The technology breakthrough that Electronic Chart Display and Information System (ECDIS) has brought to modern navigation has the capability to improve the safety of navigation. This could be achieved only when the capabilities of the system are known by an end-user. Cross Track Limit (XTL) is an ECDIS safety parameter, set by the navigator, which enhances the navigational task automation in the function of workload reduction. Determination of factors affecting the value of XTL safety parameter, with special consideration to chart data reliability, is elaborated in this paper. Chart data reliability depends on the quality of chart survey data, which in many cases are outdated and unreliable. Analysis of past research on this subject is used to define the factors affecting XTL. Practices of different shipping companies with regards to XTL are analyzed and compared in order to confirm if there is a uniform practice between them. Nevertheless, shipping companies have a different or no practice of obtaining XTL, which allows the navigator to define safety parameters by a subjective opinion. In this paper, method of XTL determination for a specific vessel is suggested, considering previously defined factors. Finally, crucial influence of survey data to the safety of navigation is presented in this study.

This paper represents observations on detection of Very High Frequency (VHF) anomalous propagation over the area of the Adriatic Sea. During the research campaign, a Software Defined Radio (SDR) Automatic Identification System (AIS) receiver was employed for collection of AIS data packets at a fixed location in the Northern Adriatic. Data were collected during the 24-h period (25 February 2023 15:32 LT to 26 February 2023 15:32 LT), providing information from 115 AIS targets, or 159 965 AIS packets with 54.3% Packet Error Rate (PER), respectively. Subsequent analysis and post-processing of successfully demodulated signals and decoded packets was presented further. In certain instances, the SDR AIS receiver detected, received and decoded data packets from AIS targets distant several orders of magnitude larger than the VHF nominal ranges. To determine the magnitude of line-of-sight and over-the-horizon radio waves propagation, the great circle distances between the SDR AIS receiver antenna and AIS packets’ decoded positions were calculated, revealing hundreds of Nautical Miles (NM). Possible reasons for these occurrences, including tropospheric scattering, diffraction, ionospheric sporadic E layer and refraction were discussed and evaluated, in accordance, among others, with the previous research. By exclusion criteria and neglection of possible causes, it was concluded that the enhanced, over-the-horizon propagation of AIS signals occurred as a result of refraction effects, namely trapping/ducting, subrefraction and superrefraction. Data from nine World Meteorological Organization (WMO) radiosondes surrounding the greater reception area were collected for the same observation periods. Atmospheric profiles were created using Advanced Refractive Effects Prediction System (AREPS) program, and analysed for each individual station measurement. The results confirmed anomalous, over-the-horizon enhanced propagation and their probable origins, i.e., the occurrence of refractive conditions in the atmosphere over the Adriatic Sea area. These findings provide a solid foundation for further research in the area of propagation of VHF signals and their anomalous features caused by the atmospheric phenomenon effects.

The tasks of an officer of the watch (OOW) on complex ships during navigation in coastal areas may be very challenging. Almost all the tasks require substantial information processing and timely decision making. Every distracting element should be avoided during navigation. Every call, made through any communication system, activates a new process that the OOW needs to conduct. The new process may interrupt a previously started task. In case of too many incoming calls, the workload of the OOW may increase significantly, thus, their situational awareness may be compromised and the risk of errors may increase. The objective of this research was to analyze the impact of incoming voice calls on the OOW. The research methods used include a questionnaire survey and a series of interviews with experienced officers. The main outcomes refer to the average frequency of incoming calls, duration of conversations and subjective assessment of their influence. The results indicate that, during one watch, an officer needs to answer 14 calls that last 16.19 min altogether. However, the officers consider 45% of calls made during watch keeping as distracting. A possible call management system with the aim to reduce distractions made by low priority calls is proposed in this paper.

Maritime non-commercial communications are performed using the equipment of Global Maritime Distress and Safety System (GMDSS), under the International Convention for the Safety of Life at Sea (SOLAS). This equipment includes numerous devices of different technologies, features and user interfaces, which every officer of the watch (OOW) must know how to use. Besides, the equipment, i.e., its technology has not changed significantly in the last 30 years. Therefore, the purpose of this research was to collect and analyze information on how often GMDSS devices are used and whether any modernization is needed. The main research method was a questionnaire survey intended for experienced officers. Each question, as well as the answers of the respondents, were analyzed in detail and presented graphically. The results of the survey analysis indicate that the VHF (Very High Frequency) radiotelephone, Navigational Telex (NAVTEX) receiver, and Enhanced Group Call (EGC) receiver are still very used, while Digital Selective Calling (DSC) devices and MF/HF (Medium Frequency/High Frequency) radios (telephone and telex) are almost unused onboard. Additionally, more than 80% of respondents believe that GMDSS needs modernization.

Maritime communication systems and devices that are required onboard ships under the SOLAS (Safety Of Life At Sea) Convention are determined by the communication functions of Global Maritime Distress and Safety System (GMDSS). This system was fully implemented on the 1st February 1999, and since then maritime communications methods have not been significantly changed. As a result, numerous researches and studies were conducted, intended to improve existing communication systems. Furthermore, the exchange of data in maritime communications is of great importance for the purpose of safety of navigation and commercial services. For this reason, the advantages and disadvantages of existing maritime communication systems for data exchange are systematically analyzed in this paper, in order to determine the guidelines for their improvement or replacement by new communication systems. The focus is on the used modulation techniques, as well as the maximum achieved data rates. According to these characteristics the possibility of applying certain communication systems in communications infrastructure of the strategy called “e-Navigation” is determined. In addition, an overview of international recommendations and guidelines for the modernization of maritime communications in the VHF frequency band is elaborated in this paper.

Sanjin Valčić, Srđan Žuškin, David Brčić, Davor Šakan; Review, pp. 135-140 Download