What Color Is a Boat’s Sternlight?

You can learn a lot about boat lights if you just think about what they are for and what they are doing. On the highway at night, a car has lights that you can identify instantly. What is the difference between bright white lights and red ones? What about flashing yellow lights?

The boat’s stern light is the rear-facing all-round white light. This all-round white light fills the 360-degree arc started by the sidelights, so its arc shall be 135 degrees centered aft. Sidelights and stern lights should show between one and three miles, depending on the length of the vessel.

The concept is the same with boats, but things get a little more complex on the water. When you see another vehicle on land, you know that it is on a road and hopefully in its lane. But at sea, there are no roads and there are no lanes. It’s up to every skipper to ensure that there is no risk of collision.

The lights on boats play other roles. By glancing at them, you need to be able to tell which way the vessel is moving, who has the right of way, and even what sort of vessel it is. So, as you might expect, boat lights get a little complicated and require some studying.

Table of Contents

• Boat Lights Overview
• Lights and Right of Way
• Boat Navigation Lights – Specific Requirements
• Specific Boat Navigation Lights Requirements
• Some Common Pitfalls and Problems with Boat Navigation Lights
• Dayshapes
• What Color is a Boat’s Stern Light? What Side is the Green Light on a Boat?
• FAQs (Frequently Asked Questions)

Boat Lights Overview

Let’s start by looking at the lights on a typical small boat using an engine for propulsion. This is the most basic lighting setup, so understanding it as a starting point makes sense.

First, on the bow of the boat is a bicolored with red and green sidelights. When you face the boat dead ahead, you can see both colors of the red and green sidelights. But when you stand to one side or the other, you can only see one of the colors. Some boats have this same light but are built in two separate lights, one green, and one red.

If you know which side of a boat has a red light at night and which side of the boat has a green light at night, you can tell which side of another boat you are looking at. And from that, you can tell which direction it is headed. Will it cross your path, or is it headed away from you? Remember, you can’t always rely on a vessel’s apparent movement while at sea. Your boat might be bouncing around, and the other vessel may be moving very slowly.

On the back, the boat has a white stern light. In some cases, boats are allowed to use an all-round white light along with the bicolored bow nav light. In any case, a proper set of nav lights has red and green sidelights on each side and all-round white light on the back.

So if you are boating at night and you see an all-round white light, you know that you are approaching a boat from behind. If you are faster, you are overtaking that boat.

Lights and Right of Way

All of this goes along with the right of way rules while operating at sea. Those rules, along with the color and placement of white, red and green sidelights on boat hulls, are covered by the COLREGs, or the international rules governing the prevention of collisions at sea.

As a quick overview, Rules 13 through 18 of the COLREGs cover what to do when two vessels are meeting head-on, crossing, or one is overtaking the other. But keep in mind, it also depends on what sort of vessel it is. For example, a powerboat should always give way to a vessel that is restricted in its ability to maneuver, or one that is engaged in fishing operations.

So the lights not only need to tell the skipper where the boat is and which way it’s headed, but they also need to identify the vessel and what it is doing. More on that later.

When two vessels are approaching head-on at night, they will each see red and green sidelights on the boat dead ahead of them. According to the COLREGs, they should each divert to their starboard to avoid a collision. So, what does a red and green sidelight indicate when seen together at night? Seeing both colors only happens when another vessel is pointed directly at you.

When two vessels are crossing, the vessel to the starboard has the right of way. The port side light color is red, so the vessel that should give way will see a red light. So, which side of a boat has a red light at night is very helpful, because you can remember that red means stop or, more accurately, give way.

From the stand-on vessel, the light color starboard side of the boat approaching will be green, so they will know to stand on and proceed on course.

Finally, what if you can only see the white stern light on a boat nearby? If you only see a white stern light, it can mean a few things. If you know it’s a stern light because you have previously seen the red and green sidelights on a boat, then you can assume that the vessel is headed directly away from you.

But if you only see the white light and it does not seem to be moving, it might indicate a vessel at anchor. An all-around white light is shown by vessels at anchor.

Boat Navigation Lights – Specific Requirements

The overview above should give you a good primer on what the red and green lights on a boat hull are seen at night. But to understand the topic, there are quite a few other specifics you should know.

For one thing, each light that is mounted on a boat must meet a minimum visible range requirement and have a finite field of view.

Masthead Light

A masthead light is one mounted on the centerline of the vessel, pointed forward, with a field of view of 225 degrees. It is white. The masthead light is used on larger motor vessels. Masthead lights shall show between two and six miles, depending on the length of the vessel.

Sidelights

These are the red and green sidelights. Each color shall be an arc of 112.5 degrees. If the vessel is less than 20 meters long, the two sidelights can be combined into a single bi-color light.

Here are some specific things you can think about in regard to sidelights.

• Which side of a boat has a green light at night? Or, what color is the starboard-powered boat navigation lights? It doesn’t matter how you look at it, the green light is on the starboard side.
• What does a red and green light indicate when seen together at night? Due to the way that the colored lights are mounted, there is only one time when you can see both red and green lights. That is when the other vessel is pointed right at you!

What Color is a Boat’s Sternlight?

This is the rear-facing white light. It fills the 360-degree arc started by the sidelights, so its arc shall be 135 degrees centered aft. Sidelights and stern lights should show between one and three miles, depending on the length of the vessel.

So, what color is the boat’s stern light? White.

Towing Light

A towing light is just like a stern light, except it shines yellow. They are used by tugs when engaged in towing or pushing operations, and there are different combinations of tow lights to indicate towing astern, pushing, or side-tied towing.

Related reading: What Is the Main Function of a Boat Trailer’s Safety Chains?

All-Around Green, Yellow, Red, or White Light

An all-around light shows 360 degrees of unbroken light, visible from every direction of the vessel. All-around lights should show either two or three miles from the vessel, depending on length.

All-round colored or white lights are used for a number of purposes and may be steady or flashing. They can also be a white light, red light, green light, or yellow light, depending on their purpose.

Often, a combination of colors is hung to indicate a vessel operating in a specific way. Here’s a list of ways that all-around lights might be used. In all cases, these lights accompany the correct boat navigation light pattern if the vessel is making its way.

• A single all-around white light shows a vessel at anchor.
• Red over green all-round lights–a vessel under sail.
• Green over white all-around lights–a vessel engaged in trawling (fishing).
• Red over white all-around lights–a vessel fishing but not trawling.
• Red over red all-round lights–a vessel not under command.
• Three all-round lights, red over white over red, show a vessel restricted in her ability to maneuver. This could be a vessel engaged in towing, dredging, or a dive boat.
• Three all-round lights, all red, mean a vessel constrained by her draft. 
• Two all-around red lights mean that a vessel is aground.
• White over red lights is shown by pilot boats.
• A flashing white all-around light that flashes between 50 and 70 times per minute is a distress signal.

Specific Boat Navigation Lights Requirements

There are many nuances to the powered boat light requirements laid out in the COLREGs. The precise arrangement and requirements for the powered boat navigation lights depend on the type of vessel, how it is being operated, and its length.

Unpowered Small Boats (Oars or Sails)

Small rowboats, sailing dinghies under seven meters long, kayaks, or canoes with no motors are not required to have standard boat navigation lights. Instead, they shall have an electric torch or flashlight that can be shown to prevent a collision.

Sailboats

There are a few different light rules for sailboats. But first, it is important to draw a distinction since most sailboats are motorboats as well. If the motor is running and in gear, the boat should show the lights of a motorboat. This includes when on a sailboat with a motor (motor sailing).

This requirement makes sense since it is noted in the COLREGs that a vessel motor-sailing does not have the right of way over another power vessel. 

The lighting requirements for a vessel under sail alone depend on its length.

• A sailing vessel shall show her sidelights and stern light.
• A sailing vessel less than 20 meters long can instead show a single all-around light at the masthead that mimics the colors of sidelights and the stern light. This single lamp is called a “tri-color masthead light” since it includes the starboard light color, port light color, and stern light color.

Powered Boats

How do these rules differ for powerboats? Powerboats are very similar, but they add a masthead light. Remember, the masthead light does not refer to an all-around, but rather to a white lamp-mounted high that shines through an arc of 225 degrees. This light is usually called the steaming light.

• Vessels less than 50 meters long shall show their sidelights, stern light, and a single masthead light.
• Vessels greater than 50 meters long shall show a second masthead light, situated aft and higher than the first.
• A power vessel less than seven meters long that is not capable of making more than seven knots can show nothing more than a single white all-around light.
• A power vessel less than 12 meters may show a single white all-around light and sidelights in lieu of separate stern lights and masthead lights.

Nav Rules and Boat Lights Overview

Some Common Pitfalls and Problems with Boat Navigation Lights

Generally, we use the lights that the boat manufacturer installed. Most are made well and will provide years of service—although age and corrosion can take their toll. Wiring problems can lead to problems with masthead lights, and lights that get sea spray can short out. 

Maintaining your lights and their wires is a good idea. Anytime you replace a bulb, clean the contacts inside the light carefully and treat the lamp with dielectric grease. 

Many boaters want to upgrade their boat navigation lights to LEDs. These are readily available on Amazon and other websites, but be careful that what you are purchasing is an approved USCG navigation light. Remember, there are specific requirements for their visibility arc and distance. Many LED assemblies being sold for small boats do not meet the minimum legal requirements. 

Furthermore, there have been documented problems with LED bulbs interfering with VHF radio transmissions. This not only includes your navigation lamps but also those little bulbs you use on the interior of your boat. No one can deny the power savings that LEDs offer, but you should check your radio to make sure that your new lights don’t reduce your radio’s usefulness.

Aftermarket LEDs available for retrofitting into older navigational lamps should also be USCG-approved. They’ll need to have the same luminosity as the bulbs they’re replacing. Remember to check things like what color is a boat’s stern light and the types of the color red or green lights on boat lights. LEDs can have radically different color temperatures than incandescent bulbs.

Finally, if you often have trouble with your all-around white light for anchoring, consider using a portable spare. Hanging anchor lights are popular with sailboaters around busy harbors. Many feel that using only the masthead, 50 feet or more in the air, might be missed by local boaters running at high speeds through anchorages at night.

Dayshapes

It’s also worth noting—although slightly beyond the scope of this lighting article—that the COLREGs require the use of dayshapes. If you’ve never heard of a dayshape, you aren’t alone. Many boaters, especially in the US, have never used or seen one.

Day shapes are the daytime equivalent to those special all-around light patterns.  

• A black ball shows a vessel at anchor.
• An inverted cone shows a sailboat operating under engine power (or motor sailing).
• A black diamond indicates a vessel towing astern, or an object being towed.
• Two cones, with their apexes together, show a vessel fishing.
• Two balls mean the vessel is not under command.
• Three shapes, ball over diamond over the ball, show a vessel restricted in her ability to maneuver.
• A cylinder shows a vessel constrained by her draft, such as a ship in a narrow channel.
• Three balls mean that the vessel is aground.

What Color is a Boat’s Stern Light? What Side is the Green Light on a Boat?

As you can see, there are a dozen different ways to look at boat lighting. Once you have studied the different arrangements, there’s not much to it. But it is one of the foundational skills of being a good skipper. Even if you don’t intend to be out after dark, learning the lights, dayshapes, and right-of-way rules helps you understand how all the pieces work together to make the system work.

You can download a Coast Guard PDF copy of the international and inland COLREGs navigation rules online.

FAQs (Frequently Asked Questions)