###### Abstract  
Due to the ever-increasing amount of data collected and the requirements for the rapid and reliable exchange of information across many interconnected communication devices, land-based communications networks are experiencing continuous progress and improvement of existing infrastructures. However, maritime communications are still characterized by slow communication speeds and limited communication capacity, despite a similar trend of increasing demand for information exchange. These limitations are particularly evident in digital data exchange, which is still limited to relatively slow and expensive narrowband satellite transmission. Furthermore, with the increasing digitalization of ships and introducing the sustainable concept of autonomous ship operation, large amounts of collected data need to be transmitted in real-time to enable remote voyage monitoring and control, putting additional pressure on the already strained means of maritime communications. In this paper, an adaptive shipboard data compression method based on differential binary encoding is proposed for real-time maritime data transmission. The proposed approach is verified on the actual data collected on board a training ship equipped with the latest data acquisition system. The obtained results show that the proposed data encoding method efficiently reduces the transmitted data size to an average of 3.4% of the original shipboard data, thus significantly reducing the required data transmission rate. Moreover, the proposed method outperforms several other tested competing methods for shipboard data encoding by up to 69.6% in terms of compression efficiency. Therefore, this study suggests that the proposed data compression approach can be a viable and efficient solution for transmitting large amounts of digital shipboard data in sustainable maritime real-time communications. m 2021 22 July 2021 23 July 2021 23 July 2021 23 July 2021 23 July 2021 23  
operation [10; 11; 12; 13; 14; 15]. The digital ship concept, illustrated in Figure 1, and the concept of autonomous ship operation imply the collection of large amounts of data from various measurement systems on board the ship [16], real-time digital data exchange, and the application of advanced information technologies for remote monitoring and control of the ship, automation of ship operation, and other advanced functions. These innovative concepts are expected to contribute to a more sustainable maritime transport, enabling energy savings and maritime environment protection [17; 18]. However, unlike the widely used Automatic Identification System (AIS) [19; 20; 21], where a limited amount of predetermined data is transmitted to vessels and coast stations within the range, the digital ship and autonomous ship concepts require continuous real-time transmission of large amounts of digital data. Moreover, since these data are to be transmitted to the land-based stations and operators for further analysis and processing, satellite communications are used for this purpose instead of terrestrial systems. In addition, the need for high-speed and reliable Internet access for both ship's crew and passengers is rapidly increasing. Thus, the previously mentioned limitations of existing maritime communications systems may hinder adopting and implementing these novel concepts in the maritime industry. Therefore, upgrades and modernization of existing systems and construction of new systems will be necessary. However, modernization requires major interventions into the equipment and the investment of significant financial and material resources. An alternative approach to relieving the load on maritime communications systems could be to reduce the size of the transmitted data by applying compression techniques based on specialized algorithms for shipboard data encoding [22; 23]. These algorithms could be efficiently implemented in the ship communication system, thus avoiding extensive interventions and investments.