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1 INTRODUCTION
During 6th session of International Maritime
Organization (IMO) Navigation, Communication,
Search & Rescue Sub‐Committee (NCSR) the “Draft
Guidelines for the Standardization of User Interface
Design for Navigation Equipment”, commonly
known as S‐Mode guidelines [IMO, 2019], were
approved, and transferred further to IMO Maritime
Safety Committee (MSC)
for final adoption.
Nowadays and in the past significant variation
betweennavigationsystemsandequipmentproduced
bydifferentmanufacturershasledtoinconsistencyin
the way essential information is presented,
understood and used to perform key navigation
safety functions [Bhuiyan, 2012; NI, 2017].
Recognisingthisfacttheobjectivesetfor
thenovelS‐
Mode guidelines is to promote standardization of
user interfaces to help meet user needs, and
specifically to locate and understand important
information quickly and enhance all levels of
situation awareness, such as perception,
comprehension and projection of situation that will
assistintheseafarerʹsdecision‐makingprocess.
While
this objective is undisputable, the question if the
guidancewithintheseguidelinesleadsto navigation
safety improvement remains valid because several
potential issues concerning its interpretation can be
identified.
In the following sections the possible negative
implicationsofcarelessguidelines’implementationin
newly designed interfaces of radars, electronic chart
display systems (ECDIS), integrated navigation
systems(INS)andothernavigationrelatedequipment
havebeendiscussed.
2 GUIDANCEWITHINTHEGUIDELINES
The key reason behind the S‐Mode guidelines
development has been
expectation that improved
standardizationoftheuserinterfaceandinformation
used by seafarers to monitor, manage and perform
navigational tasks should enhance situation
awareness and improve safety of navigation. It is
stressedintheguidelinesthatalthoughtheoperation
A Critical Analysis of IMO S-Mode Guidelines
P.Zalewski
M
aritimeUniversityofSzczecin,Szczecin,Poland
ABSTRACT: Circular on “Guidelines for the Standardization of User Interface Design for Navigation
Equipment”,commonlyknownas“S‐ModeGuidelines”,haslatelybeenapprovedbyInternationalMaritime
Organisation.Its potentialimpactondefaultandcommonusersettingsof radarequipment,electronic chart
display & information
system, and integrated navigation system has been discussed in the article. Several
issues that should be considered during technical implementation of the circular provisions and follow‐up
familiarizationofnavigatorswiththeaffectedequipmenthavebeenidentified.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 13
Number 4
December 2019
DOI:10.12716/1001.13.04.17
842
of navigation equipment requires specialist training
and familiarization, variations across different
manufacturers’ equipment for mandatory functions
should be minimal. Where there is significant
variation in buttons, icons, actions, workflows,
processes,unitsofmeasureorlocationofinformation,
thereisacommensurateincreaseinthetimerequired
for equipment familiarization and
the risk of
operational error, particularly in challenging
navigational situations. Users need to accumulate
knowledge, skills and experience of using essential
functions, which can be transferred between the
systems and equipment of different manufacturers.
Toreducefamiliarizationtimeand riskoferroneous
action,essentialfunctionsandinformationneedtobe
located in consistent locations, be of a similar size,
recognizable by location, colourand shape. Units of
measurementshould also be consistent. That is why
the standardization design principles and findings
stemmingfromresearchintohumanfactors,cognitive
science, and human‐centred design (HCD) [Mosier,
2010]havebeenappliedtothe
technicalcontentofthe
S‐Modeguidelinescomprising:
1 defaultandusersettings;
2 terminology, abbreviations and icons for
commonly‐used functions (hot keys) and groups
offunctions(shortcuts,single,andsimpleoperator
actions);
3 logicalgroupingofrelatedinformation;and
4 access requirements for essentialinformationand
functions.
Consistency
has been identified as the first most
significant standardization design principle that
increases usability. Using location and grouping for
consistency provides for recognition as the second
design principle. The third is frequency of use –
sorting, grouping and locating of information
according to frequency of use increases efficiency.
This principle requires
that navigators can access
those tasks that they frequently use. It includes the
application of hot keys, and single operator actions.
Thefourthprincipleisvisibilityofsystemstatusand
integrity that includes visibility of “processing”
information and the correct functioning of system
sensorstoillustratedegradedinformation.Projection
to
realworldisthefifthwithtwoelements:1)using
imagingorwordingthatiscontextuallyrelatedtothe
task, 2) geolocation of information providing a
linkage, or correlation, between the user, electronic
equipmentandtherealworldrelativetotheship.The
sixth is resistance to erroneous operations including
keeping
navigationcriticalinformationontopofany
interlaid information. And the last but not least,
identifiedasseventhstandardisationdesignprinciple,
is navigator’s assistance by user friendly help
functions.
Alloftheseassumptionsshouldguaranteeavery
solid foundation for future navigation equipment
designstandardsleadingtoeasieroperationand
less
operator’sworkload. Nevertheless, a criticalanalysis
of current content of S‐Mode guidelines’ appendices
revealssomepotentialissuesthatcouldactuallylead
toinconsistencywithotherIMOinstrumentsandwell
establishedgoodpracticesofseafarers’educationand
navigationequipmentoperation.
3 POTENTIALISSUES
Appendices2 to5 ofthe S
‐Modeguidelines provide
informationon2)navigation‐relatedterminologyand
iconsoffunctionsincludinghotkeysandshortcuts,3)
logical grouping of information, 4) list of functions
that must be accessible by single orsimple operator
action,5)defaultandusersettings.
Potentialissuesidentifiedintheseappendicesare:
1
Largenumberofnewiconsandabbreviations.
2 Problemswiththeinterpretationofseveraldefault
settingsrelatedto:
rangeandscaleofdatapresentation,
stabilisationofdatapresentation,
lookaheadfunction.
Thelarge number of newly introducedicons and
abbreviations in the S‐Mode guidelines’ appendix 2
seems to be inconsistent with the aim of the
guidelines to locate and understand important
information quickly. The numbers of recommended
icons for hot keys are: 40 for general navigation
functions,
42forcontrolofchartdisplayfunctions,4
forcontrolofchartfunctionality,2forrouteplanand
monitoring functions. The number of icons for
shortcutstogroupsoffunctionsis10.Thesenumbers
are doubled by the abbreviations corresponding to
icons with few cases where icons are exactly
equivalent to
abbreviations. There are 7 standalone
abbreviations for database functions, and 1 for look
ahead function (icons are not applicable). Together,
there are 204 icons and abbreviations introduced.
Takingintoconsiderationhotkeysonly,theirnumber
of 82 is close to 101 of traditional PC “qwerty”
keyboard and it will surely
imply at least several
hours of familiarization training. As there are only
vague suggestions to the order of hot keys
presentation like: logical grouping, containing
shortcutbuttonsunderonesettingmenuratherthan
adding many icons to the desktop, and keeping the
display area clear of clutter, one can assume that
variations of hot keys positions across different
manufacturers’ keyboards or softwaremenus would
notbeminimal.Oneshouldnotbesurprisedaswellif
the group of general navigation hot keys are fixed
withsignificantvariationbetweennavigationsystems
andequipmentproducedbydifferentmanufacturers
(seeFigure1showingtypical
INS/ECDISkeyboard).
So,onlyafterpracticingandsomeexperiencegained,
the user will locate the correct key quickly and
independentlyofthesystemused.
The second identified issue of S‐Mode guidelines
areproblemswiththeinterpretationofseveraldefault
settings defined in appendix 5. A set of default
settings has been defined in order to return the
equipmentto aknowndefault state afterequipment
failure or user command. Those settings are also
intended to provide a basic and minimal mode of
operationfortheequipmentthatcanbefurtherbuilt
uponbytheuser.
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Figure1.Keyboardsoftypical contemporaryINS
The first problematic default setting is default
range and scale of data presentation. ECDIS setting of
“Range / Scale” configured in response to “Default”
selection has been fixed by the guidelines to 3Nm.
Corresponding radar equipment setting of “Range”
configuredinresponseto“Default”selectionhasbeen
fixedto6Nm.
Thosesettingshavebeenadoptedfrom
Appendix 6 of IMO Performance Standards for INS
[IMO, 2007] for “route monitoring task” and
“collisionavoidancetask”.Astheadoptedvaluesare
reasonable with appropriate display offset: at 3Nm
the chart details significant for route monitoring
shouldbeclearlypresentedandat6Nmwith
applied
offset the time for anti‐collision action should be
sufficient (though it can be disputed for high speed
craftsorgenerallyvesselssailingover20ktwherethe
reactiontimecanshrinktolessthan10minincaseof
reciprocalcourses),stilltheconfusionmayarisetothe
range setting
of ECDIS display. Some contemporary
ECDIS systems recalculate user selectable scale to
range and vice versa (Figure 2). Others use scale
settingonly.
Figure2. Example of ECDIS scale panel with range
recalculated
IMOResolutionMSC.232(82)[IMO,2006]specifies
the effective size of the chart presentation for route
monitoringin ECDISasatleast 270mm×270mmand
250mm×250mm or 250mm diameter for back‐up
system. Specifications for the ECDIS display screen
arefurthersetbyIHOinrequirementsofS‐52[IHO,
2015]settingresolution
as:minimumlinespermm(L)
givenbyL=864/s,wheresisthesmallerdimensionof
the chart display area. (e.g. for the minimum chart
area, s=270mm and the resolution L =3.20 lines per
mm,giving a“pictureunit”orpixelsizeof0.312mm).
TheIMOECDISperformance
standardsrequirements
together with the display resolution requirements
[IMO,2006;IHO,2015]usuallyresultintheuseof19”
or larger flat panels for ECDIS installations [Jonas,
2003], though smaller screens are also acceptable.
Range to scale recalculation can be formulated in
generalas:
1852000
d
s
R
S
l
(1)
where:
S
d – scaledenominator,
R – themariner’sselectedviewingrangeinNm,
l
s– length of the shorter side (usually vertical) of
chartdisplayareainmm:
22
25.4
d
s
nd
dr
l
rr
(2)
where:
d– lengthofchartdisplaydiagonalininches,
r
d – denominatorofchartdisplayratio(wherethe
ratioisdefinedasproportionofhorizontaltovertical
chartdisplaylength),
r
n – numeratorofchartdisplayratio.
BecauseselectingadisplayscaleinECDISusually
meanschoosingfromalistofscalesfixedsomewhat
arbitrary by the producer (for example 1:500,000,
1:250,000, 1: 100,000, 1:75,000, 1:50,000, 1:25,000,
1:10,000, 1:5,000) thus, it can be expected that the
recalculated range will not fit
the 3Nm as default
setting.InTable1,inblack,theresultantchartscales
for typical off‐the‐shelf ECDIS monitors are shown
according to (1). In red, the scale for a hypothetical
display meeting minimum IMO standard of chart
presentation(270mm×270mm)isshown.
Table1.Chartscalescorrespondingtorangeof3Nm
_______________________________________________
Chartdisplay Chartdisplay Sizeof Chartscale
ratior
n:rd diagonald displayls 1:Sd
_______________________________________________
5:417.1”271mm 1:20,477
5:419”302mm 1:18,429
5:421”333mm 1:16,674
5:423”365mm 1:15,224
4:318.0”274mm 1:20,254
4:319”290mm 1:19,188
4:321”320mm 1:17,360
4:323”350mm 1:15,851
16:1020.1”270mm 1:20,533
16:1024”323mm 1:17,197
16:1032”431mm 1:12,897
16:1040”539mm 1:10,318
16:922.0”274mm
1:20,280
16:924”299mm 1:18,590
16:932”399mm 1:13,943
16:940”498mm 1:11,154
_______________________________________________
Basing on Table 1 it is evident that mariner will
eithergetdifferentchartscalesforthesamerangeon
differentECDISscreensormorecommonlythescale
of1:25,000astheclosestsmallertotheoneequivalent
to3Nmrange.ItisassumedthatECDISma nufacturer
designs system properly to
find the smaller scale to
the one recalculated and to load the dataset of the
better larger scale chart if present. In few cases of
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screens larger than 40” it will be also possible to
displaychartsinscalesof1:10,000orhigher.Intime
the problem of data coverage definition for 3Nm
range will probably lessen as the new IHO ENC
ProductSpecificationS‐101isintroduced[IHO,2018].
S‐101statesclearly:“When
thesystemsviewingscale
is smaller than the value indicated by minimum
display scale, features within the Data Coverage
feature are not displayed, except where the SENC
does not contain a dataset covering the area at a
smaller scale, in which case the dataset will be
displayed at all smaller
scales. When the viewing
scaleislargerthanthevalueindicatedbymaximum
displayscale,theoverscaleindication,intheformof
anoverscalefactorandpatterncoveringtheareathat
is overscale, must be shown. When own ship’s
position is covered by a dataset with a larger
maximum display scale
than the mariner’s selected
viewing scale (MSVS) an indication is required and
should be shown on the same screen as the chart
display”.Anyway,theissuewithrange/scalesetting
willexistaslongasthevaguenessofrelateddefault
settings: “Selected sea area: Around own ship with
appropriate
off‐set”inECDIS,and“OffCentre,with
appropriate look ahead” is not interpreted
unambiguously.Onecanevenspeculatethatthereare
some fuzzy terms, like “appropriate” in S‐Mode
guidelinesinsteadofstandardizedcrispones.
The second somewhat problematic issue with
default settings is stabilisation of data presentation. In
theS‐Modeguidelinesthedatapresentationhasbeen
adopted as “ground” stabilised in ECDIS and “sea”
stabilisedinradar.Whilethisiscorrectongroundsof
Colregs(anti‐collisionregulationsatseaarebasedon
headingandspeedthroughwater,soseastabilisation
isappropriateforradarwhilegroundstabilisation
for
route monitoring on chart) it will probably lead to
some confusion of users of contemporary INS
systems.InmajorityofthemthesamegroundGNSS
stabilisation is set in radar as in ECDIS by default
which enables smooth transition of radar video and
ARPA targets to chart display. New
default settings
willrequireextracautionwhileinterpretingAISand
ARPAvectorsinECDISandtheirpotentialfusion(see
Figure3).
Figure3. Ground stabilized AIS vector and sea stabilized
ARPAvectorinECDIS
ThethirdissuewiththeS‐Modedefaultsettingsis
look‐ahead setting. Look‐ahead related ECDIS setting
configuredinresponseto“Default”selectionhasbeen
adopted as “Look‐ahead time 6 min”. Look ahead
related radar setting configured in response to
“Default” selection is quite different: “Off Centre,
with
appropriate look ‐ahead”. Is it clear that radar
setting concerns display offset while ECDIS setting
concerns future prediction of ship’s position? The
same“lookahead”terminologycanbemisleadingif
it defines offset distance in one equipment and
prediction time in another. On the other hand, in
contemporary ECDIS systems look
‐ahead
terminologyisnotpresentexceptsomedefinitionsin
user manuals. Instead other equivalent terms and
functionsareused.Sothestandardlook‐aheadtermis
verywelcomed.
Figure4.GroundingalarmsetupinexampleECDIS
Figure5.CheckareasetupinexampleECDIS
InFigure4exampleof“GroundingAlarmSetup”
dialog equivalent to “Look‐ahead Setup” is shown.
TheVectorlengthandWidthforthegroundingalarmis
specified in this dialog. So, the dialog contents are:
look‐ahead time specifying how far ahead (in
seconds)groundingcheckingistobeperformed,and
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width specifying in degrees the widest part of the
groundingcheckarea,usuallyupto30º.
InFigure5exampleof“CheckAreaSetup”dialog
equivalentto“Look‐aheadSetup”isshown.
Calculation of own ship predicted movement area is
doneusingacheckareainfrontofownship
position.
Theaheadtimeor distance and aheadwidthcanbe
set (marked in blue in Figure 5). Additionally,the
“Around”: port, starboard, bow and stern check
distance can be set (marked in red). The reference
pointistheconningposition.
Figure6.SafetyframesetupinexampleECDIS
In Figure 6 example of “Safety Frame Setup”
dialog equivalent to “Look‐ahead Setup” is shown.
TheSafetyframegroupisintendedforsettingthesize
of the frame, which will be used for the chart data
analysisandforthegenerationoftheanti‐grounding
alarms,areaalertsandnavigational
alarms.Aheadis
thewindowfortheinputofadvancetimeforalarmor
warning generation. The time value determines the
length equal to the distance covered by the ship
proceedingatthecurrentSOG.Portisthewindowto
set the width of the corridor to the left of
the ship.
Starboard is the window to set the width of the
corridortotherightoftheship.
One more important conclusion is evident after
analysing Figure 4, Figure 5, and Figure 6. The S ‐
Modeguidelinesspecifyonlyoneparameteroflook‐
ahead function: time. However, look‐ahead function
implemented in ECDIS is multi‐parameter. The user
hastosetnotonlypredictiontimebutalsowidthor
port and starboard distance. Additionally in some
systems a smaller “Around” area can be set and
ahead distance can replace prediction time. IMO
Guidelines for the presentation of navigational‐
related symbols,
terms and abbreviations [IMO,
2019b]presentlook‐aheadfunctionas2Dareaaswell
(Figure7).
Figure7.Lookaheadalarmhighlight[IMO,2019b]
That means that at least the width parameter
whichinsomesystemsisdefinedasarcandinothers
as length has not been standardized. So, significant
variationbetweennavigationsystemsandequipment
producedbydifferentmanufacturerscanbeexpected
afteractivationoflook‐aheadtimedefaultsetting.
Similar issue is
valid for look‐ahead offset. This
functionisexpectedtocausethesystemtomovethe
own‐ship symbol on the screen to the position that
givesthemaximumpossiblelook‐ahead.Forexample,
ifthevesselissailingfromwesttoeast,resettingthe
centre should position the own
‐ship symbol close to
the left edge of the display and cause the vesselʹs
course vector to point through the centre of the
display.Anyway,theoffsetdistancefordefaultrange
hasnotbeenstatedspecifically.
4 CONCLUSIONS
There is a number of IMO instruments and other
internationalstandards
thatdeal withsystemdesign
and information portrayal [IMO, 2006, 2007; IHO
2015]. The S ‐Mode guidelines have been developed
notonlyonbaseofHCDbutalsoonsuchstandards.
Suchapproachisgenerallyassumedtobringpositive
effects, but in cases of uncritical adoption of source
standardsitcan
alsobringnegativeones.IncaseofS‐
Mode guidelines the discrepancy of several INS,
ECDISandradarequipmentdescendant functions is
anexampleofsuchprocess.
If the S‐Mode guidelines significantly affect
navigationsafetyinpositivesenseremainsaquestion
thatwill be answeredby simulation tests performed
before implementation of modified equipment
onboardvessels.Withoutconclusionsfromsuchtests
[Zalewski, 2012] some guidance in the S‐Mode
guidelines can be dubious and actually inconsistent
with well‐established seafarer’s practice. User
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feedback testing, stressed as key factor, is
recommended to confirm conformance with these
guidelines, especially before implementation of
systemsdesignedinaccordance tonew Performance
Standards for the Presentation of Navigation‐related
Information on Shipborne Navigational Displays
[IMO,2019a],cominginforcein2024.
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