Trawling for fish presents some of the most challenging marine conditions for both crew and equipment. Rough seas, extreme temperatures and significant towing forces are just a few elements that trawlers face. MacGregor Triplex products are designed to meet them all and ensure safe, sustainable, efficient operations for crew and vessel.
Trawling: active fishing
Trawlers use funnel or cone-shaped trawl nets to catch fish. These are towed behind the vessel, catching and storing the fish in the back of the net, called the ‘codend’. Trawling is an active fishing method. The mesh size of the net is dependent on the type of fish being caught, but typically the net has a larger mesh size near the opening than in the codend. This is because the main goal of the opening is to guide the fish towards the end.
There are different types of trawling. For example, in bottom trawling, the trawl net is towed along the sea-floor. In pelagic trawling, the trawl net is towed higher up in the water column, from mid-water and up towards the surface. As pelagic trawls do not have to withstand the forces and conditions that bottom trawls are subject to, they are usually much larger.
Keeping the nets open
The trawl net is kept vertically open by the headline, which is a floating line and by the ground line, which is a sinking line. The trawl net is kept horizontally open by the trawl doors moving forward in a seaway. During pair trawling, where two trawlers are towing the same trawl net, the horizontal opening is adjusted by altering the distance between the two vessels.
The trawl net is connected to the trawl doors via sweep lines, while the trawl doors are connected to the trawler through wires called warp lines. The sweep lines and the trawl doors are important in driving the fish in towards the opening of the trawl net. By adjusting the speed and/or the length of the warp lines, the trawler can adjust the position of the trawl net in the water column.
Proven Triplex systems
MacGregor supplies world-leading Triplex fish handling systems and equipment for trawlers. For example, our towing pins are used for the critical job of guiding and separating warp lines during operations. Triplex ice davits can also be used to prevent warp lines from being damaged by ice.
Triplex systems and stand-alone equipment, including deck cranes, are manufactured in a variety of sizes and supplied fully-adapted to suit an individual vessel’s needs. Our lengthy experience and proven performance in the industry enables us to deliver solutions that not only meet an owner’s requirements but also withstand the conditions that vessels operate in.
Numerous worldwide references include Newfoundland Victor (Canada), Ramoen and Smaragd (Norway), and Cuxhaven (Germany).