Trawlers like the 42m Enterprise, the latest to join the Newlyn fleet,..
fish with two beam trawls either side of the boat...
each trawl attached to the beam at the end of two 30mm wire warps is towed over the sea bed...
the chain mat underneath the trawl net scours the sea bed and only catches fish that appear directly in front of the beam and net...
the trawls are towed at 3.5knots and hauled around every 3 hours for the duration of a trip - the area covered by the beam trawls is approx 144000m² or 0.0114²km in one hour...
use large bottom trawls with 80mm mesh size...
attached to 50mm combination (a mixture of polypropylene and wire) 'ropes' which sweep the sea bed...
after the trawls are deployed and then hauled, the towing action covers a diamond shaped area swept by the combination ropes...
it takes around two hours for each haul, from the start, to when the catch is taken on board...
which means 2km x 2km = 4km² of the sea bed are fished every hour...
The Dutch fly-shooter Lub Senor has also been fishing south of Newlyn
Seine net fish is noted for its quality as the catching method means that the fish on the sea bed are effectively herded towards the net by the action of the combination ropes and only enter the trawl as the ropes close the nets - the smallest part of the trawl uses 80mm mesh...
as can be seen in this animated and underwater video footage...
the 23m trawler Crystal Sea works a twin-rig trawl - two nets are towed side-by-side spread apart by two trawl doors - the smallest part of the trawl uses 100mm mesh...
as can be seen in this flume tank demonstration of how to rig the trawls - the trawl doors are around 180m apart so the area of seabed covered during the course of one hour's trawling is around 1.1km² - considerably less than the are covered by a bottom trawler - even when twin-rigged trawls are used.