International Journal

on Marine Navigation

and Safety of Sea Transportation

Volume 4

Number 3

September 2010

261

1 INTRODUCTION

Although modern watercrafts have been equipped

with advanced facilities, such as satellite navigators,

anti-collision radars, electronic charts, and automatic

cabins, etc., the occurrence of shipping accidents is

still frequent. Therefore, the IMO organization and

many other organizations pay more attention to the

shipping safety. According to IMO organization’s

analysis results, there are three main reasons result-

ing in shipping accidents in recent years:

1 the failure of equipments on watercrafts;

2 the influence of navigation environments and

conditions;

3 and, human factors.

The proportion of these three factors to the whole is

shown in Fig.1, from which it can be seen that up to

eighty percent of shipping accidents are directly or

indirectly caused by human error. Under the compli-

cated circumstance, navigators lacking of watch

have poor capability of dealing with emergency,

poor qualities and little sense of duty, as well as

cannot master traffic rules on the sea well. Hence,

misoperation will occur. In order to guarantee the

safety of shipping, we should pay more attention to

human factors where not only the quality of naviga-

tors and their ability of dealing with emergency

would be developed, but also the latest modern tech-

nology for prediction of shipping accidents and

blocking the wrong order or misoperation would be

adopted. Consequently, a shipping accident forecast

model is developed in this paper. Furthermore, a

method of the shipping accident prediction and con-

trol is studied based on the proposed model.

2 ANALYSIS OF THE REASONS IN SHIPPING

ACCIDENTS

The shipping system is comprised of watercrafts,

human and the navigation circumstance. Due to the

particularity of carriers and conditions, the charac-

teristic of shipping systems which are complicated

systems is multi-category, multi-layer, multi-

attribute and multi-rule. Shipping accidents can be

classified into the following types, collision, ground-

ing, striking, heavy weather, fire & explosion,

foundering, missing, and engine failure, etc. Risk

during navigation mainly results from three factors:

a) collisions with other objects (static or moving), b)

the change of external environments (such as ty-

phoons, tidal waves, fogs, and other disasters), and

c) wrong orders sent by navigators (including

misoperations). These three factors of the system al-

so have many components which are shown in Fig.1.

In recent years, new challenges encountered in ship-

ping systems are mainly as follows:

Study on Shipping Safety Strategy Based on

Accident Forecast Model

X.Y. Meng, Y.M. Bai & X.J. Han

Dalian Maritime University, Dalian, China

ABSTRACT: The factors which would cause shipping accidents are analyzed in detail and a model which can

forecast shipping accidents is studied in this paper. During navigation, all the factors are integrated and calcu-

lated in this model which then estimate and speculate on the risk degree of collision for the own ship. Finally,

the risk level and the possibility of shipping accidents can be forecasted in real-time. The proposed accident

forecast model can estimate the possibility of collision with other ships or objects in a specific domain.

Meanwhile, the external environment such as weather, stream, etc. is taken into account in the model. Be-

sides, the validity of navigators’ orders can also be evaluated in the model which consequently can forecast

different kinds of shipping accidents effectively in that most of the factors which cause shipping accidents

have been involved in the proposed model. With the accident forecast model, the shipping safety would be

improved greatly. A practical example demonstrates the effectiveness and superiority of the proposed strate-

gy.

262

Figure.1 The influence factors of shipping accident

1) With the trend that ships become larger and larg-

er, as well as more and more rapid, the inertia of a

ship becomes larger, and therefore it is more dif-

ficult to manipulate the ship.

2) With the world economy incorporating and in-

creasing, the quantity of ships proliferates. To-

gether with the progress of ocean oil field explor-

ing and sea culture, the navigation density inshore

becomes higher. Hence, high risk would be taken

when a ship navigates in the inshore area or on

dense lane.

3) The abnormal change of the weather such as fogs

and typhoons, etc., critically influences the navi-

gation condition.

In order to cope with these problems, the technology

and techniques for shipping safety are required to be

studied and developed urgently. Especially, the hu-

man factor should be highlighted. In this paper, a

shipping accident forecast model is proposed to

avoid and control various accidents.

3 THE SHIPPING ACCIDENT FORECAST

MODEL

3.1 Structure of the model

Nowadays, there are many kinds of models describ-

ing the ship motion. Among them, models correlated

to the shipping safety are mainly: 1) OD traffic flow

model (Fuji J. et al. 1971), 2) ship field model (Da-

vis P V. et al. 1982, Goodwin E.M. 1975), and 3)

DCPA (distance of close point of approaching) and

TCPA (time of close point of approaching) model

(Zheng Zhongyi et al. 2000). These models describe

various characteristics of the shipping safety from

different points of view. They have some advantages

and are applied to large scales of areas. However,

they cannot essentially solve the problems of the

shipping safety. In this paper, a shipping accident

forecast model which integrates each kind of factors

influencing the shipping safety is proposed. As the

output of the model, the risk degree is the concept of

the possibility that accident will occur.

The shipping accident forecast model can be ex-

pressed as follows:

njitTdTT

HMUUUnW 

),()( =

(1)

where,

)(nW

——the output of the forecast model which is

defined as risk degree;

——the evaluated influence degree of naviga-

tion environments;

——the risk degree of collision with encounter-

ing targets;

——evaluation results of the operation instruc-

tion (telegraph orders and rudder orders).

The output of the accident forecast model is de-

termined by three items which correlates to three

main aspects causing shipping accidents respective-

ly. The first item in the model is

),(

tTdTT

UUU

which interprets the encounter probability and the

risk degree of collision. The second item is the eval-

uation to the validity of orders sent by navigators.

The third item is the degree of influence on the ship-

ping safety while external conditions vary. The out-

put

)(nW

∈ [0, 1] suggests that the ship has no dan-

ger while

)(nW

=0 and the ship is in danger while

)(nW

≠0. The larger the output

)(nW

is, the higher

the risk degree is.

The inputs of the model mainly come from the

scanning information of the ARPA, other navigation

operation instructions, parameters of velocity and

course, and other related information from sensors

(wind velocity and ship draft, etc.). Integrating this

information, the forecast model evaluates the risk

degree in real time.

3.2 Risk degree of collision

The risk degree of collision with encounter targets

involves the space collision risk

and the

time collision risk

. The space collision risk

mainly includes the

DCPA

, ship fields, the fuzziness

of domain boundary, the orientation of encounter

targets, observation errors in the

DCPA

, etc. Ac-

cording to the velocity and course of the own ship

263

and encounter objects, the shortest encounter dis-

tance between them is

)sin(

παϕ

−−•=

TRT

RDCPA

. After the safety en-

counter domain

and the safety passing distance

are determined, the fuzzy set

of the space colli-

sion risk can be obtained. The membership function

is defined as follows:











≤≤













−

|| if ,0

|| if ,

|| if ,1

)(

dDCPA

dDCPAd

DCPAd

dDCPA

DCPAu

The time collision risk mainly expresses the rela-

tive velocity, distance, velocity ratio between two

ships, the length of own ship, and maneuvering per-

formance, etc. According to the relationship between

encounter and movement of ships, the encounter

time between the own ship and targets is given by

RTRT

vRTCPA /)cos(

παϕ

−−•=

(2)

After the extreme time

for sending a rudder order

and the time

for ensuring the relative safety dis-

tance between two ships are determined，the verify-

ing domain of

TCPA

and the fuzzy set of the

time collision risk is

, of which the correspond-

ing membership function

is defined as follows:











≤<













−

≤

if ,0

if ,

if ,1

)(

tTCPA

tTCPAt

TCPAt

tTCPA

DCPAu

The collision risk between ships is the synthesis of

the space collision risk and the time collision risk. In

the domain

, the ship collision risk is a set of

and we have

iTdTT

uuu ⊕=

(3)

The above-mentioned synthesis operator “

⊕

” means

that,

So long as

=0 or

=0, we have

. Other-

wise, if

0≠

and

0≠

)max(

, iTdTT

uuu =

3.3 Determination of the impact item of

environment conditions

The navigation environment factors involve the

weather, hydrology and lane conditions. For the sake

of simple computations, the environment influence

parameter

(influence degree of navigation envi-

ronment) is mainly determined by the wind velocity

and the wind direction measured by wind gauges,

and determined by rocking parameters which are de-

rived from the ship’s draft of each shipboard. The

function is given by

)(

maxmax

⊗=

Where

is the wind velocity,

max

is the maximal

wind power,

is the rocking height,

max

is the max-

imal rocking height.

max

and

max

can be approxi-

mately set according to actual navigation conditions.

The value of

∈[0, 1] is the maximum of

max

and

max

, which means that the worse the environ-

ment is, the more the value of

is close to 1. It is

obvious that the environment influence parameter

makes a great impact on the risk degree

)(nW

3.4 Assessment of navigators’ orders

Most shipping accidents are caused by improper or-

ders sent by navigators. Hence, as the term for as-

sessing the validity of orders,

is included in the

forecast model. The principle of how to get the value

is shown in Fig. 2.

Figure.2 The choice of value M

i,j

① Expert system of the order assessment is stored in

the system. Each order sent by navigators will be

analyzed whether it is reasonable according to basic

operation rules and emergency operation rules. If the

order violates the rules, then

=1. Fig.2 The

choice of the value

output

)(nW

equals to ze-

ro.

264

② If the order is evaluated to be valid by the expert

system, the output

)1( +nW

, which is the output on

the time of n+1 after the order is sent, should be cal-

culated and compared with the output

)(nW

on the

time of n. The variety of

)(nW

will be obtained

through the function

)()1( nWnWW −+=∆

. If

W∆

is positive, it implies that the risk degree is increas-

ing, then

W∆

. Otherwise,

=0.

4 PRACTICAL EXAMPLE

A practical example of the shipping accident fore-

cast model will be illustrated as follows. A ship is

navigating with the course of 60° and the velocity of

14Kn, as shown in Fig. 3.

Figure.3. The navigating condition of own ship

In the definite domain, the own ship may encounter

with other five ships which are marked as G

, G

and G

. The moving condition of ships is

listed in Table 1.

Table 1. The moving condition of other ships in the domain of

the own ship

object

course（C

）

velocity（V）

distance（D）

angle of bow

（

）

120

3.85

335

136

2.75

010

5.60

035

3.20

065

4.15

121

Here, DCPA, TCPA and the collision membership

function between the own ship and other ships at the

moment t0 can be deduced, it is shown in Table 2,

from which it can be seen that the collision risk de-

gree between the own ship and G

is the highest at

the moment t

= 0. 437. Provided that

and

, we have

)(nW

=0.437. Similarly, the

output

)(nW

of the forecasting model at the time of

, t

can be calculated respectively. According

to the output of the model, navigators can take prop-

er actions to avoid shipping accidents.

Table 2. Collision membership function between the own ship

and other ships at the moment t

object

DCPA

TCPA

1.188

0.220

0.018

0.015

0.018

1.732

0.184

0.078

0.071

0.078

0.947

0.660

0.057

1.339

0.286

0.437

0.375

0.437

1.676

0.359

0.206

0.146

0.206

5 CONCLUSIONS

A shipping accident forecast model is proposed in

this paper, and the method of the predicting shipping

accident is developed based on the collision risk de-

gree, environmental influence coefficient and in-

struction assessment calculated in real-time. The key

technology is the integration of relevant information

of the shipping safety and the composition of the

model. Because many complicated factors are in-

volved in the shipping system, there are still some

factors which are not considered in this paper, to

name a few, evaluation rules of instructions, the reli-

ability of the sea scanning, and the influence of visi-

bility on sea. It is believed that with our tirelessly

work and continuous development of information

technology the complex shipping system can be

modeled accurately to predict and avoid shipping

accidents.

6 ACKNOWLEDGMENT

This paper is supported by “National Basic Research

Program of China” (No.2008CB417215). The Pro-

ject name is “Research on mechanism of shipping

safety and accident-forecasting theory”.

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