Finding position on a chart
Charts: Plotting our position on them
When we navigating it is essential that we can both put an accurate position on a chart, and take an accurate position off a Chart We can achieve this by using a parallel ruler and a pencil
Today it is very common for even the smallest craft or vessels to have a GPS (Global Positioning System) GPS receivers vary in complexity and sophistication but even the most basic models can give a reasonably accurate position, so we will assume we have a position displayed on our GPS We know from our Dead Reckoning (assumed) position we are somewhere near the Inner Gabbard (Chart 5044 top right hand corner)
Using our parallel rulers we align them to the nearest horizontal line that indicates a parallel of latitude In this case we see from the scale on the right hand side is 50’ latitude Once we have our rules lined up nicely with this horizontal line, we open our parallel rulers until the top rule aligns with the desired increment of latitude on the scale at the side We can now mark this off with our pencil at the approximate position That’s it, we have our Latitude marked on the chart and we know our exact position will be somewhere along that Parallel of latitude but where? To find out we must now draw in our Longitude
Turn the parallel ruler 90 degrees so it is running up and down the chart North to South We must line up the rules against a convenient vertical line that represents a Meridian of Longitude
In this case, the most convenient line is the scale at the right hand side of the chart Once we have our ruler nicely aligned, we can walk them across to the position by opening and closing them The meridian of longitude of our position as read off the GPS
So we walk the rules across the chart until we get to the increment of longitude we require which is indicated on the scale at the top off the chart Once we have the edge of the ruler on this position we can draw in our mark which should be perpendicular to the mark we drew to mark latitude
We now have a cross and in good tradition X
marks, the spot and we have plotted our first position Well Done
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