Pelagic trawler Themis S-144 has been the test bench for testing controllable pelagic trawl doors, and an initial round of tests earlier this year is now being followed up before the doors become available commercially.
The choice went to the company’s high-efficiency Type 22 Bluestream trawl doors that have already proved their value both for pelagic fisheries and for spreading demersal gear with the doors flown off the seabed. The Type 22 doors also come in Flipper versions, fitted with up to four flaps that can be opened to reduce the surface area of the doors by up to 11%, providing adjustment options for switching from one gear type to another.
This makes the Bluestream doors among the most versatile trawl doors on the market, according to Henrik Andreassen
“It’s about achieving more spread for less resistance,” he said, adding that the addition of a hydraulic system to the leading side of each door is set to increase this versatility further as this makes it possible to adjust the warp attachment point while towing to alter the roll of the doors – without having to haul the gear and make the adjustment manually.
“This means that the shape, symmetry, positioning and depth of the trawl can be adjusted remotely,” Henrik Andreassen said, after the initial trials on board Themis took place earlier this year.
“We were able to adjust the doors wirelessly from Themis’s wheelhouse, and saw that we could easily lift the doors from being hard on the bottom in 60 fathoms to just beneath the surface in a manoeuvre that took only a few minutes. This is a gamechanger, not just for pelagic vessels, but for groundfish trawlers as well.”
Regular customers have been aware for a while that this is in development, and Thyborøn Trawldoor has already delivered a number of pairs of its Type 22 Bluestream doors prepared for the control system to be added, and as soon as the last stage of testing the doors and the control system has been successfully completed on board Themis, these doors will become commercially available.
“There’s already a waiting list,” Henrik Andreassen said, commenting that it has been a long process to get this right, starting with extensive flume tank tests before the first full-scale trials took place, and since then they have been refining the system, which is powered by a long-life rechargeable lithium battery.
“The advantages of having control of the doors are clear. This enables precise positioning, maintaining a distance to the surface or the seabed. The gear’s depth can be adjusted more quickly and it can be positioned more accurately for the target species, plus the symmetry of the gear can be maintained in a cross-tide and it’s possible to come about while maintaining the full door spread.”