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  • UNIVERSITI TEKNIKAL MALAYSIA MELAKA

    DESIGN OF REMOTELY UNDERWATER VEHICLE (ROV)

    USING EMBEDDED SYSTEM

    This report is submitted in accordance with the requirement of Universiti Teknikal

    Malaysia Melaka (UTeM) for the Bachelor of Electrical Engineering Technology

    (Industrial Automation and Robotics) with Honours

    by

    MOHAMMAD ADIB BIN SALIKON

    B071210234

    911008 - 01 - 7075

    FACULTY OF ENGINEERING TECHNOLOGY

    2015

  • UNIVERSITI TEKNIKAL MALAYSIA MELAKA

    BORANG PENGESAHAN STATUS LAPORAN PROJEK SARJANA MUDA

    TAJUK: Design of Remotely Underwater Vehicle(ROV)Using Embedded System

    SESI PENGAJIAN: 2014/15 Semester 2

    Saya MOHAMMAD ADIB BIN SALIKON

    Mengaku membenarkan Laporan PSM ini disimpan di Perpustakaan Universiti

    Teknikal Malaysia Melaka (UTeM) dengan syarat-syarat kegunaan seperti berikut:

    1. Laporan PSM adalah hak milik Universiti Teknikal Malaysia Melaka dan penulis. 2. Perpustakaan Universiti Teknikal Malaysia Melaka dibenarkan membuat salinan

    untuk tujuan pengajian sahaja dengan izin penulis. 3. Perpustakaan dibenarkan membuat salinan laporan PSM ini sebagai bahan

    pertukaran antara institusi pengajian tinggi.

    4. **Silatandakan ( )

    SULIT

    TERHAD

    TIDAK TERHAD

    (Mengandungi maklumat yang berdarjah keselamatan

    atau kepentingan Malaysia sebagaimana yang termaktub

    dalam AKTA RAHSIA RASMI 1972)

    (Mengandungi maklumat TERHAD yang telah ditentukan

    oleh organisasi/badan di mana penyelidikan dijalankan)

    (___________________)

    Alamat Tetap:

    Pos 3, Lrg 4, Kg Seri Telok,

    Parit Yaani, 83710 Yong Peng,

    Batu Pahat, Johor.

    Disahkan oleh:

    (__________________)

    Cop Rasmi:

    Tarikh: _______________________

    ** JikaLaporan PSM ini SULIT atau TERHAD, sila lampirkan surat daripada pihak berkuasa/organisasi

    berkenaan dengan menyatakan sekali sebab dan tempoh laporan PSM ini perlu dikelaskan sebagai

    SULIT atau TERHAD.

  • iii

    DECLARATION

    I hereby, declared this report entitled “Design of Remotely Underwater Vehicle (ROV) Using Embedded System” is the results of my own research except as cited in

    references.

    Signature: ___________________

    Author: Mohammad Adib Bin Salikon

    Date: 29 MEI 2015

  • iv

    APPROVAL

    This report is submitted to the Faculty of Engineering Technology of UTeM as a

    partial fulfillment of the requirements for the degree of Bachelor of Electrical

    Engineering Technology (Industrial Automation and Robotics) with Honours.

    The member of the supervisory is as follow:

    ……………………………….

    (MR. MOHD ZAIDI BIN MOHD TUMARI)

  • v

    ABSTRACT

    The Remotely Underwater Vehicle or similarly called Remotely Underwater

    Vehicle (ROV) is a vehicle that used to dive underwater. It is non-autonomous

    vehicle and tethered by linking with neutrally buoyancy to remains constant

    underwater also can stable in rough condition in deeper water. The controlling signal

    is carry through multicore cable with 1.5 meter length to control box. The purpose is

    to replacing human limitation ability underwater where normal human can dive only

    30 feet depth before facing sensory problem such as hearing and vision. This ROV is

    suitable for freshwater and controlling using smart phone. There are two main parts

    to develop this ROV which are software design and mechanical design. Software

    design provides Arduino 1.6.3 software, SolidWorks and MIT inverter. Using MIT

    Inverter open–source web application provide by Google, ROV apps is develop

    specially to control the ROV movement either downward, upward and turning right

    or left. Arduino 1.6.3 software is used to program Arduino Mega 2560 board as a

    ROV brain and SolidWorks 2013 software is to design its shape implement by 3D

    printing. In mechanical design, there are two divisions which are electrical

    development and part assembly. The electrical development established for operate

    the ROV system such as thrusting and communicating. Radio frequency uses as

    transmission medium via Bluetooth module between smart phone and Arduino

    board. There are four DC motors as thruster which is three of it is for dive motor and

    the rest is moving thruster. Part assembly is joining process of all 3D printing part

    with other equipment via SolidWorks software for designing process. As conclusion

    one new product must be create to replacing human to a robot underwater and new

    improvement from existing product will established higher precision and technology.

  • vi

    ABSTRAK

    Kenderaan Bawah Air atau juga dipanggil Kenderaan Operasi Bawah Air

    (ROV) adalah kenderaan yang digunakan untuk menyelam di bawah air. Ia adalah

    kenderaan berpengawal dan terikat dengan apungan nuetral untuk secara berterusan

    stabil di bawah air dengan keadaan yang kasar pada kedalamannya. Isyarat kawalan

    dibawa melalui kabel berbilang sepanjang 1.5 meter panjang ke bekas kawalan.

    Tujuan utama ROV ini adalah untuk menggantikan kebolehan manusia yang terhad

    di dalam air di mana manusia normal hanya boleh menyelam sedalam 30 kaki

    sebelum berdepan dengan masalah deria seperti pendengaran dan penglihatan. ROV

    ini sesuai untuk air tawar dengan hanya menggunakan telefon pintar. Terdapat dua

    bahagian utama untuk membangunkan ROV ini iaitu reka bentuk perisian dan reka

    bentuk mekanikal. Reka bentuk perisian menyediakan perisian Arduino 1.6.3,

    SolidWorks 2013 dan MIT inverter. Menggunakan MIT Inverter iaitu sumber

    terbuka aplikasi laman sesawang yang disediakan oleh aplikasi Google, applikasi

    ROV telah dibangunkan khas untuk mengawal pergerakan ROV sama ada ke bawah,

    ke atas dan berpusing ke kanan atau ke kiri. Perisian Arduino 1.6.3 digunakan untuk

    memprogram papan Arduino Mega 2560 yang dijadikan sebagai otak ROV dan

    perisian SolidWorks 2013 adalah untuk merekabentuk ROV untuk di laksanakan

    oleh percetakan 3D. Dalam reka bentuk mekanikal, terdapat dua bahagian iaitu

    pembangunan elektrik dan pemasangan bahagian. Pembangunan elektrik yang

    ditubuhkan bagi mengendalikan sistem ROV seperti tujahan dan komunikasi.

    Frekuensi radio digunakan sebagai medium penghantaran melalui modul Bluetooth

    di antara telefon pintar dan papan Arduino. Terdapat empat DC motor yang

    digunakan, tiga daripadanya sebagai pendorong untuk selaman dan selebihnya

    bergerak sebagai pendorong kehadapan. Bahagian pemasangan adalah proses

    menyambung semua percetakan 3D dengan peralatan lain hasil dari penggunaan

    perisian SolidWorks untuk proses merekabentuk. Sebagai kesimpulan, satu produk

    baru harus dicipta bagi menggantikan manusia kepada sebuah robot di bawah air dan

    pembaharuan di perlukan untuk mendapatkan produk yang tepat dan berteknologi.

  • vii

    DEDICATIONS

    Dedicate in thankful appreciation for support, encouragement and

    understandings to my beloved mother, father, lecturers, friends and brothers who‟s

    praying for my success.

  • viii

    ACKNOWLEDGMENTS

    Firstly, Praise to Allah who‟s gives me strength for completing my PSM to

    building Remotely Underwater vehicle (ROV). Secondly, thank you to my

    supervisors which is MR.RAZALI BIN MOHAMAD SAPIEE and MR.MOHD

    ZAIDI BIN MOHD TUMARI who‟s gives me a lot of study and monitoring me to

    do this project. Thirdly, a lot of thank you to my beloved parent, siblings and friends

    who‟s give me moral support, motivation and also help me to complete this project.

    Thank you for borrowing your equipment friends. Lastly, thank you so much to Siti

    Nur Haifaa Binti Mohd Yasim who‟s give me inspiration along this study.

    THANKS ALL.

  • ix

    TABLE OF CONTENTS

    DECLARATION ................................................................................................................. iii

    APPROVAL ........................................................................................................................ iiv

    ABSTRACT ........................................................................................................................... v

    ABSTRAK ........................................................................................................................... vi

    DEDICATIONS .................................................................................................................. vii

    ACKNOWLEDGMENTS ................................................................................................. viii

    TABLE OF CONTENTS ..................................................................................................... ix

    LIST OF FIGURES ............................................................................................................ xii

    LIST OF TABLE ............................................................................................................... xiv

    CHAPTER 1 .......................................................................................................................... 1

    1.0 Introduction ............................................................................................................. 1

    1.1 Problem Statement .................................................................................................. 1

    1.2 Objective ................................................................................................................. 2

    1.3 Work scope .............................................................................................................. 2

    CHAPTER 2 .......................................................................................................................... 3

    2.0 Introduction ............................................................................................................. 3

    2.1 Programming System .............................................................................................. 3

    2.2 Communication Medium ......................................................................................... 4

    2.3 Thruster and Motor .................................................................................................. 5

    2.4 Buoyancy and stability ............................................................................................ 7

  • x

    CHAPTER 3 ........................................................................................................................ 11

    3.0 Introduction ........................................................................................................... 11

    3.1 Work flow .............................................................................................................. 12

    3.2 ROV structure design review ................................................................................ 13

    3.2.1 ROV mechanical component ......................................................................... 14

    3.3 Electrical Hardware Review .................................................................................. 14

    3.3.1 Arduino Mega Board...................................................................................... 15

    3.3.2 Bluetooth Device HC-06 ................................................................................ 15

    3.3.3 L298N Motor Driver ...................................................................................... 17

    3.4 Software Review ................................................................................................... 17

    3.5 System Development ............................................................................................. 19

    3.5.1 MIT Inverter 2.0 Software for Creating mobile apps .................................... 19

    3.5.2 Creating command block in MIT Inverter ..................................................... 22

    3.5.3 Compiling Designer and Block as APK format ............................................. 24

    3.5.4 Arduino 1.6.3 Software for programming ..................................................... 25

    3.5.5 SolidWorks 2013 Software for design ROV model ....................................... 27

    3.5.6 Converting SolidWorks Part(.SLDPRT) to STL format ................................ 34

    3.6 Mechanical Development ...................................................................................... 34

    3.6.1 Electrical Installation ..................................................................................... 34

    3.6.1.1Power supply separation ..................................................................... 35

    3.6.1.2Distribution of Input and Output from Arduino Board ....................... 36

    3.6.1.3Distribution Motor Driver Output ....................................................... 37

    3.6.2 Part assembly ................................................................................................. 37

  • xi

    3.6.2.1Build Part using 3D Printing ............................................................... 38

    3.6.2.2Combining 3D part with order stuff .................................................... 43

    3.7 Calculating Ideal ROV weight ....................................................................... 47

    CHAPTER 4 ........................................................................................................................ 49

    4.0 Introduction ........................................................................................................... 49

    4.1 ROV Buoyancy ..................................................................................................... 50

    4.2 Communication ..................................................................................................... 50

    4.3 ROV diving ability ................................................................................................ 52

    CHAPTER 5 ........................................................................................................................ 54

    5.0 Introduction ........................................................................................................... 54

    5.1 Summary of Research ........................................................................................... 54

    5.2 Achievement of Research Objectives .................................................................... 54

    5.3 Significance of Research ....................................................................................... 55

    5.4 Problems Faced During Research ......................................................................... 55

    5.5 Suggestion for Future Work .................................................................................. 55

    APPENDIX A ...................................................................................................................... 56

    APPENDIX B ...................................................................................................................... 61

    REFERENCES.....................................................................................................................62

  • xii

    LIST OF FIGURES

    Figure 2.1 : Optical Cable ...................................................................................................... 5 Figure 2.2: RS232 cable ......................................................................................................... 6 Figure 2.3: Micro-strip antenna ............................................................................................. 6 Figure 2.4 : Thruster configuration place ............................................................................... 7 Figure 2.5: Motor housing ..................................................................................................... 6 Figure 2.5: Buoyancy ............................................................................................................. 9 Figure 2.6: Solid body condition when drop into the water. .................................................. 9 Figure 2.7: Archimedes‟s principle ...................................................................................... 10 Figure 2.8 „G‟ is centre gravity and „B‟ is centre of buoyancy............................................ 11 Figure 2.9: Stability concept used for the ship. .................................................................... 11 Figure 2.10: Submarine concept .......................................................................................... 12 Figure 3.1: Work flow ROV development ........................................................................... 14 Figure 3.2: ROV back view. ................................................................................................ 15 Figure 3.3: Thruster .............................................................................................................. 16 Figure 3.4: Arduino Mega Board 2560 ................................................................................ 17 Figure 3.5: Bluetooth devices. ............................................................................................. 18 Figure 3.6: L298 motor driver board.................................................................................... 19 Figure 3.7: Home layout ...................................................................................................... 20 Figure 3.8: Control layout (diving mode). ........................................................................... 21 Figure 3.9: MIT inverter web software. ............................................................................... 22 Figure 3.10: Flow chart Mobile applications. ...................................................................... 23 Figure 3.11: Screen1 ............................................................................................................ 24 Figure 3.12: Screen2 ............................................................................................................ 24 Figure 3.13: ROV mobile application command blocks. ..................................................... 25 Figures 3.14: Compiling process.. ....................................................................................... 26 Figures 3.15: Arduino 1.6.3 software................................................................................... 27 Figure 3.16: Flow chart of programming flow..................................................................... 28 Figure 3.17: Servo command. .............................................................................................. 29 Figure 3.18: SolidWorks 2013 ............................................................................................. 30 Figure 3.19: Left and right part ............................................................................................ 30 Figure 3.20: Bottom part.. .................................................................................................... 31 Figure 3.21: Servo Part.. ...................................................................................................... 32 Figure 3.22: Rudder part. ..................................................................................................... 33 Figure 3.23: Thrusters holder. .............................................................................................. 34 Figure 3.24: Full assemble of all part................................................................................... 35 Figure 3.25: STL converted process. ................................................................................... 36 Figure 3.26: Electrical installation block diagram. .............................................................. 37 Figure 3.27: Lipo battery...................................................................................................... 38 Figure 3.28: 9 volt alkaline battery ...................................................................................... 38

  • xiii

    Figure 3.29: Pin connection ................................................................................................. 39 Figure 3.30: Motor driver connection. ................................................................................. 39 Figure 3.31: 3D printer machine... ....................................................................................... 40 Figure 3.32: Front view and back view of printer ................................................................ 41 Figure 3.33: Placing Perfboard. ........................................................................................... 41 Figure 3.34: Nozzle preheating process. .............................................................................. 42 Figure 3.35: ABS material out from the nozzle. .................................................................. 42 Figure 3.36: Part1_holder.stl and Part2_holder.stl............................................................... 43 Figure 3.37: Print setup windows. ....................................................................................... 43 Figure 3.38: Information windows. ...................................................................................... 44 Figure 3.39: Part1_holder is printed.................................................................................... 44 Figure 3.40: Rudder part is printed. ..................................................................................... 47 Figure 3.41: Top view .......................................................................................................... 47 Figure 3.42: Side view. ........................................................................................................ 47 Figure 3.43: Bottom view.. .................................................................................................. 47 Figure 3.44: Back view ........................................................................................................ 48 Figure 3.45: Front view.. ...................................................................................................... 48 Figure 3.46: 80 gallon water tank.. ...................................................................................... 49 Figure 4.1: ROV sinking 1”inch from the surface ............................................................... 52 Figure 4.2: Bluetooth distance against time. ........................................................................ 51 Figure 4.3: 7500 rpm downward speed against time ........................................................... 53 Figure 4.4: 15000 rpm downward speed against time ......................................................... 53 Figure 4.5: 7500 rpm upward speed against time. ............................................................... 54 Figure 4.6: 15000 rpm upward speed against time .............................................................. 54 Figure 4.6: Forward thruster against time. ........................................................................... 54 Figure A: Servo and Rudder for 3D printing placement. ..................................................... 61 Figure B: Motor pin and Moto holder .................................................................................. 61

  • xiv

    LIST OF TABLE

    Table 3.1: Dimension left part and right part. ...................................................................... 28 Table 3.2: Dimension for bottom part. ................................................................................. 30 Table 3.3: Dimension for Servo part.. .................................................................................. 31 Table 3.4: Dimension for Rudder......................................................................................... 32 Table 3.5: Dimension for thruster holder.. ........................................................................... 33 Table 3.7: Bluetooth frequency ranges. ............................................................................... 42 Table 3.8: Bluetooth frequency result with barrier... ........................................................... 50 Table 3.9: Thruster speed.. ................................................................................................... 52

  • 1

    CHAPTER 1

    INTRODUCTION

    1.0 Project Briefing

    The remotely operated underwater vehicle (ROV) is tethered underwater

    vehicle. It is designed to replace limited ability in humans for diving underwater in

    certain depth. The ROV is control using smart phone application. It is an

    advancement of using manual board as before. There are thrusters and propeller that

    control the movement of the ROV either downward, upward, left and right rotation.

    This ROV is tethered by cable from control box that contains embedded board and

    other component such as Bluetooth module

    The control box is linked to the smart phone that provides controlling

    applications for the ROV movement. It is powered by batteries and it is designed to

    dive underwater smoothly by its compact shapes. The material used to design the

    ROV is PVC and ABS material to maintaining buoyancy effect. This ROV is created

    for freshwater.

    1.1 Problem Statement

    The human ability is limited underwater. The ability for diving is only below

    30 meter or 98 feet depth into the water before the nitrogen narcosis become the

    significant hazard cause dehydration. Human cannot dive beyond the range. The

    endurance of human body is lesser compared to underwater robot in deep water. At

    the other hand, human physical is not rugged compared to ROV that designed using

    PVC and hardy material. But, there is a problem to design a ROV using that material.

    The problem is to find ROV buoyancy underwater.

    Unstable buoyancy underwater is the factor that cause the ROV cannot remains

    position. The wave or motion established from the water will change the position of

  • 2

    ROV. Movement of ROV is hard to control caused by this environment disturbance.

    Most of marine vehicles are used Archimedes‟s principle for maintaining buoyancy.

    This ROV is designed using this concept.

    1.2 Objective

    There are two main objectives in this project which are:

    i. To develop Remotely Underwater Vehicle for replacing limitation human

    ability underwater using mobile application.

    ii. To stabilize buoyancy underwater due to water motions.

    1.3 Work scope

    This ROV design is divided into three parts. The first part is Smartphone with

    android applications. Second part is control box and the last is ROV model. By

    controlling using the android apps, the command produced from smart phone is

    transferred using Bluetooth device to the control box. The distance range is about 2

    feet depth. Commands from control box are transferred using cable to ROV. The

    cable length is about 1.5 meter. This ROV can dive in the freshwater up to 3 feet

    depth.

  • 3

    CHAPTER 2

    LITERATURE REVIEW

    2.0 Introduction

    Before starting a project, the idea from previous researchers is vital and useful

    as reference and suggestion for the project in aspect of system control, programming

    technique and physical design. The literature review is the first step to begin a new

    project in order to understand clearly basic concept and method of project

    development. The ideas to create a ROV are much outside and various methods. In

    this chapter, details summary of component used, design procedure and some

    principle will be understand to get the best product. Some ideas will compare and

    discuss to begin the project.

    The previous researchers declared various ideas about system control,

    buoyancy effect and communication of the ROV. Thus, some ideas will be applied to

    this project with various methods.

    2.1 Programming System

    According from Nima Harsamizadeh Tehrani, Mahdi Heidari, Yadollah Zakeri

    and Jafar Ghaisar members of IEEE 2011, their products is using Arduino to control

    ROV movement underwater. The calculation and coding learning is used to get the

    precise output when thruster face load from water. Each speed of the thruster is

    controlling by PWM to remains constant in one position. As example, the ROV is

    set to dive 2 meters constant using the PWM control. PWM must be set to one value

    where the ROV can stay in one place.

  • 4

    2.2 Communication medium

    According to the J.N Lygouras (1999) the communication of their ROV is

    using RS232 and optical cable. The RS232 is used from the master computer to the

    slave computer and data collected by the sensor is transmitting by it. The cable is

    shown in Figure 2.1. By the way, this cable also used for transmits command to the

    slave computer and transferred to the ROV tethered by optical cable as shown in

    Figure 2.2. This optical cable transmits instruction through it to the motor drive

    mounted on ROV. The efficiency of this cable is high. Nevertheless, this cable need

    high costing and required additional board.

    Figure 2.1: RS-232

    Figure 2.2: Optical Cable

  • 5

    There is ROV product using wireless communication between the slave

    computer and motor drive. This method is not suitable for underwater vehicle

    because the required frequency is about 1 – 100GHz for micro-strip antenna. The

    loss is too much underwater and need repeater. Besides that, power to generate the

    signal is too high and it‟s not economic. This research has been proven by Zhang

    Hao Geng in his journals (2013). Figure 2.3 shows micro-strip antenna used by

    Zhang Hao Geng on his researches.

    Figure 2.3: Micro-strip antenna

    2.3 Thrusters and motor

    Martin A. Skoglund and Fredrik Gustafsson(1995) is defined that the output

    force as quadratic function of the input voltage is absolute propeller direction as

    shown in Figure 2.4. The dynamics is fast compared to the rest of the system and is

    therefore neglected. Physics calculation is need to define the thruster power. In their

    ROV project the configuration of the thruster as seen from below where the force is

    pointing to the left.

  • 6

    Figure 2.4 : Thruster configuration place

    On the other reference by Taro Aoki and Takashi Murashima (1997) he

    describe industrial ROVs utilize high power, high efficiency underwater thrusters,

    which are very expensive for an educational, propose ROV so the thrusters for

    DENA are designed by use of low-cost, low power 24V DC motors. Each thruster

    consists of a DC motor which is mounted in a Teflon waterproofed Cylinder and

    sealed by a metal cap at the end. A stuffing- box is placed on the other side to

    waterproof the Motor shaft as shown in Figure 2.5. ROV has two vertical thrusters,

    two horizontal thrusters located on left and right and two additional motors placed

    for lateral moves.

    Figure 2.5: Motor housing

  • 7

    Their project consists of two separated dual motor driver. Both have high

    power DC motor drivers which can control a pair of ROV thruster. It does also

    provide internal H-Bridge purposed to changing direction of ROV thruster by change

    the flow current. Their Control board provides 4 control signals for selection of

    direction and one PWM signal for controlling the speed of rotation for each dual

    motor driver. These drivers have thermal shutdown circuits that prevent the driver

    from being damaged under extreme conditions. Two identical “Thruster Board” are

    installed in the ROV to help the control of 6 ROV thrusters.

    2.4 Buoyancy and stability

    According to Yunus A.Cengel and John Cimbala (2006), they defined a fluids

    exerted an upward force on a body immersed in it is a buoyant force. The buoyant

    force is caused by the increase of pressure with depth in a fluid. To build an ROV,

    this factor must be considered. The buoyant force acting on a body of uniform

    density immersed in a fluid is equal to the weight of the float displaced by the body,

    and its acts upward through the centroid of the displaced volume. Thus, 𝑓𝐵= 𝜌𝑓𝑔𝑉.

    Where ′𝜌′ is density of force and „g‟ is gravity also volume. The buoyant force (FB)

    is equal to the displaced water. This fact is proven by Archimedes‟s on his principle

    in Figure 2.6.

    There are three conditions when a solid body drops into a fluid which is

    sink, float and remains at rest at any point in the fluid (neutrally buoyant). The figure

    2.7 shows solid body will sink at the bottom when its average density is greater than

    the density of the fluid. When the average density is equal to the density of the fluid

    it is suspended body (neutrally buoyant). The solid body will rises to the surface of

    the fluids when average density of the body is less than the density of the fluid. The

    ROV must be located at neutrally buoyant to facilitate thrust process. Figure 2.8

    shows what buoyancy is.

  • 8

    Figure 2.6: Archimedes‟s principle

    Figure 2.7: Solid body condition when drop into the water.

    Figure 2.8: Buoyancy

  • 9

    In the buoyancy concept, the stability also is important application to floating

    bodies with external attachments. This concept usually used in ships and submarine

    construction. Stability is tending of an object to return itself in equilibrium position

    when there is a small displacement.

    The stability also has three conditions which is stable, unstable and neutrally

    stable. Stable is movement of an object and its will return back to the initial position.

    Its centre of gravity must below the centre of buoyancy. The movement of an object

    to new location when there is any small displacement is neutrally stable. Centre

    gravity is coincident with centre of buoyancy. As example, ball on the field kicked

    by someone. The ball will stop in new position. It has no tendency to move back to

    its original location, nor does it continue to move away. Unstable condition is object

    maybe at rest or never at rest when there is disturbance. Its centre gravity is above

    the centre of buoyancy. Figure 2.9 shows about stability and centre of gravity.

    Figure 2.9 „G‟ is centre gravity and „B‟ is centre of buoyancy.

  • 10

    Figure 2.10: Stability concept used for the ship.

    Figure 2.10 shows a floating body is stable if the body is (a) bottom bottom-

    heavy and thus the centre of gravity G is below the centroid B of the body, or (b) if

    the metacenter M is above point G. However, the body is (c) unstable if point M is

    below point G. While, Figure 2.10 is clarifies of submarine concepts, where (a)

    stable position is used.

    Figure 2.10: Submarine concept