# Digital Twin in the Maritime Domain: A Review and Emerging Trends
## 5 Developing a Ship Digital Twin Architecture
### 4-Layer Digital Twin Framework for a Marine Vessel  
From the initial contract of a ship until the final scrapping after decommissioning of the vessel, she will undergo various lifecycle phases with different actions in each stage. It will be governed by the functional requirements of the different stakeholders and Ship DT can provide valuable insights to support each activity in her design and development, validation, production, operations, and decommissioning stages. During the total lifespan of a ship, it will surpass the actions of marketing actions, the realization of the customer's intended design, optimization of the designed model using various physical/simulated methodologies, monitoring the entire functionality during her operational phase with correct control of all the actions, prognostics, diagnostics, predictive maintenance, etc. The DT of a marine vessel can deliver and support all the actions with the merits of its inherent advantages. Hence, the following 4-layer DT framework (Figure 8) is proposed in this paper with abstracted segments of Business, Tactical, Application and Operational Layers.  
1. Business Layer: Initial specifications and ship owners' requirements will be met with the design, marketing and business analytics performed with the support of the DT. Simulation and validation of the prototype will be efficient and effective with the incorporated DT model and all information will be shared with the project team of the shipbuilder, allowing easy project management through a modular shipbuilding approach.
2. Tactical Layer: This will be mainly manipulated by the onboard crew if present or by the shore operator if unmanned during the operational phase of the vessel. With Integrated Platform Management System in the DT with real-time health monitoring,  
Figure 8: Proposed 4-Layer Ship DT Framework.  
navigation, communication, traffic control, load control and other ship functions will be governed with the support of DT with full integration of the ship's systems.
3. Application Layer: This is the primary segment of handling the collected data within the ship, shore command center, and ocean environment. Big data handling and cloud-based operations will heavily rely on the communication data uplink and downlinks. Artificial Intelligence will play a major part in future unmanned autonomous vessels, thus providing the advantages generated by higher levels of autonomy in the operational cycle. Machine Learning/Deep Learning can be incorporated as sub-layers in this process.
4. Operational Layer: This is used at the functionality level of the shore operators and system engineers to support their intended operational plans and strategies. The acquired data through the DT can be deeply analyzed and manipulated in decision-making related to every life cycle phase of the vessel. Supply chain management, CBPM and system development will be key benefits that will be availed through the ship DT in this layer.  
The above framework is proposed as a common generic architecture and it can be easily modified, transformed, and adopted as per the user requirements. DT will be available for every patron in the hierarchy of ships operation with dedicated access to the intended data and information. A DT of any ship or offshore structure will be designed to render its present state and behavior with real-time updates in a continuous manner. This update will not only be limited to the data handshake, but also the continuous addition of parallel components to support different functions introduced in different stages of the vessel lifecycle. It will be identical to the physical asset cardinality covering all functions representing the engineering model with all possible metadata in the real-time state.