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How to Plot a Fix on a Paper Chart

May 13, 2013

We enjoy introducing young sailors to the possibility of living and adventuring on a sailboat. While more "normal" parents encourage the next generation to go to college, start a career, and become slaves... I mean productive members of society, we encourage our own children and anyone else's children over whom we have any influence to be happy. If there's a wandering spirit waiting to be satisfied, then our philosophy is go, be free, scratch that itch, explore the world. And if at some point along the line you find a passion that requires further education and following a career path, then follow that dream, too. But a person's life should never be ruled by "have to's."

Keeping with this philosophy, we were quick to encourage a vagabond wanna-be who befriended our youngest son when we returned to the country a few years ago. After months of hearing stories about how David had grown up wandering the Caribbean with his crazy parents, this young man caught the bug and has been dreaming of taking his little boat at least as far as the Bahamas. We are thrilled to watch this dream develop and, in the name of simplicity, try to expose him to the skills he will need to make his travels more enjoyable.

We haven't seen this "kid" who is only still a kid in our own minds for many months now, but we keep in touch. He was proud to tell us that this summer it's finally going to happen: he's headed to the Bahamas.
"As soon as I can find a cheap iPad with electronic charts."
I nearly ruined a keyboard, spewing coffee as I shouted at the screen, "Are you f-ing kidding me, kid???"
But what I typed was, "Really? Have we taught you nothing? All you need is a cheap, hundred dollar GPS and paper charts."
His next message made me realize that his education had been incomplete. "But I don't know how to find out where I am on a paper chart once I'm out of sight of land."
I realized that if he doesn't know, there's a good chance that there are others out there who many not know, either. Maybe the push for electronic charts is the lack of knowledge of how to use paper charts. So, here it is: a short introduction to using paper charts out of sight of land.


Verify that your chart is divided into degrees and minutes

First of all, this is not the only method, it is simply the method Dave (the navigator onboard) has used countless times as the nav station falls out from under him, he leans against the strap that holds him in place as Eurisko bounces around, his dividers try to fly across the boat, and the damn parallel rule slips every other time he tries to walk it across the chart. With enough practice, you will develop your own method. The important thing is to know at least one way to do it.

Now, the point is that you are out of sight of land, which means close enough is good enough. Don't drive yourself crazy trying to plot decimals of minutes. Degrees and whole minutes are good enough. Once you spot land you can worry about determining more accurately where you are, but that requires a completely different set of skills and chart work. So let's say you have a little GPS that only gives lat and long. Perfect. When we are offshore, Dave turns on our GPS once every few hours to get our lat and long and then he plots it on the paper chart along with the date and time. For this example, we're going to say that the GPS tells us that we are at 20 degrees 55" north and 67 degrees 31" west. You stare at the paper chart and think, now what? For this method you will need a set of dividers and a parallel rule. First, determine that your chart is divided into degrees and minutes along the edges, and not degrees and tenths of degrees. (A conversion will be necessary if so. Otherwise, you may be able to change your GPS to give your position in degrees and tenths rather than minutes, in which case plotting it on a chart with the same divisions uses this same method.)


Mark the distance between the nearest latitude line and your latitude

Dave starts by lightly marking the latitude on the side of the chart closest to the longitude, in this case, on the right side of the chart. He goes back later and erases the mark, but it's easier than having to go back and check repeatedly when you get interrupted in the middle of plotting a fix.

Next, he uses a pair of dividers to measure the distance between the latitude mark and the latitude line closest to it that goes all the way across the chart. In this case, 20 degrees north is the closest line, so he measures the distance from 20 degrees north to his mark at 20 degrees 55". Put the dividers aside, in a safe place where you can reach them, but they won't bounce across the boat with the next wave.


Mark your longitude

Now, he marks the longitude with a light mark.


Walk the paralle rule from the nearest line of longitude to your longitude mark

He places the parallel rule along the nearest longitude that goes all the way up the chart, in this case 65 degrees west. He walks the parallel rule over until it lines up with the mark of the longitude at the bottom of the chart.


Mark the distance from the chosen line of latitude

Holding the parallel rule in place, he retrieves his dividers and lines up one point with the latitude mark he had chosen before--20 degrees north. The other tip of the dividers marks the latitude along the longitude mark (which is the edge of the parallel rule), meaning it is a fix.


Remove the parallel rule

Dave carefully removes the parallel rule and marks the point with a pencil.


That's a fix

And that's a fix. Mark it with an X, a date and time and you now know exactly where you are on a paper chart, out of sight of land. No electronic chart necessary. Purists may argue with our using a GPS, but it's more important to be prudent than a purist, in our minds. I'll take safety over bragging rights any time. And as cheap as small, hand-help GPS's are, there's no reason to not have a few onboard because, like everything else electronic, they will break. Our celestial navigation skills are rusty, to say the least, but if all else fails, we do have a sextant (two, actually) onboard, so at least there is a backup plan.

This method can also be used backwards, starting with the longitude and marking that distance along a line of latitude. Dave uses whichever method is easiest, depending on the approximate position of the fix on the chart, if it is closer to one edge, for example. Practice this method while you are on shore or at anchor so that when it comes time to do it on a bouncing nav station, it will be second nature.

MONDAY we'll share a knot that has so many uses that our youngest son used it as a way to baby proof their home.

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