So what do you do if your GPS batteries die, you can’t see terrain features and there is no trail system to get you back to camp? Navigation expert Blake Miller gives some tips about the dead reckoning navigation technique
by Blake Miller
It is time to return to base camp. Navigation during this trip has been by map and compass alone; no GPS. During the three days of the outing, navigation was straightforward and simple. Visibility was excellent and compass triangulation worked well. Now as the return trip is about to begin, fog has rolled in, masking terrain features. The absence of a reliable trail system will make the return trip challenging as well; travel will be overland.
A process called Dead Reckoning (DR) can be used to navigate and partially compensate for the loss of terrain features and important visual cues. DR is a method used to determine one’s estimated present and future position. Dead Reckoning can be done during periods of darkness, bad weather, in featureless terrain (e.g., the desert, whiteout conditions) or equipment failure (e.g., dead GPS batteries.)
DR is a method of navigation that dates back hundreds of years. It works well on both land and sea. It is nothing more than moving in a set direction of travel over a specified distance. By looking at a map, the hiker determines a direction of travel and attainable distance. As illustrated in Figure 1 below, travel is plotted on a map; frequent verification is important.
Figure 1
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Factors that limit the accuracy of Dead Reckoning are the hiker’s ability to walk a straight line over rough terrain, varying elevations and the ability to accurately calculate distance. For short hikes these limiters provide an acceptable degree of accuracy. Long, extended hikes of several miles must be updated on the map as the hiker obtains position fixes. The estimated position plotted is just that, an estimate. The hiker will be in the vicinity of the estimated position.
The tools needed include a quality, declination adjustable compass (such as the Silva 515CL) and topographic maps. My preference would be to have a U.S. Geologic Survey (USGS) Map (scale of 1:24,000) and a representative Forest Service or BLM map of the area. The USGS map provides the “zoomed in” details while the other maps provide a broad overview of many USGS maps but without the detail. Lastly, bring simple map tools such as a pencil, a small straight edge and a flat writing surface for support.
The personal skills needed include a solid foundation in the use of a map and compass, and the ability to pace count for hundreds of yards.
To start the Dead Reckoning process, the navigator begins from a known position fix; this is essential. A known position can be obtained through compass triangulation and map association. An operable GPS will provide acceptable position data.
Figure 2
In the example (Figure 2), the position “Start” was obtained by map association and was identified as the junction of two dirt/gravel roads. Other examples include the intersection of a road and stream, a trail crossing a road, or a trail and stream. Further, a single line of bearing was taken and plotted from the intersection to the top of Mahogany Butte. This plotted line of bearing is confirmation that “Start” is the beginning position. Using the basic map tools, the hiker should begin to update/mark up the map. From “start” mark the map the direction and distance of the intended track.
As the hiker moves out, he carefully monitors his track on the map. Distance traveled is determined by pace count or time traveled. Use the map scale information at the bottom of the topographic map to accurately plot the distance traveled. Neither method is precise.
Ideally, the plot is updated every thirty minutes but no less than hourly.
The plot should also be updated at every change of direction and rest stop. See Figure 3.
Figure 3
To improve the accuracy of the plotted DR, the hiker should be alert and take advantage of terrain association. If weather permits, visually catch terrain features and hand rails (hand rails include linear features such as roads, streams, ridgelines, fence lines, and manmade structures). Hand rails must be visible on the map to be of use.
Dead Reckoning is a process of collecting data (course and distance traveled) that is plotted on a map to determine an estimated position. It takes practice. DR is a method that will help keep you focused on navigation, keeping you safe and found.
Blake Miller
Blake Miller has made a career out of staying found and knowing where he is at all times. His formal navigation training began when he joined the U.S. Navy in 1973. He served as an officer aboard several Navy ships over his twenty-year career; many of those tours included the duty of Navigator. Blake began working with satellite navigation systems at sea in 1976, culminating with the then-new Global Positioning Systems aboard the Battleship WISCONSIN in early 1990.
In 1998 Blake started Outdoor Quest, a business dedicated to backcountry navigation and wilderness survival. Blake has taught classes to wild land firefighters, state agency staffs, Search and Rescue team members, hunters, hikers, skiers, fishermen and equestrians. He regularly teaches classes through the Community Education programs at Central Oregon (Bend) and Chemeketa (Salem, OR) Community Colleges.
As a volunteer, Blake teaches navigation and survival classes, to students in the local school district and conservation groups. He is a member of a Search and Rescue team.
Contact Information :
Website: www.outdoorquest.biz;
Phone: 541 280 0573;
Email: outdrquest@aol.com
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