Navigational Aids: the IALA Maritime Buoyage System

Navigational Aids: the IALA Maritime Buoyage System, Navigational Aids: the IALA Maritime Buoyage System

IALA Maritime Buoyage System

There are so many details to learn about the nav aids on charts so that when you are on the water; you know where your vessel should be and not be. Here I break down the basics into types of markers, how they are identified with color and light, and how the whole system actually works to keep you in the channel and off the rocks.

IALA International Association of Marine Aids to Navigation and Lighthouse Authorities 

  • Five buoy types – cardinal, lateral, isolated danger, special, and safe water
  • Uniform system of maritime buoyage in most maritime nations
  • Two regions – Region A and Region B where lateral marks differ only in the colors of port and starboard hand marks.
  • Region A, red is to port on entering.
  • Region B, (used in the US) red is to starboard on entering.

ATONS Aids to Navigation

  • Sounds
    • Gong, bell, horn, whistle
  • Buoy – floating, anchored to bottom
  • Beacon – structure permanently fixed to bottom – lighthouses, single-pile poles, can be lateral or non-lateral, lighted ones are called “lights” and unlighted beacons are called “daybeacons.”
  • Lateral aids indicate the sides – most often sides of a channel
  • Non Lateral aids do not indicate the sides – mark a navigational feature
    • Special marks – anchorages, fishing grounds, dredging/spoil areas
    • May be lighted, fixed or flashing yellow light, shape of buoys close to it
  • Beacon – fixed artificial navigation mark; Daybeacon, Daymark, LightedB, RadioB
  • Daybeacon – unlighted beacon – color, shape, number “daymark” pile with mark
  • Daymark – the daytime identifying characteristics of an aid to navigation
  • Buoy – floating device moored or anchored to the bottom as an aid to navigation
  • Can Buoy – unlighted buoy, upper above waterline is a cylinder shape
  • Nun Buoy – unlighted buoy, upper above waterline is cone shape, vertex upward
  • Lighted Beacon – a beacon exhibiting a light
  • Lighted Buoy – a buoy exhibiting a light
Navigational Aids: the IALA Maritime Buoyage System, Navigational Aids: the IALA Maritime Buoyage System

Color and Light Identifiers

  • Color, Shape, Number
  • Green Lighted Buoy, Red Lighted Buoy
  • Green Can, Red Nun (Buoys)
  • Green Daymark/Daybeacon, Red Daymark/Daybeacon
  • Green Fixed Light, Red Fixed Light
  • Preferred Channel to Starboard – Topmost Band Green
  • Preferred Channel to Port – Topmost Band Red
  • Midchannel Mark : ( / Safewater Mark / Sea Buoy RW Vertical Stripes A dot dash
  • Inland Water Traffic Signs
    • Boats Keep Out, Danger, Controlled Area, Information
    • Mooring Buoy white, blue horizontal stripe – only one can tie to boat
    • Divers Down Flags
  • Isolated Danger – double ball topmark black with at least one red band Fl(2)
  • Intracoastal Waterway
    • Double Yellow triangles – pass this by keeping it on your starboard (right)
    • Double Yellow squares – pass by keeping this on your port (left)
  • Information and Regulatory
    • Orange pattern on white background, advise/control, white light, letters, any light pattern except quick flashing and flashing(2)
      • Orange diamond with cross – don’t go there / don’t do that, boat exclusion zone, swim area, dams, rapids
      • Orange diamond – danger – open diamond, wrecks, rocks, dam, shoal, our Vilano Bridge
      • Orange circle – controlled, or restriction, as in speed or wake
      • Orange square – information or regulatory, manatees, pump out, directions, distances, locations
    • Boats Keep Out, Danger, Controlled Area, Information
  • Range Dayboards
    • Various colors, letters, a PAIR of ATONS, line up for centerline or lane.


  • Flashing – (Fl) light period is shorter than the dark phase
  • Isophase (Iso) periods of light and dark are equal
  • Occulting (Oc) period of light is longer than the dark phase
  • Group (Fl3, Fl 1+2), (Oc 2+3) periods of light or dark are grouped into patterns

The System

  • Red Right Returning – returning from the sea, red even are on starboard right side of channel, green odd are on port left side of the channel.
  • Numbers on the mark ascend when traveling from the sea to the harbor
  • The numbers get larger as you travel upstream

Intracoastal Waterway

  • For the sea buoys that delineate channels off the coast of the United States, and for the Intracoastal Waterway (ICW), red is on the right (shore side) when proceeding clockwise around the U. S. from the East Coast to the Gulf Coast, or proceeding north along the West Coast.
  • ICW marks are further identified by a small yellow reflector at the bottom of the mark. 
  • Numbers ascend traveling clockwise around the US
  • Where the IALA-B and ICW marks meet, watch for the change

Diamonds – Dayboards

  • Helps determine location on a chart
  • May be lettered, may be white lighted, color reflects nearby lateral marks
Navigational Aids: the IALA Maritime Buoyage System, Navigational Aids: the IALA Maritime Buoyage System

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