Accurate and useful, a range is a line plotted through two visually prominent charted objects. The extension of that line into navigable waters (where it changes from dashed to solid on the chart) is a fixed line of position.
In many locations, ranges are deployed to help you navigate narrow channels. Two visual navigation aids sharing the same pattern, such as three colored bars, are spaced some distance apart, with the taller one in the back.
If you are in the center of the range, the two aids line up. If you are off the range, the aids are offset. If the taller one is to the right, you are to the right of the centerline. If the taller aid is to the left, so are you.
Maintained much like other navigation aids, these charted ranges are preplotted and labeled with the bearing along the line that goes through both aids.
Look for opportunities to plot or use charted ranges when you need help navigating a channel, running an inlet or checking your position using two easily identifiable charted objects.
By providing a convenient and accurate bearing, a range becomes a valuable tool for quickly checking your GPS. If you take a bearing on another visible landmark or buoy using your hand-bearing compass, you can quickly plot a fix using the existing bearing line.
You can also use a range to check your compass and determine its deviation. Simply maneuver your boat onto the range, making sure the near marker is precisely in front of the far one, and note your compass reading as you point toward the markers. Any difference between the range’s magnetic bearing and your compass reading is your deviation for that heading. –Bob Sweet
To learn more, take the Basic Coastal Navigation seminar at a squadron near you.