299
1 INTRODUCTION
Most modern sailing or motor yachts are equipped
with an Electronic Charting System (ECS), the non‐
professional counterpart to the Electronic Chart
Display and Information System (ECDIS) in
commercialshipping.SinceanECSonapleasurecraft
generally does not meet the chart carriage
requirementssetupby
theIMOinSOLASregulations
V/18andV/19(IMO,2014,2017),thecraftisrequired
tohavenauticalpaperchartsonboard.Nevertheless,
electronic navigation continues to increase in this
domain.Forexample,inasurveyamong112German
sailingyachtsontheBalticcoast(Müller‐Plath,2018),
83%
wereequippedwithatleastoneECS:73%hada
chartplotteraspartofamultifunctiondisplay(MFD)
on board, and 30 % a tablet computer with a
navigational chart application. Users appreciate the
continuousGNSSpositioning,theintegrationofdata
from other signal transmitters like a depth sounder,
radar,
AIS,anemometer(on sailingboats), sonar(on
fishingboats),andmotorunit(onpowerboats),and
the time‐saving route‐building functions. But how
does using the small and variable digital chart
(display size of usually 7‐12 inches) with its high
level of automation affect the spatial abilities of
the
sailor? This is most interesting in coastal waters
wheremostpleasurecrafttraffictakesplace andthe
dangerofgroundingandstrandingishighest.
The most relevant spatial abilities at sea are
orienting and wayfinding. Orienting is the ability to
relate one’s ownpositionwithinthe environment. It
includesre
‐orienting,theability to re‐establishone’s
bearingsafterhavinglostthem.Wayfindingrefersto
moving towards a destination. Both rely on spatial
knowledge, the so‐called cognitive map (Tolman,
1948).Accordingtocurrentpsychologicaltheory(e.g.
Waller & Nadel, 2013), it comprises three aspects:
Landmark knowledge, route knowledge, and
How Does Digital Navigation on Sailboats Affect
Spatial Abilities at Sea?
G.Müller‐Plath
TechnischeUniversitätBerlin,Berlin,Germany
ABSTRACT: AlthoughSOLASstillrequires nautical paper charts on pleasure crafts, more and more sailors
prefernavigatingdigitally.Whataretheimpactsontheirspatialabilities?Weconductedafieldexperimentat
theBalticcoastandtwosimulatorexperimentswithaltogether40sailors.Participantsplottedand/or
piloted
routeseitherintheclassicmanneronpaperchartsordigitallyonanECS.Weassessedthesituationawareness,
thecognitivemap,and(forthesimulatoronly)the wayfindingwithand withoutthe navigationmedia.We
found that digital navigation significantly impaired the cognitive map. Its impact on situation
awareness,
however, depended on previous navigation habits: Only sailors who used their paper charts regularly and
activelybenefittedfromtheECS.WeconcludedthatECSnavigationwithitshighlevelofautomationlastingly
altersspatialperceptionatseaandimpairsorienting.Withthevulnerableelectricitysupplyonsailboats,thisis
a
safetyissueforshipping.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 13
Number 2
June 2019
DOI:10.12716/1001.13.02.05
300
geometric knowledge (overview knowledge). In the
presentresearchweinvestigatedhownavigatingwith
anECSaffectscognitivemaps,orienting,wayfinding,
andtheinterplayofthesethreeinasailor.
Our hypotheses build on the following
considerations:Westartwiththecognitivemap.The
abilitytoconstructthemisregardedinnate
toanimals
andhumans,butaspecificcognitivemapisacquired
byactiveexplorationofanenvironment.Humansalso
usesecondarymeanslikepictures,words,orsymbols
ondifferentmedia.Informationfrommultiplesources
needs to be weaved together (Nadel, 2013, p. 158).
How is cognitive map acquisition affected by
using
digital GNSS devices? In road traffic, pedestrians
using a GPS device acquired less accurate spatial
representations(Ishikawaetal.,2008).Forcardrivers,
digital GNSS navigation facilitated wayfinding but
hinderedthe acquisitionofacognitivemap(Burnett
&Lee, 2005;Münzeretal.,2012). Sincenot onlythe
tasks(navigating
atwo‐dimensionalplaneinsteadof
one‐dimensional roads) but also the devices for
maritimenavigationdiffer fromthosein roadtraffic
(e.g. no speech output), research results are not
directlytransferable.Insailing,wethushypothesized
that classic navigation supports the acquisition of a
cognitivemap:Inplottingroutes
withcoursetriangles
and dividers on large paper charts, fixing positions
via dead reckoning at open sea or cross bearing in
coastalwaters,andwayfindingbyconstantlylooking
out in order to match chart and environment while
underway, an accurate and detailed cognitive map
builds up. With the GNSS and the
high level of
automationinECSs,however,thisisnotthecase.
Secondly, spatial orienting in sailing is closely
related to the concept of situation awareness. The
concept originally stems from aviation and denotes
thecorrectperception of elements of a situation, the
comprehensionoftheirmeaning,andtheprojection
of
futurestates andevents(Endsley, 1995a)inorder to
safely guide actions in a complex and rapidly
changingenvironment,forexamplewhenthesailboat
getsintoacurrentinanarrowfairway.Inadditionto
spatialorienting,attentionplaysacrucialrolebecause
information processing is selective and depends on
actionplans.Sincesituationawarenessdoesnotonly
refer to spatial elements of a situation but also for
example to the wind, the depth of the water, or the
speed of the boat, we will use the term “route
awareness” in the remainder of the paper when we
refer to
the route‐related spatial elements of the
situation.Itissynonymoustospatialorientingwhen
sailingpre‐plannedroutes,becauseyouneedtoknow
fromanegocentricperspectivewhereyouarecoming
from, where you are heading, and where you next
have to change course. Obviously, digital GNSS‐
supportednavigationhas
twoopposinginfluenceson
situationawarenessingeneralandrouteawarenessin
particular: improved availability of situational data
butreduced attention toand cognitiveprocessingof
them. Whether this will result in improved or
diminished situational awareness is open to
investigation.The literatureisunequivocaland does
not include small
recreational vessels: Asyali (2012)
proposed that ECDIS navigation in commercial
shipping improves the situation awareness of the
navigator. However, the results were based on
subjective assessments of ship officers in
questionnaires, not on objective behavioural studies.
Grech& Horberry(2002)on theother handfounda
generally positive relationship between increasing
technologicallevelsandlossofsituationawarenessin
shipping. For the present study, we could thus not
deduceanyspecifichypothesis.
Thirdly,wayfindingisdirectlysupportedbyECSs.
Itshouldthusbenefitfromdigitalnavigationaslong
as the medium is available but should break down
whenthesailorhas
torelyonhisowncognitivemap
andorienting(routeawareness).
Finally,thethreespatialabilities(orientation/route
awareness, wayfinding, and cognitive map) develop
in close interplay with each other and with the
mediumusedfornavigation.ECSnavigationwithits
smalland variabledigitalchart anditshigh levelof
automation
might weaken this association and
thereby even lastingly alter perceptual processing at
sea.
We investigated the hypotheses with a field
experimentincoastalwatersattheBalticSeaandtwo
simulatorexperimentsinourlab(seeFigures1‐3for
anoverview).Inallthreestudies,weexperimentally
variedthe
navigationmedia(classic vs. digital),and
includedprevioushabitsofusingnavigationmediaas
additional predictors. In the field experiment, we
assessed as outcomes the situational awareness
underway (including route awareness) and the
cognitivemapaftersailing.Thewayfindingcouldnot
be examined because of safety reasons. In the
simulator experiments,
the navigation media (classic
vs. digital) were also varied but taken away at
different points: In the first experiment they were
usedforrouteplottingandforpilotingasegmentof
the route but then “lost”, in the second for course
plotting only. As outcomes, we assessed the
wayfinding with
and without the navigation media,
the route awareness underway, and the cognitive
map after sailing. In experiment 2, we analysed in
addition how the navigation media, the route
awareness, the wayfinding, and the cognitive map
related to each other, and how these relations were
influenced by previous navigation habits. The
simulator
with its highly standardized conditions
allowed the more sophisticated and more reliable
statistical analyses required for such an analysis. It
alsoallowedmorevalidconclusionsregardingcauses
andeffects.Thefieldexperiment,ontheotherhand,
was ecologically more valid. The two types of
experimentsthuscomplementedeachother.
2
FIELDEXPERIMENTONTHEBALTIC
2.1 Method
Twelve sailors from different parts of Germany and
Switzerlandparticipated.Withregardtoage(33‐68
years),sex(1woman,11men),andlevelofexperience
(500‐30,000 nautical miles sailed), the sample was
typical of the population of German‐speaking yacht
sailors on
the Baltic coast (Müller‐Plath, 2018). All
possessed a recreational marine vessel license and
thereby sound navigation skills. It was particularly
importantforourstudythattheparticipantsdiffered
intheirpersonal preferencesofnavigationmedia:In
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paperchartnavigation,theyreported0‐40yearsof
experience, with eight participants currently using
their paper charts actively, i.e. making entries of
coursesand/orpositionsintothechart.
In digital navigation, their experience was 0‐12
years, with five participants currently using an ECS
actively, i.e. entering waypoints and/or
routes. Our
study took place in the coastal waters around the
island of Rügen. None of our participants had ever
beenthere.Thetesttrackswere7‐19nauticalmiles
long.Theweathervariedfromsuntorain,withwind
fromcalmto strong with gusts. Seven of the twelve
testtrackswererunundersail,fiveunderengine.
Eachcrewconsistedofaskipper,twostudentsas
experimenters, and two participants as navigators,
and sailed on one of the two participating yachts, a
Hornet 32 and a Bavaria 46. Figure 1 depicts the
procedure: On the first day, one of
the two
participantsnavigated classically,the other digitally.
On the second day, classic and digital media were
exchanged.Thus,12testtracksweresailedaltogether,
witheachoftheparticipantsnavigatingtwice.Tools
for classic navigation were marine paper charts,
protractor triangles, dividers, pencil, eraser,
sharpener, calculator, and a handheld
bearing
compass. Tools for digital navigation was either an
MFD (Raymarine 75eS with Lighthouse 2 software
and vector chart Navionics Platinum, display
diameter 7 inches, mounted next to the helm of the
Hornet 32), or a tablet computer (Tablet Apple iPad
Air 2 with the vector chart application Navionics
BoatingHD,
displaydiameter9.7inches,usedmobile
on the Bavaria 46).The navigation task was
standardised and consisted of two parts, route
plottingandnavigationunderway(piloting):Plotting
intheclassicconditionconsistedofdrawingcourses
onthepaperchart, writingcourseand distancenext
toeachcourseline,andwriting
theestimatedtimeof
arrival (ETA) next to each point of course change.
Correcting the course for magnetic deviation,
variation, wind, or current was not part of the task.
Plottinginthedigitalconditionconsistedofbuilding
and storing a route from start to destination. Four
participantseachbuilttheroute
bysettingwaypoints
onthechartplotteroftheMFD,bysettingwaypoints
onthetabletcomputer,andbyautomaticroutingon
the chartplotter with carefully checking afterwards.
For piloting, both navigators, each from his own
medium,announcedtothehelmsmanthecoursesand
coursechanges,andinthecaseof
acontradictionthe
skipperdecided.Moreover,eachnavigatorhadtodo
apositionfixonceunderway:theclassicnavigatorvia
cross bearing and the digital navigator by reading
latitudeandlongitudefromthedigitaldevice.
The cognitive map was tested after the boat
mooredintheharbour by asking the participants
to
drawasketchmapofthenavigatedareaonablank
piece of A4 paper (Burnett& Lee, 2005). The sketch
hadtoincludethefollowingcomponents:(1)adjacent
coastlines, (2) portofdeparture,of destination, and
alternative harbours, (3) shallow waters and other
dangers to navigation, (4)
navigation aids (buoys,
lighthouses),and(5)plannedrouteandsailedtrack.
The situation awareness of the two participants
wasassessedtwicealongoneachtesttrackwiththe
freezetechnique(Endsley,1995b):Unannounced,the
twoparticipantswereinvitedbelowdeckandhadto
answer in writing and independently of each other
nine questions about the current situation, grouped
intothefourdomainsposition,wind,boatmovement,
and route. Since situation awareness means the
correct perception of a situation in order to guide
actions, the participants should not just reproduce
naked numbers but give their answers in a
meaningfulandaction‐related
format:
1 Position
Indicateourpositionbyacrossonapaperchart.
(Thechartstylewasdifferentfromthechartused
forclassicnavigation.)
2 Wind
Indicatetheapparentwindangle(AWA)byanar‐
rowataboaticon.
Indicatethetruewindangle(TWA)by
anarrowat
the position indicating cross on the above paper
chart.
3 Course
Indicatethespeedoverground(SOG).
Indicate the courseoverground (COG) by an ar‐
rowatthe position indicating cross ontheabove
paperchart.
4 Route(=spatialorienting,seetheintroduction)
Indicatethebearingofthedestinationportbyan
arrowataboaticon.
Indicatethebearingoftheportofdeparturebyan
arrowataboaticon.
Indicatethedistancetothenextcoursechange.
Indicate how many degrees to port or starboard
theboat
hastoturnthere.
On each test day, the entire procedure was
practisedinthemorning,aportorananchoragewas
calledforlunchbreak,and the actual testtrack was
sailedintheafternoon.
2.2 Predictions
According to the hypotheses stated in the
introduction, we predicted that the
cognitive map
should be impaired afterdigital compared to classic
navigation.Thisshouldmorebethecasethelongera
participant had used digital media for navigation in
the past. For the situation awareness we had no
specific predictions because we hypothesized two
contradictory influences of digital navigation
(improvedavailabilityof
situationaldatabutreduced
cognitiveprocessingofthem).
2.3 Dataanalysis,results,anddiscussion
2.3.1 Cognitivemap
ThetwofreehanddrawingsinFigure4showinan
exemplary way that the classically navigating
participanthasacquiredamuchbettercognitivemap
than the digitally navigating one. For statistical
evaluation,the
24drawnsketchmapswereratedby
four independent experts who were blind to the
condition.
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Figure1.Fieldexperiment:Procedureanddependentvariables(framed).Within‐personvariationofindependentvariable.
Figure2. Simulator experiment 1: Procedure and dependent variables (framed). Within‐person variation of independent
variable.
Figure3.Simulatorexperiment2:Procedureanddependentvariables(framed).Between‐personvariationofindependent
variable.
303
Figure4. Left: Record of the test track from Lubmin to Lauterbach (the black dots mark the two queries on situational
awareness). Middle: Freehand drawing of the classically navigating participant. It contains the coastline, shallow water
areas,twobuoys,portofdeparture,ofdestination,andalternativeports,aswellasthe
routetraveled.Right:Drawingofthe
digitallynavigatingparticipant.Coastline,shallowwaterareas,buoys,andportsaremissingorwrong,onlytheroute is
correct.
They scored the accuracy of the five required
components(seeMethodssectionandTable1)witha
maximumof 100points each.Thetotal scoreforthe
cognitivemapwastheaverageofthefivecomponent
scores. We then compared the drawing of each
participantafternavigatingclassicallywiththatafter
navigating digitally (at another day on a different
route; intra‐person‐comparison) and statistically
assessedthedifferencescoreswithone‐samplet‐tests.
All statistical analyses in this paper were conducted
withR(RCoreTeam,2018).Table1showstheresults:
The cognitive maps were significantly worse after
digital
navigation than after classic navigation not
only in the total score but also in every component,
except one: The routes/tracks were equally well
representedinbothconditions.Ontheotherhand,the
mentalrepresentationsofnavigationaids(buoysetc.)
and of shallow waters/dangers were most severely
impairedafterdigitalnavigation.
Further
linear model analyses showed that the
threemannersofdigitalnavigation(waypointrouting
onthechartplotter,onthetablet,andautoroutingon
thechartplotter)impairedthecognitivemaplikewise:
Meancostswerealmostidentical. Moreover, neither
couldthefamiliaritywiththenavigationtoolaccount
for the results nor differences between
classic and
digitalrouteplanningtime.
Withthehelpofmultiplelinearregressionmodels
wethenexploredwhichcharacteristicsoftheperson
(as linear predictors of the intra‐person digital
cost/benefit) moderated the effect of the navigation
medium on the cognitive map. From all assessed
personcharacteristics,whichcomprisedage,nautical
miles sailed, orienting abilities according to self‐
assessment, interest in electronic devices, and habits
ofusingnavigationtools‐inparticular:yearsofusing
paperchartsonly,yearsofusinganECS,yearsofnot
usingpaperchartsanymore,activeuseofanECSon
thelastsailingtrip,i.e.with
makingentries,activeuse
of paper charts on the last sailing trip, i.e. with
making entries‐, we selected the best subset of
predictorswith thecrossvalidationtechnique(Shao,
1997). The best linear model contained age, years of
using an ECS, and active use of an ECS on the last
sailingtripasmoderators.ThemodelexplainedR² =
.71ofthevarianceofthedigitalcosts(F(3,8)=6.81,p
= .0136). All three predictors were highly significant
(all p ’s < .01): Besides younger sailors experiencing
larger digital costs, previous navigation habits also
mattered:Both theyears
of usinganECSandactive
use of an ECS on the last sailing trip enhanced the
digitalcostsinthepresentexperiment.
Table1.Quality of cognitivemaps afterclassic anddigital
navigation,anddigitalcost(‐)orbenefit(+)withstatistical
intra‐person comparison (one‐sample‐t‐test) in the field
experiment.
_______________________________________________
Classic Digital Cost/Benefit
_______________________________________________
Component Meanscore(n=12) t(11) p
_______________________________________________
Total#73.4 55.4 ‐18.0 ‐4.88 .000*
Coastlines 77.8 58.7 ‐19.1 ‐2.98 .013*
Landmarks72.6 53.1 ‐19.5 ‐4.31 .001*
Shallows/ 68.8 45.5 ‐23.3 ‐2.74 .019*
Dangers
Navigationaids 77.8 51.7 ‐26.1 ‐3.67 .004*
Routes/Tracks 70.1 68.2 ‐1.9 ‐0.26 .803ns
_______________________________________________
#Averageofthecomponentscores,maximum100
*Statisticallysignificantatlevel=.05
nsStatisticallynotsignificantatlevel=.20
As predicted, the cognitive maps were
significantlyimpairedbydigitalnavigation.Personal
navigationhabitsseemtobethestrongestmoderators
ofthisimpairment,whichincreasedwiththeduration
ofdigitalmediause.
2.3.2 Situationawareness
Ateachfreezetestquery(twopertrack),therealdata
ofthesituationwithregard
totheninequestionswere
recorded at the moment the participants left the
situation.Dependentontheimpactoferrorsforsafe
navigation, the accuracy of each answer was scored
with 0‐3 points, summed up within each domain,
andrescaled toarange of0‐100 forcomparability.
Scores
werethenaveragedacrossthe twoqueries of
eachtrack.Thestatisticalanalysisofthedatafollowed
theproceduredescribedintheabovesection.
304
Table 2 shows the results: In contrast to the
cognitive map, digital navigation had no significant
impactonsituationawarenessinanyoftheassessed
domains.Thetotalmeanscorewasevenidenticalin
the classic and the digital condition although the
individual scores were different. The identity of
means
occurredbychance.(Onehastobearinmind
thatduetotherestrictedrangeoforiginalscores,0–3
peranswer, theprobabilityofidentical means isnot
assmallasitmightappearonfirstglance.)
Table2. Situation awareness regarding the four domains
position, wind, course, and route after classic and digital
navigation,anddigitalcost(‐)orbenefit(+)withstatistical
intra‐person comparison (one‐sample‐t‐test) in the field
experiment.
_______________________________________________
Classic Digital Cost/Benefit
_________________________________
DomainMeanscore(n=12) t(11) p
_______________________________________________
Total#73.6 73.6 0 0 1.00ns
1.Position 70.8 72.2 +1.4 0.22 .830ns
2.Wind70.1 80.6 +10.4 1.36 .202ns
3.Course/ 80.6 77.8 ‐2.8 ‐0.63 .540ns
Speed
4.Route72.6 68.4 ‐4.2 ‐0.86 .410ns
_______________________________________________
#Averageacrossallnineanswers,maximum100.
*Statisticallysignificantatlevelα=.05
nsStatisticallynotsignificantatlevelα=.20
Again,wethenappliedexploratorymultiplelinear
regressionanalysesinordertoexplorewhichperson
characteristics might moderate the effect of the
navigationmediumonthetotalsituationawareness,
even if it was non‐existent overall. The set of
predictorsandthestatisticalprocedureforbestsubset
selectionwereasin
thecognitivemapsection.Here,
the best linear model contained the two predictors
“years of using an ECS” and “active use of paper
chartsonthelastsailingtrip”,therebyexplainingR²=
0.58ofthevarianceofthedigitalcost/benefit(F(2,9)=
5.70,p=.025):Sailors
whoactivelyusedpapercharts
fornavigationontheirlasttrip,i.e.madeentriesinto
them, benefitted from the digital device for their
situational awareness, whereas sailors who did not
experienced costs (p = .012). Simultaneously, the
longer that the sailors had previously used digital
devices, the more they benefitted
from them in the
experiment (or the less cost they experienced; p =
.036). According to the comparison of the two
regression coefficients, waiving the active use of
paper charts is statistically compensated only by
about10yearsofECSuse.
In summary, the situation awareness in general
was not affected
by digital navigation. This
corresponded to the hypothesized opposite
influences: improved availability of situational data,
butreduced attention toand cognitiveprocessingof
them (see Introduction). Possibly the two cancelled
each other. Most interestingly, however, personal
navigation habits seem to make a difference: Sailors
whoactivelyusedpaperchartsbut
werealsofamiliar
with digital devices benefitted most from the
informationprovidedbytheECSinthisexperiment.
The two media, paper and ECS, might thus
complement each other in supporting situational
awareness. However, this result is regarded as
preliminary because it relied on an exploratory
statistical method. Itwillbe
checked and verified in
thesimulatorexperiment2.
3 SIMULATOREXPERIMENTS
Experiment1(Fig.2)largelyreplicatedthefieldstudy
inordertovalidatethesimulatorontheonehandand
theresultsfromthefieldstudyontheother.Inthree
points, however, the procedure was modified: First,
since
this was now safely possible, the wayfinding
was assessed in addition to the situation awareness
and the cognitive map. Secondly, from the four
domains of situation awareness only the route
awareness was assessed. Thirdly, the replication of
the field study comprised only the first segment of
eachrouteinthesimulator.
Onasecondsegment,in
order to examine the hypotheses for wayfinding, a
lossofthenavigationmediawassimulated,theboat
wasthenteleportedtoapositionfurtherontheroute,
andtheparticipantwasaskedtore‐orientandtopilot
the way from there on with wayfinding
as the
dependentvariable.
Experiment2(Fig.3)wasconductedwithalarger
sample of sailors and routes in order to investigate
not only the impact of the navigation media on
wayfinding,routeawareness,andthecognitivemap,
but furthermore, how these three variables relate to
each other, and what role
the previous navigation
habits play. Since we were interested in the
development of the three spatial abilities over the
courseofnavigation,thenavigationmediaweretaken
away even earlier in this experiment: They were
availableonlyforrouteplotting but not for piloting
theroute,which had tobe
accomplishedcompletely
frommemory.
3.1 Experiment1
3.1.1 Method
The sea simulator was programmed in our lab
with the open source driving simulator software
OpenDS(Mathetal.,2013).Itsimulatedsailingfrom
an egocentric perspective with a sailboat of 9.40 m
lengthand1.90mdraught(Fig. 5)on the
Isefjord, a
deeplybranchedarmoftheBalticSeaintotheDanish
island Zealand, about 18 nautical miles long and 8
nautical miles wide. The area to be navigated
contained several harbours and marinas, isles and
islets, a buoyed fairway, and some narrow
anchorages. Water depth is on average 5‐
7 m, but
shallow near the coast, in harbour entrances, and at
some single spots which are marked with cardinal
buoys. The water depths in the simulator
corresponded exactly to those indicated in the chart
withlinearinterpolationinbetween.Othernavigation
aidsincludedbuoys,harbourbuildingswithsailboat
masts, and
coastlines. The simulation contained
exactly the information provided in a navigational
paper chart (Delius Klasing boating charts set no. 5,
chartsno.20/21).Thesimulationwasdisplayedona
2D‐screen of 2 x 3 m, at the bottom of which some
navigationrelevantdataweredisplayedonsimulated
instruments
(e.g. the magnetic course on a compass,
COG,SOG,depth,latitude,longitude,andtime).The
305
participant was seated at a distance of 3.5 m to the
screen and operated the boat with a joystick.
Althoughtheboatcarriedsailsinordertovisualisea
sailboat, it was operated as a power boat because
sailing skills were not subject of the experiment.
Maximumspeedaheador
asternwas6knots.Incase
theboatgroundedorcollidedwithanobstacle(buoy,
harbour pier etc.), this was indicated by a red flash
and a deep sound. By altering the propulsion
directiontheboatcouldbefreed.
Figure5. Sea simulator: Egocentric perspective when
pilotingthesimulatedsailboatonthe“Isefjord”.
Thesampleconsistedof8sailors(1womanand7
men, age 26 – 76 years) with different levels of
experienceatsea(300–250,000nauticalmilessailed).
Allpossessedarecreationalmarinevessellicenseand
thereby sound navigation skills. As in the field
experiment,theydifferedwidelywithregard
totheir
habits of using navigation media: In paper chart
navigation, theyreported0‐45years of experience,
withfiveparticipantsusingthemactivelyatpresent,
i.e.makingentriesofcoursesand/orpositionsintothe
chart.Indigitalnavigation,theirexperiencewas0‐12
years,withfourparticipantsusingan
ECSactivelyat
present, i.e. entering waypoints and/or routes. None
of the participants had ever been to the sailing area
simulated in this experiment, and none had
participatedinthefieldexperiment.
Theprocedurewasasfollows(Fig.2):Inorderto
provide a more standardised replication and to
validatethe
simulator,theexperimentaldesignwasin
largepartsmatchedto thatofthe fieldstudy:Every
participant navigated two different routes (of 4‐6
nautical miles length each), one classically and one
digitally, in fixed order but with randomized
assignmentofmedia.Thetworouteswerelocatedin
differentparts
oftheIsefjordandplottedondifferent
paper chart sheets so that the performance on one
couldnotinterferewiththeother.
For classic route plotting, the participant was
givenapaperchart(thesameDeliusKlasingboating
chart that the sea simulator was based on), course
triangles, dividers, a calculator,
a pencil, and white
pieces of paper. In the digital condition, the
participant received a 7‐inch‐tablet computer
(Neptune Nep‐Tab 7 Outdoor) with the navigation
app Yacht Navigator (www.delius‐klasing.de/yacht‐
navigator), which allows a user‐friendly waypoint
routing. The electronic chart in this app was a
scanned image
(raster chart) of the same Delius
Klasingboatingchartthesimulatorwasbasedonand
whichintheclassicconditionwasprovidedinpaper.
Thereby,effectsofdifferencesinchartinformationor
layout were controlled. As in the field experiment,
plottingintheclassicconditionconsistedofdrawing
courses on the
paper chart, writing course and
distance next to each course line, and writing the
estimatedtimeofarrival(ETA)nexttoeachpointof
coursechange.Inthedigitalcondition,itconsistedof
buildingupandstoringaroutebysettingwaypoints
onthetabletcomputerwiththehelpof
theapp.
The participants were tested individually. They
startedwithplanning(plotting)thefirstrouteonthe
paperchartorthetabletcomputer.Then he/shehad
topilotthefirstsegmentofitonthesimulator(about
1 nm, containing a harbour exit and two course
changes) The navigation medium (paper
or tablet
with app) was available for piloting, with the GPS
position on the tablet being simulated. Along this
segment, three dependent measures were collected:
Theinitialwayfindingwasassessedandscoredwith
upto100points,dependingontheseverityoferrors
(course error with self‐correction, course error
without self‐correction, crossing shallow water,
grounding).Secondly,therouteawarenesswastested
twice on the segment (about 2 minutes after each
course change) with the freeze technique (Endsley,
1995b): The participant had to stop the boat, turn
awayfromthescreen,andanswersixquestionsabout
thecurrentsituation:bearing
anddistanceoftheport
ofdeparture,bearinganddistanceofthedestination
port,distancetothenextcoursechange,andwhereto
and how much the course was to change there
(resembling the questions in the domain “route” in
thefieldexperiment).Thesecondrouteawarenesstest
markedthe
endofsegment 1. Thirdly,thecognitive
mapofthenavigatedareawascollectedhere,witha
sketchmapdrawingonawhitepieceofA4paper.It
containedthesamecomponentsandwasscoredlike
inthefieldexperiment.Inordertoinvestigatespatial
re‐orientingand wayfinding incase
ofa media loss,
the boat was then teleported to a position in the
secondhalfoftheplannedroutewherealandmarkor
anavigationaidwasinsight,andtheparticipantwas
instructed:“Look,nowwearealreadyalittlefurther
on the route. Unfortunately, your tablet has
crashed/yourpapercharthasfallenoverboard.Please
try to sail from here towards your destination from
memory”.Thewayfindingonthissegment,assessed
as above, constituted the fourth dependent variable.
Afterabout1.5nm,thesegmentwasstopped,andthe
participant went to the navigation desk in order to
plotand
pilotthesecondrouteinthesamewayasthe
first but with the other navigation medium. After
completion of the two routes, confounding and
possibly moderating variables were gathered with a
questionnaire.
Atthebeginningtherewasapracticeruninwhich
the procedure was explained to the participants,
in
particularhowtousethetabletappandtooperatethe
“boat”. Also, they were familiarised with the tasks
andqueriesintheexperiment.
3.1.2 Predictions
Accordingtothehypothesesstatedaboveandthe
resultsofthefieldstudy,wepredictedthattheroute
awareness would not be globally affected
by one or
the other navigation medium, whereas the cognitive
306
map should be impaired after digital navigation.
Regarding the wayfinding, we expected a benefit
fromtheGPS‐supportedECSaslongasitisavailable
butacostwhenitislostandtheparticipanthastore‐
orienthimself,duetothereducedcognitivemap.
3.1.3 Dataanalyses,result,
anddiscussion
Table 3 shows the mean scores of the four
dependent variables after classic and digital
navigation, the mean cost or benefit from digital vs.
classic navigation, and the statistical results of the
intra‐person‐comparison.
Table3.Initialwayfinding,routeawareness,cognitivemap
with classic and digital navigation, later wayfinding after
medialoss,anddigitalcost(‐)orbenefit(+)withstatistical
intra‐person comparison (one‐sample‐t‐test of cost/benefit)
inthesimulatorexperiment1.
_______________________________________________
Classic Digital Cost/Benefit
_______________________________
Meanscore(n=8) t(7) p
_______________________________________________
Initialwayfinding 81 98 +17 2.65 .033*
Routeawareness# 67 65‐2‐.54 .606ns
Cognitivemap53 31‐22‐2.49 .040*
Laterwayfinding 83 73‐10‐0.60 .565ns
_______________________________________________
#Averageacrossthetwoqueriesonsegment1,maximum
100.
*Statisticallysignificantatlevelα=.05
nsStatisticallynotsignificantatlevelα=.20
On the first segment of each route (plotting and
piloting either classically or digitally, with two
situation queries underway and a cognitive map
sketch at the end), the simulator experiment closely
resembledthefieldexperiment.Theresultswerealike
aswell:Whereasthenavigationmediumdidnothave
a significant effect
on the route awareness, digital
navigationseverelyimpairedthecognitivemap.This
wasregardedasuccessfulreplicationandavalidation
ofthesimulator.
Exceeding the possibilities of the field, the
simulatoralsoallowedassessingthewayfindingwith
and without the navigation medium. As predicted,
theGPS‐supporteddigitalmediumsignificantly
bene
fittedthewayfinding,almosttoperfection,aslongas
itwasavailable.Afteritwaslostandtheparticipant
had to re‐orient, the advantage vanished. In the
sample, therewasanaverage cost of 10 points after
having navigated digitally, but contrary to the
prediction this was not statistically
significant. A
closer look into the sample revealed large
interindividualdifferences:Whereastwoparticipants
faced severe wayfinding problems after digital
navigation (running into shallow waters and even
grounding) but none after having navigated with
paper‐according to prediction‐, two others
benefittedfromECSusewhenrequiredtofind their
way from memory. The other four were perfect or
nearly perfect in both conditions. On the one hand,
theroute mighthavebeentooeasy andtooshortto
simulate a realistic situation (ceiling effect); on the
other,thedifferencesmight be explainedbyperson‐
specific characteristics, in particular previous
navigation
habits, which should affect perceptual
processing at sea. The latter is the subject of the
followingexperiment.
3.2 Experiment2
3.2.1 Method
Theexperimentwasconductedwiththesamesea
simulatorasinexperiment1.Thesampleconsistedof
20sailors(2 women and18men, age 26 – 75
years)
with different levels of experience at sea (100 –
100,000 nautical miles sailed). All possessed a
recreationalmarinevessellicenseandtherebysound
navigation skills. As in the previous studies, they
differed widely with regard to their habits of using
navigation media. In paper chart navigation, they
reported 0‐45
years of experience, with 13
participants currently using them actively. In digital
navigation,theirexperiencewas0‐16years,with12
participantscurrentlyusinganECSactively.Noneof
the participants had ever been to the sailing area
simulated in this experiment, and none had
participatedinanyofthe
otherexperiments.
The participants were randomized into two
experimental conditions, classic and digital route
planning, and tested individually. The overview of
theprocedureisdepictedinFigure3,placedfurther
upinthepaperinordertofacilitatecomparisonwith
the other experiments. Three different routes of 4‐6
nautical miles
length each had to be plotted on the
chart and piloted on the simulator. For piloting,
however,the(paperorelectronic)navigationmedium
wastakenaway.Sinceinthisexperimentwewanted
toinvestigatetheeffectsofusingpapervsanECSfor
plottingandforthesubsequentdevelopmentof
route
awarenessandcognitivemap,theparticipanthadto
pilottheroutesfrommemoryfromthebeginning.On
eachroute,threedependentvariableswerecollected.
First,theinitialwayfindingwasassessedandscored
with up to 100 points as in experiment 1. Secondly,
afterabout1.5nmandatleastone
coursechange,the
route knowledge was examined with the same
techniqueandquestionsasinexperiment1.Thirdly,
the boat was teleported to a position in the second
half of the planned route where a landmark or a
navigation aid was in sight, the participant was
instructed “look, now we
are already a little further
on the route; please sail from here towards your
destination port”, and wayfinding on this segment
was scored as initially for about 1.5 nm. The fourth
dependent variable was the cognitive map of the
entirenavigatedarea,assessedafterfinishingallthree
routes. The three routes
were located in different
partsoftheIsefjordanddidnotoverlap.Finally,the
samequestionnairewasappliedasabove.Therewas
alsoapracticerunatthebeginning.
3.2.2 Predictions
When using digital navigation media only for
plotting but not for piloting, we hypothesized that
onlytheirimpairinginfluence
onrouteawarenessbe
effective(reducedcognitiveprocessingofinformation
during planning) but not the benefitting one
(availability of situational data underway, see
introduction). Moreover, we hypothesized in the
introduction that previous navigation habits might
lastingly have altered information processing at sea.
We thus predicted the following effects of the route
plottingmediumandthepreviousnavigationhabits:
First, the route awareness, i.e. the route related
situationawareness,shouldbeimpairedafterdigital
307
plotting compared to classic. Here, previous media
useshouldbeofnoinfluence.Secondly,thecognitive
map should be affected vice versa: No effect of the
plottingmedium(thecognitive mapishypothesized
tobuildupduringpilotingwherethetwogroupsdid
not differ in navigation media), but an
increased
impairment with increasing duration of digital
navigationinthepast(alteredinformationprocessing
underway). Thirdly, the wayfinding should be
impairedasfarasitreliesonrouteawarenessand/or
cognitive map. We expected positive associations
betweenroute awareness,wayfinding,and cognitive
map. If these weaken with the duration of
digital
navigation inthepast,thiswillbeinterpretedasan
indicator of lastingly altered information processing
atsea.
3.2.3 Dataanalysesandresults
Table 4 shows how classic and digital route
plotting affected the initial wayfinding, the route
awareness, the later wayfinding, and the final
cognitivemapwhenpilotingfrom
memory.
Table4. Initial wayfinding, situation awareness, later
wayfinding, and cognitive map after classic and digital
route plotting, and digital cost (‐) or benefit (+) with
statisticalinter‐groupcomparison(two‐sample‐t‐test)inthe
simulatorexperiment2.
_______________________________________________
Classic Digital Cost/Benefit##
_______________________________
Meanscore(n=10##) t(18) p
_______________________________________________
Initialwayfinding#82 83 +1 0.66 .948ns
Routeawareness# 77 65‐12‐2.81 .012*
Laterwayfinding# 89 66‐23‐2.46 .024*
Cognitivemap58 63 +5 .44 .666ns
_______________________________________________
#Averageacrossthethreeroutes,maximum100
##Meanscores:n=10pergroup,cost/benefitbetween
groups
*Statisticallysignificantatlevel=.05
nsStatisticallynotsignificantatlevel=.20
Thetwogroupsdidnotstatisticallydifferinageor
experience,i.e. nauticalmilessailed.Again, thetime
forrouteplottingcouldnotexplaintheresults.
Afterhavingassessediftherouteplottingmedium
affectedtherouteawareness,thewayfinding,andthe
cognitive map, we analysed how they did that, and
what role previous navigation habits played.
Therefore, we regarded each pair of variables that
immediately succeeded each other in the
experimental procedure (see Figure 2) as predictor
and criterion in a regression model in which we
included the previous navigation habits as
moderating variables. In detail, we fitted the model
equation (1) of moderated linear regression to the
data,andtestedthecoefficientsforsignificance.
iiiiii ii
EY x m xm m m x
(1)
where E(Y
i) denotes the expectation (theoretical
mean)oftherandomvariableYinpersoni(i=1,...,
20),modellingthecriterionvariable, x
i the predictor
variablexinpersoni,m
ithemoderatorvariablemin
personi,and
,,,theregressioncoefficients.
Based on the exploratory results of the field
experiment, we examined the following navigation
habitsasmoderators:
1 yearsofusinganECS,
2 yearsofnotusingpaperchartsanymore,
3 active use of an ECS on the last sailing trip, i.e.
withmakingentries,
4
activeuse ofpaperchartsonthe lastsailingtrip,
i.e.withmakingentries.
From the twelve moderated regression analyses
(threepairsofpredictorandcriterion variables with
four moderators each), only those with a significant
globalF‐testareshowninTable5.
Table5. Moderated regressions: Coefficient estimates
accordingtoEquation(1)andsignificanceoft‐tests(df=16).
Thehorizontalsectionsofthetablerefertothethreepairsof
predictorandcriterionvariables,denotedwiththesymbol
=>
_______________________________________________
Moderator
ˆ
ˆ
ˆ
ˆ
_______________________________________________
Plottingmedium##=>situationawareness(route
knowledge)#
_______________________________________________
m1.YearsECS82*‐7.2 ‐0.9* ‐0.4ns
_______________________________________________
Situationawareness(routeknowledge)#=>later
wayfinding#
_______________________________________________
m1.YearsECS‐170* 3.2* 15* ‐0.2*
m2.Yearsnopaper‐65 2.0* 52*‐0.8*
m3.ActiveECSuse(0‐1) ‐802.1* 94 0.2
m4.Activepaperuse(0‐1) 42 0.5ns‐108* 1.5*
_______________________________________________
Laterwayfinding#=>cognitivemap#
_______________________________________________
m1.YearsECS4.0ns 0.8* 7.4* ‐0.1*
_______________________________________________
##Binary:0=classic,1=digital.#Metric:score0‐100
*Statisticallysignificantatlevelα=.05
nsStatisticallynotsignificantatlevelα=.20
3.2.4 Discussion
Tobeginwith,digitalrouteplottinghadnoeffect
ontheinitialwayfinding(Table4,firstrow).Because
ofthezero effect and the absenceofanysubstantial
correlations with the other dependent variables, we
didnotanalysethisoutcomeanyfurther.
Forinterpretingtheresultsoftheother
dependent
variables and the moderated regressions, one might
want to envision that
m is the intercept of the
moderated regression equation (1), i.e. the predicted
criterion value for predictor value 0. Herein,
denotesthecriterionvalueformoderatorvalue0,and
itsincrease/decreasewhen themoderator increases
by 1 unit (main effect of the moderator onto the
criterion). Likewise,
m is the slope of the
moderatedregressionequation(1).Herein,
denotes
the effect of the predictor on the criterion for
moderator value 0 (main effect of the moderator on
the criterion).
denotes how much this effect
increases when the moderator increases by 1 unit
(interactionofpredictorandmoderator).
Withthisnotioninmindwewillinterpretthemost
interesting findings. First, according to Table 4, the
digital route plotting reduced the route awareness
underway on average by 12 points (or
16 %).
AccordingtothemoderatedregressioninTable5top
row, the only alternative predictor for this criterion
was the duration of previous ECS use, reducing the
regressionintercept,i.e.thelevelofrouteawareness,
byabout1pointperyear.Theconclusionisthesame
for both predictors: The
digital plotting medium in
theexperimentaswellaspreviousdigitalnavigation
impairsorientingatsea.
308
Figure6.FourexamplesofhowtherelationshipofeverytwosuccessivelycollectedvariablesinExperiment2(theformerin
theroleofapredictor,shownonthex‐axis,thelaterintheroleofacriterion,shownonthey‐axis),isinfluencedbyprevious
navigation habits (as moderators,
indicated by the numbers at the data points and the fitted regression lines). The four
diagramsillustratetheresultsofthemoderatedregressionsintherows2,3,5,and6ofTable5.
Movingonintheexperimentalprocedure,Table4
shows secondly that the wayfinding after being
teleported to a later position on the route was even
more strongly negatively impacted by digital route
plotting than the route awareness, namely by 23
points (26 %). In addition, there was a positive
associationbetween
therouteawarenessandthelater
wayfinding(r=0.59),implyingthatthemoreaccurate
a sailor oriented himself on his route, the better he
foundhiswaylaterfromanewlocation.Accordingto
the moderated regressions in Table 5, the previous
navigationhabitsinfluencedthisinterplayinseveral
ways: The intercept m is not interesting in this
context, because a route awareness (predictor) value
of0neveroccurs.Focusingthuson
andinthefour
significantregressionmodels(rows2‐5inTable5),
we found the following: Without any previous ECS
use, every additional point of route knowledge
increases the wayfinding later on the route by 3.2
points.However,thispositiverelationisreduced by
0.2 points per year of ECS
use, consequently
(statistically)reducedtozero after16years (Table5,
row 2). This is illustrated in the upper left panel of
Figure 6. The effect of the other moderators of this
relationshipareinterpretedaccordinglyanddepicted
intheupperrightandlowerleftpanels.
The cognitive map was experimentally
assessed
afterallthree routes were plotted and navigated. In
contrast to the other two experiments, in which the
cognitivemapsufferedfromdigitalnavigation(Table
1, Table 3), there was no significant impact of the
navigation media here (Table 4). The difference is
obviouslyduetothefactthat
thechartmediumwas
employedonlyforplottingbutnotforpilotinginthe
present experiment, and suggests that the cognitive
map indeed evolves underway. In support of this
notion, we found a correlation between the later
wayfindingandthequalityofthecognitivemaps(r=
0.41)inthepresent
experiment.Wethusanalysedthe
role of previous navigation habits in this interplay,
too(Table5,row6;lowerrightpanelofFigure6).We
found that without any previous ECS use, every
additionalpointinwayfindingincreasesthecognitive
mapby0.8points.Thispositiverelationisreducedby
309
0.1 points per year of ECS use, and consequently
(statistically)vanishedafter8years.
Taken together, all these results agreed with the
prediction that long‐lasting ECS use and
abandonmentofpaperchartnavigationweakensthe
association between the three spatial abilities
investigated here (route awareness/orienting,
wayfinding, and cognitive map).
This supports our
ideathatsolelydigitalnavigationhasalastingeffect
onperceptionandinformationprocessingatsea.
4 GENERALDISCUSSION
The results of the field experiment and the two
simulatorexperimentscanbesummarizedasfollows.
As expected, an electronic charting system (ECS)
supports wayfinding. Wayfinding accuracy was
nearlyperfectinoursimulatorexperiment1inwhich
arouteinacoastalareawasplottedonatabletwitha
navigation app and piloted right after. With paper
chartandmagneticcompass,incomparison,thesame
sailors made some minor course errors or crossed
shallow waters. This is undoubtedly
a safety
advantageofGNSS‐supporteddigitalnavigation.
However,thisadvantagecomesatalargecost.In
allexperiments,we assessedthesituationawareness
underway(onlyrouteawarenessinthesimulatorbut
also other domains like position, wind, and
course/speed in real sailing). When the route was
plotted on a
navigational chart but piloted without,
after classic route plotting the route awareness was
better than after digital. When the media were
available underway, the situation awareness of the
classically navigating sailors was still just as good
although the ECS readily provided the data
questionedinthetest.ThenotionofAsyali
(212)who
proposed a better situational awareness in digital
navigation on the basis of questionnaires, was thus
not confirmed by our experiments. When taking
previousnavigationhabitsintoaccount,weevenhave
toagreewithGrech&Horberry(2002)whoproposed
thattechnologicalprogressisassociatedwithalossof
situational awareness. In the field experiment, i.e.
underrealisticconditions,asailorbenefittedfromthe
ECS only if he regularly and actively used paper
chartsfornavigationinhisownpractice.Ontheother
handthelongerasailorhadnavigateddigitallyinthe
past, the worse was his situation/route awareness
with the ECS in the experiment. We ascribe this
interaction to a defective cognitive map (see below)
andtopermanentlyalteredinformationprocessingat
sea.Notonlydoesthesailorpaytoolittleattentionto
thedataprovidedbytheECSbuthealsomightlose
the deeper understanding that
is necessary to
comprehendandcorrectlyinterpretthem.
Orienting (route awareness) and wayfinding rely
on spatial knowledge, the so‐called cognitive map
(Nadel, 2013). In both experiments in which the
sailors used the navigation media for piloting, the
cognitive maps were much poorer after digital
compared to classic navigation. This finding
is
complemented by the correlation and regression
analyses of the data of simulator experiment 2 in
which the positive statistical associations between
route knowledge and wayfinding, and between
wayfinding and the cognitive map, were weakened
bythedurationofpreviousdigitalnavigation,bynot
actively working with paper charts, or
by waiving
them completely. Taken together, these findings
suggest the following mechanism: In classic times,
after having plotted the courses on the paper chart,
duringpilotingthesailboatnavigatorconstantlyhad
to match chart data with nature in order to find his
way. By this he/she acquired the spatial knowledge,
i.e.
the cognitive map. With GNSS‐supported digital
navigation, this view into nature is not necessary
anymore. Moreover, the electronic chart frequently
variesitslook(varyingmapdetailbyzoominginand
outthevectorchart,varyingvisiblesectionofthemap
bydraggingitonthesmalldisplay).Bothwill
result
inspatialknowledgenotbeingproperlyacquiredand
stored, thus a defective cognitive map and spatial
orienting. As a result, the advantage of a more
accurate wayfinding with the ECS turns to a
disadvantage when the medium fails. This was
empiricallytestedinthetwosimulatorexperimentsin
whichthe
sailorswere“teleported”toaspotlateron
their route where they had to re‐orient themselves
andfindtheirwayonwardswithouttheir(digitalor
paper) chart. Piloting from memory was more
accurateafterclassicthanafterdigitalnavigation. In
practice,thisfindingisevenmorerelevantbecausea
medialossismuchmorelikelywithadigitaldevice
than with paper: Not only is electricity limited and
vulnerable on the small and often old sailboats but
alsothesoftwareofpleasurecraftECSsissusceptible
tobreakdownslikeanycomputersoftwarenowadays.
Especiallyincoastalareaswiththeirtypical
hazards,
adisorientedskipperisasafetyissuenotonlyonhis
ownboatbutalsoforcommercialshipping.
Concerning generalisation of the experimental
finding to realistic conditions, we assume that most
effects might even be larger in practice, where
proceduresandtestsarenotknowninadvance,and
where
the navigational challenges are more difficult
(longerandmorecomplicatedroutes,multipletasks,
harshweather,etc).
Wewillconcludewithsomeideasontechnicaland
legal implications. As argued above, we cannot
recommend doing without paper charts on pleasure
crafts.AnECS should beusedas a complementbut
not as
a supplement. However, since it is time‐
consumingtoprepareroutesontwomediainparallel
beforetheboatcancastoff,onemightwanttothink
abouttechnicalsolutionsthatcombinetheadvantages
of both: Active interactionwith a large and visually
stablechartforrouteplottingandpiloting
ontheone
hand, andGNSSsupportwith possible add‐ons like
AIS, radar overlays, weather data, etc. on the other.
Moreover,today’ssailboatcrewsareoftensmall,and
no one wants to sit for hours below deck for
navigation anymore if mobile solutions for outdoor
useareavailable.Oneidea
istoplotcoursesonpaper
(e.g. when the boat is moored in harbour) with a
digitallytrackablepencilthatcanafterwardstransfer
thedatatotheECSforunderwayoutsideusethrough
abluetoothorWiFiconnection.Also,inordernotto
permanentlylosetheabilitytoorientat
sea,an“out‐
of‐the‐looptraining”,inwhichpleasurecraftskippers
areforcedtonavigateold‐school,shouldbeexercised
310
regularly, andprobablyevenbecomea standard for
maintainingthelicense.
Acknowledgements. The author would like to
thank Richard Gross for programming the sea
simulator, 18studentsoftheM.Sc.programHuman
FactorsatTUBerlinforhelpingwithdatacollection,
and40sailorsforparticipatingastestpersons.
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