357
1 INTRODUCTION
Rule 5 – ‘Lookout’, of the International Regulations
forPreventingCollisionsatSea(IRPCS),1972requires
the ship’s Officer of the Watch (OOW) and
accompanying members of the bridge team to
maintainanefficientlookoutatalltimes[50].Various
reasons including poor design of controls and
interfaces) such as Multifunction Displays (MFDs)
appear tointerferewiththisfunction [40].TheUK’s
MarineAccidentInvestigationBranch[43]statesthat
65%ofthevesselsinvolvedincollisionscontravened
the IRPCS lookout rule, whilst 19% of the
watchkeepingofficersofthevessels,involvedinthese
collisions, lacked Situational Awareness (SA).
The
European Maritime Safety Authority indicates that
from2014to2021,atotalof563liveswerelostwith
6,155 injuries caused mainly from ship collisions, of
which59.6% of accidentsweredue tohumanaction
and68.3%ofthecontributingfactorswererelatedto
human behaviour [10]. According to
the Marine
Australian Transport Safety Bureau (ATSB)
investigationsof41collisionsover26yearsidentified
consistentfailuretomaintainaproperlookout[1].
These statistics lead to a fundamental but un‐
answered question i.e., ‘are the lookouts actually
doing their job as required by IRPCS?’ The accident
reportssuggestotherwise;therefore,
theeffectiveness
of technology on ship’s bridge needs to be assessed
from the user perspective. For example, MFDs are
now widely used on ship’s bridges to show
navigational and collision avoidance information.
They vary in shape and size but are usually
rectangular in shape with Graphical User Interface
(GUI) showing
different objects in various colours,
Analysis and Optimisation of Best Practice for Proper
Lookout at Night
A.Khalique,A.Bury&S.Loughney
LiverpoolJohnMooresUniversity,Liverpool,UnitedKingdom
ABSTRACT: A significant proportion of accidents appear to be caused by a lack of maintaining a ‘proper
lookout’ on a ship’s bridge. The root cause for theseaccidents could be the result of watchkeeper’slack of
awarenessofrequirementstomaintainaproperlookout.
Thispaperutilisestheauthors’proposeddefinitionof
thistermandthendiscussestheoutputsfromastudyonimprovingwatchkeeperbehaviourcarriedoutinship
bridgesimulators,usingeyetrackingdevices.Thestudyinvolvesapplyingtheproposedmethodofcarrying
outvisualsearchscanstogetherwithunderliningdistractionscaused
byMultifunctionDisplays(MFDs)found
onmodernshipbridges.Basedonthefindings,thepaperevaluatestheimpactoftheproposedscanmethodfor
maintaining a proper lookout, reduction in distractions caused by MFDs and discusses how it is almost
impossibletoachieveacompletedarkadaptationwiththepresenceof
MFDsandotherlightingonmodernship
bridges.Thisresearchoffersasolutiontocontroltheserisksthroughriskassessment,togetherwithtrainingand
education for watchkeepers to overcome these issues. This study is expected to contribute significantly to
improvingwatchkeeper’sbehaviourinmaintaininglookoutandapplicationoftheproposed
scanmethod.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 18
Number 2
June 2024
DOI:10.12716/1001.18.02.12
358
displayed in multiple pages accessible through soft
buttons [3]. This requires more interaction time and
effortfromtheuserthanwhenMFDsdidnotexist.
AlthoughalackofuserinputintotheMFDdesign
and the resultant design induced errors appear to
causesomeproblems[41],thewatchkeeperas
aweak
link also needs to be investigated to ensure such
errorscanbeavoided.Attheendoftheday,modern
MFDs on the bridge are meant to facilitate
watchkeepers, therefore we must know their
weaknessesandfindwaystoworkaroundthem.This
is similar to the case
of the human circadian low
where humans increase awareness to mitigate
possibleadverseconsequences.
This paper examines factors contributing to
watchkeepers’ ability tomaintainahigh level of SA
and the impact of MFD design on maintaining an
effective lookout at night. The authors also believe
that there is a lack
of appreciation of the need to
maintainaproperlookoutamongstOOWsthatneed
tobeaddressedtoimprovetheirbehaviour.Basedon
these, this paper utilises the authors’ definition of
proper lookout [34] together with an effective scan
pattern that can be used for optimised visual
searching,avoidingdistractions
causedbyMFDs.The
impact of illumination on dark adaptation and
validation of the need to raise watchkeepers’
awareness to improve night watchkeeping is also
presented.
2 STCWREQUIREMENTSFORLOOKOUTS
The STCW Code is a mandatory devicethatdefines
training standards for OOWs and others who are
tasked as a
lookout. The conduct of bridge
watchkeeping and the training for all involved in
performing watchkeeping duties is therefore
internationallyalignedtothestandardsprescribedin
the STCW Code. For lookout duties, the Code [22]
specifically uses the phrase ‘a proper lookout is
maintained at all times…’. It goes a step
further by
usingthephrase‘keepaproperlookoutbysightand
hearing’ for competence required for non‐OOW
ratings forming part of a navigational watch. In
explainingthecriteriaforevaluatingthiscompetence,
theCoderequiresthat‘soundsignals,lightsandother
objects are promptly detected and their appropriate
bearing
indegreesorpointsisreportedtotheofficer
ofthewatch’.TheCodeelaboratesthesetwophrases
furtherontheexactrequirementsbutdoesnotdefine
the term ‘proper lookout’ leaving a gap that, in the
authors’ view, is the main culprit in causing
underlyingissuesconnectedtoa
lackofmaintaininga
proper lookout. In order tofillthis gap, the authors
definedproperlookoutas[34]:
‘The application of due diligence to improve
situationalawarenessby:
1. Sight‐Through systematic visual search scans of
theenvironmentaroundownvessel.
2. Hearing‐Throughaquietwheelhousewithaccess
to
outsidesounds.
3. AllavailablemeanssuchasRadar, AISandother
bridgeequipment.’
Thisproposeddefinitionnotonlyencompassesthe
IRPCSrequirementsbut also providesreferenceto a
visualscanningapproachformaintainingalookoutas
established through the research presented in this
paper. The research methodology consisted of
using
Eye Tracking Devices (ETDs) in ship bridge
simulatorsafterprovidingguidanceonscanpatterns
to participantstocapture potential improvements in
their lookout behaviour. This paper discusses the
findings considering existing research and provides
suggestionstoimprovelookoutprocedures.
3 SITUATIONALAWARENESS
Throughanefficientvisualsearch,watchkeepersfeed
information
totheirbraintobecomeawareofobjects
in the ship’s surroundings. This is referred to as
SituationalAwarenesswhichisthecognitiveprocess
of knowing what is going on around a ship to
understanddangersothatmeasurescouldbetakento
avoidit[13].
Multitasking is intrinsic to
navigational
watchkeepingwheremaintaininganefficientlookout
is a sub‐task, yet instrumental in developing fully
informedSA.Itmustthereforeencompassperception,
comprehension and projection of a threat’s location
and movement inrelationtoown ship,asshown in
Figure1[11,46].
Figure1.ThreeLevelSAModel[34]
Inessence,theOOWperceivesandcomprehends
the current situation, and runs mental predictive
modelsaboutthelikelyoutcomes[20]withrespectto
collision avoidance. Any shortfalls in perception or
comprehension can easily lead to a lack or
inappropriatenessofSA[6],whichisa moreserious
issuethanthe judgemental
errors for poor decisions
leadingtoaccidentsi.e.,inefficientlookoutisdirectly
proportional to lack of attention or vice versa. This
couldbelinkedtodistractionsonthebridgeorafter
longperiodsofinactivity[59]duetolackoftrafficin
the vicinity of the ship. Surprisingly, the UK’s
Maritime and Coastguard Agency [45] recognises
GlobalMaritimeDistressandSafetySystem(GMDSS)
equipment,completionofadministrativetasks[47]on
bridge and routine testing of bridge equipment as
359
‘distractions’ to the watchkeeping officers’ primary
duty of keeping a proper lookout. However, no one
appearstoproposeasolutiontoovercomethemalbeit
recognisingthatthesedistractionspotentiallyleadto
low levels of SA [42]. This is where the solutions
presentedinthispaperarenotonlyrelevant
butfillin
a long standing, vital, yet fundamental gap in
maritimewatchkeepers’skills.
3.1 Visualsearchinganddistractions
Thebasicrulesforthesafetyofnavigationremainthe
same despite the introduction of significant
automation on ship’s bridge [17]. The well‐known
four stages of passage planning, i.e., appraisal,
planning,
execution,andmonitoringare stillutilised
bythemodernnavigator.Thefirststagefeedsintothe
secondandthesecondintothethirdstageandsoon.
The task‐demand from the watchkeeper increasesin
hightrafficdensityorduringcoastalnavigationwhen
monitoringtheprogressofavesselthat
isfollowinga
well appraised, planned and executed passage plan.
This stage therefore requires an increased focus and
attentionas a ‘slight’lossof attention may leadtoa
lossofSA.
In essence, SA feeds from maintaining a proper
lookoutwhichisasimple‘visualsearch’exercise.To
ensure that
a watchkeeper’s attention is suitably
focused to identify any potential hazards,
watchkeepers need to establish their own ‘visual
search technique’ which is a basic procedure
facilitatingthemaintenanceofeffectivelookoutacross
the necessary area, whilst overcoming any potential
distractors.
To gauge user input into designing navigational
and collision avoidance
information displayed on
MFDs, a questionnaire‐based survey was conducted
as part of this MarRI‐UK funded research. This
questionnaire was distributed amongst experienced
OOWsandMasterswhichshowedonly10.4%of(67)
watchkeepers will visually check their vessel’s
surroundings to verify the position of other vessels
with only 4.5% indicating
that they will verify
visibilitywhentakingoverthewatch.Thesestatistics
evidence that the modern watchkeeper does not
understand the significance of lookout by sight, let
alone the added complications for maintaining a
lookout at night or indeed the impact of MFDs on
theirabilitytomaintainlookout.They
notonlyneed
to understand it but must also appreciate the
significant differences for maintaining a night
lookout.
The watchkeepers’ primary task is to perform a
visual searchinadditiontomaintaining anauditory
attentiontoanysoundsthatmayneedtheirresponse.
Inaddition,theyalsoneedtolookat
theequipment
via the MFDs to monitor various elements for safe
navigation. Regardless of where the watchkeeper
needs to look, the visual search requires [61] the
watchkeepertorecogniseaparticularobjectamongst
other visible objects or features. This recognition
requires focused attention entwined with SA,
attention‐related errors and
other factors that
contributetothesafenavigation.
Visualsearchisanaturalprocessonegoesthrough
indailylifewhereintheindividualsactivelyscanthe
environmenttolocateaparticularobject,alsoreferred
to as a visual stimulus, among irrelevant features,
referredbysomeresearchersasthedistractors[5].For
example,thesearchforadesiredproductontheshelf
inasupermarketqualifiesasavisualsearchwhereall
other undesired products are the distractors. The
visualsearchforthedesiredproductiscontrolledby
directing the attention focus whilst scanning the
products, ignoring undesired products. This is the
veryprinciplethatthewatchkeepersneedtoapplyto
theirvisualsearchwhenmaintainingalookoutonthe
bridgeofaship.
Theeyesareconsideredagatewaytothebrain[58]
andactas theprimesourcefor updatingan OOW’s
SA.However,thebackgroundscatteroflightsinthe
coastalareas,partitionsinthebridgewindows,clouds
inthesky,allacttogetherinmostcasestocamouflage
a watchkeepers view. Furthermore, the human eye
naturallytendstofocussomewhere,evenwhenthere
is nothing to focus on such as featureless sky – a
perceptualprocess[58]knownas
‘selectiveattention’
i.e.,theabilitytofocusonsomesensoryinputswhile
tuningoutothers.Ifnostimulichallengethevisionto
attractfocus,theeyesnaturallyrevert[14]toarelaxed
intermediate focal distance of 3 to 10m, a
phenomenonknownasempty‐fieldmyopia.
Thishighlights two importantfactors
thatimpact
upon OOW’s ability to maintain SA as needed for
Endsley’s [11, 12] SA model. i) the watchkeeper is
looking without seeing anything [60] and, ii)
watchkeeperscanmisssomethingimportant,despite
lookingoutsidethewindow,becausetheyselectively
attend to only one aspect of the scene visible to
the
eye [57]. This limitation comes into effect when the
watchkeeperisactuallylooking outside the window
butwhataboutwhentheyarenot?Similarly,thereis
a tendencyforattentiontodrifttointernal thoughts
(mind wandering), which can also distract from the
primary task. Under non‐demanding conditions, the
issue of attentional control also creeps in [53]. This
couldbesignificantwhenthereislesstrafficaround
theshipcausingthewatchkeeperstobeboredwhich
mayturntheirattentiontoMFDssimplyasameans
to escape the boredom, i.e., when people are bored,
theyactivelyseeksources
ofdistractionasadeliberate
strategy. There remains therefore a need to evaluate
the impact of illumination at night, particularly to
dark adaptation, when looking at MFDs on the
bridge.
Reaction Time (RT) to an auditory or visual
stimulus[62]istheintervalbetweenthepresentation
of a stimulus, and a
voluntary responsesuch as the
press of a response key. When our nervous system
i.e., the eyes in the case ofa watchkeeper, recognise
the stimulus, the information is relayed to the brain
[31]whichreleasesinstructionsviathespinalcordfor
hands, fingers, or other body parts to react.
Our
‘sensorymemory’holdstheinformationcapturedvia
eyes for 1 to 4 seconds from where it is transferred
intoShortTermMemory(STM)[64,39].TheSTMcan
hold this information for 6‐12 seconds. It is this
duration which defines whether the OOW will deal
withtheinformationreceived,
manipulateitmentally
andtaketherequiredaction.However,ifadistraction
360
triggersanotherevent,thenthisinformationmay be
lostleadingtoaninactionbythewatchkeeper.
Thehumanbrain’sSTM[58]isa‘limitedcapacity
system’ where two operations requiring it will
interferewitheachothere.g.,adistractioncausedby
analarmwhenthewatchkeeperistryingtofocus
on
the lookoutfunction. So, the OOW is almost always
faced[40]withadauntingtaskofhavingtofocuson
onetaskwhilstdeliberatelyandactivelyinhibitingor
ignoringothertaskswhichcanliterallybeconsidered
as distractions in this context. They thus require a
continuous mental effort [64]
to shift focus to avoid
exceeding their mental capacity for retaining and
recognising hazards in the STM, process them and
takeappropriateactions.
Each navigational task [42] performed by a
watchkeeperrequiressubstantial multiple sources of
information to be processed. Based upon an
individual’s cognitive ability, they can probably
choose the
source of this information but if
overwhelmed by the visual or audible information
stimuli,thedecision‐makingisalmostalwayslikelyto
be affected [8], leading possibly to human error.
Hofheimer[19],referstoitas‘fleetingattentionspan’
andexplainsitas‘lapsesintheabilitytoconcentrate
on
astimulusortaskandsustaintherequisitedegree
of focused attention to persevere with information
processingortaskattainment’.Thiserrorisdeemedto
be the result of an incorrect decision, improperly
performedaction,oralackofaction[54].Ifitcanbe
trapped, the probability to lead to
accidents can be
reduced.Regardlessofwhatnomenclatureisusedfor
distractions that push the watchkeepers away from
theirprimarytask,theymustovercomethem, anda
potentialsolutionisthescanmethodproposedinthis
paper.
3.2 Windowwiperscanmethod
Theeyecanonlyfullyfocusandrecognise
anobject
whenitisviewedinitscentralFieldofVision(FOV)
whichresultsinclear,sharplyfocusedmessagesbeing
senttothebrain.ThecentralFOVextendsfromright
infrontoftheeyestoapproximately2.5°eitherside.
This5°monocularfieldofviewforeacheyeprovides
atotalbinocularfieldofviewof10°withbotheyes.In
comparison, peripheral vision extends to
approximately 100°‐110° on either side of the eye
(Figure 2) which is considered extremely useful in
identifying objects that may pose a collision threat.
Theobjectsthatappeartohavenorelative
motionare
unlikelytoposeanythreat,thereforeeveniftheyare
not detected through peripheral vision, they will be
picked up when the eyes gain focus in any given
block.
By contrast, any visual information that is
processed through peripheral vision will be of less
detail.Astheeyescan
onlyfullyfocusonthisnarrow
viewingarea,effectivescanningisbestaccomplished
with a series of short, regularly spaced eye
movementsthatbringsuccessivesectionsofthearea
to be scanned into the central visual field. The two
photoreceptorcellsinhumaneyei.e.,conesandrods.
The cones,
located in the centre of retina recognise
colouranddetailoftheobjectwhenlightisreflected
fromit.Therodsprovideperipheralvisionwiththeir
functionalityceilingtoluminancelevelsequivalentto
anightwithovercastskyandwithoutmoonlight.For
anormaleye,thefovealvisionprovidesa20/20
visual
acuitywiththeperipheralvisionacuityintheregion
of20/200[55].Despiteasignificantreductioninvisual
acuity, peripheral vision assists in detecting large
objectsorobjectsinmotionwithoutprovidingdetails
forshapeandcolouroftheobject.
Figure2. Human Eye Central and Peripheral Vision Field
[34]
Toscaneffectivelyawatchkeepermustknowhow
tomakethebest useoftheireyes’naturalcapabilities
andtrainthemselvestodothisrepeatedly.Thisidea
was proven in 1980’s when videogamerstrained to
use efficient visual scanning patterns showed better
performancethanthosewhoreceivedrandompattern
training
or no training at all [36]. Likewise, airline
pilots have a long history of using recommended
visualscanmethodsforkeepinganeffectivelookout.
Scanningthevisualfieldisakeyfactorincollision
avoidance and should be a continuous process used
bythewatchkeeperstocoverallareasvisible
fromthe
bridge. The proposed scan method is based on the
premisethattrafficdetectioncanbestbeconductedby
focussingona series of fixed pointsinspace. When
theheadisinmotion,visionisblurred,andthebrain
does notregisterpotentialtargets. Unlessaseriesof
fixations
ismade,thereislittlelikelihoodthatatarget
will be effectively detected. To be most effective, a
watchkeeper’svisionshouldbeshiftedandrefocused
at regular intervals but care should be taken when
refocusing because the eyes may require several
seconds to refocus, particularly when switching
betweenplacesof
differentilluminationlevels.
A scan of the visual horizon should be broken
down into approximately 10°‘blocks’, to ensure that
the field of central vision focusses on each sector in
turnbeforemovingontothenext,spendingnomore
than 4 seconds on each. Watchkeepers are used to
timemeasurement for
recognisingmaritime lights at
night. For example, if a light with characteristic of
flashing6seconds(Fl.6s)isfoundonchart,theywill
locate this light on the horizon and mentally count
‘andone,andtwo,andthree,…and6’tomeasurethe
6secondinterval.Inapplicationtherefore,
thebridge
windowistobedividedintoblocks,eachofwhichis
to be methodically scanned for traffic in sequential
order.Thisshouldbeperformedasfollows(Figure3):
1. Startinthecentreblockofthevisualfield(towards
thebowofthevessel).
361
2. Vision is moved to the port side of the vessel,
focusingforaperiodofnomorethanfourseconds
oneach10°block.Thebrainisnaturallytrainedto
process vision from left to right [15], hence scan
commencestowardstheleftshoulder.
3. Afterreachingthe
lastblockontheportside,vision
shouldresumeitsjourneybacktothecentreblock,
againscanningeach10°blockontheportsidefor
nomorethanfoursecondsineachblock.
4. Repeatonthestarboardsideofthevessel.Visionis
movedfromthecentreblockof
thevisualfieldto
thestarboardsideinblocks of10°,focusingfora
periodofnomore thanfour secondsoneach10°
block.
5. After having scanned each 10° block of the
window, vision should be switched to the
instrumentpanelwithinthebridge.Startinginthe
middle
(in line with the bow), the equipment
should be scanned to port employing the same
blockapproachthatwasutilisedtolookoutofthe
window.
6. Theninblocksbacktothecentre.
7. From the centre (in line with the bow), the
equipment should then be scanned to starboard,
employingtheblockscanapproach.
8. Theninblocksbacktothecentre.
9. Onceanappropriateamountoftimehasbeenspent
viewing the instrument panels inside the bridge,
theexternalscanprocessshouldberesumed.
Searching in sectors of 10° and focusing in each
sectorfornomore
than4secondsmeansspendinga
maximum of 84 seconds (1m 24s) to scan back and
forthacrossa210°fieldofviewinthevisualscreen
areas and 6 MFDs x 4 seconds each requiring 24
seconds maximum. This time sharing gives a ratio
betweenvisualscreensandMFDsof
3½:1whichfalls
inthesamerangeasusedintheaviationindustry(3‐
6:1) between visual screens and MFDs [15]. The
watchkeeper should remain constantly alert to all
traffic within their field of vision. This means
periodically scanning the entire visual field outside
thevesselbygoingouton
tothebridgewingtolook
astern. In addition, watchkeepers should consider
blind spots caused by fixed structures within the
bridge such as posts or window struts and take
appropriateactiontoavoidthesemaskingtheirview
ofothervessels.
Figure3.‘WindscreenWiper’Scanning[33]
4 LOOKOUTATNIGHT
Maintainingaproperlookoutatnightpresentsvery
differentbutunderstudiedchallengeforthemaritime
watchkeeper,commonlyknownas‘darkadaptation’
or adjustment to ‘night vision’. The IMO [22]
requirements in STCW Code with reference to dark
adaptationstate‘therelievingofficershallensurethat
themembers
oftherelievingwatcharefullycapable
of performing their duties, particularly as regards
their adjustment to night vision. Relieving officers
shallnottakeoverthewatchuntiltheirvisionisfully
adjustedtothelightconditions’.
Neither the Code specifies how this is to be
achievednordothe
watchkeepingindustrypractices
make allowances for this due to a lack of research‐
basedevidence.Unfortunately,ithasbeenlefttothe
interpretationoflegislaturestodevisestandardsand
guidance for watchkeepers and bridge equipment
displaymanufacturers.Asaconsequence,whilstthere
is some general guidance about it, seafarers are not
taughtaboutthesciencebehinddarkadaptationand
consequencesofnotfollowingascientificapproachto
it.Literaturereviewrevealsamajorflawinshipboard
systems in this aspect which is the lack of detailed
assessment of the impact of lighting and displays,
particularly the MFDs on watchkeeper’s ability to
achieve and maintain dark adaptation. For example,
theIMOperformancestandardsforRadar,ARPAand
ECDIS [23, 24, 25, 27, 28, 29] require that the
‘information is clearly visible to more than one
observer in the conditions of light normally
experiencedonthebridgeoftheshipbydayandby
night’. The classifications societies may apply these
ruleswiththeirowntwist,butIMOrequirementsare
theminimum.Tocontrollightingonthebridgeofthe
shipincludingthatfromVisualDisplayUnits(VDUs)
or MFDs, IMO [26] provides various requirements.
For example, during the day, the VDU background
luminance
range is 15‐20cd/m2 (candela per square
metre)withdisplayluminancerangeof80‐160cd/m2.
ButIMOdoesnotprovideaclearmin/maxluminance
at night which is where the luminance level causes
realproblemsformaintaininga proper lookout.The
IMOonlyrequires:
‘asatisfactoryleveloflighting…
tocompletesuch
tasks as maintenance, chart, and office work
satisfactorily,bothatseaandinport,daytime,and
night‐time.
Visualalarmsonthenavigatingbridgeshouldnot
interferewithnightvision.
All information should be presented emitting as
littlelightaspossibleatnight.
Displays
shouldbecapableofbeingreaddayand
night’.
Theserequirementshoweverspecifythatat night
onbridge,continuouslyvariableredorfilteredwhite
lightandoncharttablefilteredwhiteorspotlightsare
providedforilluminationfrom0–20lux.
Surprisingly,theserequirementsevidencethatthe
watchkeeper is delegated
the ability to control
variationoftheselightsbutitisdisturbingthatthey
are not educated about the effect of colours and
brightness on their vision. Keeping in view that the
typicalcomputerscreens,whichmaybedeployedon
ship’s bridge for office work or may even be the
MFDs for bridge equipment, operate with peak
luminancerangeof80‐500cd/m2[16],thustheseare
far brighter than the permissible level (0‐20lux) for
spotlight, hence will cause light pollution that will
affectdarkadaptation.
362
Figure4.IlluminationTerminology
In order to understand the function of eyes, two
aspectsofhumanvisionneedtobeunderstood;i)the
structureofhumaneyeand,–ii)thecharacteristicsof
thelightthatwhenreflectedfromobjectsandreceived
by eyes provide vision. These are discussed in the
remainingsections.
4.1 Humaneye
structure
The humaneyereceivesvastamountof information
andsendsit tothebrainfor recognition,processing,
storageandaction.Theeyescapturethisinformation
viatheraysoflightreflectedfromtheobjectstheeyes
see. If there is no light to reflect or if the eyes are
unabletocapturethereflectedlight,theeyesdonot
see.Whenlightisreflectedfromvariousobjectsand
received by human eye, the collected information
must be processed within the eye’s photoreceptor
cells.Theaverageluminanceatwhichtheeyescansee
rangesfromapproximately0.000001(10‐6)cd/m2on
darknightstoapproximately100,000,000(108)cd/m2
duringabrightsunnyday[4].
ThebasicstructureoftheeyeisshowninFigure5.
The eyescontaintwo typesofphotoreceptorcells in
theretina‐conesandrods[7].Eacheyeisestimated
tohave5‐6millionconesand
80‐90millionrods.The
fovea, a small depression within the retina, contains
mostlyconesinthecentralpartwhichisalsoreferred
toasthepointofsharpestfocus.
Conesrecognisecolour(certainfrequenciesoflight
which are not present in darkness), detail (when
bright light is reflected from any
object e.g., sun,
moonorartificiallight)anddistantobjectstoprovide
vision known as ‘photopic vision’ available in
luminancerangeof10‐108cd/m2[49].Theconesare
activated by release of a photopigment known as
Opsin and are further divided into three sub‐types
based on their colour‐
sensing ability for red, green,
andbluecolours.Amixtureofthesecoloursgivesthe
human eye an ability to distinguish thousands of
differentcolours.Conesareconsideredtofunctionin
brightness level equivalent [2] to that of 50%
moonlightatnightoraboveabout3cd/m2luminance
[37] and reach
their peak sensitivity [56] at 555
nanometrewavelengthlight.
Figure5.TheStructureofanEye[35]
Intheabsenceofluminancelevelof3cd/m2[4]or
more,thesecondtypeofcellsi.e.,rodsprovidevision,
known as ‘scotopic vision’, available in luminous
range [4, 49] of10−3‐10−6 cd/m2.Rodsaredesigned
for the best image perception in low light, but they
cannot
distinguish colours i.e., even the coloured
objects are seen but in shades of grey. This duplex
systemconsistingofconesandrodsallowstheeyeto
providevisibilityoveralargerangeofambientlight
levels.
Inordertoseeinthedark,eyesneedtoshifttheir
focus from
using cones to rods which takes time.
Whenswitchingfromseeingbrightlighttodarkness,
a photopigment [38, 2] [64] known as rhodopsin is
producedthathelpsrods’adjustmenttolowlightor
darkness. Rhodopsin is produced according to the
light intensity which takes approximately 20‐30
minutestoreachits
fulldensityataround10−5cd/m2.
Thisprocessisknownas‘darkadaptation’whichmay
take longer in some people depending upon the
quality of their eyesight, age, fitness and level of
fatigue [30]. Regardless of these variable factors,
research‐basedevidencesuggeststhattheadjustment
tonightvision
cannotcompleteinlesstimethan20‐30
minutes even though scotopic vision starts
improvement from approximately 5‐10 minutes into
theprocessofdarkadaptation.
Wheneyesaresubjectedtoabrightlightformore
than one second, the rhodopsin is decomposed
voiding the dark adaptation but at the same
time,
waitingforlightadaptation. It takes 5‐7 minutes for
cones to adjust fully to the bright light after
decompositionofrhodopsin–aphenomenonreferred
toas‘lightadaptation’.
A third function to be considered is the
simultaneous functionality of both rods and cones
suchasintwilight
conditions–aphenomenaknown
as ‘mesopic vision’ where both rods and cones
contribute to vision between luminance levels of
between0.003(10‐3)to3cd/m2[4].Atnightwhenthe
brightnessisatlowlevel,butitisnotabsolutedark,
some objects can still be seen due to
the contrast
betweentheobject such as thenavigational lightsof
another ship and the background darker sea/ocean
overlightersky.
363
Indarkness,theconesare‘unavailable’forvision
throughanareaapproximately5to10degreeswide,
therefore the vision must be off centredto ‘spot’ an
objectwithrodsintheregionsshowninFigure5.This
isbecausethecentral partofretinacannot detectan
object
iflookedatdirectlyduetothenightblindspot
intherodsareaofvision.Inthecontextofbinocular
vision (seeing with both eyes), blind spot is not an
issuesinceanobjectisunlikelytobeintheblindspot
of both eyes simultaneously, but it may remain
undetectedinmonocularvisione.g.,ifoneeye’sfield
of view was obstructed by a bridge window post.
Therefore, a process that must form a part of dark
adaptation[48]forwatchkeepersistoshiftthevision
by4–12degreestoonesidesothatrodscanbe
fully
utilised, and a blind spot avoided. Furthermore, the
headshouldremainincontinualmotionasexplained
inthe‘windowwiperscan’method,toovercomeany
issues of missing object detection due to the blind
spot.
Figure6.DayandNightVision[35]
When dark adaptation is complete, the photopic
visionisunavailablebutperipheralvisionisavailable
and extremely useful in the detection of faint light
sourcessuchasnavigationallightsofothervesselsor
dim stars – this function is vital for performing
optimum lookout, particularly collision threats from
otherobjects.In
essence,thelookoutorvisualsearch
atnightisentirelydependentuponperipheralvision
due to foveal night blind spot discussed previously.
The watchkeeper must therefore look between 5‐10°
eithersideoftheobjectwhichtogetherwithbinocular
vision provides an overall arc of 100‐110° on either
side
of the eye. This can only be achieved if the
watchkeeperdoesnotsearchforobjectsinthefoveal
regionbutscanstheareasadjacenttoit.Thisiswhere
the authors’ proposed ‘window wiper scan’ pattern
becomes more useful as thehead/eyesaremovedin
10‐degree blocks allowing the
peripheral vision to
scaneachblocktodetectobjects,bothstationaryand
moving.
4.2 Thevisiblespectrumoflight
Afurtherareatoconsiderfordarkadaptationisthe
impactofvariouscoloursusedintheMFDsorother
lightingonthebridgeofaship.Themaincomponent
that
makesitispossibletoseethingsisthelight.The
literal meaning of the word ‘photo’ is ‘light’ which
stimulates the photoreceptors (cones and rods). The
visiblespectrumoflightincludesviolet,indigo,blue,
green, orange, yellow and red (VIBGOYR) colours
withwavelengths[18]between400to720nanometres
(table
1).Ashorterwavelengthcorrespondstohigher
frequencyandenergyinthevisiblespectrume.g.,red
colour has the shortest frequency (400‐484THz),
lowest energy (1.91eV) and a wavelength of 620‐720
nanometres whereas violet colour has the highest
frequency(668‐789THz),highestenergy(3.10eV)and
a wavelength of 400‐
440 nanometres. Ultraviolet
wavelengths(<400nanometres)fallbelowthevisible
spectrum whereas infrared wavelengths (>720
nanometres) fall above this spectrum and are
consideredinvisibletohumaneye.However,someof
us may continue to see some colours in both the
ultraviolet and infrared wavelengths but prolonged
exposuretothesemaydamage
theeye.
Withrespecttothevisiblelightspectrumandthe
photoreceptor cells (rods and cones), three distinct
areas need to be considered from a watchkeeper’s
perspective, particularly when maintaining a proper
lookoutatnight:
1. Dark adaptation: As watchkeepers walk at night
intothewheelhouse,theireyesdon’tsee
anything
i.e.,totaldarkness.Thisisthetimeatwhichdark
adaptation commences which depends upon
successful release of rhodopsin which reaches its
peak sensitivity when exposed to wavelengths of
around500nanometres[32]whichcorrespondsto
blue‐greenlightwavelengths.Rodshaveahigher
sensitivity to blue light of wavelengths
460‐500
nanometres or less, no sensitivity to red light of
wavelengthsgreaterthan620nanometres.
In order to facilitate a quicker adaptation to
darkness[7], the watchkeepers are recommended
to spend some time, for example, in chart room
illuminated by red light. This is because the red
wavelengthlight
offersbiologicalbenefitsinterms
ofnottriggeringthedecompositionofrhodopsin.
This however only works with dim
monochromatic (single frequency or wavelength)
red light and not a white fluorescent light bulb
covered with red liner, coating, or filter. As rods
are not sensitive to red light wavelength,
rhodopsin continues to
be released to commence
dark adaptation and remains at the same
saturationleveliftheeyesareexposedtothesame
levelofredlight.Therefore,theuseofredlight(or
red goggles) is recommended for many control
spaces,e.g.,inship’sbridges,submarines,aircrafts
andsoonwhere
theoperatorscancontinuetobe
‘darkness’ adapted whilst performing their tasks.
Incaseofship’sbridges,then thesameapproach
canbeadaptedtoprovideabetternightvision.
Table1.VisibleLightSpectrum(Adaptedfrom[51,52])
**eV‐electron‐volt
***Therearenoagreedlimitsforthevisiblespectrum.Thevalues
usedherearefoundinmostofthereferencematerials.
364
2. Light adaptation: When a person moves from
darknessintolight,evenifthatmeansfocusingon
an MFD e.g., ECDIS display using multiple
colours, the eyes begin light adaptation which
means rhodopsin will start to decompose [49]. If
thisfocusremainsontheMFDforapproximately
5‐7minutes,
theconeswilladjustfullytotheMFD
colours,thusrequiringafurther20‐30minutesfor
theregenerationofrhodopsintodarkadaptation.
Whilst the foregoing is a basic concept to
understand the extreme situations for dark and
lightadaptation,thereishoweveranintermediate
functionthatassistsin
transitionbetweendarkand
light adaptation. This is pupil dilation i.e., the
increase in pupil diameter (to 8mm) with a
decreasing brightness and the reverse process of
decreased diameter (to 2mm) with reducing
brightnessbyuptoaboutfourtimesthannormal
diameter[4].Althoughthechangeinrodandcone
sensitivityhappensgraduallyoverseveralminutes
butthepupildilationismuchquicker.Despitethe
known changes in pupil diameter, the effect is
minimal and hence not considered in this paper
fromawatchkeeper’sperspective.
Based on the foregoing discussion,it is vital that
watchkeepersalwayscomparetheluminancelevel
on bridge to see its impact on dark and/or light
adaptation.InastudycarriedoutbyWynn etal.
[65], luminance levels (see Table 2) from various
MFDsonthebridgesofaRoPaxandanoiltanker
wererecordedatnight.TheIHO[21]specifications
for electronic chart content
require that ‘For the
ECDISthismeanssettingupthedisplayforbright
sunlight, when all but the starkest contrast will
disappear,andfornightwhensolittleluminance
istoleratedthatareacoloursarereducedtoshades
of dark grey (maximum luminance of an area
colour is 1.3 cd/m2
compared with 80 cd/m2 for
bright sun)’. For RoPax, it is clearly evident that
the EDCIS luminance was higher than the
minimumallowedbutnotsetbythewatchkeeper.
On this basis, it is only fair to assume that the
watchkeeperwaseithernotawareofthisoptionin
ECDIS and
by extension, for other MFDs or they
didnotapplythisduetoalackofawarenessofthe
impactontheirdarkadaptation.
Table2.LuminanceLevelonRealShips[65]
________________________________________________
RoPax Tanker
Luminance(cd/m
2
) Luminance(cd/m
2
)
________________________________________________
ECDIS5.8‐
Radar1Output 0.721.37
Radar2Output 0.211.15
EngineControls 2.40.14
________________________________________________
Further,themaximumluminanceofanareacolour
of1.3cd/m2allowedbyIHOfallsinthe mesopic
vision range i.e., 0.003 (10‐3) – 3cd/m2 meaning
thatdespitethewatchkeepersadjustingtheECDIS
luminancetotheminimumdesignlevel,itwillstill
beabovetheScotopicvisionluminance(<0.003(10
‐
3)cd/m2),thustheywillneverhavetheconditions
to switch to full dark adaptation. This is further
complicated by the fact that the combined
luminance for various MFDs, engine and
communication controls and other light pollution
causedbyaccommodation lights etcwillincrease
the prevailing luminance on the bridge
(wheelhouse), thus the possibility of never
achievingafulldarkadaptionremainsquitehigh.
3. Back scatter of multiple light colours: The IRPCS
‘Rule6–SafeSpeed’requirevesselstoconsider‘at
night the presence of background light such as
fromshorelightsorfrombackscatterofherown
lights’ because it may take longer to distinguish
between different colours of light exhibited on
shorethatmayconfusethewatchkeeper,requiring
more time to understand their position with
respecttothoselights.
Whenthevisionshiftsfromphotopic(conebased)
visiontoscotopic(rodbased)vision,theblueand
green lights appear relatively brighter (when
placedinproximityandlookedatsimultaneously
with 15‐20° off‐centred vision) as compared to
yelloworredlights.Thisphenomenonisknownas
Purkinje shift [9]. However, red light appears
brighterwhentheeyesarefixatingcentrally.
Relating the Purkinje shift to the
IRPCS Rule 6
requirement,thewatchkeepersmustbeabletosee
thelinkbetweensomelights,particularlytheshore
lights of different colours appearing and
disappearing with the shift from central to
peripheral vision. Thus, they must keep this in
mindwhenlookingoutatnight.
5 LOOKOUTPROCEDURES
In
order to rank ‘visual search’ high in OOW’s
priorities, they must first mentally accept its
significance. They then need to be trained in
establishing their own ‘timesharing technique’ to
sharetheirfocusedattentionbetweenlookingoutside
ofthebridgewindowsandontheothertaskswithin
the bridge that require focusing
on MFDs. A
minimumratioof3:1(infavourofvisualscanningout
of the windows) must be maintained in open sea
conditions,butthismayvarybasedonfactorssuchas
the area of operation e.g., proximity to coastline or
trafficdensityetc.Obviously,ifhigherfocusisneeded
on navigation in coastal areas, additional person to
assistinmaintainingproperlookoutwillberequired.
Similarly, where the traffic density requires more
focus on maintaining visual lookout, then an
additional OOW may need to be called upon to
monitor ship’s progress as per the passage plan. In
essence, the manning
level on the bridge can be
determined from the amount of time needed for
maintainingaproperlookout.
Thewatchkeepershouldremainconstantlyalertto
all traffic within their field of vision. This means
periodically scanning the entire visual field outside
thevesselbygoingoutontothebridge
wingtolook
astern. In addition, watchkeepers should consider
blind spots caused by fixed structures within the
bridge such as posts or window struts and take
appropriateactiontoavoidthesemaskingtheirview
ofothervessels.
To summarise the techniques for maintaining a
proper lookout at night, the following must
be
consideredbyallwatchkeepers:
1. Thewatchkeepersmustunderstandthesimplified
structureofconesandrodstoappreciatehoweyes
365
are used differently at night than during the
daylight.
2. They must treat the eyes as a precise instrument
which needs adjustment to the change in
illumination allows for avoidance of missing
potentialthreatsfrombeingvisuallyspotted.
3. It takes approximately 20‐30 minutes for dark
adaptation, but
once adapted it takes only one
secondtoloseitevenifjustbecauseoflookingat
an MFD for a brief period. This will require the
dark adaptation process to commence from the
beginningi.e.,requiring20‐30minutesforfulldark
adaptationagain.
4. It takes approximately 5‐7
minutes for light
adaptation.Thisperiodshouldnotbeoverlooked,
particularlywheninspectingdetailsonECDIS.
5. Theluminancelevels forthebridge aswellasfor
each MFD must be ‘risk’ assessed to ensure they
remain within the photopic, scotopic or mesopic
visionlimits.
6. Whenmaintainingalookout
duringtheday orat
night,thewindowwiperscanmethodcanstillbe
appliedandinfactprovidesabettermechanismto
useperipheralvision.
7. Allwatchkeepersarerecommendedtopracticethe
guidanceprovidedtofindtheirownoptimumfor
dark/light adaptation and use of window wiper
scanmethod.
6 CONCLUSION
The maritime watchkeepers’ primary task is to
maintainaproperlookoutatalltimes,butthistermis
neither suitably defined in the STCW Code nor any
guidance on its accomplishment is provided by
regulators, leaving a skill gap that prevents the
watchkeepersfromattainingafullSA.
Thisappearsto
resultfromalackofresearchonthistopiccombined
with the fact that the modern bridges now have a
largernumberofMFDsdrawingwatchkeepersfocus
away from their primary task of maintaining a
lookout. A definition of proper lookout has been
presentedforinclusioninthe
STCWCode.
In line with the proposed definition of ‘proper
lookout’, a window wiper scan method that can be
used to divide the time shared between looking
outsidevs.lookingatMFDstomaintainaratioofat
least3:1ispresented.Thisapproachhoweverneedsto
be applied at
a wider level wherein the maritime
watchkeepers’trainingincludesasupportsystemfor
the simulator instructors and assessors to train and
assess their lookout behaviours at an early stage in
watchkeepers’career.
Afurtherareaofimprovementforwatchkeepersis
alackofawarenesswithdarkadaptationatnightand
the
lightpollution caused by MFDs and otherlights
on the bridge. The researchersbelievethatcurrently
there is no risk assessment approach to gauging the
impact of lighting on night watchkeepers. Finally, a
listofrecommendationsisprovidedforwatchkeepers
tofollowandmaintainaproperlookout.
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