Auxiliary equipment as a compensation for the effect of course instability on the performance of helmsmen

NEDERLANDS SCHEEPSSTUDIECENTRUM TNO

NETHERLANDS SHIP RESEARCH CENTRE TNO

SHIPBUILDING DEPARTMENT

LEEGHWATERSTRAAT 5, DELFT

*

AUXILIARY EQUIPMENT AS A COMPENSATION

FOR THE EFFECT OF COURSE INSTABILITY

ON THE PERFORMANCE OF HELMSMEN

(HULPAPPARATUUR ALS COMPENSATIE VOOR DE PRESTATIEVERMINDERING

VAN ROERGANGERS, DIE ZICH VOORDOET OP

KOERSINSTABIELE SCHEPEN)

by

Dr. W. A. WAGENAAR

P.J. PAYMANS

(The Institute for Perception TNO)

G. M. A. BRUMMER

Ir. W. R. VAN WIJK

(The Institute TNO for Mechanical Constructions)

Ir. C. C. GLANSDORP

(Shipbuilding Laboratory of the Deift University of Technology)

Er is in de laatste jaren heel wat gepubliceerd over het manoeu-vreren van schepen waarbij veel aandacht werd besteed aan de bestuurbaarheid en andere technische problemen met betrekking tot het koershouden van het schip.

De onderlinge invloed van de mens, het schip en het

besturings-systeem heeft echter gedurende lange tijd weinig aandacht ge-kregen. De manoeuvreerproblemen veroorzaakt door het in de vaart komen van schepen met instabiele stuureigenschappen maakten duidelijk dat ook de menselijke faktor in bet integrale systeem van schip, machine en mens belangrijk was.

De introduktie van een onderzoek en manoeuvreersimulator hood de mogelijkheid de voordelen te onderzoeken van appara-tuur die ten behoeve van een betere beheersing van het sappara-tuur- en rnanoeuvreergedrag van het schip werd ontwikkeld. Bovendien kan met hehulp van een trainingskursus op de simulator de be-manning vertrouwd gemaakt worden met het schip en haar navigatie-apparatuur.

In dit rapport wordt een beschrijving gegeven van het onder-zoek naar de invloed van hulpapparatuur op de prestaties van de roergangers. 0m te onderxoeken in welke mate met behulp van een koersvoorspeller of een draaisnelheidsmeter de nauwkeurig-heid van koers houden en koersveranderíngen zou worden ver-beterd werden drie tankers met verschillende niveaus van insta-biliteit op de computer van de simulator geprogrammeerd.

Dit projekt dat door de Koninklijke Nederlandse Marine en het Nederlands Scheepsstudiecentrum TNO gezamen lii k werd gefinancierd, werd uitgevoerd door bet lnstituut TNO voor Werk-tuigkundige Constructies, het lnstituut voor Zintuigfysiologie TNO en bet Laboratorium voor Scheepsbouwkunde der Tech-nische Hogeschool Delft.

Deze eerste experimentele studie geeft niettegenstaande bet voor!opige karakter enkele hoopvolle resultaten.

NEDERLANDS SCHEEPSSTU DIECENTRUM TNO

In the past few years a great deal has been published about ship's manoeuvring and much attention was paid to the steer-ability and other technical problems in respect to maintain the ship on a straight course.

However, the mutual influence of man, ship and steering system

has not received much attention for a long time. Since the phenomenon of ships with somewhat unstable steering charac-teristics did cause manoeuvring problems it became obvious that in the integrated system ship-machine and man also the human factor became more and more important.

The introduction of a research and manoeuvring simulator created the possibility to investigate the advantages of equip-ment developed for a better control of the steering and manoeu-vring behaviour of the ship; and apart from that a training course on the simulator can make the crew familiar with the ship and her navigation equipment.

The influence of auxiliary equipment on the performance of

helmsmen was subject for the preliminary investigation, described

in this report. To investigate in what degree a course predictor or rate-of-turn indicator would improve the accuracy of course keeping and course changes, 3 tankers with different levels of instability were programmed on the computer of the simulator. This project sponsored jointly by the Royal Netherlands Navy

and the Netherlands Ship Research Centre TNO has been

executed by the Institute TNO for Mechanical Constructions, The Institute for Perception TNO and the Shipbuilding Labo-ratory of the Delft University of Technology.

The first experimental study gave, notwithstanding its explora-tory character some promising results.

Summary

7

1

Introduction

7

2

Method

8

2.1

Simulation

8

2.2

Manoeuvres

8

2.3

A second experimental condition: equipment in the wheelhouse

9

2.4

Subjects

9

2.5

Procedure

9

2.6

Recording and scoring

9

3

A preliminary experiment

IO

4 Results 10

4.1

Manoeuvres

10

4.2

Course instability and auxiliary equipment

11

4.3

Individual differences

12 4.4

Performance indices

13 5 Discussion 13 References 14 Appendix 1 15

Appendix 2

16

Appendix 3

17

Appendix 4

20

AUXILIARY EQUIPMENT AS A COMPENSATION FOR THE EFFECT

OF COURSE INSTABILITY ON THE PERFORMANCE OF HELMSMEN

by

Dr. W. A. WAGENAAR, P. J. PAYMANS, G. M. A. BRUMMER.

Ir. W. R. VAN WIJK and Ir. C. C. GLANSDORP

Summary

lt is found in a simulator study that course instability of a 250,000 ton tanker has an adverse effect on the performance of helmsmen, both with respect to course keeping and changing of course. The influence finds expression in more rudder calls and larger rudder angles, larger course deviations and overshoots, and greater loss of speed. It is possible to compensate the adverse influences of instability largely by introduction of a rate-of-turn indicator or a course predictor.

i

Introduction

In recent studies Tani [13], Rydill [12] and Motora

and Koyama [9] described some aspects of auto-pilot

steering on large tankers. Of particular interest is

course instability which can result from a hysteresis

loop in the relation between the rudder angle (5) and

the rate-of-turn (r) (fig. 1). Various authors pointed

out that a large course unstable tanker can only be

kept on a straight course

if

the automatic pilot

is

suitably adjusted to its steering characteristics.

Par-ticularly the rate-of-turn is important to the

defini-tion of an appropriate compensating rudder modefini-tion.

Up to now the effect of instability in man-steered

tankers has received less attention, probably because

of the predominant economical importance of steering

with the auto-pilot. However, the situations in which

law or seamanship prescribe steering by man, are of all

situations the most dangerous ones. It

is therefore

worthwhile to know how men react to course instability.

It is not inconceivable that men will have the same

difficulties as auto-pilots have with respect to keeping

0.8 0.6 02 o ,-0.2 -0.4 -0.6

the unstable ship on a straight course, and with

executing small changes of heading. A relevant detail

in this context is that men have severe limitations

concerning the perception

of rate-of-turn and

its

derivatives, [15]. 1f steering behaviour is deteriorated

by the instability of

the ship, it is technically possible

to improve the ship's characteristics, for instance by

enlarging the skeg area. This is often a solution typical

for the conception

of

steering as a purely technical

problem. When a ship in a manoeuvre is considered as

a man-machine system [14] solutions other than the

purely technical ones present themselves. According

to this view bad steering properties are not a

charac-teristic of a ship alone. Bad steering means that the

helmsman cannot make the ship execute prescribed

manoeuvres. The human factors approach emphasises

research on the specific problems man faces as a part of

this man-machine system. Solutions resulting from this

approach can help man to overcome these specific

problems, rather than that the problems are removed

completely, as would be the case when an unstable

ship is stabilized by enlarging the skeg area. For the

-08

-30° -20° -10° 0° 10° 20° -20°

rudder ongle ô

-10° 0°

Fig. I. Example of a stable ship (a) and an unstable ship (b).

L

0,2 S.-, 01 a,

t

H E E L HOU S E CONTROL S

present problem an ergonomic, and not too expensive solution is possibly obtained by providing the helms-man with more information about the ship's motions,

for instance on a rate-of-turn indicator, or a course

predictor.

The above mentioned topics were studied in more detail,

using the Ship Research and Manoeuvring

Simulator of the Institute TNO for Mechanical

Con-structions at Delft, as a joint effort of the Institute

TNO for Mechanical Constructions, the Institute for

Perception TNO, and the Shipbuilding Laboratory of

the Delft

University of Technology. The present

report is a result of a first experimental study which,

notwithstanding its exploratory character, gave some promising results.

2 Method

2. I Simulation

The Ship Research and Manoeuvring Simulator is

extensively described in [18]. The main parts are, as

shown in fig. 2, the wheelhouse with the helmsman,

the instruments and the controls, the analog computer

with

a mathematical

representation

of the

ship

O HELMSMAN INSTRUMENTS ENVIRONMENTAL DISPLAY

-I

WAVE DISTURBANCES ANALOG COMPUTER with ship dynamics

Fig. 2. Block diagram, representing the most important partsof

the simulator.

dynamics, and the point light source projector,

pro-jecting a realistic, moving outside-environment. The simulated ship was a tanker having a 250,000 ton displacement, with one of three different levels of

course instability. A more detailed description of the

ship dynamics due to rudder motion is presented in

appendix 1. For present purposes it is sufficient only to

mention that the instability was varied with all other

characteristics being constant. In the following the

three levels of instability will be treated as if there

were three separate ships (see fig. 3).

Ship A is a course stable ship.

Ship B is a moderately unstable ship. The width of

the instability loop is about four degrees. Ship C is an unstable ship. The width of the instability

loop is about eight degrees.

The instability of ship C is extreme. but is not

un-frequently encountered. In this way the simulation

technique enabled the experimenters to study the

effect of instability, independently of other factors. In

practice it will be very hard, if not impossible, to

manipulate instability as an experimental variable.

The manoeuvres on the simulator as desciibed in

the next section, were executed in open sea, at a

nomi-nal speed of ten knots, without effects of wind and

current. Wind influence was excluded because of the

fact that this influence as such can change steering

properties of the ships. The only disturbance was intro-duced by the swell, which corresponded to a sea state

occuring at windforce 7 on the Beaufort scale. The

simulation of the effect of waves is described in

appendix 2.

2.2 Manoeuvres

The experiment was explicitly designed to study the

behaviour of a helmsman executing course orders.

ship A

to starboard to port, to,starboo,rd ,to port,

C

30 -20 -10 0 lO 20 30 -20 -lO 0 10

rudder angle t rudde angIe 5 rudde angIe 5

Fig. 3. Results of Dieudonné spiral tests for the three levels of instability.

20 30 -0 2 -30 to starboard 0 to port 10 20 -20 -10

Hence the manoeuvres could simply be limited to course

keeping and course changing. The four manoeuvres

chosen were:

keeping the initial course of 060 (time I 5 mm)

changing the course from 0600 to 063° (time 10 mm)

C.

changing the course from 060° to 065° (time 10 mm)

changing the course from 060° to 085° (time 15 mm)

lt was assumed that the first three manoeuvres would

induce a great number of small rudder deflections,

possibly within the instability loop, whereas the fourth

manoeuvre would call for a greater number of rudder

deflections outside the instability

loop.

Henceforth

the manoeuvres will be indicated by ck (course keeping)

30, 5° and 25° (change of 3°, 5° and 25°). The duration

of each manoeuvre was chosen in such a way that

several oscillations around the desired course could

occur. The initial forward speed was always 10 knots.

It was not allowed to use the telegraph. Hence the inlet

steam flow of the turbine was kept constant. The

manoeuvres were executed in open sea, in order to

prevent the possible infiLience of additional

informa-tion from references ashore. The ship sailed on deep

water.

2.3

A second experimental condition: equipment in

the wheelhouse

In the introduction it was suggested that more

informa-tion about the ship's moinforma-tions than rendered by the

gyro compass only, could possibly improve the

perfor-mance of a helmsman, as it did with auto-pilots. Two

auxiliary sources of information were studied in the

present experiment. Consequently the manoeuvres

were executed with three states of equipment:

without auxiliary equipment (w)

with a rate-of-turn indicator (rti)

with a course predictor (cp)

The rate-of-turn indicator shows the angular velocity

of the ship, with the effect of waves filtered out

com-pletely, without time delay or a phase shift. For this

exploratory set up it was assumed that such an ideal

filtering is possible. The turning speed indicated by

the rate-of-turn indicator will be called "pure" in

contrast with the actual, "disturbed" rate-of-turn.

The course predictor

is

described in detail

in

appendix 3. For the present purpose it will suffice to

mention that the prediction was made by a simple

mathematical model of the ship. running independently

of the large model described in appendix 1. The input

data were actual course, pure rate-of-turn,

actual

rudder angle and the instability of the ship. The output

was the predicted course which would be arrived at

in a period of x seconds, provided that no new rudder

action was initiated. After a preliminary experiment

x was set at 100 seconds (section 3). The prediction

was updated every four seconds. The predicted course

was shown on an ordinary digital voltmeter. A review

of literature on predictor displays is given in appendix

4. lt should be stressed that the present course

pre-dictor was based upon only one of the many systems

that exist.

2.4

Subjects

The subjects (Ss) were nine trainees of the School of

Navigation at Rotterdam. All Ss were studying for the

rank of first mate, after having been at sea for several

years. Hence it was assumed that all of them had

steer-ing experience comparable to the experience of real

helmsmen. Only one of the Ss had sailed on a ship

larger than 70,000 ton displacement.

2.5

Procedure

The variables instability and equipment (each with

three levels) were combined into nine conditions. The

Ss were run in all conditions, while the order of the

conditions was varied systematically. In each condition

the four manoeuvres were executed in direct succession.

The order of the four manoeuvres was randomized.

Hence the total number of runs was: 3 (instability) x 3

(equipment) x 4 (manoeuvres) x 9 (Ss) = 324 runs. One

condition (= four runs) lasted somewhat tess than one

hour. For all Ss the nine conditions were divided over

three sessions of three hours each, of three consecutive

days. This experimental design counterbalanced

sys-tematic influences of practice and/or fatigue, but as a

consequence it was impossible to analyse these

in-fluences separately.

Information on the effects of

practice and fatigue may only be obtained from

dif-ferent

experiments,

designed

specifically

for this

purpose.

All Ss received a one-hour training period, in order

to get accustomed to the ships and the instruments.

During this period they steered ship A and ship C,

both without auxiliary equipment, and ship B with

the rate-of-turn indicator and the course predictor,

successively.

In the instruction the Ss were asked to behave exactly

as they would do on a real ship in open sea. No special

stress was laid on either accuracy or speed of execution

of the manoeuvres.

2.6

Recording and scoring

The following parameters were continuously recorded

on magnetic tape and/or graphic paper:

3 A preliminary experiment

In section 2.3 it was mentioned that the course

pre-dictor indicated which course would be arrived at in a

period of x seconds, provided that no new rudder

action was initiated. The optimal value of x is to be

determined in a separate experiment in which x is

varied over a large range. The theoretical dilemma is

that too small values of x give no new information to

the helmsman, whereas too large values of x induce

unreliable predictions. In the preliminary experiment

the effects of only two values of x, viz. 60 sec and 100

sec were compared. Three Ss executed three

manoeu-vres (ck, 3° and 25°) with ship B, and with both values

of x. It appeared that the two values of x induced

only very small differences with respect to the behaviour

of the helmsmen: with x = 60 they showed a tendency

to approach the desired course more quickly and with

a slightly enlarged overshoot, whereas with x = 100 a

more cautious behaviour was observed. The differences

being rather marginal, it was decided without further

experimentation to set x at 100 sec. The choice was

guided by the argument that the type of steering

behaviour observed with x = lOO sec would presumably

to a greater extent represent normal steering at open

sea.

4 Results

Rudder scores, course scores and velocity scores were

subjected to analyses of variance. The results of these

analysis are given in an interim report [19]. All

differ-ences to be mentioned in the present section were

significant or highly significant, either as a result of

the analyses of variance, or as a result of a posteriori

Newman-Keuls-tests [16].

4.1 Manoeuvres

The four manoeuvres differed with respect to the three

scores: rudder, course and velocity, as is shown in fig. 4.

The effect is trivial, since it is inevitable that the 25°

manoeuvre will call for more use of the rudder, larger

initial differences between actual and desired course,

and more speed loss. Newman-Keuls tests showed

that the manoeuvres ck, 3° and 5° did not differ

consistently, whereas each differed significantly from

the 25° manoeuvres. Therefore all analyses of variance

2 0 m,0 0.4 w WO o> 0.2

>- o-C-) o W

time r, running from O to T

rudder angle 5

C.

course angle

Ii

pure rate-of-turn r

disturbance c4

disturbed rate-of-turn rf+d

forward velocity v

For each of the 324 runs the following scores were

calculated:

rudder score =

[.

Jödi]

course score =

T 4

[TS(t_4a)2dn]

velocity score =

r1

T

L-

v,)2_d

where t,l'd

= desired course

= initial forward velocity (= 10 knots)

Additionally for the 81 runs in the course keeping

condition were calculated:

performance-index of Koyama =

TS0t'TS0t

(4)

rate-of-t urn score

0 R° w 6 o> OW L. o o

>0

_ck 30 50 ₂₅₀ manoeuvre

Fig. 4. Rudder scores, course scores and velocity scores for the

four manoeuvres, averaged over instability, equipment and Ss.

r dt

(5)

8° o f.

rudder call score = average number of rudder calls!

o> 6

o

were repeated for the ck, 3° and 5° conditions together,

and for the 25° condition separately. As the speedloss

was very small for the other manoeuvres, only velocity

scores of the 25° condition were analysed.

4.2

Course instabili,'v and auxiliar i equip/neat

The analyses of variance for the ck, 3° and 5°

manoeu-vres showed that instability affected both rudder score

and course score. At the same time it was found that

introduction of auxiliary equipment decreased the

s o o o '-0) oui

00

_o o 0 shpA B C Instobihty

Fig. 5. Manoeuvres ck, 3° and 50 Rudder scores and course

scores as a function of instability;w =without additional equipment, rfi = with rate-of-turn indicator, cp with

course predictor. Averages of nineSs.

30 + rti w w cp

Fig. 6. Manoeuvresck. 25 RLldder scores and course scores as

a function of instability. Averages of nine Ss.

rudder and course scores. The most important finding,

however, is the interaction between instability and

equipment shown in fig. 5. Newrnan-Keuls test showed

that the effect of instability was only significant for the

condition without auxiliary equipment. This means

that for course keeping and small changes of course

the detrimental influence of instability has almost

completely disappeared by the representation of more

information about the ship's motion. For the 25°

man oeuvre the analyses of variance showed rather a

different picture (see fig. 6): instability did not increase

the course scores at all. Hence there was no detrimental

effect which could be compensated for by auxiliary

equipment. Only the rudder scores showed a positive

effect of equipment, which was relatively independent

of instability.

Some typical results are presented in figs. 7 and 8.

In fig. 7 it is shown how ship C started in the

ck-condition self-sustained oscillation when no auxiliary

equipment was available. In fig. 8 a detail is shown

which was not revealed by the course scores in fig. 6:

even for the 25° manoeuvre the course is influenced by

instability. With ship C larger overshoots were made

in the condition without auxiliary equipment.

00 00 - _-1° C o e J O_2° - 1° E o C o 0° o U C a, o - 2° -3°

1111111 I

r ship A w O 5 10 15 time in min

Fig. 7. Recordings of course angles in the ck-manoeuvre.

t

C (n (n a' -30 Q) o J o - -10 -30 o

;

10 D 0)

lo

o -10 -20 -30 I I shipA -B -C -. O 5 time J mLrì 10

Fig. 8. Recordings of course angles in the Averages of nine Ss.

15

25°-manoeuvre,

The speed loss reached an important value only in

the 25° condition. The analysis of variance showed

that the velocity scores increased with instability and

decreased again by the effect of auxiliary equipment.

These results are illustrated in fig. 9.

It should be remarked that the velocity scores are

bound to give about the same information as the rudder

scores, since the two scores are highly correlated

(r = 0.85, p«O.Ol).

A posteriori tests revealed that no systematic

dif-ferences existed between the rate-of-turn indicator and

the course predictor. In figures 5-9 it is shown that

at one time the course predictor and at another time

the rate-of-turn indicator gave the better results.

4.3 IndividuaI differences

The individual differences were significant for rudder

scores, course scores and velocity scores. The

inter-action between individual performance and

manoeu-vres was due to the deviating results

with the 25°

manoeuvre. Some Ss were good at course keeping or

small changes of course, and bad at the 25°

manoeu-vre, whereas others showed the reverse effect. The

mutual correlations between the individual

perfor-1go 9.8 9.6 98 96 94 92

-\

5

slip A

cp B rti

time ir, min

Fig. 9. Speed loss during the 25°-manoeuvre. Averages of nine Ss.

manees in each of the manoeuvres are presented in

table I.

Table 1. Rankcorrelations (Spearman's r0) between individual performances in each of the manoeuvres mutually, and between those performances and experience on large ships, as defined by the displacement of the largest ship each subject sailed upon. 5% significance for r0> 0.60; 1% significance for r0 > 0.78. (S. Siegel: Non para-metric statistics, McGraw Hill 1956).

a

10 15

The figures in table

1

show that the performance

with the 25° manoeuvre was highly correlated with

experience on large ships. The latter finding is a clear

indication that Ss should be chosen carefully. A most

important finding is that the adverse effect of instability

and the favourable effect of equipment on course and

manoeuvre experience ck on large ships ck 0.38 3,,

0.05

0.85** 5° 6.47 0.85** 0.78** 25° 0.83**

0.02

0.42 0.03 O

-/

/

-lo -20 96 g4 94 10 0 .0 J C w o o o C -x C

t

0) a

t

C E 10 0 o

rudder scores were present for all Ss, even though these

effects on the course score were larger for some Ss

than for others.

4.4 Performance iiidices

Koyama [8] proposed a combination rule for rudder

and course scores. The performance index

ii=J(_4a)2d1+

=0

T1=0

dr

(4)

where:

t

= time, rLlnning from O to T

= rudder angle

= course angle

= disered course

r1

=

pitre rate-of-turn

is used as a criterion for the optimization of auto-pilot

adjustments. The index is applicable in the course

keeping conditions. The weighting factor 8 is probably

too large for the ship under study, but for the present

no sound measurements of the precise value are

available.

Another index suggested by Koyama is:

T

J2 = $ (r1)2 dt

(5) (=0 UI 200 L) U, o loo L) 150 C _-1 00 400 300 o

Fig.IO. Performance indices according to formulae(4)and (5)

as a function of instability, for the ck-manoeuvre.

AveragesofnineSs.

which represents the increase of speed loss caused by

inertial forces. This loss is larger than the loss defined

by equation (4) when the self-induced oscillation is

dominant. Values of both indices are presented in fig.

10. Again the data show an adverse effect of instability

and a favourable effect of additional equipment.

Another important index of the performance of the

total system is the number of rudder calls per minute.

Frequently a rule is used, which states that for course

keeping the steering machine should not be called

upon more than four times a minute. In this respect

again a favourable effect of auxiliary equipment is

found (Fig. li). The unstable ships satisfy the rule only

when the rate-of-turn indicator or the course predictor

is used.

5

-

it, UI o u UI 50 o UI O shipA B C instability

Fig. H. Numberofruddercalls per minute in theck manoeuvre. Averages of nine Ss.

5 Discussion

The questions stated in the introduction are both

answered affirmatively:

course instability has an adverse effect on the

performance of helmsmen, and

the presentation of additional information can

compensate for the effect of instability to a large

extent.

The effects are less straightforward for large changes

of course, but they exist there too. The auxiliary

equip-ment had a favourable effect on speed loss, performance

indices and number of rudder calls, even on the stable

ship A.

A point which deserves some extra comment is the

lack of a clear differentiation between rate-of-turn

indicator and course predictor. A first sight one would

choose for the rate-of-tLlrn indicator as a simpler and

probably cheaper instrument. It is possible, however,

that further experimentation will yield better results

shp A B C

for the course predictor. Some reasons for this

sup-position are:

the course predictor was a new and rather

sophis-ticated piece of equipment. Initially some Ss had

difficulties in understanding what was to be

predict-ed and how the prpredict-ediction could be uspredict-ed. Obviously

this effect was compensated for during the later

sessions. In these sessions some Ss tended to try a

more daring execution of the manoeuvres, since a

normal cautious execution became too easy when

using the course predictor. Hence it is really possible

that in the later sessions the course predictor gave

better results than the rate-of-turn indicator.

The course predictor was only "a" course predictor.

It is not unthinkable that other ways of

presenta-tion of the predicted course (for instance on a

two-dimension display, see appendix 4) would yield

better results.

the prediction time was chosen quite arbitrarily.

There is no guarantee that 100 sec was the best

prediction time.

These three factors, plus the problem of "cleaning"

the rate-of-turn by a filter technique, require additional

experimentation.

It is obvious that the final solution should be tested

on real ships and under various conditions, but thus

far the exploratory results carry the promise that the

adverse influence of course instability on the

perfor-mance of helmsmen may be compensated for by the

use of simple auxiliary equipment.

References

I. BERNOTAT, R. and H. WIDLOK, Principles and applications

of prediction display. Journal of the Institute ofNavigation

1966, 19, pp. 361-370.

BERNOTAT, R., D. DEY and H. WIDLOK, Die Voranzeige als

anthropotechnisches Hilfsmittel hei der Fiîrung von Fahr-zeugen. Forschungsberichte des Lander Nordrhein-West-falen. nr. 1893 Westdeutscher Verlag, Köln und Opladen,

1968.

BIRMINGHAM, H. P. and F. V. TAYLOR, A design philosophy

for man-machine control systems. In Sinaiko, H. W. (Ed.) Selected papers on human factors in the design and use of control systems. New York: Dover Publications, 1961, pp.

67-87.

BRIOGS,

G. E., Tracking behavior, Comments on Dr.

Poulton's Paper. in Bilodeau, E. A. (Ed.). Acquisition of skill. New York: Academic Press, 1966, pp. 411-424. CONKLIN, J. E., Effect of control lag on performance in a tracking task. J. Exp. Psychol. 1957, 53, pp. 261-268.

FROST, G. G. and W. K. MCCOY, A "predictor" display for on-board rendez-vous optimization. AMRL-TR-65-81,

Aerospace Medical Research Laboratories, Aerospace Medical Division, Air Force Systems Command, WRIGHT-PATTERSON AIR FORCE BASE, Ohio 1965.

KELLEY, C. R., Predictor instruments look into the future. Control Engineering 1962, 3, pp. 86-90.

KOYAMA, T., On the optimum automatic steering systemof

ships at sea. In: Japanese Society of Navel Architects, 1967,

122.

Moio., S. and T. KOYAMA, Some aspects of automatic steering of ships. Japanese Shipbuilding and Marine

Engi-neering 1966.

PouLroN, E. C., Tracking behavior, in Bilodeau, E. A. (Ed.). Acquisition of skill, New York: Academic Press, 1966, pp.

361-410.

POULTON, E. C., Tracking, in Bilodeau. E. A. and I. McD. Bilodeau (Eds.). Principles of skill acquisition, New York: Academic Press, 1969, pp. 287-318.

RYDILL, C. J., A linear theory for the steered motion of ships in waves. Transactions R.1.N.A. 1959.

TANI, H., The course-keeping quality of a ship in steered conditions. J.S.N.A. 1952.

WAGENAAR, W. A., Human aspects of ship manoeuvring and simulation, International Shipbuilding Progress 1970, 17, pp. lI-14.

5. WAGENAAR, W. A. and J. A. MIcH0N, The effect of

contract-ed time scales in scale model manoeuvring. The institute for Perception TNO, Report IZF 1968-C3.

WINER, B. J., Statistical principles in experimental design. New York: McGraw.Hill 1962, pp. 77-85.

ZIEBOLZ, H. and H. M. PAYNTER, Possibilities of a two

time-scale computing system for control and simulation of

dynamic systems. Proceedings of National Electronics Conference, 1954, 215-223 qLloted by Kelley (1962).

BRUMMER, G. M. A. and W. R. VAN WIJK, The ship

manoeu-vring and research simulator of the Institute TNO for

Mechanical Constructions. Delft, Netherlands. Report nr.

8133. September 1970.

WAGENAAR, W. A., P. J. PAYMANS, G. M. A. BRUMMER, W. R. VAN WIJK and C. C. GLANSDORP, Auxiliary equip-ment as a compensation for the effect of course instability on the performance of helmsmen, An exploratory study by simulation. Institute TNO for Mechanical Constructions. Delft. Netherlands, Report nr. 81610, July 1971. (Not

Appendix i

S/up dynamics

The mathematical models of the three tankers with

different levels of stability were programmed on the

analog computer of the steering and manoeuvring

simulator. A description of the set up of the

mathe-matical model is given in a paper by Van Wijk [I].

In order to have three different levels of stability

only some of the coefficients of the mathematical

model have to be different. The results of a Dieudonné

spiral manoeuvre for each tanker are presented in fig. 3.

It must be noted that the terms in the mathematical

model representative for masses and moments of

inertia remained unchanged according to the

assump-tion that the stability of the three tankers was only

effected by design modifications and not by a large

change of ship dimensions. lt was further assumed that

the tankers were operating in unrestricted waters for

both the horizontal and vertical direction. The nominal

speed of the ships was chosen as IO knots corresponding

to 55 r.p.m. This speed can be met during pilotage

through fairways and approaches of harbours when

the ships are very often under manual control. The

dynamic behaviour of the three tankers is demonstrated

by performing 20/20 zig-zag trials (see fig. 12).

With respect to the results of the zig-zag trials, (see

Glansdorp

[2])

it

is

noted that the tanker with

medium instability properties has characteristics as

overshoot angle and period time frequently met at this

size of tankers.

References

I. VANWiJK. W. R., Modelling of ships for simulation (Dutch), Institute TNO for Mechanical Constructions, Report 8 133/3,

December 1970.

2. GLANSOORP. C. C., Measuring methods for dynamic models (Dutch) Shipbuilding Laboratory, Deift University of

Appendix 2

Influence of waves

It was decided that for a realistic simulation the

in-fluence of waves on the course could not be dispensed

with.

Large tankers have only small motions even due to

wind and wave forces at the higher Beaufort numbers.

It was therefore decided that BF 7 should be used for

this simulation.

It was assumed that the three tankers had the same

geometric dimensions and the same distribution of

masses so that the responses of the tankers on waves

are the same in each case.

The calculation of the ship's frequency

characteris-tics was done according to the results given by Vugts

[I], using basically the strip method. A survey of the

treatment of ship motions in irregular waves is given

by Gerritsma [2].

Using the following symbols

frequency

response function

for

the yawing

motion

S

spectral density of the wave

Srr

spectral density of the yawing motion

V

ship's speed

g

acceleration of gravity

r(t) rate of turn

t

time

phase angle

a,,

randomly chosen from the uniform distribution

a,, 27t

phase response function for yawing motion

vertical displacement of the water surface

wave amplitude

direction of the waves with respect to the ship's

course

w

circular frequency of the wave

CUe

circular frequency of encounter

The power spectrum of the waves can be given by

S(w) thu =

and the wave pattern belonging to this spectrum can

be constructed by

(t)

=

's/2S (wa) Aw cos (coat + n)

EcuO

When a ship moves with respect to the waves the

frequency of encountel

is given by the following

expression:

with the aid of the well known relation

Srr(We)dWe = IHrt(We)I2S;(We)dwe

the yaw rate spectrum can be calculated. Therefore

the wave height spectrum must be transformed to the

wave height spectrum based upon the frequency of

encounter

dw

S(We) = S(a))

dWe with dw

dw = /14WeCO5/1

However it

is necessary for simulation purposes to

have a time signal of the yaw rate

r(1) =

{COS(Wet+C+Cr) t2Srr(We)We}n

AWe O

For this simulation it was considered to be sufficient

to take

r( t)

=

{cos (Wet +C + C)\Í2Srr( We) We}n

A reason for this approximation is given by the fact

that a helmsman cannot distinghuish between more

than 4 cosinusoidal signals, which means that a time

series with 5 terms appears to him to be an

unpredict-able signal, so that he identifies this signal with the

motions due to waves.

The following particulars have been used: the

Pierson-Moskowitch spectrum [3] at Beaufort 7: speed

10 knots; angle of attack of the waves 1350: ship

having a 250,000 ton displacement. The amplitudes

and the frequencies of encounter of the rate-of-turn

signal are given in the following table:

U)

w,=w

Vcost

References

I. VuGTs, J. H., The hydrodynamic forces and ships motions in waves. Thesis October 1970. Delft University of Technology. GERRITSMA, J., Behaviour of a ship in a seaway. Report nr. 84 S, Netherlands Ship Research Centre TNO, Deift. MOEYES, G.. Characterizing of windforces and seaways (Dutch) Report KM22553/SB. January 1970, Dft-University

of Teehnc4i'gy

L

r

_/

(,j° degrees/sec 0.35 0.0593 2 0.55 0.0527 3 0.75 0.0295 4 0.95 0.0121 5 1.15 0.0039

Appendix 3

where:

Course predictor

General description

A course predictor is an instrument, that predicts the

course which a ship will reach after some time ahead,

with the present rudder angle and when no rudder

movements aie made between the present moment and

the moment for which the predicted course is

cal-culated.

The predicted course is shown on a digital voltmeter.

During the time that a predicted value is presented on

the display, which is a few seconds, the next predicted

course is calculated. After the predictor has finished

the calculation the new value enters the display and

the calculations start again.

The predictor uses a simple mathematical model

describing the course changes of the ship. This

equa-tion of moequa-tion is solved, faster than real time, at the

most important part of the predictor, a small

com-puter. The input of the equation is a constant rudder

angle which has a value equal to the actual rudder

angle at the moment the computation starts. The

initial conditions are the actual course and rate-of-turn

at the beginning of the computation. To suppress the

wave influence on the initial course angle and

rate-of-turn, these signals have to be filtered.

Mathematical model

Motora and Fujino [2] presented a discussion paper

on this subject at the 12th ITTC in Rome. They

show-ed that for less stable and unstable ships a linear

second order differential equation gives better results

for course deviations than the linear

first

order

Nomoto equation, when compared to observed full

scale values. The significance of the use of this second

order model increases when course keeping is involved.

In the same paper Motora and Fujino suggested a

modified zig-zag manoeuvre to determine the

coeffi-cients involved in this model. The modified zig-zag

trial

is performed by 5 degrees helm and switching

angles of 1 or 2 degrees. A simulation with coefficients

thus derived showed good results.

Glansdorp [1] showed, however, that for simulation

of normal zig-zag trials a non linear term must be

added and in that case too, a satisfactory agreement

was found.

For a course predictor it seems justified to use the

equation:

dr

dr

dö

T1T2

2+(T1+T2)--+ar+br3=Kii+KT3----dt

dt

dt

a

integer with the value I plus sign indicating

course

instability

minus sign

indicating

course instabihty

b

non linear damping constant

K

proportionality constant

r

rate-of-turn (dí/dt = r)

T1, T2, T3 time constants

rudder angle

The ship's characteristics are given in the coefficients

of the equations:

d2r

(i

i \dr

a

b K15(1

-+--l---

r

r +

di2

T

T2) dt

T1 T2 T1 T2 T1 T2 dw

dt

The term KT3

is equa! to zero, because the input

= 5o remains constant during the calculation.

hurlai

conditions

The initial values of course and rate-of-turn have to be

measured. The time derivative of the rate-of-turn is

neglected. In particular the rate-of-turn is difficult to

determine. This is due to the fact that the influence of

waves is present in this signal, measured by means of

a compass or a rate gyro.

At the beginning of the calculation, t = t1, the

rate-of-turn can be represented by the expression (see also

appendix 2):

r(t1)

r(15(t1))+

+

{cos (OJet

i + +

:) \Í2Srr((Oe) LU)e}n

n= I

In order to get the first term only, it is necessary to

filter the signal. As can be easily understood, it is very

difficult to separate rudder influence and wave effects,

because the rate-of-turn induced by the waves can he

of a higher order of magnitude than the rate-of-turn

induced by the rudder action.

Therefore the signal should be heavily filtered,

intro-ducing a large phase shift. The phase shift has an

un-favourable effect on the prediction.

20

20

¡+00

t-

-w

D

o

40

20

20

'i'

s

/

/

s

¿.ur

H4s

t-

-w

D

P o

40-t,

_,

/

/

N

s

o

20

L-cl)

DI

0

2

¿4

predicted

head ing

N

N

\

N

N

N

I I I I

N

ship C

N

"1

time in minutes

I L I I I I I

6

8

10

Fig. 12. The performance of the predictor while a 200/200 zig-zag trial is executed. The predicted values reached over 100 seconds

V

rudder angle

/

-r

N

N

N

Predictor design used in the present experiment

reach this course was set at lOO seconds, corresponding

approximately with

l

shiplength in this case, (see

fig. 12).

The coefficients of the equation of the predictor are

determined by a trial and error method using the results

of Dieudonné spiral tests and zig-zag trials.

Because it was beyond the scope of the present

experiment, no filter has been used for the rate-of-turn.

As the signals r() and r (waves) were separately

available, only r(5) was used as input for the predictor.

The course signal was filtered by a first order filter

with a time constant of 9 seconds.

Every four seconds an updated value of the predicted

course is supplied. The time at which the ship will

References

GLANSDORP,C. C., Simulation of full-scale resultsof

manoeu-vring trials ofa 200.000 tons tanker with a simple mathe-matical model, Report 301, March 1971, Laboratory of Shipbuilding. Delft University ofTechnology.

MOTORA,S. and M. FwlNo, On the modified zig-zag

manoeu-vre to obtain the course-keeping qualities of less stable ships, 12th ITTC. Rome 1969.

Appendix 4

i

Predictor displays

I

Introduction

Human mental prediction of the future state of a

control system is an important reason for the use of

man as part of such a control system. A well-known

example is the role of man as a driver of vehicles,

where he continuously anticipates with his reactions,

on the basis of an expected (= predicted) future state

of the system.

Bernotat and Widlok [I] listed the following

condi-tions for adequate prediction:

knowledge of the actual value of the output variable

and one or more of its derivatives.

knowledge of the input variables and the dynamic

behaviour of the system under control.

insight in the disturbances acting on the system.

lt is obvious, then, that prediction will be deteriorated

by:

insufficient perception of the actual value of the

output variable and its derivatives.

insufficient mastery of the dynamic behaviour of

the systems. This may occur when the system is too

complex (high-order terms) or when it contains

long time lags (especially sigmoid lags, Conklin

[2].)

large and largely fluctuating unpredictable

distur-bances.

lt was shown by Wagenaar [3] that the operator of a

large tanker will encounter these problems to a large

extent, whereas at the same time prediction remains a

crucial factor in the steering of large ships. Hence it

is not unconceivable that the introduction of a

pre-dictor display will make the behaviour of a helmsman

much more effective.

1.2

Taxonorni.' of predictor displays

Reviews of literature on predictor

displays were

presented by Bernotat, Dey and Widlok [4] and

Poulton [5,

6]. The following techniques are to be

distinguished.

a. A quickened display shows how to move the control

in order to obtain the desired output of the system

[7]. The operator does not have to learn to

under-stand the dynamics of the control system. The

command is calculated by the use of a transfer

function which expresses the "optimal" control

motion as a function of the observed error. The

coefficients of this function are obtained

empiri-cally. An obvious disadvantage of quickening is

inflexibility: the quickening circuits are designed

for one situation only, and the same commands

will be given in all situations. lt is questionable

whether a human operator, who did not learn to

understand the system dynamics, will be able to

detect and correct the inadequate or faulty

com-mands of a quickening display. The task does not

require a man at all : once a command has been

calculated, it may be executed by an auto-pilot as

well. This leaves the operator free to obtain status

information from his displays, to check that it is

justified to use the quickening display.

The technique of "superqiiickening" [8] reduces the

action of the operator even more :

the display

signals when a button should be depressed or

released. The only task for the operator is to

decide whether to obey the command, or not.

Quickened displays are used for the automatic

control of airplanes and submarines, but thus far

little quantitative information about the

perfor-m.ance of these displays is available.

An optimal filter display predicts the future values

of the forcing function. This can be done only if

the forcing function (which contains the

distur-bances acting on the system) shows a more or less

recurring pattern. The adequate correction of the

predicted "error" is not presented. Bernotat, Day

and Widlok [4] showed that such a display may

help a human operator.

Prediction by extrapolation

is

a real prediction

technique in the sense that a future state of the

whole system is presented to the operator. The

prediction is made by extrapolation of the previous

output function. The operator has to find the

adequate actions himself. Bernotat, Dey and Widlok

[4] obtained positive results with this technique:

they found shorter training periods, better

stabiliza-tion of the system and fewer correcting acstabiliza-tions.

Prediction with a model on an accelerated scale

presents again a future state of the system. The

instrument obtains its information from a

mathe-matical model of the system under control. The

actual output, its derivatives, and the actions of the

controller are fed into the model, which produces

the predicted output over a certain period on an

accelerated time scale.

This technique may be

applied when a mathematical description of the

system is available. The principle was introduced

by Ziebotz and Paynter [9]. Kelley [10] described

an application on submarines, and Frost and

McCoy [li] mentioned the successful use of this

type of predictor displays for rendez-vous

manoeu-vres with space vehicles. Poulton [6] observed that,

Table I. Various predictor displays.

b

C

superquickening

optimal filter display

a signal to depress or release a push button expected value of the input variable

notwithstanding the manifold application of this

technique, no quantitative results were published.

The prediction may be made under the assumption

that the controls are either kept in their actual

position or put back in the neutral position. The

predicted values can be shown on a one-dimensional

display, showing the output value after a fixed

period, or on a two-dimensional display, showing a

plot of the output variable against time, see table 1.

.3

The course predictor

The course predictor used in the present experiment

belonged to class 5. The choice was guided by the

following arguments.

quickened displays do not allow the operator to

use his adaptiveness, whereas ships are steered by

hand only on occasions where man is preferred an

auto-pilot, because of his flexibility.

the optimal filter display could not be very useful,

on one hand because the disturbance had no

recurring pattern, on the other hand because the

main difficulties lie in the unpredictable dynamic

behaviour of the system, rather than in the

un-predictable input.

prediction by extrapolation does not allow for

predictions outside the near future.

Prediction

times of 60 or loo sec will result in almost

meaning-less predictions. Hence this technique is not suitable

for slow and inert systems as large tankers are.

The predicted course was shown on a one-dimensional

display. The prediction was made under the

assump-tion that the wheel was kept in its actual posiassump-tion.

by use of a transfer-function from observed error to correction by use of the recurrent regularities in the input function

References

I. BERNOTAT, R. and H. WIDLOK,Principles and applications of prediction display. Journal of the Institute of Navigation 1966, 19, pp. 361-370.

CONKLIN. J. E., Effect of control lag on performance in a tracking task, J. Exp. Psychol. 1957, 53, pp. 261-268.

WAGENAAR, W. A., Human aspects of ship manoeuvring and simulation, International Shipbuilding Progress 1970, 17, pp. Il-14.

BERNOTAT, R., D. DEYand H. WIDL0K, Die Voranzeige als

anthropotechnisches Hilfsmittel bei der Fürung von Fahr-zeugen. Forsch ungsberichte des Lander Nordrhein-West-falen, nr. 1893 Westdeutscher Verlag, Köln und Opladen,

1968.

POULTON,E. C., Tracking behavior, in Bilodeau, E. A. (Ed.). Acquisition of skill. New York: Academic Press, 1966, pp.

361-410.

POULTON. E. C., Tracking, in Bilodeau, E.A. and I.McD. Bilodeau (Eds.). Principles of skill acquisition. New York: Academic Press, 1969, pp. 287-318.

BIRMINGHAM, H. P. and F.V. TAYLOR, A design philosophy for man-machine control systems. In Sinaiko,H. W. (Ed.).

Selected papers on human factors in the design and use of control systems. New York: Dover Publications, 1961, pp.

67-87.

BRIGGS,G. E.. Tracking behavior, Comments on Dr. Poul-ton's Paper. In Bilodeau. E. A. (Ed.). Acquisition of skill, New York: Academic Press, 1966, pp. 411-424.

Zioiz,

H.and H. M. PAYNTER,Possibilities of a

two-time-scale computing system for control and simulation of

dynamic systems. Proceedings of National Electronics Con-ference, 1954, pp. 215-223 quoted by Kelley (1962).

IO. KELLEY,C. R., Predictor instruments look into the future, Control Engineering 1962, 3, pp. 86-90.

Il.

FROST,G. G. and W. K. McCoy, A "predictor" display for on-board rendez-vous optimization. AM RL-TR-65-8 I.

Aerospace Medical Research Laboratories, Aerospace Medical Division, Air Force Systems Command, WRIGHT-PATTERSON AIR FORCE BASE. Ohio 1965.

obeying the given command

find adequate action by strategy of its own method what is presented to the how? what action is to be taken?

op.'rator

a quickening extend and direction by use of a transfer- obeying the given command of control motion function from observed (position control)

error to correction

d prediction by expected value of the by extrapolation of the find adequate action by extrapolation output variable previous output function strategy of its own

e prediction with an expected value of the by using the output of a find adequate action by accelerated model output variable mathematical model of strategy of its own

PRICE PER COPY DFL. 10.- (POSTAGE NOT INCLUDED)

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

Reports

90 S Computation ofpitch and heave motions for arbitrary ship forms. w. E. Smith, 1967.

91 M Corrosion in exhaust driven turbochargers on macinc diesel engines using heavy fuels. R. W. Stuart Mitchell, A. J. M. S. van Montfoort and V. A. Ogalc, I 067.

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 Meiden. 1967.

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

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

Rem-melts, 1967.

95 M Residual fuel treatment on board ship. Part I. 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-kelnian, 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 = 0.80 "Series 60" model in waves from various directions. R. Wahab. 1967. lOI C Optimum conditions for blast cleaning of steel plate. Conclusion.

J. Remmelts, 1967.

102 M 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.

03 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, 967. 104 M Marine diesel engine exhaust noise. Part I. A mathematical model.

J. H. Janssen, 1967.

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

106 M Marine diesel engine exhaust noise. Part III. 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 decentraI-ised refrigerating installation. 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.

110 S Strain, stress and flexure of two corrugated and one plane bulk-head sublected to a lateral, distributed load. H. E. Jaeger and P. A. van Katwijk, 1968.

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

1-leeden, 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 R 502. J. A. Knob-bout and C. B. Colenbrander, 1968.

114 S The steering of a ship during the stopping manoeuvre. J. P. Hooft, 1969.

115 S Cylinder motions in beam waves. J. H. Vugts, 1968.

116 M Torsional-axial vibrations of a ship's propulsion system. Part 1. Comparative investigation of calculated and measured torsional-axial vibrations in

the shafting of a dry cargo motorship.

C. A. M. van der Linden. H. H. 't Hart and E. R. Dolfin, 1968. 117 S A comparative study on four different passive roll damping

tanks. Part II. J. H. Vugts, 1969.

118 M Stern gear arrangement and electric power generation in ships propelled by controllable pitch propellers. C. Kapsenberg, 1968.

119 M Marine diesel engine exhaust noise. Part IV. Transferdamping data of 40 modclvariants of a compound resonator silencer. .1. Buiten, M. J. A. M. de Regt and W. P. H. Hanen, 1968. 120 C Durability tests with prefabrication primers in use of steel plates.

A. M. van Londen and W. Mulder, 1970.

121 S Proposal for the testing of weld metal from the viewpoint of brittle fracture initiation. W. P. van den Blink and J. J. W.

Nib-bering, 1968.

122 M The corrosion behaviour of cunifer 10 alloys in seawaterpiping-systems on board ship. Part I. W. J. J. Goetzee and F. J. Kievits,

1968.

123 M Marine refrigeration engineering. Part III. Proposal for a specifi-cation of a marine refrigerating unit and test procedures. J. A.

Knobbout and R. W. J. Kouffeld, 1968.

I 24 S The design of U-tanks for rol] damping of ships. J. D. van den

Bunt, 1969.

125 S A proposal on noise criteria for sea-going ships. J. Buiten, 1969. I 26 S A proposal for standardized measurements and annoyance rating ofsimultaneous noise and vibration in ships. J. H. Janssen, 1969. I 27 S The braking oflarge vessels II. H. E. Jaeger in collaboration with

M.Jourdain, 1969.

128 M Guide for the calculation of heating capacity and heating coils for double bottom fuel oil tanks in dry cargo ships. D. J. van der

Heeden, 1969.

129 M Residual fuel treatment on board ship. Part III. A. de Mooy, P. J. Brandenburg and G. G. van der Meulen, 1969.

I .0 M Marine diesel engine exhaust noise. Part V. Investigation of a double resonatorsilencer. J. Buiten, 1969.

131 S Model and full scale motions of a twin-hull vessel. M. F. van

Sluijs, 1969.

132 M Torsional-axial vibrations of a ship's propulsion system. Part II. W. van Gent and S. Hylarides, 1969.

133 5 A model study on the noise reduction effect of damping layers aboard ships. F. H. van ToI, 1970.

134 M The corrosion behaviour of cunifer-lO alloys in seawaterpiping-systems on board ship. Part Il. P. J. Berg and R. G. de Lange,

1969.

135 S Boundary layer control on a ship's rudder. J. H. G. Verhagen,

1970.

136 S Observations on waves and ship's behaviour made ori board of Dutch ships. M. F. van Sluijs and J. J. Stijnman, 1971. 137 M Torsional-axial vibrations of a ship's propulsion system. Part III.

C. A. M. van der Linden, 1969.

138 S The manocuvrability of ships at low speed. J. P. Hooft and M. W. C. ()ostrrveld, 1970.

139 S Prevention of noise and vibration annoyance aboard a sea-going passenger and carferry equipped with diesel engines. Part 1.

Line of thoughts and predictions. J. Buiten. J. H. Janssen,

H. F. Steenhoek and L. A. S. Hageman, 1971.

140 S Prevention of noise and vibration annoyance aboard a sea-going passenger and carferrv equipped with diesel engines. Part II.

Measures applied and comparison of computed values with measurements. J. Buiten, 1971.

141 S Resistance and propulsion of a high-speed single-screw cargo

liner design. I..1. Muntiewerf, 1970.

142 S Optimal meteorological ship routeing. C. de Wit 1970.

143 s Hull vibrations ol the cargo-liner "Koudekerk". H. H. t Hart,

1970.

144 5 Critical consideration of present hull vibration analysis. S.

Hyla-rides. 1970.

146 M Marine refrigeration engineering. Part IV. A Comparative study on single and two stage compression. A. H. van der Tak. 1970. 147 M Fire detection in machinery spaces. P. J. Brandenburg. 1971. 148 S A reduced method for the calculation of the shear stiffness of a

ship hull. W. van Horssen, 1971.

149 M Maritime transportation of containerized cargo. Part II. Experi-mental investigation concerning the carriage of green coffee from Colombia to Europe in sealed containers. J. A. Knobbout, 1971. 150 s The hydrodynamic forces and ship motions in oblique waves.

boxes. J. A. Knobbout. 1971.

152 S Acoustical investigations of asphaltic floating floors applied on a stcel deck. J. Buiten. 1971.

153 S Ship vibration analysis by finite elcment technique. Part Il. Vibra-tion analysis. S. Hylarides, 1971.

155 M Marine diesel engine exhaust noise. Part Vi. Model experiments on the influence of the shape of funnel and superstructure on the radiated exhaust sound. J. Buiten and M.J.A. M. de Regt. 1971. 156 S The behaviour of a five-column floating drilling unit in waves.

J. P. Hooft, 197!.

157 S Computer programs for the design and analysis of general cargo ships. J. Holtrop. 1971.

158 S Prediction of ship

rnanoeuvrability. G. van Lceuwcn and J. M. J. Journée 1972.

159 S DASH computer program for Dynamic Analysis of Ship Hulls S. Hylarides, 1971.

160 M Marine refrigeration engineering. Part VII. Predicting the

con-trol properties of water valves in marine refrigerating installations.

A. H. van derTak, 1971.

161 S Full-scale measurements of stresses in the bulkcarrier mv. Ossendrccht'. Ist Progress Report: General introduction and information. Verification of the gaussian law for stress-response to waves. F. X. P. Soejadi. 197!.

162 S Motions and mooring forces of twin-hulled ship configurations. M. F. van Sluijs, 1971.

163 S Performance and propeller load fluctuations of a ship in waves. M. F. van Sluijs. 1972.

165 S Stress-analysis of a plane bulkhead subjected to a lateral load.

P. Meijers, 1972.

166 M Contrarotating propeller propulsion, Part 1, Stern gear, line shaft system and engine room arrangement for driving contra-rotating propellers. A. de Vos, 1972.

167 M Contrarotating propeller propulsion. Part II. Theory of the dynamic behaviour of a line shaft system for driving contra-rotating propellers. A. W. van Beek, 1972.

169 S Analysis of the resistance increase in waves of a fast cargo ship J. Gerritsma and W. Beukelman, 1972.

170 S Simulation of the steering- and manoeuvring characteristics of a second generation container ship. G. M. A. Brummer, C. B. van de Voorde, W. R. van Wijk and C. C. Glansdorp, 1972.

16 S Measures to prevent sound and vibration annoyance aboard a seagoing passenger and carferry. fitted out with dieselengiiies (Dutch). J. Buiten. J H. Janssen, H. F. Steenhoek and L. A. S. lIageman. 1968.

17 S Guide for the specification. testing and inspection of glass

reinforced polyester structures in shipbuilding (Dutch). G.

Hamm. 1968.

18 S An experimental simulator for the manoeuvring of surface ships. .1. B. van den Brug and W. A. Wagenaar, 1969.

19 S The computer programmes system and the NALS language for numerica! control or shipbuilding. H. le Grand. 1969.

20 S A case study on networkplanning in shipbuiIding(Dutch..l. S. Folkers, H. J. de Ruiter, A. W. Ruys. 1970.

21 5 The effect of a contracted time-scale on the learning ability for manoeuvring of large ships (Dutch). C. L. Truijens, W. A. Wage-naar, W. R. van Wijk, 1970.

22 M An improved stern gear arrangement. C. Kapsenberg, 1970. 23 M Marine refrigeration engineering. Part V (Dutch). A. H. van der

Tak, 1970.

24 M Marine refrigeration engineering. Part V! (Dutch). P. .1. G. Goris and A. H. van der Tak, 1970.

25 S A second case study on the application of networks for pro-ductionplanning in shipbuilding. (Dutch). H. J. de Ruiter, H. Aartsen, W. G. Stapper and W. F. V. Vrisou van Eck, 1971. 26 S On optimum propellers with a duct of finite length. Part II.

C. A. Slijper and J. A. Sparenbcrg. 1971.

27 S Finite element and experimental stress analysis of models of

shipdecks. provided with large openings (Dutch). A. W. van Beek and J. Stapel, 1972.

28 S Auxiliary equipment as a compensation for the effect of course instability on the performance of helmsmen. W. A. Wagenaar, P. J. Paymans, G. M. A. Brummer, W. R. van Wijk and C. C. Glansdorp, 1972.

29 S The equilibrium drift and rudder angles of a hopper dredger with a single suction pipe. C. B. van de Voorde. 1972.