# Using Digital Twin in a Shipbuilding Project
## 1 Introduction
Modern software applications enable 3D modelling from the early beginnings of an entity's development, i.e., the initial design phase, as well as interconnectivity with various software modules such as Assembly Planning or Material Planning, all as a prerequisite for prototyping the vessel in Digital Twin form and content; such a 3D model, i.e., Virtual Reality (VR), with the future upgrade to Augmented Reality (AR), enables all stakeholders involved (horizontal integration [3; 7]) to define the best possible technical-technological solutions aiming to optimise the construction, exploitation and decommissioning of the entity [9; 18]. A further precondition for creating a Digital Twin is the existence of an appropriate IT communication infrastructure (digital thread) that enables uninterrupted data flow, i.e., managing the same when integrating the virtual and real surroundings [19; 20]. Due to the lack of quantitative research related to the improvements in shipbuilding processes by implementing digital technologies, and with accepting the thesis of Digital Twin's primary importance of its role in Shipyard 4.0 [7], including to the marketing and sales activities [18], the main interest of this research is aimed towards the analysis of the  
Figure 1: Digital twin—conceptual model. impact of Digital Twin's implementation to productivity in the process and contribution to the green transformation of the shipbuilding system. Furthermore, there are very few analyses and researches considering the advanced outfitting in shipbuilding [21]: very few discuss the approach of shipyards in different market niches towards outfitting activities' distribution through the shipbuilding process [22; 23; 24], whereby only a few investigate the potential advantages of implementing advanced outfitting in the earlier stages of ship construction, though they have analysed only a particular type of new builds [25]. Following the subject gap that is shown after reviewing the literature, the main purpose of this study is to further research the eventual accomplishments in terms of the shipbuilding processes' cost deductions by improving the advanced outfitting in the shipbuilding system within the market niche of cruises, i.e., passenger vessels. Shipyards in general are looking to improve their competitiveness primarily by reducing supply and labour costs as well as construction time; in that respect, the advanced outfitting could offer a significant reduction in the number of man-hours engaged for the outfitting activities, as well as a decrease in the various types of costs, such as insurance, financing, energy, consumables and sickness leave. That being said, the authors' intention is to respond, through this research, to the following questions:  
* Q1: Does the outfitting of new builds in earlier stages of construction improve the competitiveness of the shipbuilding system acting in the niche of passenger ships, i.e., cruise vessels? * Q2: Does the 3D modelling of the vessel in the Digital Twin form and content enable a larger scope of outfitting activities to be performed in earlier stages of construction? The methodology of the research is based on a case study, i.e., the collection of statistical and empirical data gathered by one European shipyard, investigating distinctions in the realization of two new build projects considering the building duration between main events, the total number of man-hours spent on welding and outfitting activities, the electric energy consumption, as well as the injury frequency and severity rates; the basic difference in the realisation of subject vessels is that one is designed and built by using a 3D model but in the Digital Twin form and content. This paper presents the improvements achieved through implementing Digital Twin in the shipbuilding process of the observed shipyard due to the accomplishment of outfitting activities at a higher magnitude within the early stages of ship building.