In the previous post, I showed how you can figure distances using a prepared chart.
In addition to figuring distances, the next most common task for map-and-compass work is finding your bearings. The example below is taken from a real situation.
My friend Dan, and I had lunch on an island called Green Island in the archipelago off of Stonington Maine. This can be a confusing area because of all the islands scattered about. After lunch, we got back into our kayaks and paddled out of a small cove just far enough to see islands. We wanted to paddle past Russ Island and over to a campground at a place called Old Quarry Campground.
We stopped paddling to get our bearings. Dan pointed at an island some distance away and pronounced that to be Russ Island. I wasn't so sure about this, so I begged his indulgence to try to take some bearings. First, I located my best guess as to our position, which was easy as we'd just had lunch at a known location. This is shown on the figure below.
Known location for the bearing exercise - located just to the SE of Green Island.
At that point, I had two possibilities in my mind. One was that Dan was actually pointing to Camp Island and one was that he was pointing to Russ. So, I used my chart and compass as a way of getting the magnetic bearings using the lines I'd drawn to prepare the chart.
In this case, you're using the compass purely as an angle finding device, so you can ignore the magnetic needle, which I omit in the following figures. First, I took a bearing to Camp Island. In order to do this, I first take the edge of the baseplate and put it on my current assumed position. Then I rotate the edge of the baseplate to it coincides to the sighting I wanted to take. In this case, it was the left hand side of Camp Island, as appeared to me.
I then rotate the compass housing (the round part) until the lines inside the housing are parallel with the lines of magnetic declination drawn on my chart. At that point the compass is aligned. I then look at the sighting/line of direction arrow and see what the angle is. In this case it was 80 degrees.
Bearing to the north side of Camp Island.
The next figure show in detail what the alignment should look like. Note that the direction of bearing on the edge of the compass has the direction-of-travel/bearing arrow pointing in the direction of the object you're sighting, and the edge of the baseplate is also touching your current position. The lines inside the compass housing are parallel to the variation line that was drawn on the map, and the compass is indeed pointing north.
Detail of orientation of the compass on the map with the edge of the compass and bearing direction of travel arrow pointing in the direction of the bearing. The compass housing lines are rotated so that they're parallel to the variation line drawn on the map.
The figure below shows and even more blown up detail of the compass, where you can see that the other end of the bearing/direction-of-travel arrow is indicating the bearing to be 80 degrees.
Close up of the compass when aligned. The other end (non-arrow end) of the bearing/direction-of-travel line is pointing at 80 degrees, which is the (magnetic) bearing to Camp Island.
Now, be warned! There are two rookie mistakes that you can make here. Either one of them will result in you getting an answer that is 180 degrees out-of-whack with what you should be getting. In the first one, you might get the compass housing properly lined up with the variation line, and get the edge of the compass baseplate lined up along a line between your position and the direction of the bearing you want to take BUT you have the bearing/direction-of-travel arrow pointing in the opposite direction. This rookie mistake is shown below.
Rookie mistake #1 - the alignments look correct, but the bearing/direction-of-travel arrow is pointing opposite to the actual bearing you want to take.
The second rookie mistake is when you get everything aligned, but the compass housing is aligned with south pointing toward the top of the map. Here everything else looks correct, but you need to check that north is pointing in the right direction. This is show in the figure below.
Rookie mistake #2 - the alignments all look correct, but the compass is aligned so that south and north are flipped around, and you get a reading that's out by 180 degrees.
OK, now that we've gotten the details of the compass and chart alignments settled, we can proceed with the next bearing, which follows more or less the same procedure, except we're pointing into a different direction.
The next task is to find the bearing to Russ Island, which is basically the same procedure. I put one edge of the base plate on our assumed position and then rotated the edge until it pointed to the left hand side of Russ Island. Keeping that orientation, I rotated the compass housing until the internal lines were parallel to the magnetic variation lines I'd drawn. I then read off the angle by looking at the intersection of the sighting/line of travel line with the compass housing. In this case, it was 10 degrees.
Bearing to Russ Island, following the description in the text.
OK, now I knew what the bearings were to Russ and Camp Islands, and the only thing left to do was to make sightings. So, I first kept the setting of 10 degrees on the compass for Russ Island, and now I use the magnetic compass needle to get my alignment. I hold the compass at about waist height, with my shoulders aligned with the compass and look at what the direction of travel arrow points to when the magnetic needle is aligned with the arrow in the housing. This showed me the left-hand edge of one island we could see in the distance.
Likewise, I reset the compass dial to 80 degrees and made sure that the needle aligned with the arrow in the housing. Looking in the direction of the sighting/direction of travel needle, I saw the left hand edge of the island that Dan thought was Russ, but was evidently Camp Island. So, we identified Russ and headed on a course of 10 degrees magnetic toward Russ Island.
Compass settings to take a sighting on the left hand edge of Russ (left) and the left hand edge of Camp Island (right).
I should note that the above procedure probably took all of one minute while I actually carried it out, but it took about two hours to make the figures and write up the descriptions. The ease of taking the bearings was greatly aided by having the magnetic variation lines drawn on the map!
In the next post, I show how to take bearings to objects that you see.
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