Other Types of Aids to Navigation
In the first section on navigational aids, we discussed buoys that indicate "laterality". These buoys mark safe water in a channel. There are other types of buoys which indicate the center of a channel , isolated danger marks, and regulatory buoys.
Preferred Channel Buoys are a type of lateral buoy since they indicate the safe channel. A preferred channel buoy is precisely that, it indicates which of two channels is the safest for transit. Preferred channel buoys have horizontally oriented red and green bands. The top band may be green or red, just as the bottom band. The buoy or day beacon is lettered, and never numbered. If the top band is green, then, just like the usual green can buoy the preferred channel is the one to starboard. In this way, you would be keeping the "red, right, returning" mnemonic in effect by keeping the mid-channel marker on your port side. If the top band is red, then you would keep this mid-channel buoy on your starboard side and take the channel to your port side. A preferred channel buoy is a lateral buoy in that it tells you the preferred route of passage.
Cardinal Buoys or Beacons are so named since they do not indicate laterality. Lateral Buoys indicate a channel for safe navigation. Cardinal Buoys indicate areas of danger, areas closed to vessel traffic or are informational in nature. Regulatory buoys are white buoys with two horizontally oriented orange stripes. Between these stripes, there is either a diamond or circle. Diamond shaped signs, may have the diamond crossed, or open. If the diamond is crossed, it indicates any area that you should not enter. Typically, there is an explanation under the diamond as to the reason for this regulation. It may be a swimming area, rapids or other danger. An open diamond is a warning buoy. It may indicate the presence of a rock, shoal, dam, wreck or other danger. Usually, the danger present is indicated under the diamond. A regulatory buoy with a circle indicates a controlled area. For example, at Lake Tahoe, Emerald Bay has a control limiting speed in the bay to 5 miles per hour. Like other regulatory buoys, the nature of the control is indicated under the circle.
Isolated Danger Marks are buoys that indicate a danger present in otherwise navigable waters. These buoys or beacons have horizontally oriented black and red stripes. The black stripe is on top of the red stripe. The buoy or beacon may be lettered and may be lighted. This buoy has an unique shape in that two vertically oriented black spheres are located above the body of the buoy. This buoy might be used to mark a rock or a wreck in an area that is otherwise navigable.