The upper edge of the net is attached to the beam, the lower edge being attached to a stout rope—the foot-rope—the ends of which are made fast to the crossheads. This foot-rope, being considerably longer than the beam, sweeps along the ground abaft of the beam, to form a deep curve known as the “bosom” of the net. The result is that, when the foot-rope disturbs the fish so that they leap to avoid it, the beam has passed on overhead and they leap into the net.
Pockets are formed in the sides of the net by lacing the top and bottom together for about two-thirds of the distance from the mouth of the net towards the cod end. The mouth of a pocket is at the cod end of the net, so that fish reaching the cod end and attempting to return to the mouth of the net, generally enter the pockets. A flap of netting suspended some distance inside the mouth of the net serves as a valve. It is easily lifted by the incoming fish, but tends to prevent their escape.
The netting is of hemp, the mesh gradually increasing from one inch at the cod end to about two inches near the mouth, and is preserved with tar.
When fishing, the vessel moves ahead at a steady, slow rate of from two to three miles per hour, dragging the trawl behind it. Smacks always trawl with the tide. If they trawl against the tide, the net is lifted from the ground.
During fishing the cod end is closed by the cod line, but at the conclusion of the trawl the net is hoisted aboard, mouth upwards, and the contents are discharged upon the deck by drawing the cod line.
The otter trawl that is used by modern steam trawlers is from seventy to one hundred and twenty feet wide across the mouth, according to the character of the fishing, and a hundred and ten feet long from the mouth to the cod end. The otter trawl is shown in Fig. 17. It differs from the beam trawl in that its mouth is kept open, not by being attached to a beam, but by otter boards, which are attached one to each side of the mouth of the net. These are attached to the net and to the warps by which the net is towed in such a way that the pressure of the water upon them causes them to diverge, thus keeping the mouth of the net open. The size of a beam trawl is necessarily limited by the length of beam obtainable. The size of the otter trawl, however, is obviously only limited by the power of the steam trawler. The otter boards measure 11 ft. by 4 ft. 6 ins., are shod with iron, and weigh 15 cwts. each. The warps, as the ropes are called which attach the otter boards to the ship, are from three hundred to a thousand fathoms long—generally a little over three times as long as the depth of the water in which the trawl is to be used. Each board is attached to the steamer by a separate warp. The upper edge of the mouth of the net is attached to a strong rope, called the “head” rope. The lower edge of the mouth of the net is also attached to a strong rope, called the “foot” rope. As in the beam trawl, the foot rope is considerably longer than the head line, and forms a bosom. Traps and pockets also are inserted in the sides of the net. When trawling on rough ground, the foot rope is furnished with large, heavy, wooden rollers, called the “bobbins.”