Development Status The Active Trawl System concept was seeded in the 1960's but remained an idea for 30 years :- only in the last two decades or so have technologies become available and affordable to ensure that the concept could be turned into  reality. The first "concept demonstrator" model was built using scrap box  components and tested in a swimming pool to prove that practice  conformed to theory. Although it was not aesthetically pleasing, it  clearly illustrated that the concept of thrust vectoring using rotating  cylinders, is valid. A scale model of a Variable Thrust Vector Device, shown on the left,  was manufactured and tested under controlled conditions in the towing tank at the University of Stellenbosch. Besides confirming once again the validity of the thrust vectoring  concept, valuable information with respect to the hydrodynamic  characteristics of the variable thrust vector devices was obtained. Feedback from prospective customers and partners indicated that the "full on" rotor device might be too radical a change for the fishermen to accept. As such, an intermediate "rotors in a door" version was designed. This incorporates smaller rotors in a substantial frame which also provides  some additional "conventional" lift force. While this does, in some cases, influence the effectiveness of some of the attractive features of the original concept, an acceptable degree of control over the position of the trawl is still easily attainable. Some of the merits of this design are (a) it is more acceptable to the  fishermen, (b) it provides an extra measure of safety against collapsing of  the trawl, (c) additional strength and protection is provided to the rotors  and (d) the power requirement of the system is reduced. Other feedback from prospective customers and partners indicated that the fishermen were not keen on having a  third cable for power and communications as in the initial concept. Some felt that it would add to the handling  problems, increase the number of seabird deaths as well as being a potential safety hazard. The R&D focus then shifted to finding a cable-less solution, Various battery-pack and power-saving options were  investigated but all seemed to add to the weight and size of the VTVD or placed an operational limit on the trawl time and functionality. The considerable effort and resources which were put in, have resulted in a design which is cable- less and with all the features and functionality of the original cable concept but without the time constraints of a  battery system. The "design intent" of the ATS system is to keep the VTVD's off the seabed during normal trawling operations and  hence they are engineered to be unstable when they touch the seabed. This forcing to fly them off the bottom  prevents damage to the VTVD’s themselves and also makes the ATS more environment-friendly and less destructive  to the seabed than conventional trawl systems. A further spin-off is that, by not having the extra cable and associated equipment the overall cost of the system can be significantly reduced. Additionally the drag can be reduced as well. The current status is that a full size VTVD has been designed, taking into account the off-the-shelf availability of  materials and standard components, manufacturing methods, corrosion resistance, ease of assembly as well as the  ability to perform routine maintenance and to replace wear parts easily on board the trawler. A comprehensive  manufacturing data pack is being completed which will enable an accurate costing to be obtained. (Please note that the new mechanical design of the cableless VTVD's is presently not in the public domain  and the illustrations of the VTVD's on this website are therefore of the old cable-type system. Details of  the new cableless system will be made available in due course.) The ATS is a multi-disciplinary project involving many aspects of engineering and fishing technology. A number of  fishing equipment and other companies have expressed their keen interest in the system and also their wish to  participate in the project. These range from trawl door manufacturers, net makers, electronics companies, motor  drive companies to control systems specialists. Each company has its own agenda and priorities which has, to some  extent, worked against the smooth development of the system. To date, most of the development work on the system has been concerned with the fluid dynamics, mechanical and  control system design. This has reached a stage where most technical and operational aspects have been sorted out and where a simple sea-going prototype system can be built with confidence. The original concept made use of extra cores in the power cable for communication between the trawler and the  VTVD's. However, this hardware is not available in the cableless system. It is envisaged to “piggy-back” the  communications link on top of the hydro-acoustic data signal of the cableless trawl monitoring/position information  system which would also be required to provide feedback to the ATS control system. These trawl monitoring and  trawl positional information systems have become standard equipment on the modern trawler. Enquiries from interested parties in connection with participation in the Active Trawl System project are welcome and will be treated with confidentiality.
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