## 4 Feasibility of Monitoring-Sensor Technology  
In this section, the feasibility of monitoring system developed for the stow net is evaluated. Numerical sensors are installed on the location buoy and mooring line #1. Two monitoring sensors measure surge (translational) motions of the buoy and tensions of the mooring line and the rope. Tension data are aimed to efficiently confirm that the fishing gear is not broken or lost. In addition, it might also be feasible to roughly measure environmental conditions and net functionality by the motion and tension data. Figure 7: Time histories of net horizontal length (**a**), net vertical deflection (**b**), and net-entrance area (**c**) in varying wave conditions under the identical current velocity (\(V_{c}=1.0\) m/s). Figures 8 and 9 show surge motions of the location buoy in different environmental conditions. Table 4 provides the statistical results of surge motions of buoy, rope tensions, and mooring tensions for all simulated cases. As can be seen in Figure 8, the mean surge motion of the location buoy increases with current velocity up to 1.0 m/s, and then remains with little change after that. The reason is that the mean buoy-surge is significantly affected by net and deeper net means less drag forces. Because submergence depth does not change significantly at low current velocities, the mean buoy-surge increases with increasing current force. In addition, the fluctuations of the location buoy become smaller with the increase of current velocity and submergence depth. At low current velocities, since the submergence depth of the net assembly is shallow, the surge motion of the location buoy is also largely influenced by net motions. As current velocity increases, the net surge motions decrease, which results in smaller buoy-surge motions. As represented in  
Figures 10 and 11 (also Table 4) show the time histories of rope tension in different environmental conditions. Generally, as current velocity is lower than 1.0 m/s, rope tension gradually decreases with increasing current velocity. The opposite trend can be observed if current velocity is greater than 1.0 m/s. At high current velocity, the net is more submerged, and the rope becomes taut (see Figure 5), and thus the dynamic tensions increase. In this case, both surge and heave motions of buoy contribute to the rope dynamic tensions. At low current velocity, the net is close to surface and rope becomes almost horizontal (see Figure 5) and the tension is caused by the relative surge motions between the net and buoy. Interestingly, both effects become minimal at the current velocity of 0.75 m/s. As shown in Figure 11 and Table 4, when the current velocity is fixed at 1.0 m/s, the rope dynamic tensions increase with wave heights, as can intuitively be expected. When the rope is slack, the location buoy can also function as wave-measurement buoy since it vertically follows wave surface. Figures 12 and 13 show the time histories of mooring tensions under different environmental conditions. They show that the maximum mooring tension increases with increasing current velocity. It is mainly due to the increase of static tension in stronger currents. However, the variations (or dynamics) of mooring tensions decrease because of the increased submergence depth, so less wave effects, in stronger currents. On the other hand, Figure 13 shows the mooring tensions for various wave heights at fixed current velocity. In this case, the dynamic (or maximum) mooring tension increases as wave height increases, as can intuitively be expected. From the simulated results, wave/current conditions, net functionality, and net submerged depth can roughly be predicted by observing buoy surge motions and rope/mooring tensions. Rope and mooring tensions will also provide information whether the location buoy and/or the net assembly are lost. Therefore, monitoring sensors can be applied for that kind of purpose after enough simulated data are accumulated with a target stow-net design.