# Study on Reducing Towing Drag by Varying the Shape and Arrangement of Floats and Gears
## 4 Discussion
In this study, only some available ground gears were changed from the design of the conventional net in the pair trawl fishery, although other ground gears with different shapes and materials were also used for the net. It was reported that the use of a small number of large ground gears in the ground rope resulted in fish escaping from the gap between the ground rope and the seabed [27]. Because the estimation in this study is focused only on reducing the drag of ground gears, it is necessary to consider other functions of the ground rope, such as prevention of fish escape or protection of the net from contact with the seabed. Thus, if nineteen larger sphere-shaped floats and twenty-eight of the biggest ellipsoid-shaped floats are replaced on the head-rope and lacing lines of the net, the drag of the head-rope parts (Figure 11) can be presented, as shown in Table 2. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{5}{c}{**Reduction of Drag by Redesigning Floats in Each Part of the Head Rope**} \\ \hline
**Head Rope** & **Conventional Drag (N)** & **Redesigned Drag (N)** & **Difference (N)** \\ \hline No. 1F & 149 & 38 & \(-111\) \\ No. 2F & 149 & 38 & \(-111\) \\ No. 3F & 182 & 99 & \(-83\) \\ No. 4F & 219 & 147 & \(-72\) \\ No. 5F & 332 & 238 & \(-94\) \\ No. 6F & 298 & 101 & \(-197\) \\ Total & 1329 & 661 & \(-668\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The reduction of drag by redesigning floats in each part of the head rope. Figure 12: The arrangement of ground gear in conventional designed ground rope. The drag of No. 1F and 2F was reduced from 149 N to 38 N, 182 N to 99 N in No. 3F, 219 N to 147 N in No. 4F, 332 N to 238 N in No. 5F, and 298 N to 101 N in No. 6F. In total, the drag of the head rope was reduced from 1329 N to 661 N (total 50% reduction). Regarding the ground gear, forty-eight cylindrical ground gears of the ground rope, which are similar in size but slightly lighter with low drag, were changed as shown by Figures 12 and 13. The drag of No. 5G on the ground rope was reduced from 1790 N to 1718 N (Table 3). No. 1G, 2G, 3G, 4G, 6G, and 7G were not redesigned in this study because these parts were already designed for low drag and there was no alternative ground gear to replace for low drag in this study. The drag force of the total ground rope was reduced from 10,195 N to 10,123 N (total 1% reduction). From the reduction of drag of the head rope and ground rope, the reduction of fuel consumption would not be a large enough effect to reduce the drag of the head rope and ground rope. Regarding the drag in the trawl gear, the proportion of drag in the net is greater than the proportion of drag in the head rope and ground rope [28; 29]. The total reduction was only 1.2% in this study. However, the trawl fishing gear is towed continuously for catching fish [1; 2]. When calculating the drag reduction and fuel consumption rates from studies [28; 29], a 0.8% fuel reduction efficiency was demonstrated per each haul. Many hauls using low drag gear in which the head rope and ground rope have been rearranged could save fuel costs due to the lower fuel consumption effect. Figure 13: The arrangement of ground gear in redesigned by rearrangement of ground rope. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{3}{c}{**Reduction of Drag by Redesigning Ground Gear in Each Part of Ground Rope**} \\ \hline
**Ground Rope** & **Conventional Drag (N)** & **Redesigned Drag (N)** & **Difference (N)** \\ \hline No. 1G & 418 & 418 & 0 \\ No. 2G & 911 & 911 & 0 \\ No. 3G & 709 & 709 & 0 \\ No. 4G & 1693 & 1693 & 0 \\ No. 5G & 1790 & 1718 & \(-\)72 \\ No. 6G & 2716 & 2716 & 0 \\ No. 7G & 1958 & 1958 & 0 \\ Total & 10,195 & 10,123 & \(-\)72 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The reduction of drag by redesigning ground gear in each part of ground rope.