1 INTRODUCTION

Modern ship bridges comprise complex and highly

automated human-machine systems [9]. The crew’s

safety and capability to accomplish core navigation

tasks strongly depends on interacting effectively with

machines, as is characteristic for complex

sociotechnical systems. Effective interaction is most

likely to be achieved when the information flow

between humans and machines is optimally attuned

to human capabilities and skills [17, 18]. One way to

enable this adaptation is to adopt a human-centered

approach when designing the interactive system.

Human centered design aims to maximize the

usability of interactive systems by focusing on the

users, their needs and requirements [7]. This is

achieved by applying human factors and ergonomics

methods. For instance, users should be included in all

phases of the design process of the interactive system.

As a result, the users’ effectiveness and efficiency, but

also their satisfaction and safety when using the

interactive system, will likely be enhanced.

Unfortunately, human-centered approaches are

rarely employed in the design process of bridge

systems [2] with user needs being rarely the primary

focus [9], although the e-navigation concept strives to

do so [13]. As a result, ship bridge design is not well

aligned with human skills and abilities, which in turn

likely leads to impairments in efficient execution of

core tasks such as collision avoidance and navigation.

This can potentially have severe consequences.

Consistent with our reasoning, poor design has

already been identified as a contributing factor to

accidents [9, 17, 21, 23].

The concept of situation awareness comes into play

when investigating the link between poor design and

the prevalence of accidents [9, 23]. Situation

Which Radar and ECDIS Functionalities Do Nautical

Officers Really Need in Certain Navigational Situations?

S. Hochgeschurz

, F. Motz

, R. Grundmann

, S. Kretzer

& L. Thiele

Fraunhofer Institute for Communication, Wachtberg, Germany

Fraunhofer Center for Maritime Logistics and Services, Hamburg, Germany

ABSTRACT: Today’s navigation systems risk information overload and display clutter due to the multitude of

available functionalities and information. Different navigational situations present differing challenges to the

navigator, because of varying traffic or maneuvering conditions. This suggests that the need for information and

functionalities on ECDIS and radar systems depends on the navigational situation, which was investigated by

means of an online questionnaire. A sea voyage was divided into three situations, ranging from narrow

maneuvering in port areas, to confined navigable waters, and open sea. N = 80 navigators completed the

questionnaire. A compound priority measure was calculated to express the need for each functionality.

Approximately half of the functionalities were prioritized in a situation dependent manner and substantially

more functionalities were prioritized higher on ECDIS than on radar systems. The results have strong

implications for aligning navigation systems more with user needs in the sense of a human-centered design

approach.

http://www.transnav.eu

the International Journal

on Marine Navigation

and Safety of Sea Transportation

Volume 15

Number 1

March 2021

DOI: 10.12716/1001.15.01.06

awareness describes the ability to perceive events in

the current environment (level 1), to understand their

current meaning (level 2), and to be aware of what

they imply for the future (level 3) [6]. Thus, situation

awareness is highly dependent on information about

the current situation [3]. Such information is gathered

in two ways, by looking out the window and by

precisely examining bridge systems. In the latter case,

information is usually not directly available, but only

through selecting certain functionalities. If

functionalities and corresponding information are

presented inadequately or if simply too many

information and functionalities are displayed, nautical

officers may experience information overload and

retrieve relevant information too slowly [24]. This in

turn may cause impaired situation awareness [5]

which has often been directly linked to accidents as a

causal factor [23].

In the last years, a strong increase of modern

information systems and thus of available information

on ship bridges has been observed [23], well above

and beyond the scope of information and

functionality required by current performance

standards [11, 12] .Therefore, we assume that there is

a serious risk of current systems impeding the

establishment of adequate situation awareness due to

their sheer volume of information and functionalities.

Furthermore, the findings of a study suggest that not

all functionalities displayed are used frequently in

practice [24]. In this study, navigators completed an

online questionnaire indicating how frequently they

use selected functionalities and information on

integrated navigation systems (INS) during a watch.

They were additionally given the opportunity to

comment on their responses. Many navigators used

this opportunity to report that the functionalities’

frequency of use often depends on the navigation

situation.

The findings of [24] have two major implications.

First, they suggest the feasibility of reducing the

number of functionalities and presenting them

according to the navigators’ needs. Only information

and functionalities that are really needed should be

available on bridge systems to reduce clutter and

information overload [5]. The necessity of rarely used

functionalities is therefore questionable. On the other

hand, the findings of [24] also hint at how the number

of functionalities could be reduced – by presenting

only those information and functionalities that are

needed in the current navigation situation. Therefore,

in different navigational situations, different

functionalities and information could be presented

according to the navigators’ needs.

A ship’s voyage can be roughly divided into three

navigational situations [19, 20]:

1. a maneuvering phase at the beginning of the

voyage in port or in very restricted areas,

2. a phase of navigating on the open sea without

much traffic or restrictions due to shallow waters,

and

3. a phase between the port and the open sea, which is

characterized by dense traffic, traffic separation

schemes and shallow waters.

Due to the three situations’ different

characteristics, the specific tasks of nautical officers

vary with the situation. In phase 3, the attention of

nautical officers is focused on the close-range

situation (3-5 nautical miles) and on orientation

between all available aids (RADAR, AIS, VHF, Echo

Sounder) that serve to clearly identify the traffic

situation. In phase 2 however, more emphasis is

placed on an assessment of the situation in a large

range (12-24 nautical miles) and especially on efficient

and economical movement. In phase 1, coordinating

events in the immediate vicinity of the own ship is

most important, for example when coordinating along

tugs or shore lines, or managing the interaction

between the own ship, which is moving very slowly,

environmental influences, as well as fixed installations

such as piers. Phase 1 is also characterized by very

restricted areas, where sensor technology is primarily

needed for depth measurement and to determine the

ship’s drift. Those diverse situational requirements

therefore likely cause the ship’s bridge systems to be

used differently across situations. In line with this

reasoning, the range of the radar system, for example,

is used differently depending on the navigation

situation [14].

Hence, there is a strong need to examine the

situation dependent demand for functionalities in

order to enable future navigation systems to be

optimally aligned with user needs in different

navigational situations. The aim of the current study

is to shed light on this important issue by inspecting

the effect of the navigational situation on the

perceived importance of functionalities and

information and their frequency of use. For this

purpose, nautical officers were directly consulted in

the sense of a human-centered design approach [7] to

identify their specific needs and requirements. Based

on the current body of research [14, 24], the following

hypothesis was formulated: The need for

functionalities and information on ship bridge

systems depends on the navigation situation. To tap

more into measuring the need for functionalities, and

not only their frequency of use, the importance of

functionalities was additionally enquired.

2 METHODS

2.1 Participants

Navigators were recruited for participation with the

support of international organizations involved in

shipping. Recruitment was carried out online

primarily by email. To be included in the analysis,

navigators were required to have at least one year of

experience at sea as a nautical officer. This was to

ensure that all participants were familiar with the

navigation systems and their functionalities.

A total of N = 80 participants completed the online

questionnaire, with n = 25 for open sea, n = 27 for

confined waters, and n = 28 for restricted areas. On

average, participants possessed M = 13.87 (SD = 9.85)

years of sailing experience and most of them (66%)

had been sailing during the past six months prior to

the study. The navigators were most acquainted with

tankers (56%), bulkers (16%) and containers (15%),

and were employed as second officer (35%), master

(28.7%), third officer (15%), and first officer (2.5%), or

possessed another nautical position (18.8%) at the

time of data collection.

2.2 Measuring and Assigning the Priority of

Functionalities

In this study, our aim was to investigate how to

arrange functionalities on navigational displays for

different navigational situations to be optimally in

line with human skills. For this purpose, navigators

were asked to indicate how frequently they use 169

ECDIS and 168 radar functionalities and how

important they consider them when navigating in a

certain situation. We selected the functionalities for

the questionnaire based on simulator investigations of

three ECDIS and radar systems. See Table 1 for a list

of categories and a selection of example

functionalities.

Table 1. Categories and example functionalities

_______________________________________________

Categories Example functionalities

_______________________________________________

Own ship information Heading, ROT

Environmental Wind speed, direction of current

information

Display presentation Select ship centered mode, change

range/scale indication and setting

Cursor location Cursor position, cursor bearing

from own ship

Tools Select and display range rings,

select and display VRM1

Route information Route name, next WPT number

Route monitoring Set cross track distance, display

bearing to next waypoint

Targets and other Acquire Radar target, activate AIS

objects target

Chart settings Select safety depth, show deep

contour

Display of Select tidal data, select surface

environmental data currents

Own ship settings Select show stern line, select show

past track for own ship

Radar setting Select S- or X-band, set gain

Functionalities Set a trial maneuver, perform

parallel indexing

Alert handling Acknowledge alerts, temporarily

silence alerts

_______________________________________________

The same online questionnaire served as the basis

for a previous study by our research group, in which

the task dependency of functionalities was

investigated [10]. In this previous study, we examined

the interaction effect of the task a functionality

belonged to (route monitoring vs. collision avoidance)

and the device on which the functionality was

available (radar vs. ECDIS). To analyze this

interaction, a subsample of 210 of the 337 surveyed

functionalities was examined, which included only

those functionalities that could be clearly assigned to

one of the two tasks.

In contrast, the main purpose of the present study

was to investigate whether the navigational situation

had an influence on the evaluation of all 337

functionalities. As in the previous study, the variable

of interest was coined as the priority of a

functionality, consisting of an integration of the two

factors surveyed: frequency of use and importance.

Frequency of use is established as a valid indicator of

whether users really need a feature (see [24]). As a

rule, the more frequently a feature is utilized, the

faster it needs to be accessible. Yet, there are

functionalities that need to be rapidly accessible, even

though their frequency of use is low. The POB

function for example is allegedly almost never

employed but may become extremely important in a

person overboard situation. Therefore, functionalities’

frequency of use was complemented by surveying

functionalities’ importance. These two ratings were

obtained using 5-point scales. The frequency of use

scale covered ratings from “never” (1) to “always” (5),

whereas importance was classified from “extremely

unimportant” (1) to “extremely important” (5). See

Figure 1 for example questions.

Figure 1. Example questions for ECDIS and two

functionalities

To create the priority measure that accommodates

both types of information, we integrated the two

ratings on a global 5-point scale. On this scale, a high

priority rating indicates a high overall need for the

functionality, whereas a low rating corresponds to a

low need for the respective functionality. We

employed expert ratings of importance, frequency of

use and priority for developing our global priority

measure. These established the following rules: first, if

a functionality received the highest possible

importance or frequency of use rating, or both, it was

given a priority rating of five, resembling the highest

priority. Second, if the frequency of use and

importance ratings coincided, the corresponding

rating was adopted for the priority scale. Third, if the

frequency of use and importance ratings deviated by

one point, the higher rating from both scales was

taken for the priority. Fourth, if the frequency of use

and importance ratings featured a two-point

difference, the mean of both ratings was calculated

and adopted as the resulting priority. The remaining

cases were classified with a priority of three.

2.3 Situation Dependency of Functionalities

In this study, our aim was to investigate whether the

need for functionalities depends on the navigational

situation. For this purpose, three navigational

situations were defined: open sea, confined waters

and restricted areas. Open sea was described as a

situation without any land, water depth, or traffic

separation restrictions and with little traffic (e.g. the

middle of the Atlantic Ocean). Confined waters was

characterized by opposing features, as it was marked

by the presence of land, water depth, traffic separation

restrictions and heavy traffic (e.g. the English

Channel). Lastly, restricted areas were described as

areas with very limited maneuverability due to the

presence of land, port, water depth, and height

restrictions (e.g. port areas).

To quantify situation dependency, mean priority

ratings were first calculated for each functionality and

then trimmed by 20%. Trimmed means were used to

account for possible deviations from the normal

distribution, as they are less sensitive towards outliers

than untrimmed means and thus more robust [8, 16].

Trimmed means were then rounded, which enables

precisely assigning the functionalities to one of the

five priority levels. Finally, functionalities were

classified as either situation dependent or situation

independent, based on the assigned priority level.

Only if functionalities received equal priorities in all

three situations, they were coined as being

independent of the situation. Otherwise,

functionalities were classified as situation dependent.

2.4 Experimental Design

We employed a 2 x 3 mixed design with navigational

device (radar and ECDIS) as within-subjects factor

and situation (open sea, confined waters, restricted

areas) as between-subjects factor. The questionnaire

measured the frequency of use and importance of

each functionality for each device in each situation.

Those ratings were combined to a compound priority

rating. The dependent variable of interest consisted of

the trimmed and rounded means of functionalities’

priority ratings. The two independent variables are

described in more detail below.

Device. Participants rated the frequency of use and

importance of 176 functionalities available on radar

and ECDIS navigation systems (within-subjects

factor). Since 161 of the 176 functionalities (91%) are

available on both systems, whereas 8 functionalities

are available on ECDIS only, and 7 functionalities on

radar only, each participant rated a total of 337

functionalities.

Situation. Participants were randomly assigned to

one of three navigational situations in order to reduce

the questionnaires’ length. At the beginning of the

questionnaire, participants were asked to focus on the

indicated situation while answering the questions.

Thus, situation was employed as a between subjects

factor with three levels.

2.5 Procedure

Data was collected by means of an online

questionnaire, which was programmed using the

online survey tool SoSci Survey [15]. First, navigators

were provided with general information regarding

the research aim and gave their informed consent for

participation. General questions were displayed

concerning the navigators’ occupational background.

Then, information about one of the three possible

situations was given, after which a control question

was asked to assure that participants were aware of

the assigned situation. Finally, participants rated the

functionalities’ frequency of use and importance on 5-

point scales. They were given the opportunity to leave

additional comments regarding the presented

functionalities at each page of the questionnaire.

Overall, completion of the survey took approximately

90 minutes.

2.6 Data Analysis

We performed both descriptive analyses and

inferential statistical tests with the help of IBM SPSS

and R. To avoid extensive α-error accumulation, we

did not apply inferential statistics to investigate the

situation dependency individually for each

functionality. However, inferential statistics were

applied to examine the global effect of situation and

device and possible interactions on trimmed priority

ratings. For this purpose, a mixed model ANOVA was

set up with the two factors device and situation,

including only the trimmed priority ratings of

functionalities available on both devices (n = 161

functionalities per device). Testing the assumptions of

the mixed model ANOVA revealed that group

variances for ECDIS were heterogeneous, as assessed

by Levene’s test (p = .001), whereas they can be

assumed to be homogenous for radar (p = .273).

Inspection of the Q-Q-plots suggested a deviation

from the normal distribution of trimmed priority

ratings. However, our sample consisted of n = 161

functionalities per cell and mixed model ANOVAs are

considered to be robust against normality violations

and heterogeneous variances, when sample size is

large and equal in all cells [22].

A one-way ANOVA with situation as factor and

trimmed priority ratings of all functionalities included

(n = 337 per situation) was conducted to follow-up the

mixed model ANOVA. Again, Q-Q-plots indicated

deviations from a normal distribution and Levene’s

test was significant (p = .014), but sample size is

sufficiently large for the ANOVA to be considered

robust [22]. The one-way ANOVA was followed by

three independent samples t-tests. For all inferential

statistical tests, an alpha level of α = .05 was employed

and Bonferroni adjusted if appropriate. As a measure

of effect size, Cohen’s d, η

and ηp

were utilized and

interpreted according to [1].

3 RESULTS

Descriptive statistics of trimmed priority ratings are

displayed in Table 2. Untrimmed priority ratings were

included to illustrate the difference between

untrimmed and trimmed ratings. The means of

trimmed priority ratings were consistently higher

than the corresponding means of untrimmed priority

ratings on both devices and in all three situations. Our

priority scale consists of five levels, with the third

level representing the scales’ midpoint. All means

were well above a value of 3, suggesting that most

functionalities received a rather high priority. This

also explained why trimmed means were always

higher than untrimmed means, since the lowest 20%

of priority ratings that were excluded then had a

greater impact on the mean than the highest 20% of

priority ratings that were excluded.

Table 2. Means (and standard deviations) of untrimmed and trimmed priority ratings for 169 ECDIS and 168 radar

functionalities

___________________________________________________________________________

Open Sea (n = 25) Confined Waters (n = 27) Restricted Areas (n = 28)

Device untrimmed trimmed untrimmed trimmed untrimmed trimmed

___________________________________________________________________________

Radar 3.63 (0.85) 3.72 (1.03) 3.36 (0.86) 3.41 (1.12) 3.53 (0.84) 3.58 (1.03)

ECDIS 4.14 (0.52) 4.37 (0.61) 3.83 (0.67) 4.01 (0.84) 4.08 (0.58) 4.28 (0.66)

___________________________________________________________________________

Table 3. Descriptive statistics of trimmed priority ratings for the 161 functionalities applicable to both devices

_________________________________________________________________________________________

Open Sea (n = 25) Confined Waters (n = 27) Restricted Areas (n = 28)

Device M SD M SD M SD

_________________________________________________________________________________________

Radar 3.71 1.05 3.42 1.14 3.57 1.04

ECDIS 4.37 0.62 4.00 0.85 4.27 0.67

_________________________________________________________________________________________

As shown in Table 2, radar functionalities received

lower mean priority ratings than ECDIS

functionalities in all three situations. Furthermore,

irrespective of the device, the priority of

functionalities in confined waters is on average lower

than the priority of functionalities in the other two

situations. Functionalities received the highest mean

priority ratings on open sea. A mixed model ANOVA

was set up to investigate whether these observed

differences in trimmed priority ratings are statistically

significant. Only those functionalities available on

both devices were included in the mixed model

analysis, leading to an elimination of 15

functionalities (n = 161 per device). The descriptive

statistics of these do not differ substantially from

those with all functionalities included (see Table 2)

and are displayed in Table 3.

The mixed model ANOVA yielded a significant

main effect of device (F(1,480) = 111.83, p < .001, ηp

.19) as well as a significant main effect of situation

(F(2,480) = 11.50, p < .001, ηp

= .05). The interaction

between device and situation was not significant

(F(2,480) = 0.30, p = .739, ηp

< .01), indicating that the

main effects can be analyzed and interpreted

separately. Since the main effect of device was

significant, the above observations regarding the

device dependency were underpinned statistically.

Trimmed priority ratings of radar functionalities were

indeed significantly lower than trimmed priority

ratings of ECDIS functionalities with a medium effect

size (d = 0.69).

The significant main effect of situation was

investigated further by conducting a one-way

ANOVA including all functionalities (n = 337 per

situation). The ANOVA model with situation as factor

and trimmed priority rating as dependent variable

reflected a significant difference in trimmed priority

ratings between situations (F(2,1008) = 10.24, p < .001,

= .02). Consequently, three t-tests were conducted

to examine the difference. After applying a Bonferroni

correction to adjust for multiple testing (α = .017),

there were significant differences in priority ratings

with small effect sizes between confined waters and

open sea (t(661) = -4.40, p < .001, d = -0.34) and

between confined waters and restricted areas (t(665) =

2.81, p = .005, d = -0.22). The difference between open

sea and restricted areas was non-significant (t(672) =

1.64, p = .101, d = 0.13). Therefore, trimmed priority

ratings were significantly lower for confined waters

than for the other two situations, confirming the

descriptive observation above. However, trimmed

priority ratings for open sea were not significantly

higher than ratings for restricted areas.

3.1 Device Dependency

As the inferential statistical tests described only

address the global means across all functionalities, the

device dependency effect was examined more closely

in the following. On each device, the functionalities’

distributions over the five priority levels after

rounding the trimmed priority ratings were observed

and are displayed in Figure 2 and in Figure 3. Radar

functionalities (Figure 2) seem to be more evenly

distributed over the five priority levels than ECDIS

functionalities (Figure 3). On ECDIS, one can observe

a descending order: the two highest ratings (levels 5

and 4) were predominantly given, while some

functionalities received a priority of 3 and even less

functionalities received a priority of 2. No

functionality was evaluated with a priority of 1 on

ECDIS. On Radar, three functionalities received a

priority rating of 1 in confined waters. Therefore,

navigators very rarely classified functionalities as

“extremely unimportant” and as “never used” at the

same time, while a majority of functionalities were

rated as either “extremely important”, “always used”,

or both.

Figure 2. Number of functionalities in each priority level by

situation on radar

Figure 3. Number of functionalities in each priority level by

situation on ECDIS

Table 4. Examples of functionalities in the respective situation dependency categories

__________________________________________________________________________________________________

Situation Example functionalities on radar Example functionalities on ECDIS

dependency

__________________________________________________________________________________________________

OS ↑ – Alphanumerical position – Alphanumerical position

– Rudder angle – Select display orientation North Up/Head

– Set curved heading line Up/Course Up

– Select display of unknown objects – Select true/relative motion mode

– Enter geographical coordinates of any position – Enter geographical coordinates of any position

and display that position and display that position

– Set alert escalation (unacknowledged warning

escalation time)

CW ↑ -- – change displayed chart area manually

RA ↑ – Remove chart data – Select align by heading or course over ground for

– Select safety depth heading line

– Select video emphasis – Select show 2nd past track for own ship

– Distance to "TO-WPT" – Temporarily silence alerts/alarms

– ETA – POB function

– Toggle past positions on/off

OS ↓ – Show time labels – Set target vector length (time)

– Time to go to "TO-WPT" – Perform manual update

– Radius

CW ↓ – COG – Set own ship track length (time)

– Set and load user configurations – Set filters for AIS target information

– Set filters for AIS target information – Add/remove information from standard display

– Select Display Base/Standard Display/All – Plot own ship position manually (dead reckoning)

Information – Set AIS settings (transmitter, select auto/manual

– Calculate rise/set sun and moon for channel A/B, …)

RA ↓ – Water depth under keel – Water depth under keel

– Water depth (chart datum) – Select default ECDIS settings

– Show shallow contour – Set curved heading line

– Add/remove information from standard display – Time to go to cursor position

– Time to go to cursor position – Wind speed

__________________________________________________________________________________________________

3.2 Situation Dependency

Similar to the device dependency effect, the situation

dependency effect was also examined more closely by

looking at the individual functionalities. While the

priority of some functionalities appeared to be

situation independent, the priority of other

functionalities differed by situation. In total, 77 radar

functionalities (46%) and 86 ECDIS functionalities

(51%) were classified as situation dependent

according to the rules specified (see section 2.3).

Consequently, 91 radar functionalities (54%) and 83

ECDIS functionalities (49%) received the same

priority ratings in all three situations, i.e., were

classified as situation independent. Therefore, the

priority ratings of approximately half of the radar and

ECDIS functionalities can be viewed as depending on

the navigational situation.

To explore how exactly situation dependency

manifested itself, further analyses were conducted. As

the mixed ANOVA model already showed, situation

dependency stemmed mostly from the fact that

functionalities were evaluated differently in confined

waters than in the other two situations. This

difference was most pronounced with respect to

priority ratings of 5, 3 (ECDIS) and 2, but not for

ratings of 1 and 4, in which the number of priority

ratings was approximately the same in each situation,

as displayed in Figure 2 and Figure 3. In confined

waters, less functionalities received the highest

priority rating compared to the other two navigational

situations, complemented by a higher number of

lower priority ratings (i.e., ratings of 3 and 2).

Figure 4. Number of situation dependent functionalities

categorized by the situation in which they received the

highest priority (indicated by ↑) or the lowest priority

(indicated by↓). Functionalities received the same priority

in the unmentioned situations. OS = open sea, CW =

confined waters, RA = restricted areas

Figure 4 provides a clearer picture of

functionalities’ situation dependency by displaying

the number of functionalities that differed by one

priority level when comparing one situation to the

other two. If a functionality received the highest

(indicated by ↑) or lowest (indicated by ↓) priority

rating in one situation, it received the same priority in

the other two situations. There was only one

functionality on ECDIS (“ change displayed chart

area manually”) that received the highest priority in

confined waters. Again, most situational differences

originated from functionalities that received a lower

priority in confined waters than in the other two

situations. This was true for 25 radar and 41 ECDIS

functionalities, supporting the trend seen in Figure 2,

Figure 3 and the mixed ANOVA results. The second

most frequent origin for situation dependency was a

higher priority rating of functionalities on open sea

than in the other two situations, which accounted for

30 radar and 22 ECDIS functionalities. Functionalities

receiving the highest or lowest priority in restricted

areas, or the lowest priority in open sea were by far

less frequent. Table 4 displays examples of

functionalities classified in the respective situation

dependency category.

Table 4 and Figure 4 only include those

functionalities with a situational difference in priority

ratings of one level. Additionally, a difference of two

priority levels between at least two situations were

obtained in the following four functionalities: “rudder

angle” (ECDIS), “propulsion engine RPM” (ECDIS),

“select S- or X-band” (ECDIS), “set AIS settings”

(Radar).

4 DISCUSSION

The design process of ship bridge systems rarely

adheres to a human-centered design approach [2] and

seldom addresses users’ needs [9]. In our current

study, we aimed at changing this by surveying

navigators about how frequently they use

functionalities on ECDIS and radar systems and how

important they consider these. These two measures

were used to derive navigators’ overall need for the

functionality on the respective system by assigning

them to one of five priority levels. As previous

research suggests that functionalities’ use depends on

the navigational situation [24], we specifically

surveyed the need for functionalities in three separate

navigational situations: open sea, confined waters and

restricted areas.

4.1 Summary, Interpretation and Practical Relevance of

Study Results

Our analyses revealed that for about half of all 337

functionalities, the priority depended on the situation,

although the difference in priority between the

situations consisted only of one priority level for the

majority of functionalities (98%). Situation

dependency was mostly due to functionalities

receiving a higher priority on open sea or a lower

priority in confined waters than in the respective

other two situations, as confirmed by the inferential

statistical analysis. On average, functionalities

received a significantly lower priority in confined

waters compared to the other situations, regardless of

the considered navigation system.

One possible explanation for the higher

prioritization of functionalities on open sea than in the

other two situations is that on open sea, navigators

may have to rely more on navigation systems because

looking out of the window might not reveal much

information there. On the contrary, in confined waters

and restricted areas there is rather high traffic density

and a proximity to the shore. Thus, most events

happen within a close range of the own ship and

navigators retrieve most situational information by

simply looking out the window. Another plausible

explanation is that events on open sea are relatively

rare, allowing navigators to take the time to modify

routes and to prepare impending entries of busier

confined waters by adjusting limits and other settings

optimally to the circumstances in confined waters. As

a result, the need for such settings is higher on open

sea than in confined waters. The navigators’

comments underpin this assumption (see [10]).

Further, priority levels were given more

distinctively in confined waters. The need for

functionalities may thus be more differentiated in

confined waters than in the other two situations. On

open sea and in restricted areas most functionalities

were classified in only two of the five possible priority

levels, which was more pronounced for ECDIS than

for radar functionalities. In these two situations

almost all functionalities were assigned to the two

highest priority levels for the ECDIS. Therefore,

navigators are reluctant to dismiss functionalities as

extremely unimportant and never used, in line with a

central tendency bias often observed in

questionnaires, which states that participants prefer

scale midpoints over extremes [4]. However, for

higher priority levels, a central tendency bias was not

observed on the ECDIS, since most functionalities

were assigned to the two highest priority levels.

Hence, ECDIS functionalities are classified either as

extremely important, always used or both.

These findings are somewhat surprising, as one

would expect that some functionalities are not needed

due the high number of functionalities available on

the navigation systems. According to the survey

results, a large amount of ECDIS functionalities is

needed. This highlights the importance of optimally

adapting the ECDIS design to navigators’ skills and

capacities. All functionalities need to be accessible

quickly and effortlessly to allow for efficient execution

of core tasks.

In contrast to ECDIS functionalities, considerably

more functionalities on radar were assigned to lower

priority levels (see Figure 2). Accordingly, the mean

priority of radar functionalities was significantly

lower than the mean priority of ECDIS functionalities,

regardless of the situation. Consequently, the need for

radar functionalities is more nuanced than the need

for ECDIS functionalities. Results from our other

analyses underline this finding, indicating that radar

systems are mainly seen as collision avoidance tools,

whereas a less clear task allocation emerges for the

ECDIS [10].

Taken together, these results indicate that the need

for a functionality both depends on the navigational

situation in which it is used and on the device, on

which the functionality is displayed, with most

functionalities receiving a high priority rating. These

results include important insights into how ECDIS

and radar functionalities should be presented. On the

one hand, a situation dependent presentation would

be plausible, in which functionalities are presented

differently in the three situations according to the

navigators’ needs (which is in line with [13]).

However, different situation modes should be

employed with caution. According to [5], the number

of modes should be limited in order to prevent mode

confusion. Navigators may receive training to

understand and use the different modes correctly, so

that mode changes are expected and self-initiated

only. Future studies need to investigate whether

ECDIS and radar designs would benefit from

incorporating multiple situation modes when

navigators receive sufficient training. It would be

particularly interesting to see, if these new ECDIS and

radar designs perform better than traditional designs

in simulator tests, for example. In general, it would be

interesting to know, in which aspects the new ECDIS

and radar designs differ from traditional designs.

Further, the results offer implications on how

functionalities can be presented efficiently in the

navigational situations. For example, the

functionalities’ priority could be used as an indicator

of how quickly accessible the functionality should be

in the respective situation [10]. This offers a feasible

approach for radar systems, since on the radar,

different functionalities were assigned quite

heterogeneously to priority levels. On the ECDIS,

however, due to the largely homogeneous

prioritization, the accessibility measure alone will not

be sufficient to guide display design. Further

investigations and iterations with users actively

participating in the design process according to [7]

will be necessary.

4.2 Study limitations

We employed a between subjects design to investigate

the effect of the navigational situation on the priority

of functionalities. For this reason, it is not completely

clear whether the same navigator would have

prioritized functionalities differently in the three

navigational situations. However, we believe that the

between subject design was necessary to avoid

extending the already very long online questionnaire

even further. Furthermore, the relative ranking of the

functionalities’ priority within one situation is not

affected by the chosen method and is thus still

sufficient to guide display design. Nevertheless, we

will carry out further studies to investigate whether

the situation dependencies observed are solely

attributable to the design employed.

Another limitation is that we rounded the trimmed

means of priority ratings to be able to assign them to

different priority levels unambiguously and to

quantify situation dependency. Rounding sometimes

creates arbitrary differences. For instance, a trimmed

mean of 4.4 would be assigned to a priority of four,

while a trimmed mean of 4.6 would receive a priority

of five, although the difference in trimmed means is

very small. Furthermore, the practical relevance of our

obtained situational differences might be questioned,

since most situation dependencies (98%) resulted

from a difference of only one priority level. For this

reason, it is important to test a design guided by the

results of this questionnaire extensively before

establishing it in practice.

5 CONCLUSIONS

This study investigated the research question of which

functionalities nautical officers really need in which

navigational situations. Nautical officers regarded

almost none of the functionalities (< 1%) as never used

and extremely unimportant. Thus, the aforementioned

question must be answered in the following way

based on the study’s results. Nautical officers need

almost all functionalities to a certain extent regardless

of the navigational situation. However, differences in

the intensity of the need between the navigational

situations and the considered devices have been

observed. About half of the functionalities could be

classified as being used in a situation dependent

manner. Functionalities received overall higher and

more homogeneous priority ratings on the ECDIS

than on the radar, where priority ratings were on

average lower and more heterogeneous. These results

offer implications for ECDIS and radar design and

provide an important step towards a more human-

centered design approach. For instance, functionalities

might be presented in different situation-dependent

modes. Priority ratings may serve as sufficient

indicators of how fast a respective functionality

should be accessible on the radar. For the ECDIS,

where priority ratings were quite high and not as

diverse, future studies may investigate how

functionalities can be presented to avoid information

clutter and overload, allowing for an effective user-

centered navigation.

ACKNOWLEDGMENTS

The study was carried out as part of a project funded by the

German Federal Ministry of Transport and Digital

Infrastructure. We would like to thank BM Bergmann

Marine for the grateful support. In particular, we would like

to thank all the nautical officers who completed the online

questionnaire.

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