• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.7
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• pp.1051-1058
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• 2021

Barges that are towed by tugs do not have navigation capabilities and are usually connected to tugs. These kinds of combined navigation schemes have generated almost ten percent of all maritime accidents in the last five years. The study aims to reduce maritime accidents with barges towed by tugs by analyzing navigation characteristics and the current status of such combined navigation schemes. The analysis consists of the lesson learned from each verdict. The result of the study emphasizes that human factors continue to be the primary cause of maritime accidents with barges and tugs. Additionally, the research proposes that effective advertising for improving maritime safety by reducing towing barge maritime accidents should be created through associations of tugs and barges. Furthermore, relevant re-training must be conducted by maritime training institutions. The results of the study are expected to apply to the improvement of maritime safety through the advertisements to seafarers.

• Fisheries and Aquatic Sciences
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• v.14 no.2
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• pp.138-147
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• 2011

Modeling fishing-gear systems is essential to better understand the factors affecting their movement and for devising strategies to control movement. In this study, we present a generalized mathematical modeling methodology to analyze fishing gear and its various components. Fishing gear can be divided into a finite number of elements that are connected with flexible lines. We use an algorithm to develop a numerical method that calculates precisely the shape and movement of the gear. Fishinggear mathematical models have been used to develop software tools that can design and simulate dynamic movement of novel fishing-gear systems. The tool allowed us to predict the shape and motion of the gear based on changes in operation and gear design parameters. Furthermore, the tool accurately calculated the swept volume of towed gear and the surrounding volume of purse-seine gear. We analyzed the fished volume for trawl and purse-seine gear and proposed a new definition of fishing effort, incorporating the concept of fished space. This method may be useful for quantitative fishery research, which requires a good understanding of the selectivity and efficiency of fishing gear used in surveys.

• Journal of Fisheries and Marine Sciences Education
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• v.26 no.5
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• pp.966-978
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• 2014

Currently, majority small ship's clutch for power transmission to propeller relies on multi plate hydraulic clutch regardless its size. Most of the small ships do not have a spare equipments of clutch. Furthermore, many ship engineers do not have an ability as well as enough experience to solve this problem related to the hydraulic clutch during the voyage. Therefore, any small problems cause many serious marine accidents. Once the clutch has problem, almost of all ships can not sail by itself anymore and it must be towed by salvage boat, maritime police ships, or fish guidance boat etc. In this case, all the accidents will be categorized as a marine accident and they all need to go through marine accident court inquiries. In this study, an understanding of each crew on hydraulic clutch system has been profoundly measured. Furthermore, the knowledge on an emergency navigation protocol of each crew has been also profoundly checked. Additionally, various surveys on hydraulic clutch classes has been performed and its satisfaction of crews on this topic have been carefully checked based on various feedback from students who took these courses. All of the above data from this study will be used to reduce marine accidents in current marine industry.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.52 no.2
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• pp.88-95
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• 2016

Most grid sorting has been used to sort out flatfish in shrimp fisheries, while double grid systems have been tested to separate smaller shrimp. The escape of juvenile red seabream through separating panels made with steel grids or large mesh tested for masking effects in a two-species system. Fish behavior was observed in a circulating water tank. The escape rate was 20% greater with the separating codends than with the normal codend in the single-species experiments. The rates in the two-species experiments were 30% or 20% greater than the single-species rates for the normal or separating codends, respectively. The seabream retention rates in the grid separator codend decreased as rockfish retention increased, possibly due to a threat effect. Conversely, the retention rate of both species increased concurrently in the net separator, possibly due to a masking effect. The escape rates of juvenile red seabream varied by compartment in the mesh separating codend. These results suggest that grid separating codends can be used in the field as towed fishing gear to reduce juvenile catch.

• The Journal of the Acoustical Society of Korea
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• v.40 no.6
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• pp.546-554
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• 2021

In the signal processing of synthetic aperture sonar, it is subject that the platform in which the sensor array is installed moves along the straight line path. In practical operation in underwater, however, the sensor platform will have trajectory disturbances, diverting from the line path. It causes phase errors in measured signals and then produces deteriorated SAS images. In this study, in order to develop towed SAS, as tools to remove the phase errors associated with the trajectory disturbances of the towfish, motion compensation technique using Redundant Phase Center (RPC) and also Phase Gradient Autofocus (PGA) method is investigated. The performances of these two approaches are examined by means of a simulation for SAS system having a sway disturbance.

• The Journal of the Acoustical Society of Korea
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• v.25 no.4
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• pp.172-177
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• 2006

Various research and development on Synthetic Aperture Sonar technique is under way to enhance bearing resolution of a SONAR system. In this paper, we estimated perturbed array shapes, and compensated distortion by using estimated away shapes and synthesized arrays in aperture domain such as an ETAM technique. As experimental data, we used the one obtained from towed array in neighboring waters of the Korean peninsula. Through simulation on data where tow-ship speed is maintained at a constant level, we confirmed that synthesis effect of increasing SNR and narrowed beam width of main lobe was consistently demonstrated for about 1 minute when coherence of target signal was maintained. Also, we showed that the synthesis effect with respect to time was constantly maintained.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2009.10a
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• pp.40-41
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• 2009

In general, ships are towed to keep the safe operations in harbor or channel by tug boats. Due to increase in ocean traffic, many accidents are happened in harbor or channel in these days. Therefore it is necessary to predict manoeuvrability of tug-barge system, and to assure the safety of that system. Turg-barge system is composed of tug boat, barge, and towing cable, connecting both ships. Manoeuvring equations of tug-barge system are suggested, and the scopes of model tests are discussed to establish the mathematical models for tug boats in this paper.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.52 no.2
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• pp.162-168
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• 2016

This study attempted to help determine Korean fishery policies by proposing improvement plans after examining the current regulations, fishing vessels, fishing gear and fishing methods of the middle sized trawl fishery in the East Sea for targeting only squid. In general, the size, engine horse power, and net length of the middle sized trawlers are between 50 and 60 GT, 1,200 and 1,600 PS, and approximately 165 m with four seamed trawl nets, respectively. While a jigging vessel attracted squids using lights, the trawler approached a jigging vessel. The trawler let the jigging vessel know its decision for fishing, and then jigging vessel rolled up jigs. The net of the trawler was casted at 45 degrees between the bow and the stern of the jigging vessel. Once the trawler towed close to the stern of the jigging vessel upon its passing of the jigging vessel, the bow of the trawler turned 45 degrees left again. Then, squid aggregations were entered into the net. When the cod end was passed a light vessel, the trawler hoisted the net up to the otter board. Then the trawler turned 180 degrees. It repeated three to five times of fishing operations as the previous method. We recommend that the regulations allow nineteen side trawlers to catch like stern trawler, as well as the cooperative trawler and jigging vessel operations.

• Ocean and Polar Research
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• v.28 no.3
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• pp.225-236
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• 2006

Seagrass meadows are considered as critical habitats for a wide variety of marine organisms in coastal and estuarine ecosystems. In many cases, studies on the spatial/temporal distribution of seagrass have depended on direct observations using SCUBA diving. As an alternative method fur studying seagrass distribution, an application of hydroacoustic technique has been assessed for mapping seagrass distribution in Dongdae Bay, on the south coast of Korea, in September 2005. Data were collected using high frequency transducer (420 kHz split-beam), which was installed with towed body system. The system was linked to DGPS to make goo-referenced data. Additionally, in situ seagrass distribution has been observed using underwater cameras and SCUBA diving at four stations in order to compare with acoustic data. Acoustic survey was conducted along 23 transects with 3-4 blot ship speed. Seagrass beds were vertically limited to depths less than 3.5m and seagrass height ranged between 55 and 90cm at the study sites. Dense seagmss beds were mainly found at the entrance of the bay and at a flat area around the center of the bay. Although the study area was a relatively small, the vertical and spatial distributions of the seagrass were highly variable with bathymetry and region. Considering dominant species, Zostera marina L., preliminary estimation of seagrass biomass with acoustic and direct sampling data was approximately $56.55g/m^2$, and total biomass of 104 tones (coefficient variation: 25.77%) was estimated at the study area. Hydroacoustic method provided valuable information to understand distribution pattern and to estimate seagrass biomass.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.6
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• pp.228-236
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• 2014

Towed array SONAR is deformed because it operates in fluid such as an ocean. It especially undergoes significant change in shape as a towing vessel takes a turn. In this case, beam pattern synthesis of the line array is limited, resulting in degradation in quality such as signal-to-noise ratio. This paper presents a modified two-step least squares algorithm based on the two-step least squares method. The shape of the sea-operated line array formation with the towing vessel changing course(angle) was modeled and the algorithm was subsequently applied. While changing course and location of the main lobe in beam pattern was altered, signal-to-noise ratio of steering beam pattern synthesis was analyzed by algorithm (proposed and others). As a result, the proposed algorithm presented improvement in performance by 2dB compared to other algorithms while forming relatively constant beam pattern.