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The otter may have multiple different designs. Otter boards used in bottom trawling are based on a similar design principle. The design takes advantage of the shearing effect achieved when the board is positioned at an oblique angle to the current. The effect is reminiscent of that of a kite in the wind.
A trawling boat can be a small open boat with only 30 horsepower (22 kW) or a large factory ship with 10,000 horsepower (7457 kW). Trawl variants include beam trawls, large-opening midwater trawls, and large bottom trawls, such as "rock hoppers" that are rigged with heavy rubber wheels that let the net crawl over rocky bottom.
Pelagic (midwater) otter trawl. 1: trawl warp, 2: otter boards, 3: longline chains, 4 hunter, 5: weights 6: headline with floats, 7: pre-net, 8: tunnel and belly, 9: codend. The body of the trawl is funnel-like, wide at its "mouth" and narrowing towards the cod end, and usually is fitted with wings of netting on both sides of the mouth.
However, single-boat trawling is more common. Here, the horizontal spread of the net is provided by trawl doors (also known as "otter boards"). Trawl doors are available in various sizes and shapes and may be specialized to keep in contact with the sea bottom (bottom trawling) or to remain elevated in the water. In all cases, doors essentially ...
1: trawl warp, 2: otter boards, 3: longline chains, 4 hunter, 5: weights 6: headline with floats, 7: pre-net, 8: tunnel and belly, 9: codend. Midwater trawling is trawling, or net fishing, at a depth that is higher in the water column than the bottom of the ocean. It is contrasted with bottom trawling.
Otter trawl – An otter trawl is a demersal trawl which uses large rectangular otter boards to keep the opening of the trawl net from closing. Otter trawls are towed by a single trawler. Overfishing – occurs when fishing activities reduce fish stocks below an acceptable level. This can occur in any body of water from a pond to the oceans.
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One or two otter trawls can be towed from each side. Beam trawlers, employed in the North sea for catching flatfish, are another form of outrigger trawler. Medium-sized and high powered vessels, these tow a beam trawl on each side at speeds up to 8 knots. [25] Beam trawlers – use sturdy outrigger booms for towing a beam trawl, one warp on ...