# A Review of Autonomous Tugboat Operations for Efficient and Safe Ship Berthing
## 5 Conclusions  
In this paper, we analyzed previous studies on relevant topics to provide engineering knowledge and insights related to autonomous tugboats. Firstly, we explained actual projects being carried out for the autonomous operation of tugboats, and then we conducted an analysis of various required element technologies for constructing autonomous tugboats. Four types of technologies are required for ships using autonomous tugboats: perception, decision-making, modeling, and control technology. We described the necessity and detailed research trends for each technology. Previous studies for each element technology have indicated research trends from the early 2000s to the present.  
The analysis of previous studies revealed that many of them assumed the tugboats to be fully autonomous and did not address certain issues, such as determining the formation for operating tugboats as a cluster during mooring and developing algorithms that automatically assign and reassign tasks such as thrust adjustment for each tugboat. There were also few studies that considered the communication issues between the mothership and each tugboat, assuming that they were strategically positioned close enough to eliminate the need for information transmission. Furthermore, most of the studies were limited to simulations in environments such as MATLAB and Pygame [28], without verification in real-world maritime environments.  
Research on berthing using a fully autonomous tugboat requires verification of various scenarios in an environment similar to the actual environment, and it is necessary to overcome the limitations of the state of the art. Firstly, research is needed to develop an algorithm that automatically assigns and reassigns tasks to the tugboat swarm for the scenarios of the towing and berthing mode. Each individual tugboat should be reassigned roles to perform a given task by receiving control objectives and methods according to the goals required for each mode. Secondly, precise modeling of the towline, individual tugboats, and mothership must be based on multibody dynamics for the towing and berthing mode. Considering the operational method where the tugboat pushes and pulls the towline, modeling of the entire system that includes tension in the towline, friction between the tugboats and mothership, and the environmental disturbance is necessary. Finally, it is deemed necessary to have communication/network technology that allows each tugboat to exchange information, as well as fault diagnosis and response technology that can immediately detect and respond to any malfunctions in the tugboat's components.  
Previous research has made progress in control and modeling techniques, as well as various other technological elements; however, to achieve autonomous berthing of ships using autonomous unmanned tugboats, research is needed not only on individual unmanned tugboats but also on the technologies required to operate them in a swarm manner. If autonomous surface vehicles are successfully employed in ship berthing operations, significant technological ripple effects could reduce personnel costs and save time.  
Figure 24: Hierarchical structure for mooring system decision [48].  
**Author Contributions:** Conceptualization, J.W.; investigation, J.-H.C.; resources, J.-H.C.; writing--original draft preparation, J.-H.C.; writing--review and editing, J.-H.C., J.-Y.J. and J.W.; supervision, J.W.; project administration, J.-H.C., J.-Y.J. and J.W.; funding acquisition, J.W. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was supported by Korea Institute for Advancement of Technology (KIAT) grant funded by the Korea Government (MOTIE), grant number P0017006\". (P0017006, HRD Program for Industrial Innovation).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
**Conflicts of Interest:** The authors declare no conflict of interest.