BUSH DAY Navigation for Bush Navigation Day Robert Kirwan, Nunawading SES W NW N NE E If you have little or no bush navigation experience then you will have been teamed up with members that have that experience and will guide through the day. Nevertheless I would encourage you to read and absorb this knowledge in order to get the most out of the day. Bush Navigation is as easy as falling off a log, pun intended but also true. Section 1 Registration, Maps & Checkpoints SW SE On arrival at the location your Team will need to assemble with their equipment (for checking) and submit a Team Registration Form at the S Hash House. Once registered your team will be given 2 Maps and a sheet with six figure checkpoint co-ordinates. Once your team receives their map you will need to mark all the checkpoint locations using the six figure co-ordinates. You will no doubt be familiar with Longitude and Latitude co-ordinates i.e. a way to locate a particular location on earth. BND uses a similar co-ordinate system called Eastings and Northings, this system is more accurate for smaller areas and is widely used on all trekking maps. Eastings run along the top and bottom of the map increasing in number as they go East (therefore the name Eastings). Northings run along the side of the page and increase in number as they go think about it correct, North. The Easting is always expressed first followed by the Northing. Together these co-ordinates are known as a Grid Reference. Each square on the map is 1 square kilometre i.e. 1 kilometre between each Easting line and 1 kilometre between each Northing line. If you were to use just the Easting & Northing lines shown on the map you would not be able to represent most of the area on the map with any degree of accuracy. Therefore the Grid Reference divides each square by 10 along the Eastings and Northings line. The following image from the Field Operations Guide represents this. The Grid Reference for point A is 314864 N.B. Even though each Easting & Northing interval has been divided into 10 further intervals the resultant Grid Reference is still only accurate to an area 100 square meters in size and therefore the reason point A is approx 90 metres East & 40 metres North of the stated Grid Reference.
Section 2 Contours & Route Planning The next step is to plan your intended route for the day. It is however handy to have a basic understanding of contours as represented on the map. Contour lines join points of equal height and thus depict the terrain on the map e.g. hills, valleys, ridge lines etc. The following diagram shows a hill and how it would be represented in 2D on a map using contour lines. The map legend will indicate a contour interval which is the height between contour lines. The closer together the contour lines the steeper the terrain. Generally for each major interval (e.g. 100 metres) the contour height will be shown on the contour line. Spot heights will also be indicated on the map in black print these are generally shown at the highest points on the map e.g. the top of hills. At a glance it is sometimes hard to know whether the progressive contour lines on a map are heading up or down. Rivers and creeks (indicated by blue lines) help us visual the terrain. Generally progressive small creeks will be shown running into a larger creek/river. Water of course runs down hill and this allows you to quickly orient yourself to up and down on the map.
There are some common terms used in map reading to describe various physical features e.g. a hill. Saddle A depression between adjacent hills or mountain tops; also called a col. Knoll A small knob-like hill.
Spur A ridge, running out from a hill or mountain. Checkpoint 22,41,46 Ridgeline The crest along a line of hills. Checkpoint 45
Section 3 Navigation: Distance In bush navigation you only need to know two things - Direction & Distance, it s that simple. So let s start of with an example from the 2011 BND. It s the beginning of the BND and we are located at the starting point i.e. Hash House (HH). We have decided to go for checkpoint 42, the checkpoint description is creek line. How do we get there? The first obvious step is to follow the road. You don t need a precise compass bearing for this. North is depicted on our map as running to the top of the map (which on nearly all maps is the case) so a quick check of our compass will tell us which way is North (i.e. the direction the needle points) and therefore we head off in the opposite direction down the road. At some point we need to leave the road and head into the bush towards checkpoint 42. We decide to follow the creek line up from the road but how do we know when we are at the creek line we want. You could try and count off the creek lines as we pass them however creeks depicted on maps are very often dry and are largely undetectable. The better strategy is to determine the distance to the creek line on the map and then measure off our distance as we walk towards it. Step 1 Determine the Distance All maps have scales which are indicated on them. For the 2011 BND the scale is 1 to 25000 i.e. 1 cm on the map = 25000 cm or 250 m on the ground. Therefore 4 cm = 1000 m or 1 kilometre. The map also depicts the scale with a line (bar) on the map showing the length of 1 kilometre along with 250 m graduations. You may also remember from Section 1 that the Easting & Northing lines are 1 kilometre apart. So next we need a ruler. One method is to carry a piece of string and place it along the distance to be measured and then read of the distance by laying it on the scale bar. Another method is to use a piece of paper. You break the route into a series of straight sections progressively measure each section by working the paper along the route. Don t take the paper strip off the map just mark it and rotate it when you get to a bend on your route.
The final method is to use the scales on your compass in a similar fashion to the paper method. Step 2 Count Down the Distance Walked I work out the distance to be 1,450 metres but how do we know when we have travelled 1,450 metres. We pace it and pacing is a surprisingly accurate method. It s best to have worked out your pace distance before hand (i.e. mark out a 100 metres and walk it a number of times to work out your pace distance) however most people have a similar pace distance which is 65 right foot paces per 100 metres. It s easy to loss your count when pacing so I tend to use my hands and twigs to keep the count. If I m pacing 1,450 metres I ll break 14 twigs. I ll count of every 10 right foot paces with my fingers and when I get to 65 i.e. 100 metres I ll discard a twig and then start again with the 65 count using my fingers. At the end I just need to remember to count out the final 50 metres. One final point is that you need to adjust your count if travelling up or down steep slopes or walking around objects e.g. trees, boulders etc. If you ve got this far then well done. Time for another break and then come back for the final Section. Section 4 Navigation: Direction In Section 3 we could rely on features in the terrain to hit our checkpoint i.e. a road & creek line however more often than not we need to use a direct bearing we read off the map. There is one slight difference between our Maps and the Compasses we use for Navigation. On the 2011 BND Map you will notice two arrows one pointing directly up to GN (Grid North) and one pointing slightly to the right (11 degrees in fact) to MN (Magnetic North). The Map also tells us that the Grid Magnetic Angle (i.e. Magnetic variation from Grid North) is 11 degrees. For all practical purposes Grid North points to the North Pole. However our compasses, using the Magnetic fields surrounding the Earth, are only an approximation of North. Therefore when using a Map to determine the direction to a location and then using a Compass to take us to that location we must always adjust for this magnetic variation.
As an example say we are at checkpoint 45 and wish to head on a direct path to checkpoint 22. It s very simple and here are the steps (it s best to practice this with a compass if you have access to one). Step 1 (indicate as A below) Place the compass on the map with the direction-of-travel pointing to your destination and so that the side edge connects your current position to your destination. Step 2 (indicate as B below) Rotate the compass dial until the Orienting Lines are parallel with the grid (Eastings) lines on the map. Step 3 (indicate as C below) Rotate the dial 11 degrees clockwise to SUBTRACT the magnetic variation Once you have set your compass to the correct bearing simply hold the compass steady and level in front of you. Turn your body until the needle lines up with North (N) on the dial. The compass now points to your destination. Look up, align the direction of the compass with a feature and walk to it. Repeat this procedure until you reach your destination. In case you are slightly off line it s also a good idea to pace out the distance to ensure you don t overshoot the destination. And that s all there is to it. Congratulations and have a great BND.