International Journal

on Marine Navigation

and Safety of Sea Transportation

Volume 4

Number 1

March 2010

1 INTRODUCTION

Recently many researches on ship automatic naviga-

tion system have been carried out. The one of sys-

tem required for these researches is a free running

model ship. A free running model ship has been

used in ship model basin area to validify or confirm

ship’s manoeuvring/motion or resistance perfor-

mance before the ship’s building. When a free run-

ning model ship is used in a basin, usually it is

known that there are limits of basin size to fully test

the ship’s performance. Therefore many researches

have been carried out outdoor such as pond or river.

When experiment is conducted outdoor using a

free running model ship, a lot of equipments are re-

quired such as IMU (Inertial Measurement Unit),

GPS (Global Position System) and other facilities to

get other ship’s information. This paper will intro-

duce MMU (Mokpo National Maritime university)

free running model ship which can be used for

ship’s manoeuvring/motion performance tests. The

system is equipped with GPS and AIS to get ship’s

real time position and other ship’s information. Main

purpose of this model ship is to carry out ship’s in-

telligent navigation test where the ship navigate rec-

ommend sea route or ship avoid other ship in the sea

without human control automatically. The research

in this paper was carried out as the first step of these

researches. The structural and functional concept of

the free running model will be introduced. We car-

ried out basic ship’s performance tests such as tun-

ing circle and zig-zag test as a first step of ship intel-

ligent navigation tests. We found good performance

in the model ship and that the model can be utilized

in ship intelligent navigation tests in the future.

2 THE STURECTURE OF A FREE RUNNING

MODEL SHIP

The MMU free running model ship consists of fol-

lowing equipments.

− Main electric system

− Device control system

− Signal measurement system

− Communication system

− Model ship

2.1 Main Electric System

A free running model ship usually requires high ca-

pacity of power because it is operated open waters

with wind disturbances. The electric system of

MMU model supplies its electricity to servo motors

and computer power and communication system.

Two servo motors are equipped in the model ship,

one (700W) for propeller and the other (100W) for

rudder operation. In operation situations, the servo

motors always controlled, so capacity of battery is

important to keep the model powered for long time.

Two of battery are installed with a 12V deep cycle

method and 100ah class of parallel circuits. Output

Ship Manoeuvring Performance Experiments

Using a Free Running Model Ship

N. Im & J.-H. Seo

Mokpo National Maritime University, Mokpo, South Korea

ABSTRACT: In this paper, a 3m-class free running model ship will be introduced with its manoeuvring per-

formance experiments. The results of turning circle test and zig-zag test will be explained. The developed sys-

tem are equipped with GPS, main control computer, wireless LAN, IMU (Inertial Measurement Unit), self-

propulsion propeller and driving rudder. Its motion can be controlled by RC (Radio Control) and wireless

LAN from land based center. Automatic navigation is also available by pre-programmed algorithm. The tra-

jectory of navigation can be stored by GPS and it provides us with important date for ship’s motion control

experiments. The results of manoeuvring performance experiment have shown that the developed free run-

ning model ship can be used to verify the test of turning circle and zig-zag. For next step, other experimental

researches such as ship collision avoidance system and automatic berthing can be considered in the future.

power from batteries is sent to a DC/AC inverter and

converted into 220V single-phase current for each

electricity equipments. A current transformers or

SMPS (Switching Mode Power Supply) of 24V or

12V often is used for small capacities equipments.

Figure 1. Battery and converter

2.2 Device Control System

Figure 2. System flow in a model ship

Control device system consists of access point

(IEEE.802 11g), laptop computer, PMAC, servo

driver and wireless control system. The following

explains more details

− Laptop computer

It controls the total system of model ship. Its sig-

nal translated into each equipment with TCP/IP

signal through a network adopter

− PMAC

When it receives TCP/IP singal, the output of

range 0-10V is produced and sent to each servo

driver such as rudder and propeller gears.

− Serve driver

It controls the rudder and propeller motors with

siganls from PMAC.

− Radio control Receiver

The receiver get signals from radio control trans-

mitter to control rudder angle and propeller revo-

lution. The translated signal is sent to laptop

computer by way of NI USB-DAQ.

2.3 Data Acquisition System

The signals in a free running model can be into two

types roughly. The first is signal for a ship motion

control part and the second is for motion measure-

ments such as 6 DOF (Degree Of Freedom). All sig-

nals from ship’s motion and control part is translated

into laptop computer in the model where each signal

are stored or re-translated according to their purpose.

The following explain measured signal at each

equipment.

Figure 2. Data acquisition system

− PMAC

Each phase generated in encoders of servo motor

is input into PMAC via servo driver. The input

phases are converted into meaningful data for

rudder location and propeller revolution. The data

also translated into laptop computer via TCP/IP to

be stored as data log or monitoring purpose.

− NI-USB-DAQ

The data translated into radio control receiver is

converted to PWM (pulse Width Modulation)

signal. The NI-USB-DAQ translate the signal of

PWM into laptop computer in model ship via

USB port.

− 6 Axis IMU (Inertial Measurement Unit)

The signal data from IMU are translated into

computer by serial communication. They are used

for ship’s motion logging and monitoring.

− GPS (Global Position System)

The signal data from GPS also are translated into

computer by serial communication. They are used

for logging and monitoring of ship’s trajectory.

− AIS (Automatic Identification System)

It is equipped to obtain other ship’s information

such as ship’s position, heading angle and speed.

Its signal also translated as serial data into com-

puter. This system can be used as one of intelli-

gent navigation system. When a model ship

avoids collision situations, the data from AIS is

very essential to calculate the risk of collision be-

tween two ships.

2.4 Communication System

A communication system of the model ship can be

divided into three types of analogue signal, TCP/IP

and RS-232. The following are explanations of

equipments and protocol.

− Digital and analogue signal

Encoders in servo motor produce several pulse.

Control signal for servo motor ranges from 0V to

10V. The NI-USB-DAQ adopted in the model

ship has spare channel for signal I/O , therefore

additional hardware installation will be conven-

ient such as wind and current meters and addi-

tional propulsion equipment.

− TCP/IP

The access point (IEEE. 802.11g), a close range

wireless communication protocol, enable users to

transmit data with 54Mbps. The communication

between the laptop computer in the model ship

and shore control center is possible by TCP/IP.

The signal to/from PMAC is translated via access

point with form of TCP/IP to control ship’s oper-

ation.

− RS 232

Several equipments such as IMU, AIS and GPS

use serial data transmission, RS 232. All data

from these equipments are stored in laptop com-

puter system for logging and monitoring of the

ship’s situations.

− PWM (Pulse Width Modulation)

Emergency situations such as model ship power

failure or collisions require prompt and direct

control. Radio control transmitter- receiver deals

their signal with PWM method. When NI-USB-

DAQ receives pulse from radio control receiver

and decides what kinds of control should be done

using the pulse’s time from raising edge to falling

edge.

2.5 Model Ship

The model ship has 1/100 of model scale. Water-

proof was considered in every hatch to prevent cap-

sizing of the model. The table 1 and 2 show the

principal of model ship. The figure 2 explains the

model ship.

Table 1. Principal particulars of model ship

___________________________________________________

Ship Model

___________________________________________________

Scale ratio 1 100

Design speed 15.5(knots) 0.7973(m)

L.B.P(m) 320 3.2

L.W.L(m) 325.5 3.255

B(m) 58.0 0.58

Depth(m) 30.0 0.3

Draft(m) 20.8 0.2080

WSA() 27320.0 2.7320

Volume() 312737.5 0.3127

0.8101 0.8101

0.142 0.142

___________________________________________________

Table 2 Principal particulars of model ship

___________________________________________________

Rudder Propeller

Type Horn Type FP

___________________________________________________

S of rudder(m

) 273.3 No. of blades 4

Lat area(m

) 136.7 D(m) 9,86

Turn rate (deg/sec) 2.34 P/D(0.7R) 0.721

Ae/A0 0.425

Rotation C.W

hub ratio 0.155

___________________________________________________

Figure 3. The picture of the model ship

3 THE MODEL OPERATION

The operating system for the model ship can be di-

vided into two system of software operating system

and hardware operating system.

3.1 Operating System of Software

Table 3 indicates software operating system adopted

for the model ship. As shown this table, Window XP

and LabView are used for OS and computer pro-

gram language.

Table 3 Opeating System of Software

___________________________________________________

Computer OS Widows XP

Computer Language LabVIEW 8.5

device driver PMAC

NI-DAQ

___________________________________________________

3.2 Operating System of hardware

Critical control is done by inner computer on board

which is controlled from shore computer with wire-

less network communication. A priority of control is

set to radio control receiver-transmitter in specified

frequency to cope with emergency situations. This

enables users to take appropriate and prompt actions.

In case of radio control receiver failure or networks

signal errors, the inner computer of model ship is

designed to run programmed sequence or process.

The figure 4 indicates the priority of operation sys-

tem. When local control mode is selected, model

ship can be controlled by shore or inner laptop com-

puter by manual mode. If local control mode is can-

celled, radio control is searched at first. When radio

control signal is not found, automatic navigation

control mode is activated

Figure 4. Main screen of operating program

Users can use additional safety measurement, the

function of “fail safe” where radio control system

can be kept specified conditions or stopped if radio

transmitter-receiver failed to get signals or the level

of power in battery is so low. This enables the user

to cope with emergency situations such as power

failure in model ship or critical collision situation.

All data of model ship can be obtained from USB

ports. Additional equipment’s installation also is

possible through spare ports of USB.

4 EXPERIMENTS

In this research, two kinds of experiments are carried

out in the costal sea and in a towing tank. Zig-zag

test and turning test were performed. These tests are

known as very essential and important method to

evaluate a ship’s manoeuvring performances.

4.1 Zig-zag test

Zig-zag test of 10-10degree and 20-20degree were

performed. The figure 5 shows the results of 10-

10zig-zag test carried out in towing tank. The figure

6 shows the results of 20-20 zig-zag test carried out

in the costal sea side. As shown in these figures, it is

found that the model ship well perform zig-zag test

without any errors and the data of ship’s heading and

rudder angle also are very clear.

Figure 5. 10-10 zig-zag test in towing tank

Figure 6. 20-20 zig-zag test in the sea

Figure 7 shows the ship’s trajectories obtained by

GPS during ship’s zig-zag test.

Figure 7. Ship’s trajectories in 20-20 zig-zag test

4.2 Turning Circle Test

Ship’s turning test also was carried out. A turning

circle tests usually to be performed to both starboard

and port with 35 degree rudder angle. The rudder

angle is executed following a steady approach with

zero yaw rate. Figure 8 and 9 show the results of

turning test. As shown in these figure, the trajecto-

ries of the model and ship’s heading and rudder an-

gle are clearly obtained to evaluate ship’s manoeu-

vring performances. The diameters of tactical and

advance are found around 7-8 meters. This experi-

ment was performed in open sea. Environmental dis-

turbances such as wind and current effects are in-

cluded into the results of the experiment.

Figure 8. Ship’s trajectories in turning test

10' ZIG-ZAG

-20

-15

-10

-5

0 10 20 30 40 50 60 70 80 90 100 110 120 130

time(sec)

Angle(deg)

20' ZIG-ZAG

-35

-30

-25

-20

-15

-10

-5

0 5 10 15 20 25 30 35 40

Time(sec)

Angle(deg)

Heading Rudder Roll

20' ZIG_ZAG

-10

-5

0 5 10 15 20 25 30 35 40

Distance(m)

Turning Circle

0 5 10 15 20 25 30

Distance(m)

Figure 9. Ship’s data in turning test

Figure 10. Zig-zag test in towing tank

5 CONCULSIONS

The main points of research can be summarized as

followings.

− The main structure and concept of MMU free

running model ship were introduced.

− Zig-zag tests and turning tests were performed to

evaluate the model ship’s essential usefullness.

− It was found that the model ship’s software and

hardware system were enough to be used further

ship’s control research in the future such as ship’s

intelligent control fields.

PREFERENCES

SIMMAN(2008), Geomety of KVLCC1, http://www.siman

2008.KVLCC

H Shin , “Crabbing Test of a 3m Ferry Model”, Journal of the

society of Naval Architects of Korea, Vol 41. No.1 pp 40-

H Shin, 2m Class free model ship, Journal of the society of

Naval Architects of Korea, Vol 45. No.3 pp 247-257

H Yoon, Development of Free running model ship for evalua-

tion of the performance of anti-rolling devices. Journal of

Korean navigation and port, Vol 28. No.2 pp 33-39

Turnig Circle

-40

-35

-30

-25

-20

-15

-10

-5

0 10 20 30 40 50 60 70 80 90

Time(sec)

Angle(deg)

-270

-180

-90

180

270

Rudder Heading Angle

Angle(deg)