Tutorial: Dead-reckoning navigation | Basic but oft-used skill

Dead-reckoning is the simplest navigation skill. It’s much easier to learn than reading a map, or operating a compass, GPS, or altimeter watch.

Yet I find it to be one of the most useful and frequently used, especially when hiking on well-maintained trails where a consistent physical effort yields consistent results. Such trails include well-known long-distance footpaths (e.g. Appalachian, John Muir, Wonderland) and most trails in National Parks and high-use Wilderness Areas (e.g. Yellowstone, Indian Peaks).

This technique is less useful when hiking off-trail or on trails with extreme vertical change. Off-trail terrain is more variable (i.e. it’s sometimes great, sometimes awful), so results are less predictable. And in extremely mountains environments, forward progress is more a function of vertical hiking speed (e.g. 30 vertical feet per minute), and the horizontal distance over which this vertical change happens is less relevant (if not entirely irrelevant).

Benefits

I use dead-reckoning to:

  • Predict ETA at future landmarks, like water sources, trail junctions and campsites;
  • Approximate my current location relative to the last or next landmark; and,
  • Rule out “false” features like false summits and unmarked trail junctions.

In general, regular dead-reckoning helps to to “stay found” because it sets expectations about what should be happening. If reality does not match expectations (e.g. did not reach a landmark when expected, or reached a different landmark than expected), it’s a cause for a map-check.

Tools

To dead-reckon, two out of three following items are needed:

  • Distance between two landmarks, derived from a topographic map, databook, or guidebook;
  • Rate of travel, which can be measured (e.g. with a GPS unit) or calculated on past trips; or,
  • Time, using a simple watch (although if you want to get serious about backpacking, I recommend a GPS sports watch).

Advanced tip: In mountainous environments, it is useful to know the vertical change between two landmarks, because this factor may influence your calculations. Vertical change between two points can be quickly measured on a map so long as the gradient is consistently up or down; in rolling terrain, vertical change calculations are more time-consuming.

How to dead-reckon

You might recall this formula from high school physics: Distance = Rate * Time, whereby:

  • Distance = miles or kilometers
  • Rate = MPH or KPH
  • Time = Hours

The main formula can be reconfigured to solve for other variables:

  • Rate = Distance / Time
  • Time = Distance / Rate

To dead-reckon, essentially you insert two known variables to determine the third.

Tip: It’s useful to remember that 2 MPH = 30 minutes/mile; 2.5 MPH = 25 minutes/mile; and 3 MPH = 20 minutes/mile.

Examples of dead reckoning

1. I’ve been been walking non-stop for 1:20 minutes from my last known landmark, Crystal Spring. On this kind of rolling terrain, I generally walk at around 3 MPH. I’m planning to camp at Buchanan Creek, which is 5.5 miles from Crystal Spring, per my guidebook. How much further until camp?

Using the formula Distance = Rate * Time, I calculate that I’ve walked about 4 miles (3 mph for 80 minutes). That would leave 1.5 miles to camp.

2. Today is the first of a 3-day trip with two new guys I met on an ultralight backpacking forum. Normally I walk at 3 MPH, but our pace feels much slower than that — these guys have dialed kits, but it looks as if they never actually do any hiking. A 5-mile section of easy trail takes us 2.5 hours.

Using the formula Rate = Distance / Time, I calculate that we’re walking at about 2 miles per hour, or about one-third slower than my usual hiking pace.

3. My databook says that it’s 2.5 miles between Pawnee Lake and Pawnee Pass, and I know that I normally hike at 3 MPH. Using the formula, Time = Distance / Rate, I determine that it should take me 50 minutes.

However, these two landmarks are separated by 2,500 vertical feet, and yesterday on a similarly steep section of trail I climbed at about 25 vertical feet per minute. So I adjust my expectations: rather than 50 minutes, it will take about 100 minutes (2,500 vertical feet divided by 25 vertical feet per minute).

The post Tutorial: Dead-reckoning navigation | Basic but oft-used skill appeared first on Andrew Skurka.

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