• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.36 no.4
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• pp.281-286
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• 2000

To analyze the shape of the net mouth of bottom trawl which is composed with 6 seams net, the field experiment was carried out on the sea near Kokunsan Is, Western sea of Korea. The distance of otter board, net height, trawl speed and resistance of the fishing gear were respectively measured according to the change of warp length and towing speed. The results obtained are summarized as follows : 1. The spreading distance of the otter board has been increased straightly according to the increment of towing speed and warp length. The rate of increase by the warp length has been greatly higher than the rate of increase by the towing speed. The total variation of the spreading distance was 57.0-82.8m, and it was occupied 43-62% of the hand rope, net pendent and the length of nets. 2. The height of net mouth has been decreased straightly according to the increment of towing speed and warp length. The rate of decrease by the towing speed has been greatly higher than the decrease rate of the warp length. The total variation of the net height was 3.1-4.0m. 3. When the distance of wing tip is increased, the height of net mouth is decreased, but the ratio of the decreasing rate of the height of net mouth for the increasing rate of the distance of wing tip was gradually low according to the increment of warp length. 4. The ratio of the distance of both wing tip for the height of net mouth has been increased gradually according to the increment of towing speed and warp length, and the total variation of the ratio was 4.17-7.81 times.

• Proceedings of the Korean Society of Fisheries Technology Conference
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• 2001.05a
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• pp.65-66
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• 2001

쌍끌이 중층망은 대형으로 양망시 네트드럼으로 양망해야 하므로 드럼용량이 커야하고, 드럼에 감긴 그물을 투망 할 때에 뜸에 그물코가 얽혀서 파망이나 안전사고를 유발하기도 한다. 또한, 망구 깊이를 주로 끌줄길이와 예망속도로서 제어하고 있으나, 어구저항이 커서 속도의 조절에 한계가 있다. 중층망의 이러한 결점을 보완하기 위하여 최근에는 뜸 대신 카이트(kite)의 사용에 대한 연구(권, 1995)가 있고, 유럽에서는 뜸 없는 무부자(無浮子) 어구를 개발하여 어구저항의 획기적인 감소를 도모하고 있다. (중략)

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.24 no.2
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• pp.78-82
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• 1988

Near sea trawlers of Korea sometimes catch pelagic fishes like file fish by using midwater trawl gear even though usually catch bottom fish. It is reasonable to use the specific otter board as well as specific net in bottom trawling and in midwater trawling respectively. But, the trawlers are so small ranging 100 to 120GT, 700 to 100ps that it is very complicated to use different otter board for bottom trawling and for midwater trawling. The otter board for bottom trawling. is also used for the midwater trawling without any change even though the net is changed into the specific one. Although the otter board in the midwater trawling should be lighter than that for bottom trawling, to use otter board for bottom trawling directly for the midwater trawling without any change makes the net easily touch the sea bed and also make the horizontal opening of the otter boards be limited owing to the length of warp in the southern sea of Korea, main fishing ground of midwater trawling, which is 100m or so in depth. That is why the otter board for the midwater trawling should be made lighter than that in the bottom trawling, even if temporary. The authors carried out an experiment to achieve this purpose by attaching a large styropol float on the top of the otter board. In this experiment, underwater weight of the otter board was 630kg and buoyancy of the float was 510kg. To determine the depth and horizontal opening of the otter board, two fish finder was used. A transmitter of 50KHz fish finder was set downward through the shoe plate of otter board to determine the elevation of otter board from the sea bed, and a transmitter of 200KHz fish finder was set sideways on the starboard otter board to be able to detect the distance between otter boards. The obtained results can be summarized as follows: 1. The actual towing speed in the experiment varied 1.1 to 1.8 m/sec. 2. The depth of otter board was within 41 to 25m with float on the top and 45 to 26m without float in case of the warp length 100m, whereas the depth 68-44m with float and 74-46m without float in case of the warp length 150m. This fact means that the depth with float was 9-4% shallower than that without float. 3. The horizontal opening between otter boards was within 34-41m with float and 30-38m without float in case of the warp length 100m, whereas the opening was 44-50m with float and 37-46m without float in case of the warp length 150m. This fact means the opening with float was 10% greater than that without float in case of the warp length 100m, and 15% greater in case of the warp length 150m. 4. The horizontal opening between wing tips by using the otter board with float was 1m greater than by without float in case of the warp length 100m, whereas the opening by with float was 2m greater than by without float in case of warp length 150m. From this fact, it can be estimated that the effective opening area of the net mouth by using the otter board with float could be made 10% greater than by without float in case of warp length 100m, whereas the area with float 20% greater than by without float in case of warp length 150m.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.36 no.4
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• pp.274-280
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• 2000

To analyze the resistance of the bottom trawl which is composed with 6 seams net, the field experiment was carried out on the sea near Kokunsan Is., western sea of Korea. The resistance was respectively measured in the otter board and the net according to the change of warp length and towing speed. The results obtained are summarized as follows : 1. Total resistance of the test trawl gear are slightly increased according to the length of warp. 2. The resistance of net is increasing a little according to the length of warp, but it is expressed. $$ R_n/=10 \frac{d}{\ell}$representatively. 3. The resistance of otter board can be expressed $Rb=1810_{\upsilon}^0.8.$ 4. Comparing with the value of measuring resistance and Koyama formula resistance by the length of warp respectively, the resistance of test trawl gear is high in the slow towing speed, and the resistance of Koyama formula is high in the fast towing speed, and that the cross-point of the both line between the resistance of the test net and Koyama formula is moved to high according to the increment of warp length.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.39 no.1
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• pp.33-43
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• 2003

The midwater pair trawl which is being used at present in Korea have several problems. Firstly, it is difficult to control the net height on high towing speed. Secondly, net breaking often occurs owing to floats and thirdly, the volume of net on the net drum is so large. This study is aiming for examining the possibility of application for the Korean midwater pair trawl through the model experiment of non-float midwater pair trawl. The model of non-float midwater pair trawl was manufactured as 1/100 of the full scale net which is being used in bottom pair trawl for 850ps class considering the Tauti's Similarity law. The model experiment was carried out to analyze the opening efficiency according to the variation of lower warp length and the opening efficiency was investigated between th proto type and non-float type. The results obtained can be summarized as follows ; 1. The hydrodynamic resistance of non-float type was about 10~20% smaller than that of the proto type and it increased about 1ton according to the increase of dL at the condition of the same flow speed. The resistance acting on the lower warp decreased about 5% but that of the upper warp increased according to the increase of lower warp length (dL) at the condition of the same flow speed. 2. The net height of the non-float type decreased almost linearly according as the increased of flow speed and it increased in a logarithmic functional form with the increase of the lower warp length at the condition of the same flow speed. On the decreasing rate of the net height, the non-float type was lower than the proto type and the difference of the decreasing rate was about 12% at 3.0 knot, 25% at 4.0 knot, 25% at 4.0 knot respectively when dL was 30m. 3. The net width of non-float type was not varied so much as only 2m range and was larger than that of proto type. 4. The mouth area of non-float type decreased in a exponential functional form. On the decreasing rate of the mouth area, the non-float type was lower than the proto type. The filtering volume increased in a logarithmic functional form with increasing flow speed and the filtering volume of proto type decreased steeply over 3.0knot, but that of non-float type increased until 4.0knot. 5. The optimal length of lower warp was when the value of dL was about 30m and the optimal position of front weight was at the connection point of four net pendants.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.38 no.2
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• pp.164-171
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• 2002

In this study, a mass-spring model is used to dynamically describe and calculate the shape and movement of a mid-water trawl system. This mathematical model theorizes that the factors constituting the system are the material points and the external forces such as hydrodynamic load, gravity, and buoyancy act on these material points. In addition, it surmises that these material points are connected to each other by springs, the springs do not have any mass, and the internal force acts on these springs. The non-linear differential equations are implicitly integrated with time for guaranteeing a stable solution. The dynamic simulation by the mass-spring model shows the status of the gear such as fishing gear depth, distance between doors, shape of the gear, and tension of each line. It depends on the parameters such as towing force, warp length, force of a sinker, buoyancy of a float, type of door and netting materials. The validity of the model is verified by comparing simulation motions of a trawl system obtained from computed values to those from an actual experiment.

• Proceedings of the Korean Society of Fisheries Technology Conference
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• 2001.10a
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• pp.31-32
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• 2001

어구의 형상과 움직임은 어구를 구성하는 부품의 물리적인 특성 및 어구의 디자인과 예망속력 및 끌줄 길이의 변화와 같은 어구 조작방법에 따라 달라지며, 이러한 변화는 어획량에 매우 큰 영향을 미친다. 따라서 어구의 디자인과 어구 조작방법에 따라 달라지는 어구의 형상과 거동을 예측할 수 있다면 성능이 우수한 어구를 개발할 수 있으며, 어구를 운용하는데 있어서도 중요한 정보를 얻을 수 있다. (중략)

• Proceedings of the Korean Society of Fisheries Technology Conference
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• 2001.05a
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• pp.67-68
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• 2001

무부자 쌍끌이 중층망은 유속에 관계없이 뜸줄이 거의 일직선으로 유지되고 뜸줄의 깊이 변화가 없으므로 부력은 작용하지 않지만 아래 끌줄의 길이를 조절함으로써 망고를 유지할 수 있다. 또한, 무부자 쌍끌이 중층망은 발줄의 침자 외에도 추(Front weight)와 날개끝 추(Wing-end weght)의 무게를 증가시키면, 아래쪽으로의 침강력이 작용하여 망고를 더 크게 할 수 있어 기존어구보다 전개성능을 더욱 향상시킬 수 있다. (중략)

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.9 no.1
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• pp.1-18
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• 1973

For regulating the depth of midwater trawl nets towed at the optimum constant speed, the changes in the shape of warps caused by adding a weight on an arbitrary point of the warp of catenary shape is studied. The shape of a warp may be approximated by a catenary. The resultant inferences under this assumption were experimented. Accordingly feasibilities for the application of the result of this study to the midwater trawl nets were also discussed. A series of experiments for basic midwater trawl gear models in water tank and a couple of experiments of a commercial scale gears at sea which involve the properly designed depth control devices having a variable attitude horizontal wing were carried out. The results are summarized as follows: 1. According to the dimension analysis the depth y of a midwater trawl net is introduced by $$y=kLf(\frac{W_r}{R_r},\;\frac{W_o}{R_o},\;\frac{W_n}{R_n})$$) where k is a constant, L the warp length, f the function, and $W_r,\;W_o$ and $W_n$ the apparent weights of warp, otter board and the net, respectively, 2. When a boat is towing a body of apparent weight $W_n$ and its drag $D_n$ by means of a warp whose length L and apparent weight $W_r$ per unit length, the depth y of the body is given by the following equation, provided that the shape of a warp is a catenary and drag of the warp is neglected in comparison with the drag of the body: $$y=\frac{1}{W_r}\{\sqrt{{D_n^2}+{(W_n+W_rL)^2}}-\sqrt{{D_n^2+W_n}^2\}$$ 3. The changes ${\Delta}y$ of the depth of the midwater trawl net caused by changing the warp length or adding a weight ${\Delta}W_n$_n to the net, are given by the following equations: $${\Delta}y{\approx}\frac{W_n+W_{r}L}{\sqrt{D_n^2+(W_n+W_{r}L)^2}}{\Delta}L$$ $${\Delta}y{\approx}\frac{1}{W_r}\{\frac{W_n+W_rL}{\sqrt{D_n^2+(W_n+W_{r}L)^2}}-{\frac{W_n}{\sqrt{D_n^2+W_n^2}}\}{\Delta}W_n$$ 4. A change ${\Delta}y$ of the depth of the midwater trawl net by adding a weight $W_s$ to an arbitrary point of the warp takes an equation of the form $${\Delta}y=\frac{1}{W_r}\{(T_{ur}'-T_{ur})-T_u'-T_u)\}$$ Where $$T_{ur}^l=\sqrt{T_u^2+(W_s+W_{r}L)^2+2T_u(W_s+W_{r}L)sin{\theta}_u$$ $$T_{ur}=\sqrt{T_u^2+(W_{r}L)^2+2T_uW_{r}L\;sin{\theta}_u$$ $$T_{u}^l=\sqrt{T_u^2+W_s^2+2T_uW_{s}\;sin{\theta}_u$$ and $T_u$ represents the tension at the point on the warp, ${\theta}_u$ the angle between the direction of $T_u$ and horizontal axis, $T_u^2$ the tension at that point when a weights $W_s$ adds to the point where $T_u$ is acted on. 5. If otter boards were constructed lighter and adequate weights were added at their bottom to stabilize them, even they were the same shapes as those of bottom trawls, they were definitely applicable to the midwater trawl gears as the result of the experiments. 6. As the results of water tank tests the relationship between net height of H cm velocity of v m/sec, and that between hydrodynamic resistance of R kg and the velocity of a model net as shown in figure 6 are respectively given by $$H=8+\frac{10}{0.4+v}$$ $$R=3+9v^2$$ 7. It was found that the cross-wing type depth control devices were more stable in operation than that of the H-wing type as the results of the experiments at sea. 8. The hydrodynamic resistance of the net gear in midwater trawling is so large, and regarded as nearly the drag, that sweeping depth of the gear was very stable in spite of types of the depth control devices. 9. An area of the horizontal wing of the H-wing type depth control device was $1.2{\times}2.4m^2$. A midwater trawl net of 2 ton hydrodynamic resistance was connected to the devices and towed with the velocity of 2.3 kts. Under these conditions the depth change of about 20m of the trawl net was obtained by controlling an angle or attack of $30^{\circ}$.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.41 no.2
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• pp.122-128
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• 2005

The experiments were conducted to fine out the handling characteristics of the FMT(Frame Mideater Trawl) in the southern waters of Korea using a trawler "DONGBAEK" belongs to Yosu National University. The realtionship between the net depth D(m) and the warp length L(m) at the towing speeds of 2.5k't and 3.5k't werw as follows ; D(m) = 0.30L - 1.3(2.5k't), D(m) = 0.16L - 1.5(3.5k't). Therefore, the net depth was 3.0m deeper when the warp length was 10m longer at the towing speed of 2.5k't and was 1.6m deeper for 10m longer at the speed of 3.5k't, respectively. The sinking speed of FMT was 6.5m/min when the warp releasing speed was 24m/min at the towing speed of 2.5k't and was 3.8m/min for 25m/min at the towing speed of 3.5k't, respectively. The rising speed of FMT was 6.9m/min when the warp rewinding speed was 28m/min at the towing speed of 2.5k't and was 5.3m/min for 25m/min at the towing speed of 3.5k't, respectively. The mean elapsed time getting to the stable towing condition was 104sec at the towing speed of 2.5k't and was 105sec at the towing speed of 3.5k't, respectively, and there was no time difference for the towing speed variation. During the towing, the net depth was comparatively stable on the condition of no change for the warp length and the towing speed.