Frequently Asked Questions
Latest Norwegian and Icelandic Controllable Trawl Door trials - the beginning or the end for the ATS?
Active Fishing Systems welcomes and encourages these latest developments as it believes that this is a big step
forward for the trawling industry and a major boost for the Active Trawl System.
Firstly. fishermen are soon going to experience the benefits of control at the trawl net and be able to explore the
possibilities offered by this new method. Although these controllable doors cannot provide all the features and
functionality of the Active Trawl System, they can certainly be the proof-of-concept as well as the catalyst for the
change to this next generation of trawl doors.
Secondly, the fishing electronic equipment manufacturers are also going to have to match these developments and
provide the necessary control, communications and support functions to make these systems work. This takes the
pressure off Active Fishing Systems to develop these itself. Integrating the Active Trawl System with fishing
electronics has just become a lot easier and significantly less expensive.
Controllable Trawl Doors - a one-man crazy idea?
Definitely not! The idea has been around for many a year and has been put on the table a number of times by some
of the industry’s most respected and knowledgeable players. The trend towards larger boats, larger gear, larger doors
and “auto-trawl” systems that control the winch and engines have to a large extent, taken care of some of the
problems in the past and therefore dampened the drive to implement controllable doors successfully. However, the
“bigger the problem, the bigger the hammer” solution has created its own set of problems such as environmental
damage concerns and uneconomic operation and other solutions now need to be devised.
However, is the concept of trawl door control at the door end of the warps by means of controllable doors a better
option than the typical "autotrawl" trawl speed and warp length control? Active Fishing Systems certainly thinks so.
The theoretical aspects of trawl door control have recently been investigated by Karl J Reite 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.
On the practical front, companies such as Scanmar have devoted considerable resources to developing steerable
trawl doors and institutions like Sintef and MIT Sea Grant have commissioned projects on the control of trawl doors.
All these use different technologies to achieve the control. While this does not "lock in" the basic principle of
controllable doors to one particular technology, time will tell which will emerge as the most dominant.
“....There are now perhaps just two or three things left to put into place to make trawling as rational and controllable
as possible. The first of the next products in line are controllable trawl doors....”, (Henning Skjöld-Larsen, Managing
Director of Scanmar, pg 12, Scanmar Info, Anniversary Edition)
Why are there no Rotor Doors hanging from the sterns of trawlers?
Well, actually there were - in the 1970’s from the FRV Explorer and the FRV Scotia - during sea trials of the DAFS
Marine Laboratory Pelagic Trawl project. If the funding had not dried up and there were the same pressures on the
industry as there are today, rotor doors might well have become the industry standard.
Development of a system such as the Active Trawl System with its VTVD’s does not come cheaply and needs a
substantial investment of money, time and resources in order to get it to a stage where it can be sea trialed and
proven to work. No fisherman would want to commit to purchasing such a system based on paper studies, model
simulations and pretty pictures - they want to see it in action. So it is not possible to establish the true market
potential of the system. Financiers on the other hand are not keen to advance money without knowing the projected
sales. It is a bit of a catch-22 situation: investors would be willing to fund development if market interest is proven,
but the market interest can only be determined once the system has been developed and trialed. Perhaps the “fishing
storm” will be knife that cuts the loop...
Is it Technically Feasible?
Present day available and affordable technologies with respect to computer hardware and software, sensing and
detection instrumentation, motors and drive electronics, materials, design and manufacturing techniques make this
concept technically feasible. In fact, it is a lot more feasible now than when the system was first proposed in 1995!
The real challenge lies in making the system work reliably and consistently in the very harsh undersea marine
environment as well as in the operating conditions encountered on typical trawlers. Good engineering practice should
ensure this.
Why spinning rotors?
While moving flaps and shifting tow-point systems might be mechanically simpler with fewer moving parts, they also
require power to operate. The faster the response required, the more power needed. Typically these systems are
designed so that they are very stable in order to reduce the number of movements required and so they conserve
power. This does tend to make then less responsive that the spinning rotor system. These are “add-on’ type systems
so they need to be carefully packaged and integrated into standard doors.
The thrust from a spinning rotor can be varied from full thrust to zero to minus full thrust simply by adjusting the
speed and direction of rotation. This type of quick-response, high-force, low-drag generation is not really achievable
with movable flaps or shifting tow-point systems.
How will the ATS reduce Seabed Damage?
The VTVD’s can generate enough spreading force on their own, without "digging in" and ploughing the sea bottom
like conventional trawl doors do. In fact the VTVD’s should, under normal circumstances, not make contact with the
sea bottom at all. If they do, they could become unstable and unpredictable. So, by virtue of their design, the
skippers will be forced to "fly" them off the sea bottom. The trawl net, however, could still touch the bottom lightly.
This could be achieved by changing the rigging and buoyancy of the trawl net.
Because the VTVD’s are highly maneuverable, they can also be steered away from vulnerable seabed areas.
Cable vs Cableless System?
Initially the cable system seemed the best and easiest way to go. It offers a very fast and reliable two-way
communications link as well as unlimited power. Also, the technology is readily available and well-proven within the
subsea industry. On the negative side, the cost is rather high, there are certain safety concerns and it does
complicate the trawl operation.
However, with the increased reliability of hydro-acoustic communication links as well as the latest developments
regarding the powering of the VTVD's, a cableless version seems the better option to go for.
What will the ATS cost?
Difficult question - it will depend on the configuration required and the options selected. As a rough estimate, the
cost of the VTVD’s will be about three times that of the conventional otterboards they replace. However, the increased
cost of the system will be able to be recovered by reduced operating costs and improved fishing ability.
When will the the ATS be available?
A most frequently asked question. The answer lies in your hands! There have been numerous inquiries for details on
the system from fishermen and fishing companies who can readily appreciate the potential benefits of the ATS, but
who, understandably, want a proven, ready-to-use system i.e. they do not want to be involved in the development
process. Unfortunately, no sea-going system has been built or trialed to date. Why, you may well ask - there are
good reasons for this.
Firstly, while collaborating with the first overseas potential partners of repute who showed interest in the system,
seemed like a good idea initially, it turned out, in fact, to be a bad decision. The geographical distance between us
created communication and logistical problems which slowed down co-operation to a totally unacceptable level. After
months of "working together" it also became apparent that their idea of development differed considerably from the
tried and trusted development approach that is required. Taking shortcuts and reducing the cycle, as they wanted,
would only have increased the risk.
Secondly, the system was a bit ahead of its time. While some of the systems required to provide feedback to the ATS
were available in 1995, they were basically stand-alone units and not easily interfaced to the ATS. Today that has all
changed and also, new technologies are available that slot in very nicely with the requirements of the ATS.
Thirdly, the ATS (or any other new fishing concept) will not get off the ground until it has been proven in the
commercial fishing arena. Fishing companies here have expressed willingness to provide a vessel for trials, but are
not willing to fund any development of the system.
To summarize, the path from new concept to commercial product is by no means straight and, often requires ground-
breaking methods. The ATS has progressed down the path, landed in some "dead ends", reversed out of them, found
alternatives and to all intents and purposes, is still on track towards its aim of become the trawl system of the future.
"There is nothing more difficult to take in hand, more perilous to conduct, or more uncertain of success than to take
the lead in the introduction of a new order of things."
".... for the innovator has for many enemies, all those who had been successful under the old conditions and
lukewarm defenders among those who may benefit under the new scheme ...."
Copyright Active Fishing Systems 2016
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