full-sized beam trawl has a beam from 45 to 5o ft. long, and its own length is nearly twice as great : the heads hold the beam from 31 to 41 ft. from the bottom. There are, however, wide local differences in size and pattern : and the proportions of the various parts of the net and the sizes of the mesh depend also on the species sought. A North Sea trawl has a cod-end of about 12 ft., out of a total length of 75 ft.: its meshes are 3 in. in size in the front part of the net, lessening to I1 in. in the cod-end. Small pocketless trawls of 15 ft. beam are used for shrimping from open boats. Shank-nets, whose mouths are kept open by wooden rectangles, with the lower lip a few inches from the ground are also used in shrimping.
The large beam-trawl is towed a little faster than the tide, and in the same direction. It is drawn along by two ropes ("bridles") of 15 fathoms, one attached to each trawl-head and which are shackled to a 6 in. manila rope or warp. The length of warp run out is rather over 3 times the depth of the ground. Successful shooting of the trawl is an art which has to meet and overcome innumerable difficulties caused by the various combinations of wind, tide, ground and weather, and space does not permit of its discussion here. Essentially, it proceeds in the following stages. The beam and heads are put over the side and the net paid out after them: the fore bridle is run out until the beam is at right angles to the ship's side : both bridles and the warp are then run out : a rope ("guy") is how ever attached to the warp when nearly out and made fast in the bow, in such a manner that if the net "comes fast" on an obstruc tion the guy takes the strain and brings the ship head to wind, where she can lie until a change of tide enables her to free her gear. The towing generally lasts one tide (6 hours) and the hauling of the nets is now usually effected by a small steam capstan ("steam man"), whose compact engine is housed under a cover on the capstan top. When the trawl-heads are made fast the net is hauled in by hand until the cod-end is reached, when a bight of rope is put round it, passed over a "tackle" (pulley block) and the cod-end heaved in by the capstan, when the cod line is loosed and the fish fall on deck.
Although a very old net, the beam-trawl reached its highest importance in the nineteenth century. In that century the sailing trawlers which employed it increased greatly in numbers and tonnage and im proved in equipment and efficiency : and they brought the whole North Sea under the trawl. Its closing decades however wit
nessed the beginning of the rise of the otter-trawl and of the use of steam in fishing vessels : and saw also the decay of beam trawling and the decline of sailing trawlers. Thus in England and Wales there were over 2,000 first class sailing trawlers in 1893, over 90o in 1900, 817 in 1913 and 272 in 1928: in the same period the average tonnage fell from 57 to 33. In the first stages of the change the fact that the otter could not be worked with confidence from a sailing vessel no doubt accelerated the adoption of steam power, since the efficiency of the otter ren dered its use inevitable; while on the other hand the power of steam favoured the development of larger nets and enabled more distant grounds to be explored and worked, and the otter, having no rigid beam, was capable of manufacture in a large size and of yielding, on an abundantly stocked ground, the large catches necessary to pay the expenses of long voyages. It is probable that the low working expenses of sailing beam trawlers may en sure their continuance on grounds near ports in close touch with good markets, especially when the fish on the ground are of the more valuable kinds ("prime"), although even on these grounds the motor otter trawler is increasing in importance ; but in the present phase of fisheries it is clearly the great steam trawler that bears the main burden of the supply of demersal fish. In 1928 steam trawlers landed in England and Wales 415,000 tons of these fish; sailing (beam) trawlers less than 7,00o tons.
The essential feature of the otter-trawl is that its mouth is kept open not by a rigid structure but by two large boards, the otter-boards or "doors" acting like kites working horizontally instead of vertically. The device was em ployed by yachts since its invention by Hearder in 186o, and later by Danish plaice seiners, but the boards now used were first patented in 1894 and 1895 by Scott of Granton and Nielsen, a Dane, respectively.
The otter-boards resemble massive wooden doors, liberally strengthened by iron bands: they are about 8 ft. high, 9 ft. long and 3 in. thick. The net is fastened to shackles placed at the top and bottom of the after-end of the board. Like the beam trawl, the otter has many types, the proportions of the parts vary ing with the species sought. Headlines may be as much as 120 ft.