How To Read Navigation Buoys & Lights

How To Read Navigation Buoys & Lights | Life of Sailing

Last Updated by

Capt Chris German

June 15, 2022

One of the most confusing aspects of the entire marine world is the system of marks, buoys, lights and shapes that decorate the seascape.

The system that has been developed over the last 2,000 years by all the nations of the world confuses even the most seasoned captains at times.

It is for this reason that there is an entire section of the USCG License exam that is devoted to understanding only half of that system.

To add insult to injury, just when you master the system we have here in the United States, they switch it up when you go abroad to foreign ports, but not all foreign ports.

There are two systems that have been adopted by the International Maritime Organization, the governing body for all International sea trade; the IALA-A and IALA-B.


Table of contents

Navigation Systems

IALA-A and IALA-B are the acronyms they have given those two systems.

IALA stands for International Association of Lighthouse Authorities but was changed in 1957 to International Association of Marine Aids to Navigation and Lighthouse Authorities. They kept the IALA because IAMANL didn’t quite roll off the tongue the way they wanted it to.

The USA, North and South America, Japan, the Carribean, the Philippines and Korea all operate under the IALA B system of lights and aids to navigation where even numbers on red buoys are kept on the right when returning from sea.

The rest of the world operates under the IALA A system where it is nearly opposite of IALA B, where odd numbers on green buoys are kept on the right when returning from sea.

There are few other differences between IALA A and IALA B, but the big takeaway is basically if you are in the US sphere of influence, you do things one way and if you are not in the US sphere of influence you do things the other way. God bless world geopolitics right?

IALA B The Lateral Marks

I am a USCG licensed captain and a US National, so I do hope you’ll forgive me if I persist with a US-centered frame of thinking by deciding to discuss IALA B first. It's the system I grew up with and where my comfort resides, so bear with me.

For starters, we have red and green buoys. Prior to the 1970’s the green buoys were once black buoys, but to adhere to the International system of maritime colors and match what half of the Country was doing at that time, the USCG standardized signification of the right and left sides of the channels everywhere by putting even red nuns on the right hand side of the channel when returning from sea.

Even Red Nuns means that they have even numbers, will be red in color and will have the shape of a nuns habit or triangular shape. On the other side we have Odd Green Cans or green buoys with odd numbers and they are shaped like a can or cylinder.

As you travel up from sea, the right hand side of a channel, harbor, bay or river will have the number “2” on the first red nun buoy and increase with even numbers as you progress up from sea on similarly shaped and colored buoys. On the left hand side, your first buoys will be green and can-shaped and they will start at the number 1 and progress up from sea with odd numbers on similarly colored and shaped buoys.

I say similarly colored and shaped because with time, the colors fade and the shapes are not always identical. Oftentimes they have corresponding colored lights for nighttime use as well and those are slightly different shapes too.

In general these colors and shapes are accurate, but North America is a big place and the USCG has lots of buoys to maintain.

Other marks in this category sometimes don't float at all and are located on rock piles or pilings and those marks are called Day Shapes. The also will be triangular and red or square and green with even and odd numbers respectively.

Mid Channel Marks

The last mark we need to discuss under the Lateral Section of buoys is the Mid Channel Marks or Preferred Channel buoys. These are half red and half green marks that are displayed with letters instead of numbers where a channel splits and indicates which side of the split is preferred.

I always was confused by these because so many people have a tough time describing these (including me- my wife helped me write this). Think of it this way: If anyone other than Robert Frost came upon a channel that diverged in a creek and they wanted to choose the one more traveled, the side that is preferred would be indicated on the top half of the buoy.

Chart One and the Navigational Chart

If you're still with me and even if you're not, the US government has given us a system of keys to deduce what all these buoys mean and charts to help us find and identify where all these buoys might be located. The publications are called Chart One and The US light List and the charts along with the publications are (for now), produced by the National Oceanic and Atmospheric Administration or NOAA.

With the push to save a buck and privatize everything, the Government has floated the idea of no longer producing charts; which by extension, would mean they no longer will also produce Chart One and the Light List. For now however, the charts and books are available online.

If you really want to gain a good understanding of the use of these charts and publications, there are lots of online resources. Additionally, there are bricks and mortar schools that will teach you how to use the charts and even test you in their use so you can be a Licensed Captain. For our purposes, let's just acknowledge that they exist ‘cause I only have 2000 words to work with.

Other Buoys and Non-Lateral Marks for Navigation

The red and green buoys make up the lion's share of buoys you might see on the water , aka the Lateral system. However, there are a bunch of others that you really need to know about in IALA B called the Non-Lateral system.

They are called the Non-Lateral system because unlike the red and green buoys that make up lines where your boat should and should not go, non-lateral buoys are placed to identify places outside those lines where you really need to know where you are. These are like that big X that marks “you are here” at the mall. The most important of those marks and one of the happiest sights you will see when you make your way back to shore after a long voyage, is the safe water mark.

These marks will always be half & half or striped red and white longitudinally, but can be all kinds of shapes. They can carry lights, gongs, bells or whistles but they will always sound out or display morse code letter “A” (pronounced Alpha and showing or sounding one dot followed by a dash of six seconds in length or an isophase light that's equally on and off ).

They will be found where deep water starts at the end of a traffic pattern and can indicate the start of a channel or harbor. Safe water marks are always a welcome sight when returning from sea because it means home is close by. They are equally welcomed if you are leaving a port, as it means that dangers of grounding have passed.

Other marks included in this section of the system, though not as commonly seen, include the dayboards which tell you where you are, range markers which tell you where to go and isolated dangers which tell you where not to go. For more on this, check out a Chapman Piloting and Seamanship manual.

Regulatory and ICW marks

In the IALA B system, ( here in the good ol’ USA) we have another category of marks which are for regulatory and inland purposes. These buoys are not federally regulated and you will never see them on a NOAA chart, but they are integral for navigational purposes.

Orange and white marks with words on them like “NO Wake” and “Rock” are put there by local authorities to enforce local regulations. It's not that the USCG doesn’t care about them, but the people who will pull you over if you fail to honor them usually can’t put you in Federal prison (except in the National Parks).

White Balls with Blue stripes are generally mooring buoys and are privately maintained under this system and are used for storing boats. Generally speaking no one can arrest you for tying up to the wrong buoy, but if you hear the sound of shotgun cocking I would suggest you find another buoy.

Last on the list here are ICW marks which oftentimes will be attached to Lateral marks in the stretch of inland canals and waterways that lines the lower half of the eastern Seaboard. These are yellow stickers that indicate the right and left side of the ICW, regardless of the lateral marker they are attached to, as you travel from Texas to New jersey.

This is by far and away not every mark that is out there and as I suggested earlier, you really ought to take a navigation course to truly understand these marks, their meaning and how to use them properly. Before I end this thing though, I need to tell you a bit about IALA A.


As previously mentioned in IALA A, the red buoys are still even numbered but they are kept on the left when returning to port. A good way to distinguish this is to remember the European position on drinking and the memory aid, “Is there any red port left?

That obviously means that Green buoys are odd numbered and kept on the right when returning from sea. It's not like they could make them entirely opposite, just enough to make it confusing right?

Other buoys of note under IALA A include the directional buoys or Cardinal marks and you will find them in relation to the prescribed path regardless of the position of the vessel. These are strange to US-based mariners because the lateral buoy system under IALA B tells us which way to go as if there was an imaginary dotted line to follow.

The cardinal marks should be honored to the north, east, west or south depending on the direction of the two black arrows on their top. So if you want to head north up the English Channel, a black and yellow buoy with two triangles base to base vertically will indicate that a buoy on your right should be kept to the east.

As I said, these are quite foerign to me (literally) because I am a US-based mariner. But if you plan on chartering a boat in Croatia or taking a voyage through the Mediteranean, you should take a RYA course before you go and bone up on your IALA A marks.

Take a Course

I may be a little biased as a licensed captain and a long time sailing instructor, but this is not a subject that you can master by reading a simple blog post or watching a youtube video. There are literally thousands of schools around the world and tons of professional instructors that can help you get a better understanding of this subject than I can offer here.

But that being said, in my highly esteemed opinion, this is a good breakdown that I hope will entice you to learn more about this subject. And if you do want to learn more, here are two free sailing courses, along with many more that cover such topics.

It’s self-paced and based online and even if you don’t choose me as your instructor, it has a great international look at the subject of aids to navigation and can prepare you to charter catamarans from international ports of call.

As always, do good, have fun, and sail far.

How To Read Navigation Buoys & Lights
Capt Chris German

Capt Chris German

Capt Chris German is a life long sailor and licensed captain who has taught thousands to sail over the last 20 years. In 2007, he founded a US Sailing-based community sailing school in Bridgeport, CT for inner city youth and families. When Hurricane Sandy forced him to abandon those efforts, he moved to North Carolina where he set out to share this love for broadcasting and sailing with a growing web-based television audience through The Charted Life Television Network.

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