GPS accuracy / Navionics Question

[pakrat]

Just wondering if anyone knew how accurate the GPS unit should normally be. Does it matter at times how good the satellite signals are to be more accurate than at other times? I have heard they can be up to 10 meters . I am currently using an Eagle Fish Elite 500c GPS/Sonar with Navionics Premium Hot Maps chip for MN wich I have used on a couple of trips now . What seems to happen some times is when am showing I should be smack on top of a hump that should be 20 FOW my depth may show something like 50 FOW

witch IS next to the hump . Also at times after putting in at the ramp while just out a little , it often will show my curser still on the shore . Any thoughts , tips , and or adjustments I should be making would be a great help !!!

Thanks & Good luck to all !!!

[Ralph Wiggum]

Unless you are looking at lakes that are "high def" they aren't too accurate. A lot of the maps on the chip are just "enhanced DNR maps" that will get you close. Lakes like Mille Lacs and Leech that have been surveyed will get you much better data.

So I guess the answer to your question is that it is most likely the map that is off and not your GPS.

[harvey lee]

I agree 100% with Ralph. Many times on the DNR maps I have been trolling along a shorline and it shows I'm on land. The 1" contour maps are much better.

[Duck Matt]

I work for an Engineering/Environmental/Surveying firm and my work GPS is sub-meter horizontal and 10 meter vertical with correction and is about 15000.00

from what the survey people tell me most hand helds are within 10 meters horizontal and 100 feet vertical

[Stizo]

Pakrat,

It does matter how good the satellite signals are. Weaker lock ons increase positional error. You should be able to display a screen that shows how many sats you have a lock on and what the approximate positional error at that moment is. PE is constantly changing, so be careful not to bet your life safety on the accuracy of your GPS while navigating in hazardous or unfamiliar water. Additionally, with that unit, you should be able to display that PE # as overlay data (same as you can display time, temp etc etc)on your main screen so it's always visible and you won't have to keep changing pages to view it.

Stizo

[HaywardBound]

Quote:

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Additionally, with that unit, you should be able to display that PE # as overlay data (same as you can display time, temp etc etc)on your main screen so it's always visible and you won't have to keep changing pages to view it.

Stizo

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That is a great point Stizo about the overlay data! I'm going to add the EPE to my Sonar screen.

I have depth, speed, temp, local time, and now EPE on my Sonar screen. You can also change the size of the data and move it around. (I should note that I'm using a Lowrance 520c).

Try this link for a picture (it is a snap shot in simulator mode).

[Dan Brelje]

It seems to me that the HI Def maps are pretty darn close, the ones that are not are not nearly as close. This is with a handheld but i would think it to be the same with a sonar/gps unit.

[pakrat]

Thanks for those responses guys . Stizo , what you mentioned in your reply does that mean I could adjust for the error or only that I would know what errors there are .

Also say if I were to look into a better maps chip , what should I go with for better accuracy . I know high def was mentioned . Any names , prices where available would help .

Thanks again !!

[Ralph Wiggum]

Your Navionics is a great chip, it's just that not all the lakes on it are in high def. They only survey certain lakes. You should be able to figure out which maps are high def if you look on Navionic's HSOforum.

[Stizo]

Pakrat,

No, you can't make adjustments on your unit to compensate for positional error because your position in relation to the position of the sats (you're moving,the earth is rotating etc.)is constantly changing but, like you said, at least you'll know what the range of error is.

The quality of the map chip has nothing to do with this PE issue. A hi def chip (like the new Lake Master) may show 50x more lake details than the older chips (that used the old Fishing Hot Spots or DNR maps) but PE still comes into play for both. WAAS helps but unless PE is Zero (never is)you may have some difficulty finding (using your GPS feature only)that promising spot you see on the map screen. If your unit says PE is 20 feet then you know your close. Use the split screen map / sonar and search around that area till you find what you were looking for and then drop a good old fashioned marker. If you want, you can save a waypoint on the unit also (to help you get to the same general area again quickly in he future) but just remember PE will again factor in when you return.

As for which chip to purchase. It depends on what lake / lakes you'll be fishing. Me, I bought the Lakemaster Mn 2007 Premier SD chip which has all the lakes in Mn and includes all of their hi-def maps such as the new Lake Vermilion one. It's the cats a** especially on the color units that IMO are easier to read. I think I paid $110 w/tx

You can Google Lakemaser for dealers and other info.

Hope this helps,

Stizo

[pakrat]

Thanks guys again !

I primarily fish Ottertail county lakes . I might just check out those Lakemaster chips , are those the ones people say ( maybe Hi-Def ) break down the depth changes better ? Lets say instead of 5ft or 10 ft lines . Do any of the better maps show any structure on them like rock piles or underwater stumps / trees if substantial enough ?

Thanks!!

[deacon]

I live in OT county and use LM map software, is good for OT and WB, however does not have any mapping for most small lakes. It really depends on which lakes you fish to determine which chip to use.

[BoxMN]

FYI - the 2006 Navionics chips is about off by 20 yards too far to the east on Ten Mile Lake. Pelican lake it pretty close, but if I recall a bit too far south, but pretty darn close. The 2007 is supposed to have many of the lakes fixed. We also have Lakemaster, and so far Lakemaster has been right on on the lakes we tried, but it is newer chip. This is being used on h2o and eagle 642. Good luck.

[Fireguy]

Brand of GPS also makes a differance, I have an older Garmin Emap that is not WASS that is more accurate than my new Lowrance H2O that has the WASS.