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post #11 of Old 03-09-2007
Maine Sail
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Originally Posted by TrueBlue
A chartplotter depends upon coordinates provided by a Global Positioning System antenna/receiver. The chartplotter is integrated with and reliant upon the GPS to function properly.
And paper charts and plottting are depend upon a human... Human error in todays day and age is far worse than computer error IMHO. Even doctors offices are moving towards EMR or electronic medical records due to human error. To assume that humans have less errors than computers is absurd.

I do know how to use a sextant and ded/dead reckoning and plotting yet, unless it's pea-soup fog, I don't normally pre-plot on paper. I'm a firm believer that one should know old school first, as a back up, but lets face it most new boaters won't ever learn this stuff and unfortunately a chart plotter is the next safest alternative to real seamanship.

I've been in situations, racing in fog, where there were three very seasoned, old school, ded reckoning type sailors, not including myself, all disagreeing upon our position each one insisting they were right. One loose halyard in a race, in thick fog, and all bets are off and positions get lost. So who was right? Since I was not the tactician I was unsure as were the other two. Fortunatley I had thrown my Garmin GPS Map 176 in my bag and pulled up our posiion in less that 30 seconds while the other guys were still arguing about how close we were to Half Way Rock! None of them had been right and the closest one, the tactician, had us off by over a half mile! He had looked at the wrong tide table when calculating drift! This is also a guy who has done Marion to Bermuda as a tactician so he was no spring chicken and a very competent sailor, it happens! In this situation it was human error times three!!! GPS error zero!

In 12 years of using a GPS, aboard a boat, I have had no situation, even in the days of SA, where I could not get a fix. Sure I've had times where my accuracy was more than 100 feet off but I can't draw a line on a chart, with a sharp pencil, 100 feet wide so that really is not a major concern.

To answer your question a chart plotter overlays your actual lat/long positionon a chart. If the charts were bad when they were made, like many Bahamas charts, then the GPS will still show you where you are but the chart is wrong so you could still hit bottom. Relying solely on paper charts is no safer in many areas than relying on any other form of navigation because many charts are just plain inaccurate and no matter howmuc you spend on a plotter it can't correct for poor data!

I know of no less than 30 uncharted rocks along the Maine coast, many them reported years ago yet no charts show them. if these charts are scanned into a GPS and used those rocks still won't show up!

-Maine Sail / CS-36T

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Last edited by Maine Sail; 03-09-2007 at 11:34 AM.
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