Boat Navigation Lights: Complete Guide to Reading Lights at Night
Navigation lights — or “nav lights” — are the lighting system that keeps boaters safe after dark or in fog and reduced visibility. They work as a two-way signal: nav lights let you spot nearby vessels, and they let other boaters spot you, reducing the risk of collisions on the water.
Whether you’re studying for your ASA certification or just want to sail Lake St. Clair safely after sunset, understanding each light type and where it’s positioned on a vessel is essential.
Types of Navigation Lights
Masthead Light
A white light mounted along the boat’s centerline (fore and aft), visible across a 225° arc. It shines from directly ahead to 22.5° behind the beam on both the port and starboard sides — meaning it’s visible from the front and most of the sides, but not from directly behind.
Sidelights (Red and Green)
Sidelights show your boat’s orientation to other vessels:
- Green light — starboard (right) side
- Red light — port (left) side
Each sidelight covers a 112.5° arc, shining from straight ahead to 22.5° behind the beam on its respective side. On vessels under 20 meters, these are often combined into a single bow-mounted light rather than two separate fixtures.
Sternlight
A white light at the stern (back) of the boat, covering a 135° arc — 67.5° to either side of dead astern. This lets vessels approaching from behind know you’re there.
Towing Light
A yellow light with the same 135° arc as a sternlight, used specifically when towing another vessel.
All-Round Light
Exactly what it sounds like: a single light visible through the full 360° arc around the vessel.
Flashing Light
A light that flashes at 120 or more flashes per minute — fast enough to be clearly distinguished from a steady light.
Why Navigation Lights Matter
Knowing your nav lights isn’t just a rule to memorize for ASA 101 — it’s how you read the water at night. A red light on your right means a boat is crossing from starboard with right of way. Two white lights and no color means you’re likely looking at a vessel’s stern, and it’s moving away from you. Reading these patterns correctly, instinctively, is part of becoming a confident sailor.
Ready to put this knowledge on the water? Lake St. Clair Sailing School offers ASA-certified courses for every skill level — from your first time at the helm to advanced night navigation.
