50 years of fishing technology at the University of ...

WGFTFB meeting in Hirtshals, Denmark 2018 __________________________________________________________________________________

50 years of fishing technology at the University of Rostock Mathias Paschen1, Bob van Marlen2, and Harry Stengel3 1

University Rostock, Germany – Institute of Ocean Engineering, 2retired Wageningen Marine Research, IJmuiden, Netherlands, 3retired, formerly University Rostock, Germany – Institute of Fishing Technology *[email protected] , [email protected] (Corresponding authors)

Abstract This year it was 50 years ago that training in fishing technology officially started at the University of Rostock. We will look back at the major achievements in teaching and scientific research over these years. Two periods can be distinguished, the years 1968-1992 under the leadership of prof. Dr. H. Stengel, and the years 1992-now (2018) under the leadership of prof. Dr. M. Paschen. Wageningen Marine Research (former RIVO) started a cooperation with the University in 1988, and many collaborative projects have been carried out, as well as practical training of students at RIVO’s facilities. Since historical processes often quickly fall into oblivion, this article is preceded by a brief historical summary of the circumstances at the time. Especially younger generations should have the chance to recognize the value of free exchange of ideas and freedom of travel. Our talk will focus on the following topics:           

Organizational aspects of the Chair of Fishing Technology (renamed: Chair of Ocean Technology in 1992) of the University with numbers of graduates. Model tests of fishing gears using a wind tunnel. Application of photogrammetry for 3D acquisition of trawls in wind tunnels. Development of rope trawls, and other drag reduction midwater trawl designs. The Tension Element Method (TEM) as a replacement of the Finite Element Method (FEM) for hydro-dynamically loaded flexible rope and netting systems. The interaction of fishing gear components and the seabed. Prediction of the dynamics of flexible multi-body systems including integrated rigid bodies in real time. Analyses of fluid - netting structure interactions by Computational Fluid Dynamics (CFD) and Particle Image Velocimetry (PIV). Major projects carried out at University Rostock. The development of a single door trawl for towing at the surface outside the wake of the vessel. The cooperation between RIVO and the University of Rostock in times of great political changes.

Historical Background Two German states emerged as a result of the Second World War. The final political and economic division by the Allies in 1949 was formally eliminated in autumn 1990 with the reunification, as is known. Over the following 40 years, this division has led in part to very different developments in society and economy as well as in science. The German Democratic Republic (GDR), which emerged from the Soviet occupation zone, began in the late 1940s and in the 1950s to develop a shipbuilding industry that was remarkable at that time. -1-

WGFTFB meeting in Hirtshals, Denmark 2018 __________________________________________________________________________________ The design and construction of fishing vessels was one of the domains. As early as the mid-1950s, the increasing gap between the potential of the new fishing vessels and that of the old equipment, methods and materials of the coastal and deep-sea fishery of the GDR practiced at that time became clearly visible. While the development of shipbuilding in the GDR was mainly driven forward by engineers who had started their carrier before the second World War as well as by professors and graduates of the shipbuilding faculty which was founded in 1951 as a part of the established University of Rostock there was no comparable education for fishing technology. In the second half of the 1950s, a number of young shipbuilding engineers, among others, recognised a professional perspective in fishing technology. However, it was the young Harry Stengel who gave the East German fishing technology a new scientific and technological impulse. Stengel had been thoroughly educated in the theory and mechanics of fishing gears by the famous Russian professor F.J. Baranov in Moscow. As a young engineer of the former Industrial Institute for Deep Sea Fishing and Fish Processing in Rostock he built up a his young team with whom he tested, developed and introduced new methods in fishing technology. In particular the introduction of pelagic pair fishery for large trawlers should be mentioned, the use of wind tunnels for testing at model scale the design of new trawls, otter boards and trawl doors, as well as netting materials and wires. Due to the political situation at that time, almost all relevant publications were published in German and in scientific journals of the GDR, so that many results became internationally known much later. Stengel's initial successes clarified the need for both a university training programme for engineers for fishing technology and the creation of a scientific concept to enable a deeper physical understanding of the interaction of fishing gears and the marine environment, followed by the development of theoretically based numerical methods and innovative laboratory-based experiments. In 1964 Harry Stengel was offered by the University of Rostock to become a lecturer and to develop a teaching and research curriculum for fishing technology. After four years of intensive work, Stengel not only received his doctorate in engineering, he also developed a complete university training programme (broadly comparable with a Bachelor plus a Master programme) and built up a small outstanding research group. In agreement with the responsible Ministry of the former GDR, the University of Rostock decided to transform this working group into a complete faculty and to appoint Harry Stengel as professor and chair for fishing technology. This happened 50 years ago now, a fact that called for a celebration. Until 1978, scientific cooperation essentially took place only with well-known scientists from the former Technical University in Kaliningrad, Soviet Union, such as Prof. Dr. Alexander L. Fridman and Prof. Dr. M.M. Rosenschtein. This scientific cooperation was accompanied by numerous barriers especially for young scientists and students. In October 1978, Prof. Dr. J. Świniarski of the Szczecin Agricultural Academy invited Harry Stengel to sound the possibilities of scientific cooperation in the field of fishing technology between Szczecin and Rostock. This initiative was very successful. Many joint projects, publications and cooperative student exchanges followed for more than three decades. Since then, this cooperation also included joint supervision of doctorates and habilitations of scientists on both sides. In the mid-1980s, the Socialist Party under the leadership of Erich Honecker recognized that the existing technological gap to the leading industrial nations would enlarge when the GDR scientists did not get the chance to communicate with their colleagues in Western Europe. Thus Harry Stengel was -2-

WGFTFB meeting in Hirtshals, Denmark 2018 __________________________________________________________________________________ allowed by the GDR authorities to visit Scandinavian and Western European countries and relevant universities and research institutions in the second half of the 1980s. In return, a cooperation with Rostock became of interest for numerous colleagues. In particular Steinar Olsen (N), Bill Dickson (UK), Ludvig Karlsen (N), Bob van Marlen (NL), Klaus Lange (D) and others are to be mentioned. After the political reunification, the former large fishing fleet of the GDR, at that time the largest in Germany, was dissolved. At almost the same time, the higher education system in East Germany was restructured, which resulted both in personnel changes and a reorientation of teaching and research at the University of Rostock starting on October 1, 1992. As with the widespread decline of German commercial fishing, the basis for solid engineering research and teaching in the field of fishing technology ceased to exist, the responsible Ministry decided to replace fishing technology with research and teaching in the field of thematically broader ocean engineering. The acting director of the former Institute of Maritime Technologies and Fluid Mechanics, Mathias Paschen, himself a student and former associate of Harry Stengel, was appointed university professor and chair for the new field on October 1, 1992. With this decision, two essential goals were achieved: the preservation and further development of the expertise in the theory of fishing gears and related systems and the orientation towards other questions of marine engineering technology under the new social conditions of free, i.e. politically uninfluenced exchange between scientists across national borders. In order to pursue these two goals with all seriousness and to promote the scientific dialogue between scientists of different ages, different experiences and different regional origins, the international “Workshop on methods for the Development and Evaluation of Maritime Technologies (DEMaT)1” was established in 1993.

Focal points of research in fishing technology in Rostock Looking back over the past 50 years, considerable changes can be recognised, concerning both the objectives and the methodical approaches solving scientific projects. Until about 1990 almost all fisheries related projects were financed either by the fishing industry or by shipyards. The research topics mainly concentrated on the development of physicalmathematically based models that were in demand in the economic circumstances at the time. They were used for the development and technical optimisation of fishing gears and fishing technologies on board of fishing vessels i.e. the aim was to introduce the results of research direct into the development of products and techniques. Selected projects of this period focused primarily on the development of (see Stengel, Leitzke and Paschen, 1989):   

 1

Numerical methods for the computation of shape and stress of hydrodynamically loaded twines, ropes and nettings, Mathematical models for numerical analyses of the dynamic behaviour of fishing gears controlled by ship manoeuvres, Methods for the experimental determination of hydrodynamic load coefficients of fishing gear rigging elements, twines, ropes and netting structures and their application in wind tunnels, towing tanks, as well as flume tanks, and Experimental test facilities for studying scale models of fishing gears.

https://www.lmt.uni-rostock.de/demat/archiv/

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This form of undoubtedly application-oriented research often led to the desired rapid economic success. However, it had the disadvantage that research aimed at more far-reaching scientific questions, to achieve a deeper understanding of phenomenological relationships, were not in the interest of industrial sponsors and therefore rarely funded. With the decline of German deep-sea fishing and the discontinuation of building large fishing vessels in Germany at the beginning of the 1990s, the existing sources of financing ceased to exist. There was no economic or social interest in Germany to continue such research. However, new sources of funding offered the opportunity to do more basic research. Much more attention has been paid to the comprehensive scientific validation of developed methods now. In this context the experimental basis of the Faculty of Ocean Engineering has been considerably broadened. New measuring methods and devices for contactless detection of interactions between fluid and elastic structures such as nets, ropes, depressors and lifting devices, etc. were procured and adapted to the respective research requirements. These include laser-assisted methods (Particle Image Velocimetry (PIV) and Laser Doppler Anemometry (LDA)) and hot-wire measurement technologies for flow measurement, high-speed measurements of oscillating bodies due to flow separation, an optical motion capture system to follow motions of freely suspended bodies in the wind tunnel, etc. This experimental basis and the computer hardware and software available today make it possible to look much deeper into the respective systems and thus gain a much better understanding of cause-effect relationships. In this respect, we are once again dealing with methods that were developed and applied more than 25 years ago. Today, however, the scientific tasks concentrate much more on the validation of the methods as well as on their further development and generalisation in order to be able to apply them also in sectors outside the fishing industry. Some selected projects of the last few years are listed below:    



2

Analyses of the mechanical interaction between the sea bed and towed fishing gears such as bottom trawl and beam trawl, Hydrodynamic calibration of plankton nets, Explanation of hydrodynamic effects on netting and twisted ropes, Application of the theory of multi-body systems for the calculation of comprehensive hydrodynamically loaded netting structures to enable calculation and control of the dynamic behaviour of such structures in real-time, Improvement of the applicability of known simulation and calculation methods for rope and netting structures and provision as open-access solutions under OCN ACADEMY2

www.ocnacademy.org

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Short descriptions of selected research projects over a period of 5 decades Investment in development of both theoretical and experimental methods “Nothing is more practical than a good theory.” This sentence, often used by numerous scientists from the most diverse disciplines, is also fully justified in fishing technology. Theories can help to analyse situations briefly, to describe phenomena concisely and to quickly make decisions. It has happened to every fishing technician: for initially incomprehensible reasons, the fishing gear does not reach the predicted geometric parameters. It may be unbalanced, the trawl doors do not reach the desired stable position or individual meshes in the gear are broken due to local mechanical stress peaks, etc. If one has understood the physics of fishing gear based on solid engineering knowledge the fishing technologist will understand why this particular situation happened. In contrast the application of a non-knowledge-based trial and error method usually does not lead to a sustainable solution. Therefore, all students must learn to plan, conduct and evaluate experiments on a theoretical basis. In return, theories must be validated by qualified experiments. This connection has determined the concept of research and teaching in fishing technology in Rostock for 50 years. It would go too far and would not be appropriate to list the results of more than 30 dissertations, over 300 master's theses and numerous research reports. Hartmut Leitzke (1983) analysed the possibilities of introducing the “Finite Element Method (FEM)” into computation of pelagic trawls in the beginning of the 1980s, because this method is a very powerful tool and used worldwide in various fields of mechanical and civil engineering. The use of FEM implies rigidity of the system, meaning that the changes in shape are usually only first order, i.e. linear and small. Netting systems are not stiff in the sense of Hooke's Law. The "stiffness" of fishing gear is a result of hydrodynamic, hydrostatic and weight forces. Only along the netting yarn is the material stiff, but not perpendicular to it. Since the density of netting materials is approximately equal to the density of seawater, the net weight in water plays an almost subordinate role and can be neglected in many cases. Leitzke modified FEM into the so-called “Tension-Element-Method (TEM)” for flexible rope and netting constructions that does not require stiffness. With TEM it is possible to calculate only very lightly loaded net constructions. A minimum of forces is required to obtain unambiguous solutions. For example, the loads on mesh bars in drift nets are very low. Otherwise, no fish would be caught at all. Based on this theory Gerd Niedzwiedz and others created and tested a powerful computer package – the Rope Net Calculator (2002). This programme includes a self-programming tool of all necessary equations for a rope-net-system; its design had to be described by a graphic editor. It was possible to integrate additional gear components such as floats, flexible kites, weights, etc., and special characteristics of the materials applied, hydrodynamic coefficients, etc. into the mathematical model. For an automatic equation formation of a gear consisting of about 32,000 elements a PC of an average performance needed approximately 20 minutes in the late 1990s. Often, the calculation of such a gear system was very time consuming at that time (up to several hours). Because of its high reliability, we were asked several times by international well known net making firms to test and to improve some of their trawl designs based on our computer programmes. Figure 1 shows an example of a calculated pelagic trawl net from the 1990s.

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Figure 1: Example of a calculated pelagic trawl net

An essential assumption for the computation was that the flow velocity distribution inside and outside the gear is known at any place, which means that the influence of the netting structure on the fluid velocity field is neglected. However, Koritzky (1973) detected that fluid-structure interactions can be significantly influenced by the twine thickness mesh size ratio, denoted as d/a, the mesh opening as well as the angle of attack of the mesh. He quantified the range where the assumption of an undisturbed flow by the structure is not allowed. This interaction meant for example that calculations of cod-ends where not accurate enough. In recent years, this theory has been expanded, in particular by Otto, so that today flexible but shearresistant foils, cloths, etc. can also be calculated (Otto and Paschen, 2013). As to be seen from the example in Figure 2, the fabric shows wrinkles, which is conform expectation. By using modern numerical solution methods, the calculation times could also be drastically reduced. Thus, the computing times on a medium power laptop for predicting dynamic processes of small systems (> 10,000 elements) amount to approx. 1/5 of the real time of the real process taking place in nature. Martin et al. (2018) developed for simple net designs a concept for an appropriate automatic programming of the mathematical model to safe time for pre-processing. The hydrodynamic loads are still based on experimental coefficients of rigid grids. These grids consisted of round, articulated aluminium bars. They look like sliding lattice grate constructions. This technique makes it possible to adjust the mesh size as required. To simulate the thread structure, circular knitted threads were previously threaded onto the rods. The experiments are carried out almost exclusively in wind tunnels3 like presented in Figure 3 and Figure 4.

3

Changing the fluid from water to air allows to maintain similarity in both the Re-number and the Frnumber.

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Figure 2: Example of a calculated tablecloth hanging over the edge of the table

Figure 3: Test stand and net grid for determining the flow loads in the wind tunnel in 1978.(1-nozzle, 2-grid, 3-oil-filled tank for vibration damping, 4-platform for camera work, 5-rear panel with grid for photo-optical evaluation, Pi- high-precision photo cameras, Fi-tensions in the stays,i-vertical angle of the stays, -geometric pitch angle)

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0,8 u1

0,6

0.254 0.301

0,4

cl[-]

0.399 0.505

0,2

0.701

0 0

0,2

0,4

0,6

-0,2 cd [-] Figure 4: Example for a polar diagram of the investigated grid by variation of u 1, 8700 < Rn < 10660

Both the 3D Particle Image Velocimetry (PIV) measuring system and the 1D, 2D and 3D hot-wire probe technology installed made it possible to precisely determine the flow velocities near the grid and to incorporate flow deflections into the calculations of netting structures. The available PIV system is described by Knuths (2007). Results of investigations were presented and discussed. Figure 5 shows the flow pattern around and through grids with a pitch angle of 0° and 20°, respectively. Details can be found in Paschen et al. (2007). The violet stripes result from the laser shadow of the grid and that of the mesh node. The increase in velocity before the knot and the decrease in speed after the knot in case of  = 20° are clearly visible. The change in the local direction of flow can also be seen. In case of an increasing d/a these effects will increase, too. The same effects are to be observed when the mesh opening is small.

Figure 5: Vector plot of the current around a mesh in the centre of the grid,  = 0° (left) and 20° (right)

Before the PIV measurements took place in Rostock, Enerhaug (2006) carried out very interesting measurements on the distribution of fluid velocity in front of net cone models, using a speed log. The results were very interesting for the numerical as well as experimental investigations of Breddermann (2017) who studied the filtration performance of plankton nets. In the 1990s, the European -8-

WGFTFB meeting in Hirtshals, Denmark 2018 __________________________________________________________________________________ Commission, among others, supported several projects to investigate the impact of bottom trawls and beam trawls on the seabed. This mostly involved extensive trials at sea. In order to analyse the interactions between sediment and dragged structure in detail, model studies were carried out under laboratory conditions as part of several projects. One of these was the TRAPESE project, see next section. Most of the results of the laboratory tests were published by Paschen, Richter and Köpnick (2000) and Paschen (2006). Enerhaug (2011) supplemented these analyses with his own experiments. The heart of the investigations, which lasted several years, was a specially developed small towing tank which allowed a precise determination of the load of ropes, wires, cables, chains, etc. continuously towed on a straight course along the bottom filled with sediment of known grain size (Figure 6). The tank could be operated with or without water.

Figure 6: Overview on the towing tank used for the investigations of sediment-structure interactions

The movements of the sediment were determined synchronously by means of digital image processing. Two video cameras whose optical axes were offset by 90 degrees were used for this purpose. The penetration depth of each dragged element was determined by laser distance measurement. The pressure exerted by the dragged element on the sediment at a defined depth was measured by force sensors. These force sensors were time-synchronized with the video cameras. This made it possible to observe the dynamics of the entire process in and with the sediment. A visual impression of the tests is given in Figure 7. A quantitative result on the coefficient of friction of a dragged aluminum circular cylinder is shown in Figure 8 as an example.

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Figure 7: Selected examples of some tests

In addition to numerous quantitative results, the following generally valid findings were obtained, see Paschen (2006): 1. The drag of a transversely towed rope is significantly influenced by its weight. We can observe that the drag with regard to the rope’s weight (so-called reduced drag) linearly increases up to a q/d-ratio of about 200 Nm-2. Here is q weight of the rope per meter in water, and d its diameter, and therefore is q/d the amount of pressure of the rope, cable, wire, etc. on the sediment. In case of q/d > 200 Nm-2 the reduced drag is constant. This result correlates with the amount of moved sediment during towing. We could observe that the quantity of moved sediment did not more increase in case of q/d > 200 Nm-2. The sediment moved in front of the rope reached the height of the rope diameter and passed the rope on the top side. 2. The surface structure of the ropes leads to an increasing reduced drag as a consequence of higher roughness. 3. Investigations we had done in advance showed that the length of the used models of 450 mm did not have any influence on the results of the reduced drag. It is allowed to carry out those tests for a length-diameter ratio down to 17:1. 4. An increase of towing speed leads to a slight increase of the reduced drag in case of a small q/dratio. In case of a big q/d we can recognize decreasing values for the reduced drag. 5. Decreasing the angle of attack leads to a lower drag in every case. The loss of drag correlates with an increasing pressure q/d. 6. The rope twist type (S/Z) does not have any influence on the drag. 7. The resulting load vector has two components: drag and transverse force. The orientation of this load vector in relation to the towing direction is given by the angle  that depends on the angle of attack , the pressure q/d as well as the type of rope surface structure.

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WGFTFB meeting in Hirtshals, Denmark 2018 __________________________________________________________________________________ 8. Data of comparable investigations with straight and curved ropes permit the conclusion that the loads measured in model tests with straight ropes, hawsers, etc. can be also used for the prediction of loads for curved ones. Obviously the local angle of attack of the rope is significant. The influence of the curvature of the rope seems to be low.

Figure 8: Friction number

Fd  * ql

as a function of reduced weight q/d [Nm-2] and towing speed v [ms-1] in case of smooth cylinders made from aluminium

Applied research, joint project “BioBind” The primary task of university research is undoubtedly the development and improvement of validated scientific methods and their generalization. Nevertheless, there is also a certain attraction in the application of these methods in the sense of development and testing of new technical concepts. Aa technical concept is briefly presented below for the absorption of oil which is basically developed for application in coastal waters, see Paschen and Semlow (2014). It essentially consists of two components: bio-degradable oil binding agents and a collecting system in the form of a floating netting structure. The basic idea of the concept is that biodegradable oil binding agents will be released, immediately after the accident, by an airplane or by ships on the water surface concerned. The oil binders are made from wood fibres injected with microbes. Because these microbes are able to disintegrate oil molecules in water the process of oil spill removal can be extended as long as oil molecules are available. The contaminated oil binders will be collected by the netting structures. Because of the variety of tasks different partners such as oceanographers, net makers and aircraft pilots were members of the consortium.

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WGFTFB meeting in Hirtshals, Denmark 2018 __________________________________________________________________________________ To design and to test the netting structure was an essential part of the Institute of Ocean Engineering. The concept is taken from the Danish seine. It is a device floating on the water surface to be towed by two vessels. The on-board operations are quite similar to those of pair trawling. The gear is equipped with two long wings and a kind of codend. The wings are fitted with evenly distributed plastic balls to get both sufficient buoyancy and enough “freeboard” to avoid any splashing over of water and oil. The upper part of the wings is made of a flexible and impermeable synthetic material (height approx. 1.5 m). The lower part is made of close-meshed netting. When designing the codend, care had to be taken to ensure that the oil binding agents would drift in unhindered. This required various tests. Figures 9, 10 and 11 show an overview of the entire system including ships, the codend structure and the recovery process, respectively. Because of the plastic balls, the device could not be wound up a winch drum. An available deck crane enabled recovery in a short time.

Figure 9: Overview of the entire system including ships

Figure 10: Design of the codend-structure

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Figure 11: Hauling process

Cooperation between RIVO and the University of Rostock in times of great political changes. Development of rope trawls, and other drag reduction designs. In the beginning of the 1970s work started on improving the performance of pelagic trawls for species such as herring (Clupea harengus L.), Atlantic mackerel (Scomber scombrus L.), horse mackerel (Trachurus trachurus L.), and blue whiting (Micromesistius poutassou, L.). The focus at the time was to improve the efficiency of fishing operations by reducing the towing resistance of the gears whilst keeping their catchability. From 1973 so-called ‘rope trawls’ (in German ‘Jagernetze’) were tested by the “Institut für Hochseefischerei und Fischverarbeitung (IfH)” in cooperation with the University of Rostock, with follow-up in West-Germany, United Kingdom, Netherlands, Norway and France (Figure 122a). A workshop was held in Hamburg in January 1979 to discuss methods of design and calculation of these rope trawls (van Marlen, 1979). The catching efficiency of rope trawls was observed to lack behind that of conventional diamond mesh trawls. It was found out that creating cross-connections between the parallel ropes enhanced the herding effect of the trawl mouth with better catch results. A suit of alternative designs among which hexagonal mesh (Figure 12b) and large diamond mesh trawls (Figure 13) were developed and tested at model-scale and at full-scale, by scientists from Germany, Norway, United Kingdom, and France with a standing information exchange within the ICES Working Group on Fishing Technology and Fish Behaviour (WGFTFB). The work on Dutch pelagic trawl development was presented at the World Symposium on Fishing Gear and Fishing Vessel Design in St. John’s Newfoundland, Canada in 1988 (van Marlen, 1989).

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Figure 12. Designs of rope trawl (left, a) and hexagonal mesh trawl (right, b) presented by IfH Rostock.

Figure 13. Large diamond mesh trawl GM2 designed by RIVO in 1980 based on a model presented by Brabant and Portier in 1978.

Pelagic trawl towed outside the wake of the vessel. It was observed that fish could react to vessel noise especially in the wake of the towing vessel (Ona, and Toresen, 1988), and this led to the idea of avoiding this volume of disturbed water. The design of this gear introduced in 1987 by Leitzke, Niedwiedz and Paschen is based on using one spreading device and a non-spreading device at the other side, thus dragging the trawl in a path outside the centre line of the boat (Figure 14). The upper wing-ends of the trawl are towed at the sea surface. A series of model and full-scale experiments were conducted in 1987 and 1988. Part of this work was carried out in close cooperation between the Dutch RIVO, IfH and the University of Rostock.

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Figure 14. Schematic drawing of the new trawl rigging versus the original one with items to measure.

Full-scale trials took place in September 1989 on-board RV “Ernst Haeckel”, a few weeks before the fall of the Berlin Wall with the associated political changes eventually leading to the unification of Germany, events that were unknown and unthinkable at the time. Two relatively small midwater trawls were used in the trials given the beautiful names “Fanny” and “Vera”. Details of the riggings, gears, and data collection method with measured variables are given in van Marlen et al., 1990. It was a fine example of cooperation (Figure 16 and Figure 16), and resulted in showing the feasibility of this design. Model studies (scale 1 to 7) on a midwater trawl type “Fanny (II)” were conducted in lake Insko in Poland using a catamaran in June 1990 (Kwidzinski, 1986), following full-scale experiments on RV “Tridens” in May that year with Dutch midwater trawls. This work was done in cooperation with the University of Szczecin (“Instytut Akwakultury i Techniki Rybacki”), the University of Rostock and IfH. Details are given in de Jong and van Marlen, 1991. The experiments showed that the net can indeed be towed sideways outside the centre line of the boat.

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Figure 15. Research team on-board RV “Ernst Haeckel” in September 1989. From left to right: Bodo Schäfer, Anne van Duyn, Bob van Marlen, Mathias Paschen, Eberhard Kammrath and Dick de Haan. Wolfgang Buck is missing.

Figure 16. Attaching sensors on the wing-ends on-board RV “Ernst Haeckel” in September 1989.

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Figure 17. Catamaran used at Insko Research Station (source: Gabriel et al., p. 485 ).

EU-project “Trawl Penetration in the Sea bed (TRAPESE)”. This EU-project ran between 1997 and 1999 and formed a cooperation between the Sea Fisheries Department of Ostend, Belgium, the Netherlands Institute for Fisheries Research (RIVO), the Netherlands Institute for Applied Geoscience (NITG), and the University of Rostock as coordinator. The topic of research was the mechanical effect (sediment displacement and penetration) of towed fishing gear components on the sea bed. The work involved systematic laboratory tests, and in-situ measurements of penetration using full-scale 12m beam trawls with tickler chains ranging from 16 to 26 mm shackle diameter. The instrumentation featured BoxCore sampling and RoxAnn acoustic equipment. An instrumented trawl shoe was used to measure the pressure from 4m (330 hp vessel) and 10 m (1200 hp) beam trawls on the sea bed, resulting in values ranging from 0.3-3.5 for 300 hp and 0.14.0 for 1200 hp (Table 2). A mechanical computer model was developed that could be used to predict the penetration depth of fishing gears based on specifications of their components. The main finding was that penetration depth varied between 10 and 80 mm depending on sediment type for the beam trawls used (Table 2). It was one of the first studies combining biology and physics. Details are given in Paschen et al., 2000. Table 1. Results of Belgian trawl shoe pressure measurements in project TRAPESE.

Vessel Z-568

Engine power [hp] 300

Z-93

300

N-36

1200

Z-36

1200

Min [N/cm2]

Max [N/cm2]

Contact

0.3 0.9 0.8 2.8 0.1 0.8 0.1 0.9

0.5 1.6 1.1 3.5 0.5 4 0.3 2.2

full heel full heel full heel full heel

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WGFTFB meeting in Hirtshals, Denmark 2018 __________________________________________________________________________________ Table 2. Measured trawl penetration as a function of sediment type for 12 m beam trawls in project TRAPESE.

Sediment type Sand, clean, medium/course (98/04) Sand, clean, fine (98/05) Sand, clean, medium/course (99/08) Sand, muddy, very fine (M2)

Min 7.5 10 10 10

Mean 29 16.2 22.5 52.9

Max 55 60 70 80

Acknowledgements. The cooperation took place in a very turbulent era in recent German history. During the start there still existed two German nations, as a cause from the second World War, namely the German Democratic Republic (GDR or East Germany), and the BRD (“Bundes Republik Deutschland” or West Germany), separated by a guarded border. It was not easy to get access to the GDR at the time, and one needed an entry visa. Nevertheless and in spite of difficulties the cooperation was welcomed by both parties and the work brought people together for a lifetime. The turnover in 1989 changed the lives and positions of many in the former GDR, and made cooperation much easier. The University of Rostock could take up the role of project coordinator of TRAPESE in 1997 and made a success of this project. We still carry deep sympathy for all the scientists and technicians we have met and worked with in that time and since. These projects were indeed a unique experience in historic moments.

References Brabant, J.C. and Cousin, P., 1977. Calcul des differentes longueurs dans un chalut a cordes. ICES CM 1977/B:26. Brabant, J.C., and Portier, M., 1978. Le chalut pélagique a trés grande mailles. ICES CM 1978/B:18. Brabant, J.C., Prado, N., and Dahm, E., 1980. Comparative fishing trials with big meshes and rope trawls. ICES CM 1980/B:9. Breddermann, K. (2017). Filtration performance of plankton nets used to catch micro- and mezozooplancton. Dr.-Ing.-thesis, published in: Rostocker Meerestechnische Reihe, Vol. 12, Shaker Verlag Aachen Dahm, E., Lange, K. and Von Seydlitz, H., 1976. Further development of rope trawls. ICES CM 1976/B:7, p 8-12. Dahm, E., Lange, K. and Steinberg, R., 1977. Recent studies on rope trawls. ICES CM 1977/B:21. de Boer, E.J., 1976. Rope trawl development in the Netherlands. ICES CM 1976/B:7, p 21-30. Dickson, W., 1978. Construction and tests of a rope trawl. Included in ICES CM/B:4, p 23-51. Enerhaug, B., 2006. Flow through fine-meshed pelagic trawls. Workshop DEMaT’2005 in Busan, Republic of Kora, published in: Contributions on the Theory of Fishing Gears and Related Marine Systems, Vol. 4, pp. 153-164, PKNU, ISBN 89-89382-22-X 93520 Enerhaug, B., 2011. Contact forces between seabed and fishing gear components. Workshop DEMaT’2011 in Split, Croatia, published in: Contributions on the Theory of Fishing Gears and Related Marine Systems, Vol. 7, pp. 237-246, Shaker Verlag Aachen, ISBN 978-3-8440-0468-7 Gabriel, O., Lange, K., and Dahm, E., Wendt, T. (Eds.), 2005. Von Brandt’s - Fish Catching Methods of the World. Blackwell Publishing, 4th edition. -18-

WGFTFB meeting in Hirtshals, Denmark 2018 __________________________________________________________________________________ Isaksen, B., Jensen, H. and Olsen, S., 1979. Recent development on blue whiting trawls in Norway. ICES CM 1979/B:24. Jakobstovu, S.H.i., 1979. Faroese experiments with very big meshed trawls for blue whiting fishery. ICES CM 1979/B:16. Jong, H.B.H..J. and van Marlen, B., 1991. Model research on a single-door trawl at Lake Insko in 1990. ICES CM/B:21, Fish Capture Committee. Karlsen, L., 1977. Development and testing of rope and large meshed midwater trawls in Norway. ICES CM 1977/B:40. Knuths, H., 2007. Particle Image Velocimetry (PIV). Workshop DEMaT’2007 in Rostock, published in: Contributions on the Theory of Fishing Gears and Related Marine Systems, Vol. 5, pp. 217-226, Shaker Verlag Aachen, ISBN 978-3-8322-6606-6 Koritzky, H.H., 1973. Beitrag zur Bestimmung von Widerstand und Auftrieb ebener Netztücher (Contribution to the determination of drag and lift of plane netting). Dr.-Ing.-Thesis, University of Rostock, 1973 Kwidzinski, Z., 1986. A method of studying trawl models in the experimental station of the faculty of sea fisheries and food technology. Acta Ichthyologica et Piscatoria, Vol XVI Facs. 2, 1986, 43-51. Fischerei Forschung Rostock 26,1988, 38-40. Lange, K., 1978. Calculation of rope trawls. ICES CM 1978/B:7. Lange, K., 1979. Schleppwiderstand von Tauwerknetzen. Hansa 1979, No 4, p. 319-321. Lange, K., 1979. Full-scale trials with long-rope trawls. ICES CM 1979/B:6. Leitzke, H., 1983. Berechnung von Form und Kräften biegeschlaffer, räumlicher Zugsysteme (Calculation of shape and stress of flexible, three-dimensional tensile systems). Dr.-Ing. habil. Thesis (Habilitation), University of Rostock, 1983 Martin, T.; Schacht, S.; Riesen, P.; Paschen, M., 2018. Efficient implementation of a numerical model for flexible net structures. Ocean Engineering 150 (2018), pp. 272–279 Niedzwiedz, G., 2002. Model specification and further application of the calculation of rope systems. Workshop DEMaT’2001 in Rostock, published in: Contributions on the Theory of Fishing Gears and Related Marine Systems, Vol. 2, pp. 83-96, Ingo Koch Verlag und Co. KG, ISBN 3-935319-88-6 Niedzwiedz, G., Leitzke, H., Paschen, M., 1986. Schleppnetz für die Oberflächenfischerei (Pelagic trawl for surface fishery). Patent specification DD 239 935 A1, 15.10.1086. Ona, E. and Toresen, R., 1988. Avoidance reactions of herring to a survey vessel, studied by scanning sonar. ICES CM 1988/H:46. Paschen, M., 2006. Seabed-structure interactions of selected fishing gear elements. Workshop DEMaT’2005 in Busan, Republic of Kora, published in: Contributions on the Theory of Fishing Gears and Related Marine Systems, Vol. 4, pp. 207-222, PKNU, ISBN 89-89382-22-X 93520 Paschen, M., Daartz, H., 1989. Modellexperimente zur Untersuchung der Laufeigenschaften pelagischer Scherbretter (Model tests to investigate the running properties of pelagic trawl doors). In: Fischerei-Forschung (27), 1989, Vol. 4, p. 53- 65.

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WGFTFB meeting in Hirtshals, Denmark 2018 __________________________________________________________________________________ Paschen, M., Knuths, H., Winkel, H.-J., Ristow, E., 2007. Flow investigations of net panels for small angles of attack. Workshop DEMaT’2007 in Rostock, published in: Contributions on the Theory of Fishing Gears and Related Marine Systems, Vol. 5, pp. 23-34, Shaker Verlag Aachen, ISBN 978-38322-6606-6 Paschen, M., Niedzwiedz, G., Winkel, H.J., 2004. Fluid structure interactions at towed fishing gears. 23rd International Conference on Offshore Mechanics and Arctic Engineering 20-25 June 2004, Vancouver, British Columbia, Canada, OMAE2004-51525. Paschen, M., Richter, U., Köpnick, W, 2001. Untersuchung von technischen Maßnahmen zur Erhöhung der Selektivität von kommerziell eingesetzten Schleppnetzen für den Fang von Plattfischen in der Ostsee (Investigation of technical measures to increase the selectivity of commercially used trawl nets for flatfish fishing in the Baltic Sea). Final report of the research project financed by European Community and Ministry for Food, Agriculture, Forestry and Fisheries MecklenburgWestern Pomerania under the PESCA Community Initiative. Paschen, M., Richter, U., Köpnick, W., (editors), 2000. Trawl penetration in the seabed - TRAPESE. Final report of the research project EU contract No. 96-006, financed by the European Community, Directorate general XIV – Fisheries. Paschen, M., Schäfer, B., 1989. Großversuche zum seitlich versetzten Oberflächen-Schleppnetz (Fullscale tests on the laterally offset surface trawl net). In: Fischerei-Forschung (27), 1989, Vol. 4, p. 6673. Paschen, M., Semlow, C., 2014. Biodegradable oil binding agents – a new approach for air based oil spill response at sea. Twelfth international conference on marine science and technologies – Black Sea 2014, Varna, Bulgaria, 2014, DOI: 10.13140/2.1.1567.1043. Paschen, M., Winkel, H.-J., Knuths, H, 2008. Fluid-Structure Interactions in Pelagic Trawls and Probable Consequences for the Selectivity of the Fishing Gear. In: Advances in Science and Technology, Vol. 58, p. 247-256. Rehme, W., 1973. Das Jagernetz – einen Neuentwicklung im VEB Fischkombinat Rostock. Seewirtschaft 5, 1/1973, p 58-61. Steinberg, R. and Dahm, E., 1976. German experiments with a modified four panel rope trawl. ICES CM 1976/B:39. Stengel, H., Leitzke, H., Paschen, M, 1989. Research work in the field of theory and design of fishing gears in the GDR. Presentation at the international fishery energy optimization working group of the FAO, Vancouver, University of British Columbia, August 28th - 30th. Thiele, W., 1975. Produktionsergebnisse mit dem Jagernetz und dessen Weiterentwicklung. Seewirtschaft 7, 2/1975. van Marlen, B., 1979. Draft report on ad-hoc meeting in Hamburg on the design and calculation of rope trawls. Included in ICES CM 1979/B:3, p. 88-93. van Marlen, B. and MacLennan, D.N., 1979. Rope trawl development - further experiments. RIVO Report TO 79-03. Summary included in ICES CM 1979/B:3, p. 105-119. van Marlen, B. and MacLennan, D.N., 1980. Engineering trials with a conventional and a rope trawl of 2700 meshes circumference. RIVO Report TO 80-03. Summary included in ICES CM 1980/B:2, p. 2248. -20-

WGFTFB meeting in Hirtshals, Denmark 2018 __________________________________________________________________________________ van Marlen, B., 1981. Engineering and comparative fishing trials on trawls with large hexagonal meshes in the front part. RIVO Report TO 81-04. van Marlen, B. and van de Velde, R., 1982. Engineering and comparative fishing trials on a trawl with large diamond shaped meshes in the front part and a conventional trawl, both of 2700 meshes circumference. RIVO Report TO 82-02. van Marlen, B., 1989. A decade of research and development of midwater trawls in the Netherlands. In: Fox, G. (ed.), Proceedings World Symposium on Fishing Gear and Fishing Vessel design, p. 141152. Marine Institute, 1989. van Marlen, B., de Jong, H.B.H.J., Paschen, M. and Schaefer, B., 1990. Performance measurements on a single door trawl towed at the sea surface. ICES CM/B:19, Fish Capture Committee. Verbaan, A., 1977. Review of the Netherlands investigations into a pelagic rope trawl. ICES CM 1977/B:25. Von Seydlitz, H. and Kelle, W., 1978. Rope trawl experiments with commercial cutters on herring. ICES CM 1978/B:8. Von Seydlitz, H. and Kelle, W., 1979. Rope trawl experiments with commercial cutters in the Baltic Included in ICES CM 1979/B:3, p. 97-100. Winkel, H.J., Paschen, M, 2004. Investigations on the fluid-structure interactions of fishing nets. 25rd International Conference on Offshore Mechanics and Arctic Engineering 4-9 June 2004, Hamburg, Germany, OMAE2006-92156

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