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Aiming Off – A Compass Navigation Technique

Aiming Off Compass Navigation
Aiming Off Compass Navigation

Aiming off is a cross-country navigation technique for finding a destination like a shelter or a landmark that is located along a natural or man-made landscape feature (also called a linear feature) like a stream, a ridge, or a path. Instead of setting a bearing directly for your target destination, the idea is to follow a bearing that is deliberately set to the right or left of it, so you know which way to turn when you reach the linear feature.

This is a particularly useful technique in bad weather such as mist or rain when you can’t see your destination, when your view of the destination is blocked by tree cover, or the contour of the land is relatively flat and you can’t use slope angle to determine which way to turn when you reach the linear feature.

Most off-trail hikers also experience a 0-4 degree drift when following a compass bearing that makes it unlikely that you’ll hit a point on the map dead-on instead of walking past it to the side. Aiming off helps negate the impact of this variability and puts you at a known location close to your target

To illustrate, let’s say we’re standing on top of a peak named Ragged Jacket and we want to hike off-trail to the Blue Brook Shelter*. If we set a direct course to the shelter, we’d be walking along the 330 degree true bearing on the left, above. If we miss the shelter by walking past it on either side and reach the trail it’s on (dashed line), we don’t know whether to turn left or right to get to it.

If instead we aim off, and follow the right-hand 350 degree true bearing shown above, we’ll intersect the trail that the shelter is on to its right, and from there we know then to turn left to reach the Blue Brook Shelter.

Cool, huh?

* This is an old map and should not be used for navigation purposes. The Blue Brook Shelter shown here has been dismantled and moved to another location in the White Mountain National Forest. 

 

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12 comments

  1. We’ve employed this technique many times in the backcountry, it is very useful.

  2. So true, so true. It is a horrible feeling to know you are on the right trail and not know which way to go.

    But I would have picked a leftward bearing since there are three fantastic features to key off of (trail, stream, fork in stream) instead of just one (trail). Some trails can be missed as you cross them (esp in the dark) but water (even dry stream beds) is harder to miss.

    • I picked the aim-off route I did more for conceptual simplicity than anything else and because I wanted to emphasize a simple linear feature (the trail) as a backstop. But you are absolutely right, trails are easy to miss in the dark or when covered with snow. Amir and marco also make good points below

  3. Have used this technique for years, it plain works. Note that in this case, the 350 bearing less you to a point a little higher than the shelter, thus saving you energy too, as you are going downhill. Good choice. An altimeter could be handy to alert you of the vicinity of the trail, if visibility is not very good.

  4. Good technique. This is fairly standard for off-track and canoe routing. But it is not intuitive. Typically new users will point AT where they want. Without good visibility, this is a problem. Note that hiking down a small stream is often quite difficult. Blowdowns often criss-cross it making it nearly imposible to hike. I think I would have chosen Phil’s track, instead of trying to do that. Mostly trees fall down-hill, soo avoiding the gully (where there is likely more) would be a better choice.

    Try visualizing 30′ trees laying on the ground based on the direction of the slopes on the map.

  5. I’ve done it many times. My father taught me this about fifty years ago. He was the navigator on a B-24 in the Pacific Theater in WWII and this saved his crew on a mission.

    They’d gotten separated from the rest of the squadron in the fog of the battle and had their antenna shot off and thus had no radio or IFF (Identification Friend or Foe). Trying to return at night, my father couldn’t get an accurate enough star fix to fly directly to their base so he elected to fly to the chain of islands to the west and island hop to get in. Clouds build up over the islands and when they saw a string of clouds in the moonlight, they knew they were at the archipelago and made their turn. Their next problem was they were flying the course the Japanese came to bomb them, so they knew a Black Widow would be scrambled to intercept. The pilot had everyone turn on the lights, get to the windows, smile and wave. Soon they saw the night interceptor–he rocked his wings and signaled for them to follow him. Two of their engines quit on touchdown. The other two had only two gallons of fuel available each. They had been reported shot down by the rest of the squadron.

    I wouldn’t be writing this if not for aiming off.

  6. And if the Japanese aim had been a little more off, I wouldn’t have had such a good example of this technique. Of course, had their aim been a little more on, I still wouldn’t.

    …and… Thanks, Phil!

  7. I often think of hand rails and backstops but hadn’t considered this before, so thanks.

    I also think that keeping a quick and dirty log of time traveled, bearing held, and features encountered is essential.

    my single biggest problem is determining if a stream I encounter is the one shown on my topographic or just a feeder that is not called out.

    • I’ve always found a watch to be indispensable for figuring out where I am and as I get more and more into off trail travel, I’m getting better at preplanning different route options by drawing bearings on my map in advance to save having to record it in the field.

      Streams are hard to figure out. Same with hills or drops that are too small to show up as a contour on a topo. The date of the map is also a factor since the land can change after the map has been published (as can the declination).

  8. I’m sure Irene also enhanced the obsolescence of a few topos in New England.

    Ditto on the watch. Mine also has an altimeter, which I set to the elevation at the trailhead. It’s helped me several times to identify a feature on the map because I could cross check with elevation. When the weather is changing, all bets are off on the altimeter reading after a while, at least until I’m at another known elevation.

    Also, If the wind is strong, the windward side of a ridge will show lower than actual elevation because the air pressure is higher on that side. Conversely, the lee side will have higher than actual elevation readings.

    The above is also a factor in mountain flying. There is a safety margin in approaching ridges with the wind. The updrafts are on that side and the altitude shows lower than actual so when the pilot adds his clearance factor in, there will be a higher margin. Approaching a ridge into the wind subjects the plane to the downdrafts, which may exceed the airplane’s ability to climb, more turbulence and rotors, and an inaccurate altimeter making the pilot believe he’s higher than he really is.

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