# Comparative Analysis of Marine Alternative Fuels for Offshore Supply Vessels
## 2 Methodology
### Matrix Analysis (Step 8)
#### 2.8.3 Results of Scoring  
The responses were made by eight (8) persons, four from UoS and four from ORE Catapult. Table 20 shows the results of the linguistic assessment for the consortium members, which confirm the weighting factors for top and sub-attributes. Based on that, the final 'Decision matrix' has been developed and provided in Figure 9. \begin{table}
\begin{tabular}{l l l l} \hline
**Top Attributes** & **Weighting** & **Sub-Attributes** & **Weighting** & **Overall Factor** \\ \hline \multirow{2}{*}{Technical impact} & \multirow{2}{*}{0.70} & Fuel storage capacity & 0.83 & 0.58 \\ \cline{3-4}  & & \multicolumn{2}{l}{Technological maturity (availability)} & 0.68 & 0.47 \\ \hline \multirow{4}{*}{Environmental impact} & \multirow{4}{*}{1.00} & Life-cycle GHG & 1.00 & 1.00 \\ \cline{3-4}  & & Life-cycle SOx & 0.60 & 0.60 \\ \cline{3-4}  & & Life-cycle NOx & 0.60 & 0.60 \\ \cline{3-4}  & & Life-cycle PM2.5 & 0.55 & 0.55 \\ \hline \multirow{4}{*}{Economic impact} & \multirow{4}{*}{0.70} & CAPEX & 0.73 & 0.51 \\ \cline{3-4}  & & OPEX & 0.73 & 0.51 \\ \cline{3-4}  & & Fuel cost & 0.80 & 0.56 \\ \hline \multirow{4}{*}{Safety impact} & \multirow{4}{*}{0.88} & Toxicity & 0.88 & 0.77 \\ \cline{3-4}  & & Corrosiveness & 0.65 & 0.57 \\ \cline{3-4}  & & Flammability & 0.75 & 0.66 \\ \cline{3-4}  & & Rules and regulations & 0.70 & 0.61 \\ \hline \multirow{2}{*}{Fuel availability} & \multirow{2}{*}{0.68} & Infrastructure (bankering) & 0.78 & 0.52 \\ \cline{3-4}  & & Production capacity & 0.75 & 0.51 \\ \hline \end{tabular}
\end{table} 
Table 20: Weighting scores for attributes. \begin{table}
\begin{tabular}{l l} \hline
**Linguistic Scale** & **Weighting Score** \\ \hline Not important & 20 \\ \hline Less important & 40 \\ \hline Normal & 60 \\ \hline Highly important & 80 \\ \hline Extremely important & 100 \\ \hline \end{tabular}
\end{table} 
Table 19: Weighting scores for five linguistic scales. Figure 9: Decision matrix. The design scenarios are ranked in order from the highest weighted score to the lowest, as given in Figure 10.  
The results of the preliminary assessment using the decision matrix show that the use of LNG is the most viable solution overall, having obtained relatively higher scores in environmental and safety impacts. For environmental impact, green LNG is considered as a carbon-neutral fuel, and its life-cycle SOx NOx, and PM2.5 emissions are close to zero. In terms of safety impact, safety regulations for using LNG are fully developed, and its safety records with LNG carriers and LNG-fuelled ships have been excellent over several decades. Figure 10: Results with weighting factors (higher is greater). Note: MP—mechanical propulsion; EP—electric propulsion; EPBA—electric propulsion + battery; BA—battery; FCBA—fuel cell + battery. On the other hand, there are still questions regarding the use of LNG for the case ship, particularly in terms of fuel availability in a green form and bunkering infrastructure. In particular, the Scottish Government has affirmed its strong ambition to reduce GHG emissions from national shipping by 75% by 2030 and 100% by 2045. To meet this target, the use of LNG (especially in a grey or blue form) may not be the ideal option [70]. The second viable option could be battery-powered technology using on/offshore electricity. This has shown excellence in terms of environmental impact as well as safety impact. The technical maturity of batteries for marine usages is still in its early stage, and the economic impact of this option is also relatively higher than that of other options. Therefore, the application of full battery-powered technology for the case ship may not be an ideal option due to its technical immaturity and high costs. During the conceptual design, the technical availability of the full battery power systems will be thoroughly reviewed, and if necessary, hybrid concepts can also be considered to enhance viability more realistically. The third viable option involves biodiesel (green), which can possibly be a carbon-neutral fuel.