Active Fishing Systems
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| New trawl system avoids bottom
contact and saves fuel |
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Trawling is currently being hit with a double whammy – on the
one side it is being slapped with trawling bans due to
increased pressure to prevent seabed damage and, on the other
side it is being engulfed in rapidly rising fuel bills due to
it being one of the more fuel-hungry fishing methods. Both of
these contribute towards increased consumer concerns and
resistance to trawled products. |
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| Maurice Shenker, of Active
Fishing Systems South Africa, certainly believes his new
generation Active Trawl System (ATS) could be the “lifeboat”
the industry needs right now. He said: “The ATS is the only
trawling system (both in current use and near-future
deployment) which, by virtue of its design, construction and
operation, can significantly reduce the destructive impact of
trawl gear on the seabed and, at the same time, do this using
a lot less fuel.” |
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| Development of the system was
started more than 15 years ago and has now reached a point
where the technologies to make it work are ready and proven,
and the concerns as well as suggestions of potential users
have been addressed. For instance, the original concept called
for an extra cable for power and communications. The fishermen
that were consulted were strongly against this. Besides the
operational and safety issues that this would have created on
board, it was also pointed out that it could become an
additional hazard to seabirds. Another concern was the
robustness and survivability of the Variable Thrust Vector
Doors (VTVD's)for bottom trawling. |
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After looking at a number of possible options an elegant and
innovative solution to the cable problem was found which
allows unlimited operational times with all the features and
benefits of the original system. However, there is no such
thing as a free lunch and, in this case, the advantage of
removing the cable was offset by an increased number of moving
parts on VTVD's. However, when looking at the overall picture
particularly with the increasing concerns about seabed damage,
the situation was turned around from a win-lose into a win-win
state of affairs. |
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| The structure could have easily
beefed up by using tougher materials and thicker sections as
well as by adding more shrouds and guards, but this would have
also increased the costs considerably. Instead, a conscious
decision was taken to leave the VTVD's relatively light and
unprotected so that, if they were continuously in contact with
the seabed, they would suffer damage. |
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| In normal operation, the VTVD's
would be controlled to ride a few meters off the seabottom
with the trawlnet rigged and weighted to lightly touch the
bottom. In other words, the design intent of the ATS is to
keep the VTVD's off the seabed. Nevertheless it is very
important to strike the correct balance between making the
system sufficiently “hard” to withstand the rigours of normal
trawling and handling operations and, making it “soft” enough
such that damage repair costs act as an effective deterrent to
running the VTVD's on the seabed. |
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This is an image of the original cable type VTVD which has now
been superseded by the latest cable-less design |
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| Keeping the VTVD’s off the
seabottom has another advantage – it requires less fuel. But
this is not the only way it saves fuel. Maurice Shenker went
on to say: “Trawling with the ATS is very much like having an
automatic cruise control as well as an accelerator pedal and
steering wheel.” |
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| The cruise control would take
care of most of the routine adjustments, ensuring that the
VTVD's generate the minimum forces to keep the net mouth at
its optimum and at the correct depth. Should, for instance,
the trawl speed increase, the cruise control would adjust the
output forces of the VTVD's to suit these new conditions. This
is totally different to what happens with conventional trawl
doors where the forces generated are always proportional to
the square of the speed and, in many cases, the additional
forces due to the increase of trawl speed exceed that required
for the optimal net mouth opening. This results in additional
drag and hence extra fuel and the possibility of a distorted
net with less catching ability. |
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A typical multi-function screen shot from
the ATS demonstration program |
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| The overriding accelerator pedal
is another useful tool in the quest for fuel economy. For
instance, when hauling the trawl, one can take the foot off
the gas so that the trawl can be hauled up faster with less
effort. When trawling, one can push harder on the pedal in
order to lift the net to avoid an obstacle or to intercept a
higher swimming shoal. One can also use the steering wheel to
move the trawl laterally to sweep a more productive area in a
similar way that a racing car moves from side to side to
“widen” itself to prevent overtaking by a chasing driver. |
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| In effect, the ability to easily
and quickly move the trawl up and down as well as side to side
means that one can use a smaller net with a corresponding
reduction in towing power. |
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| All of the above plus the
hydrodynamic efficiency of the VTVD’s could contribute
significantly towards reducing overall power consumption and
hence reducing fuel costs. |
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| The question is often raised as
to whether the concept of trawl control at the door end of the
warps by means of controllable doors is a better option than the
typical “autotrawl” trawl speed and warp length control. The
theoretical aspects of trawl door control have recently been
investigated in a SINTEF study entitled, “Precise Control of
Trawl Systems”. In essence, this study supports the concept of
control at the trawl doors and also provides useful guidelines
for further implementation thereof. |
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| On the practical front, there is
definite movement towards this. Besides the ATS, there are at
least two other systems being developed, one in Europe and
another in the USA. “It is interesting that we have all chosen
different technologies to achieve the control required,” said
Maurice Shenker. “This is great as it does not “lock in” the
concept to one particular control method.” |
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The display screen of the ATS simulation
software |
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| Being a small R&D company, Active
Fishing Systems does not have the resources and facilities of
the above companies and this has undoubtedly slowed down
development of the ATS. While local trawling companies have
readily offered to make trawlers available for prototype sea
trials, there has not been to date the committed financial
“buy-in” necessary to get the project off the back burner.
Considering the negative reports about the fishing industry
that regularly seem to make news headlines as well as the
current economic conditions, this is not unexpected. |
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| It is, however, a project which
truly encompasses the aims and the spirit of programs and
themes of organizations and institutions such as ICES-FAO and
the European Commission, that support mitigation measures
against seabed impact damage by mobile fishing gears as well
as the development of new fishing technologies. The fact that
the development to date has taken place in South Africa should
in no way detract from its potential worldwide application. |
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| There is still a fair amount of
work to be done before the system could be commercially
available and therefore cooperation and collaboration with
role players, fishermen, manufacturers, regulators and
investors from all around the world on this project is
welcomed. |
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WorldFishingToday 21. Feburay 2009 |
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