“Four-Wheel Drive” Trawl Technology A Test Drive Trawling with the Active Trawl System could almost be compared to drive in a all-terrain four-by-four vehicle with  automatic cruise control and manual override. With a smooth type sea bottom or during a straight midwater trawl, the cruise control would take care of most of the routine "housekeeping" functions, making sure that the VTVD's generate the minimum forces to keep the trawl net  open at its optimum and at its correct depth. Should, for example, the trawl speed increase, the cruise control would adjust the VTVD's output to maintain the set depth and net spread for the changed conditions. Compare this to the case with conventional doors where the forces would increase proportional to the square of the trawl speed increase. This could result in the generation of forces  larger than actually required and hence increased fuel consumption.  Depending on the configuration of the cruise control and how it is integrated with other equipment, it could do much more, as described elsewhere. In override mode, one could take over the accelerator, brake and steering controls, while still allowing the automatic cruise control to look after the real-time adjustments required to keep the trawl operating at its best. The accelerator "pedal" could be used to provide spurts of power when needed. For instance, it could be pushed down to increase the power to move the trawl in order to avoid an obstacle or to engage a fish shoal. The pedal could also be lifted in order to reduce the forces generated for example when hauling in the trawl.  The steering "wheel" could be used to increase the trawl envelope in a similar way that a racing car weaves from side to side across the racing track to make itself as "wide" as possible to prevent overtaking manoeuvres by following  cars. Thus a smaller trawl net, requiring less power, could be used to sweep a larger volume of water. It is when trawling over rough steep undersea mountains with sharp rocky outcrops or in narrow canyons with  unpredictable strong sea currents that the ATS with its "four-wheel-drive" or, more correctly, "four-rotor-drive" really comes into its own. It can be rotated to follow a sloping contour, positioned vertically and horizontally with precision and fast response and it will keep to its planned path irrespective of surface and subsea currents             .
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