Despite the continual decrease in the shipping fleet over the past five years, the number of marine incidents has steadily increased. Among the marine incidents except for engine damage or incident from floating object twined around a propeller which are relatively minor, collision is the most frequent event at sea and its proportion has been increasing up to 40% from 180 in 2014 to 250 in 2018. In line with the total number of ships involved in casualties, fishing vessel is the most frequent ship type involved in 'casualty with a ship' by ship category. From a total of accidental events occurred on fishing vessels analyzed during investigations, a human erroneous action is represented by far the main contributing factor with 76.4% of the total. Especially, in a human erroneous action, it is analyzed that improper lookout accounts for the majority part of it with 54.2% of the total.
In order to prevent collision at sea, various studies confined to merchant ships have been already conducted but, studies related to small vessels such as fishing vessels have not been carried out enough. In the case of merchant ships, various navigational equipment with advanced technology such as RADAR and ECDIS have been developed and installed to assist an operator. However, for small vessels, only legally required navigational equipment is opted to be installed due to the narrow space on board and financial difficulties. Especially, it is common that only AIS (Automatic Identification System) is installed on small vessels in accordance with the Ship Safety Act and the Fishing Vessel Act which enforce to install AIS in passenger ships more than 2 tonnes, fishing vessels more than 10 tonnes, tugboats and oil tankers more than 50 tonnes. In this case of vessels, AIS-based collision warning device is being used to alert an operator when detecting an approaching object to own vessel within a certain range.
International Maritime Organization (IMO) allocated Channel 87 (161.975 MHz) and 88 (166.025 MHz) only for AIS frequencies to complement the shortcomings of existing RADAR or VHF. With establishing automatic identification system between ship to ship or ship to shore, AIS becomes a device to automatically transmit maritime safety information including ship static information (Ship name, MMSIs, Call Signs, etc) and dynamic information (location, course, speed, etc.) to prevent collision and support VTS operation and maritime search-and-rescue activities. However, as AIS-equipped vessels and, application services utilizing AIS have increased, the problem of the deterioration in quality of connection has been raised recently. These issues raised the need to improve AIS performance quality and many studies have been conducted to solve the problem.
Meanwhile, the government of the Republic of Korea promotes the SMART-Navigation project customized in the environment of the Republic of Korea and plans to introduce a high-speed maritime wireless network so called LTE-M within 100 kilometers off the coast. The most distinct feature of LTE-Mis that it is necessary to go through land-based station without direct communication between Device to Device. In such communication system, communication service is highly likely to be interrupted or delayed due to radio interference or a poor transmission and reception of a land-based station. In addition, when using this communication service to obtain navigation information or to avoid collision on the basis of this information, a separate device for Device to Device communication is required to deal with the unexpected situation such as service delay or data loss.
In the road transport sector, several research and pilot projects have been steadily conducted to apply mobile communication technology to vehicles such as WAVE (Wireless Access in Vehicle Environment) and DSRC (Dedicated Short Range Communication).
This study analyzed and presented wireless communication technology applied in marine traffic and in road traffic in order to develop systems that can avoid collision in small vessels. Analyzing the current status of existing communication, it was decided to develop collision avoidance system for small vessels based on sufficient demonstration and technologically advanced WAVE communication technology. WAVE Communication Technology is a technology optimized for fast-moving vehicles and allows packet frames between vehicles and vehicles or vehicles to infrastructures to be sent and received within a short period of 100 msec. Based on these technologies, it is expected that excellent and highly reliable application technology will be able to be developed when applied to marine traffic.
In this study, first of all, in order to apply WAVE wireless communication technology using in road traffic into the marine traffic, an sea trial test was conducted with the existing Shark fin antenna changed into 360-degree omni-antenna. As a result of the test, since LOS(Line of Sight) at sea is better than at land due to no structure at sea such as a building, it was found that the transmission distance increased. With the same output, comparing with that the maximum receiving distance at land was around 1 km, it was analyzed that data was possible to be stably transmitted up to 8 ~ 9 km at sea.
Collision avoidance system for small vessels developed in this study consists of data receiver, collision risk calculator, collision risk determination unit and indicator. With the risk assessment for collision in the basis of DCPA and TCPA, which are widely used, the criteria for determining collision warning were made through interview surveys by operators of similar-typed vessels. While receiving dynamic and static information of other ships through WAVE communication from the receiver, the degree of risk is calculated and determined by the criteria of determining risk of collision by the calculator and determination unit. Finally, in order to avoid risk of collision, indicator unit warns an operator of risk of collision by an alarm or the similar method.
In order to assess the reliability of alarms in collision warning system using WAVE communication, the sea trial tests for crossing and overtaking situations were conducted and the results were derived. It was assessed that when collision risk situation occurred, calculations and determinations based on the criteria for determining collision warning were properly performed and, that the process of displaying the information to the operator was also suitably performed. In particular, since the transmission cycle of information is 100 msec as the characteristics of vehicular communication systems, it was possible to precisely detect risk of collision caused by quickly changing bearing and speed of the other vessel at close range and to send the proper information to an operator. As a result of the application of the AIS-based avoidance system under the same conditions as the WAVE communication technology-based avoidance system, when signal was broken due to an error during the transmission and reception of information under AIS, it took twice as long for the signal to be transmitted again. In addition, it was revealed that when risk of collision occurred in a flash due to track lost and sudden-changed circumstance, the proper action to avoid collision or warning for collision were difficult to be suitably performed.
Compared to the existing communication technology 'AIS', WAVE-based collision avoidance system developed in this study for small vessels was analyzed to be able to perform transmission and reception of the reliable information and to quickly react to the suddenly occurred risk of collision. However, it is premature to immediately apply the existing V2X technology to marine traffic without sufficient verification and it is necessary to develop and enhance the technology into the communication technology optimized for marine environments through sufficient research and development with experimentation. In addition, with the advent of the era of MASS (Maritime Autonomous Surface Ship), not being limited to the development of collision avoidance systems, it is deemed necessary to develop various services for MASS by developing and supplementing technologies for transmission of highly reliable information and excellent communication security.