The horizontal distance between the two masthead lights or between the sternlight and the second masthead light abaft of the forward one are enlarged with the specialization and the increasing size of vessels. As an example, the navigation lights exhibited on TI-class supertanker (380 meter in length, the horizontal distance between the two masthead lights are approximately 300 meters) are taken up as a sample of a vessel and her navigation lights are displayed on the screen of a ship-handling simulator in a moonless night situation. Seafarers watching her masthead lights and her sidelights from a small craft in the simulator have mistaken one large tanker as two small ships and have also misunderstood her heading direction. As a similar problem, navigation lights of very large container vessels constructed in recent years and of towing vessels are discussed and necessities of drastic measures on navigation lights including a revision of Colregs are pointed out.
