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 investigation of issues of optimized design and modeof DC power distribution sub-systems for commercial ships, in the light of energy saving, optimization of their performance 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 Configuration of an electrical ship system with EP and electroprojection. (b) Configuration of the ship's electrical power system with DC
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 requirements for all energy systems on board to be efficient as well. Besides, the electrification of the ship's systems, including the propulsion system, has become an attractive alternative choice 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 totally used equipment is of smaller size and less 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 system of DC electricity of a ship under study is carefully designed (prevention for the installation of the specific NPP in the General Arrangement), then the total installation and operation costs can be significantly lower than the corresponding AC.
• 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 Naval Engineering School of the NTUA (NTUA / NTUA), taking into account the important scientific and economic interest already observed in the global maritime community, is at the forefront of developments with extensive research action, including publications in international conferences, scientific journals and projection of her work to representatives of the Greek and international shipping industry. Among these actions is the work "DC-Ship", which is carried out by the research team of An. Professor of SNMM / NTUA, Mr. Ioannis Proussalidis.
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.
