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1 INTRODUCTION
According to ITU Radio Regulations (such as RR
5.328A and RR 5.329) there are four main bands
dedicated to the Radio Navigation Satellite Service
(RNSS), in which the GNSS constellations operate.
These bands include:
1. 1559 – 1610 MHz used by the main navigation
signals of GPS (L1), GLONASS (G1), Galileo (E1)
and BeiDou (B1).
2. 1215 – 1254 MHz for second signals of GPS (L2) and
GLONASS (G2) used for high-accuracy positioning.
3. The 1164 –1214 MHz band is used for safety-of-life
signals, including GPS (L5), Galileo (E5), GLONASS
(G3), and BeiDou (B2) frequencies.
4. 1260 – 1300 MHz used by Galileo (E6) and BeiDou
(B3) for commercial uses and an increase in the
accuracy of position.
The above-listed signals are base signal bands to
accommodate essential navigational signals by all
presently used GNSS constellations. There is several
positioning systems with worldwide coverage
available to determine the ship’s geographical position,
and they operate within these bands. Despite this most
ships are carrying only GPS or dual-system receivers.
Modern Navigation Challenges – Case Study Based
on Students’ Practices on r/v Horyzont II in the Gulf
of Gdańsk
A. Kerbrat & J. Pietraszkiwicz
Gdynia Maritime University, Gdynia, Poland
ABSTRACT: GPS signal jamming and spoofing have been known for decades, yet an increasing number of
electronic devices rely heavily on GPS positioning. In recent years, this issue has been experienced firsthand in
Poland and on Polish Territorial Waters, but in some other parts of the world, the problem has been known for
much longer. Several alternative global range positioning systems have been developed, but none are as
commonly used as GPS. Most ships navigating international waters are equipped only with GPS/DGPS receivers
and do not carry receivers for other positioning systems. It is crucial to ensure that young navigators are
appropriately trained in the navigation process using sources of position other than GPS, especially in crowded
territorial waters and port approaches.
Each year, the research vessel “Horyzont II” takes groups of students from the Maritime University in Gdynia on
board for a few weeks of practice in manoeuvring, navigation, and radar operation. Students have the
opportunity to apply their theoretical knowledge gained over 2,5 years of study. Under the supervision of the
ship’s crew and teachers, they perform duties as officers, helmsmen, lookouts, radar and ECDIS operators. They
also learn about daily vessel operations and participate in maintenance tasks. This article aims to present
examples of GPS signal issues encountered during this year's training in the Gulf of Gdansk, their impact on
equipment, the students' reactions, and their capacity to carry out efficient and safe navigation under these
specific circumstances.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 19
Number 4
December 2025
DOI: 10.12716/1001.19.04.12
1160
Multi-systems receivers are still relatively rare in the
maritime domain.
GPS is a well-known, established by the United
States system that has been operational since the 1980s.
It operates with 31 satellites in Medium Earth Orbit
(MEO). For civilian purposes, the L1 band is utilised at
1575.42 MHz; the L2 and L5 bands are reserved for
military use and accessible only to authorised users.
GLONASS uses a 1602 MHz frequency in the L1
band for civilian use and a 1246 MHz frequency in the
L2 band for military use. Due to its FDMA (Frequency-
Division Multiple Access) structure, individual
satellites transmit on slightly different frequencies
within the same band. The L2C signal, transmitted in
the L2 band, offers improved performance for civilian
applications compared with standard L1 signals.
GALILEO operates in bands E1 (1575.42 MHz), E5a
(1176.45 MHz), E5b (1207.14 MHz) and E6 (1278.75
MHz). Galileo satellites transmit signals
simultaneously on multiple frequencies, allowing the
receiver to select the best signal. Multi-frequency signal
transmission enables improved ionospheric error
mitigation and enhances position accuracy and
integrity. Each band includes a civilian navigation
signal, whereas E1 and E6 additionally support
restricted-access or commercial services.
BeiDou Navigation Satellite System (BDS)
developed by China; the third-generation satellites
were launched into orbit by 2020. The system provides
a global range by transmitting navigational and timing
information to BeiDou receivers with an accuracy of
approx.10m. It uses 3 main frequencies: B1 (1561,098
MHz), B2 (1207,14 MHz) and B3 (1268,52 MHz).
Civilian signals are transmitted on multiple
frequencies simultaneously, facilitating the mitigation
of propagation-related errors. Military signals are
mainly broadcast in the B1 band, while the B2 and B3
bands support high-accuracy navigation.
Figure 1. Research vessel “Horyzont II”.
The training-research vessel “Horyzont II” was
built in 2000. Every year, she makes two voyages to
Spitzbergen with supplies and a science crew for the
Polish research station. For the other 8 months, she sails
with students from the Gdynia Maritime University
and some of the maritime high schools in Poland. RV
“Horyzont II” has a length of 56.34 meters, a breadth of
11.36 meters and a maximum draft of 5.33 meters. Her
maximum speed is 12 knots. The vessel accommodates
up to 40 passengers (students/scientists). Students of
the Faculty of Navigation typically complete their
onboard training during their third year of studies,
from February to April. Given the time of year, weather
conditions vary and may include light icing, fog,
stormy with a lot of precipitation. Its specific
construction, based on “Polarex” plans, gives the ship
unique manoeuvring properties. In Figure 1, a general
overview of the RV “Horyzont II” is shown. Visible are
the features of the hull, such as a high freeboard and a
navigational bridge located in the forward part of the
vessel. The ship is equipped with a bow thruster and a
pitch propeller improving manoeuvrability.
Figure 2. Navigational Bridge of the research vessel
“Horyzont II”.
The navigational bridge of “Horyzont II” has been
adapted to support training activities. Besides all
regulatory equipment demanded by SOLAS it is
equipped with additional navigational equipment
available to students. In Figure 2 the general
arrangement of the bridge is visible, out of the picture
are four students' navigational tables. Two of them are
equipped with two Furuno X-band radar displays
operating in a master-slave configuration. They use an
antenna separate from the two main ships’ radars. This
allows students to use them freely without interrupting
the safety of navigation or the general work of
navigating officers. At these two stations, two
independent GPS receivers are also available (JRC and
Furuno). The third station is equipped with a repeater
of the electronic chart (ECDIS) station NaviSailor 4000.
Functions that cannot be accessed in there can be used
by students on the master station under the
supervision of the duty officer. It is worth mentioning
that the “Horyzont II” ECDIS serves as an aid to
navigation, and the ship is required to carry paper
charts as the primary means of navigation. The fourth
workstation is dedicated to paper charts navigation
and performing all other required actions, such as
making corrections to paper charts and completing the
necessary logbooks.
2 PRACTICES AND THIS YEAR’S (2025)
CHALLENGES
Due to the limited duration and specific nature of the
training programme, navigation and practical exercises
were conducted exclusively in the western part of the
Gulf of Gdańsk. The vessel operated within the
fairways of the Gulf of Gdansk VTS or in adjacent areas
while performing tasks with students. During the two
weeks of practice, the vessel enters the port, proceeds
underway, anchors, and performs manoeuvring
exercises based on the track prepared specially for that
purpose in the ECDIS system. All these operations
were executed by the students under the close
supervision of duty officers and the master.
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Figure 3. Fragment of navigational chart BHMW 73 with area
of operating for R/V “Horyzont II”.
In Figure 3, the area of operation for R/V “Horyzont
II” is visible. The vessel, depending on weather
conditions and the day's plan, sailed along fairways
from Gdynia to the Hel Peninsula (visible in the upper
part of the chart), then crossed to the traffic separation
scheme of the port of Gdansk’s approach and returned
to the port of Gdynia or its anchorage. Most of the
manoeuvring exercises, such as person overboard,
were performed between the main fairways or south of
Gdynia anchorage. During the two weeks of practice,
increased activity of navy vessels in the area was
observed. This required careful planning and
execution of the exercises, as well as increased radio
watch for possible communication. Over the two
weeks of practice, training groups experienced GPS
spoofing and jamming events, navigation in reduced
visibility with and without access to GNSS-derived
positions. When GPS signals were unavailable,
students were instructed to rely on terrestrial
navigation techniques and radar observations.
Total of 34 students were divided into three watch
groups. Everyday group of 8-9 students maintained a
four-hour navigational bridge watch taking shifts
through the day and additional duties when they were
off-duty. There were eight students on the bridge when
the ship was underway, and two students when it was
at anchor. Students not assigned to bridge duty could
always come and observe, ask questions or learn in
their off time.
The training program under my supervision, as an
instructor on board the ship, was conducted from 3 to
16 March 2025. 34 third-year students from the
Navigation Faculty of Gdynia Maritime University
were mustered on r/v “Horyzont II”. The vessel
remained at sea almost every day, entering port every
few days for an overnight stay. Nights spent outside
port were conducted at anchor in the Gdynia
anchorage area.
2.1 GPS jamming event on 8th of March 2025 during
navigation in reduced visibility
On 8 March, the vessel departed the Gdynia anchorage
at approximately 08:00, proceeding along the planned
route within the Gulf of Gdańsk traffic lanes. The
weather conditions on that day were fair, with light
wind and visibility reduced to about 1,5 to 2,5 nautical
miles at times. Traffic in the area was light, and the seas
were calm. Nine assigned students, the Officer of the
Watch (OOW), and the onboard instructor were
present on the bridge.
Around 10.00 AM local time, the first anomalies in
the GPS data were observed. At that moment,
“Horyzont II” was passing “GD” (54 32,1’N
018 39,8’E) on port side buoy located at the junction of
TSS. The attention of the instructor and OOW was
drawn to a significant discrepancy between the vessel’s
water-referenced vector (log speed and heading) and
the ground-referenced vector provided by GPS. These
discrepancies were recorded and are presented in
Figures 4a and 4b. As visible, the data received from
the ship’s log were significantly different from the data
received from the GPS.
Figure 4a & b. Radar image (a) and ECDIS display (b)
recorded on 8 of March 2025 during GPS signal disruption.
During this period, students were primarily
focused on maintaining the planned route within the
TSS using the ECDIS. They did not initially recognize
the inconsistencies in the positional data until the
instructor and OOW pointed them out. After
informing the students that GPS receivers would be
disabled temporarily, noticeable confusion emerged,
accompanied by questions regarding how to proceed
without GPS-derived positions.
Following several minutes of clarification and brief
instructions, the situation on the bridge stabilized.
Students were reminded that GPS and ECDIS are not
the only navigational tools available and that
alternative methods—such as visual coastal references,
navigation marks, and radar observations—remain
fully effective when GNSS positioning is unavailable.
Once these methods were implemented, the remainder
of the watch proceeded correctly, despite the GPS
signal not returning to nominal values.
Figure 5. L1-band signal spectrum recorded on 8 March 2025.
Receiver: GDYNIA (Trimble BD992), Antenna: Zephyr
Geodetic 3
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Figure 5 shows the L1-band signal spectrum
recorded on the day of the event. The Z-axis represents
signal strength, while the X and Y axes represent signal
age and frequency. Standard received GPS signal levels
typically range from 30 to 40 dB. The observed values
significantly exceeded this range, clearly indicating the
presence of intentional interference (jamming).
2.2 GPS signal interference on 15th of March 2025
A similar phenomenon to that observed on 8 March
occurred one week later, on 15 March. Figure 6
presents the signal-to-noise ratio (SNR) for the
different GNSS constellations. The colours represent
the following systems: blue – GPS, black – GLONASS,
red – Galileo, and green – BeiDou. Typical SNR values
range between 40 and 50 dBHz. When the SNR drops
below 40 dBHz, receivers begin to experience
difficulties in computing a position and may
eventually lose the ability to provide a fix. As shown in
the figure, the interference caused a significant
reduction in SNR across all satellite systems, clearly
indicating broadband jamming within the L1 band
rather than interference affecting a single frequency.
Figure 6. Signal-to-noise ratio for selected GNSS
constellations on 15 March 2025. Receiver: GDYNIA (Trimble
BD992), Antenna: Zephyr Geodetic 3.
Figure 7. L1-band frequency spectrum of GNSS signals on 15
March 2025. Receiver: GDYNIA (Trimble BD992), Antenna:
Zephyr Geodetic 3.
Figure 7 shows the L1-band signal spectrum
recorded on the day of the event. The Z-axis represents
signal strength, while the X and Y axes represent signal
age and frequency. It shows very variable strength of
the signal recorded on that day.
Because a different group of students was on bridge
duty that day, a pattern similar to the 8 March event
was observed. The students initially displayed
uncertainty in interpreting the situation and
determining the appropriate course of action. With
guidance from the OOW and the instructor, they
resumed effective navigation using radar and visual
observations of navigational marks and coastal
features — techniques fully independent of GPS
availability.
2.3 Position monitoring while at anchor
The situation presented occurred on one of the
mornings when the GPS receivers and the ECDIS
system were properly functioning and providing
stable position information.
Figure 8. Positions marked by students in ECDIS while at
anchor with a properly working GPS.
Figure 8 presents a comparison between positions
obtained from the GPS system (upper section of the
display) and those plotted by students based on radar
measurements (lower section). The discrepancy
between these two sets of positions was significant and
exceeded the expected measurement uncertainty
associated with radar fixes and manual plotting.
A post-watch analysis revealed that the students
responsible for determining the radar-derived
positions committed procedural errors. These errors
concerned two principal aspects:
1. Incorrect transfer of radar data into the ECDIS
system — in several cases, distances and bearings to
radar targets were entered with rounding errors or
incorrect values, resulting in a shifted plotted
position.
2. Improper use of ECDIS plotting tools — instances
were identified in which students incor-rectly
determined the intersection point of lines of
position or failed to apply the standard procedure
for verifying consistency with the previous fix.
As a result, the radar-based positions deviated from
the true vessel position in a systematic rather than
random manner, indicating a methodological error
rather than any technical limitation of the radar.
From a navigational safety perspective, such a
discrepancy is significant. It may lead to incorrect
assessment of the vessel’s movement while at anchor—
an especially critical issue in restricted visibility, where
radar constitutes one of the primary sources of
situational awareness.
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The incident also highlighted an important training
aspect. Students demonstrated a high level of reliance
on ECDIS and GNSS-derived positions, whereas
accurate and systematic radar plotting required greater
attention and procedural discipline. This observation is
consistent with trends noted in previous years,
suggesting a gradual decline in proficiency in
terrestrial navigation and manual position fixing
within an increasingly sensor-dependent navigational
environment.
In summary, the event demonstrates that even
when GPS signals are fully available and ECDIS is
operating correctly, procedural errors may result in
substantial discrepancies in position determination.
This underscores the need for continued development
of manual navigational skills and a critical approach to
sensor data among future watchkeeping officers.
3 CONCLUSIONS
Although electronic positioning systems have served
as reliable navigational tools for many years,
observations from the training cruise demonstrate that
they remain vulnerable to electromagnetic interference
as well as human error. The absence of a continuous
and accurate position source increases the risk of
navigational incidents, particularly in areas with dense
traffic or during precision manoeuvring. Importantly,
GNSS disruptions often occur in waters where effective
radar and visual observations are fully feasible and
where the ship’s position can be determined accurately
using terrestrial methods. Nevertheless, modern
electronic systems tend to overshadow the importance
of these fundamental navigational principles.
From an educational perspective, a clear tendency
can be observed among students to rely primarily on
electronic chart systems as their main source of
situational awareness, while alternative sources—
visual observation, radar, and terrestrial navigation—
are frequently disregarded. Students also rely heavily
on AIS for information regarding the movement of
other vessels and their own motion, without cross-
checking these data against sources independent of
GNSS. Consequently, when their primary positioning
system fails, students and future watchkeeping officers
often exhibit confusion, hesitation, and delays in taking
appropriate action. Limited proficiency in radar
operation, paper-chart navigation, and the use of dead-
reckoning modes in ECDIS further exacerbates this
problem, as additional time is required to regain
situational awareness. Such delays may be critical
when attempting to avoid collision or grounding.
This highlights a significant challenge for
educational and regulatory institutions: to train
students not only in the efficient use of electronic
navigational tools but also in the critical understanding
of their limitations. As noted in several international
studies and guidelines (e.g., IMO e-Navigation
Strategy Implementation Plan, IALA VTS Manual,
IHO S-66, UKHO reports on GNSS vulnerability, ICAO
PBN guidance, RTCM papers on interference),
contemporary navigators must maintain competence
in traditional navigation techniques and be able to
operate safely in environments where GNSS
information is degraded or unavailable. The increasing
ease of access to electronic data fosters overreliance on
sensors and automation, often without adequate
verification or cross-checking. Developing manual
navigation skills and strengthening critical assessment
of sensor-derived data should therefore remain
essential components of training for future
watchkeeping officers.
ACKNOWLEDGEMENTS
This study was funded by the Gdynia Maritime University,
under the research project: WN/2025/PZ/06.
REFERENCES
[1] Gdynia Maritime University, source online:
https://umg.edu.pl/armator/horyzont-II
[2] IMO, COLREG – Convention on the International
regulations for Preventing Collisions at Sea, 1972; London
2003
[3] IMO, STCW Convention and STCW Code, Chapter III and
VIII, London 1018
[4] Source on-line: ITU Radio Regulations, edition 2024,
Vol.1, Article 5, Rule 328A and 329 and excerpts for bands
allocations.
[5] http://en.beidou.gov.cn; source on-line, access 5.05.2025
[6] https://www.gps.gov ; source on-line, access 5.05.2025
[7] https://defence-industry-space.ec.europa.eu/eu-
space/galileo-satellite-navigation_en; source online,
access 5.05.2025
[8] https://gisplay.pl/nawigacja-satelitarna/glonass.html;
source on-line access 5.05.2025
