A comparative study on four different passive roll damping tanks

NED:ERLANDS SCHEEPSSTUDIECENTRUM TNO

NETHERLANDS SHIP RESEARCH CENTRE TNO

SHIPBUILDING DEPARTMENT

LEEGHWATERSTRAAT 5, DELFT

A COMPARATIVE STUDY ON FOUR DIFFERENT

PASSIVE ROLL DAMPING TANKS

PART I

(EEN VERGELIjKEND ONDERZOEK VAN VI'ER VERSCÍ1ILLENDE.

PASS] EVE SLINGERDEMPENDE. TANKS. DEEL I)

by

Jrj H. VUGTS

Shipbuilding Laboratory Technological University Deift

In 1966 werd door zes Nederlandse rederijen een reeks onder-zoekingen opgezet met het doel enige passieve slingerdempende tanksystemen te vergelijken. Gedeeltelijk werd dit programma uitgevoerd in samenwerking met het Nederlands Scheepsstudie-centrum TNO.

Vier verschillende ontwerpbureaus werden uitgenodigd een voorstel in te dienen voor een tanksysteem dat geschikt moest zijn orn in een snel iijnvrachtschip te worden geinstalleerd.

De specificatie voor het ontwerp omvatte behalve de

nood-zakelijke gegevens van het schip, de eis dat de tanks niet meer dan een voorgeschreven volume zouden innemen.

Deopgeleverde ontwerpen,te wetentwee werkende volgens het ,,vrije oppervlakte"-principe entwee volgens'het U-tank-principe,

werden onderworpen aan een beproevingsprogramma dat uit

twee delen bestond, namelijk uitmetingenop een slinger-oscilla-tor met modellen van de tanks (schaal 1:16) door het Laborato-rium voorScheepsbouwkunde van de Technische Hogeschool te Delft en uit proeven met een model van het schip, voorzien van de slingerdempende tanks (schaal 1:40),. door het Nederlandsch Scheepsbouwkundig Proefstation. Deze Iaatste serie, proeven orn-vatte osciliatieproeven in vlak water en proeven in regelmatige dwarsin komende golven, in onregelmatige dwarsinkomeride gol-ven en in regelmatige achterinkomendegolgol-ven.

Nadat de metingen beeindigd waren zijn alle verkregen resul-taten ter beschikking van het Scheepsstudiecentrurn gekomen. De geste van de Stoornvaart Maatschappij ,,Nederland" N.V., de Koninklijke Java-China-Paketvaart Limen NV., de Konink-lijkeNederlandsche Stoomboot-Maatschappij N.V., de N .V. Ko-ninklijke Paketvaart-Maatschappij, de KoKo-ninklijke Rotterdam-sche Lloyd N.V. en de NV. Vereenigde NederlandRotterdam-sche Scheep-vaartmaatschappij orn ook het door dezerederijen gefinancierde

deel van het onderzoek ter beschikking te stellen zu hier met erkentelijkheid vermeld

iestetd mag worden dat dit onderzoek nuttige resultaten heeft

opgeleverd, hoewel er enige punten uit naarvoren zn gekomen die nader onderzoek behoeven

In dit eerste rapport worden de belangrijkste resultatenvande proeven gegeven en wordt de rekenmethode voor het opstellèn van cen prognose geverifleerd.

Een tweede rapport is in bewerking, waarin de gegevens verder worden uitgewerkt.

Geconcludeerd kan reeds worden dat deproeven geenabsolute superioriteit van een van deze tanksystemen hebben aangetoond Bovendien zijn voor sommige tanks weer gewijzigde uitvoeringen ontwikkeld,zodat voorelk schip apart zal moetenworden bezien, welk systeem de voorkeur verdient.

Gaarne wordt hier nog gememoreerd de medewerking van het Nederlandseh Scheepsbouwkundig Proefstation en het Labora-torium voor Scheepsbouwkunde.

Ook de schrijver van dit rapport komt dank toe voor het ver-zamelen, analyserenen samenvatten van de beschikbare gegevens.

I-LET NEDERLANDS SCHEEPSSTUDIECENTRUM mO

In l966six DutchShippingCompanies initiateda programme of investigations to compare anumber ofpassive rolldampingtank systems. Partly this programmewasexecuted in cooperation with the Netherlands Ship Research Centre TNO.

Four different design offices were invited to súpply their proposal for a tank system, suitable for installation in a fast

cargo liner.

Design specification for the tanks, besides the necessary data of the ship, required that the tanks should not occupy more than a prescribed volume.

The tank designsdelivered, viz. two systems-of the free surface type and two of the U-tank type, were submitted to -a test

pro-gramme that was split up in two parts: bench tests with tank

models (scale I :16) at the Shipbuilding Laboratory of the Technological University Delft and tests with a model of the

ship, equipped with the roll damping tanks (scale 1:40) at the Netherlands Ship Model Basin. The latter experiments included oscillation tests in still water and tests in regulár beam waves, irregular beam waves and regular quartering waves.

After the experiments had been finished, all results obtained were put at thedisposal of the Ship ResearchCentre. The gesture of the Nederland Line Royal Dutch Mail, the Royal Interocean Lines, the Royal Netherlands Steamship Company, the Royal Packet Navigation Company, the Royal Rotterdam Lloyd and the United Netherlands Navigation Company, also to hand over

the results of the investigations financed by these shipping

companies, is gratefully acknowledged.

-It may be stated that this research programme has provided

useful results, although it has indicated some points that need further investigation.

In this first report the most important results of the

experi-ments are presented and the calculation method to predict the behaviour of a-ship with a passive tank is verified.

A second report is being prepared in which the data will be elaborated further.

-It may be concluded already that the experiments have not shown an absolute superiority of any of these tank systems.

Besides, for some tank systems already modifications have been developed, so that for every ship the type of tank that is to be preferred must be decided separately.

The cooperation of the Netherlands Ship Model Basin and the Shipbuilding Laboratory is gratefullyacknowledged Also thanks are due to the authorfor collecting, analyziñgand summarizing the data availablè

page

Summary

7

i

Introduction

7

2 The ship data and the condition of loading

8

3 The tank installations

8

4 The bench tests

io

5 The prediction of the rolling of the ship with and without tank

11

6 The predicted and measured roll response

11

6.1

The experimental programme

.. . 11

6.2

Theoscillation tests

12

6.3

The tests in regular beam waves

12

7

Discussion and conclusions

13

8 Acknowledgement 13

References

13

B

Ship's breadth

G

Ship's centre of gravity

Virtual mass moment of inertia' about the rolling axis

K

General moment producing roll

K,

Roll exciting moment, due to the waves

Kwa

Amplitude of K

Roll exciting moment, due to the tank

(its phase is such that it counteracts the rolling motion)

Kia

Amplitude of K,

N4,

Damping coefficient against rolling

R4,

Restoring coefficient

2irk,

T4, =

Natural roll period

Vg'GM

T

Ship's draught

b

Tank breadth (measUred across the ship)

g

Acceleration of gravity

h

Water depth in the tank at rest

k ='

Wave number

k4,

Transverse radius of gyration

/

Tank length (measured. forward and aft)

s

Distance from tank bottom to axis of rotation; positive iftank above axis

Ze

Effective 'depth for the exponentially decreasing wave slope

w = kCa

Maximum wave slope at the surface

A

Weight of displacement

V

Volume of displacement

Phaseangle between wave moment K and rolling motionçb; positive if K,,, leads

4)

Phase.angle between tank moment K and rolling motion 4); positive if K leads

4)

Ca

Wave amplitude

2Ca = H

Wave height

1

Wave length

Kia 3

Qgb /

N4, 4,

Non-dimensional amplitude of tank moment

Non-dimensional roll damping coefficient

Q

Mass density of water

Mass density of tank fluid

4)

Roll angle

Roll amplitude

Circular frequency

CO4,

k4,

i

Introduction

The relative merits of different passive roll damping

systems are an important qúestion to ship owners and

officers. It is certainly not so that one system is superior

over all other systems in any desired application; B

sides, several modifications are possible to adjust each

tank more or less to the case under consideration, thus

smoothing the differences between specific designs.

Only if the respective qualities are known and

under-stood, ship owners can make a justified choice for the

specific circumstañces applyiig to their ship.

As a contribution into, this matter the Netherlands

Ship Research Centre TNO initiated bench tests with

four different tank designs to investigate their basic

performance. Each tank was designed by its own

producer or advocate for the same ship in a specified

conditiOn of loading. The loss in cubic capacity by the

tanks had to be the same. The tests were carried out at

the Shipbuilding Laboratory of the Technological

Uni-versity at Deift.

At the same time a group of ship owners had the

tanks installed in the model' of the ship, which was

subjected to a test programme at the Netherlands Ship

Model Basin at Wageningen.

The information obtained from the latter tests has

also been placed at the disposal of the Ship Research

Centre for further consideration in an extended

com-parative study. The results of this study are reported'

here.

The paper comprises the predicted behaviour of the'

ship equipped with each of the four tank installations

under different service conditions. The basic data' for

the tank action when subject to a rolling motion are

* _{Publication 36 of the Shipbuilding Laboratory, Technological}

University, Deift.

PASSIVE ROLL DAMPING TANKS *

PART I

by

IR. J. H. V'UGTS

Summary

Four passiveroll damping tank systems will be comparedfor one and thesame ship. In this part lof the report a method of calcu-lation is checked with the results of model experiments.

In part H (to be published) the actual comparison will be made by means of calculated predictions for various conditions of loading. Thetank data have been determined by bench tests; the results arepresented here

The method of prediction turns out to be areasonable basis for acomparative study and allows a comparison for additional loading conditions.

known by experiment and provide an

adequatestarting-point for further calculatións. The only uncertainty

in-volved is the response of the tanks to the other motions

of the ship, in particular to the swaying motion. The

input of ship and sea data into the motion problem,

however, is more liable to violate the assumptions

necessary for the calculations. With this in mind the

report 'is split up into two parts, having the following

contents.'

Part I. This report presents and compares the cal

culated and experimental results and assesses the limits

of the validity of the prediction. As no further model

tests Were to be carried out the method of prediction

had to be justified, using the available ship model

experiments.

Part II. This part of the report will present the

com-puted predictionsin an extended comparison. Although

it was intended beforehand that the tanks would

occupy an equal amount of space within the ship 'the

original designs showed unsatisfactory differences in

this respect. To eliminate this influence in the extended

study the'dimensi'ons of the tanks will be changed' in the

fore and aft direction, so that they effectively produce

an equal loss in cubic capacity. As the amount of water

'in the tanks is different the loss in dead weight is not

equal'. The cross-section of the tanks is essentially

un-changed and since the water flow in the tanks can be

considered as two-dimensional, this 'adjustment does

not introduce any new aspect in the tank action. The

tanks thus adapted are thought to be installed in the

ship and her predicted performance at sea will be

compared for several service coñditiöns.

For 'further information about passive tank systems

reference is' made to earlier publications ['1], [2] and

r'

- 74.52

J

PLACE ANTI ROLLING TANK

96

Fig. I Longitudinal section of ship with position of roll damping 'tanks;

2 The ship data and the condition of loading

The ship fòr which the tanks are designed is a

cargo-liner of the "Straat H"-class of the Royal Interocean

Lines. The selected loading conditión corresponds

closely to the fully loaded ship, leaving port. The

par-ticulars are listed in table L A longitudinal section of

the ship is shown in figure L

Table I.

Ship particulars without roll damping tank

The tabulated values have been used, however, as they

dO not play an important role in a comparative

inves-'tigation.

An important, but unknown quantity is the damping

of the 'hull against rolling. From an extinction curve

and some tests in regular beam waves the model values

could be derived. The analysis showed an extremely low

non-dimensional damping coefficient v, 'increasing

about linearly with roll amplitude /a. This means that

the damping in the equation of motion consists

essen-tially of a 'linear and a quadratic term, 'but they may

be reasonably replaced by anequivalent linear damping

term. The values obtained apply to the model without

bilge keels and without forward speed. Due to scale

effects and the speed of the vessel' it is doubted whether

these values are representative for the ship at sea.

Moreover it is not unlikely that a part of the'coupling

effects between the ship's roll and sway motions will be

taken into account by an adjustment of the roll

damp-ing. If so y4, has become dependent upon the position

of the centre of gravity as well. For all these reasons a

definite valúe for the hull damping is not specified.

'For the purpose of cômparison the damping coefficient

used in the calculations is chosen in such a way as to

fit the experimental resUlts.

3 The tank installations

The position of the tanks in the ship is indicated in

figure I. The various installations themselves :'are'shown

in figure 2 through 5. Table Ii summarizes several tank

data.

'it is not the intention of this report to discuss the

various tank designs themselves 'in detail. Therefore

only some explanatory notes' will be made; Thó

per-forated plates at the si'des of tank I serve as a kind of

wave breaker to decrease the noise level and the lashing

of the water against the shell and the deck. They do not

influence the damping -action of the system. In tank II

By these data the transverse radius- of gyration

is

established as k4, = 7.35 m = O.334B, using the

well-known formula

2irk4,

'1gGM

This value is rather low and it seems therefore that the

stated rolling period and metacentric 'height are not

too well in agreement. Using a more general value

k4,= '0.38B =' 8.36 m leads to

T4,, = 18.2 sec with

GM = 0.85 m, or to GM = 1.10 m with T4, = 16 sec.

Length between perpendiculars Lp,, = 146;49m

Breadth, moulded

B = 2200rn

'Depth to úpper deck

D = 13.00m

Draught forward

T1 =

941 rn

Draught aft Ta 9.85rn

Draught, mean

Tm =

9;63rn

Disphìement, moulded V

= 1840rn'

Displacement'inciuding hull in

sea-water of y = 1.025 tIm' 18962 t

Block coefficient 0596

Prismatic coefficient'

604

Waterline coefficient 0.742 Midship section coefficient 0.986 Centre' of gravity above keel

KG = 8.30m

Centre of buoyancy above keel KB 5.27 m Metacentric height GM = 0.85 rn

Natural rolling period T4, 16 sec Natural roll frequency w4, 0.393 sec-'

Table H. Particulars of the various tank installations

BULKHEAD

BULKHEAD

1.90

FR96 00 lOO

SECTION A-A DETAIL

PERFORATED PLATE HOLES 0.15 IDcOOO SPACING 0.165 Fig. 2 Tank I SECTION A-A LOWERTWEÉNÒECK I I I I I I i' I ej :t 96 _! 1GO IO? lOI 105 tOR

DIMENSIONS IN METERS

I AIR BREATHER FOR MODEL

INPROTOTYPE OTHER

SDLuEION POSSIBLE

DiMENSIONS IN METERS

- A SEE DETAIL

f

\B

AIR OPENING 0.50I.B35

/ /_'-B

BULKHEAD DIMENSIONS IN METERS - 3.30 F090 50 lOO SECTION A-A LOWERTWEENDECK

Fig 4 Tank III

SECTION A-A

Fig. 3 Tank II Fig 5 Tank -IV

DETAIL OF AIR DUCT

IN WAY OF DAM PE R SECTIDN B-B

Iví

O DAMPER AT OPEN POSITION AIRBREATHER FOR EACH TANK

SEPARATELY

MPEPL AT E

-:DAMPER ARM

DIMENSIONS IN METERS

TankI

Tank II

Tank II

TankIV

Actual tank volume in m3 219 221 205 220

Volume occupied between end bulkheads of tanks in m3 219 (notapplicablò) 277 248

Tank length in m 1.90- 9.00 2.40 2.15

Tank breadth mm 22MO 22.00 22.00 22.00

Water weightiñ tons 64M 118.4 115 1022

Water weight relative to displacement in % 0 34 0 63 0 61 0 54

GM-reduction in rn 0.18 0.34 022 - 0.31 PERFORATED PLATE 'IIIWtLNUECK I -. O N 3.50 6 09

L..

i A 22.00

E

I_/_/__\_LOWERTwpj

-0.935_f

-_=9_TANI<DECK2jrrr_==

-070

-

- Igl

-

-- TANK1OP A -1LOWERTWEENDECK _____.0.64f TANKDECK--

-'t=

--î

_o65lrtr==TANKroP__

L

I 22.00 I I

LO WERT WEEN DECK

r-0.53 070 TANKTOP I 1320 I . LO A 22.00

the "funnels" provide the free access of air to the

reservoirs. If not, the air column would be compressed

and would influence the water motion. In actual

application the funnels may be replaced by a tube

interconnecting the tops of the two reservoirs or by

some other arrangement. The air valve of system III

acts as a passive control device. The top of each

reser-voir is connected with a central air channel in which

the valve is placed. The cross-sections of the air

openings and channel should remain the same but

the construction and location of the arrangement can

be adjusted to the considered application. System IV

has air tubes to all the tanks at both sides open to

the air.

4 The bench tests

The tank models were subjected to a forced harmonic

rolling motion about an axis positioned at the ship's

centre of gravity, with an amplitude of 0.0333, 0.0667

and 0.10 radians, respectively (1.9; 3.8 and 5.7 deg.).

A photograph showing the tank oscillator is shown in

figure 6. The model scale was 1: 16. The rolling period

was amply varied from 1.9 sec to 12.6 sec for the model,

corresponding to from 7.7 sec to 50.3 sec for the ship.

Fig. 6 Tank oscillator

The moments, which the moving water mass exerted

on the tanks were measured. They are presented in the

appendix in the form of the non-dimensional amplitude

Pa and the phase difference with the rolling motion s.

Due to the essentially different configuration of tank IL

the Pa-Values cannot be compared directly in

magni-tude. The shape of the curves and the phase relations

are indicative for the performance of all tanks,

how-ever. For convenience the actual model measurements

are also presented in dimensional form in the tables

A.I through A.IV of the appendix.

The results of the bench tests show distinct differences

in character between the various designs. This point

can be illustrated by regarding figure A.1 through A.4.

The damping component of the tank moment is

Kta sin c, so both magnitude and phase lag contribute

to the ultimate effect. In general a large damping

moment is preferred over a certain frequency range at

both sides of roll resonance to make the roll response

curve as flat as possible. This frequency range extends

at least from 0.70w, to 1.25w4,, that is from w =

0.275 sec1 to about w = 0.50 sec' full

scale or

w = 1.1 to 2.0 sec' model scale. Preferably this range

must still be a little wider as the tank adds a degree of

freedom to the system ship plus tank so that a distinct

resonance point may not be present any more.

From the above it will be clear that the Kta and

e,-curves should be reasonably flat in the considered

range. The phase curves of the systems I and III do not

differ appreciably in slope but those of system II and

IV are substantially steeper. As far as the moment

amplitudes are concerned tank I shows the least

varia-tion. As an example in table III the ratio of the

maxi-mum and minimaxi-mum K0 and the difference of maximaxi-mum

and minimum e in the interval w = 1.0 to 2.0sec'

(model values) are presented for & = 0.10.

Table Ill. Variation Of Kia and e, for & = 0.10 in the

range from w = 1.0 sec_t to w = 2.0 sec1,

model frequencies

Of course these variations influence the character of

the K,,, sin e, components greatly as shown in figure

A.5 of the appendix for a roll amplitude 4,, = 0.10.

For tank I the curve is bell-shaped, while the other

three curves are more or less triangular in form. Of

course with a triangle the same required base can be

covered by making it high enough. In terms of the

problem under consideration this means by increasing

the tank dimensions and/or the water mass for these

tanks. If this is accepted deliberately the points

dis-cussed here are only differences in character between

the various systems, which need not necessarily lead to

large differences in effectiveness. A quantitative

com-parison is postponed until part II of the report as

discussed in the introduction.

In fact the basic principle of system IV is the same

as that of system I. They differ, however, in the

re-stricted height and in the rising bottom of each tank.

Tank system I 11

III

IV (Kta)max 1.23 7Odeg 1.56 136 deg 1.77 92deg 1.41 111 deg (Kta)min (Ct)max(Ct)min

This causes a rather steep decrease in Kta and increase

in

, where the water motion is hampered at the higher

frequencies óf motion. For tank lithe height of the

reservoirs is also rather limited. It turned out that the

water surface reached the top of the tank at roll angles

of about 5 deg. That is the reason why the moment

amplitude in figure A.2 does not increase much more

for

d'a =

0.10. In system ill the natural frequency of

the air valve is so high that it may be considered to

react statically to the load of air pressure and gravity.

It accomplishes a flatter phase curve, especially at the

smaller roll angles. It turned out that its effect nearly

disappeared at

d'a = 0.10.

5 The prediction of the rolling of the ship with and

without tank

Still it

is not possible to handle the true motion

of a ship in an arbitrary seaway. This is largely due to

a lack of knowledge about the various motions

in-volved and their mutual coupling effects. It can be

made plausible that the general state of motion of a

ship with six degrees of freedom may be split up into

two independent groups, namely the symmetric motions

heave, pitch and surge and the asymmetric motioñs

roll, sway and yaw. As this report deals with rolling

the discussion will be restricted to the second group.

Usually the rolling motion is from necessity sttdied

alone, as if the ship is a one degree of freedom system,

since the mutual influences with swaying and yawing

are not known. Probably the yaw effects into roll will

not be of primary importance, so that it woUld suffice

for the, time being to consider the combined sWayiòg

and rolling for a really reliable roll prediction. This

statement is certainly valid when only beam seas are

considered. Unfortunately it is not even possible to

start from this principle. The inaccuracies resulting

from a still further simplification to pure rolling may

differ from ship to ship and with a certain ship from

one condition to another. This will be immediately

clear when it is recollected that by definition swaying

is a translatory motion of the centre of gravity and

rolling is a rotation about a longitudinal axis through

this point. Thus the coupling effects depend on the

positiòn of G with respect to the water surface.

The influence of the other shipmotions on the tank

action is unknown as well. In this respect the influence

of yawing will be analogous to that of swaying, and of

pitching to that ofheaving. It can be understood that

the symmetric vertical motion will only be of minor

importance so that only the horizontal swaying would

have to be considered. But, as stated, the influence is

unknown.

By necessity, therefore, the analysis and prediction

has to be made for a pure rolling motion in beam seas

The validity of the simplifications Will be investigated

with the aid of the model experiments in waves in

sec-tion 6 and 7.

The equation of motion for the rolling ship without

tank is given by

I+Nç6R,d'

=

K

(1)

For the ship with tank the tank moment has to be

added

I6+N +R44'

=

K+K,

(2)

Here I, is the mass moment of inertia about the rolling

axis, including hydrodynamic effects, N4, the damping

coefficient of the hull against rolling and R4, the restoring

coefficient or the stability moment per radian of heel.

In the right hand side K is the wave excited moment

and K, the tank moment. R4, and 14, are constants,

known by the loading condition and roll' period; N4,

is an estimated constant.

The magnitude of the exciting moment K in

relative-ly long waves may be approximated by

Kwa

=

ggV

Ca_o2z.Ig (3)

g

where c

'is the surface wave slope, which is equal to

w2jg.

In the exponential factor, which accOunts for

the decrease in Wave slope with depth under water, the

effective depth

Ze

is taken equal to half the draught.

The magnitude and phase of the tank moment K1

are knoWn by the bench tests for three amplitudes of

motion As K is not linear in

d'a

the equation (2) has

become non-linear as well and the solution has to be

found by iteration. For d'a -

0.0333;

d'a =

0667 and:

d'a =

0.10 rad the experimental results are put into

the equation, which is solved for

d'a.

From the resulting

values of

d'a

the correct solution is obtained by

qua-dratic interpolation. It is clear that this method will

only be reliable as long as the ultimate rolling angies

remain between the two limits of the input values of

d'a' so for' 1.9 deg

< d'a <

5.7 deg. A slight

extrapola-tion will not affect the results much so that the method

may be considered to be valid between about 1.5 deg

and 7.5 deg. Outside this range the computations fail.

Of course this does not apply to the ship without tank,

for equation (1) is linear throughout.

6

The predicted and measured roll response

6.1 The experimental programme

The tests with the ship model at the N.S.M.B.

con-sisted of oscillation tests by rotating weights, tests in

regular beam waves, tests in irregular beam waves and

tests in regular quartering waves. Of each series the.

model without and with the various tanks was

inves-tigated. The tank models were constructed completely

separately and were made interchangeable, so after a

test the tank was just replaced by another one and the

test repeated. In this way it was achieved that the

measurements for the different tank systems were

obtained under identical circumstances and at the same

setting of the wave generator. The model scale was

1:40.

For comparison between calculation and experiment

the irregular beam wavesand the quartering waves are

not used, the reasons being as follows.

In the irregular beam waves the roll spectrum and

the wave spectrum were measured. The roll response

functión obtained from these data differed greatly from

the directly measured response in regular beam waves,

even for the ship without a tank. This may be partly

due to the time interval used in digitizing the records

and to the analysis procedure which involves a

smooth-ing process, but this does not account for the large

differènces. Since the exact circumstances and an

adequate explanation cannot be recovered these test

results are left out of the comparison.

The quartering waves.came in under 60 degrees. They

cover only a narrow frequency range about resonance

and the measured roll angles may be strongly affected

by the characteristics of the automatic pilot, used to

keep the model on its-track under the towing carriage.

Therefore the results .of these tests are of a very

restricted value, not only in an absolute way, but even

for mutual compar.ison. Neither can a computation be

made in quarteriñg waves dUe to. the difficulties'

ex-plained in section 5.

62

The oscillation tests

The model was forcibly oscillated in still water by

rotàting weights. In the centre pläne of the model two

contra-rotating vertical rods were installed, each

carry-iñg two weights at opposite sides of 'the rod and

sym-metrical with respect to the centre of gravity. Thus a

purely centrifugal roll moment was produced, Without

any parasitic force. When the hypothesis is accepted

that the wave exciting moment in beam waves is

proportional to the wave slope the above oscillation

corresponds to pure rolling in beam waves of constant

height and varying length. The equivalent wave height

is 1.4-m füll scale.

The prediction is calculated accordingly by the

equa-tion (2)

J6-+N,q+R,,çb =K+K,

(2)

or formulated differently

V4,.

- + l+ = S1fl

w2

co

w

- .

K1.

O4+e4,)

± - sin(ofl+c) (4)

R4,

in which

= 0.393 sec1

y4, = 0.05 and 0.10

R4, = AGM

K0, R4, R4,

The exponential factor is taken equal to i becausé

there are no waves añd consequently no decreasing

wave slope. Kta and -e

are known by the bench tests.

The equation (4) is solved for 4a and

e.

The results

of the prediction, together with the measured points

are presented in figure 7. At the low frequency side the

roll angles were so small that the prediction failed for

the rolling with tank by reasons explained in section 5,

the curves are shown as far'as the calculations were

possible.

The agreement between theoretical prediction and

experiment is good, especially when one considers that

the accuracy of roll angle measurements is not much

greater than ± 0.5 degree Apparently v = 0.05 has

to be selected for .the damping regarding the rolling of

the ship without tank.

6.3 The tests in regular beam waves

The basic' series of tests was conducted in waves

cor-responding to a constant height of 3.30 m aild lengths

between 200 and 550 m, both full scale values. Besides,

for a length of 310m the wave height was varied. The

vessel had no forward speed.

The prediction is found by solving the same

equa-tion (4), but now the exponential decrease in wave

slope is taken into account by replacing a by

WCa_{e'_c2Tl29} g

For the damping coefficient y4, again two values were

selected: 0.05 and 0.10. The rolling of the ship without

tank is given in figure 8. The results with tanks are

presented in figures 9 and 10 for the smaller and figures

11 and 12 for the larger t',. In those figures three curves

are drawn. The middle one applies to the basic wave

amplitude of Ca = 1.665 m For the other curves is

Ca = 0.550 m and

= 2.305 m respectively. The

avail-able experimental points are plotted as well. The

smallest wave height may be regarded as indicative for

a light sea condition, while the largest corresponds to a

rather severe .sea.

lt can be seen that for the ship without a tank and

with tank I v = 0.10 provides better results, while for

the other tanks y4, = 0.05 gives a better relationbetween

prediction and experiment. The agreement is quite

reasonable, considering the general state of knowledge

as discussed in section 5. For tank I it is even quite

good with v = 0.10. The fact that one tank system

apparently fits the mathematicäl model in this case

better than another cannot be explained rationally. It

must be attributed to differences in the complex whole

of interrelated modes of motion and tank performance

But in añy event the trends of the computations are

fully confirmed by the experiments. Quantitatively they

are not too far off,, except at the peak values for tank II

and IV; the predictións 'here are always loWer than the

experimental results.

It is not unlikely that part of the discrepancies at the

low frequency side with tank III in figure lOare caused

by scale effects. The air duct of system III, constructed

on a 1:40 scale, may have influenced the ship model

experiments unfavourably. This may especially be true

where the air movements are small, that is for small

rolling angles 'at low frequencies of motion.

The computed curves are stopped again where the

prediction failed to give results.

7

Discussion and conclusions

The moments, which the tanks exert on the rolling

ship, are measured in bench tests. They reveal

characteristic

differences

between

the

various

systems which, however, need' not lead to large

differences in effectiveness. The characteristics are

discussed in section 4 of this report.

Of the model experiments the forced oscillation

tests correspond best with the 'mathematical model

used for the predictions. The agreement between

experiments and calculations is good for all tanks

(figure 7). As damping coefficient y4, = 0.05 has to

be seleéted.

The model experiments in' waves can only approx

imately be represented by themathematical model.

This is due to the complex and unknown relations

of the other modes of motion with roll and with the

tank performance., Apparently a part of this effect

i's taken into account by increasing the damping of

the hull with respect to the oscillation tests from

y4, = 0.05 to 0.10 (figure 8). The agreement between

experiments and calculations is good for the ship

without tank (fi'gure 8) and with tank I (figure 11),

'and quite reasonable with tank III (figure 12). The

trends of the 'experiments with tank Il and IV are

fully predicted, but t'he peak values are rather off

(figures 11 and 12). The predictions in these cases

are always lower than the experiments. Of course

the deviations 'become larger when the wave 'height

increases.

The theoretical method is considered to be sffi

ciently supported' by the model experiments to serve

as á reasonable basis for a comparative study of

the various tank systems. Characteristic phenomena

are predicted correctly. In aquantitativecomparison

it will certainly show up large differences between

the tanks. To small differences in result no great

significance may be attached, however It seems

that the calculations underestimate the rolling with

tank II or IV in action.

The value of the predictions is a comparative and

not an absolute one. For the latter case the

hypo-thetical condition of linear, pure. rolling in

long-crested 'beam waves is too rough an approximation

of reality

The mutual comparison of the various systems is

postponed to part II of the report. As stated in the

introduction undesirable differences exist in tank

dimensions, which should be corrected first. Then

other conditions of loading will be considered as

well with the same tank installation.

8 Acknowledgement

The willingness of six Dutch Shipping Companies to

make the results of the model tests available to the

Research Centre is gratefully acknowledged The author

is also indebted to the N.S.'M.B. for their cooperation'

in furnishing the original experimental data and in

assisting him to analyse some peculiarities.

References

1. STIGTER, C., The performance of U-tanks as a passive miti-rolling device, Report 81 S of the Netherlands Ship Re-search Centre TNO, February 1966.

Z BOSCH, J. J. VAN DENand J. H. VUGTS, Roll damping by free surface tanks, 'Report 83 S of the Netherlands Ship

Re-search Centre TNO, April 1966.

3. BOOTSMA,J. and J. J.VANDEÑ BOSCH, On the efficacy of two different roll damping tanks, RepOrt 97 S of the Nether-lands Ship Research Centre T.NO, July '1967.

0.1 WITHOUT calcutaion TANK V= 0.1.0 005. s experiment ,Iit ¡

ti

WITH TANK I

s s

r

WITH TANK U

f'

1 \

,

.L.

,.

s

,..

s

WITH TANK

-WITH TANK

, s

-..

s,

'

J s / o s 2

03

06

₀₅

_0.6

₀₇

w se c.-1

Fig. 7 Comparison ofcalculated and measured rolling of the model during scillatiön tests. (full scale values)

i

de g.

i

o 5 4a OE 5

t

î

oo

25 deg. 20 i 5

i0

a

WITHOUT TÄNI<

caLculation V 010 10:05

.

experiment = 167m 0 01

02

:03 0.4 0.5 .0.6

01

sec.1

Fig 8

Comparison of calcùlàted and measuredlrolling of themodel without tank in regularbeam waves. (full scale values).

deg.

4o

i

i

o 15

l'o

u

_'03

₀₅

₀₆

07

sec.1

Fig. 9 Comparison ofcalculatedand measured rlling,of thernodól withtank I and II in.regular beamwaves; v1j O.05

(full scale values)

WITH calculation

TAÑK i

V 005 = 2.31 m 167m 055m -o experiment ' '

'Io

o e

:

a31

-m 167m '0 55 m

WITHTAÑK fi

o Q55

deg. 15

io

0

15

io

o

Fig. 10 Comparisonofcalculatedand measuredrolling ofthemodelwithtank III and IVinregularbeath'waves;.v = 0:05.

(full scale values)

.

s,

.

VAYAUVII1

»

_

05

01.

03

2 0.1 w

06

07

sec1

15 deg.

4a

lo

15 10

f

o

Fig. 11 Comparison of calculated and' measured'rollingof themodeiwith tank!: and H in regu1ar1bearnwaves;v =0.10. (full scale values)

WiTH TANK

- calcuLation

I

V =40.10 a = 2.31 m 167m 0:55m o experimeñt e e OE o S 0 =2.31m 167m 5m

WITH TANK

--o o - - -o e o 0.1

02

03

04

05

06

0.7 - U). sec:1

deg. it 15 OE 10 5 .0 15 10 o -

W:ÏH TANK

calculation. 1 V,= 0105 ' = 2.31 m 167m 055m. o experiment o e o s e, s,

eeee

-'e

a2:31rn

167m 0,55rnì

WITH TANK

' . . o

,.0

o,'

s

s e e =2.31 mj

(N

J

1'.67m 055m. OE 0:1 0.2 0.3: 0.4

05

06

_0:7 (L) _sec.

Fig 12 Comparison of.calculated and measured rolling ofthe model with tank Ill and LV in regularbeam waves; v = OElO. (full: scale, values)

Table All Tank II.

APPENDIX

Results of the bench tests

(model values, scale i :16)

Table AI Tank L

&

00333

& = 0.0667

& = 0.10

w w"b/gKgcose KtaSIfl l000FLa Ktacost Kgasin e Kta

_'°00a

t KtaCOSt KtaSIfl Kg _{1000/ea .et}

sec'

-

kgm kgm kgm

-

grad. kgm kgm kgm

-

grad. kgm kgm kgm grad.

O50 0.1872 1.77

-0.04

1.77 5.73 1.2 ! 3.71 -0.01 3.71 12.00 0.2 4.66

-0.49

4.69 15A4 6.0

075 02808

211

-007

211 681

18

404

-067

409 1322

95

473

-093

482

1558 111

100 03744

272

-092

287 928 187 377

-191

423 1366 269 445

-213

493 1592 256

125 04680

214

-216

305 984 453 291

-303

150 1356 461 361

-331

490

1583 424

150 05616

097

-279

296 955 709 165

-369

404 1307 642 229

-413

472

1524

61"

175 06552 -028

-275

276 893 959 029

-369

370 1196 855 082

-429

437 1412 79

200 07488 -162

-147

219 707 1379

-075

-333

341 1103 1027

-045

-399

402

1299 964

225 08424 -110

-005

110 355

17741 -210

-200

290

937 1364

-169

-324

366 1181 1175

250 09360 -068

-001

077 218

1790' -143

-008

143 463 1768

-226

-142

267 863 1478

275 10296 -044

0 044 143 1800

-094

-002

094 302 1786

-138

-012

139 448 1751 3.00 1;1231

-0.28

. 0' 0.28 0.91 180.0 -0.61

-0.02

61

1.96 177.6

-0.86

-0:06

0.86 2.78. 175.9 3h25 1.2168

-0.23

0 0.23 0:74 180.0

-0.33

-0.01 Ó.33 1.05 177.9

-0.51'.

005 0.51 '1.65 174.3

a00333

&00667

&0b0

W W"J'l)) KgaCOS cg Ktsin Cg Kga IOOO

-et

_K,cos KgaSIfl Cg Kta

'°00/-a - Ct

KtaCOS S KgaSIfl 6g

_1ta

_1000/a

t

sec'

-

kgm kgrn kgm

-

grad. kgm kgm kgm

-

grad. kgm kgm kgm

-

grad.

0:50 0.1872 310

-0.15

3.10 2.12 1.7 6.42

-0.26

6.42 439 2.4 '9.14

-0.84

9.18 6.28

52

075 02808'

367

-031

377 258

46

762

-084

767 524

63

1158

-140 1167

798

69

100 03744

568

-121

581 397 120 854

-315

910 622 202 915

-378

990 677 22

125 04680

512

-577

780 528 484 635

-719

959 656 486 680

-647

938 642 43 1.50 0:5616

-2i4

-703

735 5O3 107:0 0.21

-9.12

9.13 ' 6.24 88.6 1.49

-931

943 6.45 80.91 1.75 0.6552'

-4.55

-'1.17 4.70 3.22 1656

-5.76

-474

7h46 5.10 140.5

-3.81

-763

8:51 5.82 116.6 200 0.7488 247 0h05 Z47 1.69 1788 4.20 062

424

298 171.6 5.87 2.31 6.31 4.31 158.5. 2.25 0.8424 144 1104 h44 1199 1814 2.60 005 2.60 1.78 178.9 394 008 394 2.70 _178.81 2.50 119360 -1191 1107 091 1162 184.5

-1.80

1103 1.80 1.23 180.9

-2:61

1102 , 2.61 1.79 180.6 2.75 1.0296 -1159 0.07 0.59 1140 186:5 -'1.23 1103 1.23 0:84 181.4

-1.73

0iO3 . 1.73 1.18 '180.7:

300 11231

-035

003 035 024 1855

-083

005 083 057 1834

-115

003 115 078 1807 3.25 1.2168 -.1124 0.01 0.24 0;17 1828

-0:49

0:00 0.49 .0.33 180.0

-0.71

1100 0.71 0.49 180.01

Table kill

Tank HI.

Table AIV Tank IV.

40=O333

4)a0.0667

4a010

w

wVb/gKcos S KSIfl

Ka l000aua S KgCOS_c KtaSIfl S

K

_1000fa 5t Kg,COS st KtaSIfl Kg, 1000/Aa

t

sec'

-

kgm kgm kgm

-

grad. kgm kgm kgm grad. kgm kgni kgm

-

grad.

050 01872

166

-042

171 438 144 350

-068

357 914 110 550

-107

560 1425 110 0.75 0.2808 177

-0.67

1.89 4.85 20.7 3.73

-1.27

394 10.10 18.8 5.84

-2.15

6.23 H 1596 202--1.00 0.3744 2.01

-1.16

2.32 594 30.0 3.93

-2.34

4.57 11.72 308 5.48

-4.32

6.98 17.90 38.2 1.25 0.4680 1.86 -2h06 2.77 7.11 47.8 3.13

-4.20

5.23 1342 53.3 3.Ó2

-6.14

6.84 L 17.54 638 50 0.5616

63

-3O6

3.12 8.01 7&3 0.53

-4.98

5.00 12.83 83.9 0.31

-6.03

6.04 15.44 87.0 ..75 0.6552

-1.13

-2.28

2.54 6.52 116.5

-1.63

-3.77

4.11 10.53 113.4

-1.80

-4.69

502 12.87 111.0 2.00 0.7488

-1.26

-0.94

1.57 4O3 143.1 -2.11 i

-2.07

2:96 7.58 135.6

-2.57

-3.01 3.96 10.16 130.5 2.25 0.8424

-0.85

-0.37

0.93 2.39 156.4

-1.70

-1.01

1.97 506 149.2

-2.35

-1.69

2.90 7.42 144.4 2.50 0:9360

-0.58

-0.17

0.60 1.54 1614

-1.22

-0.43

1.29 3.31 160.6

-L83

-0.83

2.01 5.16 155.6 2.75 1.0296

-0.36

-0.07

0.36 0.93 1687

-0.80

-0.18

0.82 2.10 167.1

-1.23

-0.43

1.30 3.33 160.8 3.00 1.1231'

-0.20

-0.06

0.21 0.53 164.1

-0.47

-0:15

0;49 1.26 1'62.2

-0.76

-0.20

0.78 2.01 165.2 3.25 1.2168

-0.13

-0.05

0.43 0.11 159.4

-0.28

-0.14

0:32 0.82 153.2

-0.39

-0.18 0.43

.1.15155.2

-

4a =

0.0333

& =

0.0667

&

OJO

w wVb/gKcoss KgaSlfl S K 1000j1ta 5 KgaCOSt KtaSIfl S,

K

1O0OUa _5t K0coss KeaSIfl 5t Ks,, _{'0O°Pa 5t}

sec'

.- kgm kgm kgm

-

grad kgm kgm kgm

-

grad kgm kgrn kgm

-

grad

0.50 0.1872 2.61

-20 262

7.49 4.4 5.87

-37

588 1682 16 ¡ 7.64

-1.35

7.75 22.19 10.0 0.75 0.2808 3.23

-0.30

124 928 5:2 6,29 -1.31' 6h42 18.39 1.1.8 7.18

-2.57

7.63 21.83 19.1 00 0.3744 4.16

-1.25

4.34 12.43. 16.8 577

-153

676 19.35 31.5 620

-4.57

7.71 22.06 36.4 .25 0.4680 3.46

-3.58

498 1425 46.0 4h01

-577

702 20.09 55.2 4;44

-656

7.92 22.67 56.0

150 05616 -067

-536

540 1546 971

-143

-686, 701'

2005 1018 055

-774

776 2220 860 1.75 0.6552

-3.86

-1.73

423 12:11 155.8'

-3.94

-405

545 16.16 134.2 H -181

-5:94

7.10 20.31 122.7 2.00 0.7488

-2.89

s-0.42, 291 8.34 171.8

-172

-1.96

420

i203

152.2

-4;69

-3.01 5.58 15.97 147.3 2.25 08424

-1.54

0.06 1.54 4.39, 182.2

-3.12

-77

.121 9.20 166.2

-3.59

-'1.93' 4.08 11.67 151.7 2.50 0.9360

-0.96

0.07 0296 2.75 184:2

-214

-0:01 2.14 6.13 1794 -2:91

-0.86

3.04 8.69: 163.7 2.75 1.0296

-042

0.06 0:62 1.7.7 185.2 -'1.33 0:05 1.33 3:80 182.0

-2.16

-0.16

2.17 6.20, 1.75,8 3.OÓ , 1.1231

-0.43'

0S

0:43 1.23 1866

-0.98

0.02 0.98 2.79 181.0

-1.59

-0.15

140 4.57 1,74.6 3.25 1.2168

-0.28

0.03 0:29 081 186.0 -0.62. 0.04 0.62

i.8

183.3.

-1:01

0' 1.01 2.90 180:0

t

0.020 0.015 0.010 0.005 0 -180 degrees E -90

TANK I

w\T7

15 0.0333 0.1000

Fig. A. i Nondimensional amplitude and phase of tank moment for tank I; measured by bench tests.

05 10 15

0.020 0.015 0.010 0.005 -180 degrees E -90 05 P1.0 0a 0.0333 = 0.0667 = 01000 wVTh

Fig. A. I Nondimensional amplitude and phase of tank moment for tank II; measured by bench tests.

TANK II

1.5

1.5

Ra 0.015 0.010 0.005 0 C -90 o 0a = 0.0333 D 0.0667

Fig. A.3 NondimensionaUamplitude and phaseof tank moment for tank III; measûredbij'bench tests. 15

05 10 1.5

0.5 10

-180

Ia

0.020 0015 0.010 0.005 0

TANK &

05 10 w\T 15 05 10

_wV7

1.5

O TANK

I

D TANK U

TANK '

+

TANK

05 10' wVB7 1.5

Fig. A.5 Comparisonof quadrature componentsof tank moment for q = 0.10. kgt.m 9 B 7 _lKtsin Et 5 L 3' 2 U

PRICE PER COPY DFL.

io.-Reports

M = engineering department S = shipbuilding department

C corrosion and antifouling department i S The determination of the natural frequencies of ship vibrations

(Dutch). H. E. Jaeger, 1950. 37 M Propeller excited vibratory forces in the shaft of a single screwtanker. J. D. van Manen and R. Wereldsrna, 1960. 3 S Practicalpossibilities of constructional applications of aluminium

alloys to ship construction. H. E. Jaeger, 1951. 38 S Beamknees and other bracketed connections. H. E. Jaeger andJ. J. W. Nibbering, 1961. 4 S Corrugation of bottom shell plating in ships with all-welded or

partially welded bottoms (Dutch). H. E. Jaeger and H. A. Ver- 39 M Crankshaft coupled free torsional-axial vibrations of a ship'spropulsion system. D. van Dort and N. J. Visser, 1963. beek, 1951. 40 S On the longitudinal reduction factor for the added mass of vi-5 S Standard-recommendations for measured mile and endurance

trials of sea-going ships (Dutch). J. W. Bonebakker, W. J. Muller brating ships with rectangular cross-section. W. P. A. Joosen andL A. Sparenberg, 1961. and E. J. Diehl, 1952. 41 S Stresses in flat propeller blade models determined by the moiré-6 S Some tests on stayed and unstayed masts and a comparison of method. F. K. Ligtenberg, 1962.

experimental results and calculated stresses (Dutch). A. Verduin

and B. Burghgraef, 1952. 42 S Application of modern digital computers in naval-architecture.H. J. Zunderdorp, 1962. 7 M Cylinder wear in marine dieselenginès (Dutch) H. Visser, l952 43 C Raft trials and ships' trials with some underwater paintsystems.

8 M Analysis and testing of lubricating oils (DUtch). R. N. M. A. P. de Wolf and A. M. van Londen, 1962.

Malotaux and J. G. Smit, 1953. 44 S Some acoustical propertiesof ships with respect to noise control.

9S

Stability experiments on models of Dutch and French standard- Part. I. J. H. Janssen, 1962. ized lifeboats. H. E. Jaeger, J. W. Bonebakker and J. Pereboom,

in collaboration with A. Audigé, 1952.

45 S Someacoustical propertiesof ships with respect to noise control Part II. J. H. Janssen, 1962.

los

On collecting ship service performance data and their analysis.

J. W. Bonebakker, 1953. 46 C An investigation into the influence of the method of applicationon the behaviour of anti-corrosive paint systems in seawater. 1 1 M The use of three-phase current for auxiliary purposes (Dútch). A. M. van Londen, 1962.

J. C. G. van Wijk, 1953. 47 C Results of an inquiry into the condition of ships' hulls in relation

I

i

Noise and noise abatement in marine engine rooms (Dutch). to fouling and corrosion. H. C. Ekama, A. M. van Londen and Technisch-Physische Dienst TNO-TH, 1953. P. de Wolf, l962

1 3 M Investigation of cylinder wear in diesel engines by means of

labo-ratory machines (Dutch). H. Visser, 1954. 48 C Investigations into the use of the wheel-abrator for removingrust and millscale from shipbuilding steeF(Dutch). Interim report. I 4 M The purification of heavy fuel oil for diesel engines (Dutch). J. Remmelts and L. D. B. van den Burg, 1962.

A. Bremer, 1953. 49 S Distribution of damping and added mass along the length of a

I 5 S Investigations of the stress distribution in corrugated bulkheads shipmodel. J. Gerritsrna and W. Beukelman, 1963. with vertical troughs. H. E. Jaeger, B. Burghgraef and I. van der

Ham, 1954. 50 S The influence of a bulbous bow on the motions and the propul-sion in longitudinal waves. J. Gerritsrna andW. Beukelman, 1963. 16 M Analysis and testing oflubricating oils Ii (Dutch). R. N. M. A.

Malotaux and J. B. Zabel, 1956. 51 M Stress measurements on a propeller blade of a 42,000 ton tankeron full scale. R. Wereldsma, 1964. 17 M The application of new physical methods in the examination of

lubricating oils. R. N. M. A. Malotaux and F. van Zeggeren, 1957. 52 C Comparative investigations on the surface preparation of ship-building steel by usingwheelabrators and the application of shop-18 M Considerations on the application of three phase current on board coats. H. C. Ekama, A. M. van Londen and J. Remmelts, 1963.

ships for auxiliary purposes espacially with regard to fault pro- 53 S The braking of large vessels. H. E. Jaeger, 1963. tection, with a survey of winch drives recently applied on board

of these ships and their influence on the generating capacity

(Dutch). J. C. G. van Wijk, 1957.

54 C A study of ship bottom paints in particular pertaining to the

behaviour and action of anti-fouling paints A. M. van Lönden, 1963.

19 M Crankcase explosions (Dutch) J. H. Minkhorst, 1957 55 S Fatigue of ship structures. J. J. W. Nibbering, 1963. 20 S An analysis of the application of aluminium alloys in ships'

structures. Suggestions about the riveting between steel and 56 C The possibilities of exposure of anti-fouling paints in Curaçao,Dutch Lesser Antilles, P. de Wolfand M. Meuter-Schriel, 1963. aluminium alloy ships' structures. H. E. Jaeger, 1955. 57 M Determination of the dynamic properties and propeller excited 21 S On stress calculations in helicoidal shells and propeller blades.

J. W. Cohen, 1955. vibrations of a special ship stern arrangement. R. Wereldsma,1964.

22 S Some notes on the calculation of pitching and heaving in

longi-tudinal waves. J. Gerritsma, 1955. 58 S Numerical calculation of vertical hull ''ibrations of ships bydiscretizing the vibration system. J. de Vries, 1964. Second series of stability experiments on models of lifeboats. B.

Burghgraef, 1956.

59 M Controllable pitch propellers, their suitability and economy for large sea-going ships propelled by conventional, directly coupled

24 M Outside corrosion of and slagformation on tubes in oil-fired engines. C. Kapsenberg, 1964.

boilers (Dutch). W. J. Taat, 1957. 60 5 Natural frequencies of free vertical ship vibrations. C. B. Vreug-25 S Experimental determination of damping, added mass and added denhil, 1964.

mass moment of inertia of a shipmodel. J. Gerritsma, 1957. 61 S The distribution of the hydrodynamic forces on a heaving and 26 M Noise measurements and noise reduction in ships. G. J. van Os

and B. van Steenbrugge, 1957. pitching shipmodel in still water. J. Gerritsma and W. Beukelman,1964.

27 S Initial metacentric height of small seagoing ships and the

in-accuracy and unreliability of calculated curves of righting levers. 62 C The mode of action of anti-fouling paints: Interaction betweenanti-fouling paints and sea water. A. M. van Londen, 1964. J. W. Bonebakker, 1957. 63 M Corrosion in exhaust driven turbochargers on marine diesel

28 M Influence of piston temperature on piston fouling and pistonring

wear in diesel engines using residual fuels. H. Visser, 1959. engines using heavy fuels. R. W. Stuart Michell and V. A. Ogale,1965. 29 M The influence of hysteresis on the value of the modulus of

rigid-ity of steel. A. Hoppe and A. M. Hens, 1959.

64 C Barnacle fouling on aged anti-fouling paints; a survey of pertinent literature and some recent observations. P. de Wolf, 1964. 30S An experimental analysis of shipmotions in longitudinal regular

waves. J. Gerritsma, 1958 65 S The lateral damping and added mass of a horizontally oscillatingshipmodel. G. van Leeuwen, 1964. 31 M Model tests concerning damping coefficient and the increase in

the moment of inertia due to entrained water of ship's propellers. 66 S Investigations into the strenght of ships' derricks. Part I. F. X. PSoejadi, 1965. N. J. Visser, 1960. 67 S Heat-transfer in cargotanks of a 50,000 DWT tanker. D. J. van 32 S The effect of a keel on the rolling characteristics of a ship. der Heeden and L. L. Mulder, 1965.

J. Gerritsma, 1959. _{68 M Guide to the application of Method for calculation of cylinder} 33 M The application of new physical methods in the examination of liner temperatures in diesel engines. H. W. van Tijen, 1965.

lubricatingoils (Contin. of report 17M). R. N. M. A. Malotaux

and F. van Zeggeren, 1960. 69 M Stress measurements on a propeller model for a 42,000 DWT_{tanker. R. Wereldsrna, 1965.} 34 S Acoustical principles in ship design. L H. Janssen, 1959. 70 M Experiments on vibrating propeller models. R. Wereldsma, 1965. 35 s Shipmotions in longitudinal waves. J. Gerritsma, 1960. 71 S Research on bulbous bow ships. Part II. A. Still water perfor-36 s Experimental determination of bending moments for three

w. p. A. van Lammeren and F. V. A. Pangalila, 1965. 73 S Stress and strain distribution in a vertically corrugated bulkhead.

H. E. Jaeger and P. A. van Katwijk, 1965.

74 5 Research on bulbous bow ships. Part. l.A. Still water investiga-tions into bulbous bow forms for a fast cargo liner. W. P. A. van Lammeren and R. Wahab, 1965.

75 S Hull vibrations of the cargo-passenger motor ship "Oranje

Nassau". W. van Horssen, 1965.

76 S Research on bulbous bow ships. Part I.E. Thebehaviour ofa fast cargoliner with a conventionaland with a bulbous bow in a

sea-way R Wahab, 1965.

77 M Comparative shipboard measurements of surface temperatures

and surface corrosion in air cooled and water cooled turbine

outlet casings of-exhaust driven marine diesel engine turbochar-gers. R. W. Stuart Mitchell and V. A. Ogale, 1965.

78 M Stern tube vibration measurements of a cargo ship with special afterbody. R. Wereldsma, 1965.

79 C The pre-treatment of ship plates: A comparative Investigation on some pre-treatment methods in use in the shipbuilding indtis-try. A. M. van Londen, 1965.

80C The pre-treatment of ship plates: A practical investigation into the infiùence of different working procedures in over-coating zinc rich epoxy-resin based pre-construction primers. A. M. van Londen and W. Mulder, 1965.

81 S The performance of U-tanks as a passive anti-rolling device. C. Stigter, 1966.

82 S Low-cycle fatigue of steel structures. J. J. W. Nibbering and

J. van Lint, 1966.

83 S Roll damping by free surface tanks. J. J. van den Bosch and J. H. Vugts, :1966.

84 S Behaviour of a ship in a seaway. J; Gerritsma, 1966.

85 S Brittle fracture of full scale structures damaged by fatigue. J. J. W. Nibbering, J. van Lint and R. T. van Leeuwen, 1966. 86 M Theoretical evaluation of heat transfer in dry cargo ship's tanks

using thermal oil asaheat transfer medium. D. J. van der Heeden, 1966.

87 S Model experiments on sound transmission from engineroom to accommodàtion in motorships. J. H. Janssen, 1966.

88 5 Pitch and heave with fixed and controlled bow fins. J. H. Vugts, 1966.

89 S Estimation of the natural frequencies of a ship's double bottom by means of a sandwich theory. S. Hyla rides, 1967.

90 S Computation of pitch and heave motions for arbitrary ship forms. W. E. Smith, 1967.

91 M Corrosion in exhaust driven turbochargers on marine diesel en-gines using heavy fuels. R. W. Stuart Mitchell, A. J. M. S. van Montfoort and V. A. Ogale, 1967.

92 M Residual fuel treatment on board ship. Part II. Comparative

cylinder wear measurements on a laboratory diesel engine using filtered or centrifuged residual fuel. A. de Mooy, M. Verwoest and G. G. van der Meûlen, 1967.

93 C Cost relations of the treatments of ship hulls and the fuel con-sumption of ships. H. J. Lageveen-van Kuijk, 1967.

94 C Optimum conditions for blast cleaning of steel plate. J. Remmelts, 1967.

95 M Residual fuel treatment on board ship. Part i. The effect of cen-trifuging, filtering and homogenizing on the unsolubles inresidual fuel. M. Verwoest and F. J. Colon, 1967.

96 5 Analysis of the modified strip theory for the calculation of ship motions and wave bending moments. J. Gerritsma and W. Beu-kelman, 1967.

97 S On the efficacy of two different roll-damping tanks. J Bootsma and J. J. van den Bosch, 1967.

98 S Equation of motion coefficients for a pitching and heaving des-troyer model. W. E. Smith, 1967.

99 S The manoeuvrability of ships on a straight course. J. P. Hooft, 1967.

IOOS Amidships forces and moments-on a C» = 0.80 "Series 60"

model in waves from various directions. R. Wahab. l-967. 101 C Optimum conditions for blast cleaning of steel plate. Conclusion.

J. Remmelts, 1967.

those of calculations according to published formulae. N. J. Visser, 1967.

103 M The axial stiffnessof marine diesel engine crankshafts. Part Il. Theory and results of scalemodel measurements- andcomparison

with published formulae. C A. M. van der Linden, 1967. 104 M Marine diesel engine exhaust noise. Parti. A mathematical model.

J 1-L Janssen, 1967.

105 M Marine diesel engine exhaust noise. Part II. Scale models of

exhaust systems. J. Buiten and J. I-E. Janssen, 1968.

106 M Marine diesel engine exhaust noise. Part. HE. Exhaust sound

criteria for bridge wings. J. H. Janssen en J. Buiten. 1967.

107 S Ship vibration analysis by finite element technique. Part. 1.

Geñeral review and application to simple structures, statically loaded, S. Hylarides, 1967.

108 M Marine refrigeration engineering. Part. I. Testing of a

decentraI-ised refrigerating installations J. A. Knobbout and R. W. J. Kouffeld. 1967.

109 S A comparative study on four different passive roll damping tanks. Part I. J. H. Vugts, 1968.

1-10-S Strain, stress and flexure of two corrugated and one plane

bulk-head subjected to a lateral, distributed load. H. E. Jaeger and

P. A. van Katwijk, 1968.

111 M Experimental evaluation of heat transfer in a dry-cargo ships' tank, using thermal oil as a heat transfer medium. D. J. van der Heeden, 1968.

112 S The hydrodynamic coefficients for swaying, heaving and rolling cylinders in a free surface. J. H. Vugts. 1968.

113 M Marine refrigeration engineering. Part lt. Some results of te c

a decentralised marine refrigerating unit with R 502. J. A. h bout and C. B. Colenbrander, 1968.

Communications

I M Report on the use of heavy fuel oil in the tanker "Auricula" of

the Anglo-Saxon Petroleum Company (-Dutch). 1950.

2 S Ship speeds over the measured mile (Dutch). W. H. C. E. Rösingh,

1951.

3 S On voyage logs of sea-going ships and their analysis (Dutch). J. W. Bonebakkerand J. Gerritsma, 1952.

4 S Analysis of model -experiments, trial and service performance data of a single-screw tanker. J. W. Bonebakker, 1954. 5 S Determination of the dimensions of panels subjected to water

pressure only or to a combination of water pressure and edge

compression (Dutch). H. E. Jaeger, 1954.

6 S Approximative calculation of the effect of free surfaces on trans-verse stability (Dutch). L. P. Herfst, l956

7 S On the calculation of stresses in a stayed mast. B. Burghgraef, 1956

8S Simply supported rectangular plates subjected to the combined

action of a uniformly distributed lateral load and compressive

forces in the middle plane. B. Burghgraef, 1958.

9 C Reviewofthe investigations into the prevention of corrosion and fouling of ships' hulls (Dutch). H. C. Ekama, 1962.

10S/M Condensed report of a design study for a 53,000 DWT-

-nuclear powered tanker. Dutch International Team (D.I.T.)

directed by A. M. Fabery de Jonge, 1963.

li C Investigations into the use of some shipbottom paints, based on

scarcely saponifiable vehicles (Dutch). A. M. van Londen and P. de Wolf, 1964.

12 C The pre-treatment of ship plates: The treatmentofwelded joints

prior to painting (Dutch). A. M. van Londen and W. Mulder,

1965.

13 C Corrosion, ship bottom paints (Dutch). H. C. Ekama, 1966.

14 S Human reaction to shipboard vibration, a study of existing lite-rature (Dutch). W. ten Cate, 1966.

15 M Refrigerated containerized transport (Dutch). J. A. Knobbout,

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