Navigation Lights

By Andrew Spaulding

I know this subject can be a little dry, but none-the-less it is important to make sure that you are displaying the correct lights at night and that you know how to read navigation lights. Many times “reading” the navigation lights of another vessel is the only way we have to identify what is out there on the water when we are boating at night. Navigation lights, read properly, will tell you which direction the vessel is heading and what kind of vessel is displaying them. Boating out of Chicago means we have all sorts of maritime traffic at night – power boats, sail boats under power and sail and the ubiquitous “Laker” ship traffic, not to mention tugs towing or pushing. All the traffic out there is headed different directions at different speeds showing different lights. Identifying them early is the key to keeping yourself out of harms way.

There are lots of resources that will tell you what navigation lights you should display for your boat. Some of these are listed below at the end of the article. Navigation light requirements come from the International Regulations for Preventing Collisions at Sea 1972 commonly referred to as COLREGS. Besides navigation lights, COLREGS cover such subjects as traffic separation schemes, rules-of-the-road, look outs, and sound signals. The complete set of rules can be found by clicking here.

First we need to start with the definitions of the different navigation lights so that we are all on the same page:  Masthead light – white light on fore and aft centerline that has an arc of 225° that shows from ahead to 22.5° aft of the beam on both sides. NOTE: There is no requirement that a masthead light be at the top of the mast on a sailboat. Typically it is only at the top of a light/instrument mast on powerboats. Side light – green on the starboard side, red on the port side with an arc of 112.5° from right ahead to aft of the beam on the respective side. Stern light – white light with an arc of 135° that shows from right aft to 67.5° on each side. All around light – white, red, green or yellow light with an arc of 360°.

The specific degrees of arc are designed so that the navigation lights form complete circles. For example, a red side light, green side light and a stern light complete a 360° arc which is a full circle. Or, a masthead light and a stern light also form a 360° arc. It is the combinations of different colors in different arcs that allow us to discern whether a vessel is coming at us, crossing us, or going away from us.

How can these combinations of lights tell us where a boat is going? Well, it can take some practice and you have to know your navigation lights for different vessels, but I will get you started. Let us assume that you are underway at night and looking forward. If you see a green light (starboard side light) to port, you are looking at the starboard bow of another vessel. So the other vessel is heading towards you, across your path. Seeing green and red would mean the boat is headed directly for you. If you continue to look at this light and it turns to white (stern light), the other vessel has crossed your path and you are now seeing the stern light. When you see a white light (masthead light) above the green light, it is a vessel under power...if not it is under sail, or at least we hope. If you see two masthead lights separated fore and aft (the aft one will be higher) you are looking at a power vessel over 164 feet in length. If the two masthead lights are in a vertical line, you are seeing a tug with a tow behind…three vertical means that the tow is longer than 200 meters. If you see a yellow light above a white light be very cautious, you are looking at a tug with a tow from behind!

Knowing what the navigation lights are telling you about another vessel will start with you knowing what the combinations are for different vessels. It is a lot to learn and most people don’t just sit down, read the rules and remember them. My advice to get started is to remember the light combinations of the vessels that you are likely to come across at night, particularly the ones that might do you the most harm. I grew up boating in Long Island Sound where there are tons of tugs towing barges, but not too many ships, so I learned tug light combinations pretty quickly! Late one night on a delivery, dead in the water with no propulsion, knowing the lights saved our skin, but I’ll save that story for another time.

For a complete set of USCG navigation rules click here. The light section starts with Rule 20. 

For a helpful site with graphics of different light combinations, click here.

For a website with lights and shapes flash cards, click here.