Lights for Sailboats
The US Coast Guard has developed an elaborate scheme of navigation lights for boats and sailboats of all sizes on the York River and around the world so they can recognize each other at night and tell what direction they’re going.
The easiest example is the one here of a sailboat with red, green and white lights. Note that the arc of each light does not cross over into another light, so that at most you’ll only see two lights. If you look over your port bow and see green/white moving, you can assume the boat is about to cross your bow from the left. If you look starboard and see red/white approaching, then the boat is about to cross your bow from the right. If you see only white, then you are approaching another boat from behind and should take care to slow down and indicate which side you intend to pass on.
There’s a lot more to it, of course, but the system is logical and tested all the way up to commercial freighters. Some thought is required, not just memorization. Learning the nav lights makes sailing safe, comfortable and unique fun at night.
Having said that, we generally avoid sailing at night for reasons having nothing to do with lights. There is great apprehension about running through a crabpot line and fouling the prop. But that’s another story.