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post #8 of Old 03-04-2014
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Re: GPS Accuracy - how much is actually needed

Originally Posted by RichH View Post
GPS (chartplotter) 'accuracy' is totally dependent on 'resolution accuracy' of the original charting from which it is based. Problem is that for most areas that do NOT have large scale commercial marine traffic, the base chart 'may' still be based on 1927 or earlier surveys. Plus and with respect to 'resolution errors', using GPS charting based on 'old' lead-line surveys may also induce EXTREME errors especially when the GPS chartplotter MAGNIFICATION greatly exceeds the 'magnification' of the original hand surveyed charting.

FWIW .... most USA marine charts are only upgraded if and only if there is large commercial boats constantly using the area of the chart.

OEM Charting error trumps GPS accuracy; 'over-magnification' by chartplotters MAGNIFIES the original errors.


How accurate are our charts? - Ocean Navigator - January/February 2003

Originally Posted by mm2187 View Post
With an accuracy of +/- 24 feet on a 40 foot is it worth the additional money to get another few feet of accuracy?
Such accuracy within a dimension smaller than the size of your boat is really only important if you care which PORTION of your boat is at a particular geographical position on the earth's surface... in other words, with such precision on a 40-footer, you really have to decide: Do i want to know where my KEEL is, or the NAV STATION, or the BOW, or the HELM ? And then, position the antenna accordingly...

When you think about it, such accuracy really is more valuable for your 8' tender, than for the 40' mother ship... Not to mention, far less important on a $80 million 200' megayacht...

Most of which will have multiple GPS receivers both fore and aft, anyway, and at other critical locations like helo pads, and so on... :-)

As for the 'repeatable accuracy' of GPS for waypoints, LORAN was probably superior in that regard... And, if I need to rely on GPS accuracy within a few feet to keep me from hitting a submerged rock, I'm putting WAY too much faith in my gizmos, and it's probably time for me to think about taking up another hobby... :-)

Last edited by JonEisberg; 03-04-2014 at 09:34 PM.
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