Following a bearing
We have a bearing we need to follow, we have a compass, we should be set, right? Not quite. With apologies to those first-person-shooter video games out there, we can't just follow the compass arrow like we do on a video screen. It takes a bit more than that.
First we need to identify an Attack point. We did this either from the map when planning our route, or we pick it when we're on the ground. This is where we want to get to. We met that in Route planning. Getting to a good attack point is easy - sight along the bearing, locate it and go there. Oh, if life were always that easy.
Sometimes we may not have a continuous view of the attack point. For example, we may go over undulating ground so it is not always visible. It is possible our attack point is somewhere over the horizon in Botswana, and we might get a little bit overwhelmed getting there. Importantly, if we are simply going off into the ether on a bearing and a mishap occurs, we might not be able to describe our position precisely enough. "30 degrees halfway to Botswana" is not very exact. It is a good idea to break a single long trek into legs. To do this, we sight to our eventual target and look for a closer, more tractable point along the intended line of travel. This is a steering mark. It is generally selected on the ground rather from the map otherwise, it would form an attack point in its own right. Once you reach the steering mark, you will need to pick another one and kind of caterpillar towards it ie. move from point to point setting new steering marks each time. Note you don't change your compass setting - the points you select should lie along the intended route. They can be tiny - tufts of grass, piles of stones, change in vegetation and so on.
In this example, I want to get from one fishing spot to another. My primary bearing to the attack point is 258° for a leg of 1550m. A casual scan shows that the left hand side of lake d'Encamp lies along my bearing. This is my first steering mark. From the lake, scanning further ahead along the bearing I see that there is a right-left steepening at the end of a plateau about 900m away. That's my next steering mark. From there I have clear line-of sight to my attack point, so all is well. Simple, huh?
A transit line is a navigational convenience. We can identify a transit line by taking a sighting on our target point, locating an intermediate point in line with us and the attack point, then put the compass away and walk keeping the intermediate and attack point in line. Effectively this is a steering mark that just happens to be perfectly in line with our intended course. Why do this? Basically it prevents us from meandering around. If you are simply aiming at a single point, there is a tendency to take a bit of an arced or sinusoidal path due to drift, your sore leg, change in elevation, the fact your parents were related and your left leg is shorter than your right, and so on. It is easier to keep the near and far landmarks in line as you walk.
Ideally, we want aiming points to be relatively distant to reduce the proportion of direction error to the distance covered. In restricted visibility, we need to improvise. If you are by yourself, you will have to just pick shorter mini-legs. You may end up sighting to little lumps in the ground in desert, or particular trees in jungle. They may not be very far away. This is less than ideal because of the error inherent in each bearing. You can think outside the box and use this procedure in reverse. If you are on a distinguishable feature, you can march as best you can on your bearing, ensuring you can see the microfeature you were on, and ensure the back bearing is correct. Basically navigating away from your temporary marker point using backbearings. It follows also that if there is no natural feature, you can make one such as a small cairn.
This brings us to leapfrogging... Under ideal conditions - great visibility, and intervening ground is visible, with at least some modicum of terrain features - caterpillaring along is pretty straightforward. We can generally see where we need to end up. When horizontal visibility is limited we are going to need to pay very careful attention to this. So why would visibility be restricted? Jungle, rain, fog snow, night-time. All conditions under which navigation is going to be tricky. Somewhat paradoxically, when visibility is great but the terrain is featureless such as on snow plains, flat desert we still need to work out a way to leapfrog for the same reason as above. We will meander if we have no clear aiming point. You can't just walk along looking down at the compass. Sorry to disappoint you video gamers out there.
Here's where the word leapfrog is pertinent. Above we went to our aiming point, then took another bearing to another point. Each time we took a bearing, we incurred some measurement error.
If you are part of a group, you can use one of them as a mobile marker. Send them out along your bearing, and guide them with 'Left', 'Right', 'Stop' (both arms out), 'Come to me' (both arms up), 'Come to me quickly, there's something really big and fast behind you' (running away at great speed). Once they are in line with your bearing, move to their position. It is preferable to send them as far as is practicable. Remember there is error with each bearing you take. If the aiming point (ie. the person who talks too much who you send away) is further away, then the proportional error with distance is less. Now for the leapfrog. Instead of sending them out again, leave them in position and move along the bearing as best you can, periodically looking back and taking a bearing on the patrol pariah. Make it clear to them beforehand, that their job is to stay still! I have seen folks decide to wander around, not really realising that their role is simply to be a temporary cairn.
Sometimes your attack point may either not be immediately visible or indistinct even when you get there. For example a track junction that may or may not be well marked, or a spot height on a relatively flat ridgeline. It is easier to hit a feature perpendicular (or close to it) to our line of travel, such as a ridge line, river, or track then locate the feature given inaccuracies of our target bearing and the indistinctness of our target.
In this example I've been totally lazy. I want to get from the base of a scree slope to a track junction, then head on the left track fork. Climbing up the side of a little knoll on 284° was a pain, and I could stray a bit either side of the junction, so I've just aimed off a bit on 270° to hit the track, then move at approximately 340° 200m along the track to the track junction.
The amount we need to aim off depends on how far away the linear feature is from us. Let's say our linear feature to our indistinct target is 500m away from it. If we aim 3 fingers (~5-6°) to the left, reading from our Table our target point should be about 50m to our right if the linear feature is completely perpendicular. This beats missing the thing and having to do a box search to find it.
What a cute name... Handrails are features - often but not always linear - that once we are walking along, we use as convenient route markers. Roads, tracks, rivers, ridges, transmission lines, firebreaks and so on are good examples. When aiming off we are often using a feature as a handrail, but they can be navigation tools in their own right.
In this example, I've managed to get myself to spot height 2742. My initial plan was to climb down and overnight at refugi de Cabana but the rock is a bit looser than I expected, and bad weather is starting to move in. I'm going to wimp out. Following the ridge southwards down to the saddle at spot height 2653, then WSW to intersect with the GRP track is wiser. The tracks here are well marked, and if the snow hits I can just follow the track, or break track, set up shelter and hunker down safely until the blizzard passes. Serves me right for hiking in winter. This is kind of a complex example. Normally folks stick to linear handrails. Its safer.
Dead reckoning is your friend, and dead easy in principle: Distance and Direction. Starting from a known point or fix, take and follow a bearing, measure the distance travelled. Repeat as necessary. This is how the world was circumnavigated by Magellan, so it should work. Although it could be argued that it was easier for him. We are trying to get from A to B, he was just trying to get from A to A. Wimp. I digress.
Dead reckoning is always a fallback method whether in desert, polar regions, plains, and jungle. If you have limited visibility (eg. jungle), or featureless terrain (eg. desert) or navigating at night - travelling by distance and direction from a known point will get you there. Thus it has two main advantages - easy in principle, and it is very accurate particularly over shorter distances. As an aside, in one of my other lives I use it extensively underwater and even with currents, surge, next to zero visibility I can navigate over 500m to within a handful of meters with just a compass board and counting fin kicks.
All the tools for following a bearing are listed above, and I look at a detailed example in Route planning. So lets look at the specific mechanics of dead reckoning. First the bad news. In its purest sense you are relying on distance and direction only. There is error in both of these estimations. You may be out a few degrees in your initial bearing. Every time you re-take a bearing, you incur another error. Furthermore but when following a bearing we tend to favour certain sides of our bodies. This is called drift. For example, a right hander may always move to the right side of a tree in their path. On slopes, people (like other animals!) will go on the lower side of obstacles. This results in a consistent bias, which is especially pronounced in limited visibility and at night. If you alternate the side on which you pass obstacles, rest on a rock or tree - whatever you habitually do - this bias will be reduced.
There is even more error in your pace estimation. It is very important to know how your paces vary under different loads, terrain, night vs day and so on. Additionally, slope and aspect come increasingly into play. Needless to say at each leg or direction change, you must validate your position by resection and/or terrain association. You MUST record any deviations to the planned route. In this sense, dead reckoning can be very inflexible. This is not an insurmountable problem as long as you record all deviations so you can retrospectively modify the route on the map.
A distinction can be made between a priori and a posteriori (forward and reverse) dead reckoning. Forward dead reckoning is as described above - plan a route and follow it. Conversely, reverse dead reckoning is when you decide to set out on some path without planning it, but you record distance and direction to be added to the map later. This has a couple of uses. First, it is a useful habit to get into even if travelling map to ground. If you've screwed something up, you can consult your notes and backtrack on the map to see where you might have gone wrong. If for some reason you are totally lost - you got blown off course after jumping out of a plane or parapenting off a cliff in a 25 knot wind or something - and you are in a severely geographically located situation but have decided to move you will need to record your path to effectively make a map of where you have been. At worst you can backtrack, at best the shape of your path may begin to line up with the map. Kind of like linking up stars looking for the constellation of Scorpio at night.
So, our map study didn't quite pick up an obstacle on the way. Sometimes we find something on the ground that appears more important than it did on the map. Skirting around may seem easiest, and is if you have a good aiming point along your route to make your way to. If we have a clear view of the obstacle, and a clear view of a landmark behind the obstacle which lies along the the original bearing, we can simply skirt around the obstacle keeping an eye on our new target point. But arced paths are notoriously difficult to maintain yet still keep direction and distance within plan, especially when dead reckoning.
An easy way to get around without re-calculating a whole route is to box the obstacle - ie. go around it at 90° angles. Note we are not going to change the bearing on our compass. The basic principle is:
Lets say we want to go from Refugi de Valferrera to cascada Boet. I'm a softy for a good cascada... We are wandering happily along and there is a Cabana in the way. That's not so bad. But the Cabana has 20 hikers outside. OK, tolerable. I can check out their equipment as I go past. I'm an equipment voyeur. But these 20 people are all taking selfies. Hell on earth! 20 people pretending to hold up a mountain in the palm of their hands, doing 30 takes to get the perfect spontaneous supermodel hair swoosh. Oh, the humanity...! This is serious.
Simply leave the compass on the same bearing (approximately 160° in this case). Remember the compass arrow is aligned with North on the bezel when facing your original bearing. I've decided to go left (I'm army - keep the high ground advantage!), so I simply rotate body and compass until the compass arrow is facing East on the bezel. Walk enough paces until I think I will pass the obstacle sufficiently - around 200m in this case. Rotate body and compass right to get back to the original bearing and move past the obstacle - another 200m. Rotate body and compass 90° right until the needle is pointing to West on the bezel, walk back another 200m and bingo - we are back on the initial line of travel (left turn). Realign (compass needle back to North), and on my merry way way again. How has this affected your pace count? You only account for the paces spent on the bearing (ie. 200m). No compass adjustment required - no calculations required. You are just pointing the compass to either East (to go left) or West (to go right), then back to North to get back on course.
Brotherton favours a slightly different approach. He describes keeping the compass facing along the original direction of travel, and rotating just your body so you are sighting along the short side of the compass. It's six to one, really. I favor sighting along the long axis of the compass, and just realigning the needle along another cardinal point as above.
Of course it is your duty to make like a french waiter and fart in the general direction of the selfie-takers who made you walk a further 400m on your way to the cascada.
Strict dead-reckoning will get you from A to B. However sometimes we may not want to march like a robot or, under some occasions, someone may start shooting at you which can really disrupt both your intended direction and your pace counting. Let's say we are on a navigation leg from A to B on a bearing of 252°. Now there's a neat looking scree rockfall we want to have a look at - there could be some cool lizards hanging out there which we might want to photograph because we're a lizard geek with no other life. The straight line route also takes us across a wee river. There might be some neat amphibians to check out so we want to follow the creekline a bit. The line from our starting position and the attack point can be treated as our baseline. We can meander back and forth across our baseline - still heading towards the attack point - and roughly knowing where we are. When the direction to the attack point is the same as our original bearing, we know we are on the baseline.
As long as we can see our attack point and get a bearing on it, we can walk off the line (to all you sailors out there, this is called the rhumb line) and get back to it easily enough. If our post-meander bearing is West of the baseline when facing the attack point (ie. to the left of it), we need to walk to our left to get back on the baseline. Conversely if our post-meander bearing is East of the attack point (ie. to the right of it), we need to walk to the right to get back on track. Yes, we may be a bit unsure about exactly where we are along the line unless we orient ourselves map-to-ground or by resection, but at least we know we are somewhere on the navigation leg so we can either get to our attack point or go back to the last point.
In combination with a known bearing on a Catching feature you can comfortably use this method meandering along a baseline until your catching feature comes into sight along your pre-measured bearing. This is what Brotherton calls a Hook and baseline - he always comes up with the cool terms.
Angle estimation on the move
Your body can be used as a means of estimating angles on the move instead of racing to your compass every 30 seconds. Hand angles are widely used for military target indications, but are also useful for general navigation. Hold your arm outstretched. For most people (you will need to calibrate yourself with and without glove), the angles are in the order of:
Hand angles and their relationship to compass angles and distance between objects at 1 kilometer
||Distance at 1km
See why it's easier to work in mils?
It pays to practise this. Measure the angles between objects. Point straight ahead toward any obvious feature, hold out you other arm at right angles and sight along it to see what features may or may not align with your arm. How does what you see relate to the map? What about half-way between your arms (45 degrees). Yes, you may look to the outsider like you are trying to fly or summoning aliens to land, but it reinforces what direction the cardinal and intermediate points are from each other relative to the way you view the world. As an aside, this method can be used to navigate search patterns underwater without a compass using only fin kick counts and the right-angle arm action. You can navigate a 50m side square easily
to within a few meters in most conditions.
This method was described using the term Radial arms in Brotherton's book where he describes it from Ranulph Fiennes. I have to admit I'd never heard of it in these words, but have always employed a slightly more subtle version as described above. Brotherton explains that the principle is to orientate your body to navigational reference points so that you don't have to drag your compass out every minute. For example, once you have aligned your body to your direction of travel, 'point' to a reference point - for example the Sun - with your arm outstretched - and physically 'remember' that angle. You can move along the course maintaining that physical orientation for 10 minutes or so. Nav check, then re-pick your reference point. Similarly you could use a distant feature on the ground. I see it as a way of establishing your physical orientation relative to the terrain and direction of travel. I subconsciously do it anyway, looking over my shoulder and so on. It's another tool for staying on course.