In general, a high tension on the anchor and chain is placed when a ship at anchor is subjected to heavy weather. Mariners have to pay attention to whether dragging anchor occurs to keep the safety of the ship at anchorage since it is difficult to maintain the stable motion of ship and it causes collisions with other ships nearby. In this paper, the ship motion against the external forces was shown to obtain the fundamental data about characteristic of holding power due to nature of seabed at anchor, so practical trials were carried out in rocky area and muddy area using a trial ship around coastal area of South Korea. In muddy seabed, holding power showed reasonable tension values depending on the distance from anchor position of continuing swing motions of a ship corresponding to wind force. Meanwhile in rocky seabed, tension values on the chain appeared very high occasionally regardless of the distance from the anchor position and seemed to exceed its holding power to be the breaking strain of the chain although weather was not in a severe condition. Therefore, some of the cables laid on the seabed were presumed to be caught in a crack on the rock. It is assumed that even a small amount of external force may cause the chain to break in a moment in rocky seabed. Additionally, wind and current forces had a somewhat contradictory effect on holding power of the ship between them.

To decrease area of the repository for high-level radioactive waste, enhancing the disposal efficiency is needed for public acceptance. Previous studies regarding the performance assessment of KRS and KRS+ repository did not consider area-based variations of the geothermal gradient and rock thermal properties in Korea. This research estimated deposition hole spacing based on performance assessment of a repository using the distribution of geothermal gradient and rock thermal properties in Korea to increase disposal efficiency. Distributions of geothermal gradient, rock thermal properties were investigated based on 2019 Korea geothermal atlas published by Korea Institute of Geoscience and Mineral Resources (KIGAM). Effect of thermal performance parameters was analyzed using coupled thermal-hydraulic numerical simulations, and effect of rock thermal conductivity and deposition hole spacing on the maximum temperature of buffer was relatively large. In addition, distribution maps of thermal performance of a repository and deposition hole spacing were plotted using thermal performance parameters-maximum temperature of buffer regression equations and GIS data given by KIGAM. In the regions showing the highest maximum temperature of buffer in Korea, required deposition hole spacings were 10.5 m, 10.0 m, 10.1 m, respectively for KJ-II, MX-80, and FEBEX bentonite cases, and thereby additional disposal area of 40%, 33.3%, and 34.7% were required compared to that of the KRS+ repository. On the other hand, high disposal efficiency can be obtained in the regions showing the low maximum temperature of bentonite buffer. The methodology provided in this research can be used as one of the references for the selection of domestic candidate repository sites. Additional mechanical performance analysis should be conducted using distributions of mechanical properties of rock mass in Korea.

In this study, a drifting test using a experimental vessel (2,966 tons) in the northern waters of Jeju was carried out for the first time in order to obtain the fundamental data for drift. During the test, it was shown that the average leeway speed and direction by GPS position were 0.362 m/s and 155.54° respectively and the leeway rate for wind speed was 8.80%. The analysis of linear regression modes about leeway speed and direction of the experimental vessel indicated that wind or current (i.e. explanatory variable) had a greater influence upon response variable (e.g. leeway speed or direction) with the speed of the wind and current rather than their directions. On the other hand, the result of multiple regression model analysis was able to predict that the direction was negative, and it was demonstrated that predicted values of leeway speed and direction using an experimental vessel is to be more influential by current than wind while the leeway speed through variance and covariance was positive. In terms of the leeway direction of the experimental vessel, the same result of the leeway speed appeared except for a possibility of the existence of multi-collinearity. Then, it can be interpreted that the explanatory variables were less descriptive in the predicted values of the leeway direction. As a result, the prediction of leeway speed and direction can be demonstrated as following equations. However, many drift tests using actual vessels and various drifting objects will provide reasonable estimations, so that they can help search and rescue fishing gears as well.

Due to the high risk of personal injury and property damage, the safety of maritime transport is an important concern for everyone involved. Ship navigation officers usually look up a ship's collision profile for safety-at-sea information before entering an unknown coastal area. Near-ship collisions are very important when assessing the potential risk of shipping. This paper undertakes a ship encounter risk assessment, involving analyses of the trajectory data of merchant ships and then extracts ship encounter data, creates a probabilistic model to determine whether an encounter event is a near miss, and suggests risk indicators. The proposed method will be useful for navigators to plan safe passages.

In order to offer specific information needed to assist in operation of a ship with same type rudder through evaluating the maneuverability of training ship A-Ra with flapped rudder, sea trials based full scale for turning test, zig-zag test with rudder angle 10° and 20°, and spiral test at service condition were carried out on starboard and port sides around Jeju Island according to the standards of maneuverability of IMO. As a result, the angular velocity of port turn was higher than that of starboard turn. Therefore, the size of turning circle was longer on the starboard side. In addition, variation of the transfer due to various factors was more stable than those of the others. In the Z-test results, the mean of 1st and 2nd overshoot angles were 9.8°, 6.3° and 15.3°, 9.2° respectively when the port and starboard was 10°; the 1st overshoot angle were 18°, 13.7° when using 20°. Her maneuverability index Tˊ and Kˊ can be easily determined by using a computer with the data obtained from Z-test where Kˊ and Tˊ are dimensionless constants representing turning ability and responsiveness to the helm, respectively. In the Z-test under flap rudder angle 10°, the obtained Kˊ value covered the range of 2.37-2.87 and Tˊ was 1.74-3.45. Under the flap rudder angle 20°, Kˊ and Tˊ value showed 1.43-1.63, 1.0-1.73, respectively. In the spiral test, the loop width was unstable at +0.3° and –0.5°-0.9° around the midship of flap rudder. As a result, course stability was comparatively good. From the sea trial results, training ship ARA met the present criterion in the standards of maneuverability of IMO.

We collected AIS information on fishing vessels operating near Jeju Island, and analyzed appearance density of the Chinese fishing vessels and inferred the movements of the fishing grounds. AIS information was received from October 16, 2016 to October 16, 2017 and stored on a hard disk through a program called AisDecoder. Unauthorized fishing vessels within the Exclusive Fisheries Agreement Zone (EFAZ) operated near the EFAZ boundary, and the frequency of appearance of fishing vessels were high in the middle waters of Korea and Japan, 252 and 250 fishing zones. Chinese fishing vessels authorized to enter appeared scattered outside the Prohibiting Fishing Zone of the Large Trawlers (PFZLT), and the closer they were to the PFZLT boundary, the higher the appearance density. And the appearance of Chinese fishing vessels with a speed from 0 to 3 knots was mostly outside the EFAZ, showing high density in the waters close to the boundary between Korea and Japan. On the other hand, within the EFAZ, the frequency of appearance of Chinese fishing vessels was also low and scattered. The appearance of Chinese fishing vessels with a speed from 3 to 5 knots mostly shows some variability within the EFAZ, but the frequency of appearance was high and the density was high. The seasonal appearance of Chinese fishing vessels in the waters south of Jeju Island appeared in the southwest in the autumn and then moved south and southeast of Jeju Island in the winter, and in the spring and summer. They were considered going to other fishing grounds without fishing in the waters south of Jeju Island.

According to the statistics of the last five years, fishing vessel accidents accounted for about 80% of collisions of all ships and has led to many casualties. To prevent collision accidents, it is important to assess the collision risk potential related to the sailing characteristics of fishing vessels. The authors represented the traffic patterns of vessels that sail around Wando waters based on Automatic Identification System (AIS) and Radio Detecting and Ranging (RADAR) data. The authors analyzed the statistical near miss data between fishing vessels and non-fishing vessels in the Wando Vessel Traffic Services (VTS) area and assessed the risk of ship collisions. From this research, the authors identified waters with a high risk of ship collisions. The analyzed results can be used as basic data to develop collision prevention strategies which aides the decision making and efficient operation of VTS officers (VTSO.)