How to use a Universal Plotting Sheet
My apologies for not being able to scan in the entire Universal Plotting Sheet; nevertheless, what you see is all you essentially need to know in order to set the sheet up for required navigational purposes and in theory sail around the world on this one measely sheet of paper "provided of course you have a good erasure" ie. to pencil in new latitudes and longitudes as required.
The first thing that probably sticks out on the sheet is the Compass Rose, which I'm sure you are all familiar with from conventional charts. All the compass rose bearings are true bearings. You will notice the Vertical Line running due north and South through the center of the Compass Rose. This serves double duty that we will get to shortly. Next feature are the horizontal lines which will represent your desired latitudes. And lastly on the lower right, a longitude scale, which will allow you along with your dividers the means to lay off minutes of longitude.
Now getting back to the Vertical Line in the center of the Compass Rose that we indicated serves double duty. Our first observation that we make is the scale between any two horizontal latitude lines. If it's not already obvious, it's a scale breaking down one degree of latitude into 60 minutes. That's easy enough. If you designate the latitude line 28 degrees north and your indicated position is 28 degrees 10 minutes, put your divides on 28 and scale up 10 minutes, you now have your latitude.
I want to keep the mechanics of the plotting problem separate from the plotting sheet explaination which will be discussed in the next accompaning link but I want to use a few relevant areas of this plot to make my point.
Now that we have an understanding of how to plot a latitude position without having to do anything to the sheet other than fill in the latitude and scale up the minutes from the vertical compass rose, we need only to set up the sheet for longitude.
You will note by casual observation my plotted assumed position is 28 degrees north latitude, sixty two degrees thirty six minutes west longitude.
The first step in filling in latitude is that whatever whole degree of latitude that I'm either currently located in or centered upon as part of a plot will be indicated as the central latitude line. In our case, looking at the chart, 28 degrees. Since we are in North latitude the one below will be 27 degrees the one above 29 degrees. If you are in the Southern Hemisphere, you will be reversed of course. Picture latitude lines as they would appear on a globe. So now all we need to do is to account for our longitude.
The ingenuity of the sheet is found right here ie. setting up our longitude lines. Notice on the edge of the compass rose there are two dots just below 30 "one dot near the top thirty… the other dot near the below thirty…This is important the two dots on the compass rose are actually on the 28 hash marks. Note the same 28 as our central latitude. Now I draw a vertical line connecting the two points. Looking at the sheet you will see that this renders my second longitude line and consequently my longitudinal spacing. To construct additional longitude lines, merely use your dividers one point on the compass rose central line the other on the constructed line and lay them off as needed
To go over this point again if my central latitude happened to be 40 degrees north I would lay off the dots at 40 and 40 and draw my line. This of course would make the longitude lines closer. Without explaination again just take a look at how longitude sets up on a globe.
Since my plot on the sheet required a longitude of 62 degrees West, I merely picked one convenient to my position and labeled it as such seen from my atrocious penmanship. The next one that would have obvious chart significance is 63 degrees West… My point "just label in as required"
There is only one piece missing, My position is 62 degrees 36 minutes West. How do I lay off the minutes? Tuern your attention to the longitude scale lower corner. You will see I drew in an appropriate line to the scale at 28 degrees latitude. With the construction of this line, I put one point of my dividers on thirty. Extending the other point back to the zero mark would indicate only 30 degrees. The lines to the right are further broken down into increments of two degrees. Looking at the dot it is located at the scales 36 minute mark for our latitude of 28 degrees. Now just walk out the 36 minutes from 62 minutes west and you have your plotted position.
This sheet prepared and published by the US Defense Mapping Agency, normally comes in a pad of 100 at a nominal price, In theory it can take you around the world just by applying the aforementioned mechanics constructing a chart, laying out a course line, plotting positions, "and when you sail off the chart just erase and construct new latitudes and longitudes for your current and intended positions or use the back of the sheet. "It's two sided".
Understanding the dynamics of the Universal Plotting Sheet, the next Library link will concern itself with the construction of the viewed sunline plot. How I got the plot is explained in detail in Celestial One, the keystone to understanding all our required celestial navigation principles.