Able Bodied Seaman - Rules of the Road Practice Test

The important rule here is how anchor lights change for very long vessels. When a vessel is at anchor and is 100 meters or more in length, it must show two all-round white lights in a vertical line, with the forward light placed higher than the aft light, so other mariners can clearly see the vessel’s presence and tell bow from stern. In addition, the decks must be illuminated to make the vessel and its surroundings visible at night. This combination—two lights plus deck illumination—is what meets the requirement for a large anchored vessel. A single light doesn’t satisfy the length-based rule, and adding a third light isn’t part of the standard for this situation.