# Changes in Propeller Shaft Behavior by Fluctuating Propeller Forces during Ship Turning
## 5 Conclusions  
This study successfully cross-validated the effect of eccentric propeller thrust fluctuations on the shaft behavior in the case of excessive dynamic conditions through strain gauges and displacement sensors.  
The shaft measurement was performed under two conditions (FL and NB), and the following results were obtained regarding the effects of the hydrodynamic force of the propeller that was generated during port and starboard turns on the behavior of the shaft system.  
1. The moment behavior of the shaft shifted downward in the counterclockwise direction during the port turn compared with going straight ahead, while it shifted upward in the clockwise direction during the starboard turn, and the opposite trend could be observed.  
The reason why the shaft behavior patterns were contrary to each other is that the formation of the wake field at the rear of the stern tube would be completely different depending on the rudder angle.  
This was cross-validated using the shaft's vertical displacement value obtained from the displacement sensor. However, we were unable to measure the vertical displacement due to the limited number of sensor applications. Given that the shaft's moment behavior varies in the clockwise and anticlockwise directions, further studies with enhanced sensing applications should be performed to improve the accuracy.  
2. The shaft continuously moved upward for a longer period of time under the normal ballast condition compared with the fully laden condition during starboard turns. Therefore, we recommend that ships avoid rapid starboard turns under ballast draught conditions in terms of securing the stability of the shafting system. Moreover, from a long-term perspective, we recommend that the research on evaluating the effect of the bearing force on the shafting system due to a non-uniform wake distribution be further extended.
3. The key finding of this study is that, even with the same starboard turn, a greater load is applied to the stern tube bearing under ballast conditions compared with fully laden conditions. This could be a significant contribution to the literature, as the conventional quasi-static analysis methods cannot yield these results.  
In particular, this study offers a meaningful insight into the causes of the overload of bearing loads in the transient operating state as it reproduced the same situation at the time of the accident with the same type of vessel. Furthermore, we expect that the results of this study will be used in the development of the health monitoring algorithms required for autonomous ships in the future, and they may also help with the development of guidelines for improving the stability of systems in related industries.  
[PERSON] and J.[PERSON] contributed equally to this work. Conceptualization, J.-W.L. and J.-u.L.; methodology, J.-u.L. and Q.D.V.; software, Q.D.V.; validation, J.-W.L. and J.-u.L.; formal analysis, J.-W.L. and J.-u.L.; investigation, J.-W.L. and Q.D.V.; resources, J.-u.L.; data curation, Q.D.V.; writing--original draft preparation, J.-W.L., Q.D.V. and J.-u.L.; writing--review and editing, B.J. and J.-u.L.; visualization, Q.D.V. and J.-W.L.; supervision, B.J. and J.-u.L.; project administration, J.-u.L.; funding acquisition, J.-u.L. All authors have read and agreed to the published version of the manuscript.  
This work was supported by a National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (No. NRF-2021R1F1A1047115). This research was supported by the 'Development of Autonomous Ship Technology (20200615)' project funded by the Ministry of Oceans and Fisheries (MOF, Korea).  
Not applicable.  
This research was supported by the BB21 plus project funded by Busan Metropolitan City and the Busan Institute for Talent and Lifelong Education (BIT).  
The authors declare no conflict of interest.