Fishing trawler
A fishing trawler is a commercial fishing vessel designed to operate fishing trawls. Trawling is a method of fishing that involves actively dragging or pulling a trawl through the water behind one or more trawlers. Trawls are fishing nets that are pulled along the bottom of the sea or in midwater at a specified depth. A trawler may also operate two or more trawl nets simultaneously.
There are many variants of trawling gear. They vary according to local traditions, bottom conditions, and how large and powerful the trawling boats are. A trawling boat can be a small open boat with only 30 horsepower or a large factory ship with 10,000 horsepower. 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.
History
The 17th century saw the development of an early type of sailing trawler called a Dogger, which commonly operated in the North Sea. It takes its name from an earlier type of the same name, and from the area fished. The word is the Dutch word for codfish, but has come to mean a fishing vessel which tows a trawl. Doggers were slow but sturdy, capable of fishing in the rough conditions of the North Sea.The modern fishing trawler was developed in the 19th century, at the English fishing port of Brixham. By the early 19th century, the fishermen at Brixham needed to expand their fishing area further than ever before due to the ongoing depletion of stocks that was occurring in the overfished waters of South Devon. The Brixham trawler that evolved there was of a sleek build and had a tall gaff rig, which gave the vessel sufficient speed to make long-distance trips out to the fishing grounds in the ocean. They were also sufficiently robust to be able to tow large trawls in deep water. The great trawling fleet that built up at Brixham earned the village the title of 'Mother of Deep-Sea Fisheries'.
This revolutionary design made large scale trawling in the ocean possible for the first time, resulting in a substantial migration of fishermen from the ports in the South of England, to villages further north, such as Scarborough, Hull, Grimsby, Harwich and Yarmouth, that were points of access to the large fishing grounds in the Atlantic Ocean. The small village of Grimsby grew to become the 'largest fishing port in the world' by the mid 19th century. With the tremendous expansion in the fishing industry, the Grimsby Dock Company was opened in 1854 as the first modern fishing port. The facilities incorporated many innovations of the time – the dock gates and cranes were operated by hydraulic power, and the Grimsby Dock Tower was built to provide a head of water with sufficient pressure by William Armstrong.
The elegant Brixham trawler spread across the world, influencing fishing fleets everywhere. By the end of the 19th century, there were over 3,000 fishing trawlers in commission in Britain, with almost 1,000 at Grimsby. These trawlers were sold to fishermen around Europe, including from the Netherlands and Scandinavia. Twelve trawlers went on to form the nucleus of the German fishing fleet.
Advent of steam power
The earliest steam-powered fishing boats first appeared in the 1870s and used the trawl system of fishing as well as lines and drift nets. These were large boats, usually in length with a beam of around. They weighed 40–50 tons and travelled at.The earliest purpose-built fishing vessels were designed and made by David Allan in Leith in March 1875, when he converted a drifter to steam power. In 1877, he built the first screw-propelled steam trawler in the world. This vessel was Pioneer LH854. She was of wooden construction with two masts and carried a gaff-rigged main and mizen using booms, and a single foresail. Allan argued that his motivation for steam power was to increase the safety of fishermen. However local fishermen saw power trawling as a threat. Allan built a total of ten boats at Leith between 1877 and 1881. Twenty-one boats were completed at Granton, his last vessel being Degrave in 1886. Most of these were sold to foreign owners in France, Belgium, Spain and the West Indies.
The first steam boats were made of wood, but steel hulls were soon introduced and were divided into watertight compartments. They were well designed for the crew with a large building that contained the wheelhouse and the deckhouse. The boats built in the 20th century only had a mizzen sail, which was used to help steady the boat when its nets were out. The main function of the mast was now as a crane for lifting the catch ashore. It also had a steam capstan on the foredeck near the mast for hauling nets. These boats had a crew of twelve made up of a skipper, driver, fireman and nine deck hands.
Steam fishing boats had many advantages. They were usually about than the sailing vessels so they could carry more nets and catch more fish. This was important, as the market was growing quickly at the beginning of the 20th century. They could travel faster and further and with greater freedom from weather, wind and tide. Because less time was spent travelling to and from the fishing grounds, more time could be spent fishing. The steam boats also gained the highest prices for their fish, as they could return quickly to harbour with their fresh catch.
Steam trawlers were introduced at Grimsby and Hull in the 1880s. In 1890 it was estimated that there were 20,000 men on the North Sea. The steam drifter was not used in the herring fishery until 1897. The last sailing fishing trawler was built in 1925 in Grimsby.
Further development
Trawler designs adapted as the way they were powered changed from sail to coal-fired steam by World War I to diesel and turbines by the end of World War II.The first trawlers fished over the side, rather than over the stern. In 1947, the company Christian Salvesen, based in Leith, Scotland, refitted a surplus Algerine-class minesweeper with refrigeration equipment and a factory ship stern ramp, to produce the first combined freezer/stern trawler in 1947.
The first purpose-built stern trawler was Fairtry built in 1953 at Aberdeen. The ship was much larger than any other trawlers then in operation and inaugurated the era of the 'super trawler'. As the ship pulled its nets over the stern, it could lift out a much greater haul of up to 60 tonnes. Lord Nelson followed in 1961, installed with vertical plate freezers that had been researched and built at the Torry Research Station. These ships served as a basis for the expansion of 'super trawlers' around the world in the following decades.
Since World War II, commercial fishing vessels have been increasingly equipped with electronic aids, such as radio navigation aids and fish finders. During the Cold War, some countries fitted fishing trawlers with additional electronic gear so they could be used as spy ships to monitor the activities of other countries.
Modern trawlers
Modern trawlers are usually decked vessels designed for robustness. Their superstructure can be forward, midship or aft. Motorised winches, electronic navigation and sonar systems are usually installed. Fishing equipment varies in sophistication depending on the size of the vessel and the technology used. Design features for modern fishing trawlers vary substantially, as many national maritime jurisdictions do not impose compulsory vessel inspection standards for smaller commercial fishing vessels.Mechanised hauling
Mechanised hauling devices are used on modern trawlers. Trawl winches, such as Gilson winches, net drums and other auxiliary winches are installed on deck to control the towing warps and store them when not in use.Electronics
Modern trawlers make extensive use of contemporary electronics, including navigation and communication equipment, fish detection devices, and equipment to control and monitor gear. Just which equipment will be installed depends on the size and type of the trawler.Much of this equipment can be controlled from the wheelhouse or bridge. Smaller trawlers have wheelhouses, where electronic equipment for navigation, communications, fish detection and trawl sensors are typically arranged about the skipper's chair. Larger vessels have a bridge, with a command console at the centre and a further co-pilot chair. Modern consoles display all the key information on an integrated display. Less frequently used sensors and monitors may be mounted on the deckhead.
Navigational instruments, such as an autopilot and GNSS, are used for manoeuvring the vessel in harbour and at sea. Radar can be used, for example, when pair trawling to keep the correct distance between the two vessels. Communication instruments range from basic radio devices to maritime distress systems and EPIRBs, as well as devices for communicating with the crew. Fish detection devices, such as echosounders and sonar, are used to locate fish.
During trawling operations, a range of trawl sensors may be used to assist with controlling and monitoring gear. These are often referred to as "trawl monitoring systems" or "net mensuration systems".
- net sounders give information about the concentration of fish around the opening to the trawl, as well as the clearances around the opening and the bottom of the trawl
- catch sensors give information about the rate at which the cod end is filling.
- symmetry sensors give information about the optimal geometry of the trawls.
- tension sensors give information about how much tension is in the warps and sweeps.
Fish storage and processing