Trawl Systems Research Articles

Increasing the energy efficiency of a fishing vessel by estimating the motion parameters of a towed object

The optimal mode of towing fishing gear has a direct impact on the energy efficiency of the fishing vessel. To build the combined traction characteristics of the vessel and trawl systems, data are needed on the nominal moments on the winch and engine drum, as well as the traction force in the warp. Estimation of the movement parameters of the towed object will make it possible to haul warps without overloading the trawl winch and the main engine. The paper proposes a block diagram of the algorithm for estimating the motion parameters of a trawl system. Processing of the current measurements of the warp tension in real time is carried out by digital signal processing methods based on the constructed optimal linear filter, which will be used to obtain the tension on the winch without taking into account the noise that occurs both as a result of the operation of the equipment and under the influence of the random nature of the warp tension process itself. and external hydrometeorological factors. Estimation and prediction of dynamic parameters is necessary for the development of an automated control system for a ship's winch, regardless of its purpose. Therefore, the results presented in this paper can be used in solving problems of automation of lifting equipment operating in non-stationary conditions.

Производительность сил траловой системы – VI: математическое моделирование (часть III)

Performance of external longitudinal and transverse forces developed in the course of towing the trawl systems, namely, the tension and compression forces of cables, ropes and yarns of the rope-net gears in commercial fishing of the longitudinal modulus of elasticity and the transverse modulus of elasticity in the cordage products. Physical and mechanical properties of the synthetic nylon threads, ropes and nylon cords, from which most trawl systems are made, are considered. Analysis of the physical and mechanical properties of synthetic rope products and cords based on the specified parameters for possible static and dynamic loads is proposed. Algorithms for calculating the physical and mechanical properties of threads, ropes and nylon cords are proposed under the condition of constant volume and mass. Method of calculating physical and mechanical properties of the nylon threads and ropes under the condition of uncertainty gives an error not exceeding 0.4% in calculating the relative elongation δε, but the maximum error δμ in calculating Poisson's ratio μ reaches 7.12%. This proves that the formula for calculating the Poisson's ratio μ for anisotropic bodies does not allow estimating this ratio at low loads and constant volume.

Модели процессов эксплуатации донного трала с учетом комплексного влияния абиотических, биотических и антропогенных факторов

In commercial fishing the bottom trawls are recognized as one of the most intensive tools for active use. Bottom trawls seriously impact the benthos in the fishing area. As a result of this impact, the suspended benthos forms extensive tail areas of sediments and dissolved nutrients. In addition, the movement of trawl doors on the ground, as well as the ground rope and cables increase the total resistance and wear of the bottom trawls. Consequently, these factors may cause the negative environmental effects, and lower the efficiency and safety of the bottom trawl system and its fishing operations, which can contribute to greater emissions of nitrogen oxides, sulfur oxides and greenhouse gases. At the initial stage of development of bottom trawl systems, the primary task is to draw up a list of operational requirements that the bottom trawl will satisfy. Generally, the list of these requirements includes functional requirements, i.e. a list of quantitative indicators of the fishing object to which the bottom trawl is directed, indicators of special fishing conditions and restrictions under which fishing is performed, indicators of environmental friendliness of fishing, energy costs, etc. Understanding these processes allows the development of performance requirements that bottom trawls can fully meet. Models of the operation processes of the bottom trawl complex have been developed, taking into account the complex influence of abiotic, biotic and anthropogenic factors, and the impact of the human factor on the control systems of the trawl complex. Within the framework of our research, a quantitative and a qualitative assessment of the physical impact of the above factors on the elements of bottom trawl systems used in the fishery.

Автоматизированная система управления траловым комплексом

The article is devoted to the problems of developing an automated control system for a trawl complex.The analysis of trawl systems from the point of view of the concepts of lean production and lean environmental management is presented. The main design features of the developed automated trawl complex control system are described.

Совершенствование технологии тралового лова дальневосточной сардины-иваси

The paper deals with issues related to improving the efficiency of the trawl fishing of the Far Eastern sardine-ivasi by optimizing trawl systems. A trawl fishing system with a flexible spacer is considered. A method of controlling a trawl system with flexible spacers and the most effective method of equipping a trawl system is proposed, which allows you to bring the trawl into the upper layers of water and hold it to produce differentiated trawling.

Совершенствование техники промысла тихоокеанского кальмара

The paper considers the problems arising in the trawl fishery for Pacific squid and suggests ways to solve them. The necessity of using flexible spacers (GRU) for horizontal opening of trawls when working on difficult soils and for stable output of the trawl system to the surface is shown. The ease of control of the trawl system with the GRU is shown in contrast to the trawl systems with boards. To ensure a large horizontal opening of the trawl and reduce drag, it was proposed to use multi-wall trawls. According to calculations, the proposed trawl systems will reduce fuel costs by 1.7-2 times and, accordingly, will reduce the carbon component (CO2 emissions).

Производительность сил траловой системы – III: математическое моделирование (часть I)

The force performance of trawl systems directly depends on the work performed by these forces.The mechanical work of a trawl system is a physical quantity that depends on the vectors of force (hydrodynamic, tension, compression, etc.) and displacement. Thermodynamic work is the amount of energy transmitted or received by the trawl system by changing its external parameters. There is also the work of the forces of the electrostatic field when the charge moves from one point of the field to another. Equations are obtained for ideal flexible steel ropes and rope-rope products, characterizing the direct proportionality of the ratio of the productivity of forces that are directed perpendicular to each other and depend on the Poisson's ratio and the constructive elongation of ideal flexible steel ropes and cordage products. The ratio of the capacities of the forces or the ratio of the moduli of elasticity in the transverse and longitudinal directions, which arise when steel ropes and rope-rope products are stretched, are inversely proportional to the square of the coefficient k connecting the elongation λ, Poisson's ratio μ and the relative elongation ε at a constant volume of the product and its mass. There has been described an example of stretching perfectly flexible steel 
 ropes and cordage. Such constructive parameters as lay, the number of strands, wire and fiber thickness, type of weaving were not taken into account.

ПРОИЗВОДИТЕЛЬНОСТЬ СИЛ ТРАЛОВОЙ СИСТЕМЫ: ПОСТАНОВКА ЗАДАЧИ

In the design process of the trawl systems, there often arises the need for their mathematical, computer and physical modeling, because in the process of physical modeling it is possible to predict the dynamic processes in the ropes and threads during operation. Automation of the process of a rope-net trawl physical modeling using information technologies is an important problem of a scientific research. The importance of creating a unified database containing information on trawl designs, history of design changes, information on the classification and coding of trawl systems, history of fishing for aquatic organisms in different parts of the World Ocean, as well as data on the fishing gear design and places of their mounting, operation and maintenance. The terms of preparation and approval of project documentation are reduced due to using 6D-control. Competent economic and resource planning, elimination of possible risks even at the planning stage lead to the lower costs and increasing labor productivity. The concepts of productivity of forces (mechanical, electrodynamic, etc.), productivity of forces of the system (technical, biological) are considered, a new parameter is introduced - the productivity of the forces of the trawl system. The postulates operating in all the trawl systems have been proved: the differential law of motion describes the relationship between the square of force applied to a material point and the resulting productivity of the forces of this point; productivity of forces exerting on a material point is equal to the second derivative of the work of these forces in time; the productivity of a system of forces of differ-ent nature exerting on a system of material points is called the productivity of the forces of the system (technical, biological, etc.).

ПОСТАНОВКА ЗАДАЧИ ДИНАМИЧЕСКОГО ПОДОБИЯ ТРАЛОВОЙ СИСТЕМЫ

Testing full-scale mechanical systems, such as trawl systems (bottom and midwater) is connected with great economic costs, therefore, it is advisable to carry out the study of dynamic processes on the models in laboratories. The paper describes special features, advantages and weak points of units for physical modelling fishing gears and processes (testing sites, experimental tanks, water flumes, water channels), which use two different modelling principles: modelling straight motion of a fishing tool model (towing) in still fluid and modelling reversed motion when a static model is washed by the moving water. There have been given detailed specifications and capacities of a model basin under Kaliningrad State Technical University, which is an instrument for studying model fishing gears and processes (seine hauling, trawl hauling, purse seine setting, etc.), as well as of a hydraulic channel in Kaliningrad, which is one of the largest construction of such type in the world. It is noted that during investigation of dynamic processes it is necessary to follow the rules of dynamic similarity. These rules have been developed at the Department of industrial fishing in Kaliningrad State Technical University. There has been determined the base scale for setting the problem of dynamic similarity of a trawl system, substantiation of which is primary in the model developing and testing at a selected unit. There was given the formula for taking the only one and correct decision in determining the base scale. In terms of the determined value of the base scale, there are calculated all the other scales of dynamic similarity given in the table of general scales of physical characteristics of hydrodynamic, ground dynamic and tribological processes, which occur in the trawl systems under dynamic similarity.

Engineering and catching performance of five netting materials in commercial prawn-trawl systems

High-strength netting trawls have less drag due to the opportunity to use thinner twine. In prawn/shrimp trawl systems, where large otter boards spread the trawls to high spread ratios, further substantial drag reduction should occur due to the reduced size of otter boards required. Here we conducted two comparative experiments with commercial prawn trawls made from five respective netting materials including standard polyethylene (PE), high tenacity PE and three examples of Ultra High Molecular Weight (UHMW) PE. In the first experiment, a sequence of paired comparisons of engineering performance (drag and spread) was undertaken across all trawls individually connected to one of three pair of different size otter boards; in all cases codends were left open to avoid catch size confounding the measurements. In the second experiment, catch and selectivity performances were assessed by towing the five trawls simultaneously in a five-rig system, with location in the system randomly varied. The trawl-board combination with the best engineering performance for each high-strength material produced a range of drag reduction compared to the best combination for the standard PE trawl: ∼12% for high tenacity PE and ∼19–21% for the three UHMW PE trawls. The high-strength netting trawls caught larger prawns compared to the standard PE trawl, possibly due to (i) increased twine flexibility allowing smaller prawns to escape, and (ii) greater flow of water through the trawl causing increased catch efficiency for larger, more mobile prawns. A strong negative result was the large amount of bycatch for most high-strength netting trawls—it was concluded that this was driven in part by low fishing line tension, exacerbated by higher operating spread ratio. Some evidence was obtained that this could be mitigated by applying layback to the headline.

Modeling of trawl doors with account of the currents

Mathematical model of trawl doors is presented and methods of their modeling with account of the water currents are described. The model could be used for optimal tooling of trawl systems for real environments.

Influence of twin and multi-rig trawl systems on CPUE in the Danish Norway lobster (Nephrops norvegicus) fishery

One of the most effective ways to alter catch and length compositions in trawls is to adjust the mesh size or add selective devices such as sorting grids and selective netting panels. These changes are often introduced into the fishery in a top down manner whereby fishermen are forced to comply with specific legislation. However, fishermen have also introduced gear modifications that have contributed to improving species selectivity in trawls. One of the simplest and most effective modifications that came from industry was the development and introduction of twin and multi-rig trawls. Here we analyse catch rates of four target species, Norway lobster (Nephrops norvegicus), cod (Gadus morhua), plaice (Pleuronectes platessa) and haddock (Melanogrammus aeglefinus), to try and understand how the use of multi-rig trawls have altered catch rates within the Danish demersal trawl fishery over the last 16 years (1997–2012). Results showed that catch rates of Nephrops in multi-rig trawls were significantly higher (1.89–2.03) than those in single trawls. For cod, haddock and plaice there was no significant effect of gear type. The results are discussed in relation to the Common Fisheries Policy reform and the increasing importance of industry introduced gear modifications.

The 'W' prawn-trawl with emphasised drag-force transfer to its centre line to reduce overall system drag.

For prawn trawling systems, drag reduction is a high priority as the trawling process is energy intensive. Large benefits have occurred through the use of multiple-net rigs and thin twine in the netting. An additional positive effect of these successful twine-area reduction strategies is the reduced amount of otter board area required to spread the trawl systems, which leads to further drag reduction. The present work investigated the potential of redirecting the drag-strain within a prawn trawl away from the wings and the otter boards to the centre line of the trawl, where top and bottom tongues have been installed, with an aim to minimise the loading/size of the otter boards required to spread the trawl. In the system containing the new ‘W’ trawl, the drag redirected to the centre-line tongues is transferred forward through a connected sled and towing wires to the trawler. To establish the extent of drag redirection to the centre-line tongues and the relative drag benefits of the new trawl system, conventional and ‘W’ trawls of 3.65 m headline length were tested firstly over a range of spread ratios in the flume tank, and subsequently at optimum spread ratio in the field. The developed ‘W’ trawl effectively directed 64% of netting-drag off the wings and onto the centre tongues, which resulted in drag savings in the field of ∼20% for the associated ‘W’ trawl/otter-board/sled system compared to the traditional trawl/otter-board arrangement in a single trawl or twin rig configuration. Furthermore, based on previously published data, the new trawl when used in a twin rig system is expected to provide approximately 12% drag reduction compared to quad rig. The twin ‘W’ trawl system also has benefits over quad rig in that a reduced number of cod-end/By-catch Reduction Device units need to be installed and attended each tow.

The modeling of single-boat, mid-water trawl systems for fishing simulation

A mathematical model of single-boat, mid-water trawl system, together with a graphical interface have been created for training purposes. The model consists of separate components for the trawler and fishing gear. The trawler component considers the influence of wind and current and can be used to simulate trawlers in ordinary-speed and low-speed scenarios. The fishing gear component considers the towing warp, the otter board, and the fishing net. The model components are connected by coordinating boundary conditions. All trawling processes, including cruising, towing, and hauling and deploying the fishing net, can be simulated using this approach. Simulations have been undertaken based on a single-boat, mid-water trawler. The simulated trawler speed and turning circle under cruising conditions were compared to sea trials, and simulated trawl mouth height and trawl resistance to flume experiments. The hydrodynamic performance of a single-boat, mid-water trawl has been analyzed, showing that trends in fishing gear parameters together with towing speed and warp length are intuitively correct, but trawling speed is overestimated, which requires that the model component for the controllable pitch propeller be improved.

Analysis of natural and social dynamics of fishery production systems in Paraná, Brazil: implications for management and sustainability

Sustainability and management issues are discussed for eight fishery production systems (FPS) in the state of Paraná, Brazil, from an interdisciplinary perspective. FPS were defined after a set of multidisciplinary classification criteria, in an attempt to conceive fishing activities as a new level of integration between natural and social systems. Systems were compared using the Rapid Appraisal of Fisheries Status (RAPFISH) methodology, with 48 scored attributes, grouped in five evaluation fields (ecological, economic, social, technological and political). Systems were also analyzed for a subset of 14 attributes selected as sustainability indicators. All systems from Paraná showed a poor sustainability profile, yet for different reasons. Two groups of systems proved consistent: traditional systems, and the motorized shrimp trawl systems on the coastal shelf. The traditional systems are historically ancient, employ little technology, show a large diversity of fishing practices, and preserve traditional management. The second is a modern group of systems, with a gradient of technological intensification from motor pirogues or canoes to entrepreneurial trawlers; these systems are market-oriented, intensive and ecologically aggressive, but their fishermen have better living conditions. The methodology showed a great potential for offering interdisciplinary interpretations of fishery dynamics, especially in situations of scant information and several systems to compare. Yet, the analysis of sustainability proved strongly affected by the choice of attributes, which necessarily constitute a small, oversimplified fraction of reality. Management should seek a broader consideration of the complexity of socioeconomic and natural processes that govern fisheries in order to recognize differences among systems and adequately address particular development issues and critical points. A viable way to do this could be the consideration of the fishery system as a management unit, with greater participation of stakeholders to better understand the specificities and particular needs of the systems.

Mathematical Modeling of the Hydrodynamic Forces on a Trawl Door

Precise control of trawl systems is assumed to be beneficial from both economic and environmental reasons. Using the trawl doors as actuators could increase the amount of available control forces. Adequate mathematical models of the hydrodynamic fores on the trawl doors are needed for control system design and verification. This paper presents a method for mathematical modeling of the hydrodynamic forces on the trawl doors. These forces are divided into steady-state forces and transient effects. The six degrees of freedom (six dof) steady-state hydrodynamic coefficients of a trawl door have been found as a function of its angles of attack and slip, based on wind-tunnel experiments. The coefficients are parameterized for smoothing and computational performance, and methods for extending the validity of the model in terms of orientation and trawl door shape are presented. The transient effects are described as functions of relative accelerations between the trawl door and the ambient water, angular velocities of the trawl door and circulation buildup. These effects are manifestations of variations in the flow around the trawl door and its wake, and a numerical method based on potential theory is employed to investigate them. A computational efficient, nonlinear, state-space model of the hydrodynamic forces is finally proposed. It accounts for steady-state and unsteady hydrodynamic forces and moments in six dof, suitable for trawl control system design and analysis

Modelling and Control of a Trawl System in the Transversal Direction

Today trawling is probably the most important fishing tackle for the fisheries. Still, this is a tool that. is not. friendly to the environment. A lot of undesirable small fish are caught, sea floor and coral reefs are often damaged, and the efficiency in proportion to energy consumption could be increased. Conventional trawl systems are not equipped with actuators for feedback control. In this paper a mathematical model for automatic control of the trawl system in the horizontal plane is developed. Minor modifications on the trawl doors making them suitable for automatic control are suggested, and local PID controllers for motion control in sway are developed. Sway control may reduce the average towing drag. This will contribute to higher efficiency, and may also reduce the risk for collisions with obstacles on the sea bed. Numerical simulations will demonstrate the performance of the proposed control system.

Electrical Shrimp Trawl Catch Efficiency for Penaeus duorarum and Penaeus aztecus

The catch efficiency q of two electric shrimp trawl systems, fishing two commercially important species of shrimp, was determined. The variables which determined the efficiency of electric shrimp trawls are identified and defined. The efficiency of the two electric shrimp trawl systems were predicted with a mathematical model. Field studies indicated that the predictive model for Penaeus duorarum and P. aztecus is accurate to within 5% of the measured catch efficiency values. The predicted average catch efficiency value for a 21-m electric shrimp trawl was q* = 39% of the shrimp within its path as compared to q = 35% actual efficiency measured in the field. The predicted average efficiency value for a 15-m electric shrimp trawl was q* = 54% as compared to q = 54% measured in situ.