Manoeuvring trials of a 200.000 tons tanker

August 1969.

/2

Report No. 2J48.

LABORATORIUM VOOR

SCHEEPSBOUWKUNDE

TECHNISCHE HOGESCHOOL DELFT

r

MANOEUVRING TRIALS WITH A 200.000 TONS TANKER.

by

Ir. C.C. Glansdorp.

and

Contents.

urnmary

i .Introduction.

2.Description of measuring apparatus.

3.Tria1 program and ship's conditions during trials.

14.Besults and discussion of the trials.

5.

Concludixig remarks.

Acknowledgement.

9eferences.

Ô

urnrnary,

Contained in this report are the results of the manoeuvring trials of a 200.000 ton tanker and a description of the measuring apparatus used.

I _o

-2-i .Introduct-2-ion.

In the spring of 1968 Shell International Marines Ltd. London and the Shipbuilding Laboratory of the University of Technology at

Deift initiated a joint program concerning the mnoeuvring qualities of

a mammoth tanker.

The purposes of this program were:

gathering manoeuvring information for future autopilot designs accumulation of reference data for future model experiments information for a manoeuvring simulator.

Shell International Marines decided to make the 200.000 tons deadweight tanker Macoma, in service for the Dutch Shell Tankers N.y., available in november 1968 on a outward bound voyage to the Persian Gulf.

The manoeuvring trials were planned and performed in deep and unrestricted waters for both the fully loaded and ballasted conditions.

In this report a detailed description of the measuring apparatus and the measured results are given.

The presentation of the results is classical [i] and suits items (i) and (ii).

In a later report a simple nonlinear description of the shipts

behaviour due to helmangles will be given which will especially suit items (i) and (iii).

3

2.Description of measuring apparatus.

2.1.Selection of signals to be measured.

The following signals were recorded: rudderangle

rate of turn

relative course deviation ship's speed

2.2.Description of the sensors and servomechanisms.

2.2.1.Rudder angle sensor.

The rudder angle vas measured by a tenturn precision potentio-meter coupled to a wheel which was connected to the rudderstock by means of a steel wire. To eliminate disturbarEes in the long

connection cable between the wheelhouse and the steering engine-room n operti.onai amplifier with

a lov'output

impedance was fitted at the beginning of the cable. The electronical scheme is shown in fig.1.

The rudder angle sensor is shown in figure 2.

2.2.2,Rate of turn sensor.

The rate of turn sensor was essentially a rate gyro device placed in the wheelhouse of the ship. The electronic scheme is given in figure 1.

2.2.3.Relative course deviation sensor and servomechanism,

The course deviation was measured by the ship's gyro compass. It was possible to connect an extra receiver to the selsyn trans-mitter of the compass. The selsyn receiver was situated in a

servomechanism. A picture of this mechanism is given in figure 2. A linear potentiometer was coupled to the servo mechanism. By rotating the potentiometer manually before each run it was possible to measure the relative course deviation.

2.2.I.hip's speed sensor and servomechanism.

The ship's speed was measured by the ship's sallog. In this device an extra connection for a selsyn receiver was available which was situated in a servomechanism. The servomechanism is shown in figure

e 2; the electronic scheme is given in figure 1.

2.3 .Recording apparatus.

The signals were recorded on a frequency modulated magnetic taperecorder. Time reference was provided by a 10 KC oscillator and played upon the speach channel at the start of each run.

Dtring the tests the signals were checked with an UVrecorder,

2.I-L.Accuracy of the signals.

2.)3.1.Accuracy of the rudder angle signal.

In appendix I the specifications of the various parts of the measuring system are suimnarized.

From these figures the conclusion can be drawn that any recorded rudderangle is significantly accurate to the nearest +.1 degrees. With respect to an accurate calibration of the rudder's amidship's position we must conclude that this was impossible during the trials. Therefore it is possible that a shift in rudder angle records might exist of about i degree at the most.

2.L,2.Accuracy oÍ rate of turn signal.

Calibration of the rate gyro showed that no hysteresis could be detected. The resolution and linearity of the rate gyro fulfilled

the specifications, as shown in appendix I.

During the tests, however, the rate gyro's measured signals were only 5 to 7% of its maxinuim capacity.

If we compare its specifications to these values than a margin of difference of around 6% of the actual rate of turn signal can be

calculated. It is felt that this is a reliable estimate of the accuracy of the rate gyro, but only a modest degree of accuracy in relation to the desired results for such trials.

Due to the modulator drift a zeroshift could be detected of about 0.03 degrees/see, but because of the fact that the ship will never be steady during sailing with respect to the rate of turn, drift

could not be compensated for.

2.I.3.Accuracy of the course deviation signal.

The servomechanism was designed in order to minimize backlash of the gearboxes and toothwheels.

An estimation of the accuracy of course deviation is that any recoraed. angle is significantly accurate to the nearest. + 0,1 degrees.

No linearity errors may be expected in the electronic system since the servomechanism is coupled in phase with the selsynreceiver. The

accuracy of the gyrocompass is quite high.

2.I.lt.Accuracy of the ship's speed signal.

No estimation of the accuracy of the Sallog could be made because of lack of relevant data.

From an electronic point of view the servomechanism is significantly accurate to the nearest + 0,1 knots,

2.5.Performanceof the apparatus during the trials.

All the measuring equipment performed satisfactory during the trials. Due to extreme vibrations in case of the 30/30 zigzagtrial in the fully loaded condition the ten turn potentiometer broke down. After replacing the broken potentiometer the tests were completed.

2.6.Data reduction.

In order to reduce the frequency modulated data of the magnetic tapes, paper punched tapes were made with the aid of a digitizer. The paper tapes were fed into the computer for easy data handling.

3 .Trial program and ship's conditions durihg trials. The trial program is given in Table 1.

The ship's general particulars and the draft conditions are given in table 2. During the fully loaded tests which were performed in deep water near the

Canary Isles in november 1968, the weather was very good, Beaufort 2 and Beaufort 3 with peaks to Beaufort 1.

A slight to moderate swell came in from the South West with a height

.

of 14 to 8 feet.

During the ballasted tests the weather was even better, Beaufort i and Beaufort 2 and again a slight to moderate swell, 14 to 8 feet high from

the South West.

Table 1: Trial program.

6

Type Of run Condition Remarks

Straight line test Straight line test Straight line test Dieudonng Spiral Test

Zigzag

7,0

114 0 Zigzag 'iii 20 Zigzag '20 Zigzag 30/30

Straight line test Straight line test Straight line test

Dieudonn Spiral test

Zigzag

7,°

O Zigzag / 20 Zigzag '20 Zigzag 30, Turning Circle Turning Circle Loaded Loaded Loaded Loaded Loaded Loaded Loaded Loaded Ballasted Ballasted Ballasted Ballasted. Ballasted. Ballasted BallaBted Ballasted Ballasted Ballasted Helmsman

Electr. Autopilot, setting:1-14-0.1 Mech. Autopilot, setting:1-3-i

--Electr.Autopilot,setting: 2-5-0 Mech. Autopilot, setting: 1-3-1 Helmsman

--20 degrees Port Rudder 20 degrees S.B. Rudder

7

Table 2: General Particulars of the "Macoma".

Length between perpendiculars 310 ni.

Breadth moulded

1t6.9 in.

Depth nioulded 2145 In.

Block coefficient 0.81i

Prismatic coefficient

0.817

Lenth center of boyancy in percentage of Lpp 3.13 % forward

Horsepower 28.000

r.p.m. 80

Propeller type blades righthanded

Diameter

_8.8

_m.

Pitch/Diameter ratio

Rudder type Rudder area

Rudder area ratio

L/B

Draft during fully loaded trials Draft forward during ballasted trials Draf aft during ballasted trials

Deadweight 0.100 1 of balanced type 75.3 ni2

1/675

6.57

18.9 m. 7.3 m. 11 in. 220.000 tons

During the trials a mechanical and an electronical Anschütz autopilot were fitted.

4.Results and discussion of the trials.

I.1.Btraight line tests.

4.1.1.In fully loaded condition.

The results of these trials are shown in figure 3 and 1. tiring the trials, the rudderangle was recorded continously.

From these records, usingan eight second interval time, histograms

were made.

Interpretating these results with respect to Lyster's instability

8

hypothesis [2] does not lead to any adverse stability condition.

Looking ahead to section IL.2.1. concerning the results of the spiral test, it is evident that Lyster's direct relationship between the rudderangle histogram and rate of turn versus rudderangle curve does not hold in this case.

Accordingly, it is more likely that the unstable conditions do exist for the fully loaded state, contrary to Lyster's histogram interpretation. The validity of the comparing histograms is quite questionable, because of the fact that the disturbai: ces in each case are unknown. If we assume that the disturbances are equal for the runs with the helmsman, the electronic autopilot and the mechanical autopilot, and if we assume that the width of the histograms is a measure for the performance of helmsman and autopilots then the conclusion can be reached that the electronic auto-pilot has the best performance, followed by the mechanical autoauto-pilot and the helmsman.

14 1 .2 . Ballasted condition.

The results of the straight line tests are shown in figure 1 and 5.

The helmsman had a performance with a peak around zero helm and relatively wide limits. The histogram of the electronic autopilot is regular with a

band width of 5 to 6 degrees. The mechanical autopilot has nearly the

same band width but with a somewhat irregular character. The differences in the histograms are too small to base a final conclusion upon.

If we compare the histograms of the fully loaded trials with the ballasted trials no difference between the two conditions can be detected with the possible exception of the histogram of the helmsman.

14.2.Dieudonn's Spiral Manoeuvre.

l.2.1.In fully loaded condition.

The results are given in figure

6.

Figure 6A shows that the ship has an instability loop with a width of

slightly more than fciir degrees of helm. Figure 6B shows the average

value of the speed during the measuring period of a setting of the

rudderangle. Each measuring period lasted for at least four minutes and

generally five to seven minutes. The time elapsed between two subsequent

measuring periods was in general not less than seven minutes. Considering

the data in figure 6 B in greater detail it is obvious that in the vicinity

bn-9

gitudinal time constant of the ship is so large that the time intervals between two measuring periods were not and cannot be made long enough for the ship to return to the steady state.

The longitudinal time constant can be characterized by the displacement-horsepower ratio which is very high for mammoth tankers. To what extent the measured rate of turn is affected by the fact that the ship was apparently not in the steady state condition depends on the measure of interaction between the rate of turn and the ship's speed. The measured data presented in figure 6 must be interpreted with great care and are more likely an illustration of an instability effect than a basis for possible sophisticated autopilot designs in the future.

1 .2,2. Ballasted condition.

The results are given in figure 1.

In this condition the ship is course stable.

With respect to figure 7B it is obvious that the steady state had been

reached during these measuring periods.

The intervaltimes and measuring periods were chosen equal to those of the fully loa.ed spiral test. The longitudinal time constant is much smaller for the ballasted. condiion than for the fully loaded condition. This is easily understandable keeping the displacement-horsepower ratio in mind.

Looking at the general trend of figure 7B one must conclude that even at small rudder angles the speed drop is appreciable. It seems therefore advisable to incorporate ship's speed as a variable in course keeping problems for large tankers.

4 .3. Zigzagtrials.

14.3.1.In fully loaded condition.

The results of the trials are given in figure 8 and

9.

All the zigzagtrials in this condition have a definite asymmetric character due to the asymmetric flow pattern caused by the turning propeller.

In table 3 the most important data are summarized.

-lo-In general, zigzagtrials contain information concerning course stability and turning capacity.

Nomoto [3] introduced two quality numbers which were representative for each characteristic. His theory is, however, linear and does not include speed.

In the case of mammoth tankers we often meet course instability in unrestricted waters and an appreciable loss of speed while turning.

These factors urges one to seek a mathematical model which warrants a

more complete description of the ships behaviour on the basis of the

underlying zigzagtrials rather than the linear tiNomototi approach. The parameters in this mathematical model are indicative of the course instability and the turning capacity of the "Macomatt,

Therefore we will forgo discussion of the zigzagtrials until a later report.

l.3.2.In Ballasted. Condition.

The results of the trials are shown in figure 10 and figure 11.

In the next table the significant values of some parameters are given. IO

Table 3: Characteristics of zigzagtrials.

Condition First overshoot degrees

Overshoot time sec

Time to reach execute sec Period sec

7/ 0

SB

loo

110 85 1050 P

b8°

₃₀₀

o SB

21°

130 85 650 /1)4 _p 17° 110 20 ° SB '20 23.5° 110

85

630

P o 17.5°

80

30/30 SB 21°

90

₉₀

₆₃₀ P

i6.°

70

11

Table : Characteristics of zigzagtrials.

These results show a different pattern then the fully loaded zigzag-trials (table 3).

This is especially true for the cases.

14.14.Thrning Circle.

'4.1.In Ballasted Condition.

Figure 12 and figure 13 show the results of the ballasted turning circle tests.

The departure of the straight line curve of the course deviation shows that an appreciable overshoot in rate of turn exists.

These turning circle tests are an extension of the trial program performed by Ishikawajima-Hrinia, the builders of this ship.

-12-Condition First overshoot

degrees

Overshoot time sec

Time to reach execute sec Period sec 7/70 .5 50 360 /114 11 145

65

375 20/20° 13 145

70

1400

30°

114 _{'45 8} 1425

5.Concluding Remarks.

The accuracy of the measured signals deserves attention.

No special comments are needed for the rudderangle or course deviation; the rudder angle was measured with a potentiometer on the rudderstock and the course deviation by means of a selsyn receiver in connection with the transmitter on the gyrocompass.

Therefore the measuring accuracy was quite high.

The rate gyro which measured the rate of turn must satisfy stringent specifications because of the relatively low rate of turn of the ship, 0.5 degree/sec at the most.

This means that the demands with respect to linearity, resolution and hysteresis must be quite precise.

The sallog which measured ship's speed is basically a pitot tube acting, asymetriccally in this case, in the boundary layer.

It is therefore unknown to what extent the pitot tube is effected by oblique flow when the ship turns.

It may be expected that the accuracy of the sallog is not too high with respect to manoeuvring trials.

Referring to the histograms of the rudderangle it is felt that these

histograms, at least in this case, failed to arrive to the conclusion that the ship in fully loaded condition is unstable.

It is felt that a spiral test is a necessary manoeuvre even though the measuring time of a spiral test is extremely long, when the steady state

for each rudder setting has to be reached.

The primary conclusion is that the ship is stable when ballasted and, very probably, course unstable when fully loaded.

The turning capadty of the ship is good.

The loss of speed during turning is appreciable even with moderate rudderangles.

The real magnitude of the speed loss is unknown.

Nevertheless this faet,it seems necessary to include speed loss _{as a function} of the rudderangle in a description of the ship's behaviour.

The performance of sophisticated designed autopilots should be judged On

their stabilizing effect upon the hull's steering characteristics and on

the corresponding speed loss caused by the stabilizing rudder angles.

13

Acknowledgement.

The authors are indebted to captain de Geus of the Macoma and his officers and crew for the cooperation during the trials. They want to express their

gratitute to Mr. Snel of Shell Tankers LV. Rotterdam for giving

assistance when they prepared the trials.

The patience of Mr. F.J.F. de Klerk who prepared the graphs of this report is gratefully acknowledged.

The authors wish to thank Mr. S. Bristol for correcting the manuscript.

1-References.

fi]

Kempf, G.

"Manövriernorm fUr Schiffe"

2148 Mitteilung der Hamburgischen Schiffbau-Versuchanstalt.

f2]

Norrbin, N.H.

"Zigzag test Technique and Analysis with Preliminary Statistical Results".

[3] Nomoto, K.

Analysis of the Standard Manoeuvre Test of Kempf and Proposed Steering Quality Indices".

Symposium of Ship Manoeuvrability

_1960,

Washington.

(W&S 7223)

15

Appendix I: Specifications of sensors and servomechanisms.

Manufacture

type range

Rudder angle Rate of tarn Course Deviation Ships speed

Kearfott T2008-1A-12 12°/s Anschütz Jungner sal-214 log 0-214 kn. Manufacture type voltage frequency 115 V 1-iQO cps Contraves A6 M65A-1105 614V 50 cps Contraves A6 M65A-1105 614V 50 cps Manufacture type linearity resolution ç) life

Boums INC

31450 S-1-103 + 0.15% 0.008% 1000 hours Bourris INC 314653-1-103 + 0.3% 0.073% 1000 hours

Boums INC

314653-1-103 ± 0.3% 0.073 % 1000 hours Resolution Output linearity (% max.output + H % actual rate 0.012 0/sec O.2%+1% accuracy without demodulator

Figure 1: Electronic setup

of

measuring apparatus.

Figure 2: Rudderangle sensor and servomechanisms

for

course deviation and ship's speed.

Figure 3: Histograms of rudderangle.

Figure t: Histograms of rudderangle.

Figure

5:

Histogram

of

rudd.erangle.

Figure

6:

Results of spiral test.

Figure 7: Results of spiral test.

Figure

8:

Results of zigzagtests.

Figure 9: Results

of

zigzagtests.

Figure 10: Results

of

zigzagtests.

Figure 11: Results

of

zigzagtests.

Figure 12: Result of turning circle.

COMPASS SERVO.. MECHANISM .LOG SERV.0 MECHANISM SAL L 0G TRANSMIT TER

R U DOE R_ AN. G L .E SENS OR

STEERING - ENGINE I ROOM -15 V + 15V -o-1 I-15V

-I

-o 2.0'

-I

'I-o 30'

-I

-4

I-o .6.0'

Figure 1: Electronic setup 01 measuring apparatus.

I

I

100' 270' RUDD.ER_ ANGLE INDICATOR

-i---WH ElE L HO US,E 7. 14' 20' 30! HEATER 10 1(CS OSCILLATOR MAGNE TIC TAPE RECO R DE R U y. RECO ROE R RAIE OVRO GYRO COMPASS TRANSMITTER RECEIVER

HELMSÑAN

FULL

N=NUMBER OF OBSERVATIONS=64

r

T

-2

0

ELECT. AUTOPILOT

FULL

N=618

SETTING:1-4-O.i

o'

-4

ELEC T AUTO PILÔT

FULL

N=556

SETTING:i-L-0.1

Figure 3: Histograms of rudderangle.

i1,-- n

2 64

-2

o

2 .6 ¿

-4

2 - b 4

MECH. AUTOPILOT

FULL

N=573

SÈ TTÌNG: 1-3-1

r

HELMS MAN

FULL

N=339

ELECT. AUTOPILOT

BALL AST

N=335

SETTING: 2-5b

HELMSMAN

FULL N =460 MECH. AUTOPILOT

BALLAST

N=448

-SETTING:1-3-1

2

0

2ôL

:

Figure 1: Histograms of rudderangle.

HELMSMAN

BALLAST

N = 335

-L

-2

0

THF-Th1

2 - b L

o

o

O.2 0.1 -12 -1

0

0

8 6 o

-01

-0.2

o

-03

°/sec.

o

Io

o

00

6 -

8.

1 PORT

o

L 0 12

o

SB.

o

o

0

010

5

o

o

o

kn.

00

o

o

_o

o

PORT

o

0.4

o

0.3

r

-0.4

SPIRAL TEST FULL CONDITION.

15

SPIRAL TEST FULL CONDITION.

Figure

6:'

Results of spiral test.

-12 -10

-8

_-6

-4..

-2

0 2 ¿ 6

8 8°10

12

-.12

o

U/. ü3 Ui 2 _{_1} S .B. °/sec.

-8

-6

o

L

o

-2

o -0.2

-03

-0.L

o

I. o 6 60 PORT 0 12

o

o

o

kn.

o

10 i 5

u

S .B. PORT j-10

SPIRAL TEST BALLAST CONDITION.

-L

-2

0 2 L 6

SPIRAL TEST BALLAST CONDITION.

Figure 7:.Rësuits of spiral test.

6d 5 -4? LO 20 10 -10 -20 -30 -LO 3O 6 O

LOO O 1170 1270 13O I 15OO 1600 17

sor

00 1900 2100 22

- t sec.

ZIG-ZAG TRIAL 7/7 FÚtL

Z O -ZAG TRIAL iL/iL FULL

Figure

8:

Results of zigzagtests.

L

( 100 200 300 LO 500 600 00 800 °°r 11O 1200 1370 iL 0 1500 1T° 00 1800 1900 O 2100 29)0 3OO 21-00 2500 2600 2700 i

H

i

t---Q 2370 2L 500 2600 2700 5 6 3 2 10 -10 -20 30 -LO -SO

LO 30 20 10 o -lo -20 -30 -LO 00 13 60

t

Lo 30 20 10 o -10 -20 -30 - LO 50

ZIG-ZAG TRIAL 20/20 FULL

50 -4,.

j

10 80 r 00 p 70 19 O - 2130 - 22 t c. 2600 270

ZI0ZAG TRIAL 30/30 FULL

Figure 9: Results of zigzagtests.

:10 0 2600 2700.

JO 2L 250

70 2530

,, 80G

-

l50O

w

Ulililli IIIIHUIIIIUIIII

_RUlMUII

O 230 2L'. 25002650 27O -IO -20 -Lo 50 10 o -10 -20 -30 - Lo -50

ZIG-ZAG TRIAL 7/7 BALLAST.

ZIG-ZAG TRIAL IL/U BALLAST

La

r

20---lo ¿00 0 60 a 20' 12 1300 U 1500 - '"0 17)0 1920 1900 2000 2100 220 2300 2L -_J-t sec' 20 2500 2650 27O io lo

Lo 30 lo o -10 20 30 - Lo so 50

-r

5. 2 51 71 10 O l''O 1500 1630 17)0 30 19)0 210 21)0 22)0 2300 23.30 2530 261 2700

ZIG-ZAG TRIAL 20/20 BALLAST

ZIG-ZAG TRIAL 30/30 BALLAST

360 3L0 320 300 280 260 2L0 220 200 4' 180 o 160 1LO

-TURN BAL s ING CIRCLE LAST .8. 20° o 0 900

Figure 12; Result of turning circle.

120 100 80 60 40 20 20 o 3( o 5 o 6 O

-t 7(

¿0

10 20 TURN BA p o 30 ING CIRCLE LI AS T ORT 200 o ¿C 50o

600 -

t 70OE 800 900