# A Study on Identification of Development Status of MASS Technologies and Directions of Improvement
## 4 Design, Communication and Maintenance Studies of the MASS
### Design of MASS
In addition, removing the deckhouse will reduce air resistance, which typically represents about 2% of the total resistance of a vessel, and thus improve ship resistance efficiency [39]. Ship lightweight reduction, while deadweight is maintained as constant and without life-sustaining systems such as heating, ventilation, and air conditioning (HVAC) for the crew as a consequential change, will also reduce electricity and fuel oil consumption. It is also expected that the autonomous ships will use a wider range of physical sensors than current conventional ships to control autonomous functions, including global positioning system (GPS); inertial navigation system (INS); optical and infra-red (IR) cameras; light detection and ranging (LIDAR); radio detecting and ranging (RADAR); microphones; and wind and pressure sensors. It should be noted that, unlike the cost saved by removing deckhouses from the ships, these will increase costs for the additional sensors and installation, design of system integration, and maintenance with a redundancy of the sensors. Regarding the propulsion systems, it is expected that autonomous ships will have different engine systems and propulsion configurations compared to most of today's large commercial ships operating with conventional propulsion systems with internal combustion engines. With the rapid development of technology, autonomous ships are likely to introduce fully-electric propulsion systems consisting of electric propulsor, power sources (e.g., lithium-ion batteries, fuel-cells), and control systems. Recently, electric propulsion vessels have been developed and tested all over the world with a variety of multinational projects to make the MASS a reality. However, despite the advantages of the electric propulsion system for the autonomous ship, for propulsion in long-range voyage for international trades, there are still significant developments to be made in order to rely solely on electric power sources, and the space and arrangement of the sources to also be considered. In its early stages, hybrid applications, in combination with a sulfur-free fuel such as LNG, could be a solution for the ship. It is expected that a fully electric propulsion system will have a propulsion drive train that is purely electrically driven, while a hybrid system will have a combined mechanical and electrical propulsion drive train. The autonomous or unmanned ship also has a high possibility of installing a full-battery power system with a DC-grid instead of an AC-grid for electric propulsion and distribution systems, due to power stability and low economic cost [40]. A DC-grid is more suitable than an AC-grid (currently applied as a standard power system), especially for electric propulsion ships with many variable frequency drives (VFDs) to control motors such as heavy-lifting cranes, propulsion or thruster motors, pumps, and compressors. [41]. Developments in renewable energy, and energy storage systems (ESSs) have supported the growth of the DC-grid. The electric propulsion systems with DC-grids would be applied to the MASS by further demands of the market for cleaner and more efficient electric power, taking into account stricter environmental regulations. With all these taken into consideration, design changes for autonomous cargo ships above MASS 3 were investigated and are presented with their potential impacts in Table 3.  
Regarding the sensors applied to MASS, one of the main functions will be situational awareness of the ship's surroundings, especially in order to avoid grounding and collision with other ships, vessels, people, marine mammals, or other obstacles that may be encountered. Therefore, the reliability of the sensors, which failures can cause a serious threat to the safety of the system, must be ensured through design approval as well as remote and on-premise testing and periodic inspections.