Lateral marks: how buoys identify a channel

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Lateral marks: how buoys identify a channel

Lateral marks indicate the sides of a channel. They mark its port and starboard sides; these terms refer to the conventional direction of buoyage. A buoy therefore cannot be reliably identified by its color alone. In the international IALA system, color assignments depend on whether the area is in Region A or Region B.

Channels and the direction of buoyage

The conventional direction of buoyage is the direction in which lateral marks are read. It generally runs from seaward into a harbor, river, or estuary. The responsible authority may designate a different direction for a waterway; it should be indicated on the relevant nautical charts and in nautical publications. Familiarity with the terms channel, fairway, and area makes it easier to distinguish the function of lateral marks from the mere outline of a navigable area. “Port” and “starboard” describe the sides relative to a vessel proceeding ahead, not a fixed shoreline side that applies everywhere; nautical directional terms help clarify this distinction.

Region A and Region B

In Region A, a red buoy marks the port side and a green buoy the starboard side when following the direction of buoyage. In Region B, the colors are reversed: green indicates port and red indicates starboard. These color pairings apply to the lateral marks used in each system. For a specific waterway, the designated region and the direction documented for that area are what matter.

Shape and topmarks

The design also helps with identification. IALA recommendations describe cylindrical or can-shaped marks as port-hand marks and conical marks as starboard-hand marks; where the shape does not clearly serve as an identifying feature, an appropriate topmark should be used where possible. A cylindrical topmark identifies a port-hand mark, while a single cone pointing upward identifies a starboard-hand mark. Color, body shape, and topmark therefore work together to indicate which side a mark belongs to. Not every mark must display all these features, and a topmark may be absent.

When a channel divides

At a junction, a special lateral mark may indicate the main or preferred route designated by the responsible authority. It retains the basic color of the region’s system and carries a broad horizontal band in the contrasting color. A cylindrical topmark indicates a preferred channel to starboard, while a cone with its point upward indicates a preferred channel to port. This special mark does not simply mean “turn here”: its interpretation still depends on the region and the direction of buoyage. It should be distinguished from other navigational marks, such as cardinal marks and isolated danger marks, which serve different warning and orientation functions.

The nautical chart remains authoritative

The IALA system provides internationally harmonized marking, but it does not replace information for a particular area. Safe interpretation depends on the region in force there, the direction of buoyage shown on the official nautical chart or in nautical publications, and the local marks. A general color rule is therefore a guide to understanding the system, not an instruction for navigating a specific course.