The Importance Of Dead Reckoning

First of all, what is Dead Reckoning?

From Wikipedia – “In navigation, dead reckoning is the process of calculating one’s current position by using a previously determined position, or fix, and advancing that position based upon known or estimated speeds over elapsed time and course. “

For hikers, we are concerned with knowing how long it takes us to go from point A to point B.

For example, let’s say that I am walking on the Pacific Crest Trail from mile 300 to mile 306. If I walk 2 miles an hour , this 6 mile distance will take 3 hours. If I walk at 3 miles an hour, this distance will be walked in 2 hours.

This is an easy skill, and there is really no excuse to not have it in your navigation arsenal.

If you have ever asked a hiker walking towards you (i.e. coming from the opposite direction on a trail) what the distance is to a specific landmark (campsite, water source, road crossing, etc), you know how poorly some people estimate that distance. The bad estimation could be caused by one of the following: not knowing what time they were at the landmark, not knowing their pace, or that they simply do not know how to use dead reckoning.

Most hikers learn how many miles they can walk in a day, and this is a first step to understanding dead reckoning. The importance of understanding and applying dead reckoning is a great skill in navigation. Knowing where you are, whether you are using map and compass or not.

Lots of hikers on the National Scenic Trails are regularly checking their app to know where they are. Before I go further, let me say that I am not poo-poo-ing the use of an app like Guthook/Atlas Guides – on the contrary, these are excellent, and I recommend them to be included in your arsenal of navigation tools. Right along with them, you should be able to use dead reckoning. Why? You may not always have the app available on certain hikes, the phone battery may die, or you may simply need to conserve the battery on your device.

Dead reckoning (and fairly precise DR) became extremely important to SweetPea and I on the Grand Enchantment Trail this spring (there is no hiking app for this trail). This trail is more of a route, and has cross country travel, wash walking, trail walking, dirt road walking, and all of the above in various terrain – rocky, steep elevation, plodding down rivers, super sandy – and with very little if any signage telling us when to take a turn, switch trails, etc. Often,  if we had a distance that we needed to walk after entering a new feature, say a wash – we would discuss the time that we expected to get to our next landmark, say a side wash that we needed to exit the primary wash on. Since there would be other side drainages coming into the main wash where we were walking, we didn’t want to take these others prematurely or miss our wash…especially when the terrain was fairly indistinguishable on the map.

So, if it was 1:30pm as we entered a wash, and knew that we had 2.5 miles of walking in the wash before reaching a different drainage that we would need to turn into, we could then make some estimates about when we would reach that 2.5 mile mark. If it looked like the wash had fairly even walking and the wash wasn’t so sandy that we’d be slowed down from a max pace of 3 miles per hour, we could estimate our time to reach that next drainage: 50 minutes. Each tenth of a mile for a 3 mile an hour pace is walked in 2 minutes. Each mile is walked in 20 minutes.

In my mind I do the math this way.

• 2 miles. completed in 40 minutes.
• 5 tenths times 2min equals 10min. 10 plus 40 = 50 minutes.

Admittedly, you may get into this 2.5 mile segment and realize that you are walking slower for some reason, and this actually happened to us quite a bit on the GET. It is no big deal, we would use adjust our mph estimate…and recalculate.

When on an easy walking trail (much of the Pacific Crest Trail) or a rather consistent trail where a very steady pace can be kept, you will be surprised how remarkably accurate dead reckoning can be. On decent trail, 3 miles an hour is a comfortable pace for me. For SweetPea it is closer to 2.5 (we are about a foot difference in height).  If we were walking for an hour, we would generally be within a couple minutes of the 2.5 estimate (walking together at SweetPea’s natural pace).

Generally, I try not to get hyper specific with the pace. I estimate by half mphs and then may add a fudge factor. Ex. A fast 2.5 mph. A low 3mph. You may be better at quickly calculating how long it takes you to hike 4.7 miles at a 2.8 mph pace – I guess you can even whip out the calculator on your phone (hmmm, maybe not a bad idea to get really good at this)…But, I tend to do the math to 3mph, and then fudge it down to a bit less to get an overall estimate.

The more that you practice this skill , the better you will get – even when you are walking someone else’s pace. One helpful hint when starting out is to make your estimates before you hike through a section rather than start walking and try to remember the time that you left and how fast you have been walking.

In general, it:
1) start from a known spot
2) note the time
3) make an estimate about your speed expectancy
4) do the math, calculating your expected arrival at the next landmark.

If you are completely new to this idea of DR, you can simply walk for an hour and calculate how far you have waked. You can easily do this is on a road walk or on a trail. You could use an app like GAIA GPS or OSMand, walk for an hour and then check the distance you walked over that hour as a baseline. *Note – GAIA and OSMand are free when using this basic function.

If you do this on a road, you will most likely walk faster…don’t fool yourself, thinking that this will be your pace on a hiking tail. I can walk 4 mph on a road, but it is a pretty big push to do that on a trail for any significant amount of time unless it is super smooth and even (and I really feel like hammering down).

We started hiking in the pre-smart phone app age and have been day hiking since the mid 90s with regularity. Hiking around our home in New Hampshire and doing the same routes, and loops over and over again in the White Mtn National Forest helped us learn dead reckoning without much effort. Once on the AT for our first hike in 2011, we started to use DR to know when we would be arriving at a water source or our expected time to hit a road crossing for bonus pizza lunch. DR can put a mind at ease, by just having an expected arrival time at a location….if you know it is going to be dark before you arrive somewhere then you simply expect it, rather than racing your self into a frenzy.

Edit – It occurs to me that there are some safety-oriented reasons to know how to use dead reckoning competently. If you happen to be hiking with someone who gets injured or you come across an injured hiker, being able to give an approximate location could be extremely helpful. When we are in a stressful situation, our sense of time, distance and speed can all become a bit warped, particularly when we are walking in an area for the first time – nearly always the case on a long trail. Doing a legitimate check of the time when leaving the injured person and knowing what your ‘hustle’ pace is, can help search and rescue approximate someone in the backcountry more accurately.