Energy saving in ship propulsion from application of flow straightening devices

9 FEB. 1984

ARCHIEF

Ministerio de Defense

CANAL DE EXPERIENCIAS HIDRODINAMICAS, EL PARDO

PublicaciOn nOrn. 115

INTERNATIONAL SYMPOSIUM

ON

SHIP HYDRODYNAMICS AND ENERGY SAVING

El Pardo, September 6. 9, 1983

S 161.E S-83

ENERGY SAVING IN SHIP PROPULSION

FROM APPLICATION OF FLOW STRAIGHTENING DEVICES

by G. K. LUTHRA

216. Mitteilung der Versuchsanstalt fur Binnenschiffbau e.V., Duisburg

GERMANY

VIII: MODERN APPROACH TO STERN DESIGN Paper No. VIII-1

Lab.

_{v. Scheepsbouwkunde}

Technische Hogeschool

ISSHES-83 Intetmitionat Sympoz:idm on Ship Hydnodynamiu and Enek,gy Saving. Et Panda, Septeinben 1983.

,ABSTRACT

In section 1 this paper summarizes an empirical method to estimate changes in speed and power of full-bodied tankers and-bulk carriers in ballast condition,

with its possible application

in

the.

overall concept of reduced power oper-ation in mind.

From among more active measures for achieving fuel economy the paper goes on in section 2 to review two devices aimed at improving the propulsive efficiency of single-screw vessels by giving the flow entering the propeller an axial direction and more uniform velocity. Results Obtained in recent model teats are presented and discussed.

Attention is drawn to the integrated application of two earlier devices behind the propeller, which were intended to recover some losses from propeller induced rotation and contraction in screw-race, and Which found singular applications but for Various reasons did not enjoy success.

INTRODUCTION

The urgent need for fuel economy in ships- has instigated a number of new-projects, while as an-interim step many owners, have reduced the operating power of their ships. Slower steaming is a simple and effective expedient, which can be adopted readily in most cases, whereby a number of methods is available

to predetermine the changes in speed from changed power. For tankers and bulk car-riers in light ballast, however, the effects of big displacement changes and

stern trim on their speed in relation to power are less known. These effects were investigated in a study at the model tank of VBD, i.e. the Duisburg Research Labor-atory for Inland Shipbuilding and Shallow Water Hydrodynamics, whose results are

summarized in section 1.

Among more active measures for

achieving fuel

economy flow

straightening

devices in the vicinity of the propeller

VIII.1 - 1

PAPER VIII.1

ENERGY SAVING IN SHIP PROPULSION'

FROM APPLICATION OF FLOW STRAIGHTENING DEVICES

by G. K. LUTHRA

Versuchsanstalt für Binnenschiffhau e. V.

GERMANY

appear to Offer a very cost effective solution. Two examples, viz. Mitsui Integrated Duct and Mitsubishi Reaction Fin have recently become known and for both substantial power savings have been claimed.

The VBD is investigating some other devices, Which include an aerofoil fin, and as second alternative,- a small half ring nozzle positioned: on one or both Sides in front of the upper half of

propeller. The paper is mainly directed towards this development and reviews the general considerations underlying the aipplication of these devices and the results obtained with them.

1.. SPEED IN BALLAST CONDITION

Whereas tankers and bulk carriers spend a considerable part of their voyage time in light ballast, the dis-placement of larger units In this con-dition often amounts to 40 to 50 % of their- design displacement. At the same time they have to be run with a heavy stern trim in order to give the propel-ler adequate immersion. Most of the methods available to estimate the speed in relation to power at reduced draught confine themselves to changes in dis-placement Of far less than 50 % and do not extend Over the range of form para-meters of these vessels (e.g.Ref.1).

Moreover little

is

known about the

effect of trim on ahead performance and .

how the sate is influenced by depth restrictions as are encountered for example in the North Sea (ref.2).

Thus the problem resolves into three groups:

effect on speed Or power of' weight reduction at 56 to 40 % displacement while retaining even keel trim effect on speed or power Of stern trim at such reduced 'displacements effect on speed or power of depth restriction at reduced displacements as in a) and b).

The analysis of test results in Duisburg (Ref.3) has shown that basi-callythe method in which the speed ratio is expressed as an exponential function of displacement ratio can be used here, too. Starting point is the resistance or effective power curve at design dis-placement with the understanding that

the same is known.

Fig.1 shows the functional relation-ship on top. V1 and V2 are the speeds at constant effective power at design and-at ballast-even keel draught, while D1 and D2 are the respective displacements.. Terms y and k are the exponents of dis-placement ratio. The introduction of k as quotient of respective displacement

to wetted surface ratios appears to have an equalizing effect regarding differ-ences in size and displacement-length

coefficient

of

these full-bodied Ships.

Fig.1 shows the plot of the residual exponent y as function of Froude-number for six different ships indicating that size and form parameters in this case are not so significant as the effect of the

bow form. The bulbous bow apparently

remains isolated and must be treated separately, but the rest of the data appears to be within the scatter.; for Which a mean curve may be drawn. The scatter due to form effects decreases With increasing starting speed and with depth of water becoming shallower.

V2ivi = ID2 k = 1:11/si St/D2 20 Bakst IQ 1030/1? Bow Form M1066 290 8,3 Ellipsoid 111121 332 9,3 -I jConvention,a1 337 9,0 2

° °

"7

9,0 ]Ellipsoid 75, -5 a 174 8,7 .0 331 8,6 _{CyLwIth-CyL bulb} FIG.1

DISPLACEMENT EXPONENT FORTANKERS.AND BULK CARR/ERS

IN 40-50% BALLAST CONDITIONINDEEP WATER

VIII.1 - 2 yl 0,4 0,35. 0,3, o,is 0,2 -0,15 0:1 'DOS Ilk )1,2 PEskonstO trIbb,Apis2 Dliopk kr DVS2/D2 Index lEFullload 2; Ballast Ballast 150144% 40% tt 1066 0

111121

A 1:0 1,05 1,00 U 0,95 0,90 OS 0,45 0,4 in FIG.2

DISPLACEMENT EXPONENT AS FUNCTION OF WATER DEPTH FOR EVEN ICIEEL 40-50% BALLAST CONDITION

Fig.2 shows the influence of

water-depth on displacement exponent. the

ex7

ponent y or yh is plotted over the quo-tient of third root of volume of dit-placement in ballast and waterdepth in this diagram, giving a common curve for both the models irrespective of their form parameters. For shifts in dis-. placement within 40 to 50 % ballast con-dition an adcon-ditional correction has to be applied, which is given as factor "a" here. The yh-values as plotted forboth

ships refer to speed ratios

for

reduced

displacement

in

even keel condition at

constant effective power corresponding to the starting speed of Froude-numbeX Fn =0.152 or as ship related value,' roughly to 16 to 17 knots.

shows the influence of stern trim on the displacement exponent. The latter is plotted in the upper diagram as ratio of exponent in trimmed condition to-that at zero trim in deep water and can be applied as trim correction to y or yh values from Figs.1 or 2.

The lower diagram illustrates the

effect of water depth restriction on trim quotient. In contrast to yh values in Fig..2, where form parameters Appear

to have no significance, the trim

quO-tient in shallower depths shows a strong form dependence, which probably results from the differences in bow design. -0,10

0.00

o

However, the functional relations, while being essentially dapable of

further refinements from additional data, should provide a practical approach to determine the displacement exponent and its correction for trim effects. Starting with the known speed at design displace-ment in a given waterdepth these allow an assessment of speed gains. or losses at constant effective power arising from displacement changes and trim in the Whole range of coverage. With repeated calculations estimates can be made of anticipated reduction in effective power at constant speed when the Vessel runs at ballast instead of design displace-ment. 0.9 0.8 0,7 Ntoo M 1066 Stern Trim

2° e

k enst _{( Fnch)rn ig} 56; FIG.3

DISPLACEMENT EXPONENT AS FUNCTION OF TRIM

IN 40-50% BALLAST CONDITION

Ultimately the effective power has to be correlated to the theft power, which is an intricate task because of a number of factors being involved, such as size, design and arrangement of pro-peller and the main propulsive coeffi-cients. In full-bodied ships, moreover, the after body flow separation And its changes from propeller interaction can-not be ignored. However, for practical purposes it is common in preliminary calculations to convert the effective power to shaft power with the aid of propulsive efficiency, which sums up various coefficients. The changes in propulsive efficiency resulting from reducing the draught from design to

ballast displacement are given

in

04

-

3

(Ref.4). The values there refer to

un-restricted water condition and cover a range of ship lengths up to 160

m-A linearized extrapolation to bigger lengths as are cotton in large tankers and bulk carriers shows that the values compete well with those measured in VBD tests for 50 % ballast condition at even or nearly even keel- Thus such an extrapolation appears permissible to obtain sufficiently accurate results. On the other hand the effects of both, bigger trim and waterdepth restriction on propulsive efficiency are consider-ably stronger and by. nature more

difficult. to grasp. These effects are reviewed in more detail in the respec-tiveyBD report and in (Ref.3), but need to be analysed further with the help of additional data, which no doubt would enhance the proposed method. 2. FLOW STRAIGHTENING DEVICES

Among various measures to achieve fuel economy, propeller and its inter-active effects with the hull or

pro-pulsion

on the whole form an important factor. Basically the biggest gains to be made in propulsive efficiency are those obtained by using slow revving larger diameter Propellers, and those associated with stern design which provides an undisturbed or as uniform flow as possible to the propeller. The approach to realize these, as recent development shows, consists of unconventional stern design on the one hand and introduction on the other hand of outer devices to condition a good water flow to the propeller.

In single-screw vessels the flow entering the propeller follows the hull shape and has horizontally a converging, and vertically an upward inclined direc-tion. At the same time the propeller imparts a rotation to the flow not only in the screw-race but also in the wake in front of it- The clock-wise turning pro-peller thus strengthens the upward compo-nent of oncoming flow on the port side while reducing the angle of incidence for

propeller blades there. On the starboard side the directions of flow and rotation oppose each other, which increases the propeller loading on this side- The resulting asymmetrical pattern is not only detrimental for propeller induced vibrations but the inclined flow also

impairs the propeller efficiency in comparson with coaxial flow.

The viscous boundary layer and sepa-ration effects moreover cause extreme

velocity variations, particularly in .

full-bodied sterns, in wake flow into the propeller. Whereas the retarded mean wake may be advantageous for hull

efficiency, the propeller efficiency is adversely affected by the non-uniform velocity distribution in wake.

10 - 0:9-0.0" 0,7 -Trim e M 1066 P =kenst'alFitra. =0152 M 1121 1.05 a1.00 0.95 0.90 02/6.

eacs:.

In the recent past methods have been derived of constructing section shapes in the stern region, which spread the wake peaks over an acceptable sector of pro-peller disc area. Other promising methods which come in question here are to incor-porate fins or other similar devices into the stern sections to induce sufficient rotation into the flow to even the wake and with that improve the propulsive efficiency.

2.1 Aerofoil Fins

Use of horizontal fine, particularly in cases where design constraints exist, is not

hew.

These straighten the flow and have often been fitted to combat vibra-tion problems, when the same Were found to occur (e.g. Ref.5).

-If an aerofoil fin with a downward incidence angle is positioned in front of the upper half of the propeller in verti-cally inclined wake, a lift force is generated On it which has a forward com-ponent. At the same time it imparts a downward impulse to the flow at its

trailing edge, giving the sate

a

more

axial direction.. Thus such fins channel the flow into the propeller in desired manner and to some extent equalize the velocity in upper quadrants where it Matters most.

Because of the asymmetrical flow on port and starboard as described earlier, the angles of incidence for both sides

as also the obtainable gains may differ.

-FIG.4

SCHEMATIC DIAGRAM OF AEROFOIL FINS

VILT.1 - 4

Fig.4 shows a schematic diagram

of

the

fin arrangement. The resulting effects may be differentiated as

follows:

aY generation of a forward force cOmpo-ment on the fin which acts to support

propulsive force. The Viscous drag of

fin is only small and easily overcome

by positive effects from

the.prOpel-ler;

b) improvement of propeller efficiency from more axial flow;

C) improvement of propeller efficiency

from more equal flow distribution over the disc area;

d) uniform flow reduces propeller excited vibration. The improvement can either be utilized towards this end if

initially poor flow conditions exist, or it can be Used to Increase the propeller diameter, because then smaller hull clearances become permis-sible, which in turn improves the propeller efficiency.

These effects are mostly known.. As a regular design feature, however, the fins have received less attention largely because of the additional building Costs but also because of slamming, which may

occur in heavy seas. 2.2 Integrated Half Ducts

Kort nozzles or ducted propellers

are known to offer advantages in

a

n'umber

of circumstances. In the

dase

of heavily loaded propellers they enable a higher thrust whereas at speed their drag Can exceed making them less efficient than the open propeller. Ducts have also been found to be advantageous for large, full

bodied tankers (Ref.6) but after a number of installations there seems to be a decline in their use more recently, partly because such large vessels are

not on order any more.

-Another development has been in way of nozzles fitted concentrically -forward -of the propeller. The known example is

the Mitsui Integrated Duct Propeller (MIDP), (Ref.7). Such a nozzle induces a more uniform flow into the propeller but is effective over the whole disc area making a careful design and

positioning necessary for eadh individual application.

The integrated half ring ducts as being tested at the VBD under a subsidy by the German Federal Ministry of

Research and Technology are fitted for-ward of the upper half of the Propeller. In contrast to concentric MIDP these have

a

homogenising effect by accele-rating and straightening the flow

locally in upper quadrants where this is most needed, while utilizing additionally the duct thrust effect to improve pro7 puleive efficiency. This local equalizing of wake peaks leads to secondary bene-fits in reduced hull vortex cavitation

and propeller induced vibrations (Ref48, 9)4

SCHEMATIC DIAGRAM OF

INTEGRATED HAV DUCTS

Fig.5 shows a schematic diagram of thete integrated half ducts. Dividing the duct into two halves offers further benefits in geometrical design. While keeping the section profile symmetrical, the duct cross-section can be varied by arranging the two halves further apart.

Secondly the axis

of

each half can be tilted and fixed at different divergence

angles to suit the asymmetrically in= clined

flow

on port and starboard side. Smaller Size and hull Integrated con-figuration simplifies the structural

construction and reduces vulnerability .

to slamming. 2.3 Model Tests

A series of tests is being carried out at the model tank of the VBD, which are designed to investigate the effects

of these devices on the propulsive

per-formance and to Obtain basic data on size and configuration best suited for a given block coefficient and on

com-parative gains. Two model S representing a very full bodied tanker and a fast container ship are employed. Earlier a,

medium sized cargo vessel had been

used

in preliminary tests. The lines are shown in Figs. 6 to 8. Principal particulars are as follows-:

e.

VIII.]. - 5

SHIP a) - Cargo vessel (Bulbous bow)

Length/Beam ratio L/B 5.0

Beam/Draught ratio B/T 2.86

Block Coefficient cElipp 0.698

Prismatic Coefficient C 0.698

LCB as percentage of

Lpe

1.1

Screw diameter/Draught Dp/T 0.656

Screw Pitch/Diameter ratio P/Dp0.819 SHIP b) -.Tanker (Quasi cylindrical bow)

Length/Beam ratio L/B 5.8

Beam/Draught ratio B/T 2.7

Block Coefficient Critpv 0.8499

Prismatic CoefficiehE C 0.8503

P LCB as percentage of Lpp

ford of LPP/2 + 3.0

Screw diameter/Draught Dp/T 0.57

Screw Pitch/Diameter ratio P/Dp0.799

SHIP c) - Container vessel (Bow bulb) Length/Beam ratio L/B

Beam/Draught ratio BIT

Block .Coefficient Car.p.0:

Prismatic CoefficienE Cp LCB as percentage of Lpp aft of ITID/2 - 0.58 Screw diameter/Draught Dp/T 0_74 Screw Pitch/Diametettratio P/Dp0.80 6.23 3.45 0.626 0.640 11111111111111111111111F2

RILILIEM11114-IIIMFM1117_111

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FORE AND AFTER BODY PLAN SHIP a) - CARGO VESSEL

=WM

FIG.?

BODY PLAN AND BOW AND STERN PROFILES

SHIP b - TANKER INWN1111111wmrAmorAsrAmrAwas LW% N.111111111UMPAIIIIIIIMIMIIIIIi \-,7111111h1rWAVIIMINIIIIIMI

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MEM 1111=11raMI1111111MITMAN/MMIIII il111111111LIMMEMINMIIIMI1 111.11111MWMIMIIMIIM 01WW111111LINIIIIIIIIIMUMMINIAINIAWAPVIL 10411110111111111011MOIMK/MIKEVAIIIIAMPIWI FI B

BODY PLAN AND BOW AND STERN PROFILES

SHIP ) - CONTAINER SHIP

VII1 .1 6

So far fins have been tested on ships a) and c) and integrated half ducts on ships a) and b). In either case there are indications that the gains from application of these devices become bigger with increasing block coefficient. This behaviour is understandable because devices aimed at homogenising the flow from local improvements can be antici-pated to be more effective on fuller: ships which have a less good wake'dis-tribution than on finer ships with a basically good wake.

2.3.1 Aerofoil_Fins

The aerofoil fins used

on

both

models had a span, i.e. projection from

h011 of about-40 % of propeller diameter

and a chord

of

about three-quarters of

length

of

span. They were located at about 20 % of propeller diameter Above its centre just ahead of the stern apPerture with their horizontal axis at

a normal to the angle of run of water-line at this height- Thus they covered the propeller and were arranged with a sWeepback giving the trailing edge the

same clearance from the propeller at the

sternpost.

Naturally the size and correct positioning of such fins is decisive for

their success but there it a large

num-ber of parameters involved and deriving the best combination from model tests alone is not simple nor opportune for an investigation Of general nature. Near the stern the boundary layer is normally. much thicker on the model than.on the ship and can cause scaling problems. Moreover, the suitable potition will differ in different ships and ultimately

individual testing is necessary- There-fore, the intended purpose of the Model tests at this stage is not so much: to optimize the size and location of the fins, but rather to check the practical

feasibility in connection 'with power saving.

Fig.9 shows the nominal wake field of ship a), which is quite typical of

such form ratios and which together with

the section Shape of afterbody served as guide to fix the location- The fins were first fixed on each side separately whereby the angle of incidence was'

varied..

In ship a) it was found that

a

downward deflection of leading edge of

the aerofoil at 6 degreet against the

horizontal was the most effective for either side giving a saving in power of

about 4 % in each case. They were then fitted on both sides at the same deflection and here they reduced the power requitement by 5 to 6 %.

In ship d) on the other hand such a

fin

on the starboard side did not produce

any iMprOveMent. On the port side

a

down".

ward deflection of 6 degrees is

saving of about 2 %. This ship has a U-section bulb stern and a relatively flat rake to a broad transom. These and the rotation imparted to the wake from propeller action as described earlier in this section apparently straighten the flow on the starboard side or even cause a downf low here, so that a higher

location and a different configuration of the fin here would probably be better. Such extended tests as also wake

measurements with fitted flow straigh-/tening devices are still pending, but

are expected to give more insight into

the 'nature of these effects.

FIG. 9 WAKE DISTRIBUTION

SHIP

CARGO VESSEL

VAN = 0.53

2.3.2 Integrated 'Half Ducts

Half ring nozzles as integrated half ducts have been tested on ships a) and b) so far and in both cases have

shown considerable gains in power saving. Nozzles used here are of symmetrical profile having NSMB 19a section and

length to inner diameter ratio of 0.5. They were fitted with their lower end at the centre of shaft bossing. Thus the two halves were laterally so far apart as the bossing or hub diameter. The trailing edge was positioned just ahead of the end of bossing. Their upper ends were integrated into the hull, while the gap at the trailing edge

protruding aft of stern frame was given a horizontal filling.

The size and the angle of axis

VIII.1 - 7

against the longitudinal and transverse planes of ship were varied in both halves in comparative propulsion tests. The significant results can be summed up as follows:

The diameter of the nozzle should be about half the diameter of propeller or less so that its upper trailing edge just covers the propeller tip. Bigger nozzles accelerate the flow on top of the propeller as well, where this high energy fluid not only passes unutilized but also increases the frictional resistance at the rudder fixed structure;

A downward tilt of both the nozzle halves in the upflow which occurs here is beneficial. The favourable angle of inclination of centrical axis appears to be between 5 and 7 degrees on both sides;

Along with the tilt it is better to arrange the centrical axis at a

divergence in front, which amounts to 5 degrees on the port and 10 degrees for the starboard side. The reason for bigger opening on starboard is evidently to be found in the right-handed turning direction of the pro-peller. Apparently the sternpost interrupts the rotation which the propeller imparts to the wake in front and when the same is right-handed, more cross flow occurs ahead of starboard upper quadrant.

The gain in power saving in ship a) from fitting integrated half ducts as described above amounted to about 6 %.

The power saving in ship b) was still more substantial and amounted to about 10 %. This ship is from among a series of full-bodied ships systemati-cally tested at the Hamburg tank (Ref.10), where it was found to give better results than five other comparable designs in the last series. Thus a saving of this sort on a ship which can be said to have a basically good design is encouraging, and it is hoped, would give enough in-centive for trying these devices out in full scale, particularly because fitting them even subsequently to an existing ship does not involve any constructional changes.

Meanwhiles as next step tests to investigate the half ducts in ship c), which has a considerably finer block coefficient are being performed and will be followed by wake measurements, which

should give further insight into the obtainable gains.

2.4 Devices in Propeller Stream

The fitting of flow straightening devices in propeller stream is normally associated with smaller gains. There are mainly two effects which can cause losses

rotation and contraction in its wash. With the rotation the propeller wash

impinges on the upper and lower.rudder halves- from opposing direction and with different intensity leading to an in-direct steering force and its unwanted side effects. Similarly the contraction along with the eddying whirl in the

cavity behind the hub are disadvantageous and give rise to a reduction in effective thrust.

To overcome the first effect it was suggested as early as some fifty years ago to divide the rudder and position the upper and lower halves at different

incidence angles. One version came to be known as Star-Contra-Rudder (Ref.11).

Such rudders were installed on a number of ships including Victory ships during the last war but in later years their use declined probably because hanging rudders With more efficient profiles were developed but also because of some

re-ported damage to the rudder

at

the

partition, which can occur from cavi-tation effects more readily due to the discontinuity in profile being in the eddying cavity behind the hub.

The solution propagated in the 1950s to counteract the screw-race contraction . and eddy building is known. as costa pro-pulsion bulb (Ref.12). Another example

is the active rudder in which a bulb is

fitted on the main rudder and a propeller installed in it, mainly to improve

manoeuvrability at small speeds. However, use of such bulbs in divided Star-Contra-Rudder (SCR) to combat both the effects at the same time has not come to be known so far but offers a possibility to obtain some further improvements. The savings are

, essentially small and difficult to verify

in usual model tests. In Duisburg tank tests with ship b) for example it was found that the deflection for the rudder upper half should be slightly bigger than that in the lower half, the numerical values being about 5 and 3 degrees res-pectively. The gain in power from the integrated use of propulsion bulb and SCR whereby IfS profile shape was fitted, amounted to about 1 to 2 % over and above the considerable savings already obtained from the application of integrated half ducts.

3. SUMMARY

Hull and propulsive efficiency is an area in which one might hope to make use-ful gains in power saving. This paper shows that flow straightening devices in the wake used

in

the past mainly to over-come propeller excited vibration problems need not remain confined to this task but can also serve to achieve power savings. From two such devices being tested at the Duisburg tank the integrated half ducts have shown that considerable savings in power are possible.

VIII.1 -8

While tests to investigate.thablock coefficients at which these ducts offer an advantage are still in progress, the

gains determined so far at 'high block coefficients are promising enough to encourage their use in full-bodied ships. Helpful in this respect is also the fact that such ducts can be incorporated into existing ships and new buildings Alike without design alterations.

REFERENCES

Henschke, W.: "EinfluB des; . Schiffsgewichts auf die GesChwindigkeit und Antriebsleistung". SCHIFF UND HAFEN, Vol. 13, No. 1, 1961, p. 33.

Dankwardt, E.: "TrimmeinfluB ge-schleppter Schiffe". Schiffbautechnischet Handbuch,Vol. 2, 2nd Ed., p. 1009.

Luthra, G.: "Ermittlung der Wider-standszunahme bei Ballastfahrt mit stark aChterliChem Trimt auf begren2ter Wasser-tiefe". HANSA, Vol. 119, No. 22, 1982, p. 1495.

Dankwardt, E.: "PropulsionagUte-grad bei Ballasttiefgang". Schiffbau-technisches Handbuch, Vol. 2, 2nd Ed., p. 330.

Gadd, G.

E.I

"Flow deflectors a cure for vibration". The Naval

Architect, NO. 6, November 1980, p. 238. van Manen, J. D. und Oosterveld, M. W. C.: "Weitere Ergebnisse

systamati-acher Versuche mit Diisenschrauben". SCHIFFSTECHNIK, Vol. 20, No. 101, September 1973, p.35.

Watson, D. G. M.: "Designing Ships for Fuel Economy". The Naval Architect, No. 6, November 1981, p.:504.

Vossnack, g. and Voogd, A.,: "Development of ship's Afterbodies, peller Excited Vibrations". 2. Lips Pro-pellersymposium, 1973:

Huse, E.: "Effects of Aftetbody Forms and Afterbody Fins-on the Wake Distribution of Single Screw

Ships"-Ship Research Inst. of Norway, Rep- No. R 31.74.

10..Collatz, G. und Luszcz, j..::"Er-weiterung der systsmatischen Widerstands-und Fropulsionsversuche mit Modellen groBer Volligkeit". Forschungszentrum des Deutschen Schiffbaus,.Bericht Nr. 51/1975

11. Herner-Rusch:

ilaropuisionsver-beasernde Mittel: Star-Contra-Ruder" in Textbook "Theorie des Schiffes", pp.447

-450.

12- Zeno, G-: Die Costa-Propulsions-birne". SCHIFF UND HAFEN, VOL 4, 1953, pp. 447 - 450.