This document discusses controllable pitch propellers. It begins with an introduction and overview of fixed pitch propellers and controllable pitch propellers. It then discusses the advantages and disadvantages of controllable pitch propellers, including their ability to utilize full machinery power under different conditions, improve acceleration and manoeuvrability, and operate at optimal efficiency over a large speed range. The document also discusses applications and provides examples of vessel types that typically use controllable pitch propellers.

1. Controllable Pitch Propellers

3. Introduction
Fixed Pitch Propeller
Controllable Pitch Propeller
Vary RPM
Vary RPM & Pitch

4. Controllable Pitch Propeller
Open Water Diagram
J
KT
𝜼𝟎
10 KQ

5. Controllable Pitch Propeller
Advantages
❑ Full power of the machinery can be utilized in different operation conditions.
❑ Better acceleration, stopping and manoeuvring characteristics.

6. Controllable Pitch Propeller
Advantages
❑ Propulsion point can be operated at optimum efficiency for
a large range of ship speeds and displacements.
❑ Non-reversing engines can be used (if pitch can be
reversed), reducing cost, weight, and space.

7. Controllable Pitch Propeller
Advantages
❑ Can produce high astern thrust at higher efficiency.
❑ Damaged blades can be replaced conveniently.

8. Controllable Pitch Propeller
Disadvantages
❑ High initial cost and maintenance costs
❑ Complicated pitch control mechanism

9. Controllable Pitch Propeller
Disadvantages
❑ Large boss length and diameter- reduces efficiency
❑ Pitch distribution optimized at design pitch does not remain
optimum when pitch is changed.

10. Controllable Pitch Propeller
Disadvantages
❑ Blade area limited to enable pitch reversal resulting in thicker blades.
Influences cavitation and efficiency
❑ Efficiency at design point is lower than fixed-pitch propeller due to
larger boss diameter (typical ratio: 0.24 - 0.32).

11. Applications
❑ Full power operations in widely different speed regimes
❑ Acceleration and stopping capability
❑ Non-reversing propulsion machinery
Example: Tugs, Trawlers , Ferries, Warships
VIDEO

12. Problem
A 5-bladed controllable pitch propeller has a constant pitch ratio of 0.8 (at all radii) at
a particular setting. Due to change in operation conditions, the propeller pitch is
changed as follows:
Case-1: Pitch increased by turning the blades through an angle of 10 degrees.
Case-2: Pitch decreased by turning the blades through an angle of 5 degrees.
Find the pitch ratios at the blade radial sections-
r/R = 0.3, 0.5, and 0.8 for the two new pitch settings (Case-1 and Case-2).

13. Propellers on Inclined Shaft

14. Propellers on Inclined Shaft
It is required to incline the propeller shafts in
certain cases, especially in small vessels in
order to get sufficient space and clearance for
the propeller from the ship hull.

15. Propellers on Inclined Shaft
Shaft inclination gives rise to unsteady propeller forces.
VA : Speed of advance
VAP : Component along propeller axis
VNP : Component normal to propeller axis
VA
VAP = VA cos Ψ
VNP = VA sin Ψ

16. Propellers on Inclined Shaft
Considering the blade at an angle θ:
VTP = - VNP sin θ = = - VA sin Ψ sin θ
VA
VNP
[Tangential Velocity Component]
2ϖr n’(θ) = 2ϖrn + VTP

18. Propellers on Inclined Shaft
TH : Pushes the vessel forward
TV : Results in a trimming moment
TH
TV
For moderate shaft inclinations the fluctuations
of thrust and torque are small.

19. Unconventional Propulsors

20. Introduction
Propellers:
Conventional Screw Propeller
Propulsors:
General term for propulsion devices including unconventional types

21. Introduction
Unconventional Propulsors:
▪ Especially used for critical applications-
Fast vessels, restricted propeller diameter, high manoeuvrability requirement
▪ Reduced emission of greenhouse gases from shipping operations-
Improvement of propulsion efficiency
▪ Reduction of cavitation, vibration, and noise

22. Introduction
Why do we use Unconventional Propellers ?
To improve the propeller performance and thereby:
Reduce Cavitation
Minimize vibration and noise level
Improve Propulsive efficiency
When a normal conventional propeller may not
perform satisfactorily in certain operating conditions

23. Propulsion Performance
Improvements in propulsion performance/ efficiency:
▪ Reduction in kinetic energy losses in the slipstream
▪ Reduction in friction losses at the propeller
▪ Improved (more uniform) inflow into the propeller
▪ Higher thrust generation, in addition to the propeller thrust

24. Design Consideration
Selection of Unconventional Propulsors
▪ Propulsive efficiency
▪ Cavitation, vibration, and noise
▪ Initial cost, weight, volume etc.
▪ Associated machinery
▪ Reliability and maintenance aspects

25. Waterjet Propulsion
A waterjet propulsion unit consists of a pump inside the ship which draws water from outside,
imparts an acceleration to it and discharges it in a jet above the waterline at the stern.
▪ The jet reaction provides the thrust to propel the ship forward.
▪ The jet can be directed sideways for manoeuvring the ship, and can
be deflected forward to obtain astern thrust.

26. Waterjet Propulsion
Reversing Bucket
Stator
Swivelling Nozzle
Impeller
Water Inlet

28. Waterjet Propulsion
Swivelling Nozzle:
The waterjet is discharged through a nozzle which can be rotated about a vertical
axis to approximately 45 degrees on either side to turn the vessel.

29. Waterjet Propulsion
Reversing Bucket:
A bucket which can be rotated about a horizontal axis and used to deflect the waterjet
downward and forward, thereby producing an astern thrust.
By adjusting its position, the thrust of the waterjet can be varied from full ahead through
zero to full astern without altering the discharge of the pump.
**Excellent manoeuvring, stopping and reversing capabilities of the vessel.

30. Efficiency
❑ Momentum theory can be used for simple estimation of the efficiency of
a waterjet system.
❑ Efficiency Components:
ηH : Hull Efficiency
ηJ : Jet Efficiency
ηP: Pump Efficiency

31. Efficiency
❑ Losses considered in the calculation of jet efficiency:
• Inlet losses
• Energy for raising the water through a certain height
• Losses in the nozzle

32. Advantages
❑No appendages : reduction in resistance.
❑Can be used in shallow water without any limitation on the size of the pump.
❑Improved manoeuvrability, stopping and backing ability.

33. Advantages
❑Propulsion plant does not require reversing gear. Full ahead to full
astern speed can be controlled without altering the engine rpm.
❑Torque is constant over the complete speed range.
❑Less noise and vibration

34. Disadvantages
❑ The propulsion unit occupies considerable space inside the ship, and
the water passing through causes a significant decrease in buoyancy.
❑ At the water inlet grating is provided to prevent debris from getting in
and damaging the pump. This decreases the efficiency of the system.

35. Some Design Aspects
❑ Design of Inlet: Effect of boundary layer suction around the hull just
ahead of the inlet.
❑ Pump: Different types- axial flow, radial flow or mixed flow may be used.
❑ Powering: The preliminary design is usually carried out using design
charts provided by waterjet system manufacturers. The powering is
estimated based on vessel speed and thrust requirements by applying
suitable margin.
Applications: Ferries, Naval vessels etc.
(typical vessel speed > 30 knots)

36. Waterjet Design
Chart example

37. A vessel to be propelled by twin waterjets has an effective power of 2400 kW at its design
speed of 30 knots.
Carry out a preliminary design of the waterjets assuming the following values:
wake fraction 0.05, thrust deduction fraction 0.03, pump efficiency in uniform inflow 0.89,
relative rotative efficiency 0.96, inlet efficiency 0.82, nozzle efficiency 0.99, shafting
efficiency 0.95, and height of nozzles above water level 0.75 m at 30 knots.
Assume:
Overall propulsive efficiency of 0.53.
Nozzle(Jet) Area / Disc Area = 0.4

38. Multiple Propeller Arrangement
Tandem Propellers
In tandem propeller arrangement multiple (usually
two) propellers are mounted on the same shaft
and rotated in the same direction.

39. Multiple Propeller Arrangement
Tandem Propellers
Tandem propellers are applicable in situations of high thrust
requirement and restricted propeller diameter.
Usually the forward and aft propeller in tandem configuration
has the same number of blades and same propeller diameter.
Aft Propeller Forward Propeller

40. Multiple Propeller Arrangement
Tandem Propellers [Advantages]
A tandem propeller may be more efficient than a conventional propeller
at high loading where it can produce high thrust.
As the thrust is distributed between the two propellers, the propeller
diameter can be reduced.

41. Multiple Propeller Arrangement
Tandem Propellers [Disadvantages]
At normal to low propeller loadings no significant advantage is obtained
by adopting a tandem propeller, and the efficiency is often lower than
single screw propeller.
A tandem propeller has a higher weight, cost and rotational energy
losses.

42. Multiple Propeller Arrangement
Overlapping propellers
Two propellers are located at the same longitudinal
position but the their respective shafts are
separated by a distance less than the propeller
diameter. They are not commonly used.

43. Multiple Propeller Arrangement
Overlapping propellers [Advantages]
1. As the thrust is distributed between the two propellers the
efficiency may be higher.
2. Compared to a normal twin screw propeller, these propellers
work in a region of high wake, and the hull efficiency increases.

44. Multiple Propeller Arrangement
Overlapping propellers [Disadvantages]
1. The mutual interaction leads to vibration and cavitation
2. Unsteady forces are more.
3. Difficult to support two shafts close to each other

45. Contra-rotating Propeller
In a contra rotating propeller two propellers
are mounted on coaxial shafts, rotating in
opposite direction.
Cancellation of Rotational velocities in the
slipstream by the two propellers.
Aft Propeller Forward Propeller

46. Contra-rotating Propeller
The aft propeller is usually made smaller than the
forward propeller to avoid interaction with the tip
vortices generated from the forward propeller.
The number of blades of the forward and aft
propeller need not be same.
Aft Propeller Forward Propeller

47. Contra-rotating Propeller
Application
1. Used in torpedoes: The torque reactions of the two propellers
cancel each other to provide directional stability.
2. Different vessels where the efficiency improvement is important
based on the economy considerations.

48. Contra-rotating Propeller
Advantages
1. More efficient when compared to a single screw propeller [up to 15%
increase in efficiency can be obtained]
2. As the thrust is distributed between the two propellers, the propeller
diameter and blade area ratio can be reduced.
3. Reduction in pressure fluctuation and noise

49. Contra-rotating Propeller
Disadvantages
1. Mechanical complications involved
2. Higher maintenance
3. Greater weight
4. The sealing of shaft against ingress of water is critical

50. Supercavitating Propellers
Supercavitating propellers are considered certain design conditions where unacceptable
levels of cavitation cannot be avoided.
The back of the propeller blade section is fully covered with a vapour filled cavity for
supercavitating propellers.
A supercavitating propeller can provide thrust at nearly the same
efficiency as a conventional propeller, when a suitable operating
condition is adopted (combination of J and σ).

51. Supercavitating Propellers
A supercavitating propeller compared to a conventional propeller can have:
1. Better noise and vibrational characteristics
2. Reduced/ No cavitation erosion
Applications:
1. Racing motor boats.
2. Vessels having high engine power, rpm, ship
speed along with low propeller immersion and
small propeller diameter.

52. Supercavitating Propellers
The blade section shape of a supercavitating propeller should ensure complete separation of
flow on the back, and also provide high lift/ drag ratio.
Hence, blade sections with sharp leading edges are used.
Tulin Section Modified Tulin Section Cupped Trailing Edge Section

53. Supercavitating Propellers
Challenges
Propeller blade strength problems, due to thin leading edge of the blade section.
Performance in low speed range and off design conditions

54. Tip Modified Propellers
Examples:
Tip Vortex Free (TVP) propellers
Contracted and Loaded Tip (CLT) propellers
A basic version of a Tip Modified Propeller has an end plate attached to the
propeller blade tip. This enables to suppress the tip generated trailing vortices,
which allows a better circulation distribution radially so that the propeller loading at
bade tip can be increased.

55. Tip Modified Propellers
The other propeller types include- Kappel propeller and Lips tip rake propeller
Kappel propellers Lips tip rake propeller

56. Tip Modified Propellers
Advantages
1. Tip vortex cavitation is reduced
2. Improves the propeller efficiency
3. A proper end plate design may produce additional thrust
Disadvantages
Very large end plates increase the drag and reduces the efficiency

57. Cycloidal Propellers
The blades are fitted to a disc (on the ship hull) which
revolves about a vertical axis, and the blades can rotate
about their own individual axis.
The propellers generally have their axis oriented vertically, and
are hence called Vertical-axis Propellers.

58. Cycloidal Propellers
Types:
For ship speed ‘V’ and propeller angular velocity ‘ω’ the path described by each blade is:
Epicycloid (V < ωR)
Cycloid (V = ωR)
Trochoid (V > ωR)

59. Cycloidal Propellers
Applications
Examples of vertical-axis propellers:
Kirsten-Boeing propeller
Voith-Schneider propeller
Efficiency is usually lower as compared to conventional propellers.
Used in vessels where very high degree of manoeuvrability is required.
(Towing vessels, Short ferries etc.)

60. Surface Piercing Propellers
A propeller arrangement in which the propeller is
partly submerged and pierces the water surface.
Typically used in high-speed planing crafts where
propeller submergence decreases at high speeds.
Operates in partially ventilated, transition, and
fully ventilated conditions.

61. Surface Piercing Propellers
As the propeller blade leaves and enters the water in each revolution, surface tension is
an important factor to be considered.
Thus,
Wn is the weber number
𝑊
𝑛 =
𝑉2
𝐿
κ
κ: Kinematic Capillarity
𝑲𝑻
= 𝒇 𝑱, 𝑹𝒏, 𝑭𝒏, 𝑬𝒏, 𝑾𝒏
𝑲𝑸

62. Surface Piercing Propellers
Propeller shaft is generally provided with some inclination.
Unbalanced forces in the transverse plane due to both
shaft inclination and partial submergence.
In the fully-ventilated design condition, the suction
surface (back) of the propeller blades should be
surrounded by air film extending to the free surface.

63. Surface Piercing Propellers
The design of surface piercing propellers is
mainly based on model experiments.
The blade sections in a surface piercing
propeller includes:
▪ Wedge shaped section
▪ Wedge shaped section with cupped
trailing edge
▪ Diamond back shape
Wedge shaped
section
Wedge shaped section
with cupped trailing edge
Diamond back shape

64. Surface Piercing Propellers
As surface piercing propeller is located behind the hull the under-water appendages
required to support the propeller can be eliminated.
Reduction in appendage resistance helps in reducing total power requirement.
Not susceptible to cavitation as the propeller back is covered with air film.
A larger diameter is possible even in shallow waters as the propeller is not fully
submerged and hence can have applications in inland vessels and high-speed crafts
operating in shallow waters.
Advantages and Applications

65. Surface Piercing Propellers
Unsteady forces and strength related issues, as the propeller blade
leaves and enters the water in each revolution.
Fatigue and vibration due to periodic loading.
The propeller shaft and bearings are subjected to a component of
hydrodynamic forces due to partial submergence of the propeller.
Disadvantages

66. Surface Piercing Propellers
Unsteady torque affects the engine and propeller shafts.
Poor astern capability.
The immersion of the surface piercing propeller may vary with speed as
the vessel may trim. This causes variations in the propeller loading.
At low speeds high (propeller immersion) the engine may get overloaded.
Disadvantages

67. Podded and Azimuthing
Propellers
1. Podded propellers
2. Azimuthing thrusters

68. When the propeller driving unit is housed in a pod external to the
ship hull, it is termed as ‘Podded Propeller’.
The propeller powering unit may also be housed inside the ship
hull and driven by a vertical shaft (through the azimuth axis) for
Azimuthing thrusters.
Due to larger wetted surface area the podded propeller will have more drag.
Podded and Azimuthing
Propellers

69. Based on location of the propeller it can be classified into:
1. Pulling Type: Propeller ahead of the Pod
2. Pushing Type: Propeller behind the Pod
Pulling Type Pushing type
Podded and Azimuthing
Propellers

70. Multiple propeller arrangements on pod rotating in different directions.
Contra–rotating propeller at both ends
Podded and Azimuthing
Propellers
Contra–rotating propeller at one end

71. When the pod and the supporting structure can rotate about the vertical axis then the
arrangement is called ‘azipod’
Azipod Arrangement
Podded and Azimuthing
Propellers

72. Applications:
1. Tugs, offshore vessels, semi-submersible rigs (Azimuthing thrusters are usually used)
2. Icebreakers, ro-ro ferries, cruise ships, passenger liners (Pods are usually used)
Podded and Azimuthing
Propellers

73. Transverse Thrusters
Transverse thrusters are devices used to
improve the manoeuvring capability of a vessel
in confined waters.
Thrusters are usually fitted at the bow and are
known as ‘Bow Thrusters’.
However other locations are also possible like at
the stern, skeg, etc.
Source: .Wikimedia commons

74. Transverse Thrusters
For vessels requiring a higher degree of
manoeuvrability more than one thrusters are used.
The Transverse thruster unit consists of a
propeller enclosed in a tunnel.
Source: .Wikimedia commons

75. Transverse Thrusters
The propeller is driven by an electric motor or some hydraulic mechanism.
The propeller can be a fixed pitch propeller or controllable pitch propeller
The thrusters generally provide equal thrust on both
directions (port and starboard) and therefore the blades are
usually made symmetric without camber.

76. Transverse Thrusters
In symmetric blade sections, the lift is caused purely due
to angle of attack and the chances of cavitation are high.
To reduce the cavitation induced vibrations the whole
thruster unit can be flexibly mounted to the ship hull.
When the forward speed increases, the thruster
performance decreases as the water gets deflected aft
and reduced inflow.
The performance in forward motion can be improved by
using Anti suction tunnels.
AST Vent
AST Vent
Thrust

77. Optimum open water efficiency values for different
propeller types.
(van Manen, J. D.. "The Choice of the Propeller." Mar Technol
SNAME N 3 (1966): 158–171)
BP = [ KQ / J5 ]1/2

78. Oscillating Propulsors
How does a fish
propel itself?
Oscillating/ Undulating body/fin motions
Vortices generated : Propulsive Forces
Control : Muscular movement and fin structure

79. ❖For fish and other aquatic animals, there are generally two types of swimming methods: one
using Body and/or Caudal Fin (BCF) and the other using the Median and/or Paired Fin (MPF)
which may be combined behaviour of two pectoral fins or both their anal and dorsal fins.
❖There is also jet propulsion (e.g., jellyfish and scallop) as well as walkers and crawlers (e.g.,
shrimp and crab), though these are not mainstream.
❖Moreover, BCF (i.e., tail flapping) is used by approximately 85 % of the fish species, including
many fast swimmers such as sailfish, tuna, and pike.
❖Therefore, it is most studied form of swimming. Within BCF, there are roughly two kinds of motion
modes: the oscillatory motion, or the “C” mode, (e.g., carp) and the undulatory motion, or the “S”
mode (e.g., eel).
Fish Locomotion
‘Robot Fish’ (Springer)

80. Fish Locomotion

81. Oscillating Propulsors
A foil oscillating sinusoidally with frequency (f), and amplitude (θ)
θ(t) = θmax sin(2πft)
Vortices in the wake of an oscillating foil
(NACA 0012 design) in pure pitching motion

82. Fish Locomotion

83. Oscillating Propulsors
ത
𝑇 : Time averaged thrust over a complete cycle
ഥ
𝑊 : Work done to maintain the motion over a complete cycle
η =
𝑈 ത
𝑇
ഥ
𝑊
Performance depends on: geometry, motion characteristics, flexibility
Application: Bio-inspired autonomous underwater vehicle (AUV) etc.

84. Energy Saving Devices

85. Propulsion performance improvement after optimizing propeller design
Need for Energy Saving Devices
▪ More uniform inflow into the propeller
▪ Improvement of propeller efficiency
▪ Reduced cavitation, vibration, and noise
▪ Recover energy losses in the propeller slipstream

86. IMO Regulations
Energy Efficiency Design Index (EEDI)
An index for new ships that estimates grams of CO2 per transport work (g of CO2 per tonne‐mile).
𝑬𝑬𝑫𝑰 =
𝑪𝑶𝟐 𝑬𝒎𝒊𝒔𝒔𝒊𝒐𝒏
𝑻𝒓𝒂𝒏𝒔𝒑𝒐𝒓𝒕 𝑾𝒐𝒓𝒌
Energy Efficiency Existing ship Index (EEXI)
Global measures to reduce greenhouse gas (GHG) emissions from shipping
Environmentally friendly technologies to reduce the shipping industry’s carbon footprint

87. ❑ Pre-Swirl
❑ At Propeller
❑ Post-Swirl
Three Zones for ESD
Pre-Swirl
At Propeller
Post-Swirl

88. Pre-Swirl
At Propeller
Post-Swirl
▪ Fins
▪ Spoilers
▪ Asymmetric stern
▪ Stators
▪ Ducts
▪ Propeller
with End
Plates
▪ Multiple
Propellers
▪ Twisted Rudder
▪ Rudder with bulb
▪ Vane Wheel
Propeller
Wake and Boundary
layer Effects
Hub Vortex losses
Tip Vortex losses
Rotational losses
Losses due to
blade friction,
circulation
distribution etc.
Losses around a Marine Propeller & applicability of
Energy Saving Devices
Tip Vortex losses
Momentum losses

89. ESD in the Marine Industry
Mewis Duct
Source: Becker Marine Systems
Schneekluth Duct
Source: Schneekluth Hydrodynamikk
Pre-swirl Stator
Source: Daewoo Shipbuilding
Pre-Swirl
Post-Swirl

90. Hydrodynamics
Pre-Swirl Devices
Examples
The flow at the aft part of the ship where the propeller operates is quite complex due to the
stern geometry and hull-propeller interaction.
A pre-swirl device works in such a way that it modifies the boundary layer in the aft region and
also provides a better inflow to the propeller.
Fins, Spoilers, Asymmetric stern, Ducts, Stators, etc.

91. Fins and Spoilers
Pre-Swirl Devices
Fins fitted ahead of the propeller can eliminated cross flows, angular velocity variations and
thereby improve the flow into the propeller.
Can produce a small component of forward thrust
May increase the mass flow into the propeller disc.
May reduce separation and resistance, improve the propeller efficiency, and reduce vibrations.
The geometric shape, location, and other parameters need to be determined.

92. Asymmetric Stern
Pre-Swirl Devices
The transverse sections in the aft portion of the ship are not symmetric about
the center line.
The purpose of this design is to impart a swirl to the flow immediately ahead of
the propeller in order to counter the rotational flow induced by the propeller.
S: Symmetric stern
A: Asymmetric stern

93. Asymmetric Stern
Pre-Swirl Devices
Asymmetric sterns can help in making the effective wake
more uniform by introducing a pre-swirl.
S: Symmetric stern A: Asymmetric stern
The main disadvantage is the difficulty in construction and
high production cost.

94. Pre-swirl Duct
Pre-Swirl Devices
These ducts are fitted ahead of the propeller to accelerate the flow, especially
in the upper half of the propeller disc, where the velocity is generally low due to
hull effect. This reduces wake non-uniformity.
Ducts can also generate forward thrust.
Different variations in duct shape are possible: A complete ring-shaped, half on
each side of the hull, duct placed asymmetrically etc.
Pre-Swirl Duct
Source: Wikimedia commons

95. Pre-swirl Duct
Pre-Swirl Devices
• Increases the propeller efficiency,
• Reduce flow separation at stern (hence, less ship resistance)
• Reduce cavitation and unsteady propeller forces.
• Better flow into the rudder and hence improved manoeuvrability

96. Stators
Pre-Swirl Devices
Stator can be used to counter the rotational flow induced by the propeller by
increase the relative tangential velocity of the propeller blades.
Stators generally have a larger diameter compared to the propeller in order to
avoid the influence of tip vortices.
Stator
The number blades of stator and propeller are selected such that resonant vibrations
are avoided.
Stator blades are arranged non-uniformly and have unequal number of blades in port
and starboard to reduce vibrations.

97. Hydrodynamics
Energy Saving at Propeller
Examples
Modifications are incorporated by varying the propeller design or other techniques such that:
▪ Blade friction losses can be reduced
▪ Better propeller loading and radial circulation distribution
▪ Reduce tip vortices and rotational losses
▪ Better vibration and cavitation characteristics are obtained
Propeller fitted with end plates, Multiple propellers etc.

98. Hydrodynamics
Post-Swirl Devices
Examples
The post-swirl devices are located aft of the propeller. Hence, these are not able to improve the
flow into the propeller, but can recover some energy lost in the propeller slip stream
Propeller boss cap fins (PBCF), Twisted Rudder, Rudder with Bulb, Vane Wheel Propeller.

99. Propeller Boss Cap Fins
Post-Swirl Devices
PBCF arrangement consist of small blades or fins attached to the
propeller boss cap.
These fins weaken the vortex from blade roots and hub thus eliminating
the hub vortex cavitation and the reduces noise and rudder erosion.
The number, geometry, and orientation of the fins in PBCF are important design factors.
Propeller Boss Cap Fins
Source: Wikimedia commons

100. Rudder with Bulb
Post-Swirl Devices
In this arrangement a large bulb is attached to the rudder behind the
propeller hub.
This design is used to eliminate flow separation and excessive
vorticity from the propeller boss.
In other versions of rudder with a bulb, a set of fins are present around the bulb,
which generates lift and contribute to thrust.
Rudder with Bulb
Source: Wikimedia commons

101. Twisted Rudder with Bulb
Post-Swirl Devices
In this arrangement the leading edge of the rudder is
curved and aligned with the swirling flow coming from
the propeller.
Twisted Rudder with Bulb
Source: Wikimedia commons

102. Grim Vane Wheel Propeller
Post-Swirl Devices
This consist of a set of narrow vanes or blades attached
to a hub behind a propeller which can rotate freely
(invented by Otto Grim).
Grim Vane Wheel Propeller
Source: Wikimedia commons
It recovers energy from propeller slipstream (inner radii) and imparts this energy to
the flow at outer radii providing axial thrust. Significant improvement in propulsive
efficiency can be achieved.

103. Grim Vane Wheel Propeller
Post-Swirl Devices
The design of pitch distribution design is such that the inner
part act as turbine (which absorbs energy from the flow) while
the outer portion is similar to a propeller (the energy is
imparted to the flow).
The number of blades in a vane wheel is more than the number of propeller blades.
Grim Vane Wheel Propeller
Source: Wikimedia commons

104. Grim Vane Wheel Propeller
Post-Swirl Devices
The vane wheel produces thrust without absorbing additional
power. The propeller loading and the propeller diameter can
be reduced.
Reduced pressure fluctuations and cavitation.
The vane wheel diameter is usually 25% greater than
propeller diameter, and revolves at around 30-50% of the
propeller rpm.
Strength of vanes may be a factor of concern.
Grim Vane Wheel Propeller
Source: Wikimedia commons

105. Hydrodynamics
ESD Combinations
Example
The combination of a set of devices may be
effectively employed based on the hydrodynamic
advantage from each of them.
Pre-swirl Duct and/or Stator with Rudder Bulb
Ship stern fitted with Pre-swirl duct and Rudder bulb
Source: Wikimedia commons

106. ESDs in the Marine Industry
Pre-Swirl Post-Swirl
Mewis Duct Grim Vane Wheel
Schneekluth Duct Wärtsilä EnergoPac
[Integrated Rudder Propeller Hub]
Grothues Spoilers The Potsdam Model Basin (SVA)
Hub Vane Propeller
Mitsubishi Reaction Fin System Rolls-Royce PROMAS
[Integrated Rudder Propeller Hub]
Daewoo Shipbuilding and Marine
Engineering Pre-Swirl Stator
Kawasaki Heavy Industries Rudder Bulb
System
The Potsdam Model Basin (SVA)
Pre-Swirl Fin system
Becker Marine Systems Twisted Rudder

107. Retrofitting on existing vessels
ESD Applications
Fitting on Newly designed/ built vessels
SHIP SPECIFIC DESIGN

108. CFD Methods
ESD Performance Investigations
Model Tests
Self-propulsion tests with the model fitted with ESD to assess powering improvement
Scale effects for the ESDs become very critical
CFD simulations performed in the full scale, and parametric study can be done
Flow visualization to understand the hydrodynamic performance improvement

109. REFERENCES
(1) ‘Marine Propellers and Propulsion’ by John Carlton, Butterworth-Heinemann Publisher.
(2) ‘Basic Ship Propulsion’ by J.P. Ghose and R.P. Gokarn, KW Publishers Pvt. Limited.
(3) ‘Ship Resistance and Propulsion’ by A.F. Molland, S.R. Turnock, and D.A. Hudson, Cambridge
University Press
(4) ‘Marine Powering Prediction and Propulsors’ by Neil Bose, The Society of Naval Architects and
Marine Engineers