# Digital Twin in the Maritime Domain: A Review and Emerging Trends
## 3 Adoption of Digital Twin Technology for the Marine Sector
### Ship Electrification  
The first electrical propulsion system was introduced by Russian scholar [PERSON], which was a paddle boat driven by an electric motor. Due to the low battery capacity and efficiency, the maximum speed achieved was 1.5 knots, which discouraged the development of a system for a long time ahead [22]. In 1903, Swedish shipyard ASEA built the river  
Figure 3: Pathway of Digital Twin Technology within the Shipping Industry.  
Figure 2: Difference of data topologies among Digital Model, Digital Shadow, and DT.  
tanker \"Vandal\" as the first vessel to carry a diesel-electric propulsion system [23]. At the end of WWII, more emphasis was placed on the development of electrical propellers and ships such as the Ice Tanker \"Uikku\" and Passenger Ferry Queen Mary 2. Uikku was the first ship to be installed with an Azipod propulsion system where the main electric motor was installed in a separate gondola that could direct the thrust with a 360\({}^{\circ}\) control. RMS Queen Mary 2 is a luxury cruise liner propelled by hybrid diesel turbo-electric propulsion with four 18 MW Azipods driven by two gas turbine generators and four diesel engine-driven generators. This propulsion topology has provided navigation flexibility along with economical gains in varying speed demands and different passage legs while complying with emission control protocols [24].  
Integrated Full Electrical Propulsion (IFEP) is reducing fuel consumption heavily by avoiding the low load portion of fuel consumption curves in sharing the load of propulsion along with ships' service loads including the weapon systems [25]. It is far superior to the standard propulsion systems such as Combined Diesel Electric and Gas (CODLAG) systems or Combined Diesel Electric or Gas (CODLOG) [26]. The latest US Navy stealth Destroyer USS Zumwalt was commissioned in the year 2016 as the first full-electric warship equipped with an integrated power system [27]. Further, with the initial project of MS Medstraum, Norway has implemented the world's first battery-powered ferries to transfer vehicles and people with greener environmental insights [28].  
With the development of IFEP, ship designers further developed the concept of All-Electric Ships (AES) [29]. The AES concept has provided high redundancy and mission capability even at a slight initial cost. At present, most of the high-end naval ship projects have opted for this technology due to the advantages posed by the electrical-based high-power navigation, communication, and weapon systems. Royal Navy Type 45 Destroyers and the aircraft carrier HMS Queen Elizabeth [30] are a few examples of AES-based power topology. Hybrid powering topology is also developed and implemented to achieve the redundancy and advantages of both mechanical and electrical drives.  
Benefits of the Electrification in Marine Vessels [31]:  
* Efficiency is improved as a huge prime mover will be replaced by an array of diesel alternators and the load can be catered at the highest efficient speed with the generated thrust by more efficient electric motors.
* The load can be managed easily to cater to the demand based on each mission.
* Improved maneuverability of the vessel and faster response where padded propellers will allow 360\({}^{\circ}\) steering along with dynamic positioning.
* Flexibility in placing the generators in the ship without considering the shafting arrangements.
* Allowing the introduction of cleaner and more efficient future power-generating technologies such as fuel cells, renewable energy, etc., to the existing vessel.
* Emission control goals can be easily achieved.