# Coordinate accuracy?



## Sailorboy (Sep 28, 2011)

ok.. i need to be schooled.
1. what is the repeatability of coordinates between different GPS units ?
2. on the published Escambia county sites, how accurate are they ?

Thanks:notworthy:


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## DAWGONIT (Jan 16, 2009)

many factors to consider, I'm certainly no expert & my .02 below:
is the unit waas enabled?
are you using differential gps?
how much pitch/yaw is your vessel experiencing?
cloud cover/precipitation impacts to the downlink(s)?
is your receive antenna(s) in the direct field of view, or perhaps obstructed.
your overall repeatability could be a few feet up to a few yards.

shallower and smaller bottom features have had, &/or may experience relocation, shoaling, or complete coverage due to storms. it's always good practice to get in the general vicinity of the coordinates, and provided there aren't a lot of anchored vessels, perform either an expanding circle, or box search, or combination. sometimes the bottom feature may have several parts and your quarry might be some distance away, or stacked up in the water column.

catch 'em up.


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## sealark (Sep 27, 2007)

I'll sum it up in a nutshell, I have had at least 6 different GPSs Garmin, Northstar, Raymarine ECT. and never had to adjust any of my numbers In the early days there were a few differences but now with wass or differential the numbers that I have been to and recorded at the actual spots are all right on on any machine I used. As for the public numbers that were made with a GPS and not converted from LORAN they are right on. I put all the NEW public numbers from Turpins list of the new reefs and they are exact. If the numbers have LORAN be cautious about the converted accuracy. I have heard stories about MBTs numbers being off because the most likely are converted from LORAN #. Hope this helps.


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## submariner (Oct 2, 2007)

sealark makes a good point add to that things move due to storms ect, when you are at the gps numbers and don't see anything- do small circles looking for structure. You can't just go to a number and not use the bottom machine. If you don't have a bottom machine ie in a yak- set you drift so you move over the area.


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## Sailorboy (Sep 28, 2011)

"Turpins" I assume a PFF poster? 
Can u post the link. 
Is there any way to know if the public numbers have been created w GPS? 

Thanks.will check if I have a differential or waas ( not likely)


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## sealark (Sep 27, 2007)

Turpin is the person in charge of the public reef building. If you have a fairley new gps it will be wass.


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## Billybob+ (Jul 12, 2011)

GPS numbers are as accurate as the person or place you got them from. We dive private small stuff all the time. One time I had a buddy and his friends come down from St Louis, MO to dive. that Morning, guess what, My Bottom machine died. They were so bummed they were prepared to chip in and buy me a cheap bottom machine. I told them no need. When They asked how we're gonna dive I simply told them we'd pull up ot the GPS coordinate and drop the hook. We made 4 dives that day. We were 4 for 4 on finding the wrecks, all small, private stuff


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## Contender (Apr 4, 2012)

If there is difference between machines, check the format. You usually can choose between degrees minutes and seconds or degrees and decimal minutes. They are not the same. Back in the day there were also choices regarding datum though I'm not sure they are still important.

Bottom line repeatability is close to 100%.


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## WhackUmStackUm (Jan 31, 2010)

My experiance is that most of the numbers on the Escambia County artifical reef list are good. A couple spots require a bit of searching to find. As always, the more skill you have finding structure with your bottom machine, the better.


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