Some experiments with self propelled models of twin screw ships

CHALMERS TEKNISKA HOGSKOLAS

HANDLINGAR

TRANSACTIONS OF CHALMERS UNIVERSITY OF TECHNOLOGY GOTHENBURG, SWEDEN

Nr 110 (Avd. Skeppsbyggeri 4) 1951

SOME EXPERIMENTS WITH SELF=

PROPELLED MODELS OF

TWIN SCREW SHIPS

THE INFLUENCE OF LONGITUDINAL CENTRE OF BUOYANCY ON 'RESISTANCE AND PROPULSION

BY

ANDERS LINDBLAD

GOTEBORG 1951.

Introduction

It is well known that the longitudinal _{distribution of the}

displace-ment is of the greatest importance for the resistance, and this question

has often been the object of model experiments. _{The longitudinal} distribution is completely defined and fixed by the usual sectional

area curve. _{If only an approximate idea about the distribution is}

needed, it is often sufficient to state, where the _{longitudinal centre}

of buoyancy (L. C. B.) is located in reference_{to midships (L/2).}

We know nowadays quite well where, in different_{types of ships,} the L. C. B. should be placed in order to give a minimum of ship resistance. For lower speeds and full ships we have at our disposal

the results from the investigations of SADLER, BAKER, KENT,

Ro-BERTSON _{and many others. For modern high speed ships with low}

block coefficients complete data _{are not yet available, but for this}

type of ships we have during the last few _{years completed several} systematic series of model experiments at Chalmers _{University of}

Technology. We can say that, in general,_{we now know how to design} the lines also for these high speed ships.

But the question of designing good hull forms_{is only a part of the}

whole design problem. Of equal importance is the question of the

propulsion of the ship. A designer ought to be able to judge the effect

of all the different factors involved and also be in the position to understand which combinations of hull lines and propellers might give the best results. For this _{purpose he must have enough data} available to permit him to make an estimate of the engine power needed to drive the ship.

Many experiments have been carried out with_{self-propelled models,}

in order to investigate the question of _{propulsion for single-screw} ships. Very few experiments have, however, been made for twin-screw ships and the information that has been published_regarding them is _{still rather meagre. The most important investigations}

carried out in this field are probably those ofYMAGATA, HUGHES and

4 "CHALMERS TEIOTISKA HoGSKOLAS HANDLINGAR NR 110

The present research has been limited to an investigation of only a few of the factors affe.cting the propulsion of twin-sCrew ships

con-structed for medium high speeds, and the author is fully aware of

the incompleteness of the investigation, which is nowpresented.

following symbols have been used

The

diameter m.

EHP =-- Effective power with appendages HP (metric)

SHP = Power delivered to the screw HP (metric)

Volume of displacement m3 EHP

©1 = 419.5

_V3

02

Resistance coefficients = 419.5 S 2.73P17

QPC SHP

? Propulsive coefficient rT D = Screw R = Screw radius m. H

= Pitch

m.

HO7R = Pitch at radius 0.7 R m. .

Q = TorqUe .kgm.

T

= Thrust

kg.

n = Number of revolutions per second

= Speed m/sek.

ve r= Speed of advance m/sek.

V =--- Speed of ship knots (metric)

2 = Density kg sek2/m4

TV Cg

D4 n2, Thrust constant of the screw

Torque constant of the screw

e D5 n2'

V6

A D, Velocity coefficient

Screw efficiency in open water

A. LINDBLAD, EXPERIMENTS WI1H SELFPROPELLED MODELS ETC. 5 T = R

T , Thrust deduction fraction

e ; Mean wake fraction Iw` + we

v v

2

1I

, , Hull efficiency

w

The Object of the Investigation

Extensive tank experiments have previously been made with the models used in the present tests. The object was at that time to find out the effect of the longitudinal centre of buoyancy on the

resistance and to develop suitable ship lines.

The present investigation has been carried out with two different

series of self-propelled models, and this time the main object was to

ascertain whether the models Which were best from the point of view of resistance were also the best from the point of view of pro-pulsion.

For that purpose the following experiments had to be carried out.

Resistance tests with the models both in naked condition and

fitted with bossings and shaft bearings.

Experiments with the propellers run in open water.

Tests With self-propelled models.

Description of the Models and the Experiments

The experiments were carried out with two different series of models, each of which consists of three models. Series A is formed

of models With a block coefficient of 060 and series B of models with a block coefficient of 0.65.

Fig. 1 shows the body plan and profile of Series A, and Fig. 9 gives the body plan of Series B. The sectional area curves and water lines are shown in Fig. 2 for Series A and in Fig for Series B.

The particulars of the main dimensions, the coefficients and the

6 .CHALMERS TEKNISKA HoGSROLAS HANDLINGAR NR 1.10

Series A 4-050

.Body Plans rind Profiles

Fig. 1. WL If az_ 2 3. 4 5 6 7 6 9 fn. Mode/ ®

NUIE1=11111ff

IC

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8 CHALMERS TEKNLSRA HOGSKOLAS HANDLDTGAR NR 110

TABLE I.

It should be observed that in this table the block coefficient is based on length between perpendiculars (Lpp). The models were

all fitted with streamlined rudders. In the calculations of the

displace-ment the volume of rudder and appendages has beenleft out but the volume of the cruiser stern has been included.

-The complete data regarding the models are given in Tables

II

and V, and the propeller data are given in Tables III and VI.

The Resistance Experiments

Resistance tests have been carried out with all the models both with and without propeller bossings and. shaft brackets. These have

given us an opportunity to check the available data presented in

various earlier published papers.

No trip wire has been used in the tests with our models.

The details of the construction of the bossings and the shaft brackets are shown in Figs. 3 and 11, and the complete results from the resi-stance tests are presented in Tables IV and VII.

The Propeller Experiments

For each one of the model series a pair of right handed and left handed propellers has been designed. Figs. 4 and 12 show the con-struction of the propellers. They are three-bladed and intendedfor outboard turning. The propellers are designed mainly according to

the diagrams published by Troost.

Series A Series B

Length between perpendiculars m. 121.0 121.9

Beam m. 17.07 17.07 Full draught . . .

. .. . ... .

. . . m. 7.11 7.11 B/d 2.4 2.4 Block coefficient 0.60 0.65. Screw diameter m. 4.50 4.10

2.9%

2.7%

L. C. B. aft of Lpp/2 in percentage of Lpp . .

1.9

2.2

1.0

.1..4

A. LINDBLAD, EXPERIMENTS WITH SELFPROPELLED MODELS ETC. 9

.10 CHA.LMERS TEKNISKA.. HoGSKOLAS HANDLINGAit Nn 110

Table .71

Series A. Pathadars of Mode/5.

Table

Series A. Particulars of Screw 3/4.

Experiments with Self-propelled Models

These experiments have been carried out in accordance with the

Continental Method, and the friction corrections have been calculated by means of Froude's coefficients.

The wake faCtors given are means of thrust and torque

measure-ments.

Within each series propellers are placed in a fixed longitudinal

position as shown in Figs. 3 and 11.

The tests were all made on the full draught at a Bid of 2.4.

Li

Ai Model I 2 3

Lenqfl between m t2I9 121.s 12/.p

on load ziester line in

_length /260 /260 /260

Bean, m /707 I7e7 /7os

Draught 177 7.1/ 7./1 7//

Plidship section coefficient 0969 0.969 0969

Radius of bilge 177 2.44 2.44 244

Rise of floor 1r7 0.15 0.15 0./5

Displacement, foto/

--

m4 8961 8976 5023 rudder and appendages m4 20 2$ .30

.

tons a 2240 lbs ill Shl .9040 .9055 .9/03 .

Block coefficient.tolof 0604 0605 0608

lore- body 0549 0572 0.595

alifer- body 0659 0638 0.62/

Prismoilt coefficient 0623 0.a4 0.427

Vetted surf. total en° 2803 2824 2846

. rudderand appendages 1778 /06 /17 130

L.C.B. all of LA7,4 inpercentage of Lpft 2.9 1.9 1.0

Di'amelex 4.5áo Pilch (cons/on/) 4300 Pitch ratio / Bleep-thickness ra/JQ 412 0.044 0./49 /540 804.4-6/iomeier /qh.0 Di4C 42M1

Expanded blade alva mi 6.83

_.131ad_e_-_area_eatio 0.43 _R_alre eicis 5°

Alumberol blades 3

A. LINDBLAD, EXPERIMENTS WITH SELFPROPELLED MODELS ETC. ii,

Pitch (constant) 4500m.m.

Pitch /olio

:lode area ratio 0.43

Akenber of blocks 3 Series A Screw 3/4

Fig. 4.

Discussion of the Results

1) The Resistance Tests and the Effect of Bossings.

As has already been mentioned the models have previously been tested in the naked condition, and the results of these experiments

have been given in papers published in the Proceedings of Institution of Naval Architects in 1946, 1949 and 1950.

For the present tests the models have been fitted with propeller bossings and shaft brackets and in that condition again tested for resistance. We have thus had an opportunity to compare the results and to find out how large extra resistance is caused by the bossings and the shafts.

As the shorter aft bodies (associated with afterly L. C. B. positions) were fitted with bossings of smaller lengths, it was to be expected that

the resistance caused by the bossings would also be less on the models, where L. C. B. is located farthest aft. The resistance tests show that this is the case in both series. The results are summarised in the

following table.

MIMI

0

MN

Allabb.

AIM

MEIIIIIIIMIll=

,I,I

,

\

PI

IIMPIPPI

PRIIIIPM

PIM

I

,--k sts--dm,i

t

(PRIMMI1111.11111=11".

f

Li

. gfys,,,ke in mm ,'. m mm Diameter -4500 'nth

12 . CHALMERS TEKNISKA HoGSKOLAS HANDLINGAR NR 110

Resistance Due to the Bottsin,gs and the Shafts.

Series A.

Series B.

2. Propeller Tests in Open Water.

The propellers were tested in the usual way, and in plotting the results an average was taken between, the right- and the lefthanded screws.

The curves in Fig. 5 show the results from propeller P 314, which

was used in series A, and Fig. 13 shows the results from P 300 designed

for series B.

The results from the open water tests indicate that both the pro-pellers show normal characteristics and efficiencies and that they

can be considered as fairly good and suitable for out investigations, with self-propelled models.

3) Tests with Self-Propelled Models.

In an investigation of the various factors affecting the propulsion of twin-screw ships one does not expect the results of Wake, thrust deduction and hull efficiency to show an absolute regularity. Some observations will be a little »off# and the curves will always show

some observation spots, which do not fair in with the rest of the spots.

Taking this in consideration one will find that the results of the

present investigation seem to be consistent and in line with previous investigations in other tanks.

Fig. 6 gives the EHP and SHP of Series A, and Fig. 14 shows the horse powers of Series B.

Model Increase in_{resistance aft of L/2}L. C. B.

5.0% 2.9% 2 5.5% 1.9% 3 . . . ' .. 6.0 % 1.0% Model ' Increase in resistance L. C. B. aft of L/2

4 .... . .. .

. . . 3.3 % 27%

5 ... .

..

. . . 3.8 % 2.2%

6 ... . ... .

. . . 4.5 % 1.4%

A. LINDBLAD, EXPERIMENTS WITH SELFPROPELLED MODELS ETC. 13

20

0

0/ 0.2 OJ 0.4 04 0.6 a7 08 0.9

Series B Screw 300 Open water characteristics

Fig. 5.

Table A'

Series A. Propulsion test results

vtc, ./01cQ c-F11.777

ipr.i:

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Wm

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KINIMI1

_ERE

Ea

. , v 7=Knots onedo-)LIPr...6,..h)5NP % 0PC rlinin i Id 9,, '4

0 s

Mode/ / 0700 /4 1797 2566 690 962 /3.9 12.8 98.4 0637 0.908 0750 15 2252 3245 694 1042 as /19 95.7 0.649 0.933 0600 16 2795 40/2 695 1/2.2 /62 /12 94.4 0.662 0926 aeas 165 3057 4356 702 1152 162 115 95.4 opsa 0.94 0850 i9 3345 4750 705 1/82 162 /2.0 95/ 0662 0.939 0675 175 3760 5328 705 122.1 a3 122 955 0683 0965 0900 /8 4478 6/68 725 /26.8 /4.7 /2.8 976 0.747 1026 0935 /8.5 5170 7349 73., /32.8 /3.0no 978 0825 1/25 0950 /9 6366 8850 22.0 /39.5 /4.9 /2.2 970 0952 Z250 Model 2 0.700 /4 /806 26/5 640 977 /4/ 10.6 96., 0630 0.926 0750 /5 2252 3288 68.4 /053 15.2 103 94.5 0.649 0947 0800 16 2813 4086 etas /a, /5/ 94 94.0 0667 0969 aeas /6.5 3120 4488 ca. 1/6.7 /4.9 es 945 0675 0.99, oeso /7 3447 4951 656 i20/ Ka /0.2 95.0 0692 0976 0875 17.5 3884 5587 695 /24., /5.7 Ma 94.4 0704 1.013 0900 /8 4565 6458 70.4 128.5 /5.2 11.4 95.7 0.76/ 1076 0925 /65 5500 7664 7/.9 /34.6 135 114 975 0044 i195 0.990 19 6500 9227 705 /41.5 /46 110 959 0922 1.207 Model 3 0900 /4 Jen 2757 65.9 99.3 /7.9 94 906 064/ 0.973 0950 /5 2279 3059 679 /06.4 /69 9.3 91.6 0.652 0812 05820 a 2894 4094 706 /14.0 /4.4 93 94.5 (2684 0966 0825 /6.5 3289 4565 72., 117.1 /3.2 9.0 95.4 0.709 0962 nese17 3725 5/82 71.9 /21.6 12.4 9.6 97.0 0734 1.020 0875 /75 4259 5873 72.7 125.9 12.4 /0.0 975 0770 1059 ago° /8 4929 67/4 73.3 /30.4 /2.3 624 98./ 08/8 1115 0.925l8,5 5623 7735 75.4 /35.5 //.7 /1, 994 0891 1.18/ 095019 6368 9202 78,7 /41.3 /09 /1.6 loos0983 1298

0 80 70 60 20: ono 10 000 -20,

Thrust deduction factor

0

ModelL.C.8

I 2.87. -2 -1.9% 3 --- -10% 7 Hull efficiency ... ____---3 _--Model 1 ₂

i

L.C.8 29% Z9 % - ZO%

-li

VII

.1

bi

,

,

1

II

aPC , ,,, 2 7, ,,

I I

I

,,,

.., 070 080 Oso Virg 14 15 16 17 /8 knots 19 ,Woke factor 1 2

-_-.---\.

070 Oao 0.90 v/.12 14 15 /6 /7 18 knots /9

Series A. Horse Power and Q.PC.

Series A.

Propulsion factors on base of VAT

-Fig. .6. Fig.. 7. H.P Hi? 000 I/O 000 100 10 2000 0 lo00

A. LINDBLAD, EXPERIMENTS WITH SELFPROPELLED MODELS ETC. 15

/0

Thrust deduction foctOr

0.90

LC5.

Afisfq 3.0% 25% 2o%, 15%

Woke foc-/or

Series A. Propulsion factors on bose of L.C.B. Fig. 8.

Series A with a Block Coefficient of 0.60 Wake fraction (w).

The curves in Figs. 7 and 8 show that the wake increases in propor-tion to the increase of block coefficient in the after bodies, which

has been affected by the moving of the L. C. B. aft.

The increase of wake with the higher speeds is also fairly,_regular. as could be expected.

Thrust deduction (t).

When the propellers are placed close to the hull a large thrust

deduction generally occurs. This is the case in models 1 and 2, which in comparison with model 3 show rather large thrust deduction.]

7-0'8; 7.--- -+ v a0.90 -.

--' 70 so Hull

efficient-16 .,cnAr..4sEris TEKNIsKA HOGSKOLAS HANDLINGAR NE 110 Hull efficiency

ow

From a comparison of the curves in Figs. 7 and 8 it appears that the hull efficiency of models 1 and 2 is rather low especially at the

lower speed range. Model 3 shows at all speeds the highest efficiency of the models and can be considered as fairly good.

Series B with a Block Coefficient of 0.65 Table 7

-5er/es B. Parliculars of Models.

Table

Series B. Pari;cutars of Screw 300.

T

N9 oi-Nodel 4 5 6

Length be/I/Fe-if pare' nelieule rs Mi /2/.9 /21.9 /RP

Lengthen load wigsr line m 125.6.

/707 /25.4 /747 /254 1Z07 Brain . m Drawn/ m Zu 7.// 7 li

/lids/1lb .59C/%017 eye/fie/en/ 0.975a ifs 0.975

Radius of bi/fe m Iva 1.98 1:98_

Rise of /leer eh 0.15 0.1$ 0.15

Displacements. lo/a/ m3 9718 9741 9815

,=---

.ruchierand appendages ' M /7 19

--- . tons a nee /bs in .511 9027 0.055 126/4 99// eta.; _ 0639 eaefficienl. foto/ _13/0ek , fore- bad; 0/10r- body 0.701 0.686 Pri0im6lie coeffi,iene 0.674 0.674 0.679

Wetted sorfac. la/al mz 2923 2920 2956

,

rudderand appendages In'

2.7

/02

Z. /07

1.4

L.C.13.all of Lee,4 i n percentage-of Lno

Dioffirte'r m 4./00 .I.dcb ex 7R 4163 Pilch ratio 1.011 Blade-thickness ratio 0045 Eloss-diannfter ratio 0.190 Disc area /320

Expanded bladearea m2 88

Blade-area rail° 0..s7

Rake degrees

A. LINDBLAD, EXPERIMENTS WITH SELFPROPELLED MODELS ETC. 17 Model 0 r

Z3 4

5 6 7 8

Series 8O65

Body_Plonsore_PrOfi les Fig. 9. 1.4.6 IV 4 WI. 14. 4 ELL__ 511 /9 /9/* 20 W4.7 W4.8 3 -JELL

&XXVIII". '

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1 CHALMERS TEKNISKA HoGSKOLAS HANDLINGAR NR

'2

0 A P 10 II 12

.3

13 Blade area ,r07.1.0 037 . 'Number of &ads, 3 /4 OAP 2 /0 II /2 14 15 /6 /7

Series 8 Sectional Arra Curves ono' Water Lines Fig. 10.

Alch distribuiian Tip_2050 I *15

9 i845MMICE71 797 1640 WEI11203 /07 7 1435 64 4/63 1176 6 /230 81 4/47 1/83 _5_=5 98 4100 1/24 4 620 1/6 6 4015 /0/9 3 615 /33 38861 890 4/0 369/I Roo'iusabdelThYch &dim 112in narn,Thiekrii modem:eh in nvnl ram!

41111/ ,_

_{UNIIIIIIIIIIIMIM11111/ -}6 % MM.= all.11101.11M. loo. r. -s6 %

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_{IIMMIErilillINIMi} 585 % MIIMMIffallEMMIMMEk ' - 4 % .-- I SIM MI IRV I I I IN /1 941.Z_ .:---1-> 11QIIMMILMIIIIMMIllt.... .

-to

Series B Screw 300 Fig. 12. /6

_li

18 19 ER 20 10 /9 PP 20 90 --._.,-..._{,,,... ,---.1=--r'-'-_--,}

-

.

7

- . . 80 .<.. I 70 -60 .9" 0 50 0 '.7 ... .0 40 Series B cfB. 065

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A. LINDBLAD, EXPERIMENTS WITH SELFPROPELLED MODELS ETC. 19 1 1 1 1 1 1 1 1 Cl

26 CHALMERS TEKNISRA HOGSKOLAS HANDL1NGAR NR 110

Wake frctcticm, (w):

As the block Coefficientofthis series is 0.05 higher than in 'series A, the wake Values in series B can be expected to be higher than in series A. The curves in Figs. 15 arid 16 show that this is the case

with all the models of series B. ' It Can be seen that the wake values

are large in models 4 and 5, where the L. C. B. is placed more aft

than in model 6.

Thrust deduction (t)

A comparison of the curves in Figs. 15 and 16 shows, that the

thrust deduction varies in the usual way and has considerably higher

values in models 4 and 5 than in model 6.

Hull efficiency (nil).

The curves also show that model 6 at all speeds has aconsiderably

larger hull efficiency than the other models of the series. This is, of

course, due to the smaller thrust deduction of model 6. All the models of series B have, in general, higher hull efficiencythan the models of series A.

5eriesA Screw 314

Open wok.F chOroctiTris-tics Fig., 13.

70

000 _{2000 000}

10

Thrust deduction factor

20: S lloc/el 5 -22 6 -/.4 % Hull efficiency 7 ..1_... .. ---... ... ---7_147. . Model 4 5 6

--L.C.B 2.7% 2.2X

I

-L4 X . Wilighig

lirel'rarifil

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II

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r

,,,,A

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=CRP

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ii.

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070 080 V/VE 090 /4 /5 /6 /7 lmots la Woke factor . . : . .... _ -. 070 Oao v41 090 14 /5 /6 /7 knots 18 Series B.

Horse Power and ORC

Serial B.

Propulsion factors on base ofArc

Fig. 14.

Fig.. 15.

22 CHALMERS TEKNISKA. HoGSKOLAS HANPLINGAR NR 110 20 10W 075 .W Propulsive coefficient

Thrust deduction factoror

Aft 0,(4

Series B. Propulsion factors on base of LCB.

Fig. 16. tkriaiio

...inaaw..,-.74.

/0

joz _{Zs% 207. LYZ 107.}

A Comparison between shaft Horse Power (SHP) and

Effective Horse Power (EHP) and Quasi Propulsive

Coefficient (QPC)

Series A.

Fig. 6 aiid Table IV give the resistance data for series A. Model 1 shows at all speeds above V/VE of 0.80 the lowest SHP and EIIP of

the models. Model 2 requires as an average 4.5 % higher SHP and

about 2.6% higher EFIP, and for model 3 the corresponding values

- A. LINDBLAD EXPERIMENTS mum. SELFPROPELLED

MODELS ETC. .23

Table ET

Ser;es B. Propulsion test results

The QPC are shown in Fig. 6. There is _{very little difference}

bet-ween models 1 and 2. _{Model 3 has unusually high values of QPC,}

but due to the high EHP of this model _{the resulting SHP values}

are - as is shown above - very much higher than

_{in the other}

models

Series B.

Fig. 14 gives the resistance results of the three models. There is very little difference in this series in the EHP _{between model 4,}

which has L. C. B. 2.7 % aft of L/2 and model 5, which has L. C. B.

2.2 % aft of L/2. Even at the higher_{speeds the difference in favor}

of model 4 only amounts to 11/2%.

But when the SHP are compared, it is _{evident that model 5 is} much superior to the other models. At the speeds, that are suitable

from an economical point of view, _{model 5 requires about 4 % less} SHP than model 4 and about 9.5 % less than _{model 6.}

-The values of QPC are also given in Fig. 14. -The curves show that

_y_ YrT.o lenots frehlOn.thf4h9 EI-IP SHP RPC % r/h7in I % 1 w .1 % 7. Model 4 43700 /4 1886 2544 74.2 110.6 16.6 /4.3 973 asza van 0.725 /4.8 2102 2883 71.9 //O., 16.2 /4-s 972 0434 Coro 0739 15 5277 2249 728 119.0 /6.9 16s. 922 0447 0.869 0.775/2.2 2707 3690 732 /237 /6.1 142 978 Cows 0.3/2 0.006 /6 1997 4070 738 /774 /5.7 /44 944 0672 9.irt Ctozr /65 330/ 4419 744 /91.7 /5.5 /46 9115 aan 11306 0856 /7 _{3758 49/7 74o /153 /4/ /1":// 101.0 0.694 09/7} 0675 /Zs 4428 37183 753 /42.. 14., /S.. 101.o 42700 1:50s dew /8 5467 7568 22s.256. /6.3 /51 99.0 0.841 1106 I.wociel 5 21700 14 /263 ' 7580 76.5 1/1.6 /49 1.3.o 98.5 0.658 0e42' 0725 Me .241 2671 760 /156 14.3 1.7.5 365 0.65a 0e65' 0759 15 2416 31.3/ 72, //As 142 /3.o .98.5 0.423 0870 077s /2.5 2703 .3535 765 /237 143 /3e 342 4647 ee78 0.855 /6 1992 3106 .76. /275 14_9 118 38.7 0.672 0071 0822 /6.... 33/4 .4254 779 /31.3 /44 /15 313 0479 44.2/

Oars /i, 37,39 4852 744 /Ma /31 115 /623 0705 0444

0875 /75 4488 .5212 76.8 /4,32 '/4.3 /45 /00.3 0770 1.010 0350 /8 5569 752/ 7.3.9 15/. /5./ 14.7 225 0874 1.190 Model 6 arm /4 /39/ 2502 727 I/1. /3.8 ./2.1 39.0 0.663 0.8.10 0.725 Ms 22/6 1777 73.9 1/5.2 11.S /2.7 /014 0.465 0.632 Ono 1467 3153 782 /126 II.? /2.2 .101.00.6484855

0775 as 2780 .351/ 77s /24.s /2.1 ats ma.. 8.683 deal

0.602 /C 3155 4/33 774 1225 /1.2 /2.7 /060 0.7/3 0.91e

8825 /65 3558 4700 772 1917 _{11.7 /39 /01.2 0.780 0.233}

sew 17 4046 4942 7_c7 /386 //.6 /14 /021 0.754CM

0875 /is. 485i ' 6279 734 /45./ 1/.7 /11 10_c, adz, iese

24 CHALMERS TEKNISKA. HOGSKOLAS HANbLINGAR NR 1.10

models 5 and 6 have comparatively high QPC values and that model 4

has rather low values. The poor propulsive result of the latter model

is apparently due to the short and too full after body.

Conclusions

In the previous chapters the efficiencies and other data regarding wake, thrust deduction etc. are discussed in -detail. They are of value When it is a question of judging the elements of propulsion and the

merits of the various combinations of hulls and propellers. When

It is a question of estimating the horse power required, however, they

form no reliable basis for the naval architect,who is responsible for the estimate of the required horse power. Forhim the real criterion

is evidently the shaft horse power needed to propel the ship.

In Tables IV and VII there are collected all the data and the

information regarding the reaults from our model experiments. From a comparison of these data one seems justified in saying that the experiments now carried out confirm the Opinion that it is best to

construct the lines and choose the positionof longitudinal centre of buoyancy

so that one gets a minimum of hull resistance. If one does so, one can

also expect to get the smallest shaft horse powerpossible.

Acknowledgement

The experiments described in the paper were nia,de possible by

special grants from Statens Tekniska Forskningsrid (The Swedish

State Board of Engineering Research). The author wishes to express

his great thanks to Mr. TORSTEN STEPHANSSON and Mr. GUNNAR IsTiissoN for the valuable help they have givenhim in the preparation of the paper.

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