The Simple Open Free Running Test for the Evaluation of Turning

Ship Ability

Aries Sulisetyono

Department of Naval Architecture, Institut Teknologi Sepuluh Nopember, Surabaya, Indonesia

Keywords: Ship Manoeuvring, Open Free Running Test, Image Processing.

Abstract: The ship manoeuvring test using an approach of the free running model on the open water pool is described.

In this test, the most important part is to retrieve a trajectory data of the model ship while it does

manoeuvre. It is necessary to have an accurate technique of the data retrieval during the test. A technique of

image processing is proposed in this paper with the aim to analyse the ship manoeuvring path. In this

method, the manoeuvring test of the model is recorded with the camera, and the movie result is then

analysed with the movie maker software to get the trajectory points for a second step. The 6500 DWT

tanker with a 1:85 scale model is tested on the turning test with the two different type of rudder namely the

conventional and the single flap. The test results are obtained in terms of parameters including advances,

transverse, tactical diameter and turning radius. The comparison results show the ship with single flap give

better the manoeuvring performance with reducing turning diameter about 13.04% and 14.5% for the

turning of Portside and Starboard respectively.

1 INTRODUCTION

The manoeuvrability of a ship is fulfilled to avoid

the accidents of ship collision in open or restricted

water areas. The IMO (International Maritime

Organization) released the Standards for ship

manoeuvrability for all ships that are operated in the

sea. In the early step design of the ship, the ship

manoeuvrability is predicted by using the approach

of the experimental and numerical method. The free

running model test is developed for testing of the

ship manoeuvring. This experimental technique is

more efficient and practical since it considers to

follow the requirements of ITTC (25rd ITTC

Manoeuvring Commission Report 2008). The model

test is equipped with its own propeller and rudder on

the scale in which the model is controlled by the

operator through the wireless communication

system.

The ship manoeuvrability basically depends on

controllability the rudder performance and the ship

speed. The rudder is designed to get a maximum

value of side force to be able to change any

directions of the ship’s hull. In this paper, the single

flap rudder is developed to improve the performance

of ship manoeuvrability with increasing the side

force (Watson and Tupper, 2001); Lewis and

Edwards, 1989). The foil of NACA 0018 series is

selected refer to (Sulisetyono, 2014; Sulisetyono and

Nasirudin, 2010, 2014) with about 30% addition flap

of the rudder area. The turning manoeuvrability is

considered with four parameters as the results of test

such as advance, transverse, tactical diameter, and

turning diameter. The image processing technique is

proposed to analyse the turning path of the model

ship while it tested at the certain speed for the two

design cases of the rudders.

2 METHODOLOGY

The ship model is a 6500 DWT tanker with the main

dimensions such as Length of water line (Lwl) 120

m, Breadth (B) 22.1 m, Draft (T) 7.12 m,

Longitudinal centre of buoyancy (LCB) 58.7 cm

(from FP), and Coefficient block (Cb) 0.773. The

model with the scale of 1:85 is shown in Figure 1.

The turning test is conducted on the pool which

has enough width to avoid the blockage effect, is the

public swimming pool with the dimension of 12 m

length, 6 m breadth, and 1.5 m depth. The ship

models are equipped with including an AC motor, a

116

Sulisetyono, A.

The Simple Open Free Running Test for the Evaluation of Turning Ship Ability.

DOI: 10.5220/0008375901160119

In Proceedings of the 6th International Seminar on Ocean and Coastal Engineering, Environmental and Natural Disaster Management (ISOCEEN 2018), pages 116-119

ISBN: 978-989-758-455-8

propeller shaft, and a propeller. The propeller is a

single screw with 4 blades, diameter of 5 cm, and

material of brass, which is installed in the stern

model, as shown in Figure 2.

Figure 1: Lines plan and ship model of tanker 6500 DWT.

Figure 2: Propeller and rudder on the stern of model.

In order to make the ship model manoeuvre, the

model’s hull must be equipped with the rudder

system. The servo motor with the power required 5

volts is needed to rotate the rudder, and it is remoted

in order to control the directions of the ship model.

The remote-control system consists of 2 ways such

as the command is sent according to the desire of

operator by the moving stick, and the command is

received in the form of signals which is sent by the

remote control.

Figure 3: Rudder dimensions of conventional (left) and

single flap (right).

The turning test is conducted to evaluate the

performance of the two rudder types, namely the

conventional rudder of type A, and the single flap

rudder of type B. The both section of rudders are

asymmetrical foil of NACA 0018 series, and the

wetted area of rudders are 17.6 cm

, as shown in

Figure 3.

2.1 Testing Procedure

The procedures of the turning test are described as

follow: First, to set up the position of the camera to

record all trajectories of the ship model where it is

installed on over the pool with the height of 4.8 m

above the water surface, see Figure 4. The camera is

connected to the computer to save or record the ship

model manoeuvring.

Second, to obtain the point signs as the reference

to figure the turning path. The 4 plastic balls that are

given light to be seen clearly when the lights are

turned off. The plastic ball is arranged into a square

shape with the distance between ball are about 250

cm and 300 cm, see Figure 4. Later the pseudo

square formed by these four plastic balls is used as a

reference to calibrate the movement of the ship's

model.

Third, to turn of all the lights around the pool, so

that the colour recorded by the camera is the colour

of the model of the ship and the lights of the ball.

The ship model is executed and recorded.

Figure 4: Position of the camera and the light ball in the

pool.

2.2 Image Processing

The video of the ship manoeuvring tests is analysed

with the following steps: first, the video recorded is

imported into the application of movie maker. The

movie is captured into several snapshots of ship

movement per each second of time. Each picture

shows the position of the ship model at every second

on the turning track, see Figure 5. The second, each

picture is identified as a point location of the ship

model, and all points are then connected to become

the line of the ship turning, see Figure 6. This ship

turning line is further analyzed to look for the

performance of ship manoeuvring.

The Simple Open Free Running Test for the Evaluation of Turning Ship Ability

117

Figure 5: The position of the ship model for each time,

from 1st second to 16th second.

Figure 6: The point connected of the turning test, from 1st

second to 30th second.

3 RESULTS AND DISCUSSION

The testing of free running models is to determine

the manoeuvrability of the ship model in the turning

circle test. The rudder angle used is based on the

IMO standard which is a 35° towards the starboard

and portside of the ship. Two types of the rudder

which are the conventional and the single flap, are

evaluated their contribution in the turning manoevre.

Since the tests are carried out at night time, the lights

have to be installed on the model ship as well as on

the ball referenced in order to make it easier for the

visual analysis. The test is conducted when the wind

blow is very quiet since the wind factor contributes

to the accuracy of the test results.

The results of the free running model test are

expressed in plotting curve on the coordinate system

of xy-axis. The sway motion of ship is a transverse

motion obtained as the y-axis, and the surge motion

is a longitudinal motion toward the length of the ship

as the x-axis. For example, the results of turning test

for the model ship with the rudder-type A is plotted,

as shown in Figure 7. The parameters of ship turning

performance which are advanced, transfer, tactical

diameter, and turning diameter are measured based

on the curve turning circle.

Figure 7: Results of the turning test for the ship model

with the rudder type A (starboard).

Table 1 and 2 describe the results of the turning

test of the model with the rudder-type A (the

conventional rudder) and the rudder-type B (single

flap rudder). Based on both tables, the type B of

rudder produces smaller turning diameter while it is

compared to the type A of the rudder which is

decreases about 13.04% of Portside and 14.5% of

Starboard.

Table 1: The results of the turning test of the model with

the rudder-type A.

Item of performance

Rudder angle

35°

Portside

35°

Starboard

Advance (cm) 244.99 231.81

Transverse (cm) 101.47 102.61

Tactical

Diameter (cm)

202.94 196.73

Turning

Diameter (cm)

138.92 149.25

The comparative performance of rudder type A

and B is expressed in terms of the turning circle

curve of the full-scale ship, as shown in Figure 8.

This curve results also explain that the modification

ISOCEEN 2018 - 6th International Seminar on Ocean and Coastal Engineering, Environmental and Natural Disaster Management

118

of the conventional rudder with adding the flap on

the rudder could provide an additional lift of the

rudder so that the flap makes an effect in improving

the performance of the ship manoeuvring at the sea.

Table 2: The results of the turning test of the model with

the rudder-type B.

Item of

performance

Rudder angle

35° Portside

and 10

flap

35° Starboard

and 10

flap

Advance (cm) 213.05 198.21

Transverse (cm) 88.24 87.73

Tactical

Diameter (cm)

176.48 168.22

Turning

Diameter (cm)

120.81 127.62

Figure 8: Comparison result of turning test for the model

with rudder-type A and B (starboard).

4 CONCLUSIONS

The procedures of the open free running model test

are proposed which is simply an alternative of the

ship manoeuvring test in the open water pool. The

two types of rudder such as the conventional rudder

(type A) and the single flap rudder (type B) which

are both have the same wetted surface area, are

evaluated in giving influence to the performance of

the turning manoeuvring. The test results show type

B of the rudder (single flap) produces smaller

turning diameters compared to type A of the rudder.

The flap of the rudder can increase the manoeuvre

performance of the 6500 DWT tanker ship model is

about 13.04% and 14.5% for Portside and Starboard

turning, respectively.

ACKNOWLEDGEMENTS

The author wishes to tank Rizky Hariseputera as the

student for helping in the experimental setup.

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