US Navigation Buoys & Markers Explained (Red-Right-Returning)

Navigation marks are road signs for the water. The US runs on the IALA Region B system, and once a few rules click you can read almost any channel without thinking about it.

Red, right, returning

The one phrase to burn in: red, right, returning. Coming in from the sea toward a harbor, or heading upstream, keep the red marks on your right (starboard) and the green ones on your left. Going back out, you flip it. "Returning" is a convention rather than a compass heading; broadly it means heading in toward the harbor, and southward down the Atlantic coast.

The two lateral marks

Red marks are nuns, with a pointed cone on top, and they carry even numbers that climb as you come in from sea. Green marks are cans, flat on top, with odd numbers. The numbers are a running count of your progress and let you match a buoy to the chart at a glance. Lit versions flash red or green to match.

The others you'll meet

Safe-water marks wear red and white vertical stripes and mean navigable water all around, often mid-channel or at a landfall. Usually the first mark you spot coming in from sea.
Isolated danger marks are black with a red band and two black balls on top, sitting right on a hazard with clear water around it.
Special marks are yellow and flag things like anchorages, cables, or traffic zones rather than a hazard to dodge.
Junction marks wear red and green bands. The top color tells you the preferred channel under the red-right-returning rule.

Day beacons and ranges

Fixed marks on posts are day beacons: red triangles you keep to starboard returning, green squares to port. Line up a pair of them one behind the other and you've got a range. When they overlap, you're on the centerline of the channel.

Putting it together

Coming in from the sea, find the safe-water mark first, then keep the red nuns on your right and green cans on your left, watching the numbers climb. Cross-check every mark against the chart, because buoys drag off station in storms and don't always sit where they're drawn.

Pathr draws US buoys, beacons, and lights straight from NOAA data and shows where you sit relative to them in real time. See it next to live tide charts; it's free to try for two months on iOS.

Frequently asked

What does 'red right returning' mean?+

It's the rule for US (IALA-B) waters. Coming in from the sea toward a harbor or heading upstream, keep red marks on your starboard (right) side and green on your port (left) side. Reverse it heading out.

What's the difference between a nun and a can buoy?+

A nun is red with a pointed top and an even number. A can is green with a flat top and an odd number. Returning from sea, you keep nuns to starboard and cans to port.

What does a red-and-white striped buoy mean?+

Vertical red-and-white stripes mark safe water, with navigable depth all around. It often marks mid-channel or a landfall, and it's frequently the first mark you meet coming in from the open sea.