Warp Length Research Articles

Investigations on Structural, Mechanical, and Thermal Properties of Pineapple Leaf Fiber-Based Fabrics and Cow Softy Leathers: An Approach Toward Making Amalgamated Leather Products

Natural leathers processed from hides and skins of animals face major threat from synthetic leathers as an alternative material with comparable properties for most of the applications. As consumers are becoming increasingly aware of environmental issues, there is a need for ecofriendly biodegradable materials. Natural fibers have several advantages such as low cost, high strength, and biodegradabiliy. In this study, natural cow softy leathers meant for leather goods application and three types of pineapple leaf fiber (PALF)-based fabrics with various blending combination have been chosen and analyzed for physical, morphological, and thermal properties. It was found that most of the physical properties of cow softy leather and PALF-based fabrics are comparable. It is interesting to note that the tensile strength and elongation at break of select PALF-based fabrics is higher in the parallel direction (along the warp length) than in the perpendicular direction (weft). The color and light fastness properties of PALF-based fabrics are better than that of cow softy leather. Scanning electron microscopic analysis provided convincing evidence for characteristic fiber pattern in the individual fiber bundles (yarn) and also their blend fiber composition. The thermal decomposition behavior of both cow softy leather and PALF-based fabrics seems to be comparable, with uniform weight loss of 60 ± 10% during decomposition. The results of this study suggest that the identified PALF-based natural fabrics can be used for making a variety of products in combination with leather for several applications.

Determination of effective tow duration for estimation of fish and shellfish abundance in deeper-water bottom trawl surveys

Experimental trawl surveys were conducted to determine effective tow durations for estimating fish and shellfish abundances in deeper-water bottom trawl surveys. A total of 304 hauls were conducted in Kagoshima Bay, southern Japan, for preset tow durations of 10 and 20 min, using a simple trawl net fitted with depth loggers. Towing durations were recorded at the ship’s bridge based on the shooting, towing and hauling times of the trawl net, using pre-established warp lengths for different water depths. Effective tow durations were computed by plotting depth logger and echo sounder data against tow time, and compared with preset tow durations. Trawled distances and swept areas were calculated using the Euclidean distance method. Effective tow durations ranged from 9 to 23 and from 19 to 37 for the 10 and 20 min preset tow durations, respectively. Preset tow duration estimations for abundance were highly biased: −10 to 130% and −5 to 85% biases relative to the effective tow duration estimations, respectively. Moreover, the biases were more pronounced in the shorter tow durations in deeper-water trawl hauls. The computation of effective tow durations using depth loggers and the ship’s onboard instrumentation presents a simple approach for correcting inadvertent estimations of effective tow duration, swept area and abundance indices.

Effect of tow duration on estimations of CPUE and abundance of the grenadier Coelorinchus jordani (Gadiformes, Macrouridae)

The effect of tow duration on estimates of catch per unit of swept area (CPUE) and the abundance of the grenadier Coelorinchus jordani was investigated in Kagoshima Bay, southern Japan. A total of 305 tows were completed using a trawl net with mesh sizes of 37.9 mm and 20.2 mm at the body and cod-end, respectively. Towing was conducted at pre-determined warp lengths for each station and for preset tow durations of 10 or 20 min. Effective tow durations (actual fishing times) were computed from the trawl depth profiles derived from compact temperature-depth loggers that were attached to the net. All hauls were sorted by species, and the total numbers and weights of the catches were recorded. Estimations of CPUE and biomass were conducted for C. jordani, one of the most abundant fish species in Kagoshima Bay. Effective tow durations varied; on average, they were >50% longer than the preset times. CPUE and biomass estimations for C. jordani were significantly influenced by the tow duration. Estimates from 10-min tows were approximately three times higher than estimates from 20-min tows. The total catch per haul and log-transformed 10:20-min preset CPUE ratios were positively correlated, indicating that haul size might influence CPUE for C. jordani. Consequently, the influence of other species on CPUE and biomass estimations for a particular species in multi-species fisheries cannot be ignored. Coefficients of variations for CPUE and biomass estimations from both preset and effective tow durations were not significantly different. However, estimations that were based on the effective tow durations showed slightly lower coefficients of variations ( CVs), and the effective 10- and 20-min tow durations were equally efficient for estimating the CPUE and abundance of C. jordani.

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.

평판형 전개판의 3차원 운동 모델링

Otter boards in the trawl are the one of essential equipments for the net mouth to be spread to the horizontal direction. Its performance should be considered in the light of the spreading force to the drag and the stability of towing in the water. Up to the present, studies of the otter boards have focused mainly on the drag and lift force, but not on the stability of otter boards movement in 3 dimensional space. In this study, the otter board is regarded as a rigid body, which has six degrees of freedom motion in three dimensional coordinate system. The forces acting on the otter boards are the underwater weight, the resistance of drag and spread forces and the tension on the warps and otter pendants. The equations of forces were derived and substituted into the governing equations of 6 degrees of freedom motion, then the second order of differential equations to the otter boards were established. For the stable numerical integration of this system, Backward Euler one of implicit methods was used. From the results of the numerical calculation, graphic simulation was carried out. The simulations were conducted for 3 types of otter boards having same area with different aspect ratio(<TEX>${\lambda}=0.5,\;1.0,\;1.5$</TEX>). The tested gear was mid-water trawl and the towing speed was 4k't. The length of warp was 350m and all conditions were same to each otter board. The results of this study are like this; First, the otter boards of <TEX>${\lambda}=1.0$</TEX> showed the longest spread distance, and the <TEX>${\lambda}=0.5$</TEX> showed the shorted spread distance. Second, the otter boards of <TEX>${\lambda}=1.0$</TEX> and 1.5 showed the upright at the towing speed of 4k't, but the one of <TEX>${\lambda}=0.5$</TEX> heeled outside. Third, the yawing angles of three otter boards were similar after 100 seconds with the small oscillation. Fourth, it was revealed that the net height and width are affected by the characteristics of otter boards such as the lift coefficient.

The influence of warp length on trawl dimension and catch of walleye pollock Theragra chalcogramma in a bottom trawl survey

Variations in trawl dimension, bottom contact, and catch with differing warp lengths during walleye pollock surveys conducted by the Fisheries Research Agency were examined. The ratio of warp length to fishing depth (scope ratio) was set at 2.5, 3.0 and 3.5 at depths of 110 m. At tact the bottom. Footgear contact was complete when the scope ratio was 3.0 or more. Walleye pollock, sculpins and flatfishes were the main catch in all tows, and the catch increased with scope ratio. There was no difference in the length frequency of walleye pollock (n=300) captured at 2.5 and 3.0 scope ratio. However, the length frequency at 3.5 was significantly different from that of other scope ratios. These results suggest that at a scope ratio of 3.0 or more, the trawl door will not leave the bottom at any depths. To complimentecho surveys for walleye pollock, a 3.0 scope ratio would be optimal, since the catch data for a 3.5 scope ratio was dissimilar from that of scope ratios.

소형 어류 플랑크톤 채집용 FMT Net 의 운용 특성

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.

종만곡 V형 전개판의 영각 추정법

How to extimate the angle of attack of a vertical V-type cambered otter board was described. A three-dimensional semi-analytic treatment of a towing cable system was applied to the field experiments of a midwater trawl obtained by the Scanmar system. Also the equilibrium condition of the horizontal component and vertical component of forces and moment around the otter board was used. When the warp length was 300m long and the towing speed was between 2.61 and 3.86 knots, the estimated angle of attack of the otter board was ranged between <TEX>$24.7^{\circ}$</TEX> and <TEX>$26.2^{\circ}$</TEX>, though the maximum lift force was at the angle of attack <TEX>$22^{\circ}$</TEX>.

Newly designed quantitative frame trawl for sampling larval and juvenile pelagic fish

A newly designed frame trawl with a 5 m2 mouth area was constructed for quantitative sampling of larval and juvenile pelagic fishes and its performance was tested in the ocean. Towing depth of the trawl was easily controlled by adjusting the warp length, and the stability at depth increased with decreasing weight of the net in water. Larval and juvenile fishes were sampled using the trawl at stations in the Kuroshio-Oyashio transition region from 29 May to 24 June 1998. A total of 44 oblique tows were conducted and towing depths of the frame trawl had a high degree of stability despite the various sea conditions and the fluctuations in the ship speed. Larvae and juveniles of Japanese anchovy Engraulis japonicus and Myctophidae made up the majority of the specimens. It was concluded that the newly constructed trawl was appropriate for the quantitative sampling of pelagic fish larvae and juveniles.

무부자 쌍끌이 중층망 어구어법의 개발 (II) - 추와 날개끝 추의 무게에 따른 모형어구의 전개성능 -

무부자 쌍끌이 중층망은 유속에 관계없이 뜸줄은 거의 일직선으로 유지되고 뜸줄의 깊이 변화가 없었다 또한, 뜸이 없기 때문에 부력은 작용하지 않지만 아래 끌줄의 길이를 조절함으로써 망고를 유지할 수 있었다. 그리고, 무부자 썽끌이 중층망의 전개성능은 발줄의 침자 외에도 추(Front weight)와 날개끝 추(Wing-end weight)의 침강력을 증가시킴으로써 더욱 향상될 수 있었다. 연구는 회류수조에서의 모형실험을 통하여 무부자쌍끌이 중층망의 추와 날개끝 추의 무게에 따른 전개 성능을 규명하고 그 결과를 기준형과 비교 분석하였다. 그 결과를 요약하면 다음과 같다. 1. 유체저항은 유속이 2.0∼5.0knot로 증가함에 따라 거의 직선적으로 증가하였으며, 느린 유속에서는 저항의 증가폭이 작지만, 유속이 빠를 때는 저항의 증가폭이 커지는 경향을 보였다. 추의 무게 및 날개끝 추의 무게의 증가함에 따라서도 유체저항은 증가 하였다. 2. 망고는 유속이 증가함에 따라 거의 직선적으로 감소하는 경향을 나타내었으며, 망고의 감소율은 기준형보다 무부자망이 낮았다. 추의 무게가 0.70ton 에서 1.75ton으로 증가할 때 각 단계별로 약 2m씩, 날개끝 추의 무게가 0.28ton에서 1.11ton으로 증가할 때 각 단계별로 약 1m씩 각각 망고가 증가하였다. 망폭은 기준형보다 모든 무부자망이 약 10m 정도 더 컸으며, 추와 날개끝 추의 무게가 증가햄에 따라 그 변화폭은 2m 내외로 거의 일정하였다. 3. 망구면적은 추의 무게가 1.75ton 일 때, 날개끝 추의 무게가 1.11ton일 때 최대가 되었고 유속이 2.0∼3.0knot에서는 무부자망이 기준형보다 작았으나, 4.0-5.0knot에서는 무부자망이 기준형보다 더컸다. 4. 여과량은 기준형에서는 3.0knot일 때, 무부자망에서는 4.0knot일 때 각각 최대가 되었으며, 추의 적정무게는 1.40ton이었다. 팀은 환자가 원하는 영적 간호를 실시하도록 체계적인 접근 방법을 강구해야 할 것으로 사료된다.된다. 통하여 움직임 감소 장치를 사용함으로써 내부 장기 중 횡격막 움직임의 범위가 감소함과 동시에 CTV-PTV 마진이 크게 줄어드는 결과를 확인하였다. 이 결과를 통하여 흉부 또는 복부에 종양을 가진 환자 치료 시 더욱 질 높은 방사선 치료가 실현될 것으로 기대한다. 30∼40％ 정도 느렸고, 퍼레니얼라이그라스도 퍼레니얼라이그라스 100％ 단일종류에 비해 20∼30％정도 늦었다. 따라서, 뗏장 재배시 여러 종류의 초종을 천편일률적으로 혼합하여 파종하는 것은 바람직하지 않으며, 컨셉에 따라 적절하게 초종 및 품종을 선택해서 사용하는 것이 필요하다. 5. 뗏장의 뿌리 형성 능력은 퍼레니얼라이그라스가 가장 좋았고, 가장 저조한 초종은 켄터키블루그라스였다. 톨훼스큐는 켄터키블루그라스와 퍼레니얼라이그라스의 중간정도로 나타났다. 혼합구의 뗏장 형성 능력은 초종의 혼합비에 따라 뿌리 형성력 차이가 다르게 나타났는데, 특히 퍼레니얼라이그라스 혼합비율이 많을수록 뿌리 형성 능력은 증가하였다. 6. 뗏장 수확시 잔디 품질은 단일 초종구의 품질이 혼합구에 비해 양호하였는데 가장 우수한 초종은 켄터키블루그라스였고, 톨훼스큐는 켄터키블루그라스 다음으로 중간정도, 그리고 퍼레니얼라이그라스는 가장 저조하였다. 켄터키블루그라스는 균일한 잔디 면, 고밀도 및 예초 후 상태가 우수한 특성으로 품질이 양호하였고, 퍼레니얼라이그라스의 품질이 저조하였던 것은 초장이 길어 잔디 면이 누운 상태로 나타나 균일도 저하 및 예초 후 품질이 켄터키블루그라스나 톨훼스큐 보다 떨어지기 때문이다. 그리고 혼합구의 품질은 여러 종류가 혼합됨으로 인해 색상 및 밀도의 균일도가 떨어지고, 또한 예초 시 물결처럼 불균일하게 깎여 잔디 표면이 불량하였기 때문이었다. 7. 골프장이나 경기장 기본 설계 시 초기 피복도 및 뿌리 형성력이 In this study, the vertical opening of the non-float midwater pair trawl net was maintained by controlling the length of upper warp. This was because the head rope was able to be kept linearly and the working depth was not nearly as changed with the variation of flow speed as former experiments in this series of studies have demonstrated. We confirmed that the opening efficiency of the non-float midwater pair trawl net was able to be developed according to the increase in front weight and wing-end weight. In this study, we described the opening efficiency of the non-float midwater pair trawl net according to the variation of front weight and wing-end weight obtained by model experiment in circulation water channel. We compared the opening efficiency of the proto type with that of the non-float type. The results obtained can be summarized as follows：1. The hydrodynamic resistance was almost increased linearly in proportion to the flow speed and was increased in accordance with the increase in front weight and wing-end weight. The increasing rate of hydrodynamic resistance was displayed as an increasing tendency in accordance with the increase in flow speed. 2. The net height of the non-float type was almost decreased linearly in accordance with the increase in flow speed. As the reduced rate of the net height of the non-float type was smaller than that of the net height of the proto type against increase of flow speed, the net height of the non-float type was bigger than that of the proto type over 4.0 knot. The net width of the non-float type was about 10 m bigger than that of the proto type and the change rate of net width varied by no more than 2 m according to the variation of the front weight and wing-end weight. 3. The mouth area of the non-float type was maximized at 1.75 ton of the front weight and 1.11 ton of the wing-end weight, and was smaller than that of the proto type at 2.0∼3.0 knot, but was bigger than that of the proto type at 4.0∼5.0 knot. 4. The filtering volume was maximized at 3.0 knot in the proto type and at 4.0 knot in the non-float type. The optimal front weight was 1.40 ton.

무부자 쌍끌이 중층망 어구어법의 개발 (III) - 카이트를 부착한 모형어구의 전개성능 -

무부자 쌍끌이 중층망 어구어법의 개발 (III) - 카이트를 부착한 모형어구의 전개성능 -

무부자 쌍끌이 중층망 어구어법의 개발(I) - 아래끌줄의 길이에 따른 모형어구의 전개성능 -

본 연구는 현재 국내에서 사용되는 쌍끌이 중층망 어구어법에서 문제점으로 지적되고 있는 고속예망에서 망고의 제어가 어렵다는 점, 망목에 뜸이 걸려서 파망이 자주 일어나는 점, 네트드럼에 감기는 어구부피가 너무 크다는 점 등의 해결방법으로 무부자 쌍끌이 중층망의 모형실험을 통하여 우리 나라 쌍끌이 중층망에 대한 적용 가능성을 검토하는데 있다. 이를 위하여 850ps급 쌍끌이 기선저인망어선에서 현재 사용되는 실물망을 1/100로 축소 제작한 모형망에서 뜸을 모두 제거하고 끌줄을 양쪽으로 각각 두가닥으로 분리한 후 추를 부착하여 아래끌줄의 길이를 조절함으로써 망고를 제어할 수 있는 무부자 쌍끌이 중층망의 모형어구를 제작하여 회류수조에서 유속에 대한 아래끌줄의 길이에 따른 어구의 전개성능 등을 규명하고 기준형과 비교 분석한 결과를 요약하면 다음과 같다. 1. 유체저항은 무부자망이 기준형보다 약 10∼20%정도 작았으며, 무부자망의 유체저항은 동일유속에서 아래끌줄이 길어짐에 따라 약 1ton씩 증가하였다. 또, 동일유속에서 dL이 10m씩 증가함에 따라 아래끌줄에 작용하는 저항은 약 5%씩 감소하고, 그 반면에 윗 끌줄에 작용하는 저항이 증가하였다. 2. 망고는 직선에 가까운 지수함수적으로 감소하는 경향을 보였으며, 동일유속에서 아래끌줄이 길어짐에 따라 증가하여 로그함수적인 경향을 보였다. 또한, 망고감소율은 무부자망의 경우가 기준형보다 작게 나타났으며, 그 차이는 유속이 증가함에 따라 더욱 커져 dL이 30m인 무부자망을 기준으로 3.0knot일 때 12%, 4.0knot일 때 25%로 나타났다. 3. 망폭은 유속이 증가함에 따라 약 2m 내외로 거의 일정하였으며 무부자망이 기준형보다 크게 나타났다. 4. 망구면적은 유속이 증가함에 따라 지수함수적으로 감소하는 경향을 보였으며, 망구면적의 감소율은 기준형보다 무부자망이 더 작게 나타났다. 여과량은 유속이 증가함에 따라 로그함수적인 경향을 보였으며 기준형이 3.0knot 이상에서 급격히 감소하였지만, 무부자망은 4.0knot까지 증가하였다가 완만하게 감소하였다. 5. dL의 최대적정길이는 망구면적 및 여과량이 최대인 30m일 때이며, 추의 최적위치는 4개의 그물목줄이 연결되는 지점이었다. 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.

중층트롤의 어구형상과 그 변화

본 연구에서는 중층트롤의 해상실험에서 Scanmar시스템으로 여러가지 요소를 측정한 자료에, 줄에관해 신장을 포함하여 간이 해석적(semi-analytic)으로 푼 3차원 해석을 중층트롤 어구시스템의 끌줄에 적용시키고, 전개판 뒤쪽의 줄들의 형상을 임의의 지수함수(Y<TEX>$_{r}$</TEX> = <TEX>$A\chi$</TEX><TEX>$_{r}$</TEX> <TEX>$^{B}$</TEX> ) 곡선으로 대응시켜, 중층트롤의 어구(날개 및 자루그물)의 형상을 타원추대의 일부분으로서 (equation omitted)형태로 가정하여 구하는 새로운 방법을 나타냈었다. 실제의 전개판은 예망중 진동한다고 알려져 있으며, 어느 각도 내에서는 안정성이 있기 때문에 양.항력계수는 기존의 종만곡 V형 전개판의 모형실험으로부터 영각이 15<TEX>$^{\circ}$</TEX> 부터 최대값인 22<TEX>$^{\circ}$</TEX> 까지의 값을 평균하여 사용하였다. 본 연구에서는 끌줄의 길이가 300m인 경우에 대한 결과를 나타내었는데, 망입구의 형상(b<TEX>$_{e}$</TEX> /a/seb e/)은 예망속도가 빨라점에 따라 수직으로 긴 타원형에서 수평으로 커져가는 타원형이 됨을 알 수 있다 이때, 망고(즉 옆망이 망고 형성에 기여한 높이와 삼각망 및 천장망이 기여한 높이)는 낮아졌는데, 옆망이 낮아지는 것보다 천장망의 높이가 더 작아짐을 알 수 있다. 뜸줄이 수평과 이룬 경사각(a)은 이 예의 경우에서 약 9<TEX>$^{\circ}$</TEX>~11<TEX>$^{\circ}$</TEX> 사이였으며, 예망속도가 빨라질수록 경사각이 작아졌다. How to estimate the shape of trawl net and ropes of a midwater trawl on full scale was described by implementing a three-dimensional semi-analytic treatment of a towing cable system with the field experiments obtained with the Scanmar system. The shape of trawl net from wingend to the beginning of codend was assumed to be of form <TEX>$\chi$</TEX><TEX>$^2$</TEX>/ae<TEX>$^2$</TEX>+ y<TEX>$^2$</TEX>/be<TEX>$^2$</TEX>=(z - c)<TEX>$^2$</TEX>/c<TEX>$^2$</TEX>, and that of the ropes attached behind otter boards be of form yr = <TEX>$A\chi$</TEX>rB. In case of warp length 300m long, the volume of trawl net, the ratio of net height to net width at the mouth of the trawl net, and the inclination angle of float rope were estimated according to the change of towing speed. The volume and the distance between wingtips were increased with increasing towing speed. And the inclination angle of float (or ground) rope was slightly decreased with increasing towing speed.

Development of a new midwater sampling trawl

To collect he pelagic larval and juvenile fish, several kinds of midwater trawling gear have been developed.1-4) A common disadvantage of these trawls is that depth of the net changes greatly by the towing speed. In order to overcome the disadvantages of these sampling trawls, Hu et al. 1) designed a new midwater trawl with a rigid square frame and a cambered V-type depressor (MOHT). It was confirmed that the net depth hardly changed at setting flow velocities (30-100cm/s) through the model experiment in a circulating water tank. In this study, we examined the hydrodynamic characteristics of the cambered V-type depressor in a circulating water tank and the towing performance of the MOHT with various towing speeds and warp lengths at Tateyama Bay.

Simplified trawl system modeling and design of a depth control system using fuzzy logic

This paper describes a simplified mathematical model of a mid-water trawl system developed to help and understand the dynamic behavior of trawl, and to design the depth control system of the mid-water trawl operation. The equations of the motion for the vertically moved trawl system were obtained using Lagrange’s equation with respect to the variables of the displacement of the trawler, the length of the trawl warp, the angle of the warp to the horizon, and the angle of the hand rope to the horizon. These equations were modified as simplified types. A fuzzy logic controller was designed to control the depth of a mid-water trawl net. The fuzzy controller calculates the tension of the trawl warp to be changed, based on the depth error between desired depth and actual depth of the trawl net and the ratio of changes in the depth error. The error and error change are calculated every second of sampling time. The control input, i.e., the desirable tension of the trawl warp is determined by inference from the linguistic control rules, which is usually carried out by crew experienced in controlling the depth of the trawl net during manual operation. Computer simulations indicated that the calculated motion of the trawl system using the simplified mathematical model agreed reasonably with those of the original model and actual trawl system obtained from field experiments, and the proposed fuzzy controller rapidly followed the desired depth without steady-state error.

Scale model of a new midwater trawl system for sampling pelagic larval and juvenile fish

SUMMARY: A new midwater sampling trawl was designed to collect pelagic larval and juvenile fish. It has a rigid square frame of 2.25 m2, with a 12.5 m high strength polyethylene net. The cambered V-type depressor with a camber ratio of 15%, aspect ratio of 6.0, and dihedral angle of 20° was hung to the bottom of the frame with four slings based on the principle of the parallelogram. A 1/5 scale model net of the prototype was made to examine the towing performances in a circulating water tank. The depth of the net and the attack angle of the depressor were measured at various flow velocities ranging from 30 to 100 cm/s with warp lengths of 260, 310, 360, 410 cm. The depressor held the setting angle closely, and the fluctuating range of the net depth was only 2% for the longest warp length over a wide range of flow velocities. This sampling trawl could maintain near constant depth under various flow velocities by the results of model experiment.

Net depth response of a depth-controllable (towed) gillnet for fish sampling

SUMMARY: Flume-tank experiments were performed to examine the depth response of a new type of depth-controlled gillnet. Variations of net depth were investigated as the warp was paid out and wound up for different changes of warp length, main sinker weights, and winch speeds. In most experiments, when the warp finished paying out, the net continued to descend and then ascended slightly to an equilibrium depth (overshoot phenomenon). The overshoot distance was nearly constant when the warp was wound up and increased linearly with increasing winch speed when the warp was paid out. An increase in winch speed reduced net settling time, which converged on a constant value for both paying out and winding up.

A comparison between vessel and trawl tracks as observed by the ITI trawl instrumentation

Instrumentation measuring the tracks of a bottom trawl and a towed underwater vehicle relative to the track of the towing vessel was tested under varying towing conditions during a research survey in the Barents Sea in 1998. The measured mean distance between vessel and trawl track (centre of headline) varied from 27 to 213 m during the 15 hauls for which measurements were obtained. The recorded maximum distance between the tracks was 336 m. The deviance appeared to depend on vessel heading relative to wind and current and on warp length. The magnitude of the measured distance between vessel and trawl tracks may strongly affect abundance estimates based on data from trawl catches. Depending on the avoidance reactions of different species and length groups to the approaching vessel, the track of the trawl relative to that of the vessel might influence both species and size composition of the catch. Experiments quantifying the relationship between bottom trawl catches and acoustic recordings under the vessel will be particularly exposed to errors when trawl and vessel paths diverge. The magnitude of escape responses behind a vessel during trawling has been reported to vary within limited periods and over-restricted geographical areas. These escape responses have been documented using a towed underwater vehicle without knowing the exact position of the vehicle with regards to vessel and trawl. Measurements of the positions of the vehicle with regard to the position of the vessel and trawl during this experiment showed substantial variation both between and within hauls, indicating that at least part of this variability in fish behaviour could be due to the variation in position of the vehicle.

Dynamic Analysi of Midwater Trawl System by a Two-Dimensional Lumped Mass Method

This paper analyzes mathematically the dynamic properties of a midwater trawl system which is composed of a trawler, trawl net, otter boards and warp. Taking the midwater trawl system of “SINYO Maru” of the Tokyo University of Fisheries as an example, the effects of changing towing speed and warp length on the system dynamics are demonstrated. The “overshoot” phenomenon caused by sinking of the otter board while lengthening the warp is clearly explained.

中層トロールシステムの動的制御特性に関する海上実験

In order to investigate the characteristics of dynamic control of a midwater trawl, a field experiment was conducted by FRV “SINYO-Maru” of Tokyo University of Fisheries. The parameters of the midwater trawl being towed were measured with a SCANMAR system and a self-recording underwater load-depth meter. It was shown that the net and otterboards moved deeper or shallower when the towing speed was changed abruptly. However, when the warp length was changed, the handrope tension increased or decreased greatly immediately before returning to its original condition, called an “over-shoot” phenomenon and this was simultaneously observed for the otterboard.