###### Abstract  
Shipping is an indispensable tool for the sustainable global supply chain, and seafarers play a key role in safe navigation. Maritime autonomous surface ships (MASS) have been expected to reduce marine accidents by human error of the seafarers. On the other hand, MASS may have adverse effects on operators' mental workload (MWL) and increase safety risks in some cases. This research aims to provide a scheme for identifying the relationship between MWL and MASS in the maritime that can be utilised for rulemaking and technological development. The provided scheme identifies the factors that affect the MWL of operators and sub-elements of MWL through gap analysis. Five factors related to MASS operation were defined, in addition to general factors. The case study was carried out by utilising the scheme on typical cases focusing on the normal navigational situation. The NASA task load index method was used to measure MWL. Ten deck officers with various ranks, including the third officer and captain, participated in the case study. The results suggested that various causes such as conflicted situations, machine-human interfaces, mechanical-style movements of the ship, reliability of MASS, and visibility constraints affect the MWL of operators. It also confirmed the verification of the identification scheme. maritime autonomous surface ships (MASS); mental workload; identification scheme; navigation; regulation; stress +
Footnote †: journal: Medical  
safety and security. Crews are exposed to significant stress from work pressure compared to land-based work [9]; therefore, controlling MWL is vital for ship safety. One useful solution to overcome the issue is ship automation, autonomy, and remoteness. The contemporary development of information and communication technology, including computation and artificial intelligence (AI), has enabled these ships' emergence. IMO defines these ships as maritime autonomous surface ships (MASS). The broad level of autonomous ships has been demonstrated and developed technologically. Examples are international voyages using a navigation support system [10], a fully autonomous project demonstrated in coastal water [11], and an unmanned commercial ship planned in Norway [12]. On the other hand, automation and autonomy will not always decrease mental stress, but rather heighten the risk of human error in some cases. For example, a remote control system needs a higher level of cognition for operators [4] and might lead to higher mental stress. Remote operators' stress at the remote control centre (RCC) might sometimes increase due to information overload by receiving enormous amounts of visual data to compensate for the lack of the feeling of the environment inside or outside a ship [13]. According to [PERSON] [14], the workload generally increases at the decision-making stage in automation despite decreasing the situation awareness at the implementation stage. This implies that seafarers' stress navigating MASS might be higher at the decision-making stage than traditional ships, depending on the automation level. [PERSON] et al. [15] suggested a relationship between keeping psychological conditions and operating remotely controlled ships safely. Taking into account ship safety and the mental health of operators navigating MASS (from now on called \"operators\"), the MWL of operators should be retained at an appropriate level [4]. The activities to ensure the safety of MASS through international regulation have been carried out at the IMO. It adopted the interim guidelines for a trial in 2019 [16]. It has also conducted regulatory scoping exercises (RSE) of international regulations, including 13 conventions related to maritime safety [17], since 99 sessions of the Maritime Safety Committee (MSC). In the RSE discussions, the IMO [17] shows four regulatory ways to achieve safe operation of MASS, including \"amending existing instruments\" and \"developing new instruments\".