Anyones GPS play up last night?

[kc]

I have been wary of trusting GPS for a few years now after I had an accident running "blind" on a new moon night and ultimately being 400 meters off course. Last night I was moored in the marina at Hamilton Island and noticed the "track map" on my unit had actually had the boat almost to the airport and back overnight, some .37 nm from the marina and the track map had the boat wandering all over the place at between 50 meters and 600 meters distance. Never seen a track map like it (for a stationary boat). Anyone experience similar??

[Moonlighter]

During the Gulf war we had similar variations. As the U.S. implemented changes to confuse the enemy.....

Lot ot less frequent now that the old "selective availability" policy was removed.

Maybe this was just a case of satellites moving out of range before new ones came into sight?

[Muzza]

Hi KC,

At times the sun (sunspot flares and "CME's etc) can disrupt GPS/satellites etc for varying periods of time at differing locations on our planet.

I visit this website which will often predict or at least explain if this has occurred, or may occur. Also has some info on meteors and explains a bit about the sun and space weather. Looked pretty quiet for last night, may have been Obama :-)

There was this tho,

"Solar wind flowing from these minor coronal holes will buffet Earth's magnetic field on Jan. 20-22."

http://www.spaceweather.com/


Cheers
Muzza

[Noelm]

Do you have it set to head up, or north up?

[Knotpretty]

What is the best to use North Up or Head Up. KP

[Noelm]

Makes little difference to what is the "best" it's what you prefer, but, I have had times when going really slow, or drifting, when my unit is set to head up, it goes haywire, and doesn't know how to orientate itself, what happens, when stationary, the unit defaults to north up, so when going really slow, it goes north up, then thinks its moving, and goes head up, then north up again and so on, making it appear like you are all over the place, waypoints appear in front, then off to the side, then behind, sometimes the chart just spins around.... I do believe all the very new units get much quicker updates and don't do this, or an older unit (mine is 3 years old now) set to north up, doesnt get confused either!

[castlemaine]

I find this a quite common occurrence when your GPS is in one spot for a period of time. You were moored. If I leave my GPS (boat) at home in the yard overnight my Garmin will vary up to 500m while the Humminbird will vary up to 5km. But once I move the boat, all is good.
I remember reading somewhere that the GPS can detect you best when you are moving.

http://forums.groundspeak.com/GC/ind...owtopic=199005

Cheers

[Noelm]

Maybe Satnav might have a technical explanation? I just know that when mine is set to north up, it's happy, I guess there is lots a variables when various satellites come into range, while others go out of range, there will be some calculations by the unit, and this will cause "movement"

[feral cat]

Electronic compass plugged into unit will eliminate all that.

[the gecko]

Ive had similar problems with my humminbird. Sometimes I go out at night and travel up some narrow creeks in between sandbars using trusted waypoints. After stopping for a fish for a few hours, coming home I can be out by 100-300m and can persist for 15-20 mins, and that can put me on a sandbar at night. I had to install floodlights to see the riverbanks to get around this.

If Ive been sitting in one spot for a while, gps can take 2-3 mins to relocate the satellite once moving, but I always get a warning message 'no GPS active' until I locate a satellite. In these cases where I am off coure, I am getting no such warning......that is scary.

It only happens occasionally, once every 15-20 trips, and Ive never got to the bottom of it. A full power off and power on seems to fix it immediately, but you need to know you are off course in order to reset it.

My theory was that my gps receiver is mounted too low, as I have a side console and it is mounted on the gunnel, but that doesnt explain why I dont get a warning message. Perhaps is it a software glitch.

Id also like to hear some explanations.

[kc]

My unit is always set 'Heads up" and I have a few issues when anchored up overnight with a 50 meter "drift alarm" set but this was a doozey! .37 of a nm at worst and "all over the shop". I hit a tree a few years ago in Prossy Dam running at about 18 knots in pitch darkness(400 meters from where my GPS said I was) so always very wary of trusting GPS these days. Just interested to see if this was just my unit (a 3 year old hummingbird) playing up or a general glitch in the GPS systems on a wider scale , my receiver unit is roof mounted so no issue with that.

[Noelm]

Just for fun, set it to north up and give it a go, be interesting to get other people testing, and I guess when it is all said and done, we should NEVER trust electronics alone, a good pair of eyes and ears is always needed.

[Lordspink]

During the Gulf war we had similar variations. As the U.S. implemented changes to confuse the enemy.....

Lot ot less frequent now that the old "selective availability" policy was removed.

Maybe this was just a case of satellites moving out of range before new ones came into sight?

Remember been out on the old mans boat and having the GPS completely drop out, couldn't acquire any satellites for quite some time. Found out that night the US had launched into Iraq.

[back2boats]

Weather can make them drop out. I have had a car GPS lose contact with satellites a few times in misty rainy weather and lots of cloud cover. This can cause it to make large errors in it's position estimation while it sorts it all out, especially when it is down to a very few satellites only.

[MyWay]

I sold my Hummingbird 900 due to the same problem . It was't accurate at all and will not work well as soon as I pass 25nm out . I use it in Moreton bay and close to shore and there was no problem.
Going to Barwon Banks was a real challenge .