679

1 INTRODUCTION

FocusofthisresearchisanalysisofAISdatafor the

passageStraitofSplit,Splitwaterwayarea‐Croatia.

ThroughAISantennaattheMaritimeFacultyinSplit,

AISdataiscollectedfortheSplitwaterwayarea.The

data is storedon acomputer fortrafficflow/density

analysis.

TheaimistocollectAISdatacontinuously

andanalyzethemtoimproveandenhancenavigation

safety.

StraitofSplitistheshortestwaytoandfromSplit

toislandofHvar,Vis,KorculaandfurthertoStraitof

Otrant. The Strait is located between the islands of

Soltaand

Brac.Inadditiontobeingtheshortest,this

Straitisalsothemostfrequentandnarrowestchannel

comparing to the other approach channel to port of

Split. In its narrowest part, the distance between

islands of Solta and Brac is 0.42 NM (Figure 1).

Navigational area with the depth greater than

 20

metersis0.15NMwide.TheStraitismarkedwiththe

navigational lights on the Cape Razanj (island of

Brac),CapeLivka(islandofSolta)andontheisletof

Mrduja[3,4].Regardingtheregulationsthatapplyto

StraitofSplit,anchoringisprohibitedforallvessels.

Split

becomes an increasingly popular tourist

destinationandmarine trafficisintensifying. Except

mentioned navigational marks, regulation of

prohibitedanchoringandVesselTrafficService(VTS)

there are no additional safety navigational

precautionsfortheStraitofSplit.Duringthesummer

time a large number of different types of ships

navigateinthis

areaandthatiswhyriskofmaritime

accidentsexist.AlthoughtheStraitinitsnarrowpart

is only 2 NM long due increased traffic density,

especiallyduringthesummermonths,itisnecessary

to plan additionally precautions and/or regulations

that will improve safety of navigation for that area.

Regulation

would improve safety of navigation for

thatarea.Occurrenceofthemaritimeaccidentcould

have disastrous consequences for the population,

marineenvironmentandfortheeconomyoftheCity

ofSplit(tourism).

Method for Analyzing AIS Data and Determination of

Simultaneously Ships Passage via Strait of Split

M.BukljašSkočibušić

UniversityofZagreb,Zagreb,Croatia

S.Vukša&I.Pavić

UniversityofSplit,Split,Croatia

ABSTRACT:Thetrafficdensityisabasiccharacteristicofmarinetrafficforsomenavigationalarea. Inthecase

of narrow channels such as Strait of Split (Splitska vrata), apart from the traffic density, the number of

simultaneousshippassagesisalsoimportantaswellasships

characteristics.Basedonsuchdata,additional

navigational safety guidelines and regulations may be planned for the observed area. The purpose of this

researchistodeterminethenumberofsimultaneousshippassagesviaStraitofSplitforacertain period of

time.CollectedAISdatainSPNMEAformatwasdecodedby

AISDecoderonlineprogramtocsvfile.

Forfiverandomlyselecteddaysinthesummerperiod,basedonAISdata,thenumberofsimultaneousship

passageswasdeterminedandshipsinformationpresented.



http://www.transnav.eu

the International Journal

on Marine Navigation

and Safety of Sea Transportation

Volume 12

Number 4

December 2018

DOI:10.12716/1001.12.04.05

680



Figure1.StraitofSplit

(Source:http://www.hhi.hr/catalogmaps/viewmap/129)[4]

The Automatic Identification System (AIS) is an

automatedtrackingsystemusedonshipsforlocating

and identifying vessels and avoiding collisions. The

automatic identification system broadcasts

information on ship identity, speed, direction and

positionevery2to10secondswhileunderway, and

every3minuteswhileatanchor[6].

AIS is

 a carriage requirement for SOLAS vessels

(SOLASChapterVRegulation19).

TwotypesofAISdevicesareinuse,ClassAand

ClassB.TypeAismandatoryforvesselsof300GTor

more operating on international voyages, cargo

vessels of 500 GT or more not operating on

international

voyages and for passenger vessels

(carryingmorethan12passengers)regardlessoftheir

size.AIS Class B isintended foruse onnon‐SOLAS

vessels. These can include domestic commercial

vesselsandpleasurecraft.

AISClassBunitshavelessfunctionalitythanClass

Aunitsbuttheyoperateandcommunicatewith

AIS

ClassAunitsandothertypesofAISunits[1].

Static

Information

Dynamic

Information

Voyage

Information

AIS

Station

AIS

Network

VTS

Station

VTS

Center

AIS

Network



Figure2.Automaticidentificationsystemdata

(Source:https://doi.org/10.7225/toms.v01.n02.002)[1]

AISdataanalysisandpresentationoftheobtained

results are subject of many scientific studies. The

research work (K. Naus et al, September 2007)

describeoneof the waysfordecodingAISdata and

their analysis with regard to the type and speed of

shipsfortheGulfofportGdansk

[8].Byanalyzingthe

AIS data, the navigation routes of certain types of

ships with the speeds greater than 2 kt is shown.

Basedonsuchdata,itispossibletorecommendand

adopt new surveillance measures to increase the

safetyofnavigationforanarea.

Suchmethodsofprocessing

AISdatacanbeused

to determine traffic density and track navigation

routesoflargerareas.

With a such analyzes it is a possible to monitor

maritime traffic flows/density, illegal activities such

assmuggling,marineenvironmentpollution,fishing

inprotectedareas,seabordercontrol[2,9,7].

Analysisofmaritimetrafficforthe

Splitwaterway

area and AIS data (in one part) was subject for

researchoftheFacultyofMaritimeStudiesinRijeka

(2014), calledʺMaritime traffic study for the water

way area of Split, Ploce and Dubrovnikʺ

(PROMETNO‐PLOVIDBENA STUDIJA PLOVNO

PODRUČJESPLIT,PLOČEIDUBROVNIK)[12].The

International

Waterway Risk Assessment Program

(IWRAP) have been used for numerical maritime

trafficsimulation.

TheIWRAPmodelstartswiththeassumptionthat

the risk of collision or grounding is proportional to

the density of traffic. Collision and grounding risk

assessmentaccordingtotheIWRAPisjustifiedinthe

followingcases[5]:



marine traffic is enough dense that the obtained

resultshaveasatisfactoryreliability,

 the characteristics of traffic and ships  are known

withsufficientreliability,

 navigationalroutesarerecognizable.

BasedontheAISdataandtheIWRAPprogram,

the risk assessment for collision and grounding for

the Straitof

Split have been obtained. The types of

shipsandthenumberofpassagesthroughtheStrait

ofSplitarealsopresented.(Table1).

Table1.Typesofshipsandthenumberofpassagesthrough

theStraitofSplit(overoneyearperiod)[12]

_______________________________________________

TYPEOFSHIP NUMBEROF AVERAGESHIP

PASSAGESLENGTH

_______________________________________________

Ro‐Roships  949070m

Highspeedcrafts 365035m

Cruiserships  775225m

22<100m

136100–200m

96200–300

16>300m

Bulkcarriers  32660m

Tankers25090m

Yachts584040m

Fishingboats  219030m

_______________________________________________



DataanalyzedbyIWRAPareveryvaluable.Based

on those data, guidelines for additionally traffic

regulationsarerecommendedforSplitwaterway.

However, data  on the simultaneous passage of

ships via Strait of Split are not available. Annual

681

number of ship passages  via Strait of Split and the

average lengths of the ship shows the density of

traffic.Thedensityoftrafficinnarrowchannelsdoes

notgiveaclearpictureofthepossibilityofamaritime

accident/collisions. If traffic density is arranged in a

waythatships

donotpassthroughtheStraitofSplit

at the same time, the risk of collision is lower. It is

therefore important to determine the number of

simultaneouspassagesthroughtheStrait.

2 HYPOTHESIS

Trafficdensityisafactorthataffectsthenavigational

safetyoftheStraitofSplitand

Splitwaterway.Traffic

density increases, and the characteristics of ships

(type, dimensions, speed, drought, etc.) which

navigateinthisareaaresuchthattheriskofmaritime

accidentsexists.Fornavigationinnarrowchannelsit

isimportanttodeterminehowmanyshipspassingin

the same time through this area. The

 traffic density

fornarrow channels doesnot givea clearpicture of

the danger of a marine accident if we do not have

data about the ships passing simultaneously. Based

on the analysis of traffic density and simultaneous

ships passages, additional navigational safety

precautionsandregulationsmaybeplanned.

Analyzing

AIS data valuable conclusions can be

drawn and this can improve the traffic safety and

navigationforsomewaterways[11].Ifthefrequency

ofsimultaneousshippassagesislargeitisnecessary

to plan additional precautions and regulations. If a

situation such as this occurs rarely or only

periodically(summer/

seasonally),itisnotnecessary

to introduce additional safety precautions and

regulationsforthewholeyear.

The paper presents a simple method of

determining the number of simultaneous ship

passagesforStraitofSplitandinformation’softhose

shipsfor5randomlyselecteddays.

3 METHODOLOGY

A flow chart shows

the AIS data processing

methodology. The data collected were processed

usingAISDecoderandwereexportedtocvs.file.Such

data should be further processed in the Excel table.

Theprocessinggivesatableofallshipsbroadcasting

theAISsignalfortheobserveddate.Accordingtothe

operating instructions of the

 AIS Decoder, the

decoding program is set in such a way that the

followingshipinformation’sarerecordedinthetable:

 MMSI,

 nameoftheship,

 speedoverground(SOG)

 latitude,

 longitude,

 courseoverground(COG),

 UTC,

 typeofship

 length

overall(LOA),

 breadth.

Afterthat,coordinatesofareainStraitofSplitfor

which traffic analysis will be performed are

determined. Area in Strait is defined by the

geographicalcoordinates P1,P2,P3andP4(Figure3).

FilterF1testsifpositionoftheshipsareinsidegiven

area.



43°20.5'N

43°19'N

016°24.2' E

016°24.8'E

P1 P2

P3 P4



Figure3. Coordinates of determined area at Strait of Split

(Source: http://www.hhi.hr/catalogmaps/viewmap/129,

Authors)

Additionally,F2teststhenumberofshipsina6‐

minute gap at simultaneous passage, and what are

thecharacteristicsofaships(dimensions,speed,type,

navigationalstatusandcourse).

Logic for filter F1 and F2 algorithm is presented

below.

FILTERF1

Input:.csvfileI

Output:no.ofshipsinareaP1,P2,P3,P4

DefinecolumnwithLongitudeandLatitudeL1&L2



foreachrowdo

 if((L1<P1&P2)&(L1>P3&P4))then

if((L2<P1&P3)&(L2>P2&P4))then

SaveshipAISdata

else

DeleteshipAISdata

endif

 else

DeleteshipAISdata



endif

endfor

returnI1



682

FILTERF2

Input:.csvfileI1

Output:no.ofshipsineachsimultaneouslypassageand

maximumA&T

DefinecolumnwithUTC,D1



foreachrowdo

 if((D1>(D1+3))&(D1<(D1‐3)))then

countnumberofcasesT

 else

reject

 endif

endfor

foreachTdo

 countandsavenumberof

shipsA

endfor

foreachAdo

 maxofA

endfor

return((maxofA)&T)



According to the frequency of simultaneous

passagesforacertainperiodoftime,itispossibleto

planadditionallyguidelines/regulationstoimprove

thesafetyofnavigation.

Results for five randomly selected days will be

presentedforthesummerperiodwhentrafficdensity

is increased, due to amount of

data and time

necessaryfordecodingandanalysis.



Figure4. AIS data processing methodology (Source:

Authors)

Analog to described methodology in Figure 5

actualdecodingprocessispresented.

INSERT

OUTP UT

OPT ION

EXCE L CO NVE RSI ON

Step 1. Setup as per

instruction manual

Step 2. Import NMEA

file

Step 3. Decoding

process

Step 4. Excel table

(filtering)

AIS decoder



Figure5.AISdatadecodingproces(Source:Authors)

683

Table2.Thenumberofsimultaneouspassesfortheobserveddatesandthecharacteristicsoftheshipsforthe

maximumoccurrence(Source:Autors)



Figure6.Numberofshipsinpercentageforeachsimultaneouslypassage(Source:Authors)

4 RESULTS

Table 2  shows the total number of simultaneous

passagesforagivenday.Fromtotalnumberofthese

passages, the maximum occurrence and

characteristics of these ships are shown. During all

these occurrences length of only one ship is longer

than 100meters. Length of other ships, except Petar



Hektorović,islessthan50meters.Itcanbesaidthat

thelengthofshipsforobservedoccurrencesdoesnot

significantlyaffectthesafetyofnavigation.

Morethan halfof the ships passing Straithave a

speed exceeding 10 kt and in some cases speed is

higher than 20

kt. The velocity factor greatly affects

the safety of navigation, especially in narrow

passages such as Split door.It is necessary to avoid

situationswheremoreshipswithspeedgreaterthan

20 kt are passing simultaneously through Strait of

Split.Figure 6 shows the number of ships in

percentage for each simultaneously

 passage for the

observed day considering total number of

simultaneouslypassages. In more than 60% of cases

onlytwoshipsarepassingsimultaneously.

Themaximumnumberofshipsinsimultaneously

passage is five. From observed data this happened

duringtwodays.Onthe24.08.2018.ithappenedonce

andonthe

04.09.2018.twice.Inthesecaseslengthof

theshipsislessthan100meters.

5 CONCLUSION

Inthispapermethod of maritimetrafficanalysisfor

passagethroughtheStrait ofSplitusing AISdata is

presented. Although the density of maritime traffic

through Strait is high, from the number of

simultaneous

 passages and the characteristics of the

shipsitcanbeconcludedthatexistingregulationsand

arrangements (navigational markings) meet the

requirements. Also it should be considered that the

number of smaller ships without AIS is very high,

especiallyduringthesummerperiod.Becauseofthis,

navigation through Split door requires

compliance

withregulationsandextremecaution[10].

Based on such simple AIS data analysis it is

possibletopredicttrafficdensityforacertainperiod

oftimeanditispossibletodeterminestructureofthat

traffic. To get moreaccurate results while analyzing

data it is necessary to keep in

 mind technical and

humanerrorstheAISsystemissubjectto[5].

The observed analyzed period in this research is

short,andbasedonit,thefinaldecisiononplanning

684

andintroducingadditionalsecuritymeasurescannot

be made. This study represents a simple method to

trackandanalyzemarinetrafficforalongerperiodof

time.Ayear‐longsamplewouldgiveamoreaccurate

information aboutthe traffic density, the number of

simultaneouspassagesandthecharacteristicsofthose



ships. It is also a proposal for future research with

continuouscollectionofAISdatafortheStraitofSplit

area. Considering the results obtained, it may be

planned to introduce additional safety measures for

navigationthroughStraitofSplit.

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