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1 INTRODUCTION

In the maritime domain, VHF radiocommunication

plays a pivotal role in ensuring navigational safety,

ship manoeuvring, and operational coordination at

sea. The STCW Convention 1978, as amended in 2010,

explicitly requires deck officers and seafarers to

demonstrate proficiency in the use of VHF equipment,

including channel configuration, execution of routine,

urgency, and distress communication procedures,

application of IMO Standard Marine Communication

Phrases (SMCP), and strict compliance with

international radio discipline [1–4]. However, in

practical training contexts, both the delivery and, more

critically, the assessment of VHF communication

competence continue to face significant limitations.

Conventional training approaches based on physical

equipment are often constrained by limited device

availability, high maintenance costs, difficulties in

organizing simultaneous practice for large classes, and

the inability to realistically reproduce complex

emergency scenarios.

The rapid development of simulation platforms and

virtual reality technologies has created new

opportunities to enhance maritime training by

enabling high-fidelity reproduction of device

operation, communication procedures, and bridge

Objective Assessment of Maritime VHF Communication

Competence Using a Real-Time Simulation Framework

X.L. Nguyen, V.C. Do & M.C. Nguyen

Vietnam Maritime University, Haiphong, Vietnam

ABSTRACT: VHF radiotelephony remains a fundamental component of maritime safety and is mandated by the

STCW Convention as an essential operational competency for seaferer. However, existing studies largely focus

on basic button-level interaction and rarely incorporate real-time voice transmission, multi-user communication,

or standardized performance assessment. This study introduces a simulation system for the Sailor SP3520

portable VHF radio developed in Unity, integrating real-time voice exchange through the UDP protocol

combined with Photon Voice. The framework accurately reproduces half-duplex behaviour, communication

latency, channel switching, scanning modes, power settings, and Push-to-Talk operations, while supporting

STCW/SMCP-based training scenarios. A multi-dimensional competency assessment rubric was designed to

evaluate learner performance in technical operation, phraseology, situational awareness, and radio discipline. A

pilot study involving second- and third-year students demonstrates clear cohort-based performance

differentiation, consistent error reduction patterns, and procedural compliance trends aligned with training

progression. The core contribution is a multi-dimensional performance assessment framework that combines

system-logged interaction data with a structured rubric to quantify technical accuracy, channel selection errors,

Push-to-Talk misuse, and teamwork-related radio discipline. The findings confirm the potential of Unity-based

VHF simulation as a reliable tool for STCW-compliant training and highlight its applicability for multi-user and

remote learning environments in the digital transformation of maritime education.

http://www.transnav.eu

the International Journal

on Marine Navigation

and Safety of Sea Transportation

Volume 20

Number 2

June 2026

DOI: 10.12716/1001.20.02.22

486

environments. Nevertheless, a review of existing

studies indicates that most VHF simulations primarily

focus on interface replication and basic operational

interaction, while failing to adequately model key

characteristics of radio communication such as half-

duplex behaviour, transmission latency, signal

attenuation, or environmental interference—factors

that directly influence communication behaviour and

radio discipline in real-world operations [5]. In

addition, real-time multi-user simulation capabilities—

essential for STCW scenarios such as routine calls,

distress communication, and coordinated SAR

operations—remain limited, thereby restricting the

training and assessment of teamwork and coordinated

communication skills [6].

A further critical gap lies in the pedagogical

assessment dimension. Although real-time

communication technologies such as UDP and

broadband satellite networks (e.g., Starlink) are

increasingly adopted in maritime operations [7–10],

existing VHF simulations rarely exploit interaction

data generated during training to support objective

competency assessment. Most studies remain confined

to 3D device modelling or rely on learner perception-

based evaluation [11], whereas data-driven assessment

approaches—such as interaction logging, error

analysis, and response-time measurement—have been

applied primarily to other maritime simulation

domains, including bridge operations, engine-room

training, and ECDIS systems [12–14], but not to VHF

communication training.

Addressing this gap, the present study does not

approach VHF simulation merely as a technical artefact

but positions its scientific contribution in the

development of a data-driven assessment framework

for maritime VHF communication aligned with STCW

requirements. Specifically, a logging-based assessment

framework is proposed, integrating indicators that

capture procedural compliance, radio discipline, and

teamwork capability within a half-duplex

communication environment. A handheld Sailor

SP3520 VHF simulation is employed as an

experimental platform, in which real-time voice

transmission is implemented using the UDP protocol

combined with Photon Voice to accurately reproduce

essential VHF communication characteristics [15–17].

Building on this foundation, the study introduces a

Procedural Compliance Index (PCI)—a composite

metric derived from key technical and behavioural

criteria—that transforms raw interaction data into

pedagogically meaningful performance indicators. The

framework is validated through a pilot study involving

maritime students at different stages of training to

examine its ability to discriminate competency levels

and reflect skill development over the training

progression. Through this approach, the study

contributes a novel methodology for simulation-based

assessment of VHF communication competence,

supporting large-scale training, objective evaluation,

and flexible deployment in both classroom-based and

remote STCW-compliant maritime education contexts.

2 METHODS

2.1 Instructional Design Framework

2.1.1 Training Needs Analysis (Analysis – ADDIE)

The Analysis phase of the ADDIE instructional

design model [18] serves as the foundation for

identifying the specific training requirements

mandated by the STCW Convention and the

competencies that learners must acquire when

operating VHF radiotelephone equipment. A review of

the GMDSS training syllabus indicates that trainees are

required to master distress, urgency, safety, and

routine communication procedures; select the correct

working channels; understand the operational logic of

half-duplex communication; and comply with

standard Push-to-Talk (PTT) discipline.

However, observations conducted at maritime

academies reveal several persistent limitations in

conventional training environments. The number of

physical VHF units is often limited when multiple

student groups conduct practical training

simultaneously. In addition, maintenance costs are

high, emergency scenarios are difficult to replicate

realistically, and traditional setups do not allow

multiple learners to practice simultaneously in a real-

time communication setting.

A needs assessment further shows that learners

require a simulation environment capable of

reproducing authentic device behaviour, including

interface layout, audio characteristics, transmission

delays, and operational reactions of actual VHF

equipment. Training centres also express a strong

demand for an integrated logging system that records

learner actions, tracks performance development, and

supports objective competency assessment.

These requirements establish the basis for

designing a simulation system that fulfills three

essential criteria: high operational fidelity, pedagogical

alignment with maritime training standards, and

scalability for multi-user and remote training

scenarios.

2.1.2 Lesson Design and STCW-Based Training

Scenarios

The lesson design for the VHF simulation is

structured around the competency requirements

stipulated in STCW Section A-IV/2 and the IMO

Standard Marine Communication Phrases (SMCP)

[19]. Training scenarios are organised progressively—

from basic operations to advanced communication

tasks—to ensure that learners not only master

equipment handling but also perform radiotelephony

procedures in full compliance with international

maritime standards.

The simulation incorporates a complete set of

physical functions of a handheld VHF unit within a 3D

virtual environment, including power control, volume

and brightness adjustment, transmitter power

selection, keypad locking, channel switching, channel

scanning, and Push-to-Talk (PTT) operation. Each

button and rotary knob is animated with high-fidelity

movement, enabling users to experience equipment

interaction that closely resembles real-world handling.

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Building upon these functions, training scenarios

are developed in accordance with SMCP, covering

routine communication, urgency and distress

procedures, vessel manoeuvring exchanges, pilotage

requests, and watchkeeping communication. In each

scenario, trainees are required to follow prescribed

steps: select the appropriate working or distress

channel (e.g., Channel 16), verify equipment readiness,

apply correct half-duplex discipline when using PTT,

and deliver SMCP phrases accurately and concisely.

The system automatically records user actions,

response times, channel-selection errors, and phrase

inaccuracies, forming a robust data-driven foundation

for standardised competency assessment under STCW.

2.1.3 Development of the Competency-Based Assessment

Rubric

To ensure alignment with STCW training

requirements and to enable a systematic evaluation of

operational proficiency in realistic maritime contexts,

this study developed a multidimensional competency-

based assessment rubric specifically tailored for VHF

communication training. The rubric was designed on

three complementary foundations: the minimum

operational competencies prescribed in STCW Section

A-IV/2, the standardized communication procedures

defined in the IMO Standard Marine Communication

Phrases (SMCP), and empirically observable

performance behaviours captured within the 3D

simulation environment.

The assessment framework encompasses four

interrelated competency domains. Technical operation

proficiency reflects the trainee’s ability to handle the

handheld VHF radio accurately, covering actions such

as powering the device, adjusting audio and display

settings, operating the Push-to-Talk (PTT) function,

selecting and scanning channels, locking the keypad,

and configuring transmission power. Evaluation

focuses on operational precision, frequency of

handling errors, task completion efficiency, and

conformity with the functional behaviour of an actual

Sailor SP3520 unit. SMCP-based communication

proficiency evaluates the correct application of

standardized maritime phraseology, including the

execution of distress, urgency, and safety procedures,

proper call initiation and termination, compliance with

half-duplex conventions, and clarity and conciseness of

message delivery. Situational awareness capability

captures the trainee’s judgment in selecting

appropriate channels under varying operational

conditions, responsiveness during emergency

scenarios, and adaptability to simulated interference or

range limitations. Finally, PTT discipline and

collaborative communication assess adherence to half-

duplex operating rules and the ability to coordinate

orderly information exchange in multi-user

communication scenarios.

Each competency domain is evaluated using a five-

level Likert scale [20], complemented by automatic

telemetry data generated by the simulator, including

PTT activation duration, channel-switching events,

and button-press error counts. By integrating rubric-

based scoring with system-logged interaction data, the

proposed framework enables objective, consistent, and

scalable assessment of both individual performance

and skill progression across STCW-aligned VHF

training scenarios.

2.2 Key techniques for simulating the Sailor 3520 VHF

equipment

2.2.1 Create a simulated environment scene

To ensure that the simulation delivers a high level

of immersion and operational realism, the

configuration of the virtual environment is a decisive

step. The fidelity of the scene—shaped through

calibrated lighting, dynamic shadows, reflective

surfaces, and tailored visual effects—directly

influences how authentic the training space appears to

the user. Moreover, the spatial context in which the

VHF device is placed can be adapted to different

maritime training settings, such as a virtual navigation

bridge or a simulated classroom. This flexibility

enables trainees to experience the exercise as if they

were operating the equipment in an authentic

shipboard environment.

Figure 1. The practical classroom Scene

Figure 2. Ship Bridge Scene

Depending on the designer’s expertise and

familiarity with 3D modelling techniques, several

strategies may be employed to construct the simulation

environment. In practice, three core approaches are

most commonly adopted:

Top-down design method: In this approach, objects

are conceptualized starting from their most basic

geometric representations. Since many real-world

structures can be reduced to elementary shapes,

components in the virtual scene—such as walls,

consoles, or equipment surfaces—may initially be

formed using primitives like cubes, cylinders, or

spheres. Designers typically begin with simplified

volumes and progressively refine them. For more

sophisticated elements, multiple primitives may be

combined, intersected, or modified to obtain the final

form required for the simulation environment.

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Bottom-up design method: Contrary to the top-

down strategy, this method relies on detailed reference

images or orthographic projections of the target object

(e.g., front, side, or top views). This provides a high

degree of fidelity, as the 3D model is constructed

directly from accurate visual data and the designer’s

spatial interpretation. When comprehensive imagery is

available, the bottom-up technique enables the

reproduction of fine structural details; however, it is

generally more time-consuming and demands a higher

level of precision. Its use is therefore most appropriate

when the simulation requires exact replication of real-

world equipment or environments.

Hybrid design method: To effectively leverage the

advantages of both techniques, many simulation

projects apply a blended approach. This method allows

designers to model simple components using

geometric primitives while constructing complex or

critical elements using detailed visual references. By

combining analytical modelling with image-based

refinement, the hybrid strategy offers a balance

between development efficiency and technical

accuracy. As most maritime operational environments

include a mix of simple structures and intricate

equipment, this approach often yields the most

practical and realistic results within the overall 3D

simulation workflow.

2.2.2 Create 3D model of VHF

To construct a 3D representation of the VHF device,

two techniques may be employed: digitally capturing

the real unit through specialized 3D-scanning

applications, or generating the model manually using

professional 3D modelling tools. Within this study, the

second method was selected, making use of Autodesk

3ds Max. Initially, the design team captured

photographs of an actual VHF handset from three

distinct viewing angles. These reference images were

then utilized to recreate the device virtually inside 3ds

Max [21]. Image-editing software (such as Adobe

Photoshop) was subsequently applied to produce

realistic texture maps, which were layered onto the

model. Once completed, the model was exported in

FBX format—an industry-standard interchange file—

and later brought into Unity for integration within the

simulation framework.

Data acquisition for 3D model construction:

Reconstructing the VHF unit and its operational setting

begins with gathering detailed source material,

including still photographs, device schematics, and

environmental terrain information. High-resolution

images of the VHF transceiver are captured to ensure

visual fidelity, with the coverage area extending

beyond the immediate operational zone to establish a

more immersive virtual field of view. The 3D model is

generated through a semi-automated workflow in

which a high-resolution camera records both images

and video sequences from multiple orientations,

producing multi-angle visual data. The preliminary

output is a polygon-based wireframe mesh outlining

the geometry of the device. The most demanding stage

involves reproducing the various textured surfaces,

identification markings, labeling elements, and

achieving accurate color calibration. While most

components can be modeled with moderate

complexity, certain sections require higher-density

detail [22]. To optimize rendering performance, the

external surfaces of the VHF are photographed

extensively, including close-range shots from a high-

resolution camera. These photographs are then

processed into texture maps with precise perspective

alignment. The resulting textures are refined,

corrected, and digitally hand-painted for each

corresponding surface, as illustrated in Figure 3.

Simulation data construction: The structural data of

the simulation is derived from the collected visual

inputs, with raw photographs and video frames

converted into texture files specifically prepared for 3D

graphics workflows. These texture assets are

subsequently aligned according to perspective,

enhanced through editing, and manually refined

where necessary to ensure accuracy for each

designated surface area. After assembling the complete

set of texture resources, the spatial 3D environment of

the VHF device is constructed by combining individual

models and defining their hierarchical relationships.

Each component is created following the actual

dimensions, placement, and structural features of the

physical device. Once completed, the entire model and

its associated 3D scene are exported into categorized

formats optimized for real-time rendering, allowing

seamless integration and execution within the training

simulation.

Figure 3. Steps to simulate the VHF equipment

The final phase in producing the 3D model involves

ensuring that it can be rendered accurately and

efficiently on the intended hardware platform.

Although numerous 3D simulation engines are capable

of performing this task, Unity is particularly

appropriate for training-oriented applications due to

its extensive industry adoption, strong performance,

and free access for educational use. Regardless of the

platform selected, any simulation environment must

fulfil two essential functions: (1) rendering geometric

objects and (2) emulating their physical properties and

operational behaviours. In the present study, Unity is

combined with C# scripting to implement the

functional logic of the VHF device, enabling real-time

visualization and user interaction within the virtual

space [23].

Simulation refers to the digital reconstruction of

real objects, operational processes, or environmental

conditions—whether derived from physical systems or

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conceptual designs. A fully developed simulation

system contains all necessary information for users to

interact with a representative environment. Here, the

simulation serves as a visual and functional model that

reproduces the operational responses observed when

the Sailor SP3520 VHF device is used in reality. Since

the fidelity of graphical rendering is fundamental to

any VR-based system, high-quality visualization of

objects and surroundings is essential to creating a

believable interaction experience. With the capabilities

of modern rendering technologies, most visual features

of physical equipment can be convincingly duplicated,

supporting the development of advanced training

simulations and virtual reality applications. Figure 4

illustrates the resulting 3D model of the Sailor 3520

VHF device, with the upper view showing the base

mesh prior to texturing and the right-hand view

displaying the model after texture maps have been

applied.

Figure 4. Create 3D model of VHF

2.3 VR simulation of VHF Sailor 3520 equipment

2.3.1 User interface design

In Unity, the graphical interface can be developed

using either the User Interface (UI) framework or the

legacy Graphical User Interface (GUI) system. For this

study, the UI-based approach was selected to construct

all visual elements presented on the VHF display.

These elements include the active working channel,

channel mode indicators, scanning status for preset

channels, transmit-power level, battery status, keypad-

lock symbol, dual-watch operation, and other

functional icons, as shown in Figure 5.

The color presentation on the device screen is

generated using the RGB color model, with red applied

as the primary tone to emulate the visual

characteristics of the real Sailor SP3520 unit [24]. This

UI configuration ensures that the interface maintains

clarity, consistency, and readability during real-time

interaction within the simulation environment.

Figure 5. User interface of VHF

2.3.2 Simulate the functions of buttons

The functional behaviour of the buttons and rotary

knobs is reproduced by animating their movements

within the three-dimensional environment. Each

control element is assigned a specific interaction

pattern—for instance, turning the power/volume knob

to switch the VHF on or off, or rotating the brightness

knob to regulate the screen illumination. These virtual

controls allow the user to select channels, modify

operational settings, and execute adjustments required

during VHF operation.

The rotary knobs are programmed to rotate around

their respective axes, as illustrated in Figure 6. Their

motion follows the standard rotational kinematics for

an object turning about a fixed axis, expressed as:







(1)

where



denotes the mean angular velocity, 



represents the angular displacement, and t is the time

interval between states t1 and t2. This mathematical

model ensures that the simulated knob movement

reflects the mechanical behaviour of the physical Sailor

SP3520 device, thereby enhancing realism and

improving user familiarity with the real-world

equipment.

Figure 6. Knob rotation simulation

The vertical motion of the buttons is reproduced

using a position-based control mechanism. In the

released state, the button is rendered in the upper

position; when activated, it transitions to the lower

state while the upper element is hidden. This

interaction logic mirrors the physical depress-and-

release behaviour of the real VHF handset, enabling the

simulation to reproduce the tactile response and

operating characteristics of the actual equipment. The

visual and functional changes during the press action

are shown in Figure 7.

model

map

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Figure 7. Button press simulation

2.4 Setting up a call using UDP between two VHFs

2.4.1 UDP calling technique

The User Datagram Protocol (UDP) is one of the two

primary transport protocols in the TCP/IP architecture

and operates at the Transport Layer of the OSI model.

In contrast to the Transmission Control Protocol (TCP),

which requires a connection setup and continuous

state management, UDP functions in a connectionless

manner, transmitting datagrams with minimal delay

and low processing overhead. These characteristics

make UDP particularly suitable for applications that

demand real-time responsiveness, including Voice

over IP (VoIP), live media delivery, and networked

multiplayer interactions [25].

UDP transfers data as independent packets that do

not require acknowledgment from the receiving

endpoint. Each UDP segment includes an 8-byte

header composed of four fields: source port,

destination port, packet length, and checksum. Since

the protocol does not implement mechanisms for

congestion control, error recovery, or packet

sequencing, it allows rapid data delivery but may

experience packet loss or unordered arrival of

datagrams [26].

The key strengths of UDP lie in its transmission

efficiency, lightweight structure, and low system

overhead. Nonetheless, the lack of reliability features

renders it unsuitable for tasks demanding strict data

integrity, such as financial transactions or file transfers.

With the increasing adoption of high-bandwidth

satellite connectivity—such as Starlink—on modern

vessels, the application of UDP for simulating VHF

radio communication becomes not only feasible but

also aligned with current maritime digitalization

trends.

In the proposed VHF simulation system, voice

input captured from the user’s microphone is encoded

in real time (for example using Opus or PCM),

encapsulated into UDP datagrams, and transmitted

either through a Starlink link or a local area network

(LAN) [27]. At the receiving terminal, the packets are

reassembled, decoded, and played back to the user.

The low latency inherent in UDP supports highly

responsive audio interaction, enabling communication

behaviour that closely replicates the performance of a

physical VHF device. In addition, by leveraging

datagram-based socket communication, the system can

operate in multicast or peer-to-peer modes, thereby

supporting multi-participant training scenarios within

the same simulated communication environment.

2.4.2 Implementing VHF Voice Communication Using

Photon Voice 2

Within the portable VHF communication

simulation system designed for maritime training,

accurately reproducing real-time voice exchanges

between handheld units is a critical functional

requirement. To support this capability, the study

employs Photon Voice 2, a low-latency audio

transmission framework built on the Photon Realtime

architecture and operating over the UDP transport

protocol. Photon Voice 2 enables voice capture,

encoding, packetization, delivery, and playback

between clients with high responsiveness and robust

scalability—characteristics that make it suitable for

STCW-aligned training environments [28].

The operational logic underlying the simulation of

VHF voice communication using Photon Voice 2 is

designed to reproduce essential characteristics of real

maritime radiotelephony while enabling controlled

performance measurement, as illustrated in Figure 8.

Within the simulation environment, each virtual

handheld VHF device is represented as an

independent client in the Photon system and assigned

a unique identifier corresponding to a specific vessel or

radio unit in the training scenario. The learner’s

microphone serves as the audio input source, allowing

human voice signals to be transmitted through the

virtual device. When a call is initiated, Photon Voice

dynamically establishes a dedicated voice room that

conceptually corresponds to a VHF working channel,

such as Channel 16 or another designated frequency.

All clients tuned to the same channel are connected to

this shared room, ensuring channel-specific and

controlled communication.

The Push-to-Talk (PTT) mechanism is implemented

by directly coupling the virtual PTT control with the

activation of Photon Voice audio streaming, so that

voice transmission occurs exclusively while the PTT

input is engaged. This design faithfully reproduces the

half-duplex operating principle of maritime VHF

systems, in which only one user may transmit at a time.

Captured audio signals are encoded using low-latency

codecs (e.g., Opus) and transmitted via the UDP

protocol, minimizing delay and jitter and thereby

preserving the immediacy characteristic of operational

VHF communication. On the receiving side, audio

packets are decoded and rendered in real time through

the output device. Additional channel-management

logic may be applied to constrain audibility based on

channel selection, simulated radio range, or

interference conditions, allowing the simulation to

reflect practical communication limitations

encountered at sea while maintaining consistency with

STCW and SMCP communication practices.

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Figure 8. Call setup principle based on UDP method between

two VHFs

2.5 Assessment Framework

2.5.1 Action Logging

The logging system is embedded directly within

Unity and Photon to record all trainee interactions in

real time, including button-press counts, the sequence

of operations, knob-rotation duration, channel-

switching actions, PTT on/off events, and response

times. The data are stored with precise timestamps,

enabling detailed analysis of the trainee’s performance

and identification of recurrent operational errors.

Logging serves as a foundational component for

establishing quantitative assessment metrics and for

generating individualized progress profiles

throughout each training session.

2.5.2 Performance Indicators

The assessment framework is defined by four core

performance indicators designed to capture essential

operational and behavioural requirements of maritime

VHF communication training. Technical Accuracy

reflects the trainee’s ability to correctly operate the

VHF device, including powering the unit on and off,

adjusting controls, rotating knobs, selecting functions,

and executing required actions without operational

errors. This indicator is quantified as the proportion of

correctly completed tasks relative to the total number

of required actions, providing an objective measure of

device-handling proficiency.

Complementing this, the Channel Selection Error

Rate measures the frequency of incorrect channel-

related actions, such as misidentifying Channel 16,

selecting inappropriate working channels, or failing to

complete channel-switching sequences. This indicator

is calculated as the ratio of channel selection errors to

total selection attempts and serves as a proxy for

situational awareness and procedural consistency

during communication tasks.

The PTT Misuse Rate captures deviations from

proper Push-to-Talk behaviour, including excessive

key-holding, overlapping transmissions, and

violations of half-duplex discipline. This metric

directly reflects adherence to SMCP and STCW radio

communication conventions and constitutes a critical

indicator of radio discipline in time-sensitive scenarios.

Finally, Teamwork and Radio Discipline assesses

coordination among trainees during multi-user

simulations, focusing on turn-taking behaviour,

recognition of communication windows, and the

ability to maintain orderly exchanges in routine,

distress, and ship-to-ship communication scenarios.

This indicator is evaluated using a Likert-scale rubric

supplemented by system-logged interaction data.

Taken together, these indicators provide a

multidimensional representation of individual

operational competence and collaborative

communication behaviour, forming the basis for

computing overall performance scores within realistic,

STCW-aligned maritime training environments.

To reflect the level of procedural compliance

demonstrated by trainees in each simulated scenario,

the four criteria are consolidated into a Procedural

Compliance Index (PCI) expressed as:

Overall Rubric Score = ( (1 ) (1 )

TA CS PTT TW

PCI S S S S= + − + − +

(2)

where, STA denotes the Technical Accuracy score; SCS

represents the Channel Selection Error Rate; SPTT

corresponds to the PTT Misuse Rate, and STW reflects

Teamwork and Radio Discipline performance.

Because the CS and PTT indicators inherently

describe error-based behaviour, their values are

inverted to 1−S to ensure alignment in scoring direction

across all components. Accordingly, the model can be

generalized in a weighted form as:

(1 ) (1 )

TA TA CS CS PTT PTT TW TW

TA CS PTT TW

w S w S w S w S

PCI

w w w w

+ − + − +

+ + +

(3)

where wi denotes the weighting factor assigned to each

criterion according to instructional priorities, (e.g., wi =

0.3, 0.25, 0.25 or 0.20)

2.5.3 Perceptual Indicators for Contextual Interpretation

After each training session, participants completed

a structured five-point Likert-scale instrument to

capture perceptual indicators related to system use and

training context, rather than subjective satisfaction. The

instrument addressed alignment with standard VHF

procedures, consistency of device interaction logic,

clarity of task progression, and relevance to

operational communication tasks. These indicators

were not treated as independent outcome measures

but were used to contextualize objectively measured

performance results, including procedural compliance

trends, error reduction patterns, and coordination

behaviour derived from system logging and rubric-

based assessment.

3 RESULTS

3.1 Results of the Virtual Reality Simulation

Development

After the C# scripting phase was completed to emulate

the behaviour of buttons, rotary knobs, and object

rotation within the 3D environment, the final step

involved conducting a full system test prior to

exporting the executable file for deployment on the

target platform. This verification stage served to detect

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and correct any functional inconsistencies while

confirming that the simulated device accurately

mirrored the operational characteristics of the real VHF

unit.

Additionally, the author performed a series of

communication trials between two virtual VHF sets

operating on separate computers placed at varying

distances, using the UDP-based voice transmission

mechanism. These tests were carried out to validate

real-time call performance and ensure the simulation

behaved consistently across different network

conditions. Several images below illustrate the

functioning of the completed simulation programme.

Figure 9a. Simulate a call on channel 06 on Portable

Computer

Figure 9b. Simulate a call on channel 06 on Laptop

Figure 10a. Simulate a call on channel 16 on Portable

Computer

Figure 10b. Simulate a call on channel 16 on Laptop

The study achieved the development of a robust

VHF communication simulator using Unity in

combination with Photon Voice 2 operating over the

UDP protocol, enabling a highly responsive replication

of half-duplex radio communication. The user

interface, control buttons, and channel-selection

mechanisms were modelled with high fidelity, offering

trainees a realistic operational environment. The

adoption of UDP further allows the system to function

over satellite-based networks such as Starlink,

broadening its capability for remote and multi-node

training when ships remain at sea for extended

durations. Despite these advantages, enhancements

are still needed in handling jitter, simulating noise-

affected environments, and incorporating radio-

coverage mapping to strengthen operational realism.

Future developments may include expanding the

system to support Search and Rescue (SAR)

communication exercises and embedding automated

learner-performance evaluation based on operational

timing and procedural execution.

3.2 Effectiveness of Training Scenario Implementation

The VHF simulation system was trialed using three

core training scenarios aligned with STCW and SMCP

requirements, including routine call, distress call, and

multi-user (multicast) communication. The results

indicate that all exercises operated reliably and

adhered closely to the established sequence and logic

of maritime radiotelephony procedures.

For the routine call scenario, students followed the

standardized SMCP steps: conducting an equipment

check, selecting the appropriate working channel,

initiating contact, exchanging the required

information, and properly closing the communication.

Logging data shows that the frequency-selection error

rate and PTT-related mistakes significantly decreased

after three practice sessions, demonstrating that the

simulation effectively improves operational accuracy

and familiarization with the VHF device.

Figure 11. Simulation of call operation: (a) call initiated from

a portable computer; (b) call initiated from a laptop

493

Figure 12a. Simulation of device power on/off and keypad

lock operation.

Figure 12b. Simulation of channel and volume adjustment

operations

In the distress-call scenario, the simulator fully

replicates the MAYDAY procedure prescribed in

STCW Section A-IV/2, including switching to Channel

16, transmitting the distress alert, providing vessel

identification and position information, and

maintaining proper Push-to-Talk discipline during

half-duplex communication. The results indicate that

trainees quickly internalized the standardized call

structure and demonstrated more appropriate

responses under emergency conditions.

For the multicast scenario, the system enables

multiple trainees to operate on the same channel

simultaneously, accurately mirroring real shipboard

communication environments in which several parties

may need to exchange information at once. This feature

supports the development of teamwork skills, helps

learners identify the correct timing to activate PTT, and

reduces instances of overlapping transmissions.

Overall, the implemented training scenarios

performed reliably and delivered a high degree of

realism. They effectively strengthened essential

communication competencies and aligned closely with

STCW requirements for maritime radio-

communication training.

3.3 Pilot Study Results

A pilot evaluation was conducted with a total of 367

students of Navigation Faculty in Vietnam Maritime

University, comprising second-year and third-year

cohorts enrolled in the Maritime Communication

module, to assess the training effectiveness of the real-

time VHF simulation system. The aggregated results

indicate a clear performance distinction between the

two groups, reflecting the progressive development of

operational competence across academic years.

For the second-year cohort, the proportion of

correct operations on fundamental device functions—

such as powering the unit on/off, adjusting volume,

rotating knobs, and switching channels—was

generally satisfactory. However, a notable number of

errors were recorded, particularly related to incorrect

channel selection and improper timing of PTT

activation. Most of these errors stemmed from limited

familiarity with the 3D simulation interface and

insufficient understanding of half-duplex discipline,

especially in scenarios requiring rapid response.

In contrast, the third-year cohort demonstrated

considerably higher proficiency across nearly all

assessed criteria. Improvements were especially

evident in PTT discipline, teamwork coordination, and

the correct execution of SMCP procedures in

accordance with STCW standards. Channel-selection

mistakes and PTT-related errors were markedly

reduced compared with the second-year group,

suggesting that prior learning experience and greater

exposure to maritime communication protocols

contributed to stronger overall performance.

Figure 13. Simulation of a VHF call using the Push-to-Talk

(PTT) function

The aggregated rubric results, covering four core

competency domains—technical operation, SMCP

phraseology accuracy, situational awareness, and PTT

discipline—demonstrate a clear performance

distinction between the two student cohorts. Second-

year students achieved an average score of 3.6/5,

whereas third-year students reached 4.3/5. This

disparity accurately reflects the expected differences in

proficiency and operational maturity between training

levels. Furthermore, the findings confirm that the

simulation system can effectively differentiate,

quantify, and represent learners’ competencies with

high fidelity, thereby supporting its suitability for

integration into formal maritime training programmes

in alignment with STCW requirements.

494

Table 1. Student performance scores by assessment criteria

(n = 367) Likert scale: 1 = Very dissatisfied / 5 = Strongly

satisfied

Survey

Criteria

2nd-Year

Students (n =

188)

3rd-Year

Students (n =

179)

General Remarks

Technical

Accuracy

78% correctly

performed ≥

90% of required

operations

92% correctly

performed ≥

90% of required

operations

Third-year students

demonstrate higher

proficiency due to

prior exposure to

GMDSS practice.

Channel

Selection

Error Rate

14.2%

6.8%

Errors mainly

occurred on Channels

16/71/72 and from

incomplete knob-

rotation actions.

PTT Misuse

Rate

11.5%

4.1%

Second-year students

tended to hold PTT too

long or speak over

others—violating half-

duplex discipline.

Teamwork

& Radio

Discipline

3.6/5 (Likert)

4.3/5 (Likert)

Third-year students

coordinated more

effectively in Distress

and Ship-to-Ship

scenarios.

Overall

Rubric Score

78.4/100

87.9/100

Differences reflect

varying operational

experience and

situational awareness

between cohorts.

Third-year students generally achieved higher

performance scores, as they had already been exposed

to bridge-simulation environments and possessed a

more thorough understanding of STCW and SMCP

procedures through the Maritime Communication

course. Nevertheless, second-year students also

demonstrated notable improvement, supported by the

intuitive interface and the realistic operational logic of

the simulated VHF system.

3.4 Performance Trends and Procedural Compliance

Indicators

Analysis of responses and interaction data from 367

participants (188 second-year and 179 third-year

students) indicates distinct procedural compliance

trends associated with the use of the real-time VHF

simulation framework. Rather than reflecting

subjective impressions, learner feedback was

consistent with observable changes in operational

behaviour and error distribution recorded through

system logging.

Across both cohorts, repeated engagement with the

simulator led to progressive error reduction patterns,

particularly in channel selection accuracy, Push-to-

Talk (PTT) timing, and adherence to half-duplex

communication rules. Second-year students initially

exhibited higher rates of operational errors; however,

these decreased markedly over successive training

sessions, demonstrating the system’s effectiveness in

supporting early-stage skill acquisition. Third-year

students, benefiting from prior exposure to bridge

simulators and formal maritime communication

training, showed more stable procedural execution and

lower variability in performance indicators.

The results further confirm the discriminative

capability of the simulation-based assessment

framework. Differences between cohorts were

consistently reflected in response time distributions,

frequency of PTT misuse, and sequencing accuracy of

SMCP procedures. These indicators demonstrate that

the framework is capable of differentiating

competency levels aligned with training progression,

rather than merely facilitating task repetition.

Overall, the findings suggest that the VHF

simulation environment enables objective monitoring

of procedural compliance, supports structured

improvement in communication behaviour, and

provides reliable performance indicators suitable for

STCW-oriented maritime training and pre-sea

preparation.

Table 2. Perceptual Indicators Supporting Procedural

Compliance Differentiation (n = 367, Likert Scale 1–5)

Likert scale: 1 = Strongly dissatisfied / 5 = Strongly satisfied

Assessment-Related

Indicator

2nd-Year

Students

(n = 188)

3rd-Year

Students

(n = 179)

Interpretation in

Relation to Procedural

Compliance

Perceived alignment

between simulation

behaviour and

standard VHF

operating procedures

4.1 / 5

4.5 / 5

Higher ratings among

third-year students

correspond with more

stable STCW-compliant

execution observed in

logging data.

Perceived fidelity of

device interaction and

control logic

4.0 / 5

4.4 / 5

Consistent with

reduced technical

operation errors and

smoother interaction

sequences at advanced

training levels.

Perceived stability of

real-time audio

transmission and

timing

3.8 / 5

4.3 / 5

Supports observed

reductions in PTT

misuse and improved

half-duplex discipline

across cohorts.

Perceived clarity of

interaction flow

(knobs–buttons–

channels)

4.2 / 5

4.6 / 5

Aligned with lower

channel selection error

rates and faster

procedural completion

times.

Perceived readiness

for real watchkeeping

communication tasks

3.7 / 5

4.4 / 5

Reflects cohort-level

differences in

procedural confidence

consistent with PCI

score separation.

Perceived

instructional relevance

to maritime

communication

training

4.3 / 5

4.7 / 5

Indicates that

perceptual indicators

scale with training

progression rather than

subjective preference.

4 DISCUSSION

The findings of this study emphasize the scientific

value of adopting a data-driven assessment

perspective for maritime VHF communication, rather

than treating simulation solely as a training tool. While

prior research in maritime education and training has

predominantly relied on subjective observation or

learner perception, this study introduces the

495

Procedural Compliance Index (PCI) as a standardized

metric that integrates technical accuracy, channel

selection errors, Push-to-Talk misuse, and teamwork-

related radio discipline in accordance with STCW and

SMCP requirements. The clear performance

differentiation observed between second- and third-

year students demonstrates the discriminative

capability of the framework and supports its validity

for assessing communication competence across

training levels.

A key methodological contribution lies in the use of

system-level logging to capture fine-grained

interaction data during real-time communication tasks.

Logged parameters such as error frequency, response

timing, and procedural sequencing enable objective,

repeatable, and scalable assessment, thereby reducing

dependence on subjective instructor judgment. The

observed trends in error reduction and procedural

stabilization further suggest that logged interaction

data can meaningfully reflect skill acquisition and

progression.

Beyond VHF communication, the proposed

framework is transferable to other maritime domains

requiring procedural compliance and coordinated

multi-operator performance, including ECDIS

operation, bridge teamwork, and distributed training

scenarios. The reliance on networked interaction data

also supports extension to remote training contexts,

addressing emerging demands for objective, STCW-

compliant assessment in modern maritime education

systems.

5 CONCLUSIONS

This study introduces a real-time simulation-based

approach for handheld VHF communication aimed at

supporting maritime training and competency

assessment, implemented on the Unity platform with

UDP-based data transmission. The simulated

environment accurately represents the physical

configuration, display interface, and key operational

functions of the Sailor SP3520 device, including

channel switching, scanning operations, power-level

adjustment, and Push-to-Talk interaction governed by

half-duplex communication principles. The

incorporation of Photon Voice enables low-latency

real-time audio exchange, allowing communication

behaviour to be observed and measured under

conditions comparable to actual VHF operation at sea.

Implementation trials indicate that the system

operates stably, supports scalable deployment, and is

suitable for use in both shore-based training facilities

and onboard environments—particularly in the

context of widespread satellite connectivity such as

Starlink on modern vessels. Overall, the proposed

framework demonstrates effectiveness in supporting

structured learning, enabling standardized evaluation

of VHF communication performance, and meeting

STCW-defined competency requirements through

objective, simulation-based assessment.

5.1 Limitations of the study

Despite the demonstrated capability of the proposed

framework for assessing maritime VHF

communication performance, several limitations

should be acknowledged. First, the current

implementation does not comprehensively model real-

world radio propagation effects, including signal

interference, distance-dependent attenuation, or

complex environmental conditions typically

encountered in maritime operations. Second, audio

quality assessment remains limited to pilot-level

evaluation and has not yet been systematically

benchmarked against recordings captured from

operational VHF equipment under actual sea-going

conditions. In addition, the framework does not

presently integrate radio coverage mapping or

communication path modelling, which are necessary

for advanced assessment scenarios involving range

estimation, shadow zones, and decision-making under

constrained communication coverage.

5.2 Recommendations for future research

Future research may extend the proposed framework

in several directions. First, integrating advanced radio-

propagation models, environmental noise effects, and

distance-dependent signal attenuation would improve

the fidelity of simulated VHF communication

behaviour. Second, the incorporation of AI-based

analytics could support automated performance

assessment, behavioural pattern analysis, and the

generation of real-time instructional feedback. Third,

the framework may be expanded to cover advanced

STCW-oriented scenarios, including coordinated SAR

operations and ship manoeuvring under adverse

operational conditions. Finally, the adoption of VR/AR

technologies could enable visualization of VHF

coverage and communication constraints, thereby

enhancing immersion and supporting more effective,

competency-oriented maritime training.

ACKNOWLEDGMENTS

The authors sincerely thank all co-authors for their valuable

contributions, insightful discussions, and collaboration

throughout this research.

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