Wednesday, September 24, 2008

Lesson 9: Circular Direction.......

The chart’s compass rose indicates the direction of the earth’s true North Pole. As you will notice on NOAA Chart 12221 TR, true north is indicated by zero (0) degrees with an arrow. In a clockwise rotation, due east is indicated at ninety (090) degrees, due south at one hundred eighty (180) degrees, and finally, due west at two hundred seventy (270) degrees for a total of three hundred sixty (360) degrees. The compass rose’s north-south orientation always exactly matches that of meridians of longitude while its east-west orientation exactly matches parallels of latitude. Therefore, it becomes a simple matter to indicate a course or bearing from one position to another any where on the earth’s surface by making a reference to its direction relative to the earth’s true North Pole…or in a True direction.

Need to Know

Direction is the relationship of one position with respect to another position. Direction on a chart is always measured in degrees (TRUE, MAGNETIC, or PER ship’s steering MAGNETIC COMPASS or PMC).

Only take True readings from the chart and back to the chart. Never, ever inter-mix true and magnetic readings in respect to ship’s heading and course.

When taking readings to or from the compass rose, always use the sharp, finely tipped point on either leg of the dividers as a pivot point at the center mark of the rose. Holding a rule firmly against this pivot point provides for the most accurate positioning and reading of the rule’s straight edge on the degree ring of the compass rose.

Learning Exercise: Direction

In the following problems, now find the course heading in True degrees. Be careful when determining direction that you read the true compass rose in the correct direction. Please don’t remove the solutions from the chart, as they will be used for following problem sets.

1. From LAT 037º 07.5’ N LON 075º 39.1’ W to 36º 57.0’ N LON 075º 41.0’ W

- ____________ degrees True

2. From 37º 01.6’ N 075º 31.7’ W to 36º 57.0’ N 075º 41.0’ W

- ____________ degrees True

3. From 37º 00.5’ N 075º 43.8’ W to 37º 00.0’ N 075º 30.0’ W

- ____________ degrees True

4. From Wolf Trap Light to New Point Comfort Spit Light “2”

- ____________ degrees True

5. From Chesapeake Light to Buoy “NCA”

- ____________ degrees True


1. 188º T
2. 238º T
3. 092º T
4. 211º T
5. 313º T

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