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Go Back   SailNet Community > Skills and Seamanship > Seamanship & Navigation
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Seamanship & Navigation Forum devoted to seamanship and navigation topics, including paper and electronic charting tools.


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  #11  
Old 05-26-2007
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Actually Cam it does not tell you what your margin of error might be. GDOP, geometric dilution of precision relates solely to the angular differences of the various LOPs. That is what your unit is showing you. It is not showing you such things as the effect of transient noise on each individual LOP. Anotherwords, the computer is doing the thinking and evaluating for you. Similar factors are what make your shallow water alarm go off consistently in 500 fathoms of water and yet not utter a peep as you gring your way ashore.(g) Similar technology is what makes your automatic acquisition radar track minute squalls but manages to overlook a sailboat 5 miles away. Again, I am not trying to be critical of GPS, but rather the manufacturing process that leads to, "they don't need that" mind-sets.

Perhaps an illustration would make the point better. "Transit" was generally employed with a gyrocompass input and a manually entered speed input, what with very few ships having pitot logs. Theoretically, if the speed entered was off a significant amount the receiver should not be able to acheive a "fix". Nevertheless, the receiver would merrily pump out positions, some ten miles off, as if all was well in a carefree world. Advances have certainly been made, and the receiver's estimate of GDOP would reveal the potential for large errors, if monitored. But the unit still does not give the operator the type of information he needs to either accept or reject individual LOPs. "You are here" logic is the quite predictable result.
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  #12  
Old 05-26-2007
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I suspect GPS and chartplotters have overall reduced pilot error despite introducing the problem you are rightly pointing out. I imagine that there are a large number of people who now have access to a greater range of sailing experience due to GPS, they simply would have grounded before leaving the harbor otherwise.
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Old 05-27-2007
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tenuki,
Being a pessimist, as well as a contrarian, I suspect just the opposite is true. GPS and chartplotter assisted grounding, due to over-confidence or over-reliance, is a very real issue. Training in the proper use of electronic navigation equipment is essential and under-appreciated. The term "radar assisted collision" is not just a punch line to a bad joke; it happens. The small boat navigator with nothing but the Mk I, Mod 0, precision eyeball is unlikely to leave, or enter, port when the fog is dense preferring to wait for safer conditions. The GPS reliant navigator is probably more likely to say, "so what if we can't see anything, we can tell where we are right here on the black box".
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