CPP-Propulsors-ESD (1)_101528.pdf

Marine propulsion

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
K
T
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10 K
Q

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
❑Propulsionpointcanbeoperatedatoptimumefficiencyfor
alargerangeofshipspeedsanddisplacements.
❑Non-reversingenginescanbeused(ifpitchcanbe
reversed),reducingcost,weight,andspace.

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
A5-bladedcontrollablepitchpropellerhasaconstantpitchratioof0.8(atallradii)at
aparticularsetting.Duetochangeinoperationconditions,thepropellerpitchis
changedasfollows:
Case-1:Pitchincreasedbyturningthebladesthroughanangleof10degrees.
Case-2:Pitchdecreasedbyturningthebladesthroughanangleof5degrees.
Findthepitchratiosatthebladeradialsections-
r/R=0.3,0.5,and0.8forthetwonewpitchsettings(Case-1andCase-2).

13. Propellers on Inclined Shaft

14. Propellers on Inclined Shaft
Itisrequiredtoinclinethepropellershaftsin
certaincases,especiallyinsmallvesselsin
ordertogetsufficientspaceandclearancefor
thepropellerfromtheshiphull.

15. Propellers on Inclined Shaft
Shaft inclination gives rise to unsteady propeller forces.
V
A:Speedofadvance
V
AP:Componentalongpropelleraxis
V
NP:Componentnormaltopropelleraxis
V
A
V
AP =V
A cos Ψ
V
NP =V
A sin Ψ

16. Propellers on Inclined Shaft
Considering the blade at an angle θ:
V
TP = -V
NP sin θ= = -V
A sin Ψsin θ
V
A
V
NP
[Tangential Velocity Component]
2ϖr n’(θ)= 2ϖrn+ V
TP

18. Propellers on Inclined Shaft
T
H:Pushesthevesselforward
T
V:Resultsinatrimmingmoment
T
H
T
V
For moderate shaft inclinations the fluctuations
of thrust and torque are small.

19. Unconventional Propulsors

20. Introduction
Propellers:
ConventionalScrewPropeller
Propulsors:
Generaltermforpropulsiondevicesincludingunconventionaltypes

21. Introduction
Unconventional Propulsors:
▪Especiallyusedforcriticalapplications-
Fastvessels,restrictedpropellerdiameter,highmanoeuvrabilityrequirement
▪Reducedemissionofgreenhousegasesfromshippingoperations-
Improvementofpropulsionefficiency
▪Reductionofcavitation,vibration,andnoise

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
Whenanormalconventionalpropellermaynot
performsatisfactorilyincertainoperatingconditions

23. Propulsion Performance
Improvements inpropulsionperformance/ efficiency:
▪Reductioninkineticenergylossesintheslipstream
▪Reductioninfrictionlossesatthepropeller
▪Improved(moreuniform)inflowintothepropeller
▪Higherthrustgeneration,inadditiontothepropellerthrust

24. Design Consideration
SelectionofUnconventional Propulsors
▪Propulsiveefficiency
▪Cavitation,vibration,andnoise
▪Initialcost,weight,volumeetc.
▪Associatedmachinery
▪Reliabilityandmaintenanceaspects

25. Waterjet Propulsion
Awaterjetpropulsionunitconsistsofapumpinsidetheshipwhichdrawswaterfromoutside,
impartsanaccelerationtoitanddischargesitinajetabovethewaterlineatthestern.
▪Thejetreactionprovidesthethrusttopropeltheshipforward.
▪Thejetcanbedirectedsidewaysformanoeuvringtheship,andcan
bedeflectedforwardtoobtainasternthrust.

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

28. Waterjet Propulsion
SwivellingNozzle:
Thewaterjetisdischargedthroughanozzlewhichcanberotatedaboutavertical
axistoapproximately45degreesoneithersidetoturnthevessel.

29. Waterjet Propulsion
ReversingBucket:
Abucketwhichcanberotatedaboutahorizontalaxisandusedtodeflectthewaterjet
downwardandforward,therebyproducinganasternthrust.
Byadjustingitsposition,thethrustofthewaterjetcanbevariedfromfullaheadthrough
zerotofullasternwithoutalteringthedischargeofthepump.
**Excellentmanoeuvring,stoppingandreversingcapabilitiesofthevessel.

30. Efficiency
❑Momentum theorycanbeusedforsimpleestimationoftheefficiencyof
awaterjetsystem.
❑EfficiencyComponents:
η
H
:HullEfficiency
η
J
:JetEfficiency
η
P
:PumpEfficiency

31. Efficiency
❑Lossesconsideredinthecalculationofjetefficiency:
•Inletlosses
•Energyforraisingthewaterthroughacertainheight
•Lossesinthenozzle

32. Advantages
❑Noappendages:reductioninresistance.
❑Canbeusedinshallowwaterwithoutanylimitationonthesizeofthepump.
❑Improvedmanoeuvrability,stoppingandbackingability.

33. Advantages
❑Propulsionplantdoesnotrequirereversinggear.Fullaheadtofull
asternspeedcanbecontrolledwithoutalteringtheenginerpm.
❑Torqueisconstantoverthecompletespeedrange.
❑Lessnoiseandvibration

34. Disadvantages
❑Thepropulsionunitoccupiesconsiderablespaceinsidetheship,and
thewaterpassingthroughcausesasignificantdecreaseinbuoyancy.
❑Atthewaterinletgratingisprovidedtopreventdebrisfromgettingin
anddamagingthepump.Thisdecreasestheefficiencyofthesystem.

35. Some Design Aspects
❑DesignofInlet:Effectofboundarylayersuctionaroundthehulljust
aheadoftheinlet.
❑Pump:Differenttypes-axialflow,radialflowormixedflowmaybeused.
❑Powering:Thepreliminarydesignisusuallycarriedoutusingdesign
chartsprovidedbywaterjetsystemmanufacturers.Thepoweringis
estimatedbasedonvesselspeedandthrustrequirementsbyapplying
suitablemargin.
Applications: Ferries, Naval vessels etc.
(typical vessel speed > 30 knots)

36. Waterjet Design
Chart example

37. Avesseltobepropelledbytwinwaterjetshasaneffectivepowerof2400kWatitsdesign
speedof30knots.
Carryoutapreliminarydesignofthewaterjetsassumingthefollowingvalues:
wakefraction0.05,thrustdeductionfraction0.03,pumpefficiencyinuniforminflow0.89,
relativerotativeefficiency0.96,inletefficiency0.82,nozzleefficiency0.99,shafting
efficiency0.95,andheightofnozzlesabovewaterlevel0.75mat30knots.
Assume:
Overallpropulsiveefficiencyof0.53.
Nozzle(Jet)Area/DiscArea=0.4

38. Multiple Propeller Arrangement
Tandem Propellers
Intandempropellerarrangementmultiple(usually
two)propellersaremountedonthesameshaft
androtatedinthesamedirection.

39. Multiple Propeller Arrangement
Tandem Propellers
Tandempropellersareapplicableinsituationsofhighthrust
requirementandrestrictedpropellerdiameter.
Usuallytheforwardandaftpropellerintandemconfiguration
hasthesamenumberofbladesandsamepropellerdiameter.
AftPropeller ForwardPropeller

40. Multiple Propeller Arrangement
Tandem Propellers [Advantages]
Atandempropellermaybemoreefficientthanaconventionalpropeller
athighloadingwhereitcanproducehighthrust.
Asthethrustisdistributedbetweenthetwopropellers,thepropeller
diametercanbereduced.

41. Multiple Propeller Arrangement
Tandem Propellers [Disadvantages]
Atnormaltolowpropellerloadingsnosignificantadvantageisobtained
byadoptingatandempropeller,andtheefficiencyisoftenlowerthan
singlescrewpropeller.
Atandempropellerhasahigherweight,costandrotationalenergy
losses.

42. Multiple Propeller Arrangement
Overlapping propellers
Twopropellersarelocatedatthesamelongitudinal
positionbutthetheirrespectiveshaftsare
separatedbyadistancelessthanthepropeller
diameter.Theyarenotcommonlyused.

43. Multiple Propeller Arrangement
Overlapping propellers [Advantages]
1.Asthethrustisdistributedbetweenthetwopropellersthe
efficiencymaybehigher.
2.Comparedtoanormaltwinscrewpropeller,thesepropellers
workinaregionofhighwake,andthehullefficiencyincreases.

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
Inacontrarotatingpropellertwopropellers
aremountedoncoaxialshafts,rotatingin
oppositedirection.
CancellationofRotationalvelocitiesinthe
slipstreambythetwopropellers.
AftPropeller ForwardPropeller

46. Contra-rotating Propeller
Theaftpropellerisusuallymadesmallerthanthe
forwardpropellertoavoidinteractionwiththetip
vorticesgeneratedfromtheforwardpropeller.
Thenumberofbladesoftheforwardandaft
propellerneednotbesame.
AftPropeller ForwardPropeller

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
Supercavitatingpropellersareconsideredcertaindesignconditionswhereunacceptable
levelsofcavitationcannotbeavoided.
Thebackofthepropellerbladesectionisfullycoveredwithavapourfilledcavityfor
supercavitatingpropellers.
Asupercavitatingpropellercanprovidethrustatnearlythesame
efficiencyasaconventionalpropeller,whenasuitableoperating
conditionisadopted(combinationofJandσ).

51. Supercavitating Propellers
A supercavitatingpropeller compared to a conventional propeller can have:
1.Betternoiseand vibrationalcharacteristics
2.Reduced/ No cavitation erosion
Applications:
1.Racingmotorboats.
2.Vesselshavinghighenginepower,rpm,ship
speedalongwithlowpropellerimmersionand
smallpropellerdiameter.

52. Supercavitating Propellers
Thebladesectionshapeofasupercavitatingpropellershouldensurecompleteseparationof
flowontheback,andalsoprovidehighlift/dragratio.
Hence,bladesectionswithsharpleadingedgesareused.
TulinSection Modified TulinSection 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:
TipVortexFree(TVP)propellers
ContractedandLoadedTip(CLT)propellers
AbasicversionofaTipModifiedPropellerhasanendplateattachedtothe
propellerbladetip.Thisenablestosuppressthetipgeneratedtrailingvortices,
whichallowsabettercirculationdistributionradiallysothatthepropellerloadingat
badetipcanbeincreased.

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

56. Tip Modified Propellers
Advantages
1.Tipvortexcavitationisreduced
2.Improvesthepropellerefficiency
3.Aproperendplatedesignmayproduceadditionalthrust
Disadvantages
Verylargeendplatesincreasethedragandreducestheefficiency

57. Cycloidal Propellers
Thebladesarefittedtoadisc(ontheshiphull)which
revolvesaboutaverticalaxis,andthebladescanrotate
abouttheirownindividualaxis.
Thepropellersgenerallyhavetheiraxisorientedvertically,and
arehencecalledVertical-axisPropellers.

58. Cycloidal Propellers
Types:
Forshipspeed‘V’andpropellerangularvelocity‘ω’thepathdescribedbyeachbladeis:
Epicycloid(V<ωR)
Cycloid(V=ωR)
Trochoid(V>ωR)

59. Cycloidal Propellers
Applications
Examplesofvertical-axispropellers:
Kirsten-Boeingpropeller
Voith-Schneiderpropeller
Efficiencyisusuallylowerascomparedtoconventionalpropellers.
Usedinvesselswhereveryhighdegreeofmanoeuvrabilityisrequired.
(Towingvessels,Shortferriesetc.)

60. Surface Piercing Propellers
Apropellerarrangementinwhichthepropelleris
partlysubmergedandpiercesthewatersurface.
Typicallyusedinhigh-speedplaningcraftswhere
propellersubmergencedecreasesathighspeeds.
Operatesinpartiallyventilated,transition,and
fullyventilatedconditions.

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,
W
nis the weber number
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κ
κ: Kinematic Capillarity
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62. Surface Piercing Propellers
Propellershaftisgenerallyprovidedwithsomeinclination.
Unbalancedforcesinthetransverseplaneduetoboth
shaftinclinationandpartialsubmergence.
Inthefully-ventilateddesigncondition,thesuction
surface(back)ofthepropellerbladesshouldbe
surroundedbyairfilmextendingtothefreesurface.

63. Surface Piercing Propellers
Thedesignofsurfacepiercingpropellersis
mainlybasedonmodelexperiments.
Thebladesectionsinasurfacepiercing
propellerincludes:
▪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
Assurfacepiercingpropellerislocatedbehindthehulltheunder-waterappendages
requiredtosupportthepropellercanbeeliminated.
Reductioninappendageresistancehelpsinreducingtotalpowerrequirement.
Notsusceptibletocavitationasthepropellerbackiscoveredwithairfilm.
Alargerdiameterispossibleeveninshallowwatersasthepropellerisnotfully
submergedandhencecanhaveapplicationsininlandvesselsandhigh-speedcrafts
operatinginshallowwaters.
Advantages and Applications

65. Surface Piercing Propellers
Unsteadyforcesandstrengthrelatedissues,asthepropellerblade
leavesandentersthewaterineachrevolution.
Fatigueandvibrationduetoperiodicloading.
Thepropellershaftandbearingsaresubjectedtoacomponentof
hydrodynamicforcesduetopartialsubmergenceofthepropeller.
Disadvantages

66. Surface Piercing Propellers
Unsteadytorqueaffectstheengineandpropellershafts.
Poorasterncapability.
Theimmersionofthesurfacepiercingpropellermayvarywithspeedas
thevesselmaytrim.Thiscausesvariationsinthepropellerloading.
Atlowspeedshigh(propellerimmersion)theenginemaygetoverloaded.
Disadvantages

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

68. Whenthepropellerdrivingunitishousedinapodexternaltothe
shiphull,itistermedas‘PoddedPropeller’.
Thepropellerpoweringunitmayalsobehousedinsidetheship
hullanddrivenbyaverticalshaft(throughtheazimuthaxis)for
Azimuthingthrusters.
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
PullingType Pushingtype
Podded and Azimuthing
Propellers

70. Multiple propeller arrangements on pod rotating in different directions.
Contra–rotatingpropelleratbothends
Podded and Azimuthing
Propellers
Contra–rotatingpropelleratoneend

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

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

73. Transverse Thrusters
Transversethrustersaredevicesused to
improvethemanoeuvringcapabilityofavessel
inconfinedwaters.
Thrustersareusuallyfittedatthebowandare
knownas‘BowThrusters’.
Howeverotherlocationsarealsopossiblelikeat
thestern,skeg,etc.
Source:.Wikimediacommons

74. Transverse Thrusters
Forvesselsrequiringahigherdegreeof
manoeuvrabilitymorethanonethrustersareused.
TheTransversethrusterunitconsistsofa
propellerenclosedinatunnel.
Source:.Wikimediacommons

75. Transverse Thrusters
Thepropellerisdrivenbyanelectricmotororsomehydraulicmechanism.
Thepropellercanbeafixedpitchpropellerorcontrollablepitchpropeller
Thethrustersgenerallyprovideequalthrustonboth
directions(portandstarboard)andthereforethebladesare
usuallymadesymmetricwithoutcamber.

76. Transverse Thrusters
Insymmetricbladesections,theliftiscausedpurelydue
toangleofattackandthechancesofcavitationarehigh.
Toreducethecavitationinducedvibrationsthewhole
thrusterunitcanbeflexiblymountedtotheshiphull.
Whentheforwardspeedincreases,thethruster
performancedecreasesasthewatergetsdeflectedaft
andreducedinflow.
Theperformanceinforwardmotioncanbeimprovedby
usingAntisuctiontunnels.
ASTVent
ASTVent
Thrust

77. Optimumopenwaterefficiencyvaluesfordifferent
propellertypes.
(vanManen,J.D.."TheChoiceofthePropeller."MarTechnol
SNAMEN3(1966):158–171)
B
P= [ K
Q/ J
5
]
1/2

78. Oscillating Propulsors
How does a fish
propel itself?
Oscillating/Undulatingbody/finmotions
Vorticesgenerated:PropulsiveForces
Control:Muscularmovementandfinstructure

79. ❖Forfishandotheraquaticanimals,therearegenerallytwotypesofswimmingmethods:one
usingBodyand/orCaudalFin(BCF)andtheotherusingtheMedianand/orPairedFin(MPF)
whichmaybecombinedbehaviouroftwopectoralfinsorboththeiranalanddorsalfins.
❖Thereisalsojetpropulsion(e.g.,jellyfishandscallop)aswellaswalkersandcrawlers(e.g.,
shrimpandcrab),thoughthesearenotmainstream.
❖Moreover,BCF(i.e.,tailflapping)isusedbyapproximately85%ofthefishspecies,including
manyfastswimmerssuchassailfish,tuna,andpike.
❖Therefore,itismoststudiedformofswimming.WithinBCF,thereareroughlytwokindsofmotion
modes:theoscillatorymotion,orthe“C”mode,(e.g.,carp)andtheundulatorymotion,orthe“S”
mode(e.g.,eel).
Fish Locomotion
‘Robot Fish’ (Springer)

80. Fish Locomotion

81. Oscillating Propulsors
Afoiloscillatingsinusoidallywithfrequency(f),andamplitude(θ)
θ(t) = θ
maxsin(2πft)
Vortices in the wake of an oscillating foil
(NACA 0012 design) in pure pitching motion

82. Fish Locomotion

83. Oscillating Propulsors
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Performancedependson:geometry,motioncharacteristics,flexibility
Application:Bio-inspiredautonomousunderwatervehicle(AUV)etc.

84. Energy Saving Devices

85. Propulsion performance improvement after optimizing propeller design
Need for Energy Saving Devices
▪Moreuniforminflowintothepropeller
▪Improvementofpropellerefficiency
▪Reducedcavitation,vibration,andnoise
▪Recoverenergylossesinthepropellerslipstream

86. IMO Regulations
Energy Efficiency Design Index (EEDI)
An index for new ships that estimates grams of CO
2per transport work (g of CO
2per tonne‐mile).
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Energy Efficiency Existing ship Index (EEXI)
Globalmeasurestoreducegreenhousegas(GHG)emissionsfromshipping
Environmentallyfriendlytechnologiestoreducetheshippingindustry’scarbonfootprint

87. ❑Pre-Swirl
❑AtPropeller
❑Post-Swirl
Three Zones for ESD
Pre-SwirlAtPropellerPost-Swirl

88. Pre-SwirlAtPropellerPost-Swirl
▪Fins
▪Spoilers
▪Asymmetricstern
▪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
MewisDuct
Source: Becker Marine Systems
SchneekluthDuct
Source: SchneekluthHydrodynamikk
Pre-swirl Stator
Source: Daewoo Shipbuilding
Pre-Swirl
Post-Swirl

90. Hydrodynamics
Pre-Swirl Devices
Examples
Theflowattheaftpartoftheshipwherethepropelleroperatesisquitecomplexduetothe
sterngeometryandhull-propellerinteraction.
Apre-swirldeviceworksinsuchawaythatitmodifiestheboundarylayerintheaftregionand
alsoprovidesabetterinflowtothepropeller.
Fins,Spoilers,Asymmetricstern,Ducts,Stators,etc.

91. Fins and Spoilers
Pre-Swirl Devices
Finsfittedaheadofthepropellercaneliminatedcrossflows,angularvelocityvariationsand
therebyimprovetheflowintothepropeller.
Canproduceasmallcomponentofforwardthrust
Mayincreasethemassflowintothepropellerdisc.
Mayreduceseparationandresistance,improvethepropellerefficiency,andreducevibrations.
Thegeometricshape,location,andotherparametersneedtobedetermined.

92. Asymmetric Stern
Pre-Swirl Devices
Thetransversesectionsintheaftportionoftheshiparenotsymmetricabout
thecenterline.
Thepurposeofthisdesignistoimpartaswirltotheflowimmediatelyaheadof
thepropellerinordertocountertherotationalflowinducedbythepropeller.
S: Symmetric stern
A: Asymmetric stern

93. Asymmetric Stern
Pre-Swirl Devices
Asymmetricsternscanhelpinmakingtheeffectivewake
moreuniformbyintroducingapre-swirl.
S: Symmetric stern A: Asymmetric stern
Themaindisadvantageisthedifficultyinconstructionand
highproductioncost.

94. Pre-swirl Duct
Pre-Swirl Devices
Theseductsarefittedaheadofthepropellertoacceleratetheflow,especially
intheupperhalfofthepropellerdisc,wherethevelocityisgenerallylowdueto
hulleffect.Thisreduceswakenon-uniformity.
Ductscanalsogenerateforwardthrust.
Differentvariationsinductshapearepossible:Acompletering-shaped,halfon
eachsideofthehull,ductplacedasymmetricallyetc.
Pre-Swirl Duct
Source: Wikimedia commons

95. Pre-swirl Duct
Pre-Swirl Devices
•Increasesthepropellerefficiency,
•Reduceflowseparationatstern(hence,lessshipresistance)
•Reducecavitationandunsteadypropellerforces.
•Betterflowintotherudderandhenceimprovedmanoeuvrability

96. Stators
Pre-Swirl Devices
Statorcanbeusedtocountertherotationalflowinducedbythepropellerby
increasetherelativetangentialvelocityofthepropellerblades.
Statorsgenerallyhavealargerdiametercomparedtothepropellerinorderto
avoidtheinfluenceoftipvortices.
Stator
Thenumberbladesofstatorandpropellerareselectedsuchthatresonantvibrations
areavoided.
Statorbladesarearrangednon-uniformlyandhaveunequalnumberofbladesinport
andstarboardtoreducevibrations.

97. Hydrodynamics
Energy Saving at Propeller
Examples
Modificationsareincorporatedbyvaryingthepropellerdesignorothertechniquessuchthat:
▪Bladefrictionlossescanbereduced
▪Betterpropellerloadingandradialcirculationdistribution
▪Reducetipvorticesandrotationallosses
▪Bettervibrationandcavitationcharacteristicsareobtained
Propellerfittedwithendplates,Multiplepropellersetc.

98. Hydrodynamics
Post-Swirl Devices
Examples
Thepost-swirldevicesarelocatedaftofthepropeller.Hence,thesearenotabletoimprovethe
flowintothepropeller,butcanrecoversomeenergylostinthepropellerslipstream
Propellerbosscapfins(PBCF),TwistedRudder,RudderwithBulb,VaneWheelPropeller.

99. Propeller Boss Cap Fins
Post-Swirl Devices
PBCFarrangementconsistofsmallbladesorfinsattachedtothe
propellerbosscap.
Thesefinsweakenthevortexfrombladerootsandhubthuseliminating
thehubvortexcavitationandthereducesnoiseandruddererosion.
Thenumber,geometry,andorientationofthefinsinPBCFareimportantdesignfactors.
Propeller Boss Cap Fins
Source: Wikimedia commons

100. Rudder with Bulb
Post-Swirl Devices
Inthisarrangementalargebulbisattachedtotherudderbehindthe
propellerhub.
Thisdesignisusedtoeliminateflowseparationandexcessive
vorticityfromthepropellerboss.
Inotherversionsofrudderwithabulb,asetoffinsarepresentaroundthebulb,
whichgeneratesliftandcontributetothrust.
Rudder with Bulb
Source: Wikimedia commons

101. Twisted Rudder with Bulb
Post-Swirl Devices
Inthisarrangementtheleadingedgeoftherudderis
curvedandalignedwiththeswirlingflowcomingfrom
thepropeller.
Twisted Rudder with Bulb
Source: Wikimedia commons

102. Grim Vane Wheel Propeller
Post-Swirl Devices
Thisconsistofasetofnarrowvanesorbladesattached
toahubbehindapropellerwhichcanrotatefreely
(inventedbyOttoGrim).
Grim Vane Wheel Propeller
Source: Wikimedia commons
Itrecoversenergyfrompropellerslipstream(innerradii)andimpartsthisenergyto
theflowatouterradiiprovidingaxialthrust.Significantimprovementinpropulsive
efficiencycanbeachieved.

103. Grim Vane Wheel Propeller
Post-Swirl Devices
Thedesignofpitchdistributiondesignissuchthattheinner
partactasturbine(whichabsorbsenergyfromtheflow)while
theouterportionissimilartoapropeller(theenergyis
impartedtotheflow).
Thenumberofbladesinavanewheelismorethanthenumberofpropellerblades.
Grim Vane Wheel Propeller
Source: Wikimedia commons

104. Grim Vane Wheel Propeller
Post-Swirl Devices
Thevanewheelproducesthrustwithoutabsorbingadditional
power.Thepropellerloadingandthepropellerdiametercan
bereduced.
Reducedpressurefluctuationsandcavitation.
Thevanewheeldiameterisusually25%greaterthan
propellerdiameter,andrevolvesataround30-50%ofthe
propellerrpm.
Strengthofvanesmaybeafactorofconcern.
Grim Vane Wheel Propeller
Source: Wikimedia commons

105. Hydrodynamics
ESD Combinations
Example
Thecombinationofasetofdevicesmaybe
effectivelyemployedbasedonthehydrodynamic
advantagefromeachofthem.
Pre-swirlDuctand/orStatorwithRudderBulb
Ship stern fitted with Pre-swirl duct and Rudder bulb
Source: Wikimedia commons

106. ESDs in the Marine Industry
Pre-Swirl Post-Swirl
MewisDuct Grim Vane Wheel
SchneekluthDuct WärtsiläEnergoPac
[Integrated Rudder Propeller Hub]
GrothuesSpoilers 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-propulsiontestswiththemodelfittedwithESDtoassesspoweringimprovement
ScaleeffectsfortheESDsbecomeverycritical
CFDsimulationsperformedinthefullscale,andparametricstudycanbedone
Flowvisualizationtounderstandthehydrodynamicperformanceimprovement

109. REFERENCES
(1)‘MarinePropellersandPropulsion’byJohnCarlton,Butterworth-HeinemannPublisher.
(2)‘BasicShipPropulsion’byJ.P.GhoseandR.P.Gokarn,KWPublishersPvt.Limited.
(3)‘ShipResistanceandPropulsion’byA.F.Molland,S.R.Turnock,andD.A.Hudson,Cambridge
UniversityPress
(4)‘MarinePoweringPredictionandPropulsors’byNeilBose,TheSocietyofNavalArchitectsand
MarineEngineers