Electronics & NavigationSafety

The Ultimate Guide to Buoys and Flags

Boating navigation is no different from driving cars. Just as we have road signs and traffic lights that we strictly follow on land, there are also internationally recognized signs and signals, in the form of buoys, marks and flags that prevent us from damaging our vessels, and worse, putting ourselves in danger on the water.

To be more familiar with these, we have included in this article an introduction to the systems of navigation as well as images, purposes, and descriptions of buoys and marks. We also have a 2-page PDF that you can download and print for free, so you can have a hand-carry guide when you finally start your journey! Nautical flags and the International Code of Signals are also discussed thoroughly.

Systems of Navigation

Until the 70s, there was no single authority that implemented rules of navigating maritime waters, which caused confusions and lots of accidents, and only in the 80s that the International Marine Aids to Navigation and Lighthouse Authorities or IALA was established. Currently, there are two systems used by boaters around the world, the IALA Region A, that is being used in Africa, most of Asia, Australia, Europe and India, and the IALA Region B, in North, Central and South America, Japan, Korea and the Philippines.

IALA Map in Region A and Region B

There are very few differences between the two systems, in fact, they are almost identical, except that IALA Region A port (left) lateral marks and lights are colored red and starboard (right) lateral marks and lights are colored green, while it’s the opposite in IALA Region B.

Definition of Terms

Port – Left side of the boat

Starboard – Right side of the boat

Channel – Body of water between two close landmasses, e.g. river, strait, harbor

Fairway – Navigational area of a channel

Bifurcation – Point where at which a channel branches into two

Buoy – floating navigation aid in the water

Marks – fixed navigation aid in the water

Mooring – Point of anchorage

Light Flashing – Series of light flickers with different meaning

Methods of characterizing buoys and marks
  • Day time –  through the color, shape, top-mark, marks, and/or light (including color and rhythm).
  • Night time – through the color and rhythm of light and/or illumination enhancement.
  • By electronic (digital) symbology – e.g. as a complement to physical marks.

Marks vs. Buoys

An example of a buoy (left) and a mark (right). Photo by TRAVELBLOG.

Marks and buoys are navigational aids in the water that come in different colors, shapes, and markings, used to help boaters in choosing which direction to go and areas to avoid, or to provide important information to ensure everyone’s safety in the area, whether on board or not.

Marks are fixed aids usually on poles and pilings while buoys are floating aids that are anchored to the bottom. In areas where it’s shallow enough to drive a piling, marks are usually preferred as they do not require as much regular maintenance. On the other hand, in deep waters where it’s difficult to drive a piling, putting a buoy makes more sense. Also, in places where channels may shift and change over time, placing a buoy that is movable and can be anchored is the more common practice.

Lateral Buoys/Marks

Lateral buoys/marks indicate which side of the buoy is the safest to follow when in a channel. There are four kinds of lateral buoys that differ in color, namely port hand, starboard hand, port bifurcation, and starboard bifurcation.

Lateral BuoyPort Hand Buoy/Mark

Lateral Port Buoy Marks
Starboard Hand Buoy/Mark
Lateral Starboard Buoy Mark
Port Bifurcation Buoy/Mark
Lateral Bifurcation Junction Buoy Mark
Starboard Bifurcation Buoy/Mark
Lateral Starboard Bifurcation Junction Buoy Marker
MeaningMarks out the port side of passage way or channelMarks out the starboard of passage way or channelMarks where channel splits and to proceed with the channel on the rightMarks where channel splits and to proceed with the channel on the left
Keep on this side of the boatLeft if traveling upstreamRight if traveling upstreamLeft if traveling upstreamRight if traveling upstream
ColorGreen; RetroreflectiveRed; RetroreflectiveGreen with single red horizontal band; RetroreflectiveRed with single green horizontal band; Retroreflective
Body ShapeCylinder, pillar or sparCylinder, pillar or sparCylinder, pillar or sparCylinder, pillar or spar
Top MarkSingle green cylinderSingle red cone pointing upwardSingle green cylinderSingle red cone pointing upward
Light ColorGreenRedGreenRed
Light RhythmFlashing or quickFlashing or quickGroup flash (6s or 10s)Group flash (6s or 10s)
Markingsodd numberseven numberslettersletters
Light flashing

When it’s dark and we cannot rely on the colors of the buoys, light signals are our most efficient aid to navigate. When equipped, lights are usually placed on top of buoys. These lights would have different flashing frequencies and colors.

Different flashings can be characterized as follows:

Flashing – Flashes light every 4 seconds

Group Flashing (6s) – 2 consecutive flashes, pause, 1 flash and a pause in 6 seconds

Group Flashing (10s) – 2 consecutive flashes, pause, 1 flash and a pause in 10 seconds

Group Flashing (2s) – 2 consecutive flashes and a pause

Quick Flashing – 1 flash every second

Very Quick Flashing – 2 flashes every second

Safe Water or Fairway Buoy

  • Marks entrance to channel, channel centers and landfall locations
  • Always keep on the left side of the boat 
  • Red and white in color Retroreflective
  • Cylinder, pillar or spar in shape
  • Round top mark if present
  • White light if present
  • Light rhythm: group flash (6s or 10s)

Isolated Danger Buoy

  • Marks dangers that must be avoided like submerged rocks or wrecks which may increase in distance
  • Usually placed right above the danger
  • Black with one or more red horizontal bands in color
  • Retroreflective
  • Pillar or spar in shape
  • Two sphere disposed of vertically top mark if present
  • White light if present
  • Light rhythm: group flashing (2s)

For a clearer visualization of buoys and marks in the channel, here is a map that shows where they will be located while traveling upstream.

Visual bouyage guide with lateral port buoys, starboard buoys, and junction buoys

Cardinal Buoys

Cardinal buoys also mark which side of the buoy is safe to travel, however, instead of going left and right, they tell us whether to go north, south, east or west. Similar to lateral buoys, they are pillar or spar shaped. They are black and yellow in color and sometimes equipped with white light.

Cardinal Compass - North, South, East, and West
Cardinal BuoyNorthSouthEastWest
Keep on this side of the boatNorth sideSouth SideEast SideWest Side
ColorBlack above yellowYellow above blackBlack with a single yellow bandYellow with single black band
Top markTwo cones pointing upwardTwo cones pointing downwardTwo cones pointing opposite directionsTwo cones pointing towards each other
Light rhythmQuick (Q) or very quick (VQ)6 VQ + long flash or 6 Q + long flash3 VQ or 3 Q9 VQ or 9Q

Special Buoys

Special buoys mark an area for a specific purpose. They usually have no designated shape and with yellow light when equipped. Some special buoys are not labelled, while some are, and if it is, the mark is never a number.

Special Anchorage Buoy
Special Cautionary Buoy
MeaningMarks a designated area where you can anchor your boatMarks a danger and general boating is not permitted could be underwater pipeline, a firing range or seaplane base
ColorYellow; retroreflectiveYellow; retroreflective
Body ShapeCylinder, pillar or sparCylinder, pillar or spar
Top MarkCross if presentCross if present
LightYellow on any rhythm not used for white lightYellow on any rhythm not used for white light
MarkingWith anchor symbol on the bodyMarked with letters on the body if present
Special Control Buoy
Special Hazard Buoy
Special Information Buoy
No Trespass
Special No Trespass Buoy
MeaningNotes speed limits, wash restrictions, and other limitationsNotes a hazard such as a shoal or a rock that are usually in the middle of or surrounded by navigational watersShare local information like campsite, marina, etc.Designates area where boats area that prohibits entry
Body colorWhite with limitation indicated in orange circle in between two orange barsWhite with orange diamond in between two orange barsWhite with orange square in between two orange barsWhite with orange diamond with cross at the middle in between two orange bars
ShapeMostly cylinderMostly cylinderMostly cylinderMostly cylinder
Light colorYellow when equippedYellow when equippedYellow when equippedYellow when equipped
Light RhythmAny rhythm not used for white lightAny rhythm not used for white lightAny rhythm not used for white lightAny rhythm not used for white light
MarkingsWith restrictions/limits information inside the orange circleDanger can be pointed out inside the orange diamondInformation inside the orange squarenone

Special Diving Buoy

Scientific/ Ocean Data Acquisition System (ODAS)
special scientific ODAS Buoy
Swimming buoy

Special Swimming Buoy
MeaningMarks location where diving occurs and boaters should steer clear the area to avoid accidentsNotes place where boats may tie off to dock, other boats may be in the area so speed limit should be reducedBuoys that record data such as weather, water temperature, currents, etc. therefore should keep distance from this buoyMarks a swimming area and boats are not permitted to enter
ColorAnyTypically white with orange cap on the topYellowWhite
ShapeAnyAnyAnyMostly cylindrical tied on a rope
Top MarkRed flag with white diagonal stripeUsually has a sphere top markNoneNone
LightNoneNoneYellow when equipped; flashes 5 times in 25 secondsNone
The International Code of Signal

Just like the buoyage system, there is a standardized system for communications using nautical flags. The International Code of Signals (ICS) is used by marines and other boaters around the world for easy communication.

Its main goal is to prevent any misunderstanding which may arise from language barriers like meaning, spelling, and diction.

Nautical Flags

Even though we already have radio and other electronic devices available to easily communicate with other boaters, a lot still use nautical flags. The reason being that they are cheap and very reliable as they do not need power to be operated.

These are colorful flags that are used to signal other boaters just like our head and rear lights when we want to turn or change lanes on the road. However, reading nautical flags can be very confusing at the beginning as there are a lot of flags each corresponding to a letter and a specific meaning, compared to just left and right in cars.

How to Read Nautical Flags

The easiest way to read nautical flags is to look closely on their designs and meanings. Remember that nautical flags only use five colors: black, blue, red, white, and yellow. Shapes are very important as well, square/rectangular flags are used for letters, while pennant flags (triangular with flat tip) are numbers.

Below are the square flags, alphabets they represent and what they mean.

AlphaAKeep clear, diver is down.
BetaBWith dangerous cargo.
DeltaDKeep clear, trying to move.
EchoEChanging course to starboard.
FoxtrotFI am disabled.
GolfGSeeking a pilot.
HotelHPilot on board.
IndiaIChanging course to port.
JulietJBurning vessel, keep away.
KiloKNeed to communicate with you.
LimaLStop vessel immediately.
MikeMVessel is stopped.
OscarOMan overboard/out.
PapaPVessel about to sail.
QuebecQPermission to pass through.
RomeoRTurn back.
SierraSEngines going astern.
TangoTStay away.
UniformUApproaching danger zone.
VictorVNeed help.
WhiskeyWNeed medical attention.
X-RayXStop what you’re doing.
YankeeYI am dragging my anchor.
ZebraZNeed a pull.

Numbers in Flags

There are 10 flags that represent numbers. Two or more digit numbers can be represented by combining these flags.


Flying the Flags

Aside from each flag’s meaning discussed above, boats can fly combinations of flags up to seven flags in a row, which will then mean differently.

For example, if you see a solo D (Delta) flag, this means “keep clear, trying to move” and a solo V (Victor) flag, this means “need help.” However, the combination of D (Delta) and V (Victor) flags, will mean “I’m maneuvering with difficulty and require assistance.” Another, a solo J (Juliet) meaning “burning vessel, keep away” and q solo L (Lima) meaning “stop vessel immediately.” Together, these flags mean “you’re running the risk of going aground.”

As a general rule, signals with two nautical flags mean some type of distress or maneuvering issue. Three or more flags can include pennants and denote things like points of the compass, geographical signals, names of ships, time and position, as well as latitude and longitude.

Buoys and nautical flags can be really overwhelming at the beginning, that’s why we have prepared a 2-page PDF that you can download here and print to have a cheat sheet while on the water! With more opportunities of sailing and seeing these buoys and flags, you will surely be familiar with them in no time!

Also, if you find this article useful, please let us know by commenting below!

Karla Ceguerra

Karla is an explorer who loves nature and outdoors. She's a PADI Open Water Scuba Instructor and has been diving since 2015. An agriculturist by profession, she has worked on different projects to improve the agriculture sector in the Philippines. She also took MSc. in Environmental Science focusing on aquatic ecosystems.

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