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Navigating with a compass

September 27, 2015

Introduction

 

Hunting season is almost here and now is a good time to brush up on you compass skills.  I will dedicate the next few posts to the compass, maps, and basic GPS navigation skills.  These skills will help you venture out into the woods and have the confidence and skills to get back out.

 

Most people learn to use the compass in a very basic way that works well in most instances.  You head into the woods in a northerly direction and come out in a southerly direction. If you went in off of a long straight road, you should be able to come back to the road.  You may not come back to where you parked the truck, but at least you came back out on the road.  There is no worst feeling than thinking that you are lost.  You must be careful of roads that turn though.  You may miss the road if you wandered around a lot.  This is where a GPS comes in handy.  You marked where you went in and can get a azimuth back to that spot and even track your progress as you walk.  You can also get a new azimuth if you wandered off the original azimuth. I check the azimuth from time to time and make corrections as necessary.  Azimuth and bearings are often used interchangeably but there is a difference.  An azimuth is the direction of travel indicated on a compass and expressed in degrees (135 degrees).  A bearing describes an angle or difference from a point.  On the compass, you use the north and south for the reference.  An azimuth of 135 degrees is the same as the bearing 45 degrees East of South (S 45 E).  There are special compasses if you want to express direction this way.  I suggest you use a regular compass.

 

The picture in Figure 1 shows a basic compass that you should get for navigation.  It has the features you need to use on maps and an arrow to help guide you in the right direction.  The compass has three basic parts: the base plate, rotating housing, and the magnetic needle.  The housing rotates so you can set the degree dial where you need it. There is 360 degrees on the dial. North is 0 or 360 degrees and south is 180 degrees. East is 90 degrees and west is 270 degrees. There is a magnetic needle that always points to the magnetic north pole and is usually painted red on the northern pointing end.  Double check this first.  I bought a compass once that pointed the opposite way (painted wrong).  Metal can affect the needle so make sure there is not any metal next to it such as a gun. The magnetic pole is not true north unless you happen to be in the middle of the country. Maps are oriented to true north and in northern Maine, there is an approximate 18 degree difference and that changes over time (Figure 2).  A GPS will tell you the current declination for the area you are in.  The declination is the difference between true north and magnetic north. The compass also has "meridian lines" or orienting lines to help with orientation on maps.  The "index line" is used to line up the bearing you want to use.  The ruler can be used to measure and calculate distances on maps.  The "Direction of Travel Arrow" is used to follow your azimuth in your direction of travel.

 

 

     

                                                Figure 1                                                                               Figure 2

 

Navigating With a Compass

 

For correct readings, always hold the compass level so that the needle swings freely. Bend your elbows close to your side so the compass is steady. The compass should be at a height that allows you to take a line of sight reading on the 360 degree dial and also allows you to turn the 360 degree dial without unnecessary movement of the needle. Do not move your head, but raise and lower your eyes. Stand away from metal objects.

 

To follow an azimuth:

 

a. Determine the direction to be walked by checking your compass.

b. Set the azimuth on the compass by turning the degree dial until the desired azimuth lines up with the direction-of-travel arrow.

c. While holding the compass in front of you, turn until the needle lines up with the orienting arrow.

d. Sight using the direction of travel arrow or you can use the edge of the baseplate and aim towards a distant object.

e. Walk to the object without looking at the compass.

f. When you arrive at the object check the accuracy of your walk.

g. Repeat steps "a" through "g" until you reach your destination.

 

If you are not using maps, and are just using the compass to get in and out the woods, you don't have to worry about the declination.  You go in the woods at 0 degrees (magnetic north) and come back out on a bearing of 180 degrees (south).  Not all roads are running east and west though. The road may be running in northeast to southwest direction.  You must orient yourself on the road or point of departure.  Point the travel arrow in the direction you want to go.  Now turn the rotating housing until the magnetic needle is in the orienting arrow and pointing north.  Double check it is right.  You now look at the degree number at the index line.  Remember it.  You may inadvertently move the dial off of your desired azimuth.  Find an object to aim at on your course and walk to that object (tree, rock, etc.).   

 

A back azimut is used to return back to your departure point.  A back azimuth is calculated by adding 180 degrees to the azimuth when it is less than 180 degrees, or by subtracting 180 degrees if the azimuth is more than 180 degrees.  For example:  If the azimuth is 45 degrees, add 180 degrees to find the back azimuth.  The back azimuth would be 225 degrees.  If the azimuth is 270 degrees, subtract 180 degrees. The back azimuth would be 90 degrees.

 

Make sure the north pointing magnetic needle is in the proper place.  Be careful.  If you have the south end in the arrow end of the orienting arrow, you will go the wrong way.  Practice this in your yard or a small patch of woods you can't get lost in.  Gain the confidence necessary to know that it works and then you will be ready to go into the unknown and know you can get back out. Practice!!

 

I suggest that you have some sort of map like a topo map.  The map can help you locate where you are if you become lost or confused.  You can look at maps on Google Earth and see how long the road is you want to use or other features.  You could use a river or trail or something big you can't miss.  Always tell someone where you are going.  That way people know where to look if something happens.  You can get hurt or have some other sort of mishap.

 

Precautions to take when using a compass:

 

• Be sure that the correct declination is set on the compass, or that you adjust for the declination mathmetically if you are using maps.

• When running lines always follow the line of sight, not the direction of the needle.

• The compass is a delicate instrument; handle it carefully.

• Always follow the line indicated by the compass rather than relying on judgement as to the direction.

• Remember the tree, rock, or other object sighted on your line of sight. When in doubt, take another reading.

• Keep articles containing steel or iron (ferrous metals) which generate a magnetic field (such as radios) far enough away from the compass to avoid influencing it.

• Do not attempt to repair the compass except in emergencies.

• Trust your compass.  You may think the direction seems wrong but the compass is using proven technology.

 

Questions

 

1. List the three basic parts of the compass:

 

2. How should you hold the compass to get correct readings?

 

3. What is the difference between magnetic north and true north?

 

4. How many degrees are there on the rotating housing?

 

5. A back azimuth is calculated by adding 180 degrees to the

azimuth when it is ____________ than 180 degrees, or by subtracting 180 degrees if the azimuth is ____________than 180 degrees.

 

6.  Calculate the back azimuth for the following:  24 degrees, 245 degrees, 0 degrees.

 

Answer key:    Answers

 

 

The next chapter will introduce you to maps and how to use them for navigating.  I will discuss magnetic declination then.  After you understand that, you will be ready to start using your GPS for navigating.  You will also be able to plot courses on the map and GPS and start navigating.  If you have a GPS, read the book that came with it many times and familiarize yourself with the menus and buttons.  I use a Garmin GPS (GPSmap 62s).  This GPS has aerial photo capability and this can come in quite handy if you bring an aerial photo along.

 

 

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