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A ship-domain-based framework for improving the multi-ARPA collision avoidance system

Ożoga Bartosz, Rutkowski Grzegorz

Zeszyty Naukowe Politechniki Morskiej w Szczecinie

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2026

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nr 86 (158)

103--128

EN

The multi-ARPA (MARPA) system is a conceptual navigational decision-support tool intended to support the Officer of the Watch in complex ship-encounter situations, especially when several surrounding targets must be assessed simultaneously. In its original form, MARPA classifies candidate ship courses and target collision potential mainly by using predefined closest point of approach (CPA)/time to closest point of approach (TCPA)-based thresholds. Although such thresholds are operationally simple, they do not directly account for vessel dimensions, encounter geometry, uncertainty of navigational data, or the remaining maneuvering capability of a ship. This paper proposes a theoretical and analytical framework for improving MARPA hazard classification by replacing static CPA/TCPA-based heuristics with criteria derived from the ship domain and its safety-related sub-areas: the navigationally dangerous area, the critical area, and the collision zone. The proposed approach preserves the original operational structure of MARPA, including the direct hazard module and the indirect hazard module, but changes the meaning of the input hazard classes. Candidate ship courses and target collision potential are classified according to the predicted relation between the target trajectory and the domain-based safety areas. The analytical verification shows that domain-based classification changes MARPA output in several distinct ways. In the direct hazard module, the predefined scenarios produced higher, lower, and equivalent domain-based classifications when compared with static CPA/TCPA-based classification. In the indirect hazard module, the modification affected the class of direct hazard, class of course hazard, class of speed hazard, CMPH, and degree of indirect hazards through target geometry and through the course or speed change required for a target to violate the collision zone, critical area, navigationally dangerous area, or the ship domain. The collision zone provides the highest hazard class, a direct geometric meaning that refers to the possibility of physical contact rather than to an arbitrary CPA value. The practical advantage of this modification is that MARPA output can indicate not only that a course or target is hazardous but also which domain-based constraint is responsible for the classification. This study is theoretical and analytical in nature; full simulator-based, automatic identification system/radar-based, and onboard validation are identified as a necessary stage for future work.

2

Navigational Safety Assessment in Benoa Channel Based on Course over Ground and Trajectory

Asmara I.P.S., Putra G.H., Arfianto A.Z., Artana K. B., Handani D.W.

TransNav : International Journal on Marine Navigation and Safety of Sea Transportation

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2026

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Vol. 20 No. 1

47--53

EN

This study evaluated ship berthing safety in Benoa Port using AIS data and the MMG model. Firstly, AIS data derived from the AIS receiver at Udayana University was analyzed based on the COG entropy method. Secondly, the trajectory of the Passenger Ship Celebrity Solstice, the largest ship in the port with 317.19 meters LOA and 36.9 meters width, was evaluated using the shortest distance to an obstacle based on the trajectory plotted from the AIS data. Finally, a Pure Car Carrier was simulated based on the Mathematical Maneuvering Group model to berth in the port to assess berthing safety in the Port. The COG entropy method is implemented in three positions in the port channel, the course-changing, course-keeping, and turning basing areas. The study shows that ship berthing safety using the COG entropy in all areas is at high risk. The shortest distances of the Celebrity Solstice and the Pure Car Carrier were to the obstacle of shallow water, less than the distance recommended by Innoe. Based on the maneuvering simulation results, the maximum wind and current speed for the port operation is recommended.

3

Decision Support System Using Modern Methods of Collision Avoidance in Collision Situations at Sea

Mohamed-Seghir M.

TransNav : International Journal on Marine Navigation and Safety of Sea Transportation

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2026

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Vol. 20 No. 1

55--60

EN

Due to the rapid growth of maritime transport, many researchers have developed advanced methods aimed at increasing navigation safety and reducing operating costs, while maintaining compliance with the International Regulations for Preventing Collisions at Sea (COLREGs). Navigating a ship in potential collision situations requires decision-making under conditions of uncertainty and ambiguity – particularly with respect to concepts such as collision risk and safe speed. These concepts are subjective and not clearly defined. In response to these challenges, this paper presents an artificial intelligence-based method that takes into account the navigator's role as a decision-maker. The proposed solution is designed for integration with existing collision avoidance systems. A universal simulator was developed to evaluate the effectiveness of an algorithm for determining a safe ship trajectory in collision situations. Example navigation scenarios were conducted and presented using this simulator.

4

Navigational risk analysis in the area of the new container terminal in Świnoujście

Kościelecki Maciej, Kotkowska Diana

Zeszyty Naukowe. Organizacja i Zarządzanie / Politechnika Śląska

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2025

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z. 223

187--213

EN

Purpose: The purpose of this study is to analyse and assess navigational safety in the area of the planned container terminal project in Świnoujście. Due to the strategic importance of the project, the safety assessment requires a multi-faceted approach, including mathematical modelling and simulation methods. The premise of the analysis is that the level of navigational risk in the analysed area depends on the intensity and structure of vessel traffic in the designated survey sectors. The hypothesis is based on the assumption the level of collision risk is strongly correlated with the number and type of vessels registered in the AIS data for each sector. Design/methodology/approach: The research used a quantitative analysis of AIS (Automatic Identification System) data acquired for the Baltic Sea area for 2019-2022. The data was used to estimate the level of risk in terms of potential collisions and manoeuvring errors. The study is of a practical nature and is based on empirical data and analysis of local shipping conditions. Findings: The use of simulation led to results that identified high-risk sectors and could form the basis for recommendations on navigational safety and the development of future maritime traffic management strategies. Practical implications: The study aims to analyse current AIS data and local shipping conditions, which limits its application to wider geographical contexts. Further research is needed including forecasts of changes in traffic volumes and the impact of meteorological conditions. The analysis can be the starting point for more advanced risk simulations and cost- benefit analyses for shipping infrastructure investments. Originality/value: The article brings new value by analysing navigational risk based on AIS data in a specific investment context. It identifies practical steps to enhance navigational safety in one of the key transport areas in the region. It is aimed at both decision-makers responsible for port infrastructure development and professionals involved in maritime safety and spatial planning.

5

Intensity of maritime traffic on the Kołobrzeg-Bornholm route and safety of navigation: risk analysis and recommendations

Kotkowska Diana, Kościelecki Maciej

Zeszyty Naukowe. Organizacja i Zarządzanie / Politechnika Śląska

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2025

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z. 229

287--299

EN

Purpose: The objective of the study was to analyse the intensity and structure of maritime traffic on the Kołobrzeg–Bornholm route and to identify areas of increased navigational risk. Design/methodology/approach: AIS data and HELCOM accident records from 2004 to 2023 were used. The analysis was carried out using the IALA IWRAP Mk2 tool, based on the Formal Safety Assessment (FSA) methodology, taking into account risk matrices and elements of the logic tree method. Findings: Clear differences in traffic intensity were identified on three sections (LEG 9-11). The highest traffic load occurs in LEG 11 (over 5500 vessels, mainly cargo ships and tankers). LEG 10 serves as a transit route, while LEG 9 serves as a local route. The areas with the highest traffic coincide with the locations of historical maritime accidents. The results are presented in the form of intensity matrices and heat maps. Research limitations/implications: The study does not include an analysis of the costs of the proposed solutions or the legal issues related to their implementation, which limits the possibility of a full assessment of the feasibility of the recommendations. Technical risks, such as navigation system disruptions, and the perspective of local stakeholders, which is important for the practical implementation of the changes, have also been omitted. Practical implications: The results obtained may support the decisions of maritime authorities and safety system operators. It is recommended to implement a VTS system, TSS plans and improve traffic organisation in the Kołobrzeg port area. Social implications: The proposed measures may increase navigation safety, environmental protection and reduce the number of accidents, especially in the recreational and passenger sectors. The study also supports the concept of sustainable maritime transport. Originality/value: The study integrates AIS and HELCOM data and the FSA approach for a specific region of the Baltic Sea. It is one of the few studies on the Kołobrzeg–Bornholm route and may be useful for decision-makers and the scientific community involved in maritime safety.

6

Stability Analysis of a Bulk Carrier under Damage Scenarios during the Loading of Polymetallic Nodules in the Clarion–Clipperton Zone

Kacprzak Paweł

TransNav : International Journal on Marine Navigation and Safety of Sea Transportation

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2025

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Vol. 19 No. 2

431--438

EN

A potential consequence of loading polymetallic nodules (PMNs) in a marine environment is liquefaction. During loading operations in the Clarion–Clipperton Zone (CCZ), the ship is exposed to cyclic rolling and pitching, which increases the risk of cargo liquefaction. This phenomenon poses a particular danger when PMNs liquefy under certain conditions. Combined with cargo shifting, liquefaction can significantly compromise the vessel's transverse stability —even when it occurs in a single cargo hold. Due to the limited operational experience in transporting PMNs, this study investigates the key risk factors affecting ship stability. The research discusses the likelihood of liquefaction, the influence of wind lever arms, and critical roll amplitudes under conditions where the weather criterion is not fulfilled. These aspects are analyzed through three representative damage scenarios. The findings indicate that, for the vessel analyzed, flooding in a single compartment does not result in overall stability failure. However, strict monitoring of cargo moisture content in relation to the transportable moisture limit (TML) remains essential to mitigate risks. The study concludes with practical recommendations to assist ship operators in managing these challenges effectively.

7

Spatial Development of Modern Port Structure and Sustainable Urban Growth within Multifunctional Organization

Gerigk Mateusz

TransNav : International Journal on Marine Navigation and Safety of Sea Transportation

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2025

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Vol. 19 No. 2

441--446

EN

Modern port city areas face enormous opportunities due to their coastal location. The possibility of integrating water area into a city area highlights the issue of spatial planning. It is obvious that such locations allow for the development of industrial and port infrastructure. But the major question is how these areas should develop in terms of architecture and urban planning. The aim of the paper is to define the design parameters for maritime areas in the context of the modern city, as well as with regard to sustainable development of these structures. The analysis of modern port centres allows for indicating the directions of development in the pursuit of expansion into water areas. The scale of modern commercial and industrial structure may become dominant, and sometimes even limit the multidirectional development of the city. However, the key issue is how to design these areas in the future, also in relation to the social perspective.

8

Soft Values in Port-city Relationships: Case of Reidi Road and Port of Tallinn

Rauk Kristel, Tapaninen Ulla

TransNav : International Journal on Marine Navigation and Safety of Sea Transportation

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2025

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Vol. 19 No. 2

459--467

EN

Ports and cities have historically been strongly linked and developed in close association with each other. This study focuses on analysing the case of Tallinn Reidi Road. The methodology is based on tangible soft assets of ports based on framework Soft Values of Ports. The aim of this study is to clarify how cooperation between Port of Tallinn AS and the City of Tallinn, through the Reidi Road project, has influenced the visibility, perception, and integration of tangible soft values in port-city relationships. The case study demonstrates how different stakeholders assess and experience the multidimensional role of a port in society. Results indicate that the Port of Tallinn and the City of Tallinn acknowledge and value the significance of soft values. In addition, this study provides practical recommendations and suggestions that can help city and port officials, policy makers and urban planners to better understand and integrate soft values in future development projects. In particular, soft value initiatives should be incorporated by port authorities in cooperation with local authorities.

9

Project OPTIMISM: Novel Means of Finding Root Causes of Accidents and Incidence at Sea and Port, as Well as Identifying Key Factors for Improved Safety from Ship Audit and Inspection

Ziarati Reza, de Melo Rodriguez Germán, Koivisto Heikki, Uriasz Janusz, Singh Lakhvir, Barzegarsedigh Amirehsan, Makar Canessa, Chronopoulos Aris

TransNav : International Journal on Marine Navigation and Safety of Sea Transportation

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2025

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Vol. 19 No. 2

399--405

EN

This paper presents a set of methodologies for analysing accident investigation reports to enhance learning from past incidents. While these reports are primarily designed to prevent accident recurrence, they often overlook key contributing factors such as personal, organisational, and cultural influences—particularly leadership practices and potential mental health issues that may have played a role. Moreover, accident investigation reports vary in quality and do not always adhere to standardised frameworks, limiting their effectiveness. This paper proposes a novel approach to accident analysis, offering a structured method to distinguish whether an accident is crew-related or company-related - an essential differentiation, as these factors require distinct management and preventive measures. The study draws on findings from multiple recent projects, analysing over 1000 accident reports to develop a new taxonomy. This taxonomy aims to facilitate a more systematic approach to accident analysis while identifying management deficiencies and crew-related challenges, ultimately improving safety and operational practices.

10

Numerical Analysis of the Effect of Passive Free Surface Tank on Rolling Motion of Batang-Type Traditional Fishing Vessel

Chrismianto Deddy, Yudo Hartono, Arswendo Adietya Berlian, Firdhaus Ahmad, Abel Salassella Alfian

TransNav : International Journal on Marine Navigation and Safety of Sea Transportation

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2025

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Vol. 19 No. 2

407--416

EN

Ship accidents are caused by various factors, one of which is excessive roll motion that can lead to capsizing. To address excessive rolling, the passive free surface tank device is a potential solution that can be applied. In order to ensure good performance of the passive free surface tank, it is necessary to investigate the effect of the tank's dimensional configuration on the damping it generates. By identifying the best tank configuration, it is hoped that this study can provide useful references for the design of passive free surface tanks, especially for traditional fishing vessels. The analysis begins by creating several tank specimens with variations in length and fluid height. The performance of the passive free surface tank is evaluated based on the RMS values generated by the ship with the tank, which are then compared to the RMS values of the ship without a tank. In the analysis, FEM-based software is used to assist in the calculations. The results show that the ship with the addition of passive free surface tank type C1 produces the highest roll damping, with a damping percentage of 20.01% at empty load, 25.12% at half load, and 24.37% at full load.

11

Design and Implement an Automatic Smart Buoy System for a Bulgarian Safe Beach Areas – Part 1

Dimitrov Ivan, Iliev Iliyan, Hristov Daniel, Dinkov Dinko, Mavrodiev Tsetoslav

TransNav : International Journal on Marine Navigation and Safety of Sea Transportation

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2025

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Vol. 19 No. 2

381--386

EN

Drowning is the third leading cause of unintentional injury-related deaths, accounting for 9% of all injury fatalities, with over 300,250 cases reported annually by the World Health Organization (WHO) in 2021. Addressing this issue necessitates the implementation of affordable and accessible safety measures at local beaches. This paper presents an innovative, cost-effective automated system designed to improve beach safety through real-time environmental monitoring. The system consists of three primary subsystems: sensors, information processing, and action mechanisms. At its core are smart buoys, equipped with sensors and communication modules, which transmit data to an onshore station and a cloud-based platform. This platform processes, stores, and monitors the data against predefined thresholds, generating alerts when necessary. A web application provides real-time data access, enabling fault monitoring, system operation forecasting, and performance optimization.

12

Design and Implement an Automatic Smart Buoy System for a Bulgarian Safe Beach Areas – Part 2

Dimitrov Ivan, Iliev Iliyan, Hristov Daniel, Mavrodiev Tsetoslav

TransNav : International Journal on Marine Navigation and Safety of Sea Transportation

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2025

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Vol. 19 No. 2

387--391

EN

The Internet of Things (IoT) is undergoing rapid expansion, transforming industries and everyday life through interconnected devices and data-driven decision-making. As IoT adoption accelerates, ensuring its accessibility and usability for non-technical users becomes increasingly critical. Simplified interaction with IoT systems facilitates broader adoption and maximizes their potential to improve safety, efficiency, and convenience. This aspect is particularly crucial in the domain of coastal safety, where IoT technologies can play a pivotal role. By integrating IoT into a smart buoy system, real-time data on water conditions, weather patterns, and swimmer safety can be continuously monitored and seamlessly communicated to lifeguards and beach visitors. The effectiveness of such a system relies on an intuitive and user-friendly design, enabling individuals without technical expertise to engage with its functionalities effortlessly. IoT serves as the foundation of this innovation, providing seamless connectivity, data sharing, and automation. Prioritizing IoT integration in critical safety solutions such as smart buoys underscores its potential to enhance life-saving measures while contributing to the development of more intelligent, secure, and interconnected environment.

13

A Thematic Review of Port Services and Emission Reduction Strategies Using ATLAS.ti

Acomi Nicoleta, Surugiu G., Raicu Gabriel, Stanca Costel

TransNav : International Journal on Marine Navigation and Safety of Sea Transportation

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2025

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Vol. 19 No. 2

447--457

EN

The maritime industry plays a dual role as a critical driver of global trade and a significant contributor to greenhouse gas (GHG) and air pollutant emissions, posing challenges to environmental sustainability. As key nodes in the global supply chain, ports face mounting pressure to adopt greener practices. This study synthesises insights from contemporary scientific research articles, highlighting best practices, successful case studies, and obstacles in implementing emission reduction strategies and environmentally friendly port services worldwide. A two-step mixed-methods approach was utilised, combining a systematic review of literature with qualitative data analysis. The PRISMA methodology guided the selection of 27 peer-reviewed articles from the Web of Science Core Collection, spanning the period from 2015 to 2024. Subsequently, thematic coding and comprehensive analysis were conducted using Computer-Assisted Qualitative Data Analysis Software (CAQDAS) ATLAS.ti, enabling a structured synthesis of findings related to port services and emission reduction strategies. Through this analysis, three critical themes emerged as essential for enhancing environmental sustainability in port operations: innovative technologies for emission reduction, data-driven optimization for port efficiency, and policies and governance for green ports. Drivers such as financial incentives, advanced technologies, and regulatory frameworks were identified, alongside barriers like economic feasibility, technical challenges, and organisational resistance. These themes reveal the interconnected nature of sustainability efforts and the need for collaborative strategies to overcome existing obstacles. By identifying key drivers and challenges, this research offers valuable insights for advancing sustainable practices in port operations. The findings underscore the importance of aligning technological, operational, and policy-driven measures to foster environmental efficiency while mitigating emissions. This study contributes to the growing body of knowledge on sustainable port operations, providing actionable insights for stakeholders and policymakers in the maritime industry to support the transition toward greener and more efficient port practices.

14

A Novel Network RTK Technique for Mobile Platforms: Extending High-Precision Positioning to Offshore Environments

Chen Wu, Ding Junsheng, Wang Yuyan, Mi Xiaolong, Liu Tong

TransNav : International Journal on Marine Navigation and Safety of Sea Transportation

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2025

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Vol. 19 No. 2

371--380

EN

Network Real-Time Kinematic (NRTK) positioning, as the most mature real-time high-precision positioning technology, is widely recognized for its centimetre-level accuracy, operational efficiency, and extensive application potential. However, conventional NRTK systems rely on reference stations anchored to bedrock-based infrastructure, limiting their coverage to terrestrial areas within Continuous Operating Reference Station (CORS) networks. This architectural limitation renders conventional NRTK inapplicable for offshore and marine environments. To overcome this geographical constraint, we propose an innovative NRTK framework for mobile platforms featuring (1) simultaneous estimation of atmospheric delays and baseline dynamics to get precise relative coordinate movements, (2) the regularization method is applied to de-correlate the positional and atmospheric parameters and the regularization coefficients are optimized by mean square error minimization, and (3) integration of Precise Point Positioning (PPP) at a main base station to maintain an absolute position reference for the network. Experimental validation using Hong Kong's terrestrial CORS network demonstrates that the proposed marine-adapted system achieves positioning accuracy comparable to conventional bedrock-based NRTK, with three-dimensional (ENU) errors measuring (2.90, 3.22, 4.32) cm and (2.90, 2.88, 6.70) cm in two operational scenarios. This methodological advancement enables the deployment of buoy-based NRTK systems in marine environments, with significant implications for maritime applications including port traffic management, fishing fleet navigation, and offshore resource exploration. By extending NRTK's operational domain beyond terrestrial boundaries, our technique not only enhances positioning reliability for marine operations but also creates new paradigms for oceanic resource management.

15

Application of the multi-criteria navigational safety assessment method for the proposed variants of the designed waterway

Formela K.

TransNav : International Journal on Marine Navigation and Safety of Sea Transportation

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2022

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Vol. 16 No. 4

633--636

EN

The article presents an exemplary application of the multi-criteria navigational safety assessment method for the proposed variants of the designed waterway in order to verify it. This method comprehensively considers the most important environmental and technical aspects related to the implementation of the planned investment. The method can be used for the purposes of navigational analysis, i.e. an engineering document that meets the requirements of the regulation of the competent, which subject to agreement with the Director of the territorially competent Maritime Office.

16

Methodology for the development of parameters for the navigational safety risk assessment model in port approaches

Bojić F., Bošnjak R., Lušić Z., Gudelj A.

TransNav : International Journal on Marine Navigation and Safety of Sea Transportation

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2021

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Vol. 15 No. 2

365--372

EN

Risk of an accident is an ever-present component in the maritime transportation process, especially in congested waters such as port areas. Since safety is of crucial importance in the maritime industry, different models of risk assessments were developed to ensure minimal navigational danger. The aim of this paper is the development of modular, dynamic sets of parameters, applicable for future risk assessment models on port approaches by introducing top-down expert appraisal structure methodology organised in three steps. Firstly, approaches and criteria from relevant international recommendations and scientific studies on maritime risk assessment models were analysed and compared, in order to obtain general categories of navigational safety parameters. Secondly, existing risk assessment parameters were structured and combined into new dynamic sets. In the third step, these dynamic sets of parameters were selected, and numerical values were assigned to them according to the specific context of the port. Finally, this top-down methodology aims to provide relevant dynamic sets of criteria for navigational safety risk assessment development that are flexible and widely applicable for the needs and characteristics of different ports.

17

Design and application of an automated smart buoy in Increasing Navigation Safety and environmental standards in Ports

Bojić F., Karin I., Juričević I., Čipčić M.

TransNav : International Journal on Marine Navigation and Safety of Sea Transportation

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2021

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Vol. 15 No. 2

373--380

EN

The growing demand for transportation has brought even larger quantities of traffic in spatially limited port areas. Considering a diverse traffic mix, infrastructural overcapacity and busy schedule, port communities have started to face possible degradation of safety and environmental standards. To mitigate these problems, a number of different monitoring solutions of marine environment were deployed. Since conventional environmental and traffic data gathering by physical monitoring and sampling was logistically complicated and inefficient in time and resources, different approaches had to be considered. With the rise of accessible Internet of Things (IoT) technology some ports already installed smart monitoring devices such as smart buoys. The goal of this paper is to examine the concept and benefits of an automated smart buoy as a cost effective, easy to install device capable of real-time remote information sharing. Furthermore, the design and operational processes of existing automated smart buoy will be presented, along with solutions for tackling navigational safety and environmental problems.

18

The Use of a full mission bridge simulator ensuring navigational safety during the Klaipeda Seaport development

Senčila V., Zažeckis R., Jankauskas A., Eitutis R.

TransNav : International Journal on Marine Navigation and Safety of Sea Transportation

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2020

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Vol. 14, no. 2

417--424

EN

Full Mission Bridge simulating became a valuable tool to assess the conditions for safe navigation during seaport development. The article presents an overview of the works carried out at the Lithuanian Maritime Academy. The specialists of the Academy together with the pilots of Klaipeda State Seaport performed a number of trainings and tests using Full Mission Bridge simulator, related to navigational safety assessment. Overviewed works concern a wide range of directions: development of the harbour navigation channel, introduction of two-way traffic of ships, ships sailing with tugboats, coordination with vessel traffic service, emergency response of the LNG vessel in case of various scenarios, extremely big ships accessibility studies, the boundary weather conditions assessment and so on.

19

Recommender system for navigation safety: requirements and methodology

Shilov N.

TransNav : International Journal on Marine Navigation and Safety of Sea Transportation

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2020

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Vol. 14, no. 2

405--410

EN

Low maneuverability of ships together with growing intensity of marine traffic result in new challenges related to navigation safety. This paper reports a research aimed at design of methodology of operation of recommender systems for navigation safety. First, a specification of requirements to systems of the considered class has been carried out. Based on these, the major principles of functioning of such systems have been defined. The principles were a basis for development of the mentioned above methodology, which is based on the usage of context patterns and characterized by the presence of feedback to update the system’s knowledge base.

20

Impact of chart data accuracy on the Safety of Navigation

Acomi N.

TransNav : International Journal on Marine Navigation and Safety of Sea Transportation

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2020

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Vol. 14, no. 2

411--415

EN

Conducting navigation by using electronic charts is not an option anymore. With few exceptions, vessels shall carry on board electronic navigational charts and Electronic Chart Display and Information Systems. The official electronic charts are issued by or on behalf of the authority of a Government, authorized Hydrographic Office or other relevant government institutions. These nautical charts are compiled from multiple data sources, some modern and very comprehensive, while others older. The accuracy of data, named “Category Zones of Confidence – CATZOC”, differs among various navigation areas. The navigation officers of the watch rely on the chart data to calculate the safety parameters and to plan the route in advance for the intended voyage. The aim of this paper is to emphasize the impact which the data accuracy has on the safety of navigation. For this purpose, a model vessel was considered in a Strait of Dover bridge simulation scenario, assuming good weather conditions without swell or current. The Safety Contour was defined using a mathematical formula which incorporated the under keel clearance, the squat effect and the tide levels. Then, the Safety Contour was examined considering the chart data accuracy. The results of this analysis contribute to increasing awareness and better understanding of CATZOC influences on the identification of safe waters during navigation.