The School of Naval Architectural Engineering of the National Technical University of Athens (S-NMM / NTUA), which has been developing for the last few years the technology of the Fully Exploited Ship, through the MARINELIVE Center for Excellence which has created and coordinates the research project "DC-Ship" "EXISTING-I" framework of the NSRF (2007-2014), which goes towards completion.
The main innovation of the "DC-Ship" project is the in-depth exploration of optimized design and operation issues for Continuous Power Subsystems for commercial ships in terms of energy saving, performance optimization and environmental friendliness .
For this purpose, an interdisciplinary research project has been developed that penetrates the scientific areas of the mechanic engineer, electrical engineer and energy engineer, and includes theoretical analyzes, simulations and experimental tests.
(a)
(Β)
Figure 1. (a) Typical Electrical System Configuration shipy with EP and electropropulsion. (b) Configuration of the ship's electrical power system with SR
Environmental pollution and the greenhouse effect of ship exhaust emissions have led to stricter regulations in relation to pollutant emissions and fuel savings.
In turn, the need for more efficient ships leads to increased demands that all energy systems on board are also efficient. Moreover, the electrification of the ship's systems, including the propulsion system, has become a tempting alternative to increase its performance.
In fact, for specific types, the more intense their electrification (according to the idea of the All Electric Ship), the more energy efficient they become. In this context, a sub-case that has recently started to be of interest is the use of Direct Current-DC technology, especially for the electricity distribution network, Figure 1.
This technology offers obvious advantages, such as:
• the total used latest technology equipments are smaller in size and lighter in weight,
• Non-reactive power circulation and reduction of overall losses, resulting in fuel savings (used to produce the required electricity from sources),
• the parallelism of energy sources is easier and simpler, as well as the combination of various sources of environmentally friendly electricity (eg photovoltaic, fuel cells, etc.) or storage (eg batteries) or even interconnection with the electrical cold ironing,
• Monitoring and control of the electricity system is made easier,
• If the Continuous Power Electricity System of a ship under study is carefully designed (prevention of the installation of the particular NAS in the General Arrangement), then the total installation and operating cost may be significantly lower than the corresponding Alternating Power.
• utilizing all of the above, it is possible to significantly improve the performance of a ship under study. It is characteristic how in a techno-economic study carried out comparing the configurations of fig. 1 above, the layout with SF helped to save 20% more space, was 10% lighter and presented 8% less losses compared to classical electropropulsion (Figure 2). 
Figure 2. Comparison of EP and DC power systems
• By increasing system performance through optimum generator operation and volume and mass saving, it is possible to drastically reduce emissions (reduction of CO2 and greenhouse gas emissions - Figure 3).
• As a direct consequence of all the above, it is the best classification of such ships, based on the EEDI Energy Efficiency Index set by the International Maritime Organization (IMO) Figure 4. 
Figure 3. Estimated reduction of carbon dioxide emissions for modulation with DC
Figure 4. EEDI index for EP and SP configurations compared to the limits set by the IMO
It is noted that the international research around DC technology has only just begun recently to be cultivated in principle for special type ships, while interest is slowly spreading to commercial ships which are the backbone of maritime transport and for which studies are already being carried out with the aim of developing methods to reduce their pollutants.
The School of Naval Mechanical Engineering of the NTUA (SNMM/NTUA), taking into account the significant scientific and also economic interest that is already observed in the global maritime community, is at the cutting edge of developments with a rich research activity, which includes publications in international conferences, scientific journals as well and promotion of her work, in antipersonof the area of Greek and international shipping. Among these actions is included the "DC-Ship" project, which is carried out by the research group of the Senior Professor of the National Technical University of Athens, Mr. Ioannis Prousalidis.
For more information, please contact Mr. Ioannis Proussalidis, Associate Professor of the NTUA at jprousal [at] naval.ntua.gr, or visit the project website marineelectrical.gr/index.php/dc-ship-2 ή www.dc-ship.org.
