Sunrise and sunset times differ depending on location and date. Previous studies conveniently but monotonously applied day and night times set up. This research defined the daytime and nighttime while considering the time of twilight according to the date and the location of ship collision accidents. Classifying the frequency of ship collision accidents with this standard, we conducted a chi-squared test for the difference between daytime and nighttime. The frequencies of ship collision accidents according to daytime and nighttime was compared by season, month, and time, and all of them showed statistically significant differences. The highest number of daytime ship collisions was 11.6 %, in June, and nighttime collisions peaked at 13.7 %, in December. The most frequent hour for daytime ship collisions was 0700h-0800h, at 10.2 %, and nighttime collisions peaked between 0400h-0500h, at 16.9 %. It is clear that the criteria used in previous studies cited was applied without any theoretical basis and likely only for the convenience of the researchers. It was found that results depend on what criteria are applied to the same research data. This study shows that statistical analyses of marine accidents, traffic volume, and congestion density should be carried out quantitatively while considering daytime and nighttime hours for each particular location and date.

Abstract
 1. Introduction
 2. Materials and methods
  2.1 Material of Research
  2.2 Method of Research
 3. Statistical Analysis
  3.1 Analysis of Ship Collision Accidents by Season
  3.2 Analysis of Ship Collision Accidents by Month
  3.3 Analysis of Ship Collision Accidents by Time
 4. Discussion
 5. Conclusion
 References

• Cho-Young Jung(Division of Marine Industry, Transportation Science and Technology, Kunsan National University) Corresponding Author
• Sang-Lok Yoo(Wando Vessel Traffic Services, Korea Coast Guard)