Ship domain in the restricted area simulation research

152 Scientific Journals 32(104) z. 2

Scientific Journals Zeszyty Naukowe Maritime University of Szczecin Akademia Morska w Szczecinie

2012, 32(104) z. 2 pp. 152–156 2012, 32(104) z. 2 s. 152–156

Ship domain in the restricted area – simulation research

Zbigniew Pietrzykowski, Mirosław Wielgosz, Marek Siemianowicz

Maritime University of Szczecin, Faculty of Navigation 70-500 Szczecin, ul. Wały Chrobrego 1–2, e-mail: {z.pietrzykowski; m.wielgosz}@am.szczecin.pl

Key words: navigational safety, encounter situations, passing distance

Abstract The ship domain – the area around the ship that should be clear of other vessels or objects – depends on many

factors. In this paper authors present results of simulation research on ship domain determination. The

influence of ship size on domain shape and dimensions in the restricted area have been analyzed. The method

of determining ship domain is characterized. The results have been presented. The domains of ships of

different sizes have been compared and conclusions formulated.

Introduction

One of the main tasks of navigation is to ensure

ship's safety during its voyage at sea. Navigational

equipment and systems installed on board are an

important source of information for the navigator

during decision making. The use of up to date

information technologies enables the integration of

information (integrated bridge) and its automatic

processing. This is of particular importance in the

case of information referring to navigational safety,

such as a radar report (ARPA, ECDIS) including

the parameters known as CPA and TCPA. The CPA

as a safety criterion is very useful in open sea navi-

gation. Its use in restricted waters, such as narrow

channels and fairways, in most cases is difficult to

implement. The reason is that a ship has no free

choice of the route. Therefore, a lot of attention is

paid on developing methods and tools for the

determination of an area around the ship that should

be clear of other vessels or objects – ship domain

[1, 2, 3, 4, 5, 7, 8, 9, 10]. This approach is due to

the fact that the concept of domain is intuitively

accepted by the human and enables an analysis and

assessment of the situation and working out deci-

sions on manoeuvring in open and restricted areas.

The concept of domain is applicable on ships, as

well as in land-based vessel traffic centres.

The shape and size of ship domain depend on

many factors, which makes it difficult to define it.

The ship size is one of these factors.

The ship domain and methods of its determination

Domains proposed by various authors can be

divided into two- and three-dimensional ones. The

former describe an area around the ship. Typical

shapes of two-dimensional domains include a cir-

cle, rectangle, ellipsis, polygon and more complex

planar shapes.

The determination of ship domain requires that

its boundary is identified. There are three groups

of methods of ship domain determination. One in-

cludes statistical methods. These consist in record-

ing trajectories of ships' movements to get data for

identifying the area around the ship that navigators

keep clear of other navigational objects [2, 3].

Analytical methods, in turn, are based on the

analytical description of domain area. The domain

boundaries in these methods may be defined on the

basis of the closest point of approach (CPA) and

time to closest point of approach (TCPA), as well

as formulas describing ship's manoeuvrability,

hydrological and meteorological conditions and

relations applicable to ship in motion in a given

area [8, 9].

The application of methods and tools of

knowledge engineering, including artificial intelli-

gence, enables acquiring, representing and using

the procedural and declarative knowledge of expert

navigators for the identification of ship domain.

Examples are provided by artificial neural networks


Zeszyty Naukowe 32(104) z. 2 153

used for defining the level of navigational safety,

the basis for outlining the ship domain [6, 7, 11].

Chronologically, statistical methods were first

proposed methods to be used for ship domain

determination [2, 3]. The domain was determined

from registered ship trails indicated by radar. In

restricted areas the ship size has to be taken into

consideration. Using the equipment and systems

used presently on ships’ board and in land-based

centres, capable of registering ship position with

greater accuracy, it can determine ship’s trails that

depend on the ship dimensions (contours).

To determine the domain boundary these

authors adopted the method proposed in [2], based

on the density analysis of ships’ trails around the

central ship. The ships’ trails were assumed to be

the points of waterplane (waterline) of another ship

at preset relative bearings, the nearest to the centre

of the central ship (Fig. 1). Besides, it was assumed

that ship trails would be recorded at fixed time

intervals t at n relative bearings i (i = 1, ..., n) in

the 000÷359 [o] and the discretization step .

Fig. 1. Ship trails determination at defined relative bearings at

instant t

Fig. 2. Ship domain boundaries

The domain boundary is then determined by

a set of points pDi (i = 1, 2, ..., n) at the preset rela-

tive bearings i :

DnDiDDS ppppGD ...,,...,, 21 (1)

such that for a given relative bearing i the trail

density at point pDi, lying at a distance dpDi from the

centre of the central ship is maximum.

Additionally, it can determine the minimum and

maximum boundary of the domain, described, re-

spectively, by points with minimum and maximum

distances of ships’ trails (Fig. 2).

The scope of research

The research aimed at the determination of

domains of various size ships in a restricted area

and an analysis of how encountering ships’ sizes

affect the shape and size of the domain.

The primary method used was that of non-

-autonomous simulations with the participation

of expert navigators, who worked on the ECDIS

simulator at the Maritime University of Szczecin.

The navigators, of varying sea service period, were

trainees attending an ECDIS operation course run

at the same university. The research consisted in

simulated passages of ships conducted according to

pre-determined ship encounter scenarios.

The scenarios assumed good weather conditions

to exclude the influence of hydrological and mete-

orological factors. The passages, then, took place

at daylight, good weather and visibility, with no

current or wind effects.

The Singapore Strait was the area chosen for

tests. This major trading route in South-East Asia is

65.7 Nm long and about 8.6 Nm wide. The strait is

situated between Singapore Island and the Riau

Archipelago. The route traffic intensity is one of the

densest in the world. The beginning of the fairway

leading to the Port of Singapore was selected for

simulations. The port is situated southeast of Jurong

Island, where the fairway neighbours offshore traf-

fic zone, resulting in a variety of ship encounter

situations. Also, this stretch of the fairway includes

an area prohibited for navigation due to construc-

tion work. The construction work area restricts the

fairway on the port side, and the offshore traffic

on the starboard side, which limits the choice of

manoeuvres.

The Navi-Trainer Professional 4000 simulator

offers a selection of 118 ship models for simulation

tests, of which 18 can be handled by the operator.

Having considered all the ship models available,

authors chose three types of ships with various size

for planning the simulated passages. The chosen



models represent a wide spectrum of vessel types

operated in the merchant marine. Table 1 contains

basic parameters of the chosen ship models.

Table 1. Ship models

Ship model River-sea

ship 1

LO-RO

ship VLCC 1

Ship type Coaster LO-RO Tanker

Length overall (Lc) [m] 95.0 174.0 261.0

Breadth (B) [m] 13.0 23.0 48.0

Draft forward (DA) 3.7 7.5 5.8

Draft aft (DF) [m] 3.7 8.1 9.0

Moulded depth (A) [m] 11.1 24.2 37.6

Displacement (D) [t] 3510.0 19512.0 63430.0

Speed over water

(SOW) [w] 11.1/7.0 * 16.3/9.0* 16.3/11.0*

* Speed of the slower ship in scenario 4 (overtaking).

Encounter situations of two ships of the same

type on collision courses were considered, where

one ship was steered by the operator, the other was

automatically handled by a computer. Four basic

scenarios of encounters were developed:

1) encounter of ships on opposite courses;

2) encounter of ships on crossing courses, where

the ship steered by the navigator had the right of

way;

3) encounter of ships on crossing courses, where

the ship steered by the navigator had no right of

way;

4) overtaking situation, where the ship steered by

the navigator was overtaking the other ship, with

no right of way.

Research

384 passages were conducted in total: 128 pas-

sages for each ship type, including 32 passages

following each of the scenarios. The simulations

were executed in real time. The data from the pas-

sages were recorded at the preset discretization step

t = 1 [s].

The ships’ trajectories had to be calculated to

get the relative motion parameters in order to verify

the passing distances between ships and to deter-

mine their domains. The ship’s relative motion was

considered for two cases:

a) the navigator-steered ship motion was displayed

relative to the motion of the computer-operated

ship;

b) the ship operated by the computer was shown

relative to the one handled by the navigator.

Figure 3 shows example relative trajectories of

a river-sea ship 1 for the scenario 4.

The method described in Chapter The ship

domain... was used for the determination of ship

domain limits. To this end the trails of ships located

around the central ship (the one operated by the

computer) were determined. The positions of GPS

antennas on each ship were taken into account. The

ships’ contours were approximated to polygon

shapes.

The ships’ trails recorded at the time interval

t = 5 [s] were analyzed for the relative bearing

discretization = 5 . Figure 4 illustrates the

analyzed trails of river-sea ship 1 for scenario 4.

a) b)

Fig. 3. Relative trajectories of the river-sea ships 1 for the

scenario: 4; a) trajectories of the relative motion of computer-

operated ships; b) trajectories of the relative motion of ships

steered by navigators

Fig. 4. Trails of river-sea ship 1 for scenario 4

On this basis ship partial domains were deter-

mined for each scenario k (k = 1, 2, 3, 4) on preset

relative bearings i : (i = 1, 2, ..., n): domain, min-

imum domain and maximum domain, described,

respectively, by points pD ik, pDmin ik, pDmax ik (com-

pare chapter The ship domain..., Fig. 2).

On the basis of the partial domains determined

for each scenario (four scenarios in the case under

consideration), the limits of total domains GDSC,

GDSCmin and GDSCmax were defined:

-1000 0 1000-3000

-2000

-1000

0

1000

2000

3000

-1500 -1000 -500 0 500 1000 1500-3000

-2000

-1000

0

1000

2000

3000

-1000

-500

0

500

1000-3000 -2500 -2000 -1500 -1000 -500 0 500 1000 1500 2000

[m]

[m]

[m]

[m]


Zeszyty Naukowe 32(104) z. 2 155

nDCiDCDCDCSC ppppGD ...,,...,,, 21 (2)

nDCiDCDCDC

SC

pppp

GD

minmin2min1min

min

...,,...,,,

(3)

nDCiDCDCDC

SC

pppp

GD

maxmax2max1max

max

...,,...,,,

(4)

The limits were such that for a given relative

bearing i (i = 1, 2, ..., n)

4,3,2,1;min kddikDpiDCp (5)

4,3,2,1;min minmin kdd ikpDipDC (6)

4,3,2,1;min maxmax kdd ikpDCipDC (7)

where

dpDik – distance from the centre of the central

ship to the limit of the partial domain on

the relative bearing i for the scenario k;

dpD min ik – distance from the centre of the central

ship to the limit of the minimum partial

domain on the relative bearing i for the

scenario k;

dpD max ik – distance from the centre of the central

ship to the limit of the maximum partial

domain on the relative bearing i for the

scenario k.

As an example the determined partial domain

boundaries – minimum, mean and maximum – for

the river-sea ship 1 for scenario 4 are presented in

the figure 5.

Fig. 5. The partial domains of river-sea ship 1 for scenario 4

Figure 6 presents the total domains of the ships

under analysis.

The analysis of the results

The research included an analysis of passing dis-

tances between vessels accounting for their dimen-

sions (ship contours). The program recording ship

movement parameters was logging the position

of GPS receiver antenna. For this reason it was

a) b) c)

Fig. 6. Total ship domains(minimum, mean and maximum) for ships of different size: a) river-sea ship 1; b) LO-RO ship; c) VLCC1

-1000 0 1000-3000

-2000

-1000

0

1000

2000

3000

y [m]

x [m

]

granica minimalna

granica średnia

granica maksymalna

-1000 0 1000-3000

-2000

-1000

0

1000

2000

3000

y [m]

x [m

]

-1000 0 1000-3000

-2000

-1000

0

1000

2000

3000

y [m]

x [m

]



necessary to determine the distances of characteris-

tic points describing the ship contour in relation to

the antenna position.

The determination of domain boundaries al-

lowed to determine the lengths and widths of each

domain for each type of ship. The results are listed

in table 2.

Table 2. Domain boundary dimensions

Types of domain

boundaries

Ship domain

River–sea ship 1 LO-RO ship VLCC 1

Minimum Length 1495 [m] 1200 [m] 2220 [m]

Width 490 [m] 675 [m] 1135 [m]

Mean Length 2320 [m] 1900 [m] 3790 [m]

Width 600 [m] 955 [m] 1635 [m]

Maximum Length 3440 [m] 3670 [m] 4900 [m]

Width 845 [m] 1595 [m] 2168 [m]

Figures 7 and 8 graphically illustrate the param-

eters of domain boundaries.

Fig. 7. A comparison of total domain lengths

Fig. 8. A comparison of total domain widths

The analysis of data has shown that domain

shapes are similar. It has been also found that the

domain boundaries are irregular at some places.

The shapes of minimum and mean domains signifi-

cantly differ from the expected ones. This is due to

a large number of manoeuvres where the starboard

side of the central ship was being passed at a short

distance. It seems purposeful to undertake further

research.

As expected, large differences were observed in

length and width of domains depending on ship

type. Navigators steering the smallest vessels tend-

ed to maintain smaller domains than navigators

handling larger vessels.

Conclusions

The influence of ship size on domain shape and

dimensions in the restricted area has been analyzed.

Based on the simulation tests participated by expert

navigators domains of various size ships were

determined. The results confirmed a significant

influence of ship size on the shape and dimensions of

the domain. Further research is needed in reference

to the method of domain determination as well as the

analysis of other factors determining the ship domain

area in a restricted area, such as the area parameters

and hydrological and meteorological conditions.

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River – sea ship 1 LO-RO ship VLCC 1

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mai

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Ship domain in the restricted area simulation research

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