Need to Know
1. An actual known position is indicated by a FIX symbol indicated as a small dot or “X” drawn on the chart enclosed by a circle. Write the word “FIX” and time.
2. A DR track line in true degrees is plotted and always starts at a fix.
3. A new DR track line is always plotted whenever from a new fix.
4. A new DR track line is always plotted whenever there is a change in course or speed.
5. DR positions should be shown at regular or hourly time intervals. Near shore or in heavy traffic, more frequent DRs are definitely better.
6. A DR position is indicated by a small dot enclosed with a semi-circle. Write the letters “DR” and indicate time.
7. The Intended or Ordered Course should be indicated in True degrees along and above the track line.
8. Ship’s Heading (SH) is the direction in which the vessel is pointed or headed and is never plotted.
9. Ordered or Intended Speed is indicated by an S and then the speed in knots along and below the track line.
10. Distance is indicated by a D and nm along and below the track line.
11. To determine a DR position, plot a track line beginning at a fix in the direction (in true degrees) in which the vessel is to be advanced. Based on the ordered speed and run time of the vessel, DR position(s) can be computed and plotted by simply using the DTS60 formulas.
12. Always, always compare a DR position against a new or known fix and adjust DR track line accordingly. Always start over with a new DR track line from a new fix.
13. Understand the terms: Speed Over Ground (SOG), Speed Made Good (SMG), Course Over Ground (COG), and Course Made Good (CMG).
14. Wind (leeway), (water) current(s), actual vessel speed, and steering accuracy of the ship’s helmsman will influence a vessel’s actual CMG and SMG at sea.