# Digital Twin in the Maritime Domain: A Review and Emerging Trends
## 7 Challenges and Future Developments in Marine Digital Twin Technology  
DT is at the infancy stage when it comes to implementation in the shipping industry. Limited research is conducted and implemented in projects compared to other industries such as aerospace, manufacturing, agriculture, construction, city planning, etc. The effectiveness of the Cyber-Physical Fusion [132] will be another key encounter. The following salient points can be prominently identified as the bottlenecks posed to the progression and implementation of this naive technology within the maritime sector. * Lack of necessary infrastructure within the existing maritime industry. * Lack of software and hardware skills among various levels of stakeholders. * Limited connectivity due to data transmission restrictions at sea. * Communication barrier between the underwater vehicles (Submarines and UAVs) with the shore-operated DT. * The reluctance to transition to digital systems from long-used manual hardware platforms. * Knowledge gap of the DT technology and benefits reaching the industry as mostly academia is engaged in the research and development stage. * Lack of research collaboration among key researchers/institutes. * Technology readiness is lagging while concept development is at full throttle. * Data security complications in dealing with confidentiality, non-repudiation, and authentication. * Large data handling barriers in data retention, accessibility, and visualization. * Very limited research has been conducted on the functioning of DT in the retiring/decommissioning phase. With the known limitations highlighted above, DT has recently emerged as one of the most powerful tools with the aid of high-tech computational resources, AI functions, Big Data Analytics, etc. Thus, the same is being vastly adopted by academia, industry, and research organizations. In the maritime domain, one of the most critical aspects is communication, which is a mandatory prerequisite for any DT-based system. The data link between the onshore, offshore, or underwater physical model with the DT is to be established with continuous synchronization. With the development of satellite links and shore-based networks for coastal navigating vessels, DT is becoming much more practical for real-time implementations. Comprehensive data exchange and a model-based review process are to be inducted into existing manual operations. It will enable achieving a full Model-Based Definition (MBD) [133], which is mandatory in the DT implication process. However, a Digital Shadow or a Digital Model is a possibility by updating the digital image manually or whenever the communication link is established. A collaborative data handshake is mandatory with a cohesive data network accessed by all stakeholders [94]. Missing data or faulty data due to sensor failures can create an entire system failure in a DT-based system. This data should be coherent without any disparity to function in DT modules with the ability to unify the data among the cooperating partners. Further, most industries pose scattered ownership of data and the same are maintained in different formats, interfaces and software [134]. Unification and standardization of these mandatory data policies in DT can be a challenge. Furthermore, with the development of more robust underwater communication technologies, in the future, DT solutions will come into play with automated submarines and other underwater applications. DT-based solutions will be able to overcome the communication gaps in AUV operations incorporating continuous research and development will be the key to imposing a complete transition from existing obsolete platforms to DT-based suits within the maritime industry. It has been evident from the literature survey that DT technology has tremendous potential across various segments in the maritime domain and despite being in its early stages of implementation, worldwide research and development efforts are underway.