How to Read Preferred Channel Buoys and Dayboards

By World Wide Marine Training

How does the U.S. Coast Guard mark the junction of two navigable channels? When a secondary channel intersects on the side of a main channel that is marked with red dayboards, what do you do with the green “1” in the secondary channel? If the intersection is on the green side, what do we do with the number “2” red?

We use the colors red and green to guide us through the waterways.  Under what is called the “Lateral” system, red is on one side and green on the other. If we begin to “mix those colors up” every time two channels intersect, the result will be “chaos.”

While we always learn something from a situation that results in chaos, the Coast Guard might call that “learning the hard way.” In days gone by, intersections of navigable channels have been marked with either “junction” or “bifurcation” buoys. Neither of those terms is any longer in use.

Today’s channel intersections are marked with “preferred channel” dayboards or buoys. These Aids to Navigation display a color pattern like no others. Preferred Channel marks are both red and green.  They are divided horizontally, the upper half being one color and the lower half being the other.

The object of the two colors is to alert the mariner of a few issues.  First, that there is an intersection of two channels. Second, that depending on which of the two channels you are in, you will treat the preferred channel mark differently.

Preferred channel marks rely on the mariners understanding of the “Lateral System” of buoyage. We have all heard the phrase “Red Right Returning.” It reminds us that when “returning from seaward” and proceeding toward the “head of navigation,” we keep red aids to navigation on to our right.

The “head of navigation” is generally described in two ways. First, as the point in a waterway where loads are transferred between water carriers and land carriers. Second, as the point upstream or inland where a river is no longer navigable.

What it amounts to is that the head of navigation is as far inland as a vessel will carry you. Confusion arises when we are in a channel that does not lead either from seaward or to the head of navigation. An example would be the east-coast Intra-Coastal Waterway while traveling between inlets.

Due to such situations, and to maintain order on the waterways, the phrase “from seaward” is not always taken literally. In the continental United States, returning from seaward and toward the head of navigation is generally considered to be in a clock-wise direction around the continent.

That is, moving in a southerly direction on the east coast, westerly along the gulf coast and northerly on the west coast. That would explain why the east coast ICW traffic keeps red on the right, while southbound (generally). The practice of following these directions is referred to as the “conventional direction of bouyage.”

Back to the Preferred Channel Mark. When traveling in the “conventional direction of buoyage,” red and green marks with red on top indicate that the preferred channel is to port, while those with green on top indicate that the preferred channel is to starboard. Confusing? You bet it is! That’s why we keep charts on hand!

Until next time, we wish you clear skies, fair winds and calm seas!


World Wide Marine Training, LLC, is a U.S. Coast Guard Approved facility authorized to give examinations for captain’s licenses up to Master 200 Tons, Able Seaman up to Unlimited, STCW Basic Training, Radar, ARPA and other Endorsements. Please visit or call toll-free 866-249-2135.