Voith Turbo

Active Roll Damping with Voith Schneider Propulsion

The following report describes the special features of the VoithSchneider Propeller (VSP) and VoithCycloidal Rudder (VCR), whichallow very effective roll stabilizingwhile the ship is stationary or underway at low and medium speed.

The technical requirement for stabi-lizing a ship is to suppress rollingmotion – in other words to controlthe rotational movement about theship’s longitudinal axis, which isgenerated by a wave-excitedmoment that periodically opposesthe moment on the ship that causesthe rolling motion.

Generally, roll stabilization is divid-ed into two broad areas:1. Active operation2. Passive operation

Active operation produces a coun-teracting moment by means of actively controlled machines.A sensor detects the rolling motionand a regulator controls the coun-teracting moment as required.Examples are:■ Fin stabilizers (retractable or fixed)■ Roll stabilizing tanks (active)

The advantage of these systems istheir good damping property.The disadvantages are:■ Complexity and expense■ High weight (particularly the liquid

used to fill roll stabilizing tanks)■ Considerable space requirement■ High maintenance requirements■ Fin stabilizers only work at speed■ Fin stabilizers have a high resist-

ance (even when retracted)

The passive mode of operationworks on the principle of increasingthe roll resistance and thus dampingthe rolling motion, e.g. bilge keels.The Voith Schneider Propeller (VSP)working as ship propulsion and theVoith Cycloidal Rudder (VCR) work-ing in active mode can generateboth propulsion and steering forces.The thrust can be adjusted extre-mely swiftly in terms of magnitudeand direction.

The very rapid thrust variation andgeneration of very high momentsmake it possible to use the VSP, as well as the VCR for efficientreduction of the ship’s rolling motion.In particular when the ship is station-ary or during slow motion, the rollmotion can be actively reduced.

Dr. Dirk Jürgens, Ivo Beu Ivo Beu

Mwave

MVSP

FVSP FVSP

Ships Examined

Fig. 1: Frames of the Corvette Fig. 1a: Corvette

The research and developmentdepartment of Voith Turbo Marinehas examined the following ships:

1. Corvette

All calculations are based on theship theory and carried out by Prof. H. Soeding from the TechnicalUniversity of Hamburg-Harburg.Calculations were made with the following principal dimensionsfor the corvette (Fig. 1a):Loa = 84 m, Bwl = 10.8 m, D= 3.7 m,Displacement = 1,800 m3.The meta-centric height GM onwhich the computation was based

amounted to 1.2 m. Fig. 1 showsthe frame used for the computation.The calculations have been carriedout while the vessel was at stand-still.

2 VCRs with a total static thrust of117 kN were used as a basis for thecomputation of the active roll damp-ing. This value corresponds to 85 %of the max. attainable transverseforce, which was reduced in order to make allowances for the interac-tion of the two VCRs and betweenthe hull and VCRs.

The results (Fig. 1b) for the Corvettewith a wave length of 174 m over aperiod of 10.5 seconds, as found inmany natural swells, were:The roll effect could be suppressedalmost completely for a significantwave height of H 1/3 > 1 m. The rollamplitude could be reduced by halfin the case of a significant waveheight of H 1/3 = 2 m. The roll reduc-tion is smaller for higher waves.

wave height [m]

sig.

rol

l ang

le [°]

0

sig. roll angle for a Corvette GM = 1.2 m T = 10.5 s

01 2 3

without damping

with VSP/VCR damping

4

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10111213

Fig. 1b: Roll angle with and without active roll damping for a Corvette

Fig. 2b: Roll angle with and without active roll damping for a Crane Ship

2. Crane Ship

Calculations were made with thefollowing dimensions for the craneship:Lpp = 133.8 m, Bwl = 26.5 m, D = 6.5 m, displacement =15,820 m. The meta-centric heighton which the computation wasbased amounted to GM = 1.3 m.Fig. 2 shows the frames used forthe computation.

2 VCRs with a static thrust of417 kN were subjected to roll damp-ing. The reduction of the staticthrust to 85 % of the max. thrusttakes into account the interaction of the two VCRs and between thehull and VCRs.

The result for the crane ship withsuspended load is: due to the largenatural period of the crane vessel,there is almost no excitation by thesea.

However, with crane ships (Fig. 2a),even small roll moments can pro-duce large roll excursions as aresult of the load hanging on thehook.

For the most unfavorable significantwave period in a natural swell with1.5 m of wave height, it was calcu-lated that the load oscillation ampli-tudes can be reduced by approx.50 % with the VCR actively damp-ing the roll oscillation (Fig. 2b).

It was also calculated that a largerreduction in the oscillation ampli-tude is possible for smaller signifi-cant wave increases.

Fig. 2: Frames of the Crane Ship Fig. 2a: Crane Ships

wave height [m]

sig.

am

plitu

de [

m]

0

sig. amplitude of a load of 100 t, rope length 15 m

01 2 3 4 5

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101112

without damping

with VSP/VCR damping

Fig. 3: Frames of the PSV

3. PSV

(Platform Supply Vessel)

Calculations were made on the on the basis of the following dimen-sions for the PSV: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.

Resistance and propulsion testreports for this ship are availablefrom Marintek under report number601956.00.01 (February 2002).Fig. 3 shows the frames used forthe computation.

The ship (Fig. 3a) is calculated with2 VSPs, producing a transversethrust of total 467 kN, including thefactor 0.85 as stated above, causedby the mutual influence of the VSPsand hull.

Results (Fig. 3b): The roll motions ofthe PSV could be almost completelysuppressed up to a significant waveheight of 6 m (Fig. 4) and a longcrest periodic swell with a period ofT = 15 seconds.

The same damping characteristicswere computed up to a wave heightof 3 m over a wave period of T = 10seconds.

Fig. 3a: Platform Supply Vessel with Voith Schneider Propellers

wave height [m]

sig.

rol

l ang

le [°]

2

sig. roll angle for a PSV GM = 1.3 m T = 15 s

03 4 5 6 8

1

2

3

4

5

6

7

8

9

without damping

with VSP/VCR damping

7

Fig. 3b: Roll angle with and without active roll damping for a PSV

Technical

Assumptions

The technical requirements, suchas suppressing the rolling motion, as well as the rotational movementat very low and zero speed, are to be met.

Assumptions are:■ High accuracy in terms of steer-

ing (reacting) times to meet thetime criteria, governed by the rollperiod of the ship

■ Thrust (force) deviation in magni-tude and direction, according tothe ship’s movement, withoutundesirable directions

Model Testing

An investigation (Fig. 5) was con-ducted to prove, whether the VoithRoll Stabilization (VRS) system canfulfill the requirements:■ Damping of the rolling motion of

a ship without forward motion■ Damping the oscillation of a

suspended load in case of afloating crane

The damping produced by the VoithSchneider Propeller (VSP) or VoithCycloidal Rudder (Fig. 6) is referredto as active damping.

Full-Scale Trials

The research project “Roll Dampingwith Voith Schneider Technology”examined how strongly the rollingmotion of ships that are stationaryor moving slowly through water can be reduced by the use of VoithCycloidal Rudders (Fig. 6) or VoithSchneider Propellers.

The first calculations funded by theresearch and development depart-ment of Voith Turbo Marine and the computations by Professor H.Soeding showed that the technicalrequirements are already fulfilled by the cycloidal drive.

In order to verify the theoreticalcomputations concerning the appli-cability of Voith Roll Stabilizing(VRS) to roll damping, full-scaletrials were carried out in the NorthSea. Fig. 4 shows the results of themeasured roll angle.

Time [s]

roll

angl

e [d

eg]

0 5 10 15 20 25 30 35 40 45 50

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-2-4-6-8

roll damping on

Fig. 4: Measured roll angle in full-scale test Fig. 5: Voith Roll Stabilizing investigations Fig. 6: Voith Cycloidal Rudder

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Voith Turbo Marine GmbH & Co. KGP.O. Box 201189510 Heidenheim, GermanyTel. +49 7321 37-6595Fax +49 7321 37-7105vspmarine@voith.comwww.voithturbo.com/marinewww.voithturbo.com