2.2 The U.S. Aids to Navigation System: Lateral Marks (IALA Region B)

The U.S. Aids to Navigation System: Lateral Marks (IALA Region B)

Quick Answer: In the United States (IALA Region B), "Red, Right, Returning" means you keep the red marks on your starboard side when returning from the sea toward a harbor or heading upstream. Red marks are even-numbered nuns with triangular daymarks; green marks are odd-numbered cans with square daymarks.

Lateral marks are the backbone of buoyage. They tell you which side of a channel you are on and which way the safe water lies. Expect several questions on them.

Region B and "Red, Right, Returning"

The international IALA buoyage system has two regions. The United States and most of the Americas are in Region B, where returning from sea you keep red to your right (starboard). Region A (most of Europe, Africa, Asia, Australia) is the mirror image. All U.S. navigable waters follow Region B except a few Pacific possessions west of the International Date Line and south of 10 degrees north.

The memory hook is "Red, Right, Returning." Returning means coming in from seaward toward the harbor, or more generally proceeding toward the head of navigation in the conventional direction of buoyage — the direction, printed on the chart, in which aids are numbered and colored. When you return, red marks stay on your starboard hand and green marks on your port hand. Going the other way — outbound to sea — the sides simply reverse, so a green mark you kept to port on the way in is now on your starboard side.

Reading a Lateral Mark: Color, Shape, Number

Lateral marks carry three reinforcing clues:

So a green, square "7" is a can-type port-hand mark; returning from sea you keep it on your port side. A red, triangular "8" is a nun-type starboard-hand mark; you keep it on your starboard side. The numbers increase as you return from seaward, which helps you confirm you are heading the right way: if the numbers are climbing, you are returning.

A useful reinforcement: a nun (cone) points up like the triangle on a red daymark, and both are red and even. A can is flat like the square on a green daymark, and both are green and odd. Even the phonetics help many students: "even RED nuns return."

Worked Scenario

You are entering an unfamiliar harbor from the open sea at night. Ahead and slightly to port you see a flashing green light; to starboard a flashing red light. Because you are returning, you keep the red to starboard and the green to port and steer between them — you are correctly lined up in the channel. If you saw the numbers decreasing, you would know you had turned around and were heading back toward the sea.

A caution about trusting a single buoy: floating aids are moored by a chain to a sinker and can be dragged off station by storms, ice, or a collision, or their light can fail. Good practice is to treat a buoy as an approximate mark, confirm it against the chart and the numbers of nearby aids, and never fine-tune your position on one buoy alone. Fixed structures such as lighthouses, range towers, and pile daybeacons are more reliable references than floating buoys.

Preferred-Channel (Junction) Marks

Where a channel splits, a preferred-channel or junction mark shows the primary route. It has red and green horizontal bands, and the color of the topmost band identifies the preferred channel:

• Top band red — treat the mark like a red (starboard-hand) mark for the preferred channel: keep it to starboard when returning, so the preferred (main) channel is to the left of the mark.
• Top band green — treat it like a green (port-hand) mark: keep it to port, with the preferred channel to the right.

The buoy shape and any topmark match the top band (nun/triangle if red on top, can/square if green on top). Because a junction mark can also be passed on the non-preferred side, it is a decision point, not a hard boundary. Its light is a composite group-flashing (2+1) rhythm — two flashes then one — in the color of the top band. Preferred-channel marks are usually lettered, not numbered.

The Intracoastal Waterway (ICW)

Marks along the Intracoastal Waterway carry a small yellow reflective triangle or square in addition to their normal lateral color. When traveling the ICW in the conventional direction (generally southward along the Atlantic coast and westward along the Gulf coast), keep any mark bearing a yellow triangle on your starboard hand and any mark bearing a yellow square on your port hand — regardless of the mark's underlying red or green color. This lets the ICW share aids with local channels that may run the opposite way. Lights on lateral marks always match the mark's color: red lights on red marks, green lights on green marks, in flashing, quick, occulting, or isophase rhythms detailed in the next section.