Triangulation Fix

​Items you need:

  1. Paper Chart
  2. ​Compass
  3. Pencil
  4. Straight edges, preferably parallel rulers

In order to triangulate your position you'll need to identify three visible landmarks or aids to navigation that are clearly marked on your chart and are relatively far apart from each other (the farther apart, the more accurate your calculation will be). Lighthouses, points of land, water towers or cell towers, and navigational markers are prime examples. The closer you are to your known landmarks, the smaller the possible error in your triangle of position. If you continue to move while taking your ​Line of Position (LOP) understand your position and triangle will both be skewed slightly. 

First, get a line of position (LOP) by locating a landmark you can see with certainty and also find on the chart. Take a bearing with your compass from your position to the known landmark and draw a line on your chart that is the same bearing line through the landmark.

Next, you will use the parallel straight edges and the closest compass rose on the chart to get a line of the correct magnetic bearing. To do this, you first need to draw a line within the compass rose ​with the same bearing to the land mark. Then, place the edge of your rulers on the line of the magnetic bearing (inner circle) on the compass rose and carefully "walk" it over to the landmark; keeping the bearing the same, and then draw the line from the landmark as shown below. You don't need to know the distance at this point, so make the line on the chart long.

​Next, get an estimated position fix by drawing a second line of position. Do this by finding another landmark between 60 and 120 degrees off from the first landmark and drawing another long line on your chart. Use the same method described above and your parallel rulers to get the correct magnetic bearing on your line. Positions marked with only two LOPs are rough estimates of position and lack certainty due to drift and compass error. 

Taking a third fix and drawing a third LOP will provide you with a triangle on your chart and you can have some certainty you are within that triangle. The more LOPs you can plot, the greater the accuracy of your location.


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