I used to do cache huntting with a gps, the rule of thumb was my gps might be up to 60 ft. off, if you hide something yours could be up to 60 ft. off leaving you an area of 120 ft. off.....(IM using a high end garmin handheld csx 60).....

my point if I mark some navagational bouy's and allow for the varrience, do any of you that travel after dark take this in consideration or do you just steeer way clear of the area you know has the bouys, our lake places them for the houseboats so the taller ones travel away from the low part of the hanging high tension lines

-------------------------
"Come OOON Back............

High Tension Lines!!!!!!!!!


YEAOOOOOOOOW!!!!!!!!

bOB

-------------------------
I carry a gun because it's too tiring carrying a cop.

If you intend to depend on your GPS for real-time navigational precision, you might want to invest in a 'WAAS upgrade'. I have both a portable and a built-in GPS with WAAS for my other go-places toy, and the degree of accuracy for both of them is simply amazing-- less than a couple of feet off in any dimension.

-------------------------
Amelia
Edenton, NC

Agree. If your unit does not have WAAS then upgrade it. WAAS is supposed to be good for +- 3 feet. Older units 100'; and some years ago it was 100 METERS.

But how deep is the water where that buoy is? Bear in mind it's on a chain and will wander around depending on wind, etc. The deeper the water the longer the chain and the more it will wander.

-------------------------
Willie
She's a tired old barge but she's paid for! http://s71.photobucket.com/alb...p;current=ef324993.pbw

the handheld unit i bought 2 years ago was the top of the line and would still be considered up there, You might be surprised how far off your best units are. I wasnt aware there were units afordable (say under 600$) in a handheld. that would get u with-in 3 feet, but i learn something new on here every day.

-------------------------
"Come OOON Back............

I know exactly what you mean by the wind years back when docks would drag a cable across a bay to tie to tree's on the opposite bank a few houseboats on the old docks and they became like kites and those lines would stretch tight and suddenly werent so deep, IM sure the core has all that refigured to day

-------------------------
"Come OOON Back............

I'm running a Garmin 76 (I think) handheld, it's a good 5 years old, is WAAS enabled and quite accurate. It cost me just over $200.

Another "problem" with the GPS isn't the GPS but the chart. Such things as bouys and landmarks aren't always where they're charted to be. A lot of charts were originally made before GPS was available. When I leave my dock and head for the bay, for the first half mile I'm running on dry land according to the GPS. It's always the same so I'm sure it's the chart. For your nav aids, if the Coasties or the Corps didn't put them there, their exact position is suspect. Nose your boat up to them as close as you dare, and hit the "mark" button. Then use that rather than the charted position. Correct your paper chart accordingly.

Don't be so sure the Corps has it all "refigured" just yet. It takes money to resurvey and print new charts, and if it's not a big issue, it may not happen for a LONG time.

The charts ARE getting better in the heavily trafficked areas, but in the backwaters like where I am they're still somewhat off. It's not unusual; I've seen charts that turned out to be MILES off; but when they were made there was no way to know.

-------------------------
Willie
She's a tired old barge but she's paid for! http://s71.photobucket.com/alb...p;current=ef324993.pbw

stmb, try this if you get a chance with your unit, mark a spot in your yard, jot down the cordinates and have some else you for the spot using the numbers u give them. You may be surprised how much of a difference there is.
Now if you let that gps alone say for an hour and walk away it will read different than the first set of numbers you get,

now of course this is for someone to try that has to much free time on ones hand lol.

one of the big things today with gps are searching for these old geological markers along with hidden caches, the fact the gps numbers are so diffrent from one gps to another, you have to do some serious looking to find the hide cause it sure going to vary.........think about it if they were that accurate there would be no huntting you would just walk up to it......not hardley...

back to the point staying in the channel they should be fine.:

-------------------------
"Come OOON Back............

To follow your suggestion I just compared my boat's GPS against the Google Earth position... Missed it by about 12 feet after correcting seconds to minutes. I can see where it would be a problem surveying; which is probably why that GPS is a lot more expensive than mine, and why you get an average of several readings.

Then I got an idea so I took the handheld out of the houseboat and sat it right next to the antenna on my fishing boat, and turned both units on. After they settled down they were within .001 minute of each other; or about 6 feet. Two different units by two different manufacturers and built at different times. Close enough for my purposes.

Admittedly if I had waited an hour for different satellites, I might have gotten some "drift". I might walk out there in an hour and try it again.

A few year ago when I was steamboatin', I could watch the readout and actually see the ship roll, as it moved the antenna 10-20' from side to side.

Still, my charts are off by a couple hundred feet.

-------------------------
Willie
She's a tired old barge but she's paid for! http://s71.photobucket.com/alb...p;current=ef324993.pbw

I believe the best 'touted' accuracy for non-military GPS WAAS units is "3 meters" and not 3 feet. However if your units have a discrepancy greater than 12 feet between the two, you could have several problems to choose from. Antenna location; your wire run; the location of your fixed unit compared to other electrical appliances; factory antenna defect; main unit defect; etc...etc...etc..

I use solely Lowrance/Eagle products. Not because I think they are better than other GPS/Sonar units out there, but, because I can more easily identify what I see on the screen. I'm just more comfortable with this brand, and, I have had Sitex, Hummingbird, Northstar and Garmin. I have fished several wrecks and reefs and never had a problem getting back to the same place by either using way-points or simply entering Lat/Lon coordinates.

Safety point.....for anyone boating the navigable waters, large rivers, or huge lakes such as The Great Lakes, Powell or Mead, it's time to upgrade your electronics to WAAS/DSC. The combination units available make connecting these things a piece of cake. If you are boating smaller lakes and bodies of water DSC is not so important.

Now about night travel.....I simply use my route/trail. On my pontoon fishing boat I can dang near get back into my slip at night without lights. I said 'dang near'.

Keep it safe and accurate,
Edd

-------------------------
Chance Favors The Prepared Mind!

Edited: 10/30/2007 at 09:26:36 AM by Skallywag

I have been using Garmin units for several years and have found that the maps provided on the Garmin units leave a lot to be desired.

I now havee a Garmin 76Csx and the map that came with is no better, however I purchased TOPO USA 2008 and this makes almost every thing appear in the correct place. However even TOPO USA 2008 has not been updated for some time and you will find that new or changed features (roads and channel markers) that have been changed in recent years will not be correct.

I also purchased City Navigator NT and it is a great improvement over the map installed by Garmin.

Accuracy on this unit averages about 16 feet according to the display and I have found that to be about right. You can not expect channel markers to remain long in one place.

I also found Garmin's support very helpful and they all speak goog English.

The Birman

-------------------------
2005 Stardust 18 X 78 on Green River Lake Ky

WARNING! Do NOT purchase any Lynksys products.

LOLOLOLOL this is too funny and soooooo much appreciated.

Edd

-------------------------
Chance Favors The Prepared Mind!

Scallywag is right, I just downloaded the manual to my Garmin and they claim 3 meters, not 3 feet.

I also found this: http://users.erols.com/dlwilson/gpswaas.htm

Plenty close enough for MY purposes; but finding a survey mark in the underbrush could still be a problem!

-------------------------
Willie
She's a tired old barge but she's paid for! http://s71.photobucket.com/alb...p;current=ef324993.pbw

so if the one unit is 3 meters off and someone else gives you a reading to find and there unit is 3 meters off we are now up to 6 meters off,
so

the brush pile you sent me too get those bedding crappie ant going to be found with a gps, but a little effort and we will find it lol.

when they say up to 3 meters thats with all things being ideal, the rule of thumb is 60 feet, been my experience

-------------------------
"Come OOON Back............

referring to the post where they used the tracking screen to return, we did a deep woods hike not on a trail. the track my unit left I followed it back and walked in the same foot prints i traveled in on according to the leaves amazing this is handheld unit in moderate overhead cover. leaves still on the trees

-------------------------
"Come OOON Back............

That's exactly why, if you are an avid fishermans, you also need the sonar unit to actually find them crappy crappie. Remember that when you finally find your spot you should make a way-point. If I'm not mistaken your hand held unit has a provision for an SD card? And, also a provision for 'at home' mapping with the proper program? You have all the bells and whistles.





I usually find, when things are that far off kilter, that if I take the smart end of the measuring tape away from my wife, things get a lot closer.

Edd

-------------------------
Chance Favors The Prepared Mind!

be,ieve me this unit is or has all the bells and whistels, it like buying a computer and using it just for free cell with what little i can do with it, but its given me a little of fun outtings

-------------------------
"Come OOON Back............

fun is what it's about; if it weren't for that we wouldn't own boats.

-------------------------
Willie
She's a tired old barge but she's paid for! http://s71.photobucket.com/alb...p;current=ef324993.pbw

Fun huh?  OK, ya want to have some fun with mapping?  Go to www.openstreetmap.org      When you get there, do a search for Waverly,Tennessee. My friend has done all the work on Waverly and the surrounding area by himself.  He is going to expand this to the Tennessee river system in our area and do waypoints and navigation aids,etc. just like what you are talking about.  We have compared his work to available maps on paper and the internet. His are accurate, the others are ,"close".  Our town of Waverly ihas been changing the Hwy 13 coming into town this past year and his map reflects the true course of the road system now and it is amazing how this works. you actually are making the map, labeling the way points, naming the roads,etc. He is excited about this and wishes he could enlist a few folks to help map out doing this.   Anyhow, thought you might get a kick out of this.  There are a lot of tricks you can do that I don't have a clue how to tell you about, but he can sit here and ramble all day about overlays, underlays, sideways and whatever to enhance the maps(charts).  Check it out.  

-------------------------
Riverliver

I do a certain amount of poking around where there are no charts... I've discovered that I can download satellite pix from Google Earth (with co-ordinates). The free nav program Sea Clear comes with MapCal; which allows you to make your own charts from the photos or even something you drew yourself. And Sea Clear will run them. It's a lot of work, though, and my favorite program from Maptech won't. So I haven't pursued it much.

-------------------------
Willie
She's a tired old barge but she's paid for! http://s71.photobucket.com/alb...p;current=ef324993.pbw