Tests with a trawler model in waves

FOOD AND 'AGRICULTURE ORGANIZATION OF THE UNITED NATIONS ; ROME ;ITALY . 510 April 1959. To be discussed ong THURSDAY MORNING 9 April

/A7

Sessiong SEAKINDLINESS

TESTS WITH A TRAWLER MODEL IN WAVES

Essais d'un modele de chalutier dans les vagues Ensayos con un modelo de arrastrero en olas

by

J.D. van MANEN

UnderDirector, Netherlands Ship Model Basin

G. VOSSERS

Head, Seakeeping Laboratory, Netherlands Ship Model Basin H. RIJKEN

Naval Architect, Netherlands Ship Model Basin Wageningen, Netherlands Contents Abstract Page 3 Résumé 3 Resumen 3

tkerti,

ex_evvy,ZA..cxj--Introduction 3

Particulars of ship and model test conditions 3

Results when trawling 4

Results in the free running condition 5

Conclusions 6

References 6

* * * * * * * * *

Paper No. 29

WORLD -FISHING' BOAT CitINGRESS

FAO/59/3/2044

-2

Nate

To be recorded in the final proceedings, written discussions should be submitted, in three copies, before 1 May

1959.

It would, of course, be

advantageous if they were received in advance of the session so that they could be duly presented and discussed.

Those wishing to participate in verbal discussion should notify the Secretary one day in advance. Reprints, summaries and abstracts may be published by the technical press, if it is clearly stated that the papers are a contribution to this Congress.

Note

Les textes des commentaires doivent etre soumis en trois exemplaires avant le ler mai

1959,

de facon

pouvoir etre inclus dans le compte rendu final. Toutefois, 11 serait preferable que ces textes parviennent au Secretariat avant la reunion pour

etre dament presents et discutes.

Les participants desireux d'intervenir dans les discussions doivent en avertir le Secretariat le jour precedent.

Les tires a part, resumes et abreges peuvent etre publies dans la presse teohnique s'il est indique clairement que les articles originaux sont des contributions a cc Congres.

Note

Las discusiones escritas que hayan de figurar en las actas finales deberdn presentarse, por triplicado, antes del 1 de mayo de

1959.

Convendria mucho recibirlas antes de comenzar el Congreso para que se Duedan presentar y discutir en la forma debida. Los que deseen participar en el debate deberdn avisar en la Secretarfa un die antes.

La Drensa tdcnica e2td n:atorizada a publicar reimpresio-nes, restimenes y extractos, mencionando claramente que el material

de

que se trate ha sido una contribuci6n a este Congreso.

Abstract

3

Tests with a trawler model with and without nozzle in still water and in waves are described. The model was tested in the free running condition (0 to 11 knots) and when towing (4 to 6 knots). It appears that the addition of a nozzle for trawler propulsion when towing in still water can be recommended. This also applies to towing in waves, except in head seas, where unfavourable tendencies were found.

Résumé

L'auteur decrit des essais d'un modele de chalutier avec et sans tuyere, en eau calme et dans les vagues. Le modele a ete essaye en route libre (0

a

11 noeuds) et en peche (4

a

6 noeuds). Ii apparalt

que l'addition d'une tuyere pour la propulsion du chalutier en Oche

par mer calme peut etre recommandee. Cela s'applique aussi

a

la 'Ache par mer forte, sauf en cas de mer debout

_oa

on a trouve des tendances defavorables.

Resumen

Se describen los ensayos de un modelo de arrastrero con tobera y sin ella en agua tranquila y en olas. El modelo se ensay6 en ruta libre (0 a 11 nudos) y remolcando el arte

₍₄

a 6 nudos). Parece ser recomendable la adiciOn de una tobera al arrastrero cuando remolca el arte en agua tranquila. Lc mismo es verdad cuando se remolca en °las, excepto si vienen de proa, en cuyo caso se encontraron tendencias desfavorables.

Introduction

Since the successful improvement of the towing capability of tugs with the Kort nozzle (nozzle propeller or shrouded propeller), a steadily

increasing number of fishing boats, particularly trawlers, are fitted with nozzle arrangements. The advantage when trawling in still water is well

known; charts on performance and methods of design have been published

(van tbanen,

1956,

van Manen and Superina,

1959).

Sometimes reference is also made to the beneficial effects of a

nozzle propeller on the behaviour of a trawler in waves. The resistance increase in head seas is claimed to give the nozzle propeller an advantage furthermore, it is said to increase the damping, thus reducing pitch. _In order to verify these claims, a typical trawler model was tested in the Seakeeping Laboratory of the Netherlands Ship Model Basin with and without a nozzle propeller in still water and in waves.

Particulars of ship and model test conditions

The lines of the trawler are based upon one of Gueroult's

₍₁₉₅₅₎

designs. A paraffin wax model, scale 1 8 13 with bilge keels, was used.

The propellers were designed for trawling at ₅ knots, with

940

SHP (metric), and a propeller r.p.m. of 160. _{The Wageningen Bseries charts were used} for the normal propeller with a diameter of 11 ft. (3.00 m.) which was a

compromise for the trawling and freerunning conditions.

The diameter of the nozzle propeller was 93 per cent of that of the normal propeller. The dimensions and the profile of the nozzle were similar to No. 18, (the open-water test results of which were published by van Manen and Superina, 1959). The dimensions of the nozzle propeller

were chosen in accordance with the ideas presented in the same publication, and Kaplan-type blades were selected.

Particulars of the ship and propellers are given in Table I and Table Body plan, profile and nozzle arrangement are shown in Fig. 1 and 2. The still-water trawling tests revealed that the propeller did not absorb exactly 940 SHP at 5 knots and 160 r.p.m. The resulting r.p.m. for the normal propeller were 160.5, and for the nozzle propeller 157.3. These values were used in the subsequent analysis.

Because no friction correction can be applied to a model in waves, the assumption was made that the differences in torque and r.p.m. between still-water and wave tests could be calculated for full size according to Froude's law. These differences were added to the still-water torque and

r.p.m. for the ship. The still-water conversion from model to ship was made with the 1957 I.T.T.C. friction formula with an allowance of 0.0004

added for roughness.

The model was tested in 0 to 13 knots free running, and 4 to 6 knots trawling. Trawling was simulated by applying a resisting force to the

model. The wave conditions were

Directions: nearly head seas (cK 1700),

nearly following seas (cK 10°),

quartering seas (o< = 450).

Lengths: ratio wave length/ship length: >./L . 0.759 1.00, 1.25.

Heights: ratio wave height/ wave lengths h/X . 1/50 and 1/30. The recordings taken were

Pitch angle (through the centre of gravity) Heave (of the centre of gravity)

Angle of roll (through the centre of gravity) Maximum emergence and submergence of the bow

in relation to the waves (Fig. 3) Acceleration at bow and stern

(f Shaft torque

(g r.P.m.

(h Speed

Results when trawling

The results of the still-water and head-seas tests when trawling are given in Fig. 4 to 6. Quartering seas and following seas results differed very little from those in still water and are therefore omitted.

The tests when trawling in waves were analysed for three operating conditions:

Trawling with constant speed and constant power- the changes in pull, propeller torque and r.p.m. as a function of the wave length/

ship length ratio are given in Fig. 4.

Constant power and constant pull the resulting speed of the ship, propeller torque and r.p.m. as a function of the wave length/ship length ratio are given in Fig. 5.

Constant speed and constant pull the resulting SHP and r.p.m. are shown in Fig. 6.

1AO/59/3/204.4 =

(I

) . 1. 3.

-5

In still water, at 5 knots, the nozzle propeller gave a pull of 12.04 ton,-while the normal propeller produced one of 10.83 ton. The

same values were found in following and quartering waves. Therefore it can be concluded that the nozzle propeller gives a considerably increased pull (11 per cent).

In head seas, however, an unexpected phenomenon was found. The

differences between the propellers became smaller; in several conditions it was even found that the nozzle propeller gave a lower pull (Fig. 4)/ or a lower speed (Fig.

5),

or required more SHP (Fig. 6). This was

contrary to expectations as it should give a better performance at higher

loads. One explanation might be the greater sensitivity of the nozzle

propeller to changes in the direction of intake velocity, which occur with heavy pitching and heaving. Another explanation might be the greater variation in efficiency of a nozzle propeller to rudder angles, although to keep the model on course in head seas, only small rudder angles of 4 to 10° were required. Further research is therefore needed.

Subsequent tests were carried out with two rudders, each placed a quarter of the nozzle's diameter from the centre line. Although very . good steering resulted, there was no improvement in the nozzle propeller's performance when trawling in head seas.

Results in the free-running condition

Fig. 7 to 10 show only the still-water and the head-sea results the other tests produced very small differences. In Fig. 7 the SHP and propeller r.p.m. are plotted against the ship's speed and the ratios of wave length/ship length and wave height/wave length. In still water the nozzle propeller required higher SHP, which was to be expected since the propellers were designed for heavy pulls; thus in the free-running

condition with a small load, the nozzle propeller would be at a disadvantage. In head seas, especially in high waves with a length equal to the ship's length or longer, where the resistance increase is high, the difference

between the propellers became smaller, and in some conditions the nozzle propeller required less SHP. There, the advantage of the nozzle propeller working with a heavy load was demonstrated.

In general, the speed of the nozzle propeller is less sensitive to changes in load, which is of advantage for some types of propulsion

machinery. When the design situation is at

160.5

r.p.m. for the normal,

and

_157.3

_{rap.m. for the nozzle propeller, a higher sailing speed can be}

obtained with the nozzle propeller, although it will require more SHP. However, there is sufficient SHP available in the free-running condition,

due to the trawling requirements, as shown in Table III, compiled from

Fig.

7.

In certain conditions such as short wave length, small wave height and high speed, even in head seas, the SHP in waves is less than in still water. This was found on many occasions with different models. A theoretical explanation has recently been offered.

The motions in head seas are given in Fig. 8 to 10. _{Heave and pitch} are given in dimensionless form; the heave, by dividing the heave

amplitude by the wave amplitude (wave amplitude . half the wave height); the pitch by dividing the pitch amplitude (in radians) by the _{maximum wave} slope,')

21-0

9 where h/X represents the wave height _{- wave lengthrn}

ratio.

From Fig. 8, with the pitch and heave _{amplitudes, no general conclusion} can be drawn about the influence of the nozzle. _{Sometimes higher,}

occasionally smaller amplitudes were found. _{The same applies to Fig. 10,} where the emergence and the submergence of the bow is given in relation to the wave height. _{The influence of the nozzle on motions and taking water} over the bow are of a secondary nature, and no definite trends _{can be} discerned.

,7A0/59/3/20:,4

--6

However, the measurements indicate that the nozzle reduces the vertical accelerations at the stern. The influence at the bow is negligible. It is therefore likely that the nozzle influences the phase angles between the motions by its damping effect, which, while not reducing pitch and heave, does decrease the vertical accelerations at the stern.

Conclusions

The following conclusions can be drawn from these tests8

For a ship trawling in still water the nozzle propeller increases pull considerably.

This remains true in following and Quartering waves.

When trawling in head seas, the nozzle propeller is unfavourable

compared with the normal propeller, because it causes either a decrease in speed, a weaker pull, or an increase in SHP.

In the freerunning condition in still water the nozzle propeller

requires a higher SHP, although at a lower number of revolutions, which is advantageous for certain types of propulsion machinery in attaining a higher free running speed.

The same applies to the freerunning conditions in following and

quartering seas.

In the freerunning condition in head seas the differences between

the propellers become smaller, and in high waves with a length equal to the ship's length the nozzle propeller is better.

The influence of the nozzle propeller on the amplitude of pitch and heave and the wetness of the foredeck is negligible.

The nozzle propeller, however, reduces the vertical accelerations at the stern.

References

GUEROULT, E.R. French motor trawlers. Fishing Boats of the World,

1955

Fishing News, (Arthur J. Heighway Publications Ltd.), London, pp.

143-153.

MANEN, J.D. van Recent research on propellers in nozzles. New York

1956

Metropolitan Section S.N.A.M.E.

EANEN, J.D. van and SUPERINA, A. Der Entwurf von DUsenschrauben.

1959

(The design of propellers for use in nozzles), Schiff und Hafen, February

1959.

* * * * * * * * *

FA0/5V3/20:(4

1. 2. 4..

Length between perpendiculars L.B.P. 42.00 m. 137.8 ft.

Length on the waterline L _{43.99 m.} 144.3 ft.

Breadth B 8.25 m. 27.06 ft.

Draught T 3.85 m. 12.63 ft.

Displacement

A

695.1 cu.m. 24543 cu.ft.

Shaft horsepower propeller SHP 940 h.p. (metric) Shaft horsepower motor SHP 1000 h.p. (metric) Speed of the propeller r.p.m. 160

Longitudinal radius of gyration

(in percentage of L.B.P.) 25%

Metacentric height GM 0.80 m. 2.62 ft.

Rolling period Tcp 8 sec.

Bilge keelsLength in percentage

of L.B.P. 40%

Height 0.20 m. 0.66 ft.

Nozzle Diameter D 2.80 m. 9.18 ft.

Lengthdiameter ratio 1/D 0.425

Anee of the nozzle profile

relative to the shaft line i 8.5°

Thicknesslength ratio s/1 0.15

PAO/59/3/2044

7

-TABLET

....5TA0/59/4/2044 Propeller No. Propeller type Number of blades Diameter Pitch ratio P/D Blade area ratio Ad

,

Hub diameter ratio d/D Rake

8

TABLE II

Particulars of the propellers

Normal 'propeller

2655

Bseries

4 3.000 m.

9.84

ft.

0.680

0.502

0.167

10°

TABLE III

Free running speeds and shaft horsepower for fixed r.p.m. Nozzle propeller

2656

Kseries

4

2,800 m. 9.18

ft.

0.900

0.540

0.184

5o Normal propeller

160.5

r.p.m. Nozzle propeller

157.3

r.p.m. Speed SHP Speed SHP 31111 water

11.09

363

11.12

580

A/L

=

0.75; h/,),

= 1%50

10.88

₃₅₇

11.10

₅₆₃

0.75; 111,A

= 130

11.09

422

10.67

551

= 1.00;

h/A

= 150

10.83

363

10.65

588

1.00; h/A = 1%30

9.73

533

10.23

586

/YL= 1.25; h/A

= 1%50

9.60

455

9.73

610

1.25; h7A = 1%30

7.50

755

7.75

825

I -D

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FIG. 3 HAXINUN EEPCENCE AND

SUBMER-GENCE OF 33" IN RELATION TO NAVES. 175 ISO A T 17s 1500 1000

TOW ROPE FORCE TESTS 411 STILL WATER AND INHEAD SEA

WITHOUT NOZZLE WAVE DIRECTION 170

---WITH NOZZLE

-S.Prntr

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WARE LENGTHis., _LENGTH

FIG. 4 TO' ROPE FORCE, PROPELLER

TOR:ILIE AND R.P.M. VERSUS RATIO "'AVE LENGTH/SHIP LENGTH FOR CONSTANT FO7E7 AND SPEED.

WAVE HEIGHT

WAVE LENGTH

510

TOW ROPE FORCE CONSTANT ION] TON (WITHOUT NOZZLE)

TOW ROPE FORCE CONSTANT 12. TON WITH NOZZLE/

SNIP'S SPEED CONSTANT S KNOTS

IL I., 125 1 a .... 0 g .9.

TOW ROPE FORCE

WITHOUT

TESTS IN STILL WATER At. IN HERO SEA

NOZZLE WAVE DIRECTION 170.

--- WITH NOZZLE 175

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CONSTANT 10.93 CONSTANT 12.04

940 SI...,

TON (WITHOUT NOZZLE>

T. (WITH NOZZLE/

1

OS 1

WAVE LENGTH /SNIP LENGTH

FIG. E SHP AND R.P.X. VERFLE

RATIO 'NAVE LENGTH/SHIP LENGTH FOR CONSTANT TON ROPE FORCE AND

SHIP'S SPEED.

CO

golm os" p

FIG. 5 SHIP'S SPEED. PROPELLER

TORUE AND R.P.M. VERSUS RATIO NAVE LENGTH/S4IF LENGTH FOR CONSTANT FOI'ER AND TON POPE FORCE.

POWER

SHIP'S

CONSTANT 940

SPEED CONSTANT S KNOTS

WAVE DIRECTION 170° TOW ROPE FORCE TESTS IN STILL WATER ANON HERO SEA

WITHOUT NOZZLE WITH NOZZLE ROPE roRCE WAVE HEIGHT WAVE LENGTH 1.0

---

r 0

-500/ WITHOUT NOZZLE --- MIN NOZZLE ZOO It% WAvE ISHT !AIL LERSTH 30 o 11: 10 SNIPS IN 1111071

FIG.. 8 RELATIVE HEAVE AND PITCH

VERSUS SHIP'S SPEED IN

HEAD SEAS.

IS 10

S L L 01p1

SELF 1PROPULSION TESTS WI STILL WATER AND IN WOAD SEA iiyE DIRECTION 170

*WOE HEiGHT t

'.!!!AIE LENGTH 30, /,,

So ,7

PIPP'4 9 ACCELEPOTIONS tT F.P. AN1

A.P. VERSUS SHIP'S SPEED

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F4114, Slif 'ND R.P.M. vEnsus SHIPS SPEED FOR IvAnAaut

:NUDE OF VAVE LENGTH/NIP LEv'GTH.

SHIPS SPEED 0KNOTS.

MERGENCE ANC, SUINNERSIENCE 01 0110 110W IN HEAO SEA

-

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FIG,. B01 EMERGENCE AND

SUPPER-GENCE VEPSUS SHIP'S SPEED

IN HEAD SEAS.

5 10

SHIPS SPEED INIKNOTS SHIP'S SPEED AN KNOTS

7

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