After dark, you cannot see the shape of another boat, only its lights. That is why boating safety exams ask about navigation lights. The rules come from the U.S. Coast Guard's Inland Navigation Rules (33 CFR Part 83), and your state manual follows them.
When lights are required
Navigation lights must be shown from sunset to sunrise, and also during the day in restricted visibility such as fog or heavy rain. While they are on, you may not show other lights that could be mistaken for them or that interfere with keeping a proper lookout.
Related: What to Expect on Your State's Boating Safety Exam
The basic lights
- Sidelights: a red light on the port (left) side and a green light on the starboard (right) side. Each shines over 112.5 degrees, from straight ahead to just behind the side of the boat. On smaller vessels, the two can be combined in one lantern at the bow.
- Sternlight: a white light at the back, shining over 135 degrees toward the rear.
- Masthead light: a white light over the centerline, shining forward over 225 degrees.
- All-round light: a light visible from every direction (360 degrees).
What each type of boat shows
- Power-driven vessels underway show a masthead light, sidelights and a sternlight. A power-driven vessel under 12 meters (about 39 feet) may instead show one all-round white light plus sidelights, a common setup on small powerboats.
- Sailing vessels under sail show sidelights and a sternlight, but no masthead light. That white masthead light is how you tell a sailboat under sail from one running on its engine. Once a sailboat turns its engine on, it is a power-driven vessel and must show power-driven lights.
- Sailboats under 7 meters and boats under oars, such as rowboats, may instead have a white flashlight or lantern ready to show in time to prevent a collision.
- Vessels at anchor under 50 meters show an all-round white light where it can best be seen. A boat under 7 meters anchored away from channels and areas where other boats normally travel does not have to.
Reading another boat's lights
The lights tell you which way the other boat is facing:
- Red and green together: the boat is coming straight at you.
- Only green: you are seeing its starboard side. It is crossing from your left and you are generally the stand-on vessel.
- Only red: you are seeing its port side. It is crossing from your right and you should generally give way.
- Only white: you are most likely looking at its stern, overtaking it, or it is at anchor.
A common memory aid: red, right, returning is for buoys, not boats, so don't mix them up. For boats, remember that port and red are both the shorter words.
Before you head out
Check that your lights work before every trip, even a daytime one: weather and plans change, and being caught out after sunset without lights is both illegal and dangerous.