intermediate bearing. Oil is used to lubricate for the bearing. White metal is material to make the bearing.
When operating, attention must be paid to the bearing such as oil temperature, oil level, oil quality, and
condition of sealing ring.
(See Figure 2.12)

2.8 Thrust shaft and thrust bearing:
2.8.1.Thrust shaft:
The thrust shaft is installed between of crankshaft and intermediate shaft and together with this shaft;
it transmits power of the main engine to the propeller. Thrust shaft made of forged steel, has one or two

27


collars. In medium or high-speed engines, it is installed in the reduction gear, which is located in the after part of
the main engine.
2.8.2. Thrust bearing:
Thrust bearing is designed to absorb thrust force from the propeller and transmits it to the hull of the
ship. There are three kinds of thrust shaft bearing corresponding to the thrust shafts, these are:

- Thrust shaft with tapered roller bearing
- Thrust shaft with one collar
- Thrust shaft with two or more collars
a. Tapered roller bearing
A tapered roller bearing is normally installed on small ships in a reduction gear. This kind of bearing
has light weigh, small size and small friction coefficient, but for the big ships it is difficult to inspect, repair
and change the roller bearing.

28