• Economic and Environmental Geology
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• v.49 no.6
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• pp.479-490
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• 2016

Seabed drilling system has recently been used to drill seafloor mineral resources. This case report highlights the procedure and result of sea-trial of seabed drilling system at off-shore of Japan on March, 2016 as well as briefs an international-technical trend of seabed drilling system. In case of having less than 100 m drill depth, seabed drilling system is favorable for seafloor mineral deposits which are mostly distributed within a narrow district and situated between 1000~3000 m water depth, compared with vessel-mounted drilling system. The system is featured by the remotely-operated drill gear, which has top drives, drill strings and mud system on it. The core samples are generally recovered to ship with seabed driller after a dive. In this sea-trail, recovery rate of core samples averagely shows about 55% and the recovered rocks mostly correspond to fresh and/or weak-altered basalt. In case of drilling hydrothermal ore deposit, the recovery rate would be lower than 55% because of the fragile nature of ores. Alternatively it is used to collect cutting chips through riser or bins in order to increase the recovery rates. Recently a reverse circulation method is taken considered to acquire the better cutting-chips. Three-leg type outrigger system and four-leg type leveling system are the competing landing-instruments of seabed drill system. However the landing efficiency using these gears has to be further monitored due to lack of case reports.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.31 no.4
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• pp.340-349
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• 1995

There are several problems in a fishing by the midwater pair trawl net which is used in Denmark; steeply decreasing of the net height with the towing speed increasing, the larger volume of the fishing gear in comparison with the size of the trawler, and catching of a float in a mesh, etc. To prevent steeply decreasing of the net height with the towing speed increasing and catching of a float in a mesh, it is sometimes more useful to use the kite instead of floats. This paper describes the hydrodynamic drag and the opening efficiency of the midwater pair trawl net and the midwater kite pair trawl net obtained by the model test in the circulation water channel. The results can be summarized as follows; 1. The hydrodynamic drag of the midwater kite pair trawl net is about 0.7 times smaller than that of the midwater pair trawl net. 2. The net height, mouth area and filtering volume of the midwater kite pair trawl net are smaller then those of the midwater pair trawl net when the towing speed is below 2.5knots, almost the same at 2.7knots, and are larger over 3.0knots. The net width of the midwater kite pair trawl net is same as that of the midwater pair trawl net. 3. The shapes of net mouth of both net are an oval steeply flatted with the towing speed increasing. The filtering volume of the midwater kite pair trawl net is larger then that of the midwater pair trawl net by 3% at 3.0knots, 11% at 4.0knots, and 16% at 5.0knots respectively.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.41 no.1
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• pp.9-16
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• 2005

This study was conducted in order to improvement of fishing gear and fishing operating system for anchovy boat seine by labor saving improved nets. Field experiments were carried out observe geometry of nets and fishing operating system by catcher boats. The obtained results are summarized as follows : The Vertical net opening of fore wing net, wing net, inside wing net, square, fore bag net, flapper, after bag net of the labor saving improved net according to the distance between catcher boats were varied in the range of 5.0${\sim}$7.8, 14.4${\sim}$21.1, 16.2${\sim}$21.2, 14.0${\sim}$17.3, 11.7${\sim}$13.9, 5.4${\sim}$6.9, 8.2${\sim}$9.8m respectively, varied in the range of 50${\sim}$78, 25${\sim}$36, 24${\sim}$31, 31${\sim}$38, 61${\sim}$73, 71${\sim}$91, 87${\sim}$104% of the actual ratio of net opening in each part. Labor saving improved net was performed instant net opening in fore wing net and maintained stable net opening and towing depth by means of attached net pendant. Also, it was minimized as net pocket phenomenon leading to guide anchovy for more catch by means of attached body net. The opening in accordance with distance between catcher boats and towing speed. The catch of labor saving improved net was increased than traditional net due to decrement of net resistance by improvement of bag net leading to increasement of towing speed and reduction of escape anchovy as well as improve nets of whole operation system.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.42 no.3
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• pp.134-147
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• 2006

A model experiment using circulation water channel was carried out to investigate the dynamic characteristics of bottom trawl net which can be used in sea mount of North Pacific. Hydrodynamic resistance and shape variation according to the flow velocity and angle of hand rope transformation for net were measured, and experimental value was analyzed as the value of full-scale bottom trawl net. The results summarized are as follows; At the $30^{\circ}$ of angle of hand rope to net, hydrodynamic resistance varied from 0.5kgf to 2.68kgf as the flow velocity increased between 0.31m/s and 0.92m/s, and formula of hydrodynamic resistance for the model net was $F_m=3.04\;{\cdot}\;{\upsilon}^{1.53}$. At the fixed angle of hand rope, Net height was low and Net width was high according to the increase of flow velocity, and in addition, vertical opening was low and Net width was high by the increase of angle of hand rope at the fixed flow velocity. At the $30^{\circ}$ of angle of hand rope to net, net opening area was $0.214m^2$ as flow velocity was 0.61m/s, and formula of net opening area for the model net was $S_m=-0.22{\upsilon}+0.35$. At the $30^{\circ}$ of angle of hand rope to net, catch efficiency seemed to be highest as $0.319m^3/s$ of filtering volume at the 0.76m/s(51kt's) of flow velocity. Shape variation of net showed the gradual laminar transform for the variation of flow velocity but there needed some improvements due to the occurrence of shortening at the ahead of wing net.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.20 no.2
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• pp.106-113
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• 1987

The Alaska pollack longline operations, which consist of baiting, shooting, hauling and arrangement of hooks, are dependant on manual labour up to the present. The automation against this traditional way is necessary to eliminate the manual operations and to reduce crew. We have developed a prototype longline system suitable for Alaska pollack longline gear, which is composed of an automatic baiting machine, an automatic line hauler, a hook cleaner and storage rails. The automatic bailing machine driven by hydraulic power is precise baiting method controlled sequentially, and the automatic line hauler is to haul up the mainline by means of hydraulic power and at the same time to split every hook and to carry it onto storage rail automatically. A series functioning tests on shooting and hauling apparatus were carried out in the laboratory and at sea. The results obtained are as follows ; 1. As for the baiting machine, the exciting time of solenoid which operates a directional valve, bait feeding and cutting time, is shortened according to the increase of pressure, and also, after cutting the bait, the over-rotated angle of the blade increased in accordance with the increase of pressure. 2. The baiting efficiency is about $90\%$ when using sand lance (Hypoptychus dybowskii), and the most proper pressure of the hydraulic circuit in feeding and cutting the bait is between $13\;kgf/cm^2\;and\;20\;kgf/cm^2$. 3. The hook splitting rate of the automatic line hauler is about $95.5\%$ regardless of hauling speed and materials of snood. 4. The case of unseparating hook is appeared when the snood gets entangled or the hook is sticked in the mainline.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.40 no.4
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• pp.255-267
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• 2004

This study was conducted in order to improvement of fishing gear and fishing operating system for anchovy boat seine by bag net A-type and B-type was attached with half size modified nets. Field experiments were carried out observe geometry of nets by catcher boats. The obtained results are summarized as follows : The actual ratio of net opening in each part of the half size modified nets was increased from fore part to back part of the nets as shown the smallest value about 20% in wing net and the biggest value about 110% in bag net. In addition, vertical net opening of B-type net as measured as 10.9~11.8m in fore bag net and 5.8~8.0m in after bag net were 1~2m greater than 9.0~13.6m of A-type one, and 2~3m less than 9.3~10.4m of A-type one, respectively. Vertical net opening of half size modified net was shown as less variation of towing depth from wing net to inside wing net than those of traditional nets due to stable vertical performance. The mesh distortion or drift and variation of vertical net opening were decreased by improvement of bag nets in order to minimized shape of net pocket phenomenon whenever towing speed is slow. Bag net B-Type attached with dual flapper was shown as less variation in width of bag net and less escapement of anchovy.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.12 no.4
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• pp.201-207
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• 1979

The stow net now used in the Yellow Sea, are traditional bag net with the opening held by a lighter upper and a weighted lower beams standing against the current. Such bag net anchored at the bottom are known in many countries, particularly in the estuaries of large rivers, but more rarely in sea fisheries, because they are too much affected by the weather, moreover a permanent strong current is necessary. Some scientists intended to improve this fishing gear, using the shearing devices instead of a lighter upper and a weighted lower beams in order to widen mouth of the stow net however they are unsuccessful. One-fortieth scale model net of the stow net was tested in a circular water tank with an effective volume of $5.67m\times1.76m\times1.00m$ of observing the configuration and tension of the net. Experiments were carried out under the various combination including water velocity, spherical floats and elevating floats with the shearing hoods instead of the upper beam. We found those devices offered a very low resistance per net area to current compared with the spherical floats or upper beam, and had a fairly good shearing power at any velocity and direction of the current. The total resistance (R) of the model net to which shearing hoods and floats are attached can be induced by the following formula under the condition of 0.25m/sec to 0.5m/sec, $$R(kg)=3.11V^{1.54}$$ The height (h) of the improved model net (m-B) is higher than traditional model net(m-A) with upper and lower beams, m-A: h(cm)=89.22-2.42(V-15). $V\geqq15,\;cm/sec$ m-B: h(cm)=89.20-0.78V (V:cm/sec) The catch efficiency of improved model net is 1.5 times traditional model net.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.39 no.4
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• pp.326-336
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• 2003

In order to modify the construction of gizzard shad coastal purse seine net with possible to the laborsaving of fishing operation in the coastal small fishing vessels, the model experiments were carried out on the model nets for several conventional nets using in the field and the experimental nets was manufactured as 1/100 and 1/60 of the full scale net. The results obtained are summarized as follows；1. In the case of the conventional net and reduction rate 75% in conventional net with purse line the fishing efficiency decreased, the lead line was upward for the surface and the pursing depth of pursing line was very shallow to 2∼3m. 2. In the case of the net having maximum depth in center part designed in this study, the length of float and lead line was 60% of conventional net, the depth of net was fixed 20m to selvage line of the both of the end and extend gradually with 50m, 40m, 30m to the center. Among the these net, depth of pursing line was 20∼23m for 50m and 7∼15m for 40m, 30m the depth of net. These results were suitable for interception of fish school in fishing ground, but several problems will be caused by the depth and current of fishing ground.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.47 no.2
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• pp.79-87
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• 2011

A fishing lamp is fishing gear to gather fish in the night. But the cost of oil which is used to a light fishing lamp, goes significantly up to almost one hundred million won for 50 tonnage vessels and forty million won in case of vessels less than 10 tonnages. This cost has almost taken 30.40% of total fishing costs. As oil price increases, the business condition of the fishery gets worse and worse. Therefore, it is very urgent to develop an economical fishing lamp, to solve the problem of fishery's business difficulty. This research aims at developing a fishing lamp for squid jigging fishery and hairtail angling fishery using the LED, which has excellent efficiency and durability. One fishing lamp has about 160Watt capacity and five fishing lamps are installed one aluminium panel in which sea water flows to emit generated heat from LED to outside. Developed fishing lamp lights to an effective direction of jigging and angling operation. This fishing lamp can be controlled to light the direction of fish shoal because the aluminium panel can be controlled to up and down direction. The wave length of fishing lamp has white and blue color. White color light is to gather fish shoal of horizontal direction and blue color light is to gather fish shoal of vertical direction. After development of this fishing lamp, 60.110 units are established on the boat, and operated fishing. Consequently, in the case of squid jigging, spent energy was reduced to 39%, in the case of hairtail angling, 68% of spent energy was reduced. And the catch was more than another boat.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.27 no.4
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• pp.247-254
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• 1991

Mackerel purse seine fishery is one of the most important fisheries in Korea and its annual mean catch from 1982 to 1988 is 350 thousand tons. Between 1982 and 1988, the characteristics of catch at 5 sectors of the sea area was analyzed according to operating sea block and the catch by fishes based on the data obtained from daily report of fishing condition that had been made out by 48 Korean fishing boats engaged in the fishery of purse seine. In these 5 sectors of the sea area, catch per net hauling in the coastal area of Cheju Island is less than that in the other sectors. Accordingly, the shape of fishing gear during operation has been measured to analyzed the deformation of net shape caused by the bottom current. (The lunar calender is used in the paper) The results obtained are as follows; The average CPUE of purse seines is 31.6 tons and it is higher from October to April than that from May to September. In the 5 purse seine fishing grounds, the ratio of net haul in the coastal sea area of cheju Island is 42.4% and it is the highest level, but the CPUE is 25.7 tons which is relatively low level. Each CPUE in the sea areas is significant differences with 1% level. Index of seasonal variation of mackerel CPUE from May to October is lower than the standard value, whereas index from November to January is higher. The diameter of circle by net shooting becomes shorter to the minimum caused by the bottom current during loose set, becomes narrower and the efficiency of fish encirclement becomes lower. The shape of leadline by bottom current becomes long oval type along with current direction in the tight set, while it becomes long oval type in the direction of a right angle to the current direction and the enclosed area is reduced hurriedly, and the deformation of net is most serious in the loose set.