Table of Contents:

U.S. ATON System

Private Aids to Navigation

Safety Tips

Lateral System

Non-Lateral Aids to Navigation

Uniform State Waterway Marking System

Western Rivers Marking System

Visual Buoyage Guide

Nautical Chart

Bridge Lighting & Other Signals

ATON Abbreviations

USCG District ATON Offices

Report ATON Defects

Aids to Navigation — Road Signs of the Waterway

Lateral System (As Seen Entering From Seaward)

Port Side Odd Numbered Aids
green square Green Llight Only  
  Flashing (2) Illustration of patterns of flashing green lights for port side odd numbered aids.
  Flashing Flashing indicates single short flashes separated by pauses
  Occulting Occulting indicates single long flashes separated by pauses
  Quick Flashing Quick flashing indicates a very rapid sequence of single flashes
  ISO ISO indicates medium length single flashes
         
  Illustration of a green light, which is a green square with dark green border and a green numeral 1 in the center. The light is atop the square.
Light 		Chart mark for the light, which appears as a black circle with a magenta teardrop shape above it to the upper right side. First caption read "1" and second caption reads FI G 6 s. Illustration of a lighted buoy, which is a cylindrical green structure with a square in the upper left quadrant, a white numeral 9 in the upper right quadrant, and the light affixed atop.
Lighted Buoy		 Chart mark for a lighted buoy, which appears as a magenta circle with a green diamond affixed to the upper right side. First caption reads G "9" and second caption read FI G 4s.
         
  Illustration of a can, which is a narrow cylindrical structure with a square in the upper left quadrant and a white numeral 9 in the upper right quadrant.
Can		 Chart mark for a can, which appears as a clear circle with a green diamond affixed to the upper right side. First caption reads GR "A" and second caption reads FI (2+1) G 6s. Illustration of a daybeacon, which is a pale green square with a dark green border and a numeral 5 in the center, affixed to a pole.
Daybeacon		 Chart mark for a daybeacon, which appears as a green square. First caption reads GR and second caption reads C "S".

 

Preferred Channel No Numbers-May Be Lettered
Preferred
Channel To
Starboard
Topmost Band
Green
  green square Green Light Only
Composite Group Flashing (2+1)
Illustration of composite group flashing green light, which indicates two short flashes, followed by a medium pause and one short flash; the sequences are separated by a long pause.
         
 
Illustration of a lighted buoy, which has a green platform, with a rectangular structure that is red on the bottom and green on top. A square appears on the upper side of the green portion, and a white letter B appears on the right side of the green portion. A green light is affixed to the top. Chart mark for lighted buoy, which appears as a magenta circle with a diamond that is magenta on the bottom and green on top affixed to the upper right side. First caption reads RG "B" and second caption reads FI (2+1) R 6s.
  
         
  Illustration of a daybeacon, which is a square that is green on top and red on the bottom, with a corresponding border of dark green and dark red. The letter U appears in the center. It is affixed to a post.
Daybeacon		 Chart mark for daybeacon, which appears as a white square. First caption reads GR and second caption reads "U". Illustration of a can, which is a narrow cylinder that is green on the bottom, has a red band above the mid-point, and a green band above the red band. A square appears on the upper left side and a white letter S appears on the upper right side.
Can		 Chart mark for can, which appears as a clear circle with a diamond that is green on the top and magenta on the bottom affixed to the upper right side. The first caption reads GR and the second caption reads C "S".

 

Preferred Channel No Numbers-May Be Lettered
Preferred
Channel To
Port
Topmost Band
Red
  red square Red Light Only
Composite Group Flashing (2+1)
Illustration of composite group flashing red light, which indicates two short flashes, followed by a medium pause and one short flash; the sequences are separated by a long pause.
         
 
Chart mark for lighted buoy, which appears as a magenta circle, with a diamond that is green on the bottom and magenta on top affixed to the upper right side. First caption reads RG "B" and second caption reads FI (2+1) R 6s. Illustration of a lighted buoy, which has a red platform, with a rectangular structure that is green on the bottom and red on top. A square appears on the upper side of the red portion, and a white letter B appears on the right side of the red portion. A red light is affixed to the top.
  
         
  Illustration of a nun buoy, which appears as a narrow cylindrical structure with a tapering top. The structure is red, with a green band across the upper half. A red square appears in the upper left, and a white letter C appears on the right side of the green stripe.
Nun		 Chart mark for nun buoy, which appears as a clear circle with a diamond that is magenta on top and green on the bottom affixed to the upper right side. First caption is RG and second caption is N "C". Illustration of a daybeacon, which appears as a triangle mounted on a pole. The top half is red with a dark red border; the bottom half is green with a dark green border. A red letter G appears in the center.
Daybeacon		 Chart mark for daybeacon, which appears as a white triangle. First caption is RG and second caption is "G"

 

Starboard Side Even Numbered Aids
red square Red Light Only  
  Flashing (2) Illustration of patterns of flashing red lights for starboard side even numbered aids.
  Flashing Flashing indicates single short flashes separated by pauses
  Occulting Occulting indicates single long flashes separated by pauses
  Quick Flashing Quick flashing indicates a very rapid sequence of single flashes
  ISO ISO indicates medium length single flashes
         
  Illustration of a light, which appears as a red triangle with dark red border mounted on a pole. A red numeral 2 appears in the center and a red light is affixed to the top.
Light 		Chart mark for light, which appears as a black circle with a magenta teardrop shape above the upper right. The first caption reads "2" and the second caption reads FI R 6s.
"2"
FIR 6s		 Illustration of a lighted buoy, which has a red platform, with a rectangular red structure with a square in the upper left side and a white numeral 8 on the upper right. A red light is affixed to the top.
Lighted Buoy		 Chart mark for lighted buoy, which appears as a magenta circle with a magenta diamond affixed to the upper right side. The first caption reads R "8" and the second caption reads FI R 4s.
         
  Illustration of a nun buoy, which appears as a narrow red cylindrical structure with a tapering top. A red square appears in the upper left, and a white numeral 6 appears on the upper right side.
Nun		 Chart mark for nun buoy, which appears as a clear circle with a magenta diamond shape affixed to the upper right side. The first caption reads R and the second caption reads N "6".
R
N"6" 		Illustration of a daybeacon, which appears as a triangle mounted on a pole. The center is red with a dark red border and a red numeral 2 in the center.
Daybeacon

Lateral Aids to Navigation generally indicate which side of an aid to navigation a vessel should pass when channels are entered from seaward. In the absence of a route leading from seaward, the conventional direction of buoyage, generally follows a clockwise direction around landmasses. The most important characteristic of an aid is its color. The "3R" rule "Red Right Returning" is the essential rule of thumb for using the lateral system. This means that when entering one body of water from a larger body of water (i.e. returning to a harbor from a bay or sound), keep the red aids to starboard (right) side and green aids to port (left) side. In addition, each aid is numbered, and these numbers increase as entering from seaward.

Preferred Channel Marks are found at junctions of navigable channels and often mark wrecks or obstructions. A vessel may normally pass this aid on either side, but the top color band indicates the preferred channel. If the top band of the aid is red, it is treated as a red mark and kept to starboard as the vessel passes it while returning from sea. Caution: It may not always be possible to pass on either side of preferred channel aids to navigation. The appropriate nautical chart should always be consulted.
USCG red rod
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