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Make your own celestial plotting sheets

Jan 1, 2003

To the editor:In reading the very interesting account of his Pitcairn Island voyage ("Passage to Pitcairn," Issue No. 96, March/April 1999), I noted an aside J.R. Williams made regarding the plight of a fellow voyager who was relying on celestial navigation, but had no plotting charts and was using his navigational charts instead. There is an old and reliable solution for this problem that some skippers/navigators might not be aware of.

Since my on-board plotting charts could be counted on for being depleted at inconvenient times, I long ago began using a do-it-yourself version. All you need is paper, a pencil, an engineer's (sexagesimal) ruler and a protractor. While any paper can be used, I prefer quadrille-ruled paper. (A quad-ruled binder will normally yield 150 plotting sheets.) The procedure is as follows: First, you choose a scale on the ruler. Normally the 10 scale will suffice, which will easily provide 1 1/2° of latitude on an 11-by-8 1/2-inch page. Draw a horizontal line at the center of the page, label it as your DR latitude (or close to it), and, using the scale chosen, mark off at least 30' above and below that parallel.

Next, lay the protractor along a parallel, select the appropriate angle (your DR latitude) and you are ready to plot the vertical lines of longitude along that angle using the same ruler scale you used for latitude. Draw in and label your DR longitude at about mid-page and 30' or more of meridians on either side.

You now have a serviceable plotting chart. With a little practice, you can keep the chart clutter to a minimum.

Finally, plot in your DR or AP and solve for the fix as you normally would, using the protractor and the ruler for distances and directions.

The above is a simple and accurate method of supplementing commercial plotting charts. Some navigators may even learn to prefer it. I certainly have.


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