With the recent increase in the volume of liquid cargo transportation, there is a need for STS( Ship To Ship) globally. In the case of the STS mooring, the safety assessment should be conducted according to other criteria because mooring is different from the general mooring at the quay, but there is no separate standard in Korea. Thus in this study, STS mooring simulation and sensitivity analysis using OPTIMOOR program, the numerical analysis program, was conducted to identify the characteristics of the STS mooring. The target sea modeled the Yeosu port anchorage in Korea and the target ship was selected as the case of VLCC (Very Large Crude Oil Carrier)-VLCC. Through the numerical simulation and sensitivity analysis, the characteristics of STS mooring were identified. Also based on these results, we focused on establishing the standard for STS mooring safety assessment. Numerical simulation results show that the STS mooring safety can be changed according to a ship's cargo loading condition, pre-tension of mooring line, sea depth, encounter angle with the weather, and the weather condition. Additionally, the risk matrix is prepared to establish the safe external force range in the corresponding sea area. This result can be used to understand the mooring characteristics of STS and contribute to the revision of mooring safety assessment criteria.

Abstract
1. Introduction
2. The status of Ship-to-ship transfer
3. Mooring safety assessment of STS
    3.1 Summary of mooring safety assessment
    3.2 Sensitivity analysis
4. Risk matrix based on weather condition
5. Conclusion
References

• Sang-Won Lee(Graduate School of Maritime Sciences, Kobe University)
• Hyeong-Tak Lee(Graduate School, Korea Maritime and Ocean University)
• Dae-Gun Kim(Korea Institute of Maritime and Fisheries Technology)
• Ik-Soon Cho(Division of Global Maritime Studies, Korea Maritime and Ocean University) Corresponding author