Research on bulbous bow ships Part I.A and Part II.A

(1)

STUDIECENTRUM T.N.O. VOOR SCHEEPSBOUW EN NAVIGATIE

NETHERLANDS' RESEARCH CENTRE T.N.O. FOR SHIPBUILDING AND NAVIGATION

SHIPBUILDING DEPARTMENT MEKELWEG 2, DELFT

*

RESEARCH ON BULBOUS BOW SHIPS

Part l.A

STILL WATER INVESTIGATIONS INTO BULBOUS BOW FORMS FOR A FAST

CARGO LINER

(ONDERZOEK IN VLAK WATER BETREFFENDE DE AFMETINGEN VAN

BULBBOEGEN VOOR EEN SNEL VRACHTSCHIP)

by

Prof. Dr. Ir. W. P. A. VAN LAMMEREN

and

Jr. R. WAHAB

(Netherlands' Ship Model Basin)

Eo

issued by the Council This report is not to be published unless verbatim and unabridged

(2)

tions reported here aimed at a fast cargo liner, the

results obtained are of a more general value. The

investigations into the application of a bulbous

bow for a bulkcarrier published in two earlier

reports have been to a large extent governed by

the results arrived at in the present report. Only

due to circumstances publishing has been delayed.

The actual investigations again are carried out

by the Wageningen towingtank, the "Nederlandsch

Scheepsbouwkundig Proefstation".

The assistance and support received from the

shipbuilders' and shipowners'

associations,

the

"Centrale Bond van Scheepsbouwmeesters

in

Nederland" and the "Koninklijke Nederlandsche

Reedersvereniging" respectively, is gratefully

ack-nowledged.

(3)

page

Summary

5

1

Introduction

5

2

Investigations

6

3

Theoretical approach

9

4

Location and diameter of sphere

10

5

Interaction between bow and bulb

12

6

Application of a bulb versus a

modifica-tion of principal dimensions

15

7

Conclusions

20 Acknowledgement

21

(4)

4 112 La distance between the centre of the sphere and the fore perpendicular in m

beam of the ship in m

amplitude of source distribution.

= 427.1 DHPIZI'l. Vs' dimensionless power coefficient

© = 427.1 EH P

dimensionless resistance coefficient

immersed volume of the ship in m'

DHP delivered horse-power in units of 76 kgm/sec

EHP power required to tow the ship, in units of 76 kgm/sec = VIV gL Froude number

= '12 Lf ' distance between the centre of the sphere and the still water surface in m f (0) function of 0

acceleration (9.81 m/seet) due to gravity length between perpendiculars in m

11 length between perpendiculars in feet

M strength ofa doublet

rn distribution of source strength

P'(0) function of 0 Q(0) function of 0

wave resistance in tons of 1000 kg.

RF contribution of the bow to the wave resistance RFB wave resistance of the combination of bow and sphere

Rw wave resistance in tons of 1016 kg radius of the sphere in m

T draft in m

T a draft at A.P. m

T mean draft in m

7;

draft at F.P. in m

speed of ship in m/sec

V8, speed of ship in knots

distance along X-axis, see figure 4 distance along Y-axis, see figure 4 distance along Z-axis, see figure 4

a. double angle of entrance of the water lines

fl midship area coefficient

specific gravity in ton/m3

6 block coefficient

displacement in seawater. in tons of 1016 kg

= EHP/DHP propulsive efficiency wave height in m

C(0) functionof 0

parameter

kinematic viscosity coefficient density ofwater

dlogA form factor according to LAP-TROOST b V33

F

r in x z A = v

(5)

RESEARCH ON BULBOUS BOW SHIPS

STILL WATER INVESTIGATIONS INTO BULBOUS BOW FORMS FOR A FAST

CARGO LINER

by

Prof. Dr. Jr. W. P. A. VAN LAMMEREN

and

Jr. R. WAHAB

Summary

The research reported in this paper has been carried out to investigate the effect of large bulbous bows on the resistance and propulsion of a ship. The basic shape of the investigated bulbs was a sphere, connected to the ship in such a way that the original hull form was maintained as much as possible.

The basic ship was a fast cargo liner of 150 in (500 ft) length. Her trial speed corresponds to about Vs/ A/Lf -= 0.90.

The application of a bulb of conventional size and shape would not favourably affect the resistance in the speed range of

interest. The application of a bulb based on a big sphere, however, did reduce the required power at equal speeds. For the ship under consideration this reduction was 8.9 per cent. at V,/,/Ef = 0.90.

The size of the sphere, needed to reduce the bow wave system as much as possible, was determined by a simple approx-imative theory. The experiments concerned in the first instance the location of the sphere relative to the bow, the effect of

a variation of the diameter of the sphere and of the angle of entrance of the water lines of the ship.

When the ship was fitted with a large bulb faired into a more conventional shape, the resistance curve of the ship obtained the character of that of a ship one or two knots faster than the basic ship.

Finally the effect of a bulbous bow was compared with the effect of small changes in the main dimensions of the ship.

1

Introduction

Rather fast ships have been fitted for a long time

with bulbous bows in order to reduce the wave

resistance.

The line of thoughts followed then is that the

ship and the bulb may be considered as two distinct

bodies travelling at equal speeds. The

wavesys-tems of these bodies interfere and if the sphere has

a certain position relative to the ship, both wave

systems may flatten each other. This effect reduces

the ship's wave resistance.

The shape of a bulbous bow has been

investi-gated many times. Wellknown are e.g. the

exper-iments with systematically varied bulb shapes

carried out by TAYLOR [2]. In 1935 WIGLEY [5]

tried to introduce modern theories of wave

resist-ance, as developed i.a. by HAVELOCK into the bulb

design. He considered the combination of a ship

and a sphere, both parts travelling at equal speed.

In this setup the following parameters are to be

considered:

the radius r of the sphere

the distance a from the centre of the sphere to

the fore perpendicular of the ship.

The distance f from the centre of the sphere to the

still water surface is generally determined by the

requirement that no parts should protrude below

the base line of the ship. Minimum resistance of

the combination of ship and sphere is designated

to belong to optimum values of the radius r and the

distance a. The bulbs found in this way are bigger

than usually considered acceptable for practical

application. This is shown in a comparison made

by SAUNDERS [8] between the optimum sizes of

bulbs according to WIGLEY and the sizes used in

practice. The experiments of LINDBLAD [6], [7]

may be mentioned as examples of investigations

of a later date, as well as the calculations and

experiments carried out at the Tokyo University

by INUL TAKAHEI and others [9], [10], [11].

The theory of wave resistance of ships indicates

that the main contributions to the wave resistance

are provided by the bow and the stern.

This is proved for a so called Michell ship [11],

the breadth of which is small in comparison with

the length. The slender body theory reaches the

same conclusion.

INan [11] uses a bulbous bow for flattening the

bow wave system only. For the elimination of the

stern wave system a stern bulb is needed. According

to INut the splitting up of the waves into a bow and

a stern wave system is essential for the

determina-tion of optimum bulb dimensions. The other

aspects of his theoretical approach are in principle

equal to those of WIGLEY [5].

Many questions are, however, still unanswered

by this theory. It is assumed that the wave systems

of ship and sphere may be superimposed linearly,

(6)

from a hydrodynamic point of view, was not taken

into account. These assumptions do not prevent

the theory from providing a clear insight into the

effects of the application of a bulbous bow.

Recent investigations into bulbous bows carried

out at the Netherlands' Ship Model Basin are

reported in this paper. The purpose was to obtain

an insight into the order of magnitude of reductions

in required power owing to large bulbs. Next, an

endeavour is made to obtain an insight into the

relative importance of the parameters, which

determine the size and the shape of the bulb. A

scheme of the hull form variations investigated

is shown in figure 1. Finally, the effect of a bulbous

bow is compared with that of small changes of the

principal dimensions of the ship.

7°

2 000

11° 15°

EN TRANCE OF WATERLINE AT T. 717m

Fig. 1. Investigated variations of hull form.

2

Investigations

The basic ship for the investigations was a fast

cargo liner, of which some particulars are given

in table I.

She was originally designed without a bulbous

bow and to the statistical records of the

Nether-lands' Ship Model Basin the hull form is favourable.

The block coefficient 6 = 0.62, makes this ship

suitable for a speed of about 20 knots on trials

(V3//L1 = 0.90). A conventional bulb did not

affect the required power favourably at this speed.

In order to study the effect of a wave resistance

reduction on the total resistance, the total resistance

is splitted up in figure 2. The wave resistance is

determined with the method of LAPTROOST [12].

The speed range of interest under service

con-ditions is between 18 and 20 knots. In this range

Table I. Main particulars of the ship.

the wave resistance was about 20 to 25 per cent.

of the total resistance. So the application of a

bulb would only be of importance if the wave

resistance was considerably reduced.

J-;t

without bulbous bow 5 10 ₂₀ vs.mots 7 1

II

( I i 1 1 i 1 006 one ano 012 0.14 016 015 020 0122 0.24 025 028 F . ,i__-;.

Fig. 2. Splitting up the resistance of the ship without bulb.

The lines of the basic ship are given in figure 3a.

The bulbs investigated on the ship model were

based on a sphere located in front of the ship. The

ship and the sphere were connected in such a way

that the original hull form was maintained as

much as possible. On the other hand, care was

taken that boundary layer separation was avoided.

This procedure leads to ship lines, as given in the

figures 3b and 3c. These bow shapes deviate

strongly from conventional bulb forms. The

pro-cedure followed provided the advantage that the

effect of a bulb could be analysed as closely as

possible. In the first instance bulbs of various

sizes were investigated on the basic hull form. The

parameters chosen were the location a and the

radius r of the sphere. The centre of the sphere

was always in the longitudinal plane of symmetry

Length between perpendiculars L m 150.00

Length of the submerged part of ship En 152.31

Moulded breadth B m 22.00

Draft at F.P. m 7.16

Draft at A.P. m 8.08

Mean draft Tin m 7.62

Immersed volume moulded D m3 15593

Block coefficient DILBT 0.6202

Midship section coefficient 0.9748

Wetted area without appendages m2 3922

Wetted area with appendages m2 3955

Displacement in seawater (y= 1.025) LI

ti,

15731

Location of centre of buoyancy aft

of .121, 2.82

Angle of entrance of water lines

for Tv= 7.16 m a/2 11 1 11. 1

//

-I 1 m IL

(7)

0 AP

Fig. 3a. Lines of the basic ship.

FEEL

Fig. 3f. Lines of the ship without bulb and with angle of

.:ntrance a/2 of 15 degrees.

201

Fig. 3b. Lines of the ship of figure 3a, fitted with a bulb

based on a sphere: 100r/L 2.00 and alL = 0.

Fig. 3d. Lines of the ship without bulb and with an angle

of entrance a/2 of 7 degrees.

FRO REEL

Fig. 3c. Lines of the ship of figure 3a, fitted with a bulb based on a sphere: 100r/L 1.667 and alL = 0.

ELL

Fig. 3e. Lines of the ship of figure 3d, fitted with a bulb based on a sphere: 100r/L = 1.667 and alL - 0.

201,

0

1,0 XEEL

Fig. 3g. Lines of the ship of figure 3f, fitted with a bulb

based on a sphere 100r/L 1.667 and alL = 0.

=

(8)

of the ship and the lowest point of the sphere on

the base line. The most favourable location of the

sphere was determined first. In, this optimum

posi-tion bulbs of various diameters were investigated.

As a logical continuation to this investigation

attention was paid to small changes in the shape.

of the foremost part of the ship. It might be

ex-pected that a change of the hull form changes the

optimum size of the bulb as well. The quantities

determining the shape of the ship's foremost

part are:

the slope of the curve of sectional areas

the angle of entrance of the water lines

the shape of the bow sections.

If one of these quantities is changed, the others

change also in general. Therefore a systematic

re-search to obtain an optimised bulb ship requires

more extensive experiments. As already mentioned

this was not the purpose of the investigations

re-ported here. These were restricted to a systematic

variation of the angle of entrance of the water

lines. The curve of sectional areas could be kept

almost equal in all cases because the shape of the

bow sections was changed. A reduction of the

angle of entrance gave more U-shaped sections,

an increase more V-shaped ones than those

of

the basic ship.

The result is given in the figures 3d, 3e, 3f and

3g. This procedure has also the advantage that

the largest part of the ship and the centre of

buoyancy are unchanged, so that the interaction

between bulb and bow is set up as clearly as

possible. The variations thus far discussed are

tabulated in table II. Some further investigations

were carried out as to the shape of the

bulb. For

this purpose the ship was fitted with a faired bulb

of conventional shape. Here the area of the

con-ventional bulb section at the fore perpendicular

was equal to that of the spherical bulb

which

proved to be most favourable on the basic ship.

The complete research was carried out on

models to a scale of 1

:

28. Resistance and

self-propulsion tests were conducted with all models

The resistance and power of the model were

extrapolated to full scale using the Schoenherr

mean line with a roughness correction of

0.00035.

No corrections were made for scale effect in

wake and additional resistance due to sea waves

or wind. The characteristics of the screw

used for

the self-propulsion tests are given in table III.

The displacement of the ship was unavoidably

changed when a bulb was fitted as described

above.. However, these changes were small. Their

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(9)

--Table III. Propeller characteristics.

influence may be partially eliminated by using

the displacement for the calculation of the

dimen-sionless resistance-, power- and speed coefficients

0,

0 and V5[4, respectively.

3

_{Theoretical approach}

In this section an effort is made to determine the

diameter of the sphere, giving a maximum

reduc-tion in resistance. The first part of the calculareduc-tions

are similar to those given by INUI [1 1] .

The procedure is worked out further so that a

formula is obtained which gives an approximate

value for the optimum diameter as a function of

some parameters determined by the ship.

According to HAVELOCK [3], [4] the free wave

pattern of a ship which is travelling at a constant

speed is given by:

+2s/2

sec20

I f (0) sin [(x'cos 0 -ky'sin 0)

F2 dO . . (eq. 1) --;42

The wave resistance of the ship is given by:

,71/2

R Q172 {f (0) }2cos30 dO (eq. 2)

2

The diagrammatic representation and the set of

axes used is given in figure 4.

F PP

Fig. 4. Diagrammatic representation of the submerged part of the ship and the bulb. The origin of the set of axes

is located on the water line at the fore perpendicular.

The symbols are explained in the List of

nota-tions. The function f (0) is fixed by the shape of

the ship.

It is assumed that the hull may be represented

by a source distribution on the longitudinal plane

of symmetry. The strength of the source

distribu-tion is given by:

m(x' ,z') -= b sin 172 (1 -

x')I

(eq. 3)

.2

=

+712 Q (0) sin --;a2 -T

tail AREA WITH SOURCEDISTRIBUTION

OF STRENGTH rn 9111{ (I- A

FPP APP

(b) THE SHIPFORM

Fig. 5. Scource distribution and shipform taken from reference [11] .

The ship form described by (eq. 3) is shown in

figure 5. Since the source distribution is

repres-ented by an analytical function, the endings of the

ship contribute mostly to the wave resistance. A

proof is given by INui [11]. The wave pattern

generated by the bow and its contribution to the

wave drag are:

=

P(0) sin [(x'cos

0 - y 'sin 0)

sec20] dO

(eq. 4)

F2

;c2

RF =

0172 {P(0)}2cos30 dO . . . . (eq. 5)

Where:

P(0) =

b "c'iLF2)sec20 7( F2 sec20 F4

A doublet in

(

a'

,

0, f') generates a wave

system, represented by:

7,2

ri

(X' +a') cos 0 ± y'sin 0}

sec21 dO

F2 (eq. 7) . . (eq. 8) Q (0)

=

V L2F4

sec40f se00/ LP

. . (eq. 6)

Here M is the strength of the doublet.

The resistance of the combination bow and

doublet is minimum if the waves generated by

these two bodies are as low as possible. A trough of

the wave system of the doublet then coincides with

a crest of the bow wave system.

Diameter 6230 mm

Pitch at blade root 4509 mm

Pitch at blade tip 5646 mm

Pitch at 0.7 radius ratio 5698 mm

Developed blade area ratio 0.580

Number of blades 4 A PP

=

.

CF(xV)

+n/2 . ..

(10)

From (eq. 4) and (eq. 7) follows that this takes

place if:

a' = 0

(eq. 9)

This requirement cannot be applied directly to

actual ship forms. It holds only for the considered

ship form, which has a vertical stem and may be

represented by a simisoidal source distribution.

For a ship which is represented by another source

distribution the optimum location of the doublet

is somewhere else. A second factor of importance

is that the optimum distance a is also affected by

viscous effects and these are not taken into account.

The resistance of the bow and the doublet

to-gether is:

as/2

RFB = ne V2

f {

P(0)

Q(0) rcos30 d0 (eq. 10)

This resistance will be small if {P(0)Q(0)1 is

small.

Imo' [11] shows that P(0) and Q(0) are

dom-inant for low values of 0. Therefore, the required

strength of the doublet is derived from:

P(0) = Q(0)

(eq 11).

In an unbounded medium the flow round a

dou-blet

is

identical to that round a sphere. The

;elation between the strength of the doublet and

the radius of the sphere is given by:

M = 270 V

(eq. 12)

From (eq. 10) and (eq. 11) it follows that :

)

b F6 ef/LF. - TILP

\LJ

2t

I 2F4

In MICHELL'S theory [1] the relation between the

geometry of the ship and the source distribution

is given by:

nz(x',z') -= 2

(

ax'

At the bow this results in:

m(0,z') = b = 2 (

ax'

the amplitude of the source strength is

twice the angle of entrance of the water

that (eq. 13) gives:

(r-)3 L 2-.7-.7

F6 efi 1(

Tin

1_,2F4

The main conclusion drawn from (eq. 16) is that

there is a distinct relation between the bulb size,

the angle of entrance of the water lines and the

ship's speed. The physical interpretation of (eq. 16)

must be derived from experiments. As already

. . . (eq. 13) (eq. 14) (eq. 15)

equal to

lines, so

. . (eq. 16) 3 00 2 50 200 0 1.50 1 00

z

0.14 016 018 0.20 0.22 0.24 0.26 0,28 0.30 F V 161:

Fig. 6.

Required radius of the sphere, calculated with

(eq.

16) for the ship. particulars of which are given in

table I and according to figure 3a (a = 0).

mentioned, the optimum location of the sphere

should be determined experimentally as well.

Application of (eq. 16) to the basic ship leads to

figure 6. It shows that the bulbs needed for

elim-inating the bow wave system are bigger than those

applied at present.

4

Location and diameter of the sphere

The effect of a variation of the distance a from the

fore perpendicular to the centre of the sphere is

given in the figures 7 and 8. The curves show that

the optimum location of the sphere centre is in the

neighbourhood of the fore perpendicular. It

is

noted that the model was not tested in the design

condition but at an average loading condition

under which the ship was supposed to sail in

ser-vice. So the optimum location of the sphere found

by experiment is slightly forward of the theoretical

optimum. Moreover, this optimum moves

for-ward with increasing speed. This dependence

must be due to viscous effects.

In the speed range of interest for the ship,

3.6 < Vsltr° < 4.0, the optimum position of the

sphere is bounded by:

0< 100 al L < 0,5

In the speed range considered a small shift of the

sphere in the neighbourhood of the fore

perpendic-ular has only a minor effect on the required power.

The effect of a variation of the diameter of the

sphere was investigated with bulbs based on

10 12 14 16 18 20 22 Vs ( knots ) I . So a 1 I

(11)

0 0.9 0.8 1.3 2 10 0.7 -1.5 0 1.5 100

Fig. 7. Effect of the location of the sphere on resistance.

spheres, having the centres on the fore

perpendic-ular.

The application of such a bulb increased the

wetted surface of the ship. For spherical bulbs

with radii given by 100r/L = 2.00 and 100r/L

--1.667 the increment is

2.5 and 3.5 per cent.

respectively. The frictional resistance increases by

the same percentage in the first instance, since the

influence of the increased length on the frictional

coefficient is small..

For a further analysis, following LAP-TROOST

[12], the residuary resistance is subdivided into

the wave resistance and a part depending on the

Reynolds number: As a measure for the latter

part the quantity 4 log A is used. This is the shift

Table IV. Measured log A values, for

the ship forms

investigated.. 0.5 16 IL a22 17 18 (knots) 0.24 19 0.26 .20 0.28 F

Fig. 9. Effect of the application of a bulb ion wave

resistance. 22 0130 1 t r 1 10,0- =2.00_L 1 _

d

vs 4 AV6 -1

470

I( .,,

Am

ol ...MOM 36

without bulb I log A = 0.45

100r/L = 2

100a/L= 6.0

log A = .0.55 -2 100r/L = 2 , 100a/L = 3.0 log A = 0.50

, , 100r/L = 2 l'00a/L = 1.5 log A = 0.50

.i.: 100r/L = 2 I 1100a/L ,--- 0 log A = 0.50

.:-.3 100r/L = 2 1 I00a/L =-1.5 I log A = 01.45 100r/L = 1.667 100a/L = 0 L log A = 1145 ill WITH BULB a

\

k

,

\

100_.2.00 \

\

, \

\

.._

\

. \ \

\

\\ '\

,\

.

...--'

/

I / `,...,---

-..._,---\

.

/

'...,,,...,

\

. \100 r ..il '6 67 1 L N1,.,_ 1 1 1 1 I 1 1 1

t

rL 100 - =2.00

Ilia

;

14 rAill

04i0111

AV/II

_{r " r}

1=

3 6 1 «1.5, .30 .4 5 .6,0 100

8. Effect of Idle location of the sphere on required power.

.30 «4 5 1.1 1 4.0 0

/

-15 0 . Fig. 21 11 V5

(12)

5 cr 12 0 5.0 0.5 a 'WITHOUT BULB

WITH BULB 0 100-E 2,00

WITH BULBt = loa.f 1.667

30' 36 40'

of the txtrapolatorline along the axis, indicating

the logarithm of the Reynolds number. This

quantity takes into account the viscous part of

the residuary resistance. The measured values of

A log A for the investigated ship forms are given in

table IV. The influence of the differences between

these values

is

small. The wave resistance is

changed considerably by the application of a bulb.

As shown in the figures 9 and 10, the reduction

of the wave resistance is very large in a certain

speed range. At low speeds however, the wave

resistance is changed in an unfavourable way,

apparently the bow wave is "overcan.celled" then.

The biggest sphere gave the largest reduction at

high speeds, however, the lower speed range in

which the bulb has an unfavourable effect extends

to a higher speed then.

The total effect of the above aspects is illustrated

in figure 11. Figure 12 shows that when the resist,

ance is reduced, the propulsive efficiency increases

generally. This may partially be due to the higher

efficiency of the propeller at a lower loading.

5 Interaction between bow and bulb

'This aspect was investigated by varying the angle

C-I

i.0 0.9 ;7' 081 71

Fig. 110. Effect of the .application of a bulb on wave Fig. 11. Effector the applkation of a bulb on total

resistance, resistance.

of entrance of the water lines of the basic ship. It

appeared to be possible to keep the curve of sectional

areas constant for the hull forms discussed in this

0,90 0'80 0.70 'O. 60 0.50 3 0 .3,5 40 5 1

--

WITHOUT 1 BULB Ta...-=0 ;00'i - 2.00

t

=0 Z MO

i

=1)567 I 7 / i .1 --- WITH BULB WITH BULB I It / / , I I 1 / -g >^ r I t I -i --.... N., _.. 1 5... .

irliv

_/

1 ,

---Ilk

_ - WITHOUT 1 BCILBi BULB It.-= 0 ,1 10 a BULB i=.-0 : 1 O0 0-ir: - 2O,0 lc.1.667

._._ WITH

WITH I ' , 30 3,5 - 4.0 r_k_ dye

Fig. 12. Effect of the application of a bulb on propulsive.

efficiency. pqs Ave 1 5 0 = 0 ;

(13)

0 16 17 18 19 Vs (knots) 0.22 0.24 0.26 _ F V VTI---0.28 0730

Fig. 13a. Effect of the angle of entrance of the water lines, on wave resistance.

section. The figures 13a and 14a show that a

re-duction of the angle of entrance reduces the wave

resistance, and thus the total resistance. This is in

agreement with the general experience that

U-shaped sections in the forebody of the ship are

more favourable than V-shaped sections.

How-ever, an increase of the angle of entrance of the

ship had only a minor effect on the resistance in

this case.

The three hull forms Idiscussed here were fitted

with spherically shaped bulbs. The spheres had

their centres on the fore perpendicular. The

fi-gures 13b, 13c, 14b and 14c show that also the

experiments indicated a relation between the

dia-meter of the sphere and the angle of entrance of

the water lines. Each of the two investigated

dia-meters gave the most favourable results in

combi-nation with a certain angle of entrance of the

water lines. The experiments indicated also that

Fig. 13b.

Effect of the angle of entrance of the water

lines on the resistance of the ship with bulb rIL = 1.667.

Fig. 13c. Effect of the angle of entrance of the water lines on the resistance of the ship with bulb rIL =

§ 2.0 10 '20 .19. .20 0.26 y ' a, -,-L t-

--

- it -WITH BULB = 0 .; 100" =T.667 1 ...

\

_\

\ \

_A\

-\ \

\

N N

\

.

/

_ii

/

""="--...

Ill

11 I , WITHOUT BULB. --... _2-15° . - ,---- _-D1 it _t _li 1 WITH BULB' "100TI: =2.00 \ 1 1 \ \ \ ' \ . \ \

\=i5°

.4,... . 7° 1 \ _1.10 'N. 0. 1 ...

\

\ i t t II I II 16 17 18 19 20 21 22 Vs ( knots ) 0.22 0.24 0.26 .0 28 0.30 F V gl_ 17 18 V5( knot s) 0.22 0.24 F 20 21 22 21 22. 02'8, 0.30 1 5 I-D 0 CL 10 WI VY 1 05 20

=

= 2.00. 0 16 V L

\

_\

\

I 0

(14)

Fig. 14b. Resistance of the ship forms with bulb and

without bulb having an angle of entrance ofaI2 11 degrees.

1

Vs

6v6

Fig. 14a. Resistance of the ship forms without bulb and with entrance angle variation,

Fig. 14c. Resistance of the ship forms with bulb and without

bulb having an angle of entrance of a/2 = 11 degrees.

0.8

lb

09 .0.8

it

1 0 0.9 06

/

L I 100 r =1.667'7 I " 1

/

)

WITHOUT BULB 2.11° 2 2.15°2 > , ....II° 4 (3 WITHOUT BULB 1 8 1.7

i

"

a.

,.-..-.11 __....-4 ....--_....-

,

... ..."_-.--- -15° ---I 7° I I _ 1 WITH 'BULB - 0 =2.0 .,,

.

> , 0 ,, 100 I L II r L , ./.

/

>

/

/I

'N, 7° -...

.,

--..._ _ \ 11°'

\\\

I > ... >.

/

./ .11 WITHOUT BULB 0- 35 4,0 Vs 30 35 40 61/6 30 40. CD 0.

=

06 35

=

07

(15)

0.90 0.80 0.70 050 F-0.80 0.70 050

Fig. 15b. Propulsive efficiency of the ship forms with bull}

and without bulb having an angle of entrance of a/2 =- 11

degrees., 090 080 070 0,60 0.50

the optimum diameter is smaller than prescribed

by (eq. 16) of section 3 and illustrated in figure 6..

The relation between the bulb diameter and the

speed of the ship found experimentally is not as

important as was found theoretically.

The figures 15a, 15b and 15c show the influence

of entrance angle- and bulb diameter variation on

propulsive efficiency.

Experience indicates that if the angle of entrance

is reduced, the bow wave system tends to move

aft. So the optimum location of the sphere on

which the bulb is based is expected to move aft

as well.. The curves of figures 16a and 16b do

not confirm this. This leads to the supposition

that the angle of entrance of the water lines has

only a minor effect on the optimum location of

the sphere.

A more extensive investigation into this aspect

should be performed, however.

6 Application of a bulb versus a

modifica-tion of principal dimensions

The application of a bulbous bow of the size and

shape discussed still meets with some opposition,

because of practical difficulties encountered in

running the ship.

° - m I WITH auLB 00

f= o

,,

loo

EL-= 2 ..-.-, g.ii° WrTHOUT BULB 7 ' =11° 2

i

...-\, I 15- .11,,,..

\

_\

1 I II I WITHOUT BULB 1 cc .,,, 2 15° !I

--...

-,.._ i WITH BULB a Oi T

'' T

r .1.6 6.7 >1" BULB a T . /5c. -. CiC=11 WITHOUT 3 0 3.5 40 35 4.0 Vs Avi6, p1/6

Fig. 1115a. Propulsive efficiency of the ship forms without Fig. 15c. Propulsive efficiency of the ship forms with bulb and

bulb, without bulb having an angle of entrance of a/2 =. 11 degrees.

30 3 4.0 090 060 30 Vs

=

(16)

z

10 09 &0.8 0.7 06 vs

Fig. 16a. Effect of the location of the sphere on the resist-ance of ship forms with bulb.

Therefore it

is interesting to investigate what

gains could be achieved by slight modifications

in the length, the beam and the block coefficient

of the ship.

Another aspect discussed in this section is the

effect of a bulb of the same size but of another

shape. Therefore a bulb was tested resembling the

more conventional bulb shapes. Its sections and

water lines were more faired than for the bulb

based on a sphere discussed previously.

The basic ship was the same as that used for the

former bulb tests. The ship with conventional bow

is designated "ship A". A bulb, based on a sphere,

was fitted to "ship A". On "ship B" the radius of

the sphere is 2.0 per cent. of the ship's length and

on "ship C" 1.667 per cent. (see table V). The

reductions of the required power obtained in this

way are compared with the gains obtained by

slight modifications of the principal dimensions.

Since the application of a bulb in the case of

"ship B" increased the length of the submerged

part of the ship by 2 per cent, it was obvious to

in-vestigate the effect of an increase in length of "ship

0 GO 080 0.70

II

La 060 0.50 30 3.5 vs 40

Fig. 16b. Effect of the location of the sphere on the propul-sive efficiency of ship forms with bulb.

A" by the same percentage, combined with a

corresponding reduction of the block coefficient.

For this analysis the diagrams of LAP [13] and

GERTLER [14] were used. The results of both

analyses were in good agreement. (See table VI).

The effect of an increase of the beam was

in-vestigated experimentally. Therefore, tests were

carried out with a ship form ("ship D") having

the beam increased by four per cent. in regard to

the basic "ship A", and a correspondingly reduced

block coefficient.

In order to retain the same metacentric height

above the centre of buoyancy for both ships, the

moments of inertia of the conctruction water line

relative to the longitudinal plane of symmetry

were kept the same. This resulted in more

U-shaped sections. "Ship E" was composed of "ship

D", fitted with a bulb of the same size as "ship B".

Finally experiments were carried out with a model

of a ship fitted with a bulb of conventional shape.

The cross section of the bulb of this "ship F" at the

fore perpendicular equals that of "ship E", viz. 16.7

per cent. of the midship section, a considerably

larger area than used for conventional bulbs at

present. A bow view of the "ship E" and "ship F"

is shown in the figures 17a and 17b respectively.

The ships mentioned above were designed for

a draft of 8.50 m. However, the resistance and

WITH BULB -/ / i / z -5.1= 7°1002:=1.667_L .:. i 1 i 1 1 i R > I I i I I 1 1 t 1. 100! .,,

.

3 > / t51 / / i / /

/

----

mo.0

L WITH BULB 2 100 1 =1667L

/oot.-/.5

. _. 1 > > 100-!. 0 -...

\

30 35 4.0 = 7°,

(17)

20

A B C D E F

without with with without with with

Ship particulars: bulb bulb bulb bulb bulb bulb

Length between perpendiculars L m 150.00 150.00 150.00 150.00 150.00 150.00

Length of the submerged part of ship m 152.31 155.84 155.34 152.49 156.03 156.46

Moulded breadth B m 22.00 22.00 22.00 22.86 22.86 22.86

Draft at F.P. T. m 7.16 7.16 7.16 7.16 7.16 7.16

Draft at A.P.

Ta m

8.08 8.08 8.08 8.08 8.08 8.08

Mean draft

T. m

7.62 7.62 7.62 7.62 7.62 7.62

Immersed volume moulded D ma 15593 15880 15801 15699 16030 15958

Block coefficient --- DILBT 6 0.620 0.595 0.611

Midship section coefficient fl 0.975 0.975 0.975 0.975 0.975 0.975

Wetted area without appendages ma 3922 4064 4031 3931 4077 3997

Wetted area with appendages ma 3995 4136 4104 4004 4149 4070

Displacement in sea water (y = 1.025) 4 t1016 15731 16021 15941 15838 16172 16099 Location of centre of buoyancy aft of 1/21,

Angle of entrance of water lines at 7',. = 7.16 m

m a/2 2.82 110 1.42 110 110 2.82 11" 9.75 11 8'

Bulb particulars: _{based on based on} _{based on} _faired

Shape of bulb a sphere a sphere a sphere

Radius of the sphere in per cent. of L % 2.000 1.667 2.000

Location of the centre of the sphere in

longitudinal direction at F.P. at F.P. at F.P.

100>< max.bulb section/midship section `)/O 17 2 12.0 16.7 16.7

Fig. I8a. Lines of ship D with increased breadth and reduced block coefficient with regard to ship A. SWF` 0

Fig. I7a. Model of ship E. Fig. 17b. Model of ship F.

(18)

0 AP

A7 PEPL

Fig. 18c. Lines of ship F fitted with a large bulb of conventional shape.

Table VI. Reduction of resistance in percentages at constant immersed volume.D= 13593 ma.

Table VII. Reduction of required power in percentages at constant immersed volume.

D -

15593 ma.

PP

Fig. 18b. Lines of ship E composed of the lines of ship C fitted with a bulb based on a sphere.

Speed knots 18 18.5 19 19.5 20 20.5 21 21.5 22

\ pplication of bulb, based on a sphere with

radius 3 m

Application of bulb, based on a sphere with

(),,, 2.5 2.1 1.5 2.2 5.3 9.7 14.4 16.6 17.6

radius 2.5 m 0/ 5.7 4.0 2.8 4.2 6.8 10.1 11.0 10.9

Length of submerged part of the ship increased

by 2° +reduction of block coefficient by 2%

(mean value of estimates with Lap and Gertler)

.,,, 0.8 1.0 1.9 3.5 5.7 7.9 9.8

Beam of the ship increased by 4% + reduction

of block coefficient by 4% °'/0 0.7 -0.2 -1.0 -0.6 1.6 4.2 7.3 8.9 10.3

Beam of the ship increased by 4%H- reduction

of block coefficient by 4% + application of bulb

based on a sphere with radius 3 m

Oc -6.2 -5.8 -4.6 -1.5 4.4 11.9 18.6 22.0 23.6

Application of a faired bulb with a cross section

at F.P. of 16.7% of midship section area

% -12.9 -12.3

-9.4 -3.4 5.5 15.4 23.0 27.1 20.;

Speed knots 18 18.5 19 19.5 20 20.5 21 21.5 22

Application of a bulb, based on a sphere with

radius 3m

Application of a bulb, based on a sphere with

3.7 4.6 4.7 5.7 8.9 13.6 17.8 20.6 21.7

radius 2.5 m o _8.0 _7.5 _5.9 _5.3 _5.7 _8.3 _11.3 _13.5 _15.2

Beam of the ship increased by 4% + reduction

of block coefficient by 4% r, 1.6 1.4 1.1 1.4 2.0 3.4 5.6 6.9 10.4

Beam of the ship increased by 4% r reduction

of block coefficient by 4% + application of a

bulb based on a sphere with radius 3 m

-3.2 -2.1 -0.9 2.9 8.7 15.5 21.8 26.0 29.1

Application of a faired bulb with a cross section

at F.P. of 16.7% of midship section area ° ,0

-9.8 -12.8 -10.5

-4.2 5.2 16.0 24.0 29.7 33.7

I

'

(19)

propulsion tests were carried out at a reduced draft,,

which was the average value to be expected for

the ship in service as already explained in section

4. A survey of the main characteristics of these

ships at this reduced draft is given in table V. The

body plan, stem and stern lines of some of these

ships are given in the figures 18a, 18b, and 18c.

The basic "ship A" has a block coefficient

which makes the ship suitable for a service speed

of 19.5 knots ( Vs/z1v.

3.90). So the speed range

of interest for this ship is between 18 and 20 knots.

When judging the measurements, special attention

will be paid to the performance in this speed range.

Tables VI and VII, in which the results are

summarised show that an increment of the length

by two per cent. is very effective. However, the

application of a bulb of proper size reduces the

resistance even more effectively.

Figures 19,20 and the tables VI and VII indicate

that increasing the beam of the ship by four per

cent., combined with a corresponding reduction

of the block coefficient, was clearly less effective.

than the application of a bulb.

For the ship with increased beam and reduced

block coefficient, combined with a bulb, the re

10 09 0 !CLIO_

II

IUJ 0 0 9 08 07 06 05 0 -1 -DI. ) , I I , SHIP E C ----.. ----,--.. --- -...._:--,..

ii

5, .-1 D"..._-1 D 1 1 II I , 1 SHIP o il A 1

i

i 1 I 7 / / 1I 1 1 / / I 1 3 14h111/ I i PP _

gIIIIIPIIIIIW.-.

...,.. -___

-7---r

ffitia, tr

Pr

....->c,..."

,--.7"-1 35 4 0, Vs

Fig. 19. Resistance of the ships A, B C D, E and F.

35

-

4a

Vs AVa

Fig. 20. Propulsive efficiency of the ship A, B, C, D,: E and F.

duction of the resistance was very important.

However, this reduction is less than the sum of the

reductions each of both changes would cause

separately.

The reason is that a sharp ship encounters less

wave resistance than a full ship. So a bulb will he

less effective when applied to a sharp ship.

Figures 19, 20 and the tables VI and VII show

also that the shape of the bulb appeared to be very

important. The fitting of a "faired bulb", a shape

resembling that of conventional bulbs, changed

the resistance curves of the ship considerably. The

ship seemed to have become suitable for a 1.5 to

2 knots higher service speed. This is contrary to

the effect of the bulbs based on a sphere.

The propulsive efficiency of the ships considered

behaved in the same way as mentioned before,

viz., if at a certain speed a reduction of the

resist-ance is attained, the propulsive efficiency improved

slightly. This rnay partially be due to the higher

efficiency of the propeller when the loading is

decreased.,

It may be remarked that in a previous section of

this report the effect of changes in the shape of the

foremost part of the ship was already discussed.

N

30

(20)

Table VIII. Speeds to be attained on trials with 000 allowance.

7

Conclusions

If a given ship which is to navigate in a certain

speed range has to be fitted with a bulb based on

a sphere, the most favourable location and

dia-meter of the sphere are to be determined

exper-imentally. A bulb obtained in this way may be

very effective. Even at rather low speeds it

affects

the required power favourably.

A bulb of proper size reduces the wave

resist-ance considerably: viz, by about 25 to 50 per cent.

The angle of entrance of the water lines

prob-ably affects the optimum location of the sphere, on

which the bulb is based, only slightly. The

theo-retical analyses and experimental investigations

indicated a relation between the angle of entrance

of the water lines and the diameter of the sphere.

A reduction of the angle of entrance of the water

lines reduced the optimum diameter of the sphere

at equal speeds.

Slight increments of the length and the beam

of the ship combined with a corresponding

decre-ment of the block coefficient appeared to be less

effective than the application of a bulb of proper

size. A combination of a change of the ship's

principal dimensions and the application of a bulb

based on a sphere gave, as could be expected, the

largest reduction of the propulsive power.

The application of a faired bulb, a shape

resem-bling the conventional bulbs, but whose cross

section at the fore perpendicular equals the area of

one of the spheres, changed the character of the

resistance curve of the ship considerably.

Its resistance and propulsion curves acquired

the character of those of a ship with a 1.5 to 2

knots higher service speed. As an illustration of the

influence of a spherical bulb, the tables VIII and

fable IX. Speeds to be attained under service conditions with 23% allowance.

WITHOUT BULB

BULB t . 0 ; 100f. 1.66

__--WITH 7

- --

WITH BULB 1.-. 0 ; 100i. 2.00

BOW

ev.-'7.;

/

.7/ /

_/

7/

.ZZ

_/

7 '

.

/

./"/

zz

/. /

/

_./.

/

STERN

.

---'1 __-1 I I Power absorption DHP 10,000 12,000 14,000 16,000 18,000

Ship without bulb knots 18.9 19.6 20.1 20.5 20.7

Ship with bulb based on a sphere with radius 3 m knots 19.1 19.9 20.4 20.9 21.3

Ship with bulb based on a sphere with radius 2.5 m knots 19.2 19.8 20.3 20.7 21.0

Power absorption D HP 10.000 12,000 14,000 16,000 18,000

Ship without bulb knots 17.8 18.8 19.5 19.9 20.2

Ship with bulb based on a sphere with radius 3 m knots 18.0 19.0 19.7 20.2 20.6

Ship with bulb based on a sphere with radius 2.5 m knots 18.2 19.1 19.7 20.0 20.4

15 16 17 18 19 20 2 22

Vs_(knots)

0.20 0.22 v 024 0.26 0.28

F

Fig. 21. Sinkages of the ships A, B and C.

As noted, a reduced angle of entrance of the water

lines resulting in more U-shaped sections, gave an

interesting reduction of the resistance of the ship.

However, the reduction thus obtained was also

smaller than when a bulb of proper size was fitted.

For completeness the influences of a bulb on

sinkage of the bow and stern have been measured

and presented in figure 21.

4.0 3,0 In 0 2.0 1.0 1 .1

(21)

IX indicate the speed that the ship considered will

have on trials and under service conditions.

Acknowledgement

The research reported here has been made possible

by the Netherlands' Research Centre T.N.O. for

Shipbuilding and Navigation. The theoretical

contribution is due to ir. W. P. A. Joosen. The

experimental part of the project has been carried

out under the supervision of Mr. J. Kamps.

References

MICHELL, J. H., The wave resistance of a ship.

Philoso-phical Magazine, Vol. 45, 1898, p. 106.

TAYLOR, D. W., Influence of the bulbous bow on resistance. Marine Engineering and Shipping Age,

September 1923.

HAVELOCK, T. H., Wave patterns and wave resistance.

Trans. I.N.A., Vol. 75, 1934, p. 340.

HAVELOCK, T. H., The calculation of wave resistance.

Proc.

of the Royal Society, London, England.

Series A, Vol. 144, 1934, p. 514.

WIGLEY, W. C. S., The theory of the bulbous bow and

its practical application. Trans. N.E. Coast

Institu-tion of Engineers and Shipbuilders, Vol. LH, 1935-6, p. 64-88.

LINDBLAD, ANDERS, Experiments with bulbous bows.

The Swedish State Shipbuilding Experimental Tank, Goteborg, Publication no. 3, 1944.

LINDBLAD, ANDERS, Further experiments with bulbous

bows. The Swedish State Shipbuilding Experimental Tank, Goteborg, Publication no. 8, 1948.

SAUNDERS, HAROLD E., Hydrodynamics in Ship design,

Vol. I and II. Published by the S.N.A.M.E., New

York, 1957.

'NUL TAKAO, TETSUO TAKAHEI and MICHIO KUMANO,

Tank experiments on the wave making characteris-tics of the bulbous bow. Part I.

TAKAHEL TETSUO, A study of the waveless bow. Part. I.

The references [9] and [10] are parts of the publication entitled: _Three recent papers by Japanese authors on the

effect of bulbs on wave making resistance of ship".

Translated by MICHELSEN and KIM, University of Michigan,

Dept. of Naval Architecture and Marine Engineering, Ann Arbor, Dec. 1961.

INUI, TAKAO, Wave making resistance of ships. Trans.

S.N.A.M.E., 1962, Vol. 70, p. 283-353.

LAP, A. J. W., Fundamentals of ship resistance and

propulsion. Part A: Resistance. Publication no. 129a. of the Neth. Ship Model Basin.

also in Intern. Shipbuilding Progress 1956 and 1957. LAP, A. J. W., Diagrams for determining the resistance of single-screw ships. International Shipbuilding

Progress, 1954.

GERTLER, MORTON. A reanalysis of original test data

for Taylor standard series. David Taylor Model

Basin, Report 806.

.5.

(22)

The determination of the natural frequencies of ship vibrations (Dutch).

By prof. it H. E. Jaeger. May 1950.

Practical possibilities of constructional applications of aluminium alloys to ship construction.

By prof. it H. E. Jaeger. March 1951.

Corrugation of bottom shell plating in ships with all-welded or partially welded bottoms (Dutch).

By prof. ir H. E. Jaeger and ir H. A. Verbeek. November 1951.

Standard-recommendations for measured mile and endurance trials of sea-going ships (Dutch).

By prof. it J. W. Bonebakker, dr it W. J. Muller and it E. J. Diehl. February 1952.

Some tests on stayed and unstayed masts and a comparison of experimental results and calculated stresses (Dutch).

By it A. Verduin and it B. Burghgraef. June 1952.

Cylinder wear in marine diesel engines (Dutch).

By ir H. Visser. December 1952.

No. 8 M

Analysis and testing of lubricating oils (Dutch).

By ir R. N. M. A. Malotaux and ir J. G. Smit. July 1953.

No. 9 S

Stability experiments on models of Dutch and French standardized lifeboats.

By prof: ir H. E. Jaeger, prof. ir y. W. Bonebakker and y. Pereboom, in collaboration with A. Audige. October 1952. No. 10 S On collecting ship service performance data and their analysis.

By prof. it J. W. Bonebakker. January 1953.

No. 11 M The use of three-phase current for auxiliary purposes (Dutch).

By ir y. C. G. van Wijk. May 1953.

No. 12 M Noise and noise abatement in marine engine rooms (Dutch).

By "Technisch-Physisthe Dienst T.N.0.-T.H." April 1953.

No. 13 M Investigation of cylinder wear in diesel engines by means of laboratory machines (Dutch).

By ir H. Visser. December 1954.

No. 14 M The purification of heavy fuel oil for diesel engines (Dutch).

By A. Bremer. August 1953.

No. 15 S Investigation of the stress distribution in corrugated bulkheads with vertical troughs.

By prof. ir H. E. Jaeger, it B. Burghgraef and I. van der Ham. September 1954.

No. 16 M Analysis and testing of lubricating oils II (Dutch).

By it R. N. M. A. Malotawc and drs J. B. Zabel. March 1956.

No. 17 M The application of new physical methods in the examination of lubricating oils.

By it R. N. M. A. Malotaux and dr F. van Zeggeren. March 1957.

No. 18 M Considerations on the application of three phase current on board ships for auxiliary purposes especially with

regard to fault protection, with a survey of winch drives recently applied on board of these ships and their

in-fluence on the generating capacity (Dutch).

By ir J. C. G. van Wijk. February 1957.

No. 19 M Crankcase explosions (Dutch).

By it 3. H. Minkhorst. April 1957.

No. 20 S An analysis of the application of aluminium alloys in ships' structures.

Suggestions about the riveting between steel and aluminium alloy ships' structures.

By prof. ir H. E. Yaeger. January 1955.

No. 21 S On stress calculations in helicoidal shells and propeller blades.

By dr ir J. W. Cohen. July 1955.

No. 22 S Some notes on the calculation of pitching and heaving in longitudinal waves.

By it 3. Gerritsma. December 1953.

No. 23 S Second series of stability experiments on models of lifeboats. By it B. Burghgraef. September 1956.

No. 24 M Outside corrosion of and slagformation on tubes in oil-fired boilers (Dutch). By dr W. j. Taat. April 1957.

No. 25 S Experimental determination of damping, added mass and added mass moment of inertia of a shipmodel.

By it 3. Gerritsma. October 1957.

No. 26 M Noise measurements and noise reduction in ships.

By ir G. J. van Os and B. van Steenbrugge. May 1957.

No. 27 S Initial metacentric height of small seagoing ships and the inaccuracy and unreliability of calculated curves of

righting levers.

By prof. it 3. W. Bonebakker. December 1957.

No. 28 M Influence of piston temperature on piston fouling and piston-ring wear in diesel engines using residual fuels.

By it H. Visser. June 1959.

No. 29 M The influence of hysteresis on the value of the modulus of rigidity of steel.

By it A. Hoppe and ir A. M. Hens. December 1959.

No. 30 S An experimental analysis of shipmotions in longitudinal regular waves.

By it J. Gerritsma. December 1958.

No. 31 M Model tests concerning damping coefficients and the increase in the moments of inertia due to entrained water

of ship's propellers.

By N. 3. Visser. October 1959.

No. 32 S The effect of a keel on the rolling characteristics of a ship. By ir y. Gerritsma. July 1959.

No. 33 M The application ol new physical methods in the examination of lubricating oils. (Continuation of report No. 17 M.)

By it R. N. Al. A. Malotaux and dr F. van Zeggeren. November 1959. No. 34 S Acoustical principles in ship design.

By it 3. H. Janssen. October 1959. No. 35 S Shipmotions in longitudinal waves.

By it 3. Gerritsma. February 1960.

No. 36 S Experimental determination of bending moments for three models of different fullness in regular waves. By it 3. Ch. De Does. April 1960.

No. 37 M Propeller excited vibratory forces in the shaft of a single screw tanker.

By dr it j. D. van Manen and ir R. Wereldsma. June 1960. No. 38 S Beamlmees and other bracketed connections.

By prof. it H. E. Jaeger and it 3. 3. W. Nibbering. January 1961.

No. 39 M Crankshaft coupled free torsional-axial vibrations of a ship's propulsion system. By it D. van Dort and N. 3. Visser. September 1963.

No. 40 S On the longitudinal reduction factor for the added mass of vibrating ships with rectangular cross-section.

By ir W. P. A. Joosen and dr 3. A. Sparenberg. April 1961.

No. 41 S Stresses in flat propeller blade models determined by the moire-method.

By it F. K. Ligtenberg. June 1962.

No. 42 S Application of modern digital computers in naval-architecture.

By it H. 3. Zunderdorp. June 1962.

No. 43 C Raft trials and ships' trials with some underwater paint systems.

By drs P. de Wolf and A. M. van Londen. July 1962.

No. 44 S Some acoustical properties of ships with respect to noise-control. Part I. By it 3. H. Janssen. August 1962. No. 1 S

No. 3 S

No. 4 S

No. 5 S

No. 6 S

No. 7 M

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in seawater.

By A. M. van Londen. August 1962.

No. 47 C Results of an inquiry into the condition of ships' hulls in relation to fouling and corrosion.

By ir H. C. Ekama, A. M. van Londen and drs P. de Wolf. December 1962.

No. 48 C Investigations into the use of the wheel-abrator for removing rust and millscale from shipbuilding steel (Dutch) Interim report.

By ir J. Remmelts and L. D. B. van den Burg. December 1962.

No. 49 S Distrtbution or (damping and added mass along the length of a shipmodel.

By prof. ir J. Gerritsma and W. Beukelman. March 1963.

No. 50 S The influence of a bulbous bow on the motions and the propulsion in longitudinal waves.

By prof. ir J. Gerritsma and W. Beukelman. April 1963.

No. 51 M Stress measurements on a propeller blade of a 42,000 ton tanker on full scale.

By

it

R. Wereldsrna. January 1964.

No. 52 C Comparative investigations on the surface preparation of shipbuilding steel by using wheel-abrators and the

application of shop-coats.

By ir H. C. Ekama, A. M. van Londen and ir y. Remmells. July 1963.

No. 53 S The braking of large vessels.

By prof ir H. E. Yaeger. August 1963.

No. 54 C A study of ship bottom paints in particular pertaining to the behaviour and action of anti-fouling paints.

By A. M. van Londen. September 1963.

No. 55 S Fatigue of ship structures.

By ir J. J. W. Nibbering. September 1963.

No. 56 C The possibilities of exposure of anti-fouling paints in Curacao, Dutch Lesser Antilles.

By drs P. de Wolf and Mrs M. Meuter-Schriel. November 1963.

No. 57 NI _{Determination of the dynamic properties and propeller excited vibrations of a special ship stern arrangement.}

By ir R. Wereldsma. March 1964.

No. 58 S Numerical calculation of vertical hull vibrations of ships by discretizing the vibration system.

By 3. de Vries. April 1964.

No. 59 M Controllable pitch propellers, their suitability and economy for large sea-going ships propelled by conventional, directly-coupled engines.

By ir C. Kapsenberg. June 1964.

No. 60 S Natural frequencies of free vertical ship vibrations.

By ir C. B. Vreugdenhil. August 1964.

No. 61 S The distribution of the hydrodynamic forces on a heaving and pitching shipmodel in still water.

By prof. ir J. Gerritsma and W. Beukelmart. September 1964.

No. 62 C The mode of action of anti-fouling paints: Interaction between anti-fouling paints and sea water.

By A. M. van Londen. October 1964.

No. 63 M Corrosion in exhaust driven turbochargers on marine diesel engines using heavy fuels.

By prof. R. W. Stuart Mitchell and V. A. Ogale. March 1965.

No. 64 C Barnacle fouling on aged anti-fouling paints; a survey of pertinent literature and some recent observations.

By drs P. de Wolf. November 1964.

No. 65 S The lateral damping and added mass cola horizontally oscillating shipmodel.

By G. van Leeuwen. December 1964.

No. 66 S Investigations into the strength of ships' derricks. Part I.

By ir F. X. P. Soejadi. February 1965.

No. 67 S Heat-transfer in cargotanks of a 50,000 DWT tanker.

By D. 3. yonder Heeden and ir L. L. Mulder. March 1965.

No. 68 M Guide to the application of "method for calculation of cylinder liner temperatures in diesel engines". By dr ir H. W. van Ten. February 1965.

No. 69 M Stress measurements on a propeller model for a 42,000 DWT tanker.

By jr R. Wereldsma. March 1965.

No. 70 M Experiments on vibrating propeller models.

Byit R. Wereldsma. March 1965.

No. 71 S Research on bulbous bow ships. Part II.A.

By prof. dr ir W. P. A. van Lammeren and irJ. 3. Muntjewerf. May 1965.

No. 72 S Research on bulbous bow ships. Part II.B.

By prof. dr ir W. P. A. van Lammererz and ir F. V. A. Pangalila. June 1965.

No. 73 S Stress and strain distribution in a vertically corrugated bulkhead.

By prof. ir H. E. Jaeger and ir P. A. van Katwijk. June 1965.

No. 74 S Research on bulbous bow ships. Part I.A.

By prof. dr ir W. P. A. van Lammeren and ir R. Wahab. October 1965.

No. 75 S Hull vibrations of the cargo-passenger motor ship "Oranje Nassau".

By ir W. van Horssen. August 1965.

Communications

No. 1 M Report on the use of heavy fuel oil in the tanker "Auricula" of the Anglo-Saxon Petroleum Company (Dutch).

August 1950.

No. 2 S Ship speeds over the measured mile (Dutch).

By ir W. H. C. E. Riisingh. February 1951.

No. 3 S On voyage logs of sea-going ships and their analysis (Dutch).

By prof: ir Y. W. Bonebakker and ir 3. Gerritsma. November 1952.

No. 4 S _{Analysis of model experiments, trial and service performance data of a single-screw tanker.}

By prof. ir J. W. Bonebakker. October 1954.

No. 5 S _{Determination of the dimensions of panels subjected to water pressure only or to a combination of water pressure}

and edge compression (Dutch).

By prof. ir H. E. Jaeger. November 1954.

No. 6 S Approximative calculation of the effect of free surfaces on transverse stability (Dutch). By ir L. P. Heifst. April 1956.

No. 7 S On the calculation of stresses in a stayed mast.

By ir B. Burghgraef. August 1956.

No. 8 S

Simply supported rectangular plates subjected to the combined action of a uniformly distributed lateral load and

compressive forces in the middle plane. By ir B. Burghgraef. February 1958.

No. 9 C

Review of the investigations into the prevention of corrosion and fouling of ships' hulls (Dutch). By ir H. C. Ekama. October 1962.

No. 10 S/M Condensed report of a design study for a 53,000 dwt-class nuclear powered tanker.

By the Dutch International Team (D.LT.) directed by ir A. M. Fabery de Jonge. October 1963.

No. 11 C Investigations into the use of some shipbottom paints, based on scarcely saponifiable vehicles (Dutch).

By A. M. van Londen and drs P. de Wolf. October 1964.

M = engineering department S = shipbuilding department C = corrosion and antifouling department

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STUDIECENTRUM T.N.O. VOOR SCHEEPSBOUW EN NAVIGATIE

(NETHERLANDS' RESEARCH CENTRE T.N.O. FOR SHIPBUILDING AND NAVIGATION)

SHIPBUILDING DEPARTMENT MEKELWEG 2, DELFT

RESEARCH ON BULBOUS BOW SHIPS

Part II.A

STILL WATER PERFORMANCE OF A 24,000 DWT BULKCARRIER WITH A

LARGE BULBOUS BOW

(RESULTATEN VAN PROEVEN IN VLAK WATER MET EEN 24.000 DWT

BULKCARRIER VOORZIEN VAN EEN GROTE BULBBOEG)

by

PROF. DR. IR. W. P. A. VAN LAMMEREN

and

IR. J. J. MUNTJEWERF

(Netherlands Ship Model Basin)

Issued by the Council

This report is not to be published

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erlands' Research Centre T.N.O. for Shipbuilding

and Navigation undertook arrangements to carry

out research on the application of bulbous bows.

The research project thus drawn up was strongly

supported by the shipowners'- and the shipbuilders'

associations in the Netherlands, the "Koninklijke

Nederlandsche Reedersvereeniging" and the

"Cen-trale Bond van Scheepsbouwmeesters in

Neder-land" respectively.

The actual work involved has been carried out

by the Wageningen towingtank, the "Nederlandsch

Scheepsbouwkundig Proefstation".

The present report is the first one of a series of

reports to be published, giving the results of tests

performed with bulbous bows on a bulkcarrier and

on a fast cargo-ship.

The assistance

received from Messrs. N.V.

Koninklijke Paketvaart-Maatschappij in making

available data of the bulkcarrier

is

gratefully

acknowledged.

(26)

page

Summary

5

1

Introduction

5

2

Method of extrapolation

5

3

Main dimensions of the ship

5

4

Main characteristics of the propeller

7 5

Results of the resistance and propulsion

tests 7

6

Additional tests and calculations to

sub-stantiate the obtained results

8

7

Results of manoeuvring tests

10

8

Conclusions

11

Reference

11

.

(27)

RESEARCH ON BULBOUS BOW SHIPS

by

PROF. DR. IR. W. P. A. VAN LAMMEREN

and IR. J. J. MUNTJEWERF

Summary

Model tests were carried out to determine the still water performance of a 24,000 DWT bulk carrier, provided with a large bulbous bow of hemi-spherical form. A comparison of the results with those of the same ship model, however, with con-ventional bow was made both for the loaded and ballast condition.

Considerable savings in power were found for the ship with bulbous bow in the ballast condition. In the loaded condition practically no influence of the bulbous bow could be established.

The results were checked on possible laminar flow effects by carrying out additional tests with extra turbulence stim-ulators. Flow observation by underwater television and flow tests with paint showed that separation of flow on the forebody did not occur.

Overshoot manoeuvring tests have indicated that the manoeuvrability of the ship model is hardly affected by fitting the bulbous bow. A comparison of the maximum rates of change of heading at given rudder angles shows that there is only

a very slight difference between the values of the model with conventional bow and those of the model with bulbous

bow, which means that the bulbous bow has practically no effect on the directional stability either.