Day beacon

They are the most common navigation aid in shallow water, as they are relatively inexpensive to install and maintain.

When proceeding from open water towards harbor, marks with cylindrical topmarks or square dayboards are kept to port in both regions, but colors and numbers are reversed.

Interior or exterior placement can be determined based upon the passing side (port or starboard) dictated by beacon designation.

However, a current chart should always be consulted for all but the shallowest-draft vessels, as channel conditions are rarely ideal.

This makes them meaningful regardless of the direction or position of the approaching vessel, in contrast to the lateral mark system.