Ship Propulsion system

Yasser B. A. Farag
MSc. of Maritime Energy Management - - Sweden
Lecturer at Institute of Maritime Upgrading Studies
Maritime Chief Engineer
Maritime Upgrading Studies Institute - 2 0 2 0 -
Marine Engineering Knowledge
UE231

M a r i n e E n g i n e e r i n g K n o w l e d g e U E 2 3 1 | Y A S S E R B . A . F A R A G20 October 2020
How the ship thrust is created?
37

Shafting system
38

ENGINE
PROCESS
8.5 kg/kWh
168 g/kWh
1 g/kWh
HEAT
WORK
EXHAUST
GAS
AIR
FUEL
L.O
21% 𝑶𝑶𝟐𝟐
79% 𝑵𝑵
97% 𝑯𝑯𝑯𝑯
0.5% 𝑺𝑺
97% 𝑯𝑯𝑯𝑯
2.5% 𝑪𝑪𝑪𝑪
0.5% 𝑺𝑺
13% 𝑶𝑶𝟐𝟐
75.8% 𝑵𝑵
5.6% 𝑪𝑪𝑶𝑶𝟐𝟐
5.35% 𝑯𝑯𝟐𝟐 𝑶𝑶
1500 ppm 𝑵𝑵𝑶𝑶𝑥𝑥
600 ppm 𝑺𝑺𝑶𝑶𝑥𝑥
60 ppm 𝑪𝑪𝑪𝑪
180 ppm 𝑯𝑯𝑯𝑯
120 mg/N𝒎𝒎𝟑𝟑
𝑷𝑷𝑷𝑷
??
** All numbers are general and differs according to the engine type, manufacturer and technology updates.
Engine’s Emissions
39

Shafting system layout
40

Ship Drive Train and Power
Engine
Reduction
Gear
Bearing Seals
Screw
Strut
DHP
THP
EHP
BHP
SHP
Shaft Horse Power (SHP)
Power output after the
reduction gears
SHP=BHP - losses in
reduction gear
Brake Horse Power (BHP)
Power output at the shaft
coming out of the engine
before the reduction gears
Ship’s movement
41
Delivered Horse Power (DHP)
Power delivered to the
propeller
DHP=SHP – losses in shafting,
shaft bearings and seals
Thrust Horse Power (THP)
Power created by the
screw/propeller
THP=DHP – Propeller losses
Effective Horse Power (EHP)
The power required to move the
ship hull at a given speed in the
absence of propeller action

Effective Horse Power (EHP)
 EHP is not related with Power Train System.
 EHP can be determined from the towing tank experiments at the various speeds of the model ship.
 EHP of the model ship is converted into EHP of the full scale ship by Froude’s Law.
Towing Tank Towing carriage
Measured EHP

Efficiencies
Screw
Propeller Efficiency
DHP
THP
propeller =η
Propulsive Coefficients
SHP
EHP
p =η
propellerdesignedfor well6.0≈pη
SHP DHP
THP
EHP
Hull Efficiency
THP
EHP
H =η
Hull efficiency changes due to hull-propeller interactions.
Well-designed ship :
Poorly-designed ship :
𝜼𝜼𝑯𝑯 > 𝟏𝟏
𝜼𝜼𝑯𝑯 < 𝟏𝟏

Input = ṁ x CV
B.P 49.3%
Jacket water cooling
5.2 %
Exhaust losses
22.3%
Mechanical Energy
Waste Heat
Waste Heat
Thrust
28%
Radiation 0.6%
Waste Heat
Lubrication 2.9%
Chemical
Energy
100% Fuel
171 g/kw.hr
Thrust
T/C
Air Cooler 14.2%
Propeller Losses
10%
Hull
Friction
10%
29%
** All numbers are general and differs according to the ship type, design and technology updates. @ Yasser B. A. Farag 2020
To other waste heat recovery techniques, such as Economizer, Exhaust Gas Boiler, Turbo Generators…
Part of heat can be recovered in the fresh water generator
Waste Heat
44

Shaft alignment definition
• Propulsion shafting: is a system of revolving rods that transmit power and motion from the
main drive to the propeller. The shafting is supported by an appropriate number of bearings.
• Propulsion shaft alignment: is a static condition observed at the bearings supporting the
propulsion shafts.
(ABS Definitions)
46

Dynamic loads
• Hog and Sag due to state of loading and draught, effect of waves, etc., can be quite easily as
much as 1mm per 1m of ship length
• The effect of the waves and sea action over the main engine’s rigid bedplate length of about 16
m can be ignored.
• It’s difficult to perfectly align heavy engine and shafting length into the flexible beam form of a
ship that is subjected to the influence of the forces of the sea.
• The initial alignment is carried out in the dry dock with the final alignment in the water
verified by alignment survey.
47

1. Alignment by Piano Wire
48

2. Alignment by light
The survey will verify at different
loading conditions the calculations,
and stiffening in the way of tank tops
and engine seating supports, together
with the use of rigid bedplates, can
reduce the central deflection to a
maximum of about 13 mm over the
engine room length and to about 2 mm
maximum over the bedplate length.
49

2. Alignment by light
50

3. Alignment by Laser
Laser alignment tools are the
modern method of completing
the process. The tools are light,
easy to set up and relatively
low cost. The precision laser is
accurate to less than half a
millimeter over 15 meters .
51

External factors affecting shaft alignment readings
52

Shaft alignment
53
Reference datum are the height of
the shaft above the keel at the Aft
end and the height of the crank shaft
centre above the keel extended to
the forward machinery space
bulkhead

Dynamic Loads
54

Shaft alignment Variation at different loading conditions
55
The bedplate has a sag form when light ship of say 1 mm
and a hog form when fully loaded of say 1 mm.
Main Engine
Datum
1.25 mm
15 mm
3.5 mm
Datum
Scale 4mm = 1m
Scale25mm=1mm
Bulkhead
BRG-2
BRG-1
BRG-3
BRG-4
BRG-5
Source: adopted from many sources
Wp B B
B B B
B

Checking bearing load by Jacking
56

Crank shaft alignment
57

Crank shaft alignment
Excessive crankshaft deflections
readings in reciprocating machinery
will mean that there is a continuing
variation in the distance between
crank webs as the shaft moves through
a full engine revolution. This will
cause dangerous bending stresses in
the web and fillets between crank pin
and web.
58

shaft alignment measurement after grounding
59

Thrust Block

Shafting system
61

Thrust Bearing
62

Thrust Bearing construction
63

Clearance = 1mm
64
Thrust Bearing construction

Thrust pads
65

M a r i n e E n g i n e e r i n g K n o w l e d g e U E 2 3 1 | Y A S S E R B . A . F A R A G20 October 2020 66
Thrust pads

Oil wedge
67

Collar
68

Pads design
• Conventional Type (Kidney shape) • Round Type (Circular)
69

Plain and Tilting Pad bearings
1/3 bearing area Full bearing area
70

Hydrodynamic lubrication
71

hydrodynamic lubrication
72

Hydrodynamic and hydrostatic lubrication
73

Roller bearing
Roller Bearings are not dependent on speed
for effective lubrication. Friction is low at all
speeds. This make them suitable for steam
turbine installations and in ships where slow
steaming may be necessary
74

Stbd Side Thrust Block in Normal
Use
Port Side Thrust Block Prior to
Lifting
Thrust Collar and Pads Through
Inspection Cover
Thrust Bearing overheating-case study
Close up of Ahead Pad and
Thrust Collar through Inspection
Cover
Lifting Cover
Astern Pads and Collar Showing How
Pads Are Linked. Note White Metal
Debris
Wiped Ahead Pads
75

Removing Astern Thrust Pads
Thrust Bearing Repair
Turning Out Bottom Half of Shell
Bearing After Jacking Shaft
Grinder Set Up
Temporary Thrust Arrangement
To Prevent Fwd Movement of
Shaft
76

Thrust Bearing Repair
77

Stern tube

OIL-lubricated stern tube
• Wear rate = ¼ mm every 4 years for
white metal
• Low coefficient of friction = 0.003
• To be inspected every 6 years
• Stern tube length = 2D
• Clearance = 0.002 – 0.001 D
D
79

80

81

Water-lubricated S/T
• The staves are shaped with V or U grooves
between them at the surface.
• Bearing length = 4D (3D for TUFNOL)
• Bronze liner to be examined every 3 years.
• Wear rate of 1mm/year.
• No pollution.
• Has less Load carrying capacity
• Rubber bearing surfaces may be used in small
ships.
• TUFNOL(Plastic resin compound) has a lower
coefficient of friction and twice compressive
strength of Lignum Vitae.
D
82

Water-lubricated S/T
83

Water lubricated S/T
84

Propeller shaft inspection
Examining a tail shaft and stern tube
1. Before the periodic inspection the
bearing wear down should be
measured.
2. After shaft removed given thorough
examination.
3. On water lubricated shafts the integrity
of the fit of the bronze liner should be
checked by tapping with a hammer
along its length listening for hollow
noise indicating a separation.
4. Measure wear of shaft.
5. Examine key way for cracks especially
the nut thread area.
6. replace rubber rings
85

Comparison
86

Water lubricated seals
87

Sealing ring shape
88

Sealing rings
89

Sealing rings
90

Air sealing
91

Air sealing
92

Propeller removal

Removal of a keyed propeller
1. Slack Propeller nut. DON’T REMOVE IT
2. Propeller must be safely secured with a group of chains.
3. Flange between the Tailshaft and Intermediate shaft
slacked, a piece of wood to be inserted between them to
absorb any inward thrust.
4. NO HEATING UP TO THE PROPELLER HUB.
5. Dismantling special tool to be mounted firmly against the
propeller hub.
6. While tightening the special tool nuts against the
propeller nut, the propeller withdrawn from the shaft.
7. Special care given to the shaft screw teeth and a source
of protection must be applied.
8. Key ways to be inspected, Cracks and rust if present to
be found.
94

Pilgrim nut

Poisson’s ratio
A metal with the same elastic properties in all
directions will have a constant relationship
between axial strain and lateral strain. This is
termed by POISSON’s RATIO.
𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑛𝑛′ 𝑠𝑠 𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟 =
𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠
𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠
96

Pilgrim type hydraulic coupling bolt
• The Bolt is Hollow and before being fitted is
stretched with hydraulic pressure (within its
elastic limits) .
• These bolts used in FLANGE COUPLINGS and FLANGE
MOUNTED PROPELLER
• Easy to remove for inspection and maintenance.
97

• Pilgrim nut is used to ensure a solid frictional grip
between the propeller and shaft. The use of
pilgrim nut facilitates the transmission of the
engine torque without using the key.
• Pilgrim nut is basically a hydraulic jack with
threads, which is screwed into the slot provided
on the tail shaft . The propeller is forced onto the
tapered tail shaft region by using a steel ring,
which receives the thrust from a hydraulically
pressurized nitrile rubber tyre.
• In simple, when the tyre is pressurized the
propeller will come off the tapered region.
Pilgrim nut
98

Propeller fitting by using pilgrim nut
Assembly: Propeller bedded to tailshaft and
jacked up to usual shop mark. The Pilgrim nut
is then screwed on the shaft with the loading
ring against the prop boss. With the lever
operated, high pressure grease gun, grease is
pumped into the inner tube inside the nut at
around 600 bar, ( w.p. stamped on nut, not to
be exceeded), the prop will be pushed
sufficiently up the taper to give the required
frictional grip. The pressure is then released
and the nut is rotated until it is hard up against
the aft face of the prop hub and locked, fair
water cone then fitted.
99

Propeller withdrawal by using pilgrim nut method
Wood
Block
Withdrawal : After removal of fair
water cone and the locking plate, the
pilgrim nut is removed, reversed and
together with a loose shock ring is
screwed back onto the shaft.
• A strong back is fitted and secured
with studs to the prop boss. Grease is
now inserted to the system
expanding the inner tube forcing the
loading ring, strongback, withdrawal
studs and prop aft.
100

SKF oil injection method
1
2
Assembly
101

SKF oil injection method
• Oil is injected between the shaft taper and the bore
of the propeller by means of high pressure pumps.
• Oil penetration is assisted by a system of small
axial and circumferential grooves or a continuous
helical groove, machined in the propeller bore.
• The oil reduces the CoF between the surfaces to
about 0.015.
• A development of the keyless method involves a cost
iron sleeve which is bonded into the propeller boss.
• The sleeve is easier to handle when machining and
bedding than a complete propeller. Another benefit
is that cost iron has a CoF nearer to that of the
shaft than to propeller bronze.
102

Keyless propeller

Keyless propeller
Advantages
• Precise tightening working on a measured
applied load
• Adequate interference fit
• no heat used
• Simple and safe to operate
• No shock loads applied
• Considerable saving in man power and time
105

Muff coupling
Tailshaft
• When the coupling is in position, the outer sleeve is
hydraulically driven on the tapered inner sleeve.
• At the same time, oil is injected between the contact
surfaces to separate them and thus overcome the friction
between them.
• When the outer sleeve has been driven on to a
predetermined position,
1. the forced lubrication pressure is released and
drained.
2. Oil pressure is maintained in the hydraulic space
until the oil between the sleeves drains and normal
friction is restored.
3. After disconnecting hoses, plugs are fitted and
rust preventive applied to protect exposed
seatings
Intermediate Shaft
1
2
106

Muff coupling
Tail shaft
• The grip of the coupling is checked by
measuring the diameter of the outer sleeve
before and after tightening. The diameter
increase should agree with the figure stamped
on the sleeve.
• To disconnect the coupling, oil pressure is
brought to a set pressure in the hydraulic space.
Then with the shafts supported, oil is forced
between the sleeves. The outer sleeve slides off
the inner at a rate controlled by the slow
release of the hydraulic oil pressure.
Intermediate Shaft
1
2
107

Muff coupling
Intermediate ShaftTailshaft
Assembly :
1. Apply 1 at the same time 2
2. release 1 then 2
Dismantling :
1. Apply 2 then 1
2. release 2 slowly so the
outer sleeve slides off the
inner then release 1
1
2
Note: The thin inner sleeve has a bore
slightly larger than the shaft diameter
108

Muff coupling
SKF Hydraulic Muff Coupler on 5.5" Shaft
The hydraulic coupler installation requires an exact fit and a light touch between the steel coupler
sleeve and the shaft ends. There are no fasteners in this system – no bolts, no keys or key-ways.
Approximately 7″ of shaft ends that are inside the coupler must be machined to within tenths of a
millimetre to the coupler sleeve.
109

Shaft stresses

Shaft Stresses
• Stress is expressed as the total load divided by the area that it is acting through.
• The intermediate shaft is subject to torsional shear stress which influences the factor of
safety and hence resultant working stress, bending and possible variation of torque
• Thrust shaft will require thicker diameter at the collar root (1.15d)
• Stern tube shaft diameter is 1.14d. If any part of the shaft is in contact with sea water
these sizes are to be increased 2.5%
• For propeller shaft, there is fluctuating, combined bending and twisting, with end thrust
and the possibility of corrosion attack.
111

Propeller Shaft Stresses
• Due to the considerable weight of the propeller, the tail
shaft is subject to a bending stress. There are however
other stresses which are likely to be encountered. There is
a torsional stress due to the propeller resistance and the
engine turning moment, and a compressive stress due to
the prop thrust. All these stresses coupled with the fact
that the shaft may be in contact with highly corrosive sea
water makes the likelihood of corrosion attack highly
probable.
112

Propeller Shaft Faults
1. Before the periodic inspection the
bearing wear down should be
measured.
2. After shaft removed given thorough
examination.
3. On water lubricated shafts the
integrity of the fit of the bronze liner
should be checked by tapping with a
hammer along its length listening for
hollow noise indicating a separation.
4. Measure wear of shaft.
5. Examine key way for cracks especially
the nut thread area.
6. replace rubber rings
113

Shaft balancing

Simple revolving mass
• An unbalanced mass m at radius r, to balance introduce
an opposite mass, B at radius b, in the plane of rotation
such that:
𝑩𝑩𝝎𝝎𝟐𝟐
b = m𝝎𝝎𝟐𝟐
𝒓𝒓
i.e. equal centrifugal force effects.
𝑩𝑩b = m𝒓𝒓
115

Several revolving masses in one plane
Draw a mass moment (actual mass x radius) polygon and closing side give Bb magnitude and direction.
116

Several Revolving Mases in Different Planes
• A couple is a tendency to rock the shaft in its bearings in the form
of an end to end turning moment. Magnitude of the couple shown
= Px
• Proceed as before and draw the mass moment polygon to find the
unbalance mass moment
• Assume it is necessary to add say two balance masses, having
equivalent mass moment to that found, for convenience at say X
and Y, i.e. one big mass to a particular point may not be
convenient so the mass is split up
117

Several Revolving Mases in Different Planes
• These two masses are also in different
planes.
• By using one of the planes, X or Y, as a
fixed reference it can be fixed and then
ignored, having no moment.
• Then a couple polygon or a tabulation is
drawn for the other position. Thus the
masses, radii and location of the planes
for balance are determined.
118

Vibration

General Vibration
• Vibration is a mechanical phenomenon whereby
oscillations occur about an equilibrium point.
The oscillations may be periodic, such as the
motion of a pendulum or random, such as the
movement of a tire on a gravel road.
• There are three modes of vibration:
1. Transverse vibration.
2. Longitudinal vibration (Axial).
3. Torsional Vibration
120

General Vibration
• Modern shafting is built after consideration of both low
cycle and high cycle fatigue.
• Every vibration problem reduces to the solution of an
equation of forces:
Inertia + Damping + Spring + Exciting = 0
Spring-mass Undamped
Spring-mass over-damped
Spring-mass under-damped
Spring-mass critically-damped
121

Transverse Vibration
• This occurs in the athwart ship direction with large
reciprocating engines. It is' usually due to cylinder
pressure forces and inertia forces giving a resulting
couple about the engine crankshaft centre line and
through the guide shoe.
• Propeller torque variations can increase or
decrease this couple.
• The usual solution is to stay the engine to the hull
with lateral stays. Such stays must be connected to
the hull by pins that would shear if the hull was
distorted in collision

Axial Vibration
• Some axial movements of amplitude ± 2.5 mm have been noted, a
movement of ± 1 mm can quite easily introduce crank bending
stresses of 28 MN/m2.
• Invariably these movements are propeller excited occurring as say
4th order vibrations (8 vibrations per second at 2 rev/s of shaft).
• In this respect a 4 bladed propeller is causing the axial vibration
with 2 blades passing the aperture every 1/4 rev giving an axial
pulse.
• the introduction of 5 bladed propellers and more rigid thrust
seating have done much to reduce such amplitudes of vibration.
• Some experiments have been tried to utilise the principle of the
Michell thrust indicator to introduce a dashpot damping effect.
123

Torsional Vibration
• A node is a point at which the shaft is undisturbed by vibration, i.e.
at the node the shaft can be imagined as clamped, the sections at
each side vibrating opposite in phase but with the same frequency.
• One node gives one mode of vibration, two nodes two modes, etc.,
most shafting systems can be simplified to a one or two mode form,
i.e. first or second degree of vibration as at least a first
assumption.
• This means for calculation the shaft system is considered as a 3
mass system, engine in one, flywheel and propeller.
• Only one serious critical occurs in the running range usually, for aft
end installations commonly above the maximum revolutions and for
midship installations commonly below.
124

Introduction to hydraulic systems

Introduction to Hydraulic system
Hydraulics are used in many applications onboard ships:
• Steering/control systems (rudder)
• CPP
• Deck machinery (anchor windlass, capstans, winches)
• (loading & launching)
• Other: elevators
126

Hydraulic system
 Hydraulics
• Covers the physical behavior of liquids in motion
• Pressurized oil used to gain mechanical advantage and perform work
 Important Properties
• Shapelessness
• Incompressibility
• Transmission of Force
127

Features
“Shapelessness”
Liquids have no neutral form
Conform to shape of container
Easily transferred through piping from one location to another
Incompressibility
Liquids are essentially incompressible
Once force is removed, liquid returns to original volume (no permanent distortion)
Transmission of Force
Force is transmitted equally & undiminished
in every direction -> vessel filled with pressure
128

PASCAL’s Law
Magnitude of force transferred is in direct proportion to the surface area (F = P*A)
Pressure = Force/Area
Liquid properties enable large
objects (rudder, planes, etc.) to
be moved smoothly
129

Theory
• Piston/cylinder used if desired motion is linear
• Hydraulic pressure moves piston & ram
• Load is connected to ram (rudder, planes, masts, periscopes)
Piston
Cylinder
RAM
Hydraulic Fluid Supply/Return Ports
Seal
130

Pros & Cons
Advantages disadvantages
• Convenient power transfer
Few moving parts
Low losses over long distances
less wear
• Flexibility
Distribute force in multiple directions
Safe and reliable for many uses
Can be stored under pressure for long periods
• Variable speed control
Quick response (linear and rotary
• Requires positive confinement (to give shape)
• Fire/explosive hazard if leaks or ruptures
• Filtration critical - must be free of debris
• Manpower intensive to clean up
131

Controllable pitch
propeller

Theory
133

CPP
134

Types
135

Construction
136

Construction
137

Construction
The advantage of this
arrangement is that
the operating piston is
easily accessed in the
event of failure.
138

Control
139

Control

Mechanism
141

Mechanism
142

CPP hub actuator
143

Mechanism
Ahead
Astern
144

CPP hub
145

Hub return spring
146

Defect location
147

Illustration
148

Illustration
149

Pros & Cons
Advantages disadvantages
• Fast stop manoeuvres are possible.
• The main engine does not need to be
reversible.
• Fine control of thrust can be achieved without
the need to accelerate or decelerate the
propulsion machinery.
• These propellers allow engagement of shaft
generator to be driven from the main engine
which is efficient and cheap. Variable ship
speeds can be obtained with constant
propeller rpm as required by the generator.
• consumption is higher. The higher propeller rpm at lower
speed is hydrodynamically suboptimal.
• It require a thicker hub (0.24-0.32 D). The pitch
distribution is suboptimal. The usual almost constant pitch
in the radial direction causes negative angles of attach at
the outer radii at reduced pitch, thus slowing the ship
down. Therefore such propellers usually have higher pitch
at the outer radii and lower pitch at the inner radii. The
higher pitch at the outer radii necessitates a large
propeller clearance.
• Higher costs for propeller.
• Complicated design
150

Ship Propulsion system

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