Offshore Supply Vessels equipped with Voith Schneider Propellers

Voith TurboOffshore Supply Vesselsequipped with Voith Schneider PropellersDr. Dirk Jürgens, Ivo BeuIvo Beu1. Introduction2. Hydrodynamic Principle of aVoith Schneider Propeller3. Model Testing“Comparison study between VSPand CRP” at Marintek/Norway4. Model Testing “PSV with VSP,Optimisation of Hull Form andSlamming Testing” at SVA,Vienna/Austria5. Roll Damping with VoithSchneider Propeller –Calculation for a PSV6. Dynamic Positioning withVoith Schneider Propellers7. Conclusion/SummaryThis document, and more, is available for download at Martin's Marine Engineering Page - www.dieselduck.net

1. IntroductionFig. 1: Voith Schneider PropellerFig. 2: Voith Water Tractor, AjaxBenchmark model scale testswere performed and showedthat the efficiency of the VSPis superior to other competitivepropulsors.These competitive model scaletests as well as other modeltests and developments ofVoith Turbo Marine and thefirst PSV for Rederi ØstensjøAS are the topics of this paper.The Voith Schneider Propeller(VSP) is a propulsion system allowingstepless, highly accurate andfast control of thrust in terms ofmagnitude and direction. The mainadvantages of the Voith SchneiderPropeller (Fig. 1) for the propulsionof modern Offshore Supply Vesselsare as follows: Stepless control of thrust in termsof magnitude and direction Thrust and propulsion efficiencyare equal in all directions Thrust control corresponds withthe ship's main axis, i. e. in accordancewith certain X-/Y-coordinates Main engines can be operatedwith constant or variable speed,adapted to the manoeuvring, DPand free running condition, withoptimum fuel efficiency of dieseldirectand/or diesel-electric drivesystems without reversing The Voith Schneider Propeller isextremely slow-running andtherefore reliable with high safetymargins against rough service,and its service life is at least aslong as that of the vessel. Due toits X-/Y-coordinate logics, theVSP does not generate undesirableside thrust vectors duringmanoeuvring.On a VSP-driven PSV, very fast andprecise thrust changes are necessary.Such features are guaranteedby the VSP with very precisemanoeuvres with quick responsetimes in normal and emergencyoperating conditions – an essentialsafety aspect for the captain, as thevessel is under control at all times.This aspect is of paramount importanceduring operation at offshoreinstallations in heavy weather conditions.This document, and more, is available for download at Martin's Marine Engineering Page - www.dieselduck.net

Fig. 3: Voith Water Tractor, VeloxFig. 4: Voith Water Tractor, TenaxAn important feature is the redundancyof the entire propulsionsystem, which guarantees full controlof the vessel even with only onepower train in operation.The very rapid and precise thrustvariation according to Cartesiancoordinates makes the VSP anideal propulsion system for efficientdynamic positioning even inextremely rough weather conditions.The Voith Schneider Propelleroffers additional roll stabilization forOSVs, which reduces the rollmotion of the PSV while it is stationary.This additional function hasbeen proven by Voith in theoreticalcomputations with the University ofHamburg-Harburg, during modeltank tests and full scale measurementsin the North Sea.The main features of the VoithSchneider Propulsion system wereproven by Østensjø Rederi AS,Haugesund, Norway, on the basis ofthe design, the construction and theoperation of three “state-of-the-art”Escort Voith Water Tractors – the“Ajax” (Fig. 2), the “Velox” (Fig. 3)and the “Tenax” (Fig. 4), that arenow used to safeguard tankers at oilterminals.All of these Voith Water Tractorshave demonstrated the uniquecharacteristics of the Voith SchneiderPropellers in terms of manoeuvrability,dynamic positioning,redundancy, controllability andlifecycle costs.The purpose of the joint investigationprogram between ØstensjøRederi AS and Voith Turbo Marinewas the analysis of propulsionefficiency of VSPs on modern OSVsin comparison to other new andhighly sophisticated propulsionsystems such as the CRP acrossthe entire operation range, as wellas the analysis of the sea-keepingbehaviour of the different aft bodyconfigurations adopted to the specificpropulsion system requirements.This document, and more, is available for download at Martin's Marine Engineering Page - www.dieselduck.net23

2. Hydrodynamic Principle of a Voith Schneider PropellerαFig. 5: Kinematics of the VSPFig. 6: Cycloidal path of a bladeThe idea of this unique propulsionand manoeuvring system wasinitially developed by the Austrianengineer Ernst Schneider in 1926.Several thousand cycloidal propellershave been produced byVoith over the past 80 years.On the VSP, the blades projectvertically below the ship’s hull androtate on a rotor casing about avertical axis, performing an oscillatorymotion around their own axisthat is superimposed on this uniformrotation. The oscillating movementof the blades determines themagnitude of thrust through varyingthe amplitude (pitch), while the fastcorrelation determines the thrustdirection between 0 and 360degrees. Therefore, an identicalthrust can be generated in anydirection. Both variables – thrustmagnitude and thrust direction – arecontrolled by the hydraulically activatedkinematics (Fig. 5) of thepropeller, with a minimum of powerconsumption. The lift varies duringthe revolution of the blades (Fig. 6).The integration of the componentsof the lift forces created across theentire circumference shows: The lift components acting in thedirection of motion generatethrust The lift components acting atright angles to the direction ofmotion cancel each other outThe thrust can be produced in anydirection merely through movementof the steering center. Due to therotational symmetry, identical thrustcan be generated in all directions.For free running conditions, a steeringforce can be produced in additionto the longitudinal force up toavailable pitch and power limits.This document, and more, is available for download at Martin's Marine Engineering Page - www.dieselduck.net

3. Model Test “Comparison Study betweenVSP and CRP” at Marintek/NorwayGeneralOur customer Østensjø Rederi ASfrom Norway carried out calm watertests with two models of an 85.5 mlong PSV (Platform Supply Vessel),to compare two different propulsionsystems. Test no. 601956.00.01was carried out with Voith Schneiderpropulsion (Fig. 7), while test no.601956.00.02 was carried out withcontra-rotating propellers (CRP)(Fig. 8).The conditions for this comparison,for example the major dimensions,required ship performance, operatingconditions, as well as the fuelconsumption of specific engineswere identical.This allowed a very accurate comparisonof the propulsion systemsas such.Although the two vessels have verysimilar dimensions, the aft ship linesdiffer from each other, due to thespecial requirements of the propellers.The vessels were required toachieve 15 kn speed on two drafts,5.2 m and 6.0 m.The model test showed clearly thatthe Voith Schneider Propeller is anideal propulsion system for offshoresupply vessels.In addition to the absolute trust ofmany of our customers in the lifecycle,lifecycle costs, safety andunbeatable manoeuvrability of ourpropulsion system, these tests alsoproved the superiority in propulsionefficiency even in comparison tocontra-rotating Z-drives.Fig. 7: Position of VSP in the stern of thePSV model. Propulsion: VSP size 32 R5Fig. 8: Position of CRP in the stern of thePSV modelThis document, and more, is available for download at Martin's Marine Engineering Page - www.dieselduck.net45

Principal Hull Data VSP propelled:Hull dataDraught 5.2 m WL1Draught 6.0 m WL2SymbolModelShipModelShipLength of WaterlineLWL(m)5.39686.3405.34285.470Length betw. perpendicularsLPP(m)4.83877.4004.83877.400Breath waterlineBWL(m)1.20019.2001.20019.200Draught at L PP /2T(m)0.3255.2000.3786.050Draught at FPTFP(m)0.3255.2000.3976.350Draught at APTAP(m)0.3255.2000.3595.750Trim(m)00-0.038-0.600Volume of DisplacementV (m 3 )1.1984,905.61.4595,977.2Principal Hull Data CRP propelled:Hull dataDraught 5.2 m WL1Draught 6.0 m WL2SymbolModelShipModelShipLength of WaterlineLWL(m)5.05785.1705.03784.830Length betw. perpendicularsLPP(m)4.59677.4004.59677.400Breath waterlineBWL(m)1.14019.2001.14019.200Draught at L PP /2T(m)0.3095.2000.3566.000Draught at FPTFP(m)0.3095.2000.3566.000Draught at APTAP(m)0.3095.2000.3566.000Trim(m)0000Volume of DisplacementV (m 3 )1.0274,905.61.2465,952.5power [kW]2,0001,500Power Effective P E Draught 5.2 / 6.0 m1,000CRP 5.2 mVSP 5.2 m500VSP 6.0 mCRP 6.0 m012.0 12.5 13.0 13.5 14.0 14.5 15.0speed [kn]power [kW]3,0002,5002,0001,5001,0005000Brake Power P B Draught 5.2 mCRPVSP12.0 12.5 13.0 13.5 14.0 14.5 15.0speed [kn]power [kW]3,5003,0002,5002,0001,5001,0005000Brake Power P B Draught 6.0 mCRPVSP12.0 12.5 13.0 13.5 14.0 14.5 15.0speed [kn]Diagram 1: Power Effective/Draughts 5.2 m and 6.0 mDiagram 2: Brake power/Draught 5.2 mDiagram 3: Brake power/Draught 6.0 mThis document, and more, is available for download at Martin's Marine Engineering Page - www.dieselduck.net

Ship Resistance:To evaluate the different designsof the ship lines, a resistance testfor both drafts was performed. Theresult shows the values of P E (powereffective) which is the amountof power needed to tow the shipthrough the water at different speeds.Diagram 1 shows that the effectivepower needed to tow the VSPdesigned ship lines is higher thanthat of the ship with CRP ship lines.In the area that is most importantfor the customer – design speed of15 kn – the difference is 3 % at5.2 m draught and 7 % at draught6.0 m. This result shows the valuesfor the ship resistance only, withoutthe propulsion systems.This means, that there is room forfurther improvement of the VSPship lines. But this option was notconsidered in this first Marintekmodel test series.Propulsion Test/Performance PredictionTo evaluate the brake power(PB = effective engine power) toachieve the desired speed, apropulsion test/performance predictionwas performed. The measuredpower applied was calculated forthe real ships.Diagrams 2 and 3 show very goodresults for Voith Schneider Propellers,since the required brakepower across the entire speedrange is lower than the CRP values.The CRP-propelled ship neededsome 8 % more brake power for thedesign speed.Note: The PB for the VSP was lowercompared to the CRP (about 8 %)even when the ship resistance forthe chosen VSP hull form wasapproximately 3 to 7 % higher comparedto the chosen hull form of theCRP vessel.Propulsion Efficiency DThe propulsion efficiencies D ofthe different propeller systems areshown in diagrams 4 and 5.They demonstrate clearly that theVSP has a higher efficiency acrossthe entire speed range. This willresult in lower power requirementsand lower fuel consumption for theactual ship.The wave picture on the designspeed is very homogenous (Fig. 9).propulsive efficiency [...]Propulsive efficiency Draught 5.2 m0.800.750.700.650.60VSP0.55CRP0.5012.0 12.5 13.0 13.5 14.0 14.5 15.0speed [kn]propulsive efficiency [...]Propulsive efficiency Draught 6.0 m0.800.750.700.650.60VSP0.55CRP0.5012.0 12.5 13.0 13.5 14.0 14.5 15.0speed [kn]Diagram 4: Propulsive efficiency/Draught 5.2 mDiagram 5: Propulsive efficiency/Draught 6.0 mFig. 9: Wave picture at 14 knotsThis document, and more, is available for download at Martin's Marine Engineering Page - www.dieselduck.net67

4. Model Testing “PSV with VSP, Optimization of HullForm and Slamming Testing” at SVA, Vienna/AustriaFig. 10: Modified aft body with VSP installationFig. 11: Modified aft body with VSP installationDuring the second phase of the jointinvestigation program, additionalmodel tank tests were performed atSVA in Vienna, Austria. A newmodel was built at Vienna with thesame main dimensions testedbefore at Marintek (Fig. 10, 11).To validate the results of the newmodel with the former model atMarintek, a comparative measurementwas performed at Viennaproving the results of Marintek.To achieve an optimum sea-keepingbehaviour especially for slammingat zero speed with waves comingfrom the stern, the aft lines weremodified, using the same V-shapedaft body as previously applied forthe CRP hull at Marintek.power [kW]3,5003,0002,5002,0001,5001,000CRPVSP Marintek500VSP Vienna012.0 12.5 13.0 13.5 14.0 14.5 15.0speed [kn]Diagram 6: Brake Power/Draught 5.20 m.SVA Vienna results for VSP in comparisonwith Marintek results for CRP solutionThis document, and more, is available for download at Martin's Marine Engineering Page - www.dieselduck.net

The comparison of the brake powerfor the modified aft lines of theVSP hull with the investigated CRPversion at Marintek confirmed theearlier results and power savings.range. The V-shape of the aft bodywill secure the desired slammingcharacteristics at zero speed withwaves coming from the stern, asalready examined at Marintek.The second test series performedat SVA in Vienna reconfirmed thepower savings achieved with theVSP compared to the CRP solutionthat had been tested at the first testtank series at Marintek. With themodified VSP aft body, even higherpower savings could be achievedfor the entire operating draughtspectrum, as well as the speedThe slamming investigations performedat SVA revealed that peakpressures that were already rathersatisfactory can be reduced furtherwith the VSP (Diagram 9).The reason of this reduction is thesuction effect of the VSP even atzero pitch.power [kW]3,5003,0002,5002,0001,5001,0005000CRPVSP MarintekVSP Vienna12.0 12.5 13.0 13.5 14.0 14.5 15.0speed [kn]difference [%]40302010Power difference (CRP-VSP) / VSPWL 1WL 2012.0 12.5 13.0 13.5 14.0 14.5 15.0-10speed [kn]Pmax1.210.80.60.40.201 2 3 4 5 6 7Load CellVSP onVSP offDiagram 7: Brake Power/Draught 6.0 m.SVA Vienna results for VSP in comparisonwith Marintek results for CRP solutionDiagram 8: Power saving with VSP forboth draughts of 5.20 m and 6.0 m comparedto the CRP solution over the entirespeed rangeDiagram 9: Maximum slamming pressurewith and without operation of VSP(hw = 3.0 m, D = 5.2 m)This document, and more, is available for download at Martin's Marine Engineering Page - www.dieselduck.net89

5. Roll Damping with Voith Schneider Propellers –Calculation for a PSVFig. 12: Frames of the PSVFig. 13: PSV in a SwellThe special features of the VoithSchneider Propeller allow veryeffective roll stabilization with theship stationary or underway at lowspeed.The technical requirement for stabilizinga ship is to suppress rollingmotion, or, in other words, the controlof rotational movement aboutthe ship’s longitudinal axis, whichis generated by a wave excitingmoment that periodically opposesthe moment on the ship that causesthe rolling motion.Generally, roll stabilization is dividedinto two broad areas:1. Active operation2. Passive operationActive operation produces a counteractingmoment by means ofactively controlled machines. A sensordetects the rolling motion and aregulator controls the counteractingmoment as required. Examples are: Fin stabilizers (retractable orfixed) Roll stabilizing tanks (active)The advantage of these systemsis their good damping property.The disadvantages are: Complexity and expense High weight (particularly the liquidused to fill roll stabilizing tanks) Considerable space requirements High maintenance effort Fin stabilizers only work at designspeed Fin stabilizers have a high resistance(even when retracted) Fin stabilizers increase thevessel’s draughtThe passive mode of operationworks on the principle of increasingthe roll resistance and thus dampingthe rolling motion, e.g. bilgekeels.Very rapid thrust variation andgeneration of very high momentsmakes it possible to use the VSPfor efficient reduction of the ship’srolling motion, in particular whenthe ship is stationary or during slowmotion along the longitudinal axis,where the aforementioned othersystems are limited.Technical AssumptionThe technical requirements, suchas suppressing the rolling motion,as well as the rotational movementat very low- and zero speed, are tobe met.Assumptions are: High accuracy in terms of steering(reacting) times to meet thetime criteria, governed by the rollperiod of the ship Thrust (force) deviation in magnitudeand direction, accordingto the ship’s movement, withoutundesirable directionsThis document, and more, is available for download at Martin's Marine Engineering Page - www.dieselduck.net

ObjectiveAn investigation was conducted toprove whether the Voith Roll Stabilization(VRS) system can fulfill therequirements: Damping of the rolling motion of aship without forward motionThe damping produced by theVoith Schneider Propeller (VSP)is referred to as active damping.Calculation for a PSVCalculations were made by the TUHamburg, Prof. H. Soeding, in May2004 “Rolldämpfung mittels VoithSchneider-Technologie” (Roll Dampingwith Voith Schneider Technology)based on the following dimensions:Lpp = 77.4 m, Bwl = 19.2 m,D = 6.05 m, trim = 0.6 m.The meta-centric height on whichthe computation was basedamounted to GM = 1.3 m.The resistance and propulsion testreports were used in this investigationas per chapter 1.1. (Fig. 12)shows the body section used for thecomputation.The ship is calculated with 2 VSPs,producing a transverse thrust oftotal 467 kN, including the factor0.85 as stated above caused by themutual influence of the VSPs.Results: The roll motions of thePSV could be almost completelysuppressed up to a significant waveheight of 6 m (Fig. 13) and a longcrest periodic swell with a period ofT = 15 seconds.The same damping characteristicswere computed up to a wave heightof 3 m for a wave period of T = 10seconds.Contrary to other ship types suchas corvettes, etc., the roll motionreduction for an OSV becomeslarger with increasing GM andsmaller with diminishing GM for awave period of 10 seconds.The research project “Roll Dampingwith Voith Schneider Technology”investigated how strongly the rollingmotion of ships that are stationaryor moving slowly through water canbe reduced by the use of VoithSchneider Propellers.The first calculations funded by theresearch and development departmentof Voith Turbo Marine andthe computations by Professor H.Soeding showed that the technicalrequirements are already fulfilled bythe cycloidal drive.In order to verify the theoreticalcomputations concerning the applicabilityof Voith Roll Stabilization(VRS) to roll damping, full-scaletrials were executed in the NorthSea in autumn 2004.A buoy layer equipped with VSPwas used to show the system inoperation. The results were veryconvincing, because they demonstratedthat the VSP is capable ofreducing the roll motion.sig. roll angle for a PSV GM=1.3 m T=10ssig. roll angle for a PSV GM=1.3 m T=15s610sig. roll angle [°]4203 5 7wave height [m]without dampingwith VSP/VCR dampingsig. roll angle [°]503 5 7wave height [m]without dampingwith VSP/VCR dampingDiagram 10: Calculation of significantroll angle for T=10sDiagram 11: Calculation of significantroll angle for T=15sThis document, and more, is available for download at Martin's Marine Engineering Page - www.dieselduck.net1011

6. Dynamic Positioning with Voith Schneider PropellersIn the past only specialized vessels,such as dive support, constructionsupport and survey vessels, werefitted with dynamic positioning systems.These vessel types wererequired to maintain their positionand head within very strict parameters.Automatic heading andposition control systems werehence essential for safe operation.The new roles for standard PlatformSupply Vessels now require that thevessels can be positioned with ahigher degree of accuracy, and areable to maintain their position forextended periods of time. Mostnewly built PSV are therefore fittedwith dynamic position systems asstandard, exceptions are rare.The following section provides anoverview of DP operation and theadvantages of Voith SchneiderPropellers for dynamic positioning.At its very basic concept, dynamicpositioning is a system that is utilizedto maintain a vessel in a designatedposition and/or with a designatedheading in order to provide astable platform for different tasks.Any vessel has 6 freedoms of movement,named yaw, surge, sway,heave, pitch and roll. The heave,pitch and roll of the vessel cannotbe controlled by a DP system(these movements belong to thesea-keeping behaviour of the ship).Fig. 14: Voith Schneider PropellerThe function of the DP system is tocontrol automatically the yaw, surgeand sway, and therefore maintainthe vessel in the desired location ormaintain the required headingcontrol. Yaw: The change of heading dueto the vessel’s rotation about thevertical axis Sway: The vessel’s movement inthe transverse direction (sidestepping) Surge: Vessel’s movement in thefore and aft directionA DP system is used to maintainthese movements and rotation invery strict parameters. It is thereforeimportant to have a propulsionsystem with an overall outstandingperformance. The propulsion systemhas to meet the followingrequirements:Fig. 15: The 3 m blade of a VSP for a PSV Thrust and efficiency are identicalin all directions Extremely fast and precise thrustchanges Stepless control of thrust inmagnitude and direction accordingto X and Y coordinates. Thrustcontrol has to correspond withthe ship’s main axisThe above mentioned requirementsare fulfilled by the concept of VoithSchneider Propellers. Quick andprecise steering, long service life,high availability and fast stopping,as well as high acceleration propertiesmake the VSP propulsion systema perfect partner for DP operation.The above arguments are the reasonfor efficient dynamic positioningunder extremely hard weatherconditions!13This document, and more, is available for download at Martin's Marine Engineering Page - www.dieselduck.net

7. Conclusion/SummaryThe comprehensive joint investigationprograms performed by ØstensjøRederi AS and Voith TurboMarine at Marintek and SVA Viennahave proven the excellent propulsionefficiency of the VSP solutionacross the entire operation draughtrange, as well as the speed range.Under consideration of the operationspectrum of an OSV, considerablefuel savings are possible.Additionally, the excellent sea keepingbehaviour of the VSP wasproven and documented alongsidethe renowned and proven advantagesof the VSP in terms of: Redundancy Controllability Fast and extremely precise thrustcontrol for DP mode Long lifetime and very low downtimes Automatically built-in c.p. characteristicallowing optimum adaptationof the entire power train tothe different operation modesThe function of roll stabilization canbe offered for OSV applications. Asa result, the performance of modernOSVs improves significantly.This document, and more, is available for download at Martin's Marine Engineering Page - www.dieselduck.net

Voith Turbo Marine GmbH & Co. KGP.O. Box 201189510 Heidenheim, GermanyTel. +49 7321 37-6595Fax +49 7321 37-7105vspmarine@voith.comwww.voithturbo.com/marineG 1953 e 06.06 3000 MSW/WA Dimensions and illustrations without obligation. Subject to modifications.This document, and more, is available for download at Martin's Marine Engineering Page - www.dieselduck.net