597
1 INTRODUCTION
Koreaʹs VTS (Vessel Traffic Service) is currently
installedin15portsand3coastalareas,inorder to
maintainmarinetrafficsafetyusingradar,VHF,AIS,
etc., and to protect the marine environment. VTS
monitors identified vessels in the VTS area and
provide the necessary information. As a result of
theseeffort
s,marinecasualtieswerereducedby39.3
%, from 126.6 cases to 76.8 cases after the
establishment of the VTS (Kim, 2015a). However,
therearestillmarinecasualtiesintheVTSareaand
there is no quantitative VTS officer’s control
guideline,sothattheserviceuser,theshipoperator,
ma
yreceivedifferentservicesaccordingtotheVTSO
evenunderthesamecircumstances.
IntheVTSarea,generalreportingsuchasarrival,
departures,andpassageofvessels,aswellasspecific
instructions on vessel traffic, are made by the VHF
control channel. Therefore, it is possible to analyze
communicationpa
tternofVTSOandmovementofa
shipthroughcommunicationanalysisofVTSarea.
We have obtained various information by
analyzing the communication of the VTSO (Kim,
2015b)andproposedthecontroldistancethroughthe
communicationanalysis(Park,2015).However,there
is no study on the probability of the dangerous
control through the communication analysis or the
minimumsafetydomainoftheVTSO.
Inthi
spaper,weanalyzedthecommunicationin
theVTSareaanddrewtheprobabilityofoccurrence
ofthecommunicationofthedangeroussituationby
the VTSO, and suggested the guideline of the
quantitativecontrolbydrawing theminimumsafety
domain.
For thi
s purpose, Busan Port, which has the
largest number of vessel traffic in Korea, has been
monitored for 7 days and the shipʹs AIS data were
collected to confirm the risk level at the time of
communication.
Themonitoring frequency ofthe dangerous ship
wasconfirmedtofollowthePoissondistributionand
the int
erval of the control was calculated using the
A Study on Basic VTS Guideline based on Ship’s
Operator’s Consciousness
S.W.Park,Y.S.Park&J.S.Park
KoreaMaritimeandOceanUniversity,Busan,Korea
ABSTRACT: VTS controls vessels using VHF for 24 hours a day. Therefore, from the analysis of VHF
communication,wecanunderstandthecurrentstatusofmarinetrafficandVTS’scontrolpatterninVTSarea.
This study objective is to propose a basic VTS guideline with ship’s CPA/TCPA, collision risk, control
frequency,and minimumsafetydistance usinganalysis of VHFcommunication. We analyzeda 7 dayVHF
communicationand AIS data from Busan VTSarea, thereafter calculatedrisk of collision using Park model
whichisba
sedonshipoperator’sconsciousnessandplottedminimumsafetydistanceandvessel’shigh‐risk
controlfrequencyusingPoissondistribution.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 11
Number 4
December 2017
DOI:10.12716/1001.11.04.04
598
exponential distribution. In addition, the minimum
safety domain of the VTSO was drawn using the
bearing and distance at the time of control of the
dangerousships.
2 VHFCOMMUNICATIONANALYSISINBUSAN
PORTVTSAREA
2.1 Researchmethodsandtargets
InoueandHara(1973)suggestedthat6to7
daysof
marinetrafficobservationwould be appropriatefor
representativepopulation.
Based on this reason, we analyzed the
communicationofVTSOintheBusanPortareaand
identifiedthedangerousencountersofthevesselsfor
3days(6
th
April,2015~8
th
April,2015),forfourdays
(11
th
December2015~14
th
December2015),atotalof
7 days (168 hours). We also collected the AIS
informationoftheshipatthesametimetocalculate
themaritimetrafficrisk.
Figure1.BusanportVTSarea.
2.2 RiskmodelbasedonShipOperatorConsciousness
VTSOuseCPAandTCPAinmanycases,butthisis
the value indicated by the distance, speed, and
heading factors between the vessels. However, it is
commonfortheship’soperatortodeterminetherisk
betweenvesselsbyreflectingthefactorssuch
asthe
size of the vessel, the type of the vessel, and the
surroundingsearoom.
Therefore,thisstudyintendstousethePotential
Assessment of Risk (PARK) model, which is
implemented for the risk of the ship operator who
navigates the actual coastal waters of Korea. PARK
modelis
basedontheshiptype,tonnage,shiplength,
ship width, angle and direction of approaching the
ship, the relative speed of ships and the distance
betweenships(Parketal.,2015).
Therisk ofthe PARKmodel rangesfrom 1 to7,
with0to3beingsafe.3to5
areclassifiedassafeand
not dangerous, and 5 or more are classified as
dangerous. In this paper, we analyzed the control
communication with a risk value of 5.0 or more,
whichisconsideredtobeadangeroussituation.
2.3 Identificationofrisksituationbasedon
communicationanalysisofBusan
PortVTS
The communication in Busan Port VTS area was
classifiedasVTStoship,shiptoVTSandshiptoship
calls.Theamountofcommunicationwasanalyzedas
showninTable1for7days.
Table1. Number of communication via VHF Ch.12 in
7days
_______________________________________________
Day ShiptoVTS VTStoshipShiptoship Total
_______________________________________________
1
st
day 73914393882
2
nd
day 702132102 834
3
rd
day 787149118 936
4
th
day 5539962652
5
th
day 64117288813
6
th
day 847135130 983
7
th
day 853167981,020
_______________________________________________
Total 5,122998691 6,811
_______________________________________________
Atotalof6,811communicationswereconducted
on the VTS VHF channel 12 of Busan Port for a
period of 7 days. The average number of
communication per hour was 40.54 at every 1.5
minutes. To identify the case where the VTSO
instruct the vessels directly, among the contents
of
the VHF channel No.12 of the Busan Port VTS, the
analysis was divided into 7 items: control, radio
check, intention, information, vessel check, channel
change and others. To identify the case where the
VTSOmonitorstheshiptoshipcommunication,the
analysiswasdividedinto4items:intention,channel
change,
chat,andothers.
Table2.NumberofVTScommunicationitemsin7days
_________________________________________________________________________________________________________
TimeControl RadioCheck Intention Info. VesselCheck ChannelChange etc. Total
_________________________________________________________________________________________________________
0000‐0200 1801962238
0200‐0400 1203641026
0400‐0600 1602980439
0600‐0800 8607199112134
0800‐1000 4416301018100
1000
‐1200 433224112590
1200‐1400 470524143598
1400‐1600 480419150894
1600‐1800 68052515211126
1800‐2000 81071214212128
2000‐
2200 30068601060
2200‐2400 350115120265
_________________________________________________________________________________________________________
Total528 4492001241479998
_________________________________________________________________________________________________________
599
2.3.1 VTStoshipcommunicationanalysis
Table2showsthecontentsoftheVTScallingthe
shipfor7daysandthenumberofcommunicationby
thetimeofday.
Asfortheamountofcommunicationperhour,it
wasfoundthatthe daytimezone(06:00‐18:00) was
642andthenight timezone (18: 00‐next day06:00)
was 356.The number of communication in the
daytimezone was 1.8timesthatofnight time zone.
Table3 showsthe comparisonof trafficvolume and
communication volume by time. It is observed that
VTShadmanycallsto
theshipatdaytimebecauseof
highvesseltraffic.
Table3.Comparisonoftraffic volume and communication
bytimeline
_______________________________________________
DaytimeNighttime
_______________________________________________
Traffic Communication Traffic Communication
volumevolume
(ships) (case)(ships) (case)
_______________________________________________
2,230642819356
_______________________________________________
In order to analyze the VTS to ship
communication, we extracted 145 cases of direct
control in two or more of the 528 communications
thattheVTScalledthevesselfor7days.
However,thispaperexcludecaseswherethereis
no AIS information, and that there is no
interconnection between the ship, berthing and un‐
berthingships
In order to check the risk of VTSO control of
vessels, the location of the vessels with 145
communicationsplottingisasillustratedinFigure2.
Figure2.VTSadvicestartingpointbyRiskvalue.
Inthiscase,thesafesituation(1~3)isgreen,the
safebutnotdangeroussituation(3~5)isyellow,and
thedangeroussituation(5~7)isred.
WhentheVTSOinstructthevesseldirectly,there
were48cases(33.1%)ofthe145caseswithariskof
5.0ormore,andmostofthemwereintheport.
2.3.2 VesselcommunicationonVTSchannelanalysis
Table 4 shows the contents of the vessel’s
communication on VTS channel for 7 days and the
numberofcommunicationbythetimeofday.
Table4.NumberofvesselcommunicationviaVHFchannel
_______________________________________________
TimeIntention Channel Chat etc. Total
Change
_______________________________________________
0000‐0200 801 0 9
0200‐0400 3623 0 41
0400‐0600 3022 0 34
0600‐0800 71412 4 91
0800‐1000 6839 0 80
1000‐1200 6044 0 68
1200‐1400 5738 0 68
1400‐1600
57310 2 72
1600‐1800 7065 1 82
1800‐2000 4683 0 57
2000‐2200 3833 1 45
2200‐2400 3932 0 44
_______________________________________________
Total580 4162 8 691
_______________________________________________
Thecontentsofcommunicationbetweenvesselson
theVTSchanneloftheBusanportcanbeviewedas
partoftheobservationconfirmation,whichisthefirst
stage of the VTS’s control procedure (MOF,
2014)becausetheVTSOcanalsolistentothecontents.
Inthe case ofintention confirmation
communication
regardingthetraffic,VTSOcanmonitorthesituation
withoutinterveningwhenitisjudgedthatthetraffic
situation at that time is appropriate. Therefore we
assumedthisprocedureasanindirectcontrol.
Amongthe 580 communicationsbetween vessels,
145 cases which were between two or more vessels
were extracted, except
when there was no AIS
information.Theship’slocationsandriskvaluewere
plottedasshowninFigure3.
Figure3. Passing vessels communication starting point by
riskvalue
Inthiscase,thesafesituation(1~3)isgreen,the
safebutnotdangeroussituation(3~5)isyellow,and
thedangeroussituation(5~7)isred.
Therewere44cases(30.3%)ofthe145caseswitha
riskof5.0ormore,anditwasconfirmed
thatvessels
communicateovertheentireVTSarearatherthanthe
directcontrolfromVTS.
600
3 ANALYSISANDPREDICTIONOFRISK
TRAFFICINTERVALUSINGPOISSON
DISTRIBUTION
3.1 Amethodofriskinterval
Poisson distribution is the distribution of random
variables that are less likely to occur in a particular
event among many events. It is also a discrete
probability distribution that represents how many
events
occurwithinaunitoftime.Thus,thePoisson
distribution is used to determine the number of
occurrences of events occurring in a given time and
space(Parketal.,2013).
Inthisstudy,weusedthePoissondistributionto
predict the probability of controlling the dangerous
situationin the
VTSarea per unittime. The Poisson
distributioncanbeexpressedasEquation(1).
!
x
e
fx
x
(1)
where,
:Numberofcontactswithariskof5.0ormoreper
unittime
:Theexpectedvalueofcontrollingtheriskabove5.0
foraunitoftimewithintheVTSarea
3.2 AnalysisandpredictionofriskintervalintheVTS
area
Basedonthe7dayscommunicationintheBusanport
area,weanalyzedhowmuchcontrolwasconducted
perunittime
forthedangerous trafficvessels,directly
orindirectly,bytheVTSO.
3.2.1 Case1(Directcontrol)
Figure4isagraphofthefrequencyofcontrolby
VTSOfordangerousvessels(riskabove5.0)andthe
probability of occurrence by Eq. (1) at intervals of 2
hourswithintheBusan
portVTSarea.
Figure4. Observation No. and probability of control for
dangerousshipsinVTSarea.
UsingthedatainFigure4,verificationofwhether
thisdistributionfollowsthePoissondistributionwas
carried out using chi‐squared for 84 samples (168
hours/2hours)
Ifthefrequencyislessthan5(usingchi‐square),it
affectsthevalueofexpectedfrequency(Tabata,1994).
Therefore,thesizeof
thesampleshouldbeincreased,
or two or more categories should be reduced or
integratedintoone.
Inthispaper,thefrequencyofobservationsof2to
5categoriesisintegratedinto9.
Table5showsthechi‐squaretestresults. Pvalue
was 0.21. The null hypothesis that there
is no
differencebetweentheobservationfrequencyandthe
expected frequency can not be rejected at the 5%
significance level, and this distribution follows the
Poissonprobability.
Table5. Chi‐square test for validation of the Poisson
distributiononVTScontrol(N=84)
_______________________________________________
FrequencyExpectation Observation Degreeof
(times)freedom
_______________________________________________
0 47.43(51.58) 52
1 27.10(25.16) 23
2 7.74(6.14) 5(9)11.52*
3 1.47(0)2(0)(0.21)
4 0.21(0)1(0)
5 0.02(0)1(0)
_______________________________________________
*p>.05
Sincethefrequencyofcontrollingtheshipswitha
riskof5.0ormoreper2hourshasprovedtofollow
thePoissondistribution,itcanbesaidthatanaverage
of0.57 times per unittime controlstheships with a
risk of 5.0 or more. The waiting time
to control the
next ship with a risk of 5.0 or more follows an
exponential distribution with an expected va lue of
0.57andcanbeexpressedasEquation(2).
0.57
0.57 0
T
fT e T
(2)
where,
T= Waiting time to next dangerous communication
(unit:2hour)
Figure5.Probabilityofcontrol fornextdangerousshipsin
VTSarea
601
Figure 5 is a graph showing the exponential
distributionofthewaitingtimeuntilavesselwitha
risk of 5.0 or more is controlled within the control
area of the Busan Port. The x‐axis represents the
waiting time until the ship is in danger of 5.0 or
higher
and the y‐axis represents the probability. For
example, it can be seen that the probability of
controllingariskof5.0orhigheragainafter2hoursis
32.2%.
Sincetheexpectedvalueofcontrolriskover5.0for
2hoursintheVTSareais0.57(timesper
unittime),
the average of the control time interval probability
variable is 1.75 unit time (2 hours) and controls the
vesselindangerousconditiononceevery3.50hours.
The exponential distribution is a probability
distributionwiththeelapsedtimebetweeneventsasa
randomvariable.Ifaneventoccursaccordingto
the
Poisson distribution probability, the time elapsed
during the occurrence of this event follows the
exponential distribution. In this study, it is verified
that the frequency of communication with vessels
withariskof5.0ormoreperunithourdependson
the probability of Poisson distribution. This means
that
the time interval between the execution of the
dangeroussituationandcontrolofthenextdangerous
situation follows the exponential distribution. This
exponential distribution is used to predict control
intervalofvesselsindangeroussituation
3.2.2 Case2(Indirectcontrol)
Figure 6 is a graph of the frequency of
communicationof
dangerousvessels(riskabove5.0)
and the probability of occurrence by Eq. (1) at
intervals of 2 hours within the VTS area of Busan
Port.
Figure6. Observation No. and the probability of
communicationofshipsinadangeroussituation.
Usingthefigure6data,theverificationofwhether
thisdistributionfollowsthePoissondistributionwas
carriedoutbyusingchi‐squaredfor84samples(168
hours/2hours)
Table6showsthechi‐squaretestresults. Pvalue
was 0.56. The null hypothesis that there is no
differencebetween
theobservationfrequencyandthe
expected frequency can’t be rejected at the 5%
significance level, and this distribution follows the
Poissonprobability.
Table6. Chi‐square test for validation of the Poisson
distributiononVTSmonitoring(N=84)
_______________________________________________
FrequencyExpectation Observation Degreeof
(times)freedom
_______________________________________________
0 61.90(52.80) 52
1 29.76(24.51) 25
2 3.57(5.69) 3(7)10.32*
3 3.57(0)3(0)(0.56)
4 1.19(0)1(0)
_______________________________________________
*p>.05
Figure 7 is a graph showing the exponential
distributionofthewaitingtimeuntiltheshiptoship
communicationoccursagainatariskof5.0ormore.
Forexample,itcanbeseenthattheprobabilityof
ship to ship communication on the risk of 5.0 or
higheroccurring
againafter2hoursis31.0%.
Figure7.Probabilityofmonitoringnextdangerousships
Sincetheexpectedvaluetocommunicatebetween
vesselsonriskover5.0 for2hoursintheVTSareais
0.52(timesperunittime),theaverageof thecontrol
time(indirect)intervalprobabilityvariableis1.92unit
time (2 hours), and VTSO indirectly controls the
vesselindangerousconditiononce
every3.84hours.
4 MINIMUMCONTROLDOMAINUSING
COMMUNICATIONDISTANCE&BEARING
While monitoring VTS area, VTSO calls the vessel
whentheyneedtocontrolthesituation. Shipoperator
alsocallsothervesselswhentheyneedtochecktheir
intention.WeassumedthatVTSOandshipoperator
contact point on
VHF channel is minimum control
domain
4.1 Ship’slengthandcommunicationdistance
To draw minimum control domain in VTS area, we
researchedship’slengthandcommunicationdistance.
Figure 8 is a graph showing the relationship
betweenthelengthofshipsandvesselsunderdirect
control or indirect control from VTSO. The
average
length of the ship under VTSO direct control was
602
82.9mand 68.1m for the ship under indirect control
from VTSO. This means that VTSO controls large
vessels on average because small vessels have
relativelygoodmaneuverabilityandthereweremany
shiftingvesselsinVTSarea.
Figure8.Communicationvessel’slength
Figure9isagraphshowingthedistanceatwhich
the VTSO started to control the ship directly and
indirectly. The case of direct control was 2,617m
(1.41NM), indirect control was 2,357.7m (1.27NM).
The case of indirect control was shorter than direct
controlbecausethereweresomecasesthatindividual
vessels
contacted other vessels again after VTSO’s
controltoconfirmeachother’sposition.
Figure9.Communicationdistance(m)
4.2 Minimumcontroldomain
4.2.1 Method
To draw VTSO’s minimum control domain, we
putthe object vessel to zero pointand used relative
bearinganddistanceasdemonstratedinFigure10.
Figure10.Amethodofplottingdomain
where,
=Relativebearing(Rad)
R=ContactRange(m)
L=Ship’sLength(m)
4.2.2 Minimumdomain
Figure 11 is a graph showing VTSO’s direct and
indirect control starting plot. VTSO’s direct control
domainwas4LX2Landindirectcontroldomainwas
2LX2L.ThismeansthatVTSOcontrolsthevesselin
advancecompared to ship operator. Andalsoit can
be seen
that a lot of control communication is
performedwithrespecttotheshipaheadoftheship
inastern.
Figure11.VTSOcontroldomain
5 CONCLUSION
ThecommunicationcarriedoutbytheVTSOandthe
vessel operator for safety operation on the VHF
withintheVTSareareflectstheperception,scope,and
intentionoftheriskoftheVTSOortheshipoperator.
Therefore,itcanbeusedasameas ure oftheriskin
VTS area. This study analyzed the VHF
communicationofBusanPortandconfirmedthatthe
probabilityofcontrollingthevesselswithariskof5.0
ormorebythePARKmodelperunittimeintheVTS
area follows the Poisson distribution. The time
interval was predicted. Also, based on
the distance
603
from which the communication was started, the
minimumcontroldomainofthe VTSOwas derived.
Theresultsofthisstudyareasfollows.
1 Atotalof6,811communicationsover7dayswere
found at Busan Port VTS VHF Channel 12, with
40.54 average communication per hour and 1.5
minutes
per hour. Of these, the communication
that the VTSO called the ship was analyzed that
the day time had about 1.82 times the
communicationamountthanthenighttime.
2 WithintheVTSarea,theprobabilitythattheVTSO
will,directlyandindirectly,controlthevesselina
dangerous situation
(risk above 5.0) for a unit of
timeisanalyzedtofollowthePoissondistribution.
3 Based on the verification of the Poisson
distribution, the VTSO in the VTS area were
observed to monitor dangerous vessels on an
average of 3.50 hours and indirectly control the
vesselsunderriskconditionsevery
3.84hours.
4 Itwas analyzedthatVTSOhas4LX2Lminimum
control domain and ship’s officer have 2L X 2L
minimumdomain.
In next step, the relationship between the
probabilityofthePoissondistributionandtheactual
marineaccidentwillbeverifiedtoformamodelthat
can
estimatethenumber ofmarineaccidents.Astudy
on VTSO’s control guideline based on VHF
communication analysis in the VTS area should be
continued.
ACKNOLEDGEMENT
This research was a part of the project titled
‘Development of Ship‐handling and Passenger
EvacuationSupportSystemʹ,fundedbytheMinistry
ofOceansand
Fisheries,Korea.
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