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Backpacker Magazine – May 2010

Navigation: Lakes and Oceans

Triangulate, forge through wind, and learn the tides with these water-bound navigation tips.

by: Kristin Bjornsen and Dougald Macdonald



clutch skill
Master the Rule of Thumb
Even if you can see your destination across a broad lake or bay, gauging its distance is tough. That info is critical, however, in the face of changing tides, incoming storms, or impending darkness. You can estimate the mileage to a landmark—such as a cliff, island, or the mouth of a bay—using your thumb.

1. Determine the landmark’s width using your map (for example, a 600-foot-wide island). Now, with your right eye closed, stretch out your arm and hold your thumb upright so its right edge lines up with the right side of the landmark. Then close your left eye and open your right one; note how far the right edge of your thumb moved to the left. All the way across the landmark? Halfway? Twice as far?

2. The distance to that landmark is about 10 times the distance that your thumb shifted—thus, the phrase "rule of thumb." (The reason: Most people’s arms are 10 times longer than the distance between their eyes, which, when you work out the geometry, yields the rule of thumb.) If your outstretched thumb moved halfway across the 600-foot-wide island, your distance away is about 3,000 feet—600 divided by two, times 10. Depending on the individual, the factor may be closer to 11 or 9, but your estimate will still be in the ballpark.

Triangulate Your Position
With a map and compass, you can pinpoint your position on a lake or bay. First, grab a true bearing on a landmark you can positively identify on the map—say, a lighthouse at 300 degrees. Draw a long, 300-degree line through the landmark. (Notice the line could also be considered a 120-degree line. This is called the back bearing—300 minus 180 equals 120.) Repeat this with another landmark, ideally about 90 degrees apart from the first. Where the two lines intersect is your location.


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READERS COMMENTS

Star Star Star Star Star
AZ Hiker
Mar 01, 2014

Navigate using your compass! When you lose sight of the trail and landmarks, stay found by using a compass and reading Felix the Sugar Glider Be Safe Hike Smart (Amazon). This book makes learning how to use a compass easy. Before you hit the trail, be sure to calibrate your compass to the declination of where you will be hiking or skiing. Go to: http://magnetic-declination.com. A compass doesn't need satellites, a signal, or batteries and works in all types of weather, day or night, but you need to know how to use it. Look for it on Amazon, "Felix the Sugar Glider Be Safe Hike Smart". Learn how to orient yourself using a compass, a compass and a map, a map and no compass, no compass and no map. The ability to know your way and know where you are is something we all need in any survival situation not just while hiking and skiing. Learn to stay found by using a compass and paying attention to your surroundings. Learn what to do if you get lost, how to get rescued, and survival packing (for the car and for the trail) just in case you end up unexpectedly spending the night outdoors.

Star
Liam
Feb 28, 2014

With any kind of luck if you are BACKPACKING you will not find yourself on a lake or an ocean.

Star
Liam
Feb 28, 2014

With any kind of luck if you are BACKPACKING you will not find yourself on a lake or an ocean.

Anonymous
May 13, 2011

If you followed the directions, eye dominance doesn't matter

n.t.
Sep 25, 2010

Some people have dominant left eye, thus their thumb will "jump" to the right using this method.

n.t.
Sep 25, 2010

Some people have dominant left eye, thus their thumb will "jump" to the right using this method.

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