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1 INTRODUCTION
Many marine accidents are caused by errors on the
partofthenavigator.Inparticular,shipcollisionsare
often causedby improper lookout of navigator. The
improper lookout that is pointed out as the major
cause of ship collisions is regarded as an error in
situation awareness of navigators. Grech and
Horberry indicat
e that 71% of navigators’ errors are
SArelatedproblems(Grechetal.2002).
Inordertodecreasethenumberofshipcollisions,
many analytical studies of marine accidents have
been published (Romer & Petersen 2009, Corovic &
Djurovic2013, Akyuz & Celik 2014). One of these
studies focused on the assessment of navigators’ SA
using the Situation Awareness Gl
obal Assessment
Technique (SAGAT) (Endsley 1988, Koester &
Sorensen 2003). In pilot training using a ship
maneuvering simulator, the possibility that trainees’
navigationskillscouldbemeasuredbySAGATwas
indicated(Okazaki&Ohya2012).
Authorshaveconfirmedthefeat
uresofnavigators’
SAwithbridgesimulatorexperimentsandbehavioral
analysis (Nishizaki & Itoh 2015). However, it is
difficulttounderstand theprioritylevelofotherships
by relying solely on behavioral analysis.
Consequently, in previous study, interviews on
prioritylevelsofrecognizingshipsfornavigatorsare
conducted,andnavigators’SAweremea
suredinship
maneuvering simulator experiments using SAGAT.
Astheresults,anewriskcategorydesignatedasthe
“attention area,” which covered ships with high
priority level in navigators’ SA was proposed
(Nishizaki & Takemoto 2016). The category was
createdbasedontworiskcategories(dangerareaand
A Characteristic of a Navigator's Situation Awareness
for Crossing Ships
C.Nishizaki,T.Takemoto&Y.Kunieda
TokyoUniversityofMarineScienceandTechnology,Tokyo,Japan
ABSTRACT:Manyshipcollisionshavebeencausedbyanavigator’serrorinthesituationawareness(SA)of
thenavigator.Incongestedseaareas,navigatorsclassifyshipsonthebasisofdifferentprioritylevels.For safety
measuresagainstshipcollision,itisimperativefornavigatorstorecognizetheshipswithhighprioritylevels.
In previous study, navigators’ SA was mea
sured in a ship maneuvering simulator using the Situation
AwarenessGlobalAssessmentTechnique(SAGAT).Fromtheresultsofthepreviousstudy,weproposedanew
risk category, named as “attentionarea,” that covers ships withhigh priority level inthe SAof navigators.
However,theextentofdatafornavigators’SAwaslimit
ed.Therefore,thepurposeofthisstudyistoconfirm
thevalidityofthecategoryusingadditionaldataofnavigatorsSA.Inthisstudy,thevalidityoftheproposed
categorywasconfirmed,andalimitlinesurroundingshipswithhighprioritylevelswasidentified.Inaddition,
itwas evidenttha
tthe categorywasabletodetect ships with highprioritylevelaroundthetimewhenthe
collisionavoidancewasperformed.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 11
Number 2
June 2017
DOI:10.12716/1001.11.02.12
296
cautionarea)thatproposedbyKiyoshiHara(Hara&
Nagasawaetal.1990,Hara&Nakamura1995).
We employed only three subjects who had
onboardexperienceascaptainsinpreviousstudy,so
theextentofdataaboutSAinnavigatorswaslimited
in the previous study (Nishizaki & Takemoto 2016).
Therefore,thepurposeofthisstudyistoconfirmthe
validityoftheriskcategoryof“attentionarea”using
additionaldataontheSAinnavigators.
Inthecurrentstudy,foursubjectsemployedwere
different from previous studies. They were
interviewedabouttheirinformallookoutusingsame
listofquestions
asinpreviousstudies,andtheSAin
navigators was measured using SAGAT under the
sameexperimentalconditionsasinpreviousstudies.
The“attentionarea”wasdefinedbya functionof
distance and rate of bearing change of other ships.
Because 3 subjects employed in previous study put
emphasis on them
in determining priority level.
Therefore, in current study, through the interview
questions, it was reconfirmed that navigators
emphasized distance and rate of bearing change of
othershipsindeterminingprioritylevel.
Inaddition,itbecameobviousfromthesimulator
experiments with SAGAT in this study, that the
“attentionarea”covered
shipswithhighprioritylevel
innavigators’SAasinthisstudy.As theresults,the
validityofthe“attentionarea”wasconfirmed,andit
became obvious that there was a limit line covered
ships with high priority level. Furthermore, it was
evident that the “attention area” can assist in
detecting
ships with high priority level around the
timewhenthecollisionavoidancewasperformed.
Inthispaper,themethodsemployedinsimulator
experimentswithSAGATareexplainedinSection2.
Subsequently, the experimental conditions and
scenariosaredescribedinSection3.Theresultsofthe
interviews and simulator experiments are
presented
in Section 4. Based on these results, discussions are
explainedinSection5.Weprovidetheconclusionsof
thisstudyarehighlightedinsection6.
2 METHODFORMEASURMENTOF
NAVIGATORS’SITUATIONAWARENESS
SAGATisaneffectivemethodtomeasurenavigators’
SAs in the simulator experiments. The original
SAGATwas
developedandproposedtomeasurethe
SA of aircraft pilots in cockpits, and the procedural
standardsofSAGATwereestablished(Endsley1988).
ThroughtheuseofSAGAT,itispossibletomeasurea
pilot’s situation awareness directly, independent of
their memory of the experiments after these
experimentsareover.
In
order to maintain the continuity of the
simulation,theinterruptiontimeshouldbeselectedto
be as short as possible. However, there are
ambiguities in the oral reports about all ships in a
congestedseaarea,anditisdifficulttoaccountforall
recognizedshipsinashortinterval.
In
order to measure the situation awareness of
ship navigators, we adopted the method where
subjectsfillinrecognizedshipsonaradarchart.This
method was proposed as an evaluation method for
marinepilottrainees(Okazaki&Ohya2012).Weset
interruptiontimeasoneminutetoenabletestsubjects
toanswerbasedonradarwatchinformationbyuseof
theradarchart.A sample report based on the radar
chartisshowninFigure1.
Figure1.ExampleofareportforSAGAT.
3 EXPERIMENTS
3.1 BridgeSimulator
Thepurposeofthesimulatorexperimentsistoobtain
dataonnavigators’SAinkeepingwatchbytheuseof
SAGAT.ExperimentswithSAGATwereconductedin
the ship maneuvering simulator of the National
MaritimeResearchInstitute.Withinthebridgeofthe
simulator, general navigational equipment
were
installed,suchasacompass,pairofbinoculars,radar,
ECDIS, and steering stand. It is possible to record
behaviors of the subject in response to navigational
orders and other ships situations using behavioral
analysissystemsinthesimulator.
3.2 Subjects
Inthisstudy,foursubjectsdifferentfromtheprevious
study and with onboardexperience wereemployed.
The informationof subjects in a previousstudy and
thatinthisstudyareshowninTable1.
Table1. Comparison between the previous and current
studyonsubjectinformation.
_______________________________________________
Experimental
SeasonSubjectIDAppointment
_______________________________________________
Previousstudy Sub.ACaptain
Sub.BCaptain
Sub.CCaptain
Currentstudy Sub.DChiefOfficer
Sub.E2ndOfficer
Sub.F3rdOfficer
Sub.GChiefOfficer
_______________________________________________
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In this study, the subjects kept watch using the
general navigational equipment (compass, pair of
binocular, radar, ECDIS and steering stand).
Furthermore, they were instructed to keep their
simulated ships on a steady course and speed if
possible. When the subjects felt an imminent risk of
collision,they wereinstructed
to maneuver to avoid
thecollisions.
Before the experiment, to conform with ethical
standards in humanresearch, we requested that the
all subjects fill informed consent forms for human
research, which all subjects accepted and signed to
signifytheirinformedconsent.
3.3 ExperimentalScenarioandMeasurementMethodfor
navigators’SA
Navigators’SAsweremeasuredusingSAGATunder
the same experimental scenario as used in the
previous study (Nishizaki & Takemoto 2016).
Therefore, an open sea was used as thesea area for
the experimental scenario, and there are 24 other
ships with each having various