# Digital Twin in the Maritime Domain: A Review and Emerging Trends
## 4 Present Digital Twin Manipulations in Marine Industry
### Embryonics in the Shipping Industry  
DNV GL has tested a fully autonomous 60 m-long concept vessel, ReVolt, which is a battery-powered cargo carrier with zero crew [49]. DT is an integral part of the design and testing of this conceptual vessel and the same will be utilized during the operation of the vessel. Testing of the vital systems is being carried out using the DT of the concept vessel, which has saved time and money. The same institution also provides a cloud networking solution, Veracity [50], which can be used to design, access, and manipulate the data in DT. Similarly, Siemens has also launched the Mindsphere [51] venture, which has governance capabilities and data management under the concept of Maritime Data Space (MDS) [52], which is originally based on the concept of the Industrial Data Space (IDS) model. Meanwhile, it also allows for performing safety-critical tests and high-risk maneuvers for any number of attempts as desired in all varying conditions, which would have been a daunting task in a physical model. Using the historical data during the operational phase is used to predict the lifespan of components under varying conditions including position, dynamic environmental factors, speed, load conditions, etc. [53]. The South African polar supply and research vessel \"SA Agulhas II\", which operates in rural and risky arctic environments, has tested the feasibility of implementing a DT-based solution to operate with its benefits such as remote polar research capability, reduction of human impact on sensitive untouched environments, avail of real-time research data for scientists, etc. [54]. Further, the \"Probabilistic Twin\" risk-management tool used by DNV-GL also aims to forecast the probable accidents/damages based on analysis of past data and trends as an extension to the existing Blue Denmark DT Solution [55].  
Having an unmanned vessel in connection to DT will deduct the human error factor in ship operation, and crew space can be spared for vital cargo space. Reduction of energy consumption and waiving of the extra maintenance expenses are other benefits of a DT-based system. Revolt itself is estimated to save a cost of 34 million USD in its 30 years of service life due to autonomous operation along with DT [56]. Emission control is also a huge benefit in such a system. Reducing the machinery and moving parts will further reduce the downtime for maintenance/repairs, reduce human fatalities and be cost-efficient. The vessel can also be designed into a more aerodynamic shape due to the absence of the huge superstructure used for crew accommodation and bridge.  
Not only the direct merchant sector, but even the fisheries, ecological and maritime archaeologists have opted for DT-based solutions for underwater operations. In projects such as SUSHI DROP in Sweden, AUVs are developed and operated in DT-based systems to monitor/survey the marine environment investigating the fish population in a large sea space [57]. This DT-based module can further be incorporated into the ship's HVAC system to optimize the heat usage and distribution in waste heat recovery systems, charge air coolers, heat exchangers, etc. [58].