When using a range, you will maintain an imaginary line drawn between yourself and your distant target. If you are still "on range," the near target, in this case the buoy, will be located on that line. However, if you are drifting in the current, the buoy will drift off that line.

When crossing current, you must adjust the ferry angle to ensure that the buoy remains on the line drawn from your boat to the tree. See the animation of crossing a current using a range for a demonstration.

For example, let's say that you have chosen a ferry angle that is too large. In the demonstration window, click the button "Too Much Ferry Angle:" you'll see that the buoy shifts downstream from the range line. This shift means that you are heading too far upstream and should reduce your ferry angle.

Alternatively, perhaps you did not realize there was a crossing current and started across without ferrying. Click the button "No Ferry Angle" and watch the buoy shift upstream from the range line. This drift means that you are losing ground and are being swept downstream from your desired target. To compensate, increase your ferry angle.

The goal, obviously, is to choose the ferry angle that properly compensates for the current. Click the button "Correct Ferry Angle:" the buoy remains on the range line. When both your targets remain aligned, you are maintaining your range and are still on course.

The most important aspect of selecting a range is that the distant target must be very near your desired heading. Using ranges does not work if you do not want to follow the range line.

When selecting a distant target, you can use any fixed object near your desired heading. If you can't see a house or a buoy, use a peak or dip on the horizon line, a light-colored rock, or a dark spot in the fog. Use anything that you'll be able to pick out easily while crossing the channel.

To select the near target, choose any fixed object that lies on or very near the range line. Lobster buoys, the edge of an island, or an anchored boat will work as long as the object is fixed. Again, use something that you can quickly pick out while paddling.

Once you reach the near target, you'll need to select another. For this reason, it is often better to select a "near target" that is some distance away.

If you cannot identify an appropriate near target, do your best to estimate the required ferry angle. Check your progress as you cross by taking compass bearings to your target. These bearings should remain the same throughout your crossing; if not, adjust your ferry angle accordingly.

For a much more extensive treatment of crossing currents and using ranges, read David Burch's wonderful book, Fundamentals of Kayak Navigation.