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» Online Classroom   » Celestial Navigation   » Public Discussion of Cel Nav   » Practicing DR Plotting

   
Author Topic: Practicing DR Plotting
Miguel


 - posted April 18, 2007 11:00 AM      Profile for Miguel           Edit/Delete Post 
Dear all;

Section 4.6 of the celestial navigation course includes 5 exercises of DR plotting. Each problem gives course and speed but not time. Instead they give a series of log reading What are those? How do I used log reading values to plot DRs?

Thank you,

Miguel

From: Rochester,MN
David Burch


 - posted April 18, 2007 11:43 AM      Profile for David Burch           Edit/Delete Post 
The log is like the odometer on a car. I believe it is discussed in some detail in the Glossary. If not let me know. It counts the miles through the water, which is precisely what you need to know for the DR Plot.

If you were given Speed and time, for example, the first thing you would need to do is compute distance = speed x time. Then you plot that distance along the course given for that leg of the plot. When you have log readings, you have this automatically.

Also note that in practice, log readings are more accurate way to do DR than using time and speed, since they average out the unavoidable fluctuations in speed at waves and so on.

From: Starpath, Seattle, WA
Miguel


 - posted April 18, 2007 01:03 PM      Profile for Miguel           Edit/Delete Post 
And this will be nautical miles?
From: Rochester,MN
David Burch


 - posted April 18, 2007 01:33 PM      Profile for David Burch           Edit/Delete Post 
Yes. All "miles" are nautical miles. I believe that somewhere in the Introductory material we make the general statement that any reference to miles means nautical miles... this is generally true throughout marine navigation, where one often uses the term miles to mean nautical miles.

The exception is navigating along the Great Lakes and navigating along the major navigable rivers, where is is customary to use statute miles.

And a final point, when navigating along the Intercoastal Waterway from NY to FL, one has to be especially careful as both systems are in use— in signage and in reference publications.

From: Starpath, Seattle, WA
Miguel


 - posted April 18, 2007 02:13 PM      Profile for Miguel           Edit/Delete Post 
Thank you.
From: Rochester,MN


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