Scientific Journal of Gdynia Maritime University
No. 113/20, 17–28 Submitted: 01.12.2019
ISSN 2657-6988 (online) Accepted: 31.12.2019
ISSN 2657-5841 (printed) Published: 31.03.2020
DOI: 10.26408/113.02
PRACTICAL ASPECTS OF USING RADAR
IN MARITIME NAVIGATION WITH ANALYSIS
OF ITS POTENTIAL ERRORS AND LIMITATIONS
Grzegorz Rutkowski
Gdynia Maritime University, Morska 81-87, 81-225 Gdynia, Poland, Faculty of Navigation,
ORCID 0000-0002-7455-7069
e-mail: kptgrzegorzrutkowski@gmail.com
Abstract: In this article, the author will try to explain the basic principles of the practical
focus of using radar in maritime navigation, analysing its potential errors and limitations.
An attempt will also be made to describe the basic seamanship practice of how to set up the
radar, determine the radar blind sectors, calculate the radar position accuracy, generate
a basic anti-collision radar report, calculate CPA, TCA, BCR, BCT etc., and verify the
effectiveness of a trial anti-collision manoeuvre by using the radar in the different radar
modes when navigating in restricted sea areas.
Keywords: radar, ARPA, closest point of approach (CPA), time for closest point of
approach (TCPA), bow crossing rage (BCR), bow crossing time (BCT), radar blind sectors,
true motion, relative motion, true vectors, relative vectors, sea stabilised mode, ground
stabilised mode, parallel indexing (PI).
1. INTRODUCTION
Since radar systems first appeared on the bridges of merchant ships in the 1950s,
they have undergone considerable change, both in their technology and in their
functionality [Bilden and Norris 2008; Brunicardi 2012]. They have changed from
being an occasionally used aid, brought into play in unusual and difficult
navigational circumstances, to central and always available tools on watchkeepers’
consoles [The American Practical Navigator Bowditch 2002; Wróbel 2019]. The
presentation of radar information to the officer of the watch (OOW) has undergone
considerable modernisation and computerisation [Brunicardi 2012]. Recent new
performance standards produced by the IMO [IMO 2004; IMO SN/Circ.243 2004]
have recognised this changing technology [Brunicardi 2012]. In fact, the OOW
[STCW 2010] shall know how to set up the radar, how to determine the radar blind
sectors, how to calculate the radar position accuracy, how to generate a basic anti-
collision radar report, and how to calculate the CPA, TCA, BCR, BCT, etc.
Scientific Journal of Gdynia Maritime University, No. 113, March 2020 17
Grzegorz Rutkowski
Unfortunately, evidence [Brunicardi 2012] and practice [MCA 2007; Rutkowski
2019; Wróbel 2019] indicates that these activities are not always known or
properly understood, resulting in numerous comments on observations and/or
nonconformities being made during maritime inspections (Port State Control,
vetting, etc. [VIQ Vessel Inspection Questionnaires for the Oil Tankers 2017;
Maersk Line Internal Documentation 2018; Teekay Shipping SA 2019]).
The author’s intention in this paper was to prepare a short guide for OOW about
the basic principles of using radar and ARPA, and describing their limitations.
2. THE USE AND LIMITATIONS OF RADAR
Radar (from radio detection and ranging) is a radio system which measures
distance and usually direction by comparing reference signals with radio signals
reflected or retransmitted from the target whose position is to be determined
[Bilden and Norris 2008; Brunicardi 2012]. If the radar is also equipped with
a tracking computer, called an ARPA (Automatic Radar Plotting Aid) [IMO 2004;
Brunicardi 2012], it helps in tracking targets when assessing navigational situation
awareness (CPA, TCPA, BCR, BCT). For shipboard navigational applications,
pulse-modulated radars are used. In this type of radar, the distance to the target is
determined by measuring the time required for an extremely short burst or pulse of
radio-frequency energy to travel to the target and return to its source as a reflected
echo. Directional antennas allow the direction of the target echo from the source to
be determined [IMO 2004; Bilden and Norris 2008; Brunicardi 2012].
Most of the main requirements and legal provisions for radar equipment and
ARPAs are included in the SOLAS convention [SOLAS 2019] with amendments,
the STCW convention [STCW 2010], and a number of IMO Resolutions [IMO
2004; IMO SN/Circ.243 2004] (i.e. MSC.192(79) Annex 34 “Adoption of
The Revised Performance Standards for Radar Equipment”, A.422 (XI), A.823(19)
etc.).
According to the SOLAS requirements [SOLAS 2019], all ships of 10,000 GT
and upwards shall be fitted with 2 radars, each being capable of being operated
independently of the other, and one of which must be capable of operating at
9 GHz (3 cm, X band), to determine and display the ranges and bearings of other
surface craft, obstructions, buoys, shorelines, and navigational marks to assist in
navigation and in collision avoidance. Usually such ships are fitted with one
X-band radar and one S-band radar. X-band radar has a short wavelength (3 cm)
for better directivity, and small, light-weight antennas, but with increased
attenuation in precipitation than S-band radars. S-band radar has a longer
wavelength for long-range detection, a larger antenna than X-band radar, and can
penetrate precipitation for much better performance than X-band radar in inclement
weather.
18 Scientific Journal of Gdynia Maritime University, No. 113, March 2020
Practical Aspects of Using Radar in Maritime Navigation
with Analysis of its Potential Errors and Limitations
The officer of the watch (OOW) shall remember that both visual and radar
position fixing and monitoring methods should be used whenever possible. This
means that frequent checks should be made of the ECDIS by using a different
position fixing system (normally DGPS/DGNSS) [Weintrit 2009; Rutkowski 2018]
as well as by the use of radar to check the accuracy of the charted position by
comparing the location of the radar target against the charted symbol [IMO
SN/Circ.243 2004] plus parallel indexing and/or the use of clearing radar bearings
and/or distances [The American Practical Navigator Bowditch 2002; Rutkowski
2019; Wróbel 2019].
The officer of the watch (OOW) is also responsible for checking the operating
status of each navigational radar [STCW 2010]. He/she shall adjust the brilliance,
gain, sea clutter, and rain clutter in order to obtain the optimum picture, be familiar
with the radar’s limitations, radar horizon (the sensible horizon of a radar antenna),
radar blind sectors, and radar effectiveness.
Examples of radar limitations are as follows [Rutkowski 2019]: the minimum
range is given by a ½ pulse length (typical error = 15–20 m) over a short range, the
range accuracy is given as a percentage of the radar range and the installation
calibration (typical error = 5–15 m), antenna location (setup), beam width
(typically 1 x 30° (-3db)/approx. 2 x 60°(-6db), geometric dependent measurement
at a short range, bearing accuracy is given e.g. by the gyro limitations (reference
high latitude problems), shadows and multiple ghost echoes close to the ship,
stabilising is dependent on the gyro, log and GPS/GNSS performance.
Fig. 1. The graphical method used for the Radar error mD and mB
with reference to Radar Range (RR)
Source: Author’s own research based on [Rutkowski 2019].
The accuracy of a fixed position obtained by radar with a probability P = 95%
can usually be calculated as mD = ±50 m or 1% of the radar range (RR) with
reference to the distance measurements, and mB = ±1º with reference to the bearing
measurements (e.g. gyro error). In such a case, the error for the distance
measurements can be calculated as mD = ±50 m for RR≤1.5 NM, and 1% of the RR
Scientific Journal of Gdynia Maritime University, No. 113, March 2020 19
Grzegorz Rutkowski
for RR>1.5 NM. For RR=3 NM, it will be mD = 55.6 m, and for RR = 12 NM, it
will be mD = 222.4 m. With reference to the measurements of bearing, the total
error (mB = RR×tg(1º)×1852 m) will be calculated accordingly as mB = 24.2 m for
RR = 0.75 NM, mB = 48.5 m for RR = 1.5 NM, mB = 97 m for RR = 3.0 NM,
mB = 387.9 m for RR = 12 NM, etc.
Considering radar accuracy [IMO 2004] for larger radar ranges (usually
RR>1.5 NM), it is always recommended to use the radar distances techniques for
position fixing and monitoring [Rutkowski 2019]. By using this method, the
position fixing error can be reduced. It is also recommended to use simultaneous
bearings techniques for radar ranges smaller than 1.5 NM [Rutkowski 2019]. Both
methods can be used, i.e. two bearings and/or two distances techniques, at a radar
range of RR = 1.5 NM for position fixing and monitoring [Rutkowski 2019]. The
error for position fixing at a radar range of RR = 1.5 NM will be more or less the
same, that is to say, about 50 m.
The effectiveness of the radar measured using a Radar Performance
Monitor should be recorded by the OOW at the end of each watch whenever the
radar is operational to ensure that optimal efficiency is being maintained. Radar
minimum performance standards are set by the IMO Resolution MSC 192(79)
Annex 34 “Adoption of the Revised Performance Standards for Radar Equipment”
[IMO 2004].
A numerical, percentage, graphical, or other measurement value should be
recorded. Records should be maintained whether the vessel is on an international
voyage or not. This is not only a question of good practice [Maersk Line Internal
Documentation 2018; Teekay Shipping SA 2019]. There are also the Oil
Companies International Marine Forum (OCIMF) requirements (for reference, see
i.e. VIQ Vessel Inspection Questionnaires for the Oil Tankers, Combination
Carriers, Shuttle Tankers, Chemical Tankers and Gas Carriers [VIQ Vessel
Inspection Questionnaires for the Oil Tankers 2017]).
Fig. 2. Radar performance test result [Rutkowski 2019]
The OOW needs to turn on the performance monitor referred to in the
appropriate paragraph in the radar’s manual, and after observing the results, should
turn the performance monitor back off [IMO 2004; Rutkowski 2019]. As an
20 Scientific Journal of Gdynia Maritime University, No. 113, March 2020
Practical Aspects of Using Radar in Maritime Navigation
with Analysis of its Potential Errors and Limitations
example in Figure 2, the radar range scale is automatically set to 24 NM. The radar
screen will show one or two arcs. If the radar transmitter and receiver are in good
working condition, the innermost arcs should appear between 13.5 and 18.5 NM.
The performance monitor can observe a total of 10 dB of loss in the transmitter and
receiver. The lengths of the arcs may vary according to the installation
environment. The OOW needs to judge the strength of the echo which appears
within 90° behind their own ship to confirm if the radar is working properly or not.
Fig. 3. The Radar blind sectors form commonly used in the shipping industry
(on the left) and the Radar blind sectors recommended by the author prepared
for mt Navion Hispania in May 2018
Fig. 4. A practical method recommended by the author to determine
the Radar blind sector and shadow areas around the ship by means
of the ships drawings, General Ship Arrangement Plan, and/or Thales’ theorem
Source: Author’s own research.
Another point, and quite an important matter to discuss, is the Radar Blind
Sectors. In some operational sectors (relative bearings) and/or distances of the
ship’s radar especially at low radar ranges (RR), the loss of targets/echos may
occur. Unfortunately, the evidence [Maersk Line Internal Documentation 2018;
Teekay Shipping SA 2019] as well as experience [VIQ Vessel Inspection
Questionnaires for the Oil Tankers 2017; Rutkowski 2019] have also shown that on
most of the ships in the shipping industry, the radar blind sectors and/or “shadow
distances” are not available and/or not prepared properly (see Fig. 3 and 4).
Scientific Journal of Gdynia Maritime University, No. 113, March 2020 21
Grzegorz Rutkowski
If the radar blind sector on your ship is described as can be seen in the form on
the left of Figure 3, this means that your form is not completed and you still need to
specify the additional areas around your ship where the radar is not able to detect
a target, due to the ship’s hull construction, the radar antenna position etc. In such
a case, the radar blind sectors and shadow areas all around the vessel shall be
obtained (calculated and/or described) for each direction (forward, aft, port, and
starboard) and calculated at least for a normal ballast (minimum draft) and the
normal loaded (maximum draft) conditions. The final result can be presented or
described as seen on the right of Figure 3.
To specify those blind sectors and shadow areas all around the vessel, you can
use a simple mathematical formulae (i.e. the intercept theorem, also known as
Thales’ theorem) and/or determine the blind sectors and shadow areas by means of
a graphical method i.e. by using ship’s drawings and/or the General Ship
Arrangement Plan (see Fig. 4).
3. THE USE OF RADAR FOR COLLISION AVOIDANCE
It must be noted that the use of radar and an ARPA as aids to collision avoidance
[COLREG 1972; MCA 2007; STCW 2010], particularly in poor visibility, must
not detract from the requirement that a good visual lookout is kept. If the task is
going to preoccupy your time, post a lookout [COLREG 1972; STCW 2010;
Rutkowski 2019].
Table 1. Advantages and limitations of radar and direct sight
when maintaining a proper lookout at all times
Advantages of Direct Sight Advantages of Radar
Reliable, sensitive to colour, can assess Generally reliable, does not get tired, produces
aspects, can identify small targets, can see light accurate range information and a stable bearing
configuration, can assess ship types, can platform, simplifies overview, can penetrate fog,
identify some conspicuous marks, can identify has better penetration in rain and snow, is useful
the flashing lights, has better discrimination, can for predictive collision avoidance, predictive
see the changing weather patterns, can see the navigation (parallel index), can have a longer
effects of the sea on vessels, not affected by range (height of the aerial), an excellent tool
blind arcs (if the observer moves) when cooperating with AIS and ECDIS
Limitations of Direct Sight Limitation of Radar
Poor at assessing distance (worse at night), Radar blind sector, misses some small targets,
subject to night adaptation, degradation through can miss substantial targets in a clutter, can de-
glare, gets tired while searching, binoculars tune, prone to inherent and input errors, targets
needed for early identification, other need transponders for positive identification, is
environmental phenomena influencing eye prone to interference, cannot discriminate as
accuracy, such as fog, rain, darkness (a dark well as direct sight, cannot identify ship types as
unlit object cannot be seen with the eyes), the well sight, cannot assess the aspects
influence of environmental conditions on human immediately, bearing less accurate than
health and perception, limited field of view etc a compass
Source: Author’s own research.
22 Scientific Journal of Gdynia Maritime University, No. 113, March 2020
Practical Aspects of Using Radar in Maritime Navigation
with Analysis of its Potential Errors and Limitations
Table 1 shows the advantages and limitations of radar and direct sight when
maintaining a proper lookout at all times.
Another issue with which the OOW should be familiar is the correct settings of
the radar (to adjust the brilliance, gain, sea clutter, and rain clutter to obtain an
optimum picture), and how to use the radar for trial maneuvers. History shows us
that a lack of knowledge regarding the proper set-up of the radar and/or even a
misunderstanding of the navigational situation presented on the radar screen may
be a direct cause of some navigational incidents leading to ship collisions at sea
[Bilden and Norris 2008; Brunicardi 2012; Rutkowski 2019].
Fig. 5. Practical method used determine the “risk of collision” by means of CPA & TCPA
on radar set on relative motion (A) and true motion (B)
Source: Author’s own research.
According to Rule No. 7 of COLREG [COLREG 1972], the risk of a collision
shall be deemed to exist if the compass bearing of an approaching vessel does not
appreciably change. Such a risk may sometimes exist even when an appreciable
bearing change is evident, particularly when approaching a very large vessel or
a tow or when approaching a vessel at a close range.
Figures 5 presents a practical method used to determine the risk of collision by
means of CPA and TCPA on a radar set on relative motion and true motion. Figure
6 depicts a typical radar (ARPA) risk of collision report, which includes bearing to
a target (BRG), range to a target (RNG), target closest point of approach (CPA),
time to closest point of approach (TCPA), target aspect (A), target bow crossing
range (BCR), target bow crossing time (BCT), target heading (HDG), and target
speed (SPD). In addition, when the radar is integrated with an Automatic
Identification System (AIS), it can also recognise a target course through water
(CTW), a target speed through water (STW), a target course over ground (COG),
and a target speed over ground (SOG).
Scientific Journal of Gdynia Maritime University, No. 113, March 2020 23
Grzegorz Rutkowski
The ship’s radar display can be set on true motion or relative motion. In
relative motion, we can choose the following modes of display: north up
stabilised, head up unstabilised and course up stabilised. Your own ship can be
displayed at a fixed position on the display either centred or off-centred.
Fig. 6. A practical method used to formulate a typical radar (ARPA) risk
of collision report by means of a radar set in relative motion
Source: Author’s own research.
In true motion, we can choose the
display mode with a true motion moving
origin or a true motion fixed origin.
Both modes can be sea or ground
stabilised. Both can be north up or
course up.
In a moving origin display, the ship
moves across the display until it reaches
a pre-defined distance from the edge of
the screen, at which point it then jumps
to an initial starting position. Before the
advent of ARPAs, these display modes
were reasonably named; now they
should only be considered to be a name
for whether the ship remains in a fixed
position on the radar display, or whether
it moves across the screen.
Parallel Indexing (PI): On a rela- Fig. 7. The use of radar
tive motion display, the PI line will for Parallel Indexing
remain static. On a true motion display, Source: Author’s own research.
the PI line moves across the display with the same motion as the ship. Although
24 Scientific Journal of Gdynia Maritime University, No. 113, March 2020
Practical Aspects of Using Radar in Maritime Navigation
with Analysis of its Potential Errors and Limitations
normally used in a north up configuration, PI can be used in any orientation mode
(Fig. 7).
Target vectors in true motion or relative motion mode can be either true or
relative, and therefore the displayed vectors do not change their reference when
changing between display modes. On a radar screen, we can also select a sea-
stabilised display or a ground-stabilised display.
Sea stabilisation shows the ship’s course and speed through the water, and no
allowance is made for water flow (tide stream & current).
Ground stabilisation shows the ship’s course and speed over the ground,
where allowance is made for the tide stream and current.
Fig. 8. The same navigational situation presented on radar screens set north-up,
with a ship heading of HDG=045°, where target TGT1 generated a potential risk
of collision (small CPA) and a Trial Manoeuvre of a 45° alteration to starboard
is presented on radar screens set on True Motion with Relative Vectors (A, C),
and True Motion with True Vectors (B, D)
Source: Author’s own research.
In Figure 8, we can compare the same navigational situation presented on radar
screens set north-up, with a ship heading of HDG = 045°, where target TGT1,
generated a potential risk of collision (small CPA). The radar mode has been set on
true motion with relative vectors (Fig. 8A), and true motion with the true vectors
(Fig. 8B). In addition, Figure 8 presents the trial manoeuvre effect of a 45°
alteration to starboard on radar screens set on true motion the relative vectors (Fig.
8C), and true motion with true vectors (Fig. 8D).
Figure 9 shows a comparison between a ship water track, a ground track, the
sea-stabilised true vector, and a ground-stabilised true vector. In Figure 10, one can
observe how to use the radar to plan a maneuver with the ship course and speed
when considering the declared safe distance of passing, and the time necessary to
carry out the anti-collision maneuver. When we use radar for the CPA and TCPA
calculations, it is recommended that all target ranges and bearings are plotted at
equal time intervals, i.e. every 6 minutes. There is also a recommendation to use
a radar with ARPA, AIS and ECDIS integrated together [Weintrit 2009; Rutkowski
2019]. If the input into the ARPA is our own vessel course and speed through the
Scientific Journal of Gdynia Maritime University, No. 113, March 2020 25
Grzegorz Rutkowski
water, the target outputs, both alphanumerical and vectors, are the course and speed
through the water.
If the input into the ARPA is our own vessel’s course and the speed over the
ground, the targets outputs are the course and speed over the ground. Input errors in
ARPA can be the heading, speed, or both. A speed input error and/or course input
error changes the output of the target true course and speed. An error in speed input
produces a large error in the course output and a small error in the speed output. An
error in the course input produces a large error in the speed output and a small error
in the course output. However, the relative motion and CPA will always be correct.
Fig. 9. Comparison of the water track (sea stabilised true vector)
and ground track (ground stabilised true vector)
Source: Author’s own research.
We must also remember that according to the Maritime and Coastguard
Agency (MCA) recommendation MGN63, sea-stabilised displays should be used
on radar for anti-collision, as the operator is able to get an accurate focus on the
target, i.e. they know the target’s heading. Ground stabilised displays should
NOT be used for any anti-collision work, only for pilotage and navigation [MCA
2007; Rutkowski 2019]. Nowadays, modern radars give us unparalleled choice of
configurations [Bilden and Norris 2008; Brunicardi 2012]. Automatic clutter
suppression mode, even when close to land, totally eliminates the need to adjust the
radar gain as the operator changes the range or pulse length [The American
Practical Navigator Bowditch 2002].
26 Scientific Journal of Gdynia Maritime University, No. 113, March 2020
Practical Aspects of Using Radar in Maritime Navigation
with Analysis of its Potential Errors and Limitations
The operator is left free to concentrate on the important navigation activities
without the distraction of optimising the marine radar settings [Brunicardi 2012].
As you gain experience, you will become comfortable with your own radar set-up
with regard to the display modes, etc. When selecting an operating range, one shall
bear in mind the visibility and closure speed with other vessels. If off-centred too
far, there is a risk of missing fast targets approaching from astern [Rutkowski
2019].
Fig. 10. The use of Radar for planning a maneuver with our own ship course
and speed when considering the declared safe distance of passing
and the time necessary to carry out the anti-collision maneuver
Source: Author’s own research.
4. CONCLUSION
The officer of the watch (OOW) is responsible for checking the operating status of
each navigational radar. They shall also know how to set up the radar, how to
determine the radar blind sectors, how to calculate the radar position accuracy, how
to generate a basic anti-collision radar report, calculate CPA, TCA, BCR, BCT, etc.
In the case of errors and/or disturbances in the operation of the radar or other
navigation devices, the captain of the ship should be immediately informed and an
appropriate record should be made in the ship’s log.
According to good seamanship principles, it is also recommended that every
navigational officer is requested to check frequently on each watch radar’s
performance (performance monitor), the radar working mode, radar configuration,
Scientific Journal of Gdynia Maritime University, No. 113, March 2020 27
Grzegorz Rutkowski
heading marker, heading marker alignment, VRM against fixed range rings, EBL
against visual bearings, etc. In fact, these activities are not always known or
properly understood, resulting in numerous observations made during maritime
inspections. This paper has been prepared as a short guide for OOWs about the
basic principles of practical focus of mariner’s radar usage in real waterways.
REFERENCES
Bilden A.V., Norris A., 2008, RADAR and AIS, The Nautical Institute, London, UK.
Brunicardi D., 2012, Radar and AIS for Watchkeeping Officers, Brown, Son & Ferguson Ltd.
Nautical Printers, Glasgow, Scotland.
COLREG, 1972, International Rules and Regulation for Prevention of Collisions at Sea.
IMO Resolutions for ‘Performance Standards For Automatic Radar Plotting Aids (ARPAs)’, 2004,
Res. A.422 (XI) adopted on Nov.1979, Res. A.823(19) adopted on Nov. 1995) and IMO Res.
MSC 192(79) Annex 34 ‘Adoption of The Revised Performance Standards for Radar
Equipment’, December.
IMO SN/Circ.243, 2004, Guidelines for the presentation of navigation-related symbols, terms and
abbreviations, December.
Maersk Line Internal Documentation, 2018, Safety Management System (SMS) Including Ship
Handling (8.02.01) and Ship Manoeuvrability (L203-L210) for E-class Container Vessel Emma
Maersk, http://www.ships-info.info/mer-emma-maersk.htm, December.
MCA, 2007, The Maritime and Coastguard Agency (MGN 324 (M+F), Operational Guidance on the
Use of VHF Radio and Automatic Identification System (AIS) at Sea, July 2006 and MCA MGN
63 (M+F) Merchant Shipping Notice 1158 ‘Use of Electronic Aids to Navigation’, May.
Rutkowski, G., 2018, ECDIS Limitations, Data Reliability, Alarm Management and Safety Settings
Recommended for Passage Planning and Route Monitoring on VLCC Tankers, TransNav, The
International Journal on Marine Navigation and Safety of Sea Transportation, vol. 12, no. 3,
pp. 483–490.
Rutkowski, G., 2019, Voyage Planning, Seafarers’ Competencies and Watchkeeping Procedures in
the Restricted Sea Areas, in the Narrow Channels and Sharp Bend Fairways, LAP Lambert
Academic Publishing, Schaltungsdientst Lange o.H.G., European Union OmniScriptum
Publishing Group, Berlin, Germany.
SOLAS, 2019, International Convention for the Safety of Life at Sea, http://www.imo.org/, December
2019.
STCW, 2010, Manila Amendments, 2017, IMO, http://www.imo.org/, December 2019.
Teekay Shipping SA, 2019, Internal Safety Management System (SMS) and Navigational Procedure,
February 2019.
The American Practical Navigator Bowditch, 2002, No. 9, National Imagery and Mapping Agency,
Washington, USA.
VIQ Vessel Inspection Questionnaires for the Oil Tankers, 2017, Combination Carriers, Shuttle
Tankers, Chemical Tankers and Gas Carriers, Oil Companies International Marine Forum
(OCIMF).
Weintrit, A., 2009, The Electronic Chart Display and Information System (ECDIS). An Operational
Handbook, A Balkema Book, CRC Press, Taylor & Francis Group, London, UK.
Wróbel, F., 2019, Vademecum for Watch Officer, Trademar Publisher, Gdansk, Poland.
28 Scientific Journal of Gdynia Maritime University, No. 113, March 2020
