# Study on the Propeller Rope Cutter Concerning Transient Torsional Vibration Due to Cutting Action
## 6 Conclusions  
The rope cutter system poses a great advantage in protecting the propulsion system. However, it produces transient torsional vibration during the cutting action. In this study, the optimal size selection and calculation method of the connecting bolt for the rope cutter was studied considering the permissible torsional stress of the propulsion shaft. If the rope cutter encounters foreign substances that cannot be cut, such as a large diameter rope or a piece of wood, the connecting bolts can be damaged first either in the thread or body part according to the force distribution condition so that the rope cutter is released, thereby ensuring the safety of the ship's engine and propulsion system. Therefore, by applying this method when designing scaled rope cutters in actual application, it is considered that the connecting bolts can act as a safety device to protect the propulsion system. Moreover, the effect of the rope cutter on the power performance and transient torsional stress characteristics of the propulsion system was studied on the basis of experiments in a water tank and in the shipboard test. In both tests, a strain gauge with a telemetry system was used to measure the transient torsional stress at the intermediate shaft. From the result of the experiment in a water tank, it was found that the shear stress of ropes with the same material was almost the same regardless of the rope diameter, and the transient torsional stress can be estimated to prevent fatigue failure of the shaft. Then, regarding the permissible transient torsional stress, the cutting capability of the cutter system was determined as the rope diameter of 59.4 mm for the laboratory-scale experimental system and 180 mm for the propulsion system in the shipboard test. These results are applied for the polypropylene objects, which are the most common marine debris. In case of the other material, the same experiment can be performed to determine the corresponding cutting capacity of the cutter system. Finally, it was confirmed that the operation of the rope cutter has no significant effect on the power performance and the structure vibration characteristic of the propulsion system.  
Figure 17: Comparison of rotating angular velocity at the intermediate shaft during engaging test No. 2.  
**Author Contributions:** [PERSON]-S.K. and [PERSON] have contributed equally to this work. Conceptualization, W.-S.K., Q.D.V. and W.-J.L.; methodology, W.-S.K., Q.D.V. and W.-J.L.; software, S.-K.Y.; validation, Q.D.V., W.-J.L.; formal analysis, Q.D.V.; investigation, S.H.Y. and M.-H.P.; resources, W.-J.L.; data curation, A.J.N.; writing--original draft preparation, Q.D.V. and W.-S.K.; writing--review and editing, J.-u.L., J.-w.L. and W.-J.L.; visualization, W.-S.K.; supervision, J.-H.C.; project administration, J.-H.C. and W.-J.L.; funding acquisition, W.-J.L. All authors have read and agreed to the published version of the manuscript.  
This research was supported by the BK21 Four program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education of Korea(Center for Creative Leaders in Maritime Convergence) and by the \"Leaders in Industry-university Cooperation +\" Project funded by the Ministry of Education and National Research Foundation of Korea.  
**Data Availability Statement:** Not applicable.  
The authors declare no conflict of interest.