# A Study on Identification of Development Status of MASS Technologies and Directions of Improvement
## 4 Design, Communication and Maintenance Studies of the MASS
### Maintenance and Repair  
As there will be no seafarer for maintenance and repair of autonomous ships above MASS degree 3 that are operating in isolation from repair and spares facilities, malfunctions of hardware and software could cause more serious problems than current conventional ships. In addition, the software or hardware malfunctions in daily and periodic operations can propagate on a few other components, and the results of such propagation can be both immediate and devastating [51]. To this end, relevant investigation and studies should be proactively conducted in order to identify potential failures that can defeat the functions of MASSs. It is also necessary as preventative measures to improve reliability in terms of hardware and software functions, solve functional problems through remote diagnosis and selection of applicable and effective tasks, and develop a system to make a ship return to a port as a last measure when the ship cannot function or operate appropriately anymore. With the development of automation technologies, a strategy for predictive maintenance and repair would be a better approach to reduce the potential failures, as well as preventive and corrective manual maintenance that is currently carried out during voyages [38]. One of the most important factors of the safety and seaworthiness of a ship is the proper, daily, periodical, and timely maintenance of all her systems, structures, and hull. There has been much research conducted on developing methods of maintenance and repair to solve challenges even in the maintenance approaches currently applied in shipping. [PERSON] et al. [52] applied condition-based maintenance (CBM) to a propulsion system to monitor it and send a signal to the engine room crew in case of degradation of its performance. [PERSON] et al. [53] proposed reliability-centered maintenance (RCM), which focuses on the maintenance resources that affect the system's reliability, thereby making the maintenance program cost-effective during the life cycle of a ship. One of the principles of RCM is that RCM uses a logic tree to screen maintenance tasks; that is, it uses broad categories of consequences of failure to prioritize failure modes [54]. Another approach is risk-centered maintenance (Risk-CM), which uses a combination of probability and consequence, that is, the risk of prioritizing failure modes [55]. To ensure the sufficient reliability of systems and equipment, including sensors as well as any other devices, both RCM, including CBM and Risk-CM, should be considered to find the appropriate  
Figure 2: Systems and functions of MASS and SCC and their relationship. solution for maintenance. The MASS is also required to be equipped with a high level of redundancy and durability and to be highly modular to avoid failures as all equipment and device installed onboard will be interconnected and integrated to enable the collection, management, and analysis of data. However, it should be noted that it may not be desirable in shipping where critical systems usually have only a single redundancy failure, which could be catastrophic. Typically, the most important safety sensors should consider homogeneous and/or heterogeneous redundancy, and diagnostics and/or prognosis [56]. Issues identified and items to be considered for maintenance and repair of autonomous cargo ships are presented in Table 4.  
Autonomous ships without a crew onboard will call for wider adoption of condition-monitoring systems with efficient diagnostic and prognostic algorithms to assess and reduce the potential risk of failures. They are also likely to require a wider and more complex maintenance scheme in port, taking into account resilience to failures and extension of maintenance intervals.