i

TOW ROPE LENGTH AND ARRANGEMENT DESIGN FOR A TOWED SHIP

UMAR IMRAAN BIN ZAN

A thesis submitted in fulfilment of the

requirements for the award of the degree of

Master of Engineering (Marine Technology)

Faculty of Mechanical Engineering

Universiti Teknologi Malaysia

SEPTEMBER 2014

iii

To my beloved mother, father and family members,

For your love and affection.

To my dedicated lecture,

For the encouragement and guidance.

To my loving wife and son,

Ashikin & Naimil

For having faith in me,

Your unconditional love and unfailing support

Those keep me going.

iv

ACKNOWLEDGEMENT

First of all, I would like to express my gratitude to God Almighty because of

His blessing finally, I have completed this research successfully even though there

are so many obstacles that I had to go through during completing this research.

My special thanks to my supervisor, Dr. Koh Kho King, for his invaluable

guidance, professionals comments and suggestions, as well as encouragement. He

spends his precious time in refining my draft and sharing his knowledge with me. I

learnt a lot from every moment of the meetings with him.

In completing this thesis, I would like to thank Prof. Dr. Adi Maimun Bin

Abdul Malik and Dr. Ahmad Fitriadhy for spending their time to give comments and

contribute ideas and also to Prof. Hironori Yasukawa from Hiroshima University for

lending the Rake-barge model and FORTRAN source code.

Not to forget, I would like to thanks all the technicians for spending their time

in conducting the model test for this research. I wish them all the best in whatever

they do. Thank you.

v

ABSTRACT

This research presents the investigation on the effect of different tow rope

lengths and arrangements for a towed ship in calm water by using the experimental

model conducted at Marine Technology Centre, Universiti Teknologi Malaysia.

Three variations of tow rope arrangements were tested in the experiment: Straight-

tow, V-tow and Kite-tow. A total of fourteen types of tow rope arrangements were

tested at a constant speed of 0.5 m/s and a rake-barge were captured via Qualysis

Track Manager (QTM) „Image Processing Techniques‟. From the experiment, it was

observed that for Straight-tow, the tow rope length increment was proportional to the

oscillation where for every increment of Lv length (length of tow rope in V shape

arrangement) reduced the oscillations by around 12%. Kite-tow arrangement design

offered a better safety towing system and has nearly zero sway motion but large

water width due to the drift distance from the tow point which is around 0.64 and 1.1

times barge length. The result from Straight-tow with different skegs arrangement s

showed significant improvement in reducing the sway motion pf the towed barge.

Similarly, V-tow barge with different skegs arrangements also presented a substantial

improvement in decreasing the amount of sway motion. In the final part of the

research, computer simulation using FORTRAN program and codes from Yasukawa

& Fitriadhy (2010) were carried out and the results were compared with the

experimental model of Straight-tow barge. Computer simulations and model

experiment results showed less than 10% deviation in sway motions.

vi

ABSTRAK

Kajian ini membentangkan hasil kajian penyiasatan kesan perbezaan panjang

dan susunan tali tunda bagi tundaan kapal di air tenang dengan menggunakan model

eksperimen ujikaji yang telah dijalankan di Pusat Teknologi Marin, Universiti

Teknologi Malaysia. Tiga variasi susunan tali tunda telah diuji dalam eksperimen:

Straight-tow, V-tow dan Kite-tow. Sebanyak empat belas jenis susunan tali tunda

telah diuji pada kelajuan tetap 0.5 m/s dan rake-barge telah digunakan sebagai kapal

yang ditunda dalam kajian ini. Pergerakan ayunan huyung daripada rake-barge

direkodkan melalui Qualysis Track Manager (QTM) Image Processing Techniques.

Daripada eksperimen ujikaji, dapat diperhatikan bagi Straight-tow; pertambahan

kepanjangan tali tunda adalah berkadar langsung dengan pergerakan huyung di mana

untuk setiap kenaikan 0.5L tali tunda tersebut, pergerakan huyung telah meningkat

sebanyak 35%. Untuk V-tow pula, pertambahan panjang Lv (panjang tali tunda

dalam susunan bentuk V) adalah berkadar langsung dengan pergerakan huyung di

mana ia telah menyebabkan pengurangan pergerakan huyung sebanyak 12%. Reka

bentuk susunan Kite-tow menawarkan tundaan kapal yang lebih selamat dan hampir

tiada pergerakan ayunan huyung direkodkan tetapi ia memerlukan ruang air yang

besar kerana jarak hanyut dari titil penundaan iaitu sekitar 0.64 dan 1.1 kali ganda

kepanjangan kapal. Kombinasi Straight-tow dengan susunan skegs yang berbeza

telah menunjukkan penambahbaikan yang ketara dalam mengurangkan gerakan

huyung. Begitu juga dengan kombinasi V-tow dengan susunan skegs yang berbeza

yang juga menunjukkan penambahbaikan dalam mengurangkan pembentukan

huyung. Di bahagian akhir kajian ini, simulasi komputer yang menggunakan

program FORTRAN dan kod dari Yasukawa & Fitriadhy (2010) telah dilakukan

untuk dibandingkan dengan model eksperimen Strainght-tow tundaan barge. Hasil

keputusan daripada simulasi berkomputer dan model eksperimen ujikaji tersebut

menunjukkan kurang daripada 10% sisihan dalam pergerakan huyung.

vii

TABLE OF CONTENT

CHAPTER

TITLE PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES x

LIST OF FIGURES xi

LIST OF APPENDIX xiv

1

INTRODUCTION

1

1.1 Background of Study 1

1.2 Problems Statement 5

1.3 Research Objectives 6

1.4 Scopes 6

1.5 Significance Of Study

7

2 LITERATURE REVIEW 8

2.1 Introduction 8

2.2 Barges Particulars 9

2.3 Tow Rope Length 12

2.4 Towline Arrangement

2.4.1 Straight-tow Arrangement

13

13

viii

2.4.2 V-tow Arrangement 14

2.5 Skegs 15

2.6 The Problems In Towing Operation

2.6.1 Six Degree of Freedom

2.6.2 Sway Motion and Slewing Motion

2.6.3 Stable Barge Towing System

16

17

18

19

2.7 Software Used For The Past Research

2.7.1 Lamped Mass

20

20

2.8 Tension Force on Towing Cable 21

3

RESEARCH METHODOLOGY

23

3.1 Introduction 23

3.2 Research Flowchart 24

3.3 Model Test Framework

3.3.1 Straight-tow Arrangement

3.3.2 V-tow Arrangement

3.3.3 Kite-tow Arrangement

3.3.4 Skeg

25

25

26

27

28

3.4 Apparatus

3.4.1 Towing Tank

3.4.2 Qualisys Track Manager

3.4.3 Oqus Camera

3.4.4 Wand Stick and L-Frame

3.4.5 Qualisys Marker

3.4.6 Load Cell

30

31

32

34

35

36

37

3.5 Experiment Setup

3.5.1 Model Preparation Procedures

3.5.2 Calibration

3.5.3 Experiment Procedures

37

38

40

42

3.6 Motion Equation Derivation

3.6.1 Assumptions

3.6.2 Coordinate System

3.6.3 Motion Equations of a Towed Ship

43

43

45

46

ix

3.6.4 Motion Equation of Tow Rope

3.6.5 Dynamic Tow Rope Tension Equation

49

51

4

RESULTS AND FINDINGS

52

4.1 Introduction 52

4.2 Experimental Results 53

4.2.1 Straight-tow 53

4.2.2 V-tow 56

4.2.3 Kite-tow 57

4.2.4 Combination of Skegs with Straight-tow 59

4.2.5 Combinations of Skeg with V-Tow 60

4.3 Computer Simulation Results 64

5

DISCUSSION

65

5.1 Introduction 65

5.2 Suitable Tow Rope Length for a Towed Ship 65

5.3 Effectiveness of the Kite-Tow Arrangement Design 66

5.4 The Advantages of Skegs 67

5.5 Result Comparison 68

6

CONCLUSION AND RECOMMENDATION

72

6.1 Conclusion 72

6.2 Recommendation 73

REFERENCES

APPENDIX A

75

80 - 85

x

LIST OF TABLES

TABLE NO.

TITLE

PAGE

2.1 Principal dimensions of rake barge model 10

2.2 Resistance coefficient, added mass coefficients and

hydrodynamic derivatives on maneuvering

11

3.1 Details of Straight-tow configurations 25

3.2 Details of V-tow configurations 26

3.3 Details of Kite-tow configurations 27

3.4 Details of Straight-tow and V-tow configurations

with skegs modification

28

xi

LIST OF FIGURES

FIGURE NO. TITLE

PAGE

2.1 Rake Barge model 9

2.2 Rake barge body plan 10

2.3 Single towline 14

2.4 Regular V-tow arrangement 15

2.5 Uncontrolable movement during towing 16

2.6 Translational and rotational components of ship

motion

18

2.7 Definitions of course stability of a towed barge:

stable (top), unstable (middle), and marginally

stable (bottom)

19

2.8 Lumped mass model for tow rope 21

3.1 Research flowchart 24

3.2 Straight-tow Arrangement 25

3.3 V-tow Arrangement 26

3.4 Kite-tow Arrangement 27

3.5 Position of 3 skegs (S3) 29

3.6 Position of 2 skegs (S2) 29

3.7 The skeg dimension pasted at the side of the ship 30

3.8 The skeg dimension pasted at the center of the ship 30

3.9 Towing basin 31

3.10 Towing carriage 32

3.11 The visual of QTM software 33

3.12 Processing setup 34

xii

3.13 Oqus camera 35

3.14 Wand Stick and L-frame 36

3.15 Qualisys markers 36

3.16 Load cell 37

3.17 Swinging frame 39

3.18 Model ballasting 39

3.19 QTM calibration in progress 40

3.20 Calibration data 41

3.21 Coordinate system 44

4.1 Sway motion of Straight-tow ST-1L, ST-1.5L and

ST-2L

54

4.2 Tow force comparison between Straight-tow 55

4.3 Sway motion of V-tow VT-1L-05, VT-1L-08 and

VT-1L-10

56

4.4 Tow force comparison between V-tow 56

4.5 Sway motion of Kite-tow KT-20 and KT-40 57

4.6 Tow force comparison between Kite-tow 58

4.7 Sway motion of ST-1L-S3 and ST-1L 59

4.8 Tow force comparison between Straight-tow with

and without skegs

59

4.9 Sway motion of VT-1L-05-S3 and VT-1L-08-S3 60

4.10 Tow force comparison between VT-1L-05-S3 and

VT-1L-08-S3

61

4.11 Sway motion of VT-1L-08-S2 and VT-1L-08-S3 61

4.12 Tow force comparison between VT-1L-08-S3 and

VT-1L-08-S2

62

4.13 Sway motion of VT-2L-08-S3 and VT-2L-08-S3 63

4.14 Tow force comparison between VT-2L-08-S3 and

VT-2L-08-S2

63

4.15 Sway motion of Straight-tow ST-1L-CS, ST-1.5L-

CS and ST-2L-CS

64

5.1 Sway motion comparison between ST-1L and

ST-1L-CS

69

xiii

5.2 Sway motion comparison between ST-1.5L and

ST-1.5L-CS

70

5.3 Sway motion comparison between ST-2L and

ST-2L-CS

70

xiv

LIST OF APPENDIX

APPENDIX

TITLE

PAGE

A Qualysis Track Manager User Manual 80

1

CHAPTER 1

INTRODUCTION

1.1 Background of Study

According to Toxopeus et al. (2013), offshore going barges are one of the

preferred means of transportation for the transport of large structures over sea. This

is because the barge is important in transporting the large quantity of cargo in the

need for water way transportation. It is very convenient to use the barge since there

are a lot of problems in inland way transportation such as cramped traffics,

maintenance cost and etc. As mentioned by Yasukawa et al. (2007) and Phelan

(2008), there are many potential hazards that might occur such as collision and/or

grounding in barge towing system. Fitriadhy et al. (2012) mentioned that the barge

towing system might intrude sea traffic ways, especially in the restricted waters

where it will lead to serious towing accidents which might cause the towed barge

collides and affects the safety of the ship or shore installations and even worse when

tow rope breakage and barge capsizes.

It can be observed that not all ships have the ability to remain steady

especially during the towing operations. Some of the ships might face problems in

terms of steadiness. As a result, this may lead to the difficulty in towing progress

2

where the ships tend to move in a dangerous pattern or motion; in other words, it can

be regarded as the uncontrollable movement during towing as reported by Lee,

(1989). The towline can cause fatal accidents and many forget how quickly things

can go wrong when a line is under load.

According to Recreational Boating Statistics (2011) there were 22 cases

reported on the vessel operation in year 2011 involving 1 death and 7 injuries. The

Maritime Accident Casebook (2010) also showed an increasing number of incidents

occurred during ocean towage. In 2007, Flying Phantom was girted and sank while

acting as a bow tug for Red Jasmine which resulted in 3 fatalities and 1 injury as

reported by European Maritime Safety Agency (2007). Because of the complicated

routines in towing and lack of safety, there are many potential hazard and risks that

could occur during ship towage as mentioned by Phelan (2008).

Generally, towing can be defined as an operation that often includes long

hours of tedious routine which involving short periods of intense activities and works

as stated in International Maritime Organization (1998). In order to reduce the risk

of accidents, everyone especially the crew must be diligent and cautious towards the

successful completion of the mission. This is because, even the slightest lapse in

attention or effort may result in major accidents and mishaps as specified in

International Maritime Organization (1998).

Based on the Canadian Coast Guard Auxiliary Search and Rescue Crew

Manual (2011), the crew must ensure all gears (lines, shackles, messenger, drogues,

tow bits, chafing gear, fairleads, etc.) have been checked for wear and tear. The

inspection of equipment especially the towing gear and towline should be carefully

carried out in order to have a clear and smooth towing operation. According to the

International Maritime Organization (1998), the tow should not proceed to sea until a

satisfactory inspection of the tow has been carried out by the towing master and if

requested or for any reason considered necessary, by any other competent person.

The tow assessment and planning are very important in considering the safety aspect

3

of the towing operation. During the assessment, the obvious danger and primary

factors to look for and be reported including the vessel state, people on board,

environmental factors and so on as mentioned in Auckland Council Harbourmaster‟s

Office, (2011). Besides that, it is crucial to communicate constantly and clearly

during towing operations when asking questions and giving instructions. Other than

that, all aspects of the towage should be planned in advance, taking into

consideration the factors such as maximum anticipated environmental conditions,

including tidal streams, current and water depths, as well as the size, displacement

and draft of the tow as detailed in International Maritime Organization (1998).

Rescue and salvage towing generate a necessary sense of urgency. There are

several important aspects that need to be considered while conducting the towing

operations. One of the most significant aspects is the tow-rope used in towing a ship

or vessel. According to The American Heritage Dictionary (2009), tow-rope is „a

line used in towing vessels and vehicles‟. The function of tow-rope is to assist the

tugboat by holding another vessel during the towing process. Because of that, there

are many important aspects that need to be considered while conducting the towing

operations. According to Wang et al. (2008) suitable tow rope length may contribute

to towing maneuvering while offering the great level of safety and sway motion.

According to Yang et al. (2010) the unstable motions such as the sway motion and

yaw motion will occur inevitably during towing. Effects of sway motion need to be

minimized in order to ensure safe and smooth towing operation as acknowledged by

Shigehiro et al. (1998) and Bhattacharyya and Vendan, (2000).

In improvising the method of controlling the course stability in barge towing

system, the skegs were later added in the rake barge model. According to Lee (1989)

the course stability of the towed ship is significantly improved by adding the skegs.

The advantages of the skegs are considered as one of the test subject in providing the

smooth and safe barge towing system. Considering all these factors, this work

focuses on the effect of two different parameters, tow rope length and tow rope

arrangement design.

4

The main purpose of this research is to determine the optimum tow-rope

length and arrangement for a towed ship (60.96 m rake barge) during a tow operation

in calm water condition. This research also investigates the effectiveness of the kite-

tow arrangement design in term of steadiness as compared to straight-tow and V-tow

arrangement, while investigating the pattern of the towed ship motion during the

towing operation. In addition, this research also determines the effect of the new

design of towing arrangement which is called as kite-tow arrangement. As far as this

study is concerned, this arrangement has never been investigated by any researchers

before. From this type of arrangement, the ship will be towed from the port or

starboard of the ship using the combination of tow-rope in certain angles. The details

of this towing arrangement are discussed in the tow rope arrangement section.

As mentioned before, this study also caters on the arrangement of the rope

which can be exploited during the towing progression. There are many types of tow

rope arrangements used by ship towing company. Each of the arrangement will give

a different effect on a towed ship in terms of controlling, course stability, safety and

steadiness. As stated by Bernitsas (2004), the towed ship cannot be returned to their

original path which resulted from the effect of the sway motion unless they are

pulled by exciting forces or moments. In this research, the focus is more on the

steadiness of towing a ship and at the same time learning and identifying the patterns

of the towed ship motion.

5

1.2 Problem Statement

One of the problems that can be addressed to the need of this research is

about the safety of the towing operation system. Today, towing a large ship is

fraught with potential risks and accidents during towing operations. In port, tugs are

often working in a restricted space with limited room for maneuver, while long

distance offshore tows have their own particular problems. Safety can be regarded as

the serious and important issues as it involves not only the ship and the lives of the

crews but, any accidents happen will give a great impact to the environment such as

oil spill.

The main problem that needs to be overcome is to determine the suitable tow

rope length and applicable towline configuration. This is due to the fact that these

factors may assist in reducing the sway motion which is regarded as one of six-

degrees-of-freedom (6DOF) as stated by Price (1991). This is because the sway

motion may lead to the uncontrollable or large oscillation movements during the

towing operation. This is crucial as this issue involves the safety of the ship and the

crews.

Considering of all these factors, this study emphasizes on several different

tow rope arrangements designs and of towing methods in order to reduce the sway

motions. Besides that, it also aims to produce a better towing operation where the

towed ship can be towed steadily and has almost zero of the sway motion

characteristics.

6

1.3 Research Objectives

The aims of this research are:

i. To examine the effect of tow rope length on sway motion and towline

tension for barge towing system.

ii. To investigate the effectiveness of the kite-tow arrangement in term of

reduction of barge sway motion and towline tension as compare to

straight-tow and V-tow arrangement.

iii. To compare the experimental results with the established computer

simulation results on the motions of the towed ship.

1.4 Scopes

The scopes of this research are:

i. Rake barge model as towed ship to be used in the study.

ii. Model experiments to be performed in Marine Technology Centre.

iii. Model test to be performed in calm water condition.

iv. Comparison with the established computer simulation programming.

v. Tug motion is assumed to be given.

7

1.5 Significance of Study

There are many significant points that can be highlighted from this research.

One of the crucial points that can be seen is in terms of the safety aspect. Therefore,

this study can offer some ideas on the optimal length of tow rope that can be used in

order to avoid any accidents from occurring.

Besides that, this research could improve the ship steadiness and reduce the

sway motion. So, from the various arrangements conducted, it may help in solving

the problem of unsteady sway motion characteristics of the towed ship. This

research also introduces the new tow rope configuration which is called as “Kite-

tow”. This towline arrangement may reduce the huge oscillation of sway motion

create by barge during towing operation.

75

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