A comparative study on four different passive roll damping tanks (Part I)

R-r

2

I _-

P

REPORT No 109 S

Sgo/ 107-108-109-1 09a-1 39)

NEDERLANDS SCHEEPSSTUDIECENTJ.UM TNO

NETHERLANDS SHIP RESEARCH CENTRE TNO

SHIPBUILDING, DEPARTMENT LEEGHWATERSTRAAT 5, DELFT

*

A COMPARATIVE STUDY ON FOUR DIFFERENT

PASSIVE ROLL DAMPING TANKS

PART I

(EEN VERGELIJIKEND ONDERZOEK VAN VI:ER VERSCHILLENDE

PASSIEVE SLINGERDEMPENDE TANKS. DEEL I)

by

Ir.J.H.. VUGTS

Shipbuilding. Laboratory Technological University Deift

July 1968

VOORWOORD

In 1966 werd door zes Nederlandse rederijen een reeks onder-zoekingen opgezet met het dod 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 tanksystcem dat geschikt moest zijn om in een snel lijnvrachtschip te worden geinstalleerd.

De specificatie voor het ontwerp omvatte behalve dc

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

Dc opgeleverde ontwerpen, te weten twee werkende volgens het ,,vrije oppervlakte"-principe en twee.volgens het U-tank-principe,

werden onderworpen aan een beproevingsprogramma dat uit

twee-delen bestond, namelijk uit metingen op een slinger-oscilla-tor met modellen van de tanks (schaal 1:16) door het'Laborato-rium voor Scheepsbouwkunde 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 laatsteserie proeven -om-vatte -oscillatieproeven in vlak water en proeven in regelmatige dwarsinkomende golven, in onregelmatige dwarsinkomende gol-yen en in regelmatige achterinkomende golven.

Nadat de metingen beeindigd waren zijn alle verkregen resul-taten ter beschikking van het Scheepsstudiecentrum gekomen.

Dc geste van de Stoomvaart Maatschappij ,,Nederland" N.y.,

de Koninklijke Java-China-Paketvaart Lijnen N.y., de Konink-luke Nederlandsche Stoomboot-Maatschappij NV., de N.Y.

Ko-N _{ninklijke Paketvaart-Maatschappij, dc Koninklijke}

Rotterdam-sche Lloyd N.y. en de N.y. Vereenigde NederlandRotterdam-sche Scheep-vaartmaatschappij om ook het door deze rederijen gefinancierde

dccl van het onderzoek ter beschikking te stellen, zij hier met

erkentelijkheid vermeld.

Gesteld mag worden dat dit onderzoek nuttige resultaten heeft opgeleverd, hoewel er enige punten uit naar vorenzijn gekomen die nader onderzoek behoeven.

In dit eerste rapport worden de belangrijkste resultaten van-dc proeven gegeven en wordt de rekenmethode voor het .opstellen van een prognose geverifieerd

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

Geconcludeerd kanreeds wordén dat de proeven geen absolute superioriteit vaneen van deze-tanksystemen hebben aangetoond. Bovendien'zijn voor sommige tanks weer gewijzigde uitvoeringen ontwikkeld, zodatvoor elk schip apart zal moetenworden bezien, welk systeem de voorkeur verdient.

Gaarne wordt hier nog gernemoreerd de medewerking van het Nederlandsch Scheepsbouwkundig Proefstation en het Labora-toriurn voor Scheepsbouwkunde

Ook de schrijver van dit rapport komt dank toe voor het ver-zamelen, analyseren:en samenvatten van debeschikbare gegevens

HET NEDERLANDS SCHEEPSSTUDIECENTRUM ThO

PR E F A CE

In 1966 six Dutch ShippingCompanies initiated a programme of investigations to compare a number of passive roll damping tank systems. Partly this programme was executed in cooperation with the Netherlands Ship Research Centre TNO.

Four different design offices were invited to supply 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 designs delivered, viz. two-systémsof 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 1:16) 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 regular beam waves, irregular beam waves and regular quartering waves.

After the experiments had been finished, all results obtained were put at the disposal'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 grateful' 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 systemsalready 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 gratefully acknoWledged. Also thanks are due to the'author for collecting, analyzingandsummarizing the data avaiIable

NETHERLANDS SHIP RESEARCH CENTRE TNO Report No. 109 S (July 1968)

ERRATA

-

The figures (not the subscriptions) on pages 17 and 19

must be interchanged.

- On pages 20 and 21, in tables At. .

. Aiv, e is expressed

in degrees (7th, j2th and

column of each table).

- In the subscription on page 23 read Fig. A.2 instead of

CO NTENT S

page

Summary

. . 7

1

IntroductIon

. .. . .

...

7

2 The ship data and the condition oflOading

. . 8

3

TIe tank installations

8

4 The bench tests ...10

5

Theprediction of the rolling of the shipwlth and without tank

11

6 The predicted and iñeasürcd roll response

11

6.1

The experimental programme

I'

62 The osculation tests ...

12

6.3

The tests in regular beani waves

12

7

Disussion and conclusiOns

13

8

Acknowledgement ...

13

References

13

LIST OF SYMBOLS

B

Ship's breadth

G

Ship's centre of gravity

Virtual mass moment of inertia about the rolling axis

K

General moment producing roll

Roll exciting moment, due to the waves

Kwa

Amplitude of K,,.

K,

Roll exciting moment, due to the tank

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

Kta

Amplitude of K,

N,

Damping, coefficient against rolling

R,,,

Restoring coefficient

2irk

T4, /

Natural roll period

V g GM

T

Ship's draught

b

Tank breadth (measured across the ship)

g

Acceleration of gravity

h

Water depth in the tank at rest

2n

k = -

Wave number

A

k

Transverse radius of gyration

1

Tank length (measured: forward and aft)

s

Distance from tank bottom' to axis of rotation; positive if tank above axis

Ze

Effective depth for the exponentially decreasing wave slope

= kCa

Maximum wave slope at the, surface

A

Weight of displacement

V

Volume of displacement

Phase angle betweenwave moment K,,, and rolling motin 4; positive if K leads

a,

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

Ca

Wave amplitude

2Ca = H

Wave height

A

Wave length

Kia Pa Q,gb I

N,

V.,,

=

Non-dimensional amplitude of tank mOment

Nondimensional roll damping coefficient

Q

Mass density of water

Mass density of tank fluid

Roll angle

Roll amplitude

w

Circular frequency

=

Natural roll frequency

1

Introduction

The relative merits of different passive roll damping

systems are an important question to ship owners and

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

over all other systems in any desired application.

Be-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 circumstances applying 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 Delft.

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

thç tank action when subject to a rolling motion are

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

University-Delft.

A COMPARATIVE STUDY ON FOUR DIFFERENT

PASSIVE ROLL DAMPING TANKS *

PART I

by

JR. J. H. VUGTS

Summary

Four passive roll damping tank systems will be compared for one and the same ship. In this part I of the report a method of

calcu-lation is checked with the results of model experiments.

In part II (to be published) the actual comparison will be made by means of calculated predictions for various conditions of loading The tank data have been determined by bench tests;the.resultsare presented here.

The method of prediction turns out to be areasonablebasisfor a comparativestudy and allows a comparison for additional loading conditions.

known byexperiment and provide an adequate

starting-point for further calculations. 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 predictions in 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 dimensions ofthe tanks will bechanged 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 conditions.

For further information about passive tank systems

reférencè is made to earlier publications [1 J, [2] and

8

74.52

2 The ship data and the condition of loading

The ship for which the tanks are designed is a

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

Lines. The selected loading condition corresponds

closely to the fully loaded ship, leaving port. The

par-ticulars are listed in table I. A longitudinal section of

the ship is shown in figure 1.

Table I.

Ship particulars without roll damping tank

Length between perpendiculars = 146.49 m Breadth, moulded

B = 22.00 m

Depth to upper deck

D = 13.00m

Draught forward

T1 =

9.41 m Draught aft

Ta =

985 m Draught, mean

= 963 m

Displacement, moulded V 18410 m3

Displacement including hull in

sea-water of y = 1.025 t/n13

= 18962t

Block coefficient 0596

Prismatic coefficient 0.604 Waterline coefficient 0:742 Midship section coefficient 0i986 Centre of gravity above keel

KG =

8.30 m Centre of buoyancy above keel

KB =

527 m Metacentric height GM = 0.85 m Natural rolling period T4 16 sec

Natural roll frequency = 0.393 sec-1

By these data the transverse radius of gyration is

established as k4, = 7.35 rn = 0.334B, using the

well-known formula

T

/ -

2ith4

'JgGM

This value is rather low and it seems thereforethat the

stated rolling period and metacentric height are not

too well in agreement. Using a more general value

k=-0.38B = 8.36 m leads

to

Tf, 18.2 sec with

GM

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

1 6

PLACE ANTI ROLLING TANK

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

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 showedanextremelylow

non-dimensional damping coefficient

v4,

increasing

about linearly with roll amplitude

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 v, has become dependent upon the position

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

definite value for the hull damping is not specified.

For the purpose of comparison 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 1. 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. The

per-forated plates at the sides 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

Table 'II.

Particulars of the various tank installations

A

Fig. 2Tank I

HOLES Oi5 I SPACING 0.165 BULKHEAD DIMENSIONS IN METERS LOWER TWEENDECK BULKHEAD SECTION. A-A LOWERTWEENDECK DOD Fig. 3 Tank I]

AIR BREATHER FOR MODEL IN PROTOTYPE OTHER SOLUTION, POSSIBLE DIMENSIONS IN METERS AIR OPENING 1 FORD 98 DOO DIMENSIONS IN METERS SECTION A-A 10 WENT WEENDECI(

DETAIL OF AIR' DUCT IN WAY OF DAMPER

I DAMPER

AT OPEN POSITION I DAMPERARM

Fig. 4 Tank III

3.30 15L0 Fig. 5 Tank IV gIWEENOEcK"T'" SECTION B-B O50 ° AIR BREATHER FOR EACH TANK SEPARATELY

DIMENSIONS IN' METERS

9

Tank I Tank II Tank Ill Tank IV

Actual tank volume in m3 219 221 205 220

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

Tank length in m 190 900 240 2.15

Tank breadth in m 22.00 2200 . 22.00 2200

Waterweight intons 64.0 1184 115 102.2

Water weight relative to displacement in % 0.34' 063

01

0.54

GM-reduction in rn ' , 0.18 '0.34 0.22

03l

I DV.O5)T3(

-'

N If IL PERFORATED PLATE ,I II

11=--- '.-- ..---

TANKOECK

-'I

ff350 ' . '" TANKTOP -A , 22.00' ' 093

I--.-.--

_-:s

O,7O

j

.--=

-_

TANKTOP-A -' 22.00 A LOWERTWEENDECK 0.8' 2.50-TANKDECK fl 5'

'_Lr' -'

________________ 06L ---TANKDECK I

-

-L_

:1 -zO6sIrjrzrTANKToP_ i A 22O0. II

TA

SEE DETAIL

SECTION A-A DETAIL

PERFORATED PLATE BULKHEAD

'F

00

10

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 I : 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

p0 and the phase difference with the rolling motion a.

Due to the essentially different configuration of tank H

the pavues 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.IY 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

KM sin a,, 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 1.25w,,, that is from w =

0.275 sec

'

to about w = 0.50 sec1 full

scale or

to = 1.1 to 2.0 sec1 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

a,-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 Kia and the difference of maximaxi-mum

and minimum a, in the interval to = 1.0 to 2.Osec'

(model values) are presented for 4 = 0.10.

Table III.

Variation of K,0 and a, for 4a = 0.10 in the

range from to = 1.0 sec 'to to = 2.0 sec

model frequencies

Of course these variations influence the character of

the K,a sin s components greatly as shown in figure

A.5 of the appendix for a roll amplitude 4a = 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 I II III IV I (Kta)mx 1.23 7Odeg 1.56 136 deg 1.77 92deg 1.41 I 111 deg (K,a)min (8,)mnx(Ct)mjn

This causes a rather steep decrease in Kta and increase

in a where the water motion is hampered at the higher

frequencies of 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 /a = 0.10. In system III 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 4a = 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 motions

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 studied

alone, as if the ship is a onedegree of freedom system,

since the mutual influences with swaying aüd yawing

are not known. Probably the yaw effects into roll will

not be of primary iinpOrtance, so that it would suffice

for the time being to consider the combined swaying

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

position 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 of heaving 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 st ç,_he 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+N4,q+R,,çb =

(1)

For the ship with tank the tank moment has to be

added

K,,,±K,

(2)

Here 14, 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 = QjV Q8V COCa _w2z/ (3)

g

where cc,, is the surface wave slope, which is equal to

w2,,/g. 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 K

are known by the bench tests for three amplitudes of

motion. As K, is not linear in 4

the equation (2) has

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

found by iteration. For 4'a = 0.0333; ba = 00667 and

= OjOrad the experimental results are put into

the equation, which is solved for

.

From the resulting

values of 4a 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 angles

remain between the two limits of the input values of

so for 1.9 deg <

< 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 moLat the_N.S.M.B..

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

regular beam waves, tests in irregular beam waves and

12

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 wasjust 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 waves and 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

function 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

differences. 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 60degrees. They

cover only a narrow frequency range about resonance

and the measured roll angles may be strongly affected

by the characteristics of the antomatic 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 comparison. Neither can a computation be

made in quartering waves due to the difficulties

ex-plained in section 5.

6.2

The oscillation tests

The model was forcibly oscillated in still water by

rotating weights. In the centre plane of the model two

contra-rotating vertical rods were installed, each

carry-ing 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 l.4m full scale.

The prediction is calculated accordingly by the

equa-tion (2)

I; + ±R= K + K

(2)'

or formulated differently

+

=

sin(wl+e )+sin(wt+a) (4)

K.

R4,

in which

= 0.393 sec'1

v4, = '0.05 and 0.:lO

Rç1, =AGM

=

K0 R, R

The exponential factor is taken equal to 1 because

there are no waves and consequently no decreasing

wave slope. Kta and s are known by the bench tests.

The equation (4) is solved for 4a and c. 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 and lengths

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

for a length of 310 m 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 ci,,, by

O)ta_&T/2g

g

For the damping coefficient vç, 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 v. In those figures three curves

are drawn. The middle' one applies to the basic wave

amplitude of

= I;665 m For the other curves is

= 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

alighrsea'coiidition;while-theiargest-corresponds-to-a-rather severe sea.

it can 'be seen that for the ship without a tank and

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

theother tanks v

0:05 gives a better relation.between

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 mathematical model in this case

better than another cannot be explained rationally. It

must be attributed to differences in the complex Whole

ofinterrelated modes of motionand tank performance.

But in any 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 predictiOns 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 10 are 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 v4, = 0.05 has to

be selected.

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

is taken into account by increasing the damping of

the hull with respect to the oscillation tests from

v = 0.05 toO.l 0 (figure 8). The agreement between

experiments and calculations is good for the ship

without tank (figure 8) and with tank I (figure 11),

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

trends of the experiments with tank Ill and IV are

fully predicted, but the peak values are rather off

(figures 11 and' l2) 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

suffi-ciently supported by the mode1experimentsto serve

as a reasonable basis for a comparative study of

the various tank systems. Characteristic phenomena.

are 'predicted correctly. In a quantitative comparison

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 thecalculations underestimate the rolling with

tank II or Win 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 IL 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

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

BOSCH, J. J.VAN DENand J. H. VUGTS Roll damping by free

surface tanks, Report 83S of the Netherlands Ship

Re-search Centre TNO, April 1966.

Boorasu, J. and J. J.VAN DENBoscH, On the efficacy of two

different roll damping tanks, Report 97S of the

Nether-landsShip Research Centre T.NO,, July 1967.

14 deg.

4o

1 1 0 5 0 0.1

02

₀₃

_OL U)

05

0.6

07

Fig 7 Comparison of calculated and measured rolling of the model during oscillation tests (full scale values)

WITHOUT caLculation 1ANK Vt,= 0.10 0.05

.

experiment S il

WITH TANK I

.

.

WITH TANK U

-._ S

WFH TANK III

WITH hANK 12

J

.

S

25 deg. 20 15 10 0 1s WITHOUT caLculation

TANK

V, =0.10 005 = 1.67m experiment I I I I! I I I 'I .t

0i

02

03

0.4 0.5 0.6 0.7 sec

Fig. 8 Comparisonofcalculatedandmeasured rolIingofthe model withouttank inregular beamwaves. (full scale values)

16 deg.

I

15 10 5 0 15 10 1°5 0' 01

02

03

0.4

-- w

05

06

sec.

07

Fig. 9 Comparisonofcalculated.and measured rolling of the model with tank I and II in regular beam waves; v = 0.05. (full scale values)

WITH caLcuLation

TANK I

Vq 0.05 = 231 m 1.67m 055m

-o experiment 0 0 S.

a231m,

'1.67m 055m

WITH TANK U

0=231m

deg 15 10

a

15 110 0 01

02

03

-

01. .- U)

05

06

0.7 sec.1

Fig; 10 Comparison ofcalculated and measured rolling of the model With tank III and IV in regularbeam waves; v# = 0.05; (full scale values)

.17 WITH TANK

- colcutation

UI

V =0.10 o =2.31 m 1.67m 055m o experiment e -0

I..

S S . -. 0 0.55.m WITH TANK 0 S. 0' 0=231m

.

1.67 m: 055th

18 deg. 15 1:0 0 15 10 a

WITH TANK I

- calculation

V, 0.10 o experiment = 2:31 m o 1.67m .;. 055m

WITH TANK

sec.

Fig. 11 :Comparisonofcaiculatedand measuredrollingofthemodd with tankIand ii in regular beam waves;v =0.10. (full scale values)

deg.

40

15 10 10 UI 0

WITH TANK III

catculotion V = 0.05 .o experiment 2.31 m 1.67Th o 0.55m UI

i5

WiTHI TANK ]

0.1 0.2 0 0.3 0.1.

-- w

0.5 m 1.67 rn 0.55'm

06

07

sec:1

Fig. 1'2 Comparison of calculated and measured rollingofthe model with tank III andIV in regularbeam waves; v4, = 0.10. (full scale values)

20

Table Al! -Tank -Il.

APPENDIX

Results of the bench tests

(model values, scale 1: 16)

Table A I Tank I.

& = 0.0333

0.0667

_&

0.10

(1) &/b/gKjCOSe, KtaSlfl g Kg, _{j000/a KtaCOSet KtaSlfl e K}

'000/ia -

_{Kt0cos KgasIn Et Kta}

_'°°04a

-Et

-sec-'

-

'kgm kgm kgm

-

grad. kgm kgm kgm

-

grad kgm kgm kgrn

-

grad.

0.50 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 15.14 6.0 0.75 0.2808 2.11

-0.07

2.11 6.81 1.8 4:04

-0.67

4.09 13.22 9:5 4.73

-0.93

4.82 15.58 11.1 1.00 0.3744! 2.72 -0.92. 2.87 9.28 18.7 337

-1.91

4.23 13:66 26.9 4.45

-2.13

4.93 15.92 25.6 1:25 0.4680 2.14

-2.16

3.05 9:84 45.3 2:91

-3.03

1.50 13.56 46.1 3.61 -3.31 4.90 15.83 42.4 1.50 0.5616 0.97

-2.79

2.96 9.55 70:9 1.65

-3.69

4.04 13.07 64.2 2.29

-4.13

4.72 15.24 61.0 1.75 0.6552

-0.28

-2.75

2.76 8.93 95.9 0.29

-3.69

3.70 11.96 85.5 0.82

-4.29

4.37 14.12 79.2 2.00- 0:1488

-1.62

-1.47

2.19 7.07 137.9

-0.75

-3.33

3.41 11.03 102:7

-0.45

-3.99

4.02 12.99 96.4 2.25 0:8424

-1.10

-0.05

1.10 3.55 '177.4

-2.10

-2.00

290 9.37 1364 1.69 324 3.66 '11.81 117.5' 2:50 0.9360

-0.68

-0.01 0.77 2.18 179.0

-1.43

-0.08

1.43 4.63 176.8

-2.26

-1.42

2.67 8.63 147.8 2.75 1.0296

-0.44

0 0.44 1.43 180.0

-0.94

-0.02

0.94 3.02 178.6

-1.38

-0.12

1.39 4.48 175.1 '3.00 1.1231

-0:28

0 0.28 0.91 180.0 -0.61

-0.02

061 1.96 177.6

-0.86

-0.06

0:86 2.78 175.9 3.25 1.21681 -0.23 0 0.23 0:74 180:0

-0.33

-0:01

0.33 1.05 177:9

-0.51

-0.05

0.51 1.65 174.3

4a = 00333

4a = 0.0667

t'a

0.10

w m'/b/,gKeossg Kgasin 8

_'ta

I000SUa _t 1ta(08t KtaSIfl S

'°00/'a 5t J(tacosnt KtasflSg 1Q0 l000ILa

sec-'

-

kgm' kgrn kgm

-

grad. kgm kgm kgm - grad. kgm kgm kgm

-

grad.

0.5O 0.1872 3.10

-0.15

3.10 2.12 1.7 6.42

-0.26

6.42 4.39 2.4 9.14

-0.84

9.18 6.28 5.2 0.75 . 0.2808 3.67 -0.31 3.77 2.58 .

46

7.62. --0:84

7.67 5.24 6.3 .11.58

-1.40

1-1.67 7.98 - 6.9 1.00 0.3744 5.68 -1.21 5.81 3.97 12:0 8.54

-3.15

9.10 6.22 20.2 9.15

-3.78

9:90 6.77 22.4 1.25 0.4680 5.12

-5.77

7.80 5.28 48.4 6.35 .

-7.19

9.59 6.56 48:6 6.80

-6.47

9.38 6.42 43.6 1.50 0.5616

-2.14

-7.03

7.35 5.03 107:0 0,21

-9.12

9.13 6.24 88:6 1.49 .

-9.31

9.43 6.45 80:9 1.75 0.6552

-4.55

-1.17

4.70 3.22 165:6

-5.76

-4.74' 7.46 5.10 140.5

-3.81

-7.63'

8.51 5.82 116.6 2.00 0.7488

-2.47

-0.05

2.47 1.69 178.8

-4.20

-0.62

4.24 2.98 171.6

-5.87

-2.31

6.31 4.31 158.5 2.25 '0.8424

-1.44

0.04 1.44 0:99 181.6

-2.60

-0.05

2.60 1.78 178.9

-3.94

-0.08

3.94 2.70 178:8 2.50 0.9360

-0.91

0.07 0.91 0:62 184.5,

-1.80

0.03 1.80 1.23 180.9

-2.61

0.02 2.61 1.79 180.6 2.75 1.0296

-0:59

0.07 0.59 0.40 186:5

-1.23

0:03 1.23 0:84 181.4

-1.73

0:03 1.73 1.18 180.7 3.00 1.1231

-0.35

0.03 0.35 0:24 185.5

-0.83

0.05 0.83 0.57 183.4 -1.-IS 0:03 1.15 0.78 180:7 3.25 1.2168

-0.24

0.01 0.24 0:17 182.8 -0.49 - 0.00 0.49 0:33 180.0

-0.71

0.00 0.71 0.49 180:0

Table All Tank HI.

21

Table AIV Tank IV.

= 0.0333

= 00667

= 0.10

a) oV'b/gKacos E KtaSIfl 8 Kia l000aUa KgaCOS Kt0sIn g Kta l000fLa St KCOS KtsIn K0 1000i,

-sec'

-

kgrn kgm kgm

-

grad. kgm kgm kgm

-

grad. kgm kgm kgm

-

grad.

050 01872

166

-042

171 438

l44

350

-068

357 914 110 550

-107

560 1425 110

075 02808

1 77

-067

189 485 207 373

-127

394 1010 188 584

-215

623 1596 202

100 03744

201

-116

232

594 300 393

-234

457 1172 308 548

-432

698 1790 382 1.25 04680 186

-206

2.77 7.11 47.8 3.13

-4.20

523 13.42 53.3 3.02

-6.14

6.84 17.54 63.8 1.50 0.5616 063

-306

3.12 8.01 78.3 0.53

-4.98

5.00 1283 83.9 031

-6.03

6.04 15.44 87.0 1.75 0.6552

-1.13

-2.28

2.54

6.52116.5

-1.63

-3.77

4ii

10.53 113.4

-1.80

-4.69

5.02 12.87 111.0 2.00 0.7488

-1.26

-0.94

1.57 4.03 143.1 -2.11

-2.07

2.96 7.58 135.6

-2.57

-3.01 3.96 10.16 130.5 2.25

08424 -085

-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 09360 -0.58

-0.17

0.60 1.54 163.4

-1.22

-0.43

1.29 3.31 160.6

-1.83

-0.83

2.01 5.16 155.6 2.75 1.0296

-036

-0.07

0.36 0.93 168.7

-080

-0.18

0.82 2.10 167.1

-1.23

-0.43

1.30 3.33 160.8 3.00 1.1231

-020

-006

0.21 0.53 164.1

-0.47

-0.15

0.49 1.26 162.2

-0.76

-0.20

0.78 2.01 165.2 325 1.2168

-0i3

-005

0.43 0.11 1:59.4

_-0.28

_-0.14

0.32 0.82 153.2

-0.39

-0.18

0.43. 1.15 155.2

--

& = 0.0333

& = 0M667

& = 0.10

w wVbgKcoss 1<taSil Cp Kta

'°°0/-a -

KgaCoSeg KtaSjfl E Kta

_'°°°1a

t KCOS E Ksin Ct

Kta _{'000Ia -8g}

sec'

-

kgm kgm kgm

-

grad.: kgm kgm kgm

-

grad. kgrn kgm kgm

-

grad. 0.50 0.1872 2.61

-0.20

2.62 749 4.4 587

-037

588 16.82 3.6 7.64

-1.35

7.75 22.19 100 0.75 0.2808 3.23

-030

324

9i8

5.2 629 -1.31 6.42 18.39 11.8 7.18

-2.57

7.63 21.83 19.7 1.00 0.3744 4.16

: -1.25

4.34 12.43 16.8J 5.77 -3.53' 6.76 19.35 31.5 620 4.57 771 22.06 364 1.25 0.4680 3.46

-3.58

498. 1425 460 401

-577

7.02 20.09 55.2 4.44

-6.56

7.92 22.67 56.0 1.50 0.5616

-067

-536

5.40 1546 97.1

-1.43

-686

7.01 20.05 .101.8 0.55

-7.74

7.76 22.20 860 1.75 0.6552

-386

-1.73

4.23 l211' 1558

-394

-4.05

5.65 16.16 134.2

-3.81

-'5.94 7.10 20.31 122.7 2.00 0.7488

-289

-0.42

2.91 8.34

171.8.: -372

-1.96

.4.20 12.03 152.2

-4.69

-3.01 5.58 15.97 147.3 2.25 0.8424i

-1.54

0.06 1.54 439H 182.2

-3.12

-0.77

321 9.20 166.2

-3.59

-1.93

4.08 1167 151.7 2.50

09360l -0.96

th07 096. 2.75 184.2

-2i4

-0.01

2.14 6.13 179.6

-2.91

-086

3.04 8.69 163.7 2.75

1.0296' -062

'006 0.62 1.77 185.2

-1.33

0.05 1.33 380 182.0:

-2.16

-0.16

2.17 6.20 175;8 3.00 1.1231

-0.43

005 0.43 L23 186.6

-098

0.02 0.98 2.79 181.0

-1.59

-0.15

1.60 45r/ 174.6 3.25 1.2168:

-0.28

0.03 0.29 081 186.0

-062

0.04 0.62 1.78 .183.3 : -1.01 0 1.01 2.90 1800

22 ILa 0.020 0.015 0.010 0.005 0 -180 degrees -90

TANK I

05 tdVB7

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

is

G

_0a 0.0333

o

0.0667

o

_0a 0.1000 10

wVi

1.5 1.0 05

0.020 0.015 .0.010 0.005 0 05 10 b/g

g. AtNondimensional .amplitude-and-phase of thk mQment for tank II; measured by bench. tests.

15. 00333

o

= 00667 0a 1.5 23

TANK ii:

.

SU

.

.

.

--180 degrees C -90

wV7

.05 1!0

24 Pa 0.020 0.015 0.010 0.005 0 C -90

TANK Ili

0.0333 0.0667

0

= 0.1000

- Fig. A.3 Nondimensionalamplitude and phaseof tank moment for tank III; measured bij benchtests.

0.5 10 iS

05 _{.1 a wV 1.5}

-180

0.020 0.015 0.010

I

0.005 0'

£ -90

'TANK &

Fig. A.4 NoAdiñiensiOnal amplitude and phase of tank moment for tank IV; measured by bench tests

0a = 00333 0a = 0.0667 0.1000' 25. 0.5 '10

w\f

15 0.5 10

wVi

1.5 -180 degrees

26 kgf.m 10 .9 8 7 sinEt 6 5 4 3; 2 0.

0

TANK I

0

TANK U TANK

+

TANK iS

Fig. A.5 Comparison of quadrature componentsof tank moment for = 0.10.

big

PUBLICATIONS OF THE NETHERLANDS SHIP RESEARCH CENTRE TNO

(FORMERLY THE NETHERLANDSRESEARCH'CENTRE TNO FOR SHIPBUILDING AND NAVIGATION)

PRICE PER COPY DFL

10-Reports

M -, engineering department S = shipbuilding-department

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1 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. Wereldsma, 1960.

3 S Practical possibilities 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-beck, 1951.

39 M

405

Crankshaft coupled free torsional-axial vibrations of a ship's

propulsion system. D. van Dort and N. J. Visser, 1963., On the longitudinal reduction factor for the added mass of vi-5 vi-5 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 andJ. A. Sparenberg, 1961. and E. J. Diehl, 1952. 41 5 Stresses in flat propeller blade models determined by the

moire-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, t962. 7 M Cylinder wear in marine diesel engines (Dutch). H. Visser, 1952. 43 C Raft trials and ships' trials with some underwater paint systems.

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 properties of ships with respect to noise control'. 9 S 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 Some acoustical properties of ships with respect to noise controlPart II. J. H. Janssen, 1962.

10 S 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.

11 M The use of three-phase current for auxiliary purposes (Dutch). 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

12 M 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, 1962.

13 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 steel (Dutch). Interim report.

14 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 15 S Investigations of the stress distribution in corrugated bulkheads shipmodel. J. Gerritsma and W. Beukelman, 1963.

with vertical troughs. H. E. Jaeger, B. Burghgraef and I. vander

Ham, 1954. 505 The influence of a bulbous bow on the motions and the propul-sioninlongitudiñalwaves. J. Gerritsma and W. Beukelman, 1963. 16 M Analysis and testing of lubricating 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 usingwheel-abrators and the applicationof 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 Londen,

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 Wolf and 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 5 Numerical calculation of vertical hull vibrations of ships bydiscretizing the vibration system. J. de Vries, 1964. 23 S Second series of stability experiments on models of lifeboats. B.

Burghgraef, 1956. 59 M Controllable pitch propellers, their suitability and economy forlarge 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 S 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 instill 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 pertinentliterature and some recent observations. P. de Wolf, 1964. 30 S An experimental analysis of shipmotions in longitudinal regular

waves. J. Gerritsma, 1958. 65 5 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!. 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.

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

and F. van Zeggeren, 1960. 69 M Stress measurements on a propeller model for a 42,000 DWTtanker. R. Wereldsma, 1965. 34 S Acoustical principles in ship design. J. 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

72 S Research on bulbous bow ships. Part. II.B. Behaviour of a

24,000 DWT bulkcarrier with a large bulbous bouw in a seaway. 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 S 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.B. The behaviour of a fast cargo liner with a conventional and 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 indus-try. A. M. van Londen, 1965.

80 C The pre-treatment of ship plates: A practical investigation into the influence 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.

84S 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 as a heat transfer medium. D. J. van der Heeden,

1966.

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

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

1966.

89 5 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. cOgale, 1967.

92 M Residual fuel treatthent on board ship. Part 11. Comparative

cylinder wear measurements on a laboratory diesel engine using filtered Or centrifuged resk!ual fuel. A. de Mooy, M. Verwoest and G. G. van der Meulen, 1967.

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

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

1967.

95 M Residual fuel treatment on board ship. Part 1. The effect of cen-trifuging, filtering and homogenizing on the unsolubles in residual fuel. M. Verwoest and F. J. Colon, 1967.

96 S 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.

100 S Amidships forces and moments on a GB= 0.80 "Series 60"

model in waves from various directions. R. Wahab. 1967. 101 C Optimum conditions for blast cleaning of steel plate. Conclusion.

J. Remmelts, 1967.

102M The axial stiffness of marine diesel engine crankshafts. Part I. Comparison between the results of full scale measurements and

those of calculations according to published formulae. N. J.

Visser, 1967.

103 M The axial stiffness of marine diesel engine crankshafts. Part II. Theory and results of scale model measurements and comparison with published formulae. C. A. M. van der Linden, 1967. 104 M Marine diesel engine exhaust noise. Part 1. A mathematical model.

J. H. Janssen. 1967.

105 M Marine diesel engine exhaust noise. Part II. Scale models of exhaust systems. J. Buiten and J. H. Janssen, 1968.

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

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

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

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

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

decentral-ised refrigerating installation. J. A. Knobbout and R. W. J.

Kouffeld. 1967.

109 5 A comparative study on four different passive roildamping tanks. Part I. J. H. Vugts, 1968.

110 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 II. Some results of testing a decentralised marine refrigerating unit with R502. J. A. Knob-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. G.E. Rosingh,

1951.

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

4 S Analysis of model experiments, trial and service performance

data of a single-screw tanker. J. W. l3onebakker, 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, 1956.

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

1956.

8 S 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 Review of the 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-class nuclear powered tanker. Dutch International Team (D.LT.)

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

11 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 treatment of welded 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, 1967.