# Using Digital Twin in a Shipbuilding Project
## 4 Using Digital Twin in the Shipbuilding Process
### Digital Twin Development Phases  
The modern software programs for 3D modelling enable the defining of ship outfitting technology that could, with (i) highly developed planning documentation, (ii) an accurate overview of technological assembly requirements to outfit (position, function, dimensions) and (iii) timely procurement of the same, theoretically result in the almost complete outfitting of the ship in the construction phase before blocks assembly, i.e., joining at the slipway (advanced outfitting).  
Following the initial requirements of the client in terms of the development of the vessel, in the initial design phase, the observed shipyard models the ship [15], using program tools such as Rhino, version 5, and NAPA 2022.1, which, by their software content, enable, among other things [27], the parallel implementation of hull shape optimisation by CFD analysis and ship stability calculation, in iterations until the criteria for the ship's input parameters are met; hull optimisation is approached after the ship's speed prediction data confirm the adequacy of the modelled form. Further on, in the initial design stage, a preliminary designed key outfit (engines, generators, air conditioning units and all other big outfitting items in terms of volume and weight) is positioned into the ship model, which creates the \"Digital Twin ship of early stage\" [1].  
After signing the shipbuilding contract, 3D ship modelling continues [15] by implementing CAD software application such as AVEVA Marine, version 12.1, which enables designers (modellers) and technologists to choose the best technical-technological solutions in the virtual surrounding of the ship space [6] aiming to define the highest possible outfitting level in the blocks's section phase, i.e., before lifting them on the slipway (\"On-time Outfitting\"). Virtual ship modelling in this design phase creates a \"Digital Twin ship prototype\" [1]--a 3D ship model supported by the material components, technological data sheets and other documents required to extract workshop documentation (from the 3D model), meaning the start of production (steel cutting). The interaction of the shipyard's, client's, classification society's and the key suppliers' teams through work on the ship's digital prototype enables the advanced optimisation of design solutions to meet customer requirements with reduced costs in the ship's construction and operation, and thus greater cost-effectiveness of the project [18]. A segment of the 3D ship model developed by the AVEVA program tool is shown in Figure 6.  
From blocks's section until the ship's delivery, the virtual model becomes an \"Experimental Digital Twin ship\" [1]. With constant interaction between the designers, technologists and outfitting workshops [15], the preparatory (initial) designed state and the performed one are compared and analysed, i.e., outfitting situations between the virtual and physical spaces are harmonised; this prevents errors in outfitting and allows for timely changes in the design (i.e., if the client requests the same or different outfit is chosen), while avoiding or minimising the need to engage (additional) production hours in outfitting. The mentioned interaction can be upgraded to a far higher level with the help of Augmented Reality (AR) tools [14; 18] and result in even better, i.e., more timely, harmonisation of the virtual and physical environments, and thus reducing the \"Design department-Production\" communication hours about the subject. Furthermore, involving the owner's representative in Augmented Reality using appropriate devices (tablefor instance, speed up the adjustments, i.e., decision making about the implementation of possible requests for modifications.  
Ultimately, depending on the software tools available to the client, as well as outfitting the ship with appropriate sensors and actuators [1; 10], the Experimental Digital Twin ship, after the ship's delivery to the owner, can become a Digital Twin ship in the full sense [9]. Figure 7 shows the Digital Twin development phases.