## 3 Methodology
### Flow Analysis  
Another challenge encountered is that the Indonesian government has yet to implement green environmental fuel regulations to support vessel owners to change from conventional to alternative fuel. The government must provide some incentives to attract these individuals to use alternative fuels such as LNG. Figure 8 illustrates Indonesian vessel owners' challenging situation before changing their fuel management to an alternative type, such as LNG. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **High Scenario** & **Medium Scenario** & **Low Scenario** \\ \hline LNG price & USD 1100/MTon & USD 1100/MTon & USD 1100/MTon \\ \hline Maintenance cost & \multirow{2}{*}{10\% increase} & No difference between existing and retrofitted vessels & Lubricating Oil reduce by 50\%, Spare parts reduce by 50\%, and maintenance becomes 33\% lesser than the initial cost \\ \hline Operational cost based on & \multirow{2}{*}{Average} & Average & Average \\ Moore Maritime Index & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Maintenance and crew cost scenario. The data were analyzed using the lower scenario, assuming that the maintenance cost and spare parts were reduced due to LNG usage. This study employed some processes to obtain the cost recovery factor for investing in LNG fuel existing 600 TEU vessels. The first step for the analysis is gaining engine information from vessel owners. The expected data are engine power, specific fuel consumption, and type. The next step is to select the maintenance and crew cost scenarios. In addition, this study compared the high and low scenario investments. A particular study on Niigata's engine manufacturing proved customer satisfaction with gas engine series with low running cost and required maintenance at 4000 h running intervals [40]. [PERSON] stated that switching to LNG as a marine fuel, whether new build or converting existing technology, will generate significant savings in fuel cost, thereby increasing profitability [41]. Operating Expenditure (OPEX) consists of the spares, lubricant, repair and maintenance. Retrofit investment for container vessel 600 TEU constitutes modifying the fuel and gas supply system. This is realized by installing the LNG tank, piping, changing the main engine and installing a gas combustion unit. As discussed earlier, vessel owners usually consider these, including vessel modification and additional equipment installation. The economic analysis requires a 10-year scheme because it is sufficient to review the potential payback from the vessel owners' view and offers future plans for vessel acquisition. Net Present Value (NPV), with respect to a 10-year investment scheme, shows differences between the present cash inflows and outflows. Furthermore, the vessel owner requires an analyzed loan payment in a different scenario. It is calculated based on loan principal, interest, payment, and remaining amount. Figure 8: Flow Diagram for data analysis. Figure 7: Marine fuel price differentials. Some formulas used to calculate NPV and CRF [20] are as follows:  
\[\text{NPV}=\sum_{t=1}^{t}\frac{C_{t}}{(1+r)^{t}}-C_{0} \tag{1}\]  
where:  
\(C_{t}=\text{cash flow for time (t)}\)  
\(r=\text{interest rate}\)  
\(C_{0}=\text{initial investment on year 0}\)  
\(t=\text{time}\)  
\[\text{CRF}=\frac{i(1+i)^{n}}{(1+i)^{n}-1} \tag{2}\]  
An economic analysis of the investment in trans-ocean LNG-fueled container ships, 9300 TEU sailing between Asia and Europe, showed that the LNG low-speed diesel vessels compared to oil-fueled SCR is more attractive [27]. Furthermore, [PERSON] et al. discovered that the NPV with a lifetime of 20 years is larger, while the refund time to payback is shorter for LNG vessels. [PERSON] et al. also economically analyzed the lowest CAPEX for retrofit fuel gas supply systems and discovered a lower LCC on the auxiliary scheme [18]. LCC analysis allows the assessment of some shipping costs.