Coast Guard Nav Light Safety Alert

Posted by Darrell Nicholson at 12:24AM - Comments: (9)

Photo by Ralph Naranjo
Photo by Ralph Naranjo

Practical Sailor compared various LED mastlights in the February 2010 issue. All complied with the angular requirements for sailing vessels.

The U.S. Coast Guard has determined that an increasing number navigation lights being used on sailboats do not meet the basic requirements for these lights, making them less visible to nearby ships. According to the Coast Guard's Inspections and Compliance Directorate, part of the problem is that some owners are retrofitting existing incandescent nav lights with LED lights, or LED components that were designed for powerboats. Manufacturers are also at fault, to some degree, for not clearly labeling navigation lights designed for sailboats. 

In mid-March, the Coast Guard's Inspections and Compliance Directorate published Marine Safety Alert 02-19, “Not all navigation lights are created equal,” to assist all mariners in understanding the difference between navigation lights used on power driven vessels and those used on sailing vessels.

Navigation lights intended for use on power driven vessels may be different from navigation lights intended for use on sailing vessels. Although the horizontal arc of visibility is the same for all lights, the vertical divergence (i.e. vertical arc of visibility) requirements for lights on vessels under sail are larger to accommodate greater heeling. Manufacturer labeling may not discriminate between the different requirements. Navigation lights that claim compliance with the navigation rules may meet the vertical visibility requirements for a power driven vessel, however, they may not comply with the vertical visibility standards for sailing vessels.

It isn't always easy for sailors to confirm they are purchasing the right light. Manufacturer labeling may not indicate that the lights are designed for use on power-driven vessels only. In some cases, you'll have to contact the manufacturer or search for this detail in the specification sheets to determine whether the light is approved for sailboats. Most brand-name lights marketed for use on sailboats do meet the vertical angle requirements according to the Coast Guard.

Annex I (COLREGs section 10 and Inland 33 C.F.R. part 84.16 “Vertical sectors”) prescribes the degrees and intensities that navigation lights must meet on the vertical plane. Many boat owners may not be aware of the +/- 25 degree vertical light divergence requirement for sailing vessels, a 17.5 degree increase from the power-driven vessel standard. Installing a navigation light, designed for use on a power driven vessel, on a sailing vessel may result in the light losing visibility when the vessel heels beyond the narrower +/- 7.5 degree vertical divergence angle established for power-driven vessels. A sailing vessel operator in this situation would likely not realize that the sailing vessel’s lights were not visible when heeling beyond 7.5 degree.

graphic showing degree of navigation lights on sail boats

What does this mean?
If your sailboat does not have the correct lights (sidelights, masthead lights, all-round lights, and/or combined lantern) and it heels past a certain degree, it may not be observable by other vessel operators.

Why is that important?
You may not know that other vessels cannot see you due to the heel of your vessel. Failure to operate with the correct navigation lights may create a situation where you mistakenly believe another mariner is able to ascertain your vessel’s aspect or operational condition, which increases risk of collision.

line graphic showing arc of nav lights on sail vessels

Although a navigation light designed for a sailing vessel will have a greater vertical visibility than required for a power driven vessel, it does not pose a commensurate safety concern and it is permissible for a sailboat to show these lights when powering (see diagram above). Manufacturers should be aware of the larger vertical visibility requirement for lights installed on sailing vessels. Likewise, sailing vessel operators and vessel repair facilities should ensure the installed lights meet the applicable requirements in Annex I. Since not all navigation lights are designed similarly, ensure that when you install a navigation light it is USCG certified for the length and type of boat. Such information should be readily available from reputable sources such as the light or vessel manufacturer.

Safety Alert 02-19 is provided for informational purposes only and does not relieve any domestic or international safety, operational, or material requirement. It was developed and distributed by the Office of Navigation Systems. Questions may be sent to

For more on LED navigation lights see our February 2010 report, as well as our February 2019 Special Report on how to determine if your navigation lights are interfering with your AIS.

Comments (9)

We tested the Lopolight and several other LED tri-colors for Voiles et Voilers, a French sailing magazine, at the Bureau Vertitas lab at ENSTA in March of 2018. The Lopolight failed all the vertical angle by a considerable margin. It lost 55.68% of the red side intensity between 0 and 25 degrees, 77.42% on the green side, and 54.87% on the white.

Posted by: Marinebeam | April 17, 2019 12:38 PM    Report this comment

Dow this is true. I have sailing Tricolor LED on my masthead and a steaming LED light about 15/ off the deck on the forward side of the mast. I only use the appropriate lights at the time under power /steaming Under sail masthead tricolour. Bow and stern lights on all the time.

Posted by: SV/FatBottomGirl | April 14, 2019 10:07 AM    Report this comment

A rough but simple test for existing masthead lights is to observe how close to your boat the light remains BRIGHT. If the masthead is 50 feet above your eye (about 58' if you are standing on a dock), the light should be bright at 100 feet, before fading as you approach more closely. A light with a 7.5 degree angle will begin to fade at 380 feet. This does NOT prove the angle above the masthead is the same.

Another common problem concerns bow lights mounted in non-vertical topsides; frequently they are angled considerably downwards.

Posted by: Drew Frye | April 4, 2019 11:21 PM    Report this comment

It appears if it is not broken don't fix it. I prefer LED however there is also interference with the VHF radio antenna.
I will wait before I do a complete change over of lights after some research.

Posted by: Fine Lee 23N | April 4, 2019 3:06 PM    Report this comment

Sadly, some of this is so preventable, but not without consensus and willpower. While the USCG may be the ones wagging the "you may not be in compliance" flag, the larger issue is that COLREGS are a collaboration between nations -- all of which move slowly to correct mistakes and even more slowly to keep pace with technology. A simple fix would be to make sure that there is ONE standard regardless of power or sail. It appears that (for the most part) the sailboat standard is the more rigid. Taken further, if 50% is okay for sailboats and 60% is okay for powerboats (although the angle "wedge" is different, making the standard 60% for both would resolve the issue -- especially if the angle is also widened to accommodate the more rigid standard. Sadly again, since it's a collaboration of nations, even if they jumped on the technology bandwagon today, by the time it gets around to being approved and published, it will be a decade or two past today's technology and would need a couple more decades to catch up with the "then technology" which will exist when new standards ARE published. I, for one, would be VERY interested to know how many collisions occurred where the current light scheme -- mis-installed -- was primary contributor to the incident. I suspect no one has that number handy....

Posted by: livnaboard | April 4, 2019 12:46 PM    Report this comment

Sailboat lights are fine for sailboat under power. Text has been edited to reflect this. DN

Posted by: sailordn | April 4, 2019 11:00 AM    Report this comment

Does the picture at the start of the article include in it a picture of nonconforming lights? If they are conforming it is very confusing. At the Lopo light website Lopo says their trilight is colregs72 compliant. Since a trilight would only be used on a sailboat is it good? The paper also states that all the other lights are compliant but makes no distinction between sail and power when ordering! How is one to know? Does Lopo know?

Posted by: And | April 4, 2019 10:47 AM    Report this comment

As noted in the article, the slight difference in required minimum light intensity (60% vs 50%) beyond the region above and below 5 degrees above and below horizontal "does not pose a commensurate safety concern". This appears to be the main disfference between power and sail.

More importantly, the article misses an opportunity to note that the mileage visibility requirements are the minimum acceptable, and that in this age of greatly increased lighted traffic both at sea, on soundings, and along the shore, brighter bulbs, such as LED, that still meet the angular requirements and don't interfere with the helmsman's visibility, can provide an increased margin of safety.

Posted by: Oldwoodboats | April 4, 2019 10:30 AM    Report this comment

If I am reading this correctly, in order to be in compliance a sailboat would have to have lights for both power boats and sailboats if you power and sail at night? So if you don't and are involved in a collision it could be noted in the investigation? You had lights but they weren't in compliance.

Posted by: dow webber | April 4, 2019 10:02 AM    Report this comment

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