Article by Capt. Mark Sampson
Most boaters probably know little more about the lights on their boats other than the fact that they have red and green on the bow and a white one somewhere closer to the stern. On small boats the red and green are often together and illuminated by one bulb, on larger boats there usually two separate lights mounted on either side of the cabin, hull, or t-top. These lights are usually referred to as "running lights" or "bow lights" but the proper term for them is "sidelights". The average boat also has an all-round white light mounted farther back somewhere on the top or on a post at the stern. Most folks call that the "anchor" or "stern" light.
Red, green, and white makes for "three" lights right? Actually "no" those lights represent a total of "five" of the navigation lights required on every vessel! But only if you know the Coast Guard "Navigation Rules" or "Rules of the Road" do you know how this wacky math actually works.
Under the rules, power vessels while underway are required to display at least one white (220°) "masthead" light that can be seen from another vessel off your bow and your port and starboard sides. Also required is a green (112.5°) "sidelight" facing forward and off the starboard side, a red (112.5°) "sidelight facing forward and off the port side, and a white (135°) "stern" light facing aft. Anchored boats are to display at least one white (360°) all-round light. All that makes for a total of five lights. "But wait!" You say. "There are only two light bulbs on my boat. How can I have five lights?"
The answer is woven into how the Navigation Rules work and here's the way they describe the lighting requirements for power vessels:
(Rule 23) A power driven vessel underway shall exhibit: a white masthead light forward, red and green sidelights, and a white stern light.
(Rule 23) A power driven vessel of less than 12 meters in length may exhibit an all-round white light and sidelights.
(Annex 1) on a vessel of less than 20 meters sidelights may be combined in one lantern.
(Rule 30) A vessel at anchor shall exhibit, where it can best be seen, an all-round white light.
An important thing to know about lights is that they are not designed just to tell other boaters "I'm here" but they also inform other boaters about the direction you're actually headed and how they must navigate while in close proximity. For example; if you see only one white light on the other vessel, it's moving and you're approaching from its stern, or else it's anchored, and either way, you need to steer clear of it.
If you see a red and white light you're looking at the port side of a boat that's moving ahead and by the rules you should not pass in front of that vessel as it's the "standon vessel" in a crossing situation and has right of way over you who are the "giveway" vessel. If you see green and white you're the standon and he's the giveway vessel. If you see red, green, and white at the same time it's a boat under power that's headed straight at you, so you'd better do something!
So hopefully you can see how knowledge about how boats are lighted at night will help a boater know what they must do to follow the Rules of the Road, stay safe and avoid a collision.
So what about those two bulbs that account for five lights? Two (112.5°) side lights, one (225°) masthead light, one (135°) stern light, and one (360°) anchor light - that makes five total lights.
However, there are provisions in the rules that allow relatively small vessels to combine lights. So the two side lights are often combined into one light with both a red and a green lens. The 225° white masthead light is often combined with the 135° stern light, and when the boat is anchored and not in need of its underway lights, if the combined masthead and stern light is “on” it covers the requirement for a 360° anchor light because 225° + 135° = 360°. Simple (but confusing) math.
The Navigation Rules or “Rules of the Road” are essentially regulations that describe how boats are supposed to be operated when they are in close proximity (or sometimes just in sight) of one another, as well as lighting requirements, sound signaling, and a whole lot of other stuff that, is supposed to help keep us all from playing bumper boats out on the water. It would be comforting to think that most folks who operate boats on our local waterways have even the slightest knowledge of what the rules are. But since most don’t even know that 1+1=5, my only advice is to “be careful out there!” §
