# Developments in Electric and Green Marine Ships
## 3 Technologies that Did or Will Shape the Future of Naval Travel and Trade
### Wind Power Re-Emerges in the Maritime Industry
As mentioned before, the maritime industry receives significant pressure in order to reduce its emissions. Furthermore, technological breakthroughs and improvements have secured a solid know-how on numerous green technologies. In the naval sector, there has been attempts to implement green technologies on board. As far as wind energy is concerned, two representative technologies share the same philosophy with rigid and rotor sails respectively, but this time, discoveries in the material sector (e.g., alloys, carbon fiber) along with digitalization and monitoring (e.g., automations and sensors) can make the difference toward successful implementation. Starting with the rigid sail concept, the idea is the same as the one in 1980. The main difference is that this time, the sail is equipped with numerous sensors, which combined with an automated system give the sail the capability of turning to the specific angle, in order to provide the optimum propulsion force. Moreover, such rigid sails seem to be capable of simultaneously utilizing solar energy by having photovoltaic panels attached onto them. An example of this technology can be seen in Figure 5. The specific rigid sail is part of an integrated energy system that incorporates photovoltaics, the battery system, fuel consumption monitoring, and a central control panel that is added to the preinstalled control panel of any vessel. It is reported that it has been evaluated for more than four years in test labs, outdoor evaluation areas, and during a joint trial project in Greece with one of the leading companies in RoRo and passenger vessels in the region. This project resulted in the first installation of combined marine solar power and fuel consumption monitoring system on board of a high-speed RoRo ferry [49]. As far as Flettner rotors are concerned, they have been successfully implemented since 2008. Although they did not reveal any operating malfunctions and have operated since then, they did not expand commercially. Ten years later, the interest for these rotors is revived, due to new research and development of a new generation of Flettner rotors. The philosophy of the rotor is again the same, entirely based on the Magnus effect for providing moving force. However, there have been significant technological improvements mostly in the design features, such as lightweight materials, high-performance bearings, and the ability to rotate at high speeds that could possibly commercialize Flettner rotors in the modern maritime industry [48]. Figure 5: Aquarius Marine Renewable Energy MRE [50], © 2019 Eco Marine Power Pty. Ltd. Both of the above systems do provide increased efficiency compared to their older version. This increased efficiency is mainly due to the technological improvements that the new versions incorporate. In greater detail, both systems exploit the capabilities of multiple installed sensors, acquiring big data that are read by a computer system. Then, the computer system is capable of optimizing the whole operation of the sail (i.e., rigid or Flettner rotor), increasing the total efficiency of the system. Both sails have finished sea trials.