Effect of spray rails on the resistance of planing hulls

TECH4ISCHE UNN1ER$ThIT Laboratorlum voor Scheepshydromechan(ca Archief Mekelweg 2,2628 CD Uelft Tel.: O1-78573. F 015 . 781836

EFFECT OF SPRAY RAILS

ON THE RESISTANCE OF PLANING HULLS

G.J. Grigoropoulos National Technical University of Athens Greece

T.A. Loukakis National Technical University of Athens _Greece

ABSTRACT

A new systematic series of planing hull forms possessing improved characteristics with respect to both resistance and seakeeping is being slowly created at the Laboratory for Ship and Marine Hydrodynamics of the National Technical University of Athens. Before the slocton of the parent hull, five "equivalent" models with the same main particulars and

different hull forms have been designed and tested for resistance, both with and without

spra1 rails. The existence of spray rails affects differently the various hull forms as discussed in the paper.

1. INTRODUCTION

For several techno-economic reasons, which are not to be discussed in this paper, the planing monohull vessel has emerged recently as the clear winner in the ufast category" of both commercial and naval vessels of ever greater sizes. Thus, recent Italian and Spanish designs of commercial car-ferries are the largest planing craft ever constructed with lengths

of over 100 m, displacements of over 1000 mt and speeds in the 40 knotrange.

In this respect, the academic endeavour of creating a new series of planing hulls with improved resistance and seakeeping characteristics, which was initiated _{some years ago at}

the Lboratory for Ship and Marine Hydrodynamics of the National Technical University of

Athens, has become more important than initially expected.

On the way to the creation of the new systematic series, five preliminary models have been designed and tested for both resistance and seakeeping in a comparative fashion. The five

(HI) Series 62 single chine, Clement and Blount (1963) Deep-V single chine, Keuning and Gerritsma (1982)

Double chine based on Series 62, Savitsky, Roper and Benen (1972) Double chine with wide transom, same as above reference

Rounded bilge variant of H4, Grigoropoulos and Loukakis (1994).

During the preliminary investigation it became obvious that the existence of spray rails

affected the resistance characteristics of the five hull forms seriously enough but in a disimilar manner. Therefore, it had to be included in the investigation.

The purpose of the paper is to demonstrate in both a qualitative and quantitative manner, the

effoc' of spray rails, which can provoke effective flow separation even when large deadrise

angles and/or more rounded transverse sections are used, on the calm water characteristics of planing hull forms and to discuss their area of application.

2. DESCRIPTION OF THE HULL FORMS

The length to beam ratio (L/B) is the dominant parameter in the generation of a systematic

series of planing hull forms, when both their resistance and seakeeping characteristics are to be amined. On the basis of the various existing systematic series and of many existing hull forms, it was decided that an L/B range between 4.0 and 7.0 was appropriate, with LJB = 5.5 to be used for the parent hull form of the series. The most widely known single chine systematic series, Series 62, created by Clement and Blount (1963), was selected to be used

fOr comparison purposes. In order to select the parent hull form of the new series, single

chine, double chine, and rounded bilge transverse sections, combined with mostly constant of varying deadrise angles, were used.

In t'-S fashion five hull forms, whose body plans are shown in Figures Ia to le,

were

designed as stated in the Introduction. The first three ofthese hull forms, Hi, H2 and H3, are

based on the Series 62 geometry and have the same form on and above the (upper) chine. The deadrise angle at the stern is 12.5°, 25° and 10°, respectively, and is constant for about

60% of the length for Hi and H2, whilst in the case of H3 the deadrise angle varies

continuously along the length from 10° to about 50°. The fOUrth hull form has a wider transom

and a varying deadrise angle distribution', from 100 to about 70° stern to bow, as suggested

by Savitsky et al (1972). The last hull form is quite similar to the previous one and differs only in that the transverse sections above the lower chine are founded.

Woo'en models of the five hull forms, with an overall length of about 2.2 m, have been cop3tructed for the preliminary test program and tested for speeds up to 5 m/s model scale.

3. TEST PROGRAM

3.1 Testina Conditions

The five hull forms have been and are being tested extensively for both resistance and

seakeeping characteristics. The models, with respect to the width at the transom, form a

group of three with a narrow transom I H2, H3) and a group of two with a wide transom

(H4, H5). As the last two models can support more weight, the two groups were not tested in

general at the same displacementl. Tests were done for both groups at three displacements

and three trim angles for the central displacement. The heavier displacement of the

narrow-transom group was the same with the central displacement of the wide narrow-transom group for

comparison purposes. The test conditions for the two groups are shown in Figure 2 and are

numbered CI to C5.

3.2 The Effect of Spray Rails

The models were tested without and with spray rails fitted at the (lower) chine. For the Series

62 and the deep-V models, Hi and H2, the rails were fitted as Suggested by Clement and

Blount (1963, Fig. I, p. 493). The two double chine models and the rounded bilge one, H3,

H4 and H5, were fitted with spray rails as suggested by Savitsky (private communication, 1993) and shown in Figure if. In Figures 3 to 7, the total model resistance, running trim and

C.G. rise are shown vs. the model speed for all five models.

The following comments can now be made (all tests are for the corresponding central condition C3):

Hull HI: The effect of the spray rails is felt at speeds above 2.5 rn/s. The rails cause the C.G. to rise more consistently, while the running trim results are mixed. The combined effect resul in a resistance decrease of about 10%, when rails are fitted (Figure 3).

Hull H2: The effect of the rails is more pronounced for the deep-V hull form. At the higher

speed region the C.G. rises more, the running trim is higher and the resistance lower by up to 25%! (Figure 4).

Hull H3:. The same as above comments are valid for the double chine, _{narrow-transom hull}

form. A resistance reduction up to 15% is observed (Figure 5).

Hull H4: For the wide-transom1 double chine hull form, the effect of the spray rails is small. A

differ slightly only for all speeds (Figure 6 However, if all conditions are examined, Figure

13, the effect of the rails on resistance is mostly negative!

HuU H5 The results for the rounded bilge variant of the previous hull form are very similar.

Although C.G. rises comparatively more, the running trim angle and the resistance curves are. qUite similar (Figure 7).

From the above, it is obvious that the narrow-transom group of hull forms has a lower resistance when spray rails are fitted. The resistance of the three models at the same

displacement (C3) and with spray rails fitted is compared in Figure 8. The double chine hull

form has a slightly lower resistance for all, except the very high, speeds. The same

comparison for the two models with the wide transom is shown in Figure 9, with and without spray rails. Again the double chine hull form has a lower resistance, except at the very high

speeds. But, for these models the effect of the rails is relatively small and usually not beneficial.

Finally, the resistance of the two double chine models at the same displacement (H3 C2 with

spray rails and H4 C3 Without spray rails, i.e. in their best condition, respectively) and static trim angle is compared in Figure 10. Although the differences are small, the wide-transom

model has lower resistance for most of the speed range.

The effect of the spray rails on resistance for all five conditions tested (Cl to C5) and for hull forms, H2 and H4 is shown in Figures 11, 12 and 13, respectively. From these figures and for the narrow-transom hull forms, it can be deduced that the use of spray rails is always

beneficial at the higher speed range and especially for the deep-V hull form. The same is not

true for the wide-transom double chine hull form, where the effect of the. spray rails can be

negative, albeit on a small scale, throughout the speed range. CONCLUSIONS

The effect of spray rails on the resistance characteristics of planing craft can be significant, especially in the case of the traditional narrow-transom hull forms. In the case of the wide-transom hull forms, either double chine or rounded bilge, the effect of the spray rails on the

resistance is small and can be either positive or, mostly, negative. ACKNOWLEDGEMENTS

Most of the tedious experimental work for the new series is being done by last. (5th) year students in the framework of their diploma theses. In this respect, the authors are indebted

to Mrs. S.Peppa and to Messrs. G. Halkias, E. Kritsinelis, C. DOUSIS, M. Pasalaris, and H.

Monokrousos. The same holds true for the carriage crew Messrs. M. Nounos and F. Kasapis.

6. REFERENCES

Clement, E.P. and Blount, D.L., 1963, "Resistance Tests of a Systematic Series of Planing

Hull Forms", Trans. SNAME, Vol. 71, P. 491

Grigoropoulos, G.J. and Loukakis, T.A., 1994, "Development of a Systematic series of High

Speed Craft for the Greek Seas", NTUA, Dept. of N.A. & M.E., Lab. for Ship and

Marine Hydrodynamics, Techn. Rep. No. NAL 106-F-i 994

KeLng, J.A. and Gerritsma, J., 1982, "Resistance Tests of a Systematic Series of Planing

Hull Forms with 25° Deadrise Angle", Int. Shipbuild. Progress, Vol. 29, No. 337, p. 222 Savitsky, D., Roper, J.K. and Benen, L., 1972, "Hydrodynamic Development of a High Speed

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a. Sries 62 b. Deep-V

c. Double chine based on Series 62 _{d. Double chine with wide transom}

e. Rounded bilge _{f. Spray rails form for models H3, H4 and H5}

Fig. I Body plans of the five equivalent hull forms and _{cross section of the spray rail as fitted} n models H3, H4 and H5.

Displ.29.72 Kp C5 LCG-0.204 m tnm0.9° by stem Dispi=36.19 Kp C2 LCG=-0.294 m trimIevel keel

b. Wide-transom models H4 and H5

Fig. 2 Test conditions for the two groups of models

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spray raiI

-:with spr4y rails

,0

0.00

0.00 1.00 2.00 3.00 4.00 5.00

Model speed VM (m/sec)

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0.00

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- - - without prCy roi ,with eprQy raili

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0.00 1.00 2.00 3.00 4.00 5

ode1 speed V1 (rn/eec)

Fig. 3 Model resistance, running trim and C.G. rise for the Series 62 model (HI) at condition C3

Dispt.=20.66 Kp C4 LCG-0.024 m

tnml° by bow

Displ.=15.44 Kp Displ.=20.66 Kp Displ.=29.66 Kp

Cl LCG-O.144 m trim4evel keel C3 LCG=-O.144m trimleveI keel C2 LCG-0.144 m tnmlevel keel Displ.20.66 Kp C5 LCG-0.264 m triml° by stem a. Narrow-transom models HI, H2 and H3

Displ.=29.72 Kp C4 LCG-0.354 m trirn0.6° by bow Displ.=21.51 Kp Displ.=29.72 Kp Cl LCG=-0.294 m trimlevel keel C3 LCG-0.294 m trimIevel keel 2.00 1.00 5.00 4.00 3.00 w 2.00 10.00

t1i.without *Pray rci

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I-Fig. 4 Model resistance, running trim and C.G. rise for the deep-V model (H2) at condition C3

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1.00 2.00 3.00 4.00 5.00

Model speed VM (rn/see)

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Model upeed V (rn/eec)

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Fig. 5 Model resistance, running trim and C.G. rise for the. double chine model based on

Series 62 (H3) at condition C3

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Model speed VM (rn/see)

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fodeI Ipeed V1 (rn/..c)

Fig 6 Model resistance, running trim and C.G. rise for the double chine wide-transom

model (H4) at condition C3 2.00 3.00 2.00 U X0.QO I --I I I I I I I 1.

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_{odeiodVñ00/ie*} 5

Model speed VM (rn/see)

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Fig. 7 Model resistance, running trim and C.G. rise for the rounded bilge model _{(H5) at}

condition C3

2.00

raip

with .prQy rail!

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adel ipeed V1. (in/s.c)

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_____ H1 with spray rails

0 0 with spray rails

_____ H3 with spray rails

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r-

1

r

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0.00 1.00 2.00 3.00 4.00 5.00

Model speed VM (m/sec)

Fig. 8 Model resistance of the narrow-transom models , H2 and H3 at the central

loading condition C3, with spray rails

...!.H4 without spray' rails

to.zo.H5 withut spray rails

,H4 with spray rails 00000lH5 with 'spray rails

.1.

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1.00

---IT1 1 Ti FT1 I

0.00 1.00 2.00 3.00 4.00 5.00

Model speed VM (m/sec)

Fig. 9 Model resistance of the wide-transom models H4 and H5 at the central loading

6.00 _1H3 at C2 Q.9.9'H4 at C3 5.00 ---+ '4.00 3.00 0 2.00 1.00 --I

0.00 I(TT1I!II LIttIIlIl

.,,..,,,I

0.00 1.00 2.00 3 00 4.00 5.00 6.00

Model speed V (rn/sec)

Fig. 10 Resistance of the double chine models H3 and H4 at the equivalent conditions C2

and C3, with and without spray rails, respectively.

6.00 i I

0.00

withut spray rails t°'....C2 withqut spray1 rails t_p..,C3 without sprayi rails

5.00 _wC4 .v bu_t.. p!Q..rgLs__{t._.. C5 without sproy1 rails}

-______ Cl with spray rails

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C2 with spray ro'ls

a a C3 with spray rails

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i, 3.00 -0 11t1IIlJ TITIuIlIlI 0.00 1.00 2.00 3.00 4.00 5.00 6.00

Model speed V (rn/sec)

Fig. 11 Model resistance of the Series 62 model (HI) at all five conditions tested (CI to C5) with and without spray rails

6.00

1 withoiit spray ,'rails t.t.. ç2 withoyt spray rails

C3 withowt spray trails i i i

5.00 c4_withot spay_oil____{5 withoyf spray 1roils} _____ Cl with spray rails u

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_{itPbyt ipFay7atis}

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Model speed V11 (rn/see)

Fig. 13 Model resistance of the double chine model (H4) at all five conditions tested (Cl to

C5) with and Without spray rails

0.00 1.00 2.00 3.00 4.00 5.00 6.00

Model speed VM (rn/see)

Fig. 12 Model resistance of the deep-V model (H2) at all five conditions tested (Cl to C5)