• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.5
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• pp.566-573
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• 2017

The chine of high speed vessels does not only play a role in changing position when planing but also helps balancing the hull. It also has a great influence on resistance performance. However, designing a chine requires a lot of experience because it is influenced by various factors such as displacement, transom shape, draft and width. Such a design is not based on an empirical formula, but the purpose of this study is to provide basic guidelines regarding the shape of chine through calculation. This design was developed using Yacht-one, a commercial design program, and analysis was performed using Star-CCM+, also a commercial analysis program. Analysis of the hull selected in this study was carried out by Dynamic Fluid Body Interaction (DFBI) method. Analysis of the chine was carried out at chine angles of 15, 16, 17, and 19degrees, at a speed of 30knots. The result indicated that the highest trim occurred at 16 degrees among the four chine angles considered, and the highest heave occurred at 15degree. In terms of resistance performance, minimum resistance was observed at 16 degrees. Consequently, for minimum ship resistance, it is necessary to complete calculations in accordance with the chine angles, ${\pm}2$ degrees from the initial chine angle, which should be carried out a the design stage.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.5
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• pp.595-602
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• 2017

In Korea, much research and development have occurred to enhance the technological competitiveness of tuna purse seining fisheries. Due to these efforts, fishing efficiency has been improved with the development of radar, sonar and global positioning systems for fish detection and revisions to the hull forms of tuna purse seiners. However, for skiff boats, net boats and speed boats, which are auxiliary working boats mounted on tuna purse seiners, technology has lagged behind relative to the modernization of the main vessel. In this study, the hull of an existing propeller-based net boat with steel wire net to protect tuna was changed to the hull of a water jet propulsion vehicle to reduce resistance and improve maneuverability. As a result, a prototype of a water jet propulsion option was produced according to the aluminum structure strength standards specified by the Ministry of Oceans and Fisheries, and safety was confirmed by performing a drop test. Moreover, through a sea trial test, an existing net boat was shown to have a speed of 12.0knots and a towing force of 2,545 kgf at 2,500 RPM. The prototype had a speed of 26.7 knots and a towing force of 2,011 kgf at 3,200 RPM, which satisfied the towing capacity standards of auxiliary working boats mounted on tuna purse seiners.

• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.2
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• pp.139-148
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• 2020

The most important factor affecting the berthing energy generated when a ship berths is the berthing velocity. Thus, an accident may occur if the berthing velocity is extremely high. Several ship features influence the determination of the berthing velocity. However, previous studies have mostly focused on the size of the vessel. Therefore, the aim of this study is to analyze various features that influence berthing velocity and determine their respective importance. The data used in the analysis was based on the berthing velocity of a ship on a jetty in Korea. Using the collected data, machine learning classification algorithms were compared and analyzed, such as decision tree, random forest, logistic regression, and perceptron. As an algorithm evaluation method, indexes according to the confusion matrix were used. Consequently, perceptron demonstrated the best performance, and the feature importance was in the following order: DWT, jetty number, and state. Hence, when berthing a ship, the berthing velocity should be determined in consideration of various features, such as the size of the ship, position of the jetty, and loading condition of the cargo.

• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.1
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• pp.1-7
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• 2020

In recent years, cargo lashing has received much importance, to help prevent the sinking of passenger ships due to the failure of vehicle and cargo lashing during the transshipment of cargo. Consequently, the standards for lashing equipment and the structure of car ferries have been revised. According to the current standards, all vehicles loaded on a car ferry sailing in smooth sea areas must be secured if the wind speed and wave height exceed 7 m/s and 1.5 m, respectively. In this study, we measured the roll and pitch of a passenger ship sailing in smooth sea areas, and compared the measurements with the results of the New Strip Method (NSM). The vessel had a maximum pitch of 1.41° and a maximum roll of 1.37° at a wind speed of 6-8 m/s and a wave height of 0.5-1.0 m, and a maximum pitch of 1.49° and a maximum roll of 2.43° at a wind speed of 10-12 m/s and a wave height of 1.0-1.5 m. A comparison of the external forces due to the motion of the hull and the bearing capacity without lashing indicated that the bearing capacity was stronger. This suggests that vehicles without lashing will not slip or fall due to weather conditions. In future, the existing vehicle lashing standards can be revised after measuring the hull motions of various ships, and comparing the external force and bearing capacity, to establish more reasonable requirements.

• Journal of the Korean Society of Marine Environment & Safety
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• v.22 no.1
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• pp.74-81
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• 2016

Because most of the passengers are not accustomed with onboard environments, it is very important to analyze and predict the behaviors' characteristics of passengers under disasters' conditions, and apply those results for making countermeasures. On this view point, this study focused on the walking characteristics of onboard-novices are tested and analyzed under blackout condition that has high possibility to happen. As a result, comparing to under normal lighting conditions, the waking times under blackout conditions are 155.8~247.1 % longer on full path, 56.9~331.7 % on corridors, 75.3~152.9 % on stairs, respectively. And under the same blackout conditions, walking times in cases of the exit guidance marks being attached on top side of walls saved times, like 21.6~24.0 % on full path, 37.7~58.9 % on corridors, 18.7~19.2 % on stairs, comparing to the cases of exit guidance marks being not attached. On the other hand, after tests under without exit guidance marks, 60.7% among respondents answered that internal structures like wall/stair (35.7 %) and handrail (25 %) are very helpful to decide way findings, and 28.6 % selected personal instincts is important. But 50 % responded that exit guide marks are effective to find ways, after the tests under with exit guidance marks.

• Journal of the Korean Society of Marine Environment & Safety
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• v.22 no.1
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• pp.98-107
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• 2016

The purpose of this study is for Human error prevention to acquire Collision Risk Perception Index (CRPI) sensed by the Officer Of the Watch (OOW) when the approaching distances are reduced in six types of ship encountering situations (Head on, $045^{\circ}$, $090^{\circ}$, $135^{\circ}$, Overtaking, Overtaken) between own ship and a target ship and then to predict CRPI fitting coefficients with polynomials in the curve-fitting process. CRPI acquisition experiments are carried out on two coast-guard ships and with the total of 30 crew members. Analysing results shows that CRPI data have goodness of fit to the six types of encountering situation. Futhermore, the One-Way ANOVA results show that CRPI has a negative affect to the OOW's age, career and license grade as the approaching distances is reduced. The availability of CRPI curve fitting with 3 degrees of polynomial was testified through the RMSE as 1.19 to Head on, 0.87 to $045^{\circ}$, 0.81 to $090^{\circ}$, 0.71 to $135^{\circ}$, 1.29 to Overtaking and 0.87 to Overtaken.

• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.6
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• pp.709-716
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• 2018

In 2017, there was an accident in which a cadet onboard training was killed. This cadet worked 12 hours a day. No regulation has yet been laid down to define hours and breaks for interns. Therefore, the purpose of this study is to investigate the working status of commissioned training, the satisfaction survey of commissioned training, and to improve the treatment of commissioned trainees. The survey was conducted on students commissioned from merchant vessels, and 461 respondents answered the questionnaire. The results of the survey are as follows. First, 43.0 % of cadets said that they worked 10 hours a day on average, regardless of the vessel type, and 35.2 % said that the average rest time was 8 hours. 15.6 % of respondents said they had worked more than 12 hours. Unreasonable order cases deviating from the purpose of education were "making ramen, working at rest time, instruction of dangerous work, making night snack and private errands." Second, the satisfaction level of cadets who practiced on LNG carriers was high, while the satisfaction level of cadets on bulk carriers and container carriers was low. It was confirmed that the ship's size, ship's age, working hours, rest time and training support costs had little minor effect on educational satisfaction. Lastly, 56.8 % of the cadets answered 'commissioned training is like work.' Based on the results of the questionnaires, we proposed the following improvement methods; providing legislation for working hours and rest time for commissioned training cadets, protection system against violence and sexual harassment and victim protection. This study focuses on the working and rest time of merchant ship's cadet and it is meaningful to investigated the onboard training satisfaction by ship's type, size and age.

• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.6
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• pp.818-824
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• 2018

CFRP is often used as lightweight hull material for luxury yachts or special-service ships. An electric propulsion system is also eco-friendly, and has been trialled to equip a small vessel as its main propulsion. In this study, replacing the hull materials and propulsion system with CFRP and electric motors, we made an estimate of the effect of weight reduction and compared it to the original design, for this purpose a case study was conducted on a 45-ft yacht. When redesigning structures with CFRP, we applied the reinforcement content of the carbon fiber in the same way as the original (GC = 0.4), and when changing to the electric propulsion system, we designed motors and battery packs to achieve the same performance as the original. The result showed that CFRP and the electric propulsion system could make the structural and machinery weights 45 % and 58 % lighter, respectively. However, in terms of efficiency, it was confirmed that the electric propulsion system is practically inefficient because it requires a huge amount of battery packs for the same navigation range with diesel engines.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.9
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• pp.876-880
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• 2015

In 2016, the IMO's new rules for an 80% reduction in NOx emissions in newly built ships will necessitate the use of LNG as a clean fuel. So far, the developed European countries have led the development of LNG bunkering ships and related facilities. An LNG bunkering system stores LNG in a horizontal or vertical IMO "C"-Type tank insulated with perlite powder, and a vacuum in the annular space between the double walls, like the cryogenic liquid nitrogen tank. Current storage tanks have high heat leakage, evaporating over 2.0% daily, and are difficult to build with the required vacuum. A more efficiently insulated storage tank could reduce the evaporation rate. This research carried out thermal analysis on a new effective insulation method that separates high vacuum in the annular space between two tanks with a solid insulation material, such as urethane foam, lining the outer vessel. This highly efficient insulation system obtained an evaporation rate of 0.03% per day under a $10^{-3}torr$ vacuum, and an evaporation rate of 0.11% at $10^{-45}torr$. Even if the space loses its vacuum, the new insulation system showed a lower evaporation rate of 4.12% than the present perlite system of 4.9%. This newly developed tank can increase the efficiency of LNG storage tank and may help keep LNG bunkering systems safe.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.6
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• pp.688-697
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• 2014

In this study, electrode bonding technology needed for high density of rechargeable battery is studied, which is recently researched for electric vehicle, the small leisure vessel. For the alternative overcoming the limit of stacking amount able to be stacked by conventional ultrasonic welding, the low temperature bonding method, eligible for minimum of degeneration of chemical activator on the electrode surface which is generated by thermal effect as well as the increase of conductivity and tension strength caused by electrode bonding using filler metal, not using conventional direct heating on the electrode material method, is studied. Specifically to say, recently used more generally the ultrasonic welding and spot welding method are not usable for satisfying stable electric conductivity and bonding strength when much electrode is stacking bonded. If the electrical power is unreasonably increased for the welding, due to the effect of welding temperature, deformation of electrode and activating material degeneration are caused, and after the last packaging, decline of electrical output and generating heat cause to reduce stability of battery. Therefore, in this study, induction heating system bonding method using high frequency heating and differentiated electrode method using filler metal pre-treatment of hot dipping are introduced.