Mechanised Fishing Boats
trawler means any vessel that pulls a bag net through the water. There are many types of
trawlers varying in size from open boats, powered by outboard engines to huge factory
ships, which can fish in the most distant waters.
requirements are common to all trawlers. One is the need for towing power and the other
for winch or mechanical hauling system. In order to have a good towing power a trawler
should have a reasonable draft or, displacement and should have a large slow-turning
propeller. Many trawlers are fitted with propeller nozzles to give them more towing power.
The winch or hauling machinism is the next important requirement for a trawler. Hauling or
pulling power is usually expressed in tonnes, kgs. per speed (feet or metres per minute)
for bare drum, or full drum.
use of otter boards to open the trawl net month horizontally in preference to a beam was
introduced over 100 years ago, and it is the single most productive method of fishing.
Although otter trawlers are of three categories e.g. side trawlers, stern trawlers and
double rig trawlers: there are actually a large number of variations in the gear used.
They are shrimp trawls, prawn trawls, combination trawls, wing trawls, bobbin trawls,
herring trawls, semi-pelagic trawls and mid-water trawls. All but the smallest of otter
trawlers have gallows, derricks to handle the heavy otter boards.
distinguishing feature of all side trawlers is the two steel gallows frames, one place aft
and one forward on the starboard side. The starboard otter door is hauled up to the
forward gallow and port otter is hauled up to the aft gallow block.
over the stern can be a very efficient way of trawling. It is particularly successful on
the large factory trawlers and freezer trawlers, which could accommodate a stern ramp and
a fish deck below the main gear deck. Setting and hauling the gear from a stern trawler is
an easier operation than from a side trawler. The main points to be decided, when
designing a stern trawler layout are the positions of the bridge, engine room, winch and
whether the vessel will have a stern ramp.
double-rigged "Mexican" type used in 1955 is the best known. The features of
shrimp rig have been developed to suit a particular type of low-head line net with long
otter boards attached close to the wing ends. One such net is pulled from each of the side
booms, which are extended during fishing operation. A small Try-net is sometimes also
operated over the stern.
trawling is not used much today except in some shrimp and sole fisheries. Before the
invention of the otter trawl, most bottom trawlers used a beam trawl. Beam trawls are
cumbersome to use and are always fished over the side. Modern beams are made of steel.
Several tickler chains are added near the foot rope to increase the weight of the gear.
many ways scallop draggers resemble beam trawlers. The scallop draggers are small steel
beam trawls with metal ring instead of netting on the underside. They scrape up scallops
and other shellfish from the sea bed. Large scallop draggers may work three dredges, on
each side, from booms as on double rigged beam trawlers.
trawling fleets operate in Europe, Scandinavia, North America, Japan, Taiwan, Korea and
Thailand of fish shrimp, hake, herring, cod, flatfish and also for miscellaneous fishes.
Pair trawls are towed by two boats. The boats maintain a distance apart equal to about
half the warp length. No otter boards are needed for pair trawling operations. This
reduces the overall drag on the gear and permits the use of larger net. Long heavy cables
are inserted between the net and the warp end at which point a weight and a swivel are
usually attached. For most pair trawlers, a stern trawler or sade trawler deck arrangement
is appropriate. The larger pair trawler fish over the stern and the smaller ones mostly on
the side. If one vessel has more power than the other, then the stronger vessel will take
the starboard side of the gear since it requires more helm.
type of bottom trawler is the Danish seiner used to catch demersal fish like cod, haddock,
hake, pollock, flatfish, skate, sole and prawns. This vessel used no otter boards, but
instead it sets over a mile of rope in an arc or L shape on each side of the
net. The net itself resembles a large light trawl with long wings. The rope warpe scrape
slowly over the seabed, all the while herding fish in towards the advancing net. Ones the
ropes are almost closed or parallel to each other, the vessel speeds up to drive the
remaining fish into the net and then the warps are winched quickly. The whole operation
takes one to two and a half hours and in that time an area of the sea bed measuring over
one mile by half a mile will have been "Swept" clean of fish.
nets of many types have been used the world over to catch surface swimming fish. Ring
nets, lampara nets and tuck seines are the best known of the numerous kinds of surround
net that preceded the best known and most efficient, their use has seriously depleted
stocks of herring, anchovy, pilchard and mackerel in different parts of the world. The
chief distinguishing feature is that a pursue seine has purse rings fitted all the way
round the foot. A ring net or lampara may have a few rings or none at all but a purse net
must be rigged with a continuous series of rings so that it may be "pursed" or
closed in a single winch operation.
common features to most pursers are:
need to have fish holds large enough to accommodate the big catches and equipped with fast
and efficient ways of loading and unloading;
vessel requires a considerable amount of equipment for fish detection and communication
with other searching vessels. In areas where visible sighting is possible a crows
nest or look-out may be constructed on the foremast;
the purse seiner, must be able to maneuover in close proximity to the net without fouling
the propeller must of them require the assistance of a power skiff or small tow-boat;
hauling equipment is another vital part of seiners outfit. The net hauler used on
purse seiners is the hydraulic power block.
Ring net boats: -
nets or lamparas are small surround nets, which if they are rigged with purse rings, only
have a few of them located usually at the central bunt. Lampara nets are tapered towards
the wings ends and have relatively long wings. Both ring netting and lampara fishing have
been largely displaced by purse seining. Ring net boats are small and lightly powered.
Most ring net boats work on two-boat system, which is much handier when the net has to be
towed. Both ring netters and lampara boats tow their gear some length before closing.
purse seine boats use lights of 500-1000 watts to attract fish before setting the net.
Light attraction is important in the tropical bait and sardine fisheries and in squid-jig
fisheries. Fish attraction by lamp is not possible on moon lit nights or in areas of very
are still used effectively today to catch tuna, skipjack, mackerel, squid, snapper, cod
and dog fish. There are many methods or line fishing, such as tuna long lines, bottom set
long lines, pole and line gear for skipjack, trolling lines, squidjigs, mackerel jigs.
Line fishing involves lots of labour as fish are hooked, on by one and lines need to be
baited, cleaned, untangled and recoiled for setting as well as to be attended during
fishing as in case of jigs and hand lines. Most line boats are small, but some measure
over 200 tonnes with over 500 h.p.engines.
long liners: -
are mostly large vessels, ranging from 90 feet (27 metres) 400 h.p to around 180 feet (55
metres) 1500 h.p which traverse the ocean in search of the migratory tuna. Because of the
long distances they must travel, the catch needs to be frozen and the vessel requires
large fuel and water capacities. Tuna lines are the "longest" long lines in the
world. Many miles of line may be set with the baited hooks hanging from 100 or even 150
fathoms below the surface. The line hauler on the deck coupled with a coiler is used to
set long line vessels: -
set long lines are used in tropical and sub-tropical waters to catch snapper, grouper,
ray, shark, eels and various reef fishes. These long lines carry hundreds of baited hooks
rigged close together on short branch lines or snoods. The lines are anchored at each end
with a buoy line attached to each anchor.
line boats tow lines extending on either side to catch skipjack, yellowfin, salmon,
mackerel and other surface swimming pelagic fishes using unbaited hooks. Tuna trollers tow
at up to 6 knots speed but usually in the range of 3 to 5 knots. They prefer to troll with
the sun behind them, just after dawn, or before sun-set. When they pass through a school
of fish, the crews are hard-pressed to haul in and clear the lines, the fish strike so
rapidly. Trollers may be small open boats, or refrigerated vessel of 25 or 30 metres
line and jigging line boats: -
line boats operate all over the world, some in shallow waters and some in seas up to 200
fathoms deep. Traditional hand liners use no winch. One needs a strong back and tough
hands to pull in lines from those great depths. While hand lines are usually baited and
carry only one or two hooks, jigging lines carry only artificial lures but may have dozen
of hooks in one line or jig. They are used to catch all kinds of demersal fish. Special
fishing reels developed for hand liners have been proved to be most beneficial. These
reels may be electrically or hydraulically operated.
jig vessels: -
is done by using a hand reel, which is oval shape to create the erratic jigging motion.
Jigging is tried at various depths, until the fishermen determine, where the main squid
concentrations are located. All the jigs are then set for that depth. The squid are
attracted by means of powerful lamps strung on lines stretched between the masts.
and line fishing vessels: -
of the most modern and productive methods of line is fishing. Pole and line vessels are
fitted with a narrow platform protruding all around the vessel at deck level, outside the
rail or bulwarks. The platform extends forward from the stern to forend like a bowsprit.
The crew stands on this platform with their backs to the rail when fishing with the
polers. Successful pole fishing depends on the use of live bait to attract skipjack and
albacore and seawater spray to excite and keep the fish close by. Schools of skipjack swim
very fast, chasing small fish, which they feed on voraciously. When the boat sights a
school it approaches the fish and the crew casts live bait into the sea beside them, Once
the skipjack begin to attack the bait fish, the sea water pumps water from perforated or
nozzled pipes extending fore and aft on each side and across the stern. At this point the
crew begin to cast their lines among the fish. The poles the crew begins to cast their
lins among the fish. The poles are made of bamboo or fiberglass, the lines are of bylon
and hooks of hooks in their excitement and are hooked and swung on board. Ten, twenty or
more crewmen are employed at one time using the fishing poles. When fish are very large,
two poles are attached to one line to enable the crewmen to swing them on board. As the
hooks have no bards, the fish fall off the hooks as they strike the deck.
nets are used the world over to catch every kind of fish in the sea. The nets may be
bottom set, surface net, anchored of drifting but these variations of not affect the
vessel layout much. The nets are set over the side or stern, and hauled in over the bow.
The main problems with all gill nets are that of preventing entanglement of fauling. Most
gill nets used to be hauled by hand. The fish are picked out or shaken out as the nets
come on board. Modern gill net haulers are powered sheaves, somewhere between a line
hauler and a power block in shape.
net boats: -
nets and stick-held dip nets are used to catch sardine, anchovy and baitfish, where lights
are used to attract fish to the surface. The lamps are hung from booms, which can swing
out over the dip net. The net is held by strong bamboo poles, which are made secure on the
vessel and have tackle lines extending from the outer ends up to a block on each mast. The
net is a stocking shaped bag attached to an iron ring and pole. The hoop is passed through
the fish and taken up on deck. The end of the stocking bag is lifted up and the fish slide
out through the ring on the deck.
boats and potters: -
fish traps are used to catch lobsters, crabs shrimp, octopus, eels and all kinds of reef
fish. A small vessel using 20 or 30 traps and landing 20 to 30 kgs. of fish or shellfish
per day may make a profitable living. Traps are always baited with flesh or artificial
baits. The traps are set on the bottom in series with a small anchor buoy at each end.
Mexican inventor has developed a bicycle-type under water vehicle, suitable for fishing,
known as "Bucicleta". The vehicle is shaped like a small aeroplane. The fuselage
is a plastic tube measuring 10-16 cm. In diameter and 2.20 m., in length. The wings are
shaped like shark fins and the tail is an aerodynamic T-shaped. It is run either by
pushing or by pedaling. The vehicle can also be built with a propeller.