GPS accuracy

[catfishcentral]

I'm wanting to finally get around to getting a gps and had a question for all that use one. How accurate is the route's the you make with your gps. I know there are suppose to be off a little bit 10 to 20 feet for exact coordinates but how far off is the route that you make. The reason I ask is I fish a lake that's fairly hard to navagte during the day because of the LOTS of standing timber. There's ten of thousands of stumps and trees right below the surface of the water. I follow the creek and river channels during the day by following the trees that tilt into the river channel. This tells me where the orginal river bank was and I following these clues to my spots. Night time is a different story even with a powerful spotlight it's hard to find my tell tale signs where to turn and not to turn. The river channel in this lake is pretty narrow 20 feet give or take. I would like to have my gps be able to keep me exacty in my river channel via the route I came in through. I know this lake very well but at night I've gotten turned around in the forest of trees at night. Thanks

[Cyclops01]

Chris,

I have been using GPS, for several years, for both land and water navigation. They really are very accurate BUT, you can't put 100% total trust on the water at night or during fog conditions though, only because hazards are constantly changing.

A GPS is great for marking and saving all kinds of locations and considering the lower prices, I wouldn't go out on a farm pond without one.

Mike

[jim]

Depending on how many satellites you acquire from your location you can not count on more then 20 foot accuracy.Even with differential capability or WAAS ,20ft is the least accuracy I would count on.On any given day you CAN get accuracy up to 3-5 ft or so,but you simply can't count on it.We have centimeter capabilty in the military but generally 20 ft is average for civilian applications ALTHOUGH let me say you can get a larger error ie MORE than 20 ft depending on conditions.What I would do is get some reflective tape and mark key points on the trees,like a hard turn.Then save that location as a waypoint so you will know when it is coming up and can look for it with your spotlight.when I used to fish for smallmouths at night on Percy Priest lake inNashville I would mark the underwater rockpiles with a chemlight it a Pepsi bottle used as a bouy.You could do the same but they tape will be there for a long time.Most GPSs give a warning when turned on to not use them as a primary navigation aid. :D

[bearcat]

I wouldnt trust them for exact navigation, but they will get you close enought to allow you to look for your land marks. They will also allow you to keep heading in the right direction if you get turned around.

Like jim said get some reflective tape to make the trees or other land marks you use.

[catfishcentral]

I appreciate the repleys guys. This particular lake is about 5000 acres and two thirds of it is uncleared. My best fishing spots are probably 2 1/2 miles back in a twisting and turning forest of trees. I've put out a lot of relective tape over the years but the I could spend days trying to mark ever dang turn in the forest. I usually spend nights on the southern third of the lake at night because it's so easy to get turned around in the forest at night. I mostly take it easy and slow and just roll over the tops of trees and stumps but sometimes you can get high centered on several trees at one time. It's not too fun getting stuck by yourself at night in the middle of winter. I knew the current gps were off a little but just wondered as how accurate the routes that you plot. I'm sure with a gps in hand it won't be too hard at all to navagate at night.

Thanks

[sal_jr]

Is it not true that civillian GPS systems were meant to be off by as much as 30 feet just to keep them from being used in guidance for weaponry and such?

Or is this an urban myth? My take on it is that if you know how to make a guided rocket, you surely can bypass that dang GPS error, but WTH- I am not a rocket scientist so what do I know! LOL

My question:
What type of GPS would you fellas recommend? comnpany, model and why...


Im thinking of getting one but I am not sold on a brand yet- I had a garmin 5 years ago, but its at the bottom of a very deep lake right now with some of my other fishing equipment after a rogue wave nearly took me under.

[blackwaterkatz]

I agree with what the others said, but they are a great tool, to be used along with or in addition to other navigation aids (compass, maps, reflective tape, etc). However, I will say this: you must have confidence in them. I have been fogged in several times, and the gps would show where I was or where I needed to be, but my instincts said differently. I finally learned to trust the gps. I have used mine to carry me across bays and lakes in heavy fog (slowly!, and stop to listen for other traffic). It helped me return to the boat landing from 8 miles up the twisting, turning Santee river one night (at idle speed) by zooming in on my track and following it when I could see neither bank at times for fog.
So, there are great advantages to having one, just don't rely totally on them. They can fail, just like anything else, so have a 'plan B', compass, etc.
Also get one that will zoom in very close ~80' or so on the screen if you want to follow the tracks on a river, and a screen large enough to read while underway.

[jim]

Sal,Selective Availabilty(SA) was a fact not an urban legend.It was a pre-programed error built into the system to prevent an enemy from using it to target us.With certain types of missiles ;ICBMS targeted at specific missile silos, pinpoint accuracy is necessary, just like flying weapons in windows as opposed to just hitting the building.Our military had the codes to receive the precision signal but SA was turned off finally about 4-5 years ago.Any one buying a GPS today should make sure that it is WAAS enabled,and Lowrance,Garmin and the other manufacturers all make fine units.One should shop for the capabilities that are important to you.More bells and whistles ,= more cash.When SA was on the error was 100 meters on average but could go lower or higher.30 FT is the upper limit of accuracy with SA off but normally it is much better.The military still get a signal with 1cm capabilty.

[Mark J]

This will explain how SA works, but alot of your Gps discrepency still comes from the antennae, antennae orientation, and the unit itself.
If you own a GPS you should test its capability. there are websites telling you how to do this and it has to be done repeatedly to determine your unit's ability.

[Link only for Registered Members]

[jtrew]

Since the Titan II missiles have all been deactivated, I'll pass on some info about them. During a briefing about our survivability from a near miss with a Soviet ICBM, we were shown a film simulating a nuclear strike point 1/4 mile from the control center. I'm sure that everyone has seen the home video taken of an office during an earthquake in Japan, where people and equipment are flying around. If you can imagine something like that, but roughly 10 times worse, you have an idea of what the simulation showed. Also, the missile sites were located on a few acres of government property, not on large reservations. That means that anybody could legally survey within a few hundred yards of the silo. A little triangulation, and the exact point would be located within inches. As the largest ICBMs in America's nuclear arsenal, we were told that each site was targeted with 2 or 3 Soviet ICBMs. Our job was to simply get the missile launched before we became a great big radioactive hole in the ground.
Now that there are things such as smart bombs and cruise missiles, accurate pinpointing of certain buildings, or even parts of buildings might be helpful to certain 'bad folks' who would like to do us harm, so there definitely used to be a difference in accuracy between civilian and military GPS units. Whether that difference still exists, I don't know.

[jim]

Jerry you SILO rats should have been proud.It only costs 3 Cents to buy a round of rifle ammo with which any grunt can be done in.Costs about 600-1000$ for an anti tank round to knock out guys on tanks like me.WOW think of how much you would have depleted the Russian Treasury to vaporize you guys.No wonder they collapsed,it was wackos like you with a BIG bullseye painted on your back.GOOD JOB :0a31:

[sal_jr]

thanks for the help AS WELL AS the ICBM and other missile info.


Thats really neat to learn bout those things that had our existence hanging on the depression of a button for a couple of generations. lol

[bearcat]

I have a lowrance fish finder /gps unit all in one. I really like it and the price wasnt bad around 300. If you dont need a fish finder they make stand alone units also. I get along with it very good. I even use it in the car when I travel.

They make GPS units that we use in farming that cost around 3000 that is capable of accuracy with in inches. They also can hook them up to do the stearing of the tractor. The tracks of the tractor in the field looks like it is lazer straight. Some of the farmers around here are letting them steer the combine thru the field also.

[TDawgNOk]

Holy moly, nope, couldn't do that.

Couldn't give up control of the tractor/combine/car to the machine/computer.

Nope, not gonna happen here.

[Mark J]

Seen them use GPS on the fertilizer hoppers. It takes about 3 years to build a good data base.

[blackwaterkatz]

Scott, I don't what kind of gps you have, sounds like a handheld. I have some handhelds, too, and I sometimes use one of them as a backup when I go offshore into the ocean, but they won't give the detail a larger screen will.
In my boat I have a Garmin gpsmap162 with the Mapsource charts for my area. I can assure you that I can follow a 20' wide channel, admittedly with caution, and have done so several times. I don't do this routinely, because it certainly is not without considerable risk, but I have been fogged in at night or early morning on several occasions and had to use the gps, which is the primary reason I have it permanently mounted in the boat. My unit zooms in to 20' map scale, and at that level I can hold my boat on track without a problem at slow speed. Now, be aware that I'm talking about using a route that I have programmed in, or following the track where I've already been, not just running blind. However, the charts that are loaded in are extremely accurate in most cases. I still use extreme caution, because as someone else said, the signal accuracy can vary. My unit usually indicates 6-12' accuracy, but there is an icon to indicate when the signal is weak and may be inaccurate. I have confidence in my unit, but also realize that it is only a tool, and I keep a set of charts in the boat in case the gps fails and I have to use the compass.


There is NO LONGER a difference in accuracy of civilian GPS vs Govt. It used to be the case, but that restriction was lifted a few years ago.

There is NO WAY that anybody could stay in a 20 ft wide channel using a GPS. Even if the GPS accuracy was perfect, by the time you identified a need to make a course correction you'd be out of the channel.

I use my GPS in low vis conditions (at night in fog) in a pretty narrow channel (nowhere near 20 ft) COMBINED with visual queues. Basically, my GPS tells me that a turn is coming up, I visually identify WHEN to make the turn. In low vis, that's only a few feet. And, of course, we're talking idle speeds here.

The Magellan Meridian series GPS are great. The Garmin ETREX stinks for use if you're operating a tiller steer boat with your left hand. It was designed to be used with a left hand. Any attempt to adjust settings with your right hand on the GPS while you're running the boat amounts to blocking the screen with your thumb to get to the buttons.

Magellan - Highly recommended.
Etrex - Avoid, unless you're in a console boat or operate the tiller with your right hand.

/Scott

[Mark J]

Tommy, do you use Loran C at all?
Just curious. I see alot of people going offshore using both.
And those old charter captains won't go without it.
I think those towers get cut off in 2015.

[blackwaterkatz]

No, Mark, I've never used Loran. In fact, when I say offshore, I'm usually speaking of 3-6 miles, in good weather. I'm one who likes to see the beach, never got into the tuna, marlin scene. I primarily fish inshore waters along the coast, as far as saltwater fishing goes, but I do venture out to some of the near shore reefs occasionally. I really enjoy just fishing those places for flounder, weakfish, spadefish, black sea bass, etc. Inshore, I'm perfectly content catching a good mess of whiting to eat, or something like that. I also like to catch redfish in the fall and speckeled trout this time of year when I can work it in.
Oddly enough, I have a good friend who lost his sight about 10-12 years ago to diabetes, but he used to captain a fishing boat, and still has all those loran coordinates written down, and a lot in his head. People will still hire him sometimes to go with them and teach them how to catch the fish at those spots. I think they convert from loran to gps somehow.

[Mark J]

yes, they do convert.
Those old salty dogs have those coordinates memorized like a southern baptist preacher has verses from revelations memorized.
I used to do alot of king and spanish fishing 3-10 miles off.
I love dragging lines.
I love to hear them jibber back and forth in code talk on the VHF and try to cipher where they are at or talking about.
Some of it is outright code you would need an enigma for.

[Catfish Fever]

Chris, all of the above are fact. What I do when I want to save something like a channel I just create my own track and save it in the "My trails" feature. The mouth of the Repulican on the North end of Milford is flooded, so there's really no way to know if your on track, specially when it's dark. I started a new trail going in during the day and saved it as a "new trail". Once I was in the main river, I turn it off and went to the current trail. When I go in or come out of the river, I just turn on the "saved trail #1" and follow it. I've been extremely fortunate here, the greatest EPE (error) I've experienced is 14ft, this is with the WAAS enabled. I also keep my zoom in set very high which makes it easier and more accurate following the trail. Hope this'll help.

[catfishcentral]

Well I ended up getting a Lowrance portable GPS unit about two months ago and I have been very happy with it's accuracy. My main concern is how accurate it would be in very narrow creek and river channels. My local lake has tons of uncleared timber and getting there during the day is one thing but at night is a whole nother story. Lowrance has some free enchanced lake maps of local lakes in my area that are free to download. These maps are great and show contours and very small creek channels also. These maps were accurate enough to keep me in my creek channel which at some points is less than 15 feet. Getting in and out of these area at night can be a nightmare even with a spotlight and reflective tape to help guide the way. I feel very confidate between the free downloaded maps and my own routes that I create that it keeps me within a couple feet of accuracy. I'll be doing a lot of night fishing back in these area's that I wouldn't go without a gps to help guide me in the night.

[center12]

Chris, I've used mine up here on the KS river for the same purpose as you...........only it's shallow water that causes the problems here. If you'll heed blackwaterkatz's first post you'll be surprised how tight you can stay on course, your track on the 100 mile scale isn't near as accurate as it is on the .2 scale. That little difference put me dead on a sandbar one morning!!! Between your GPS, spotlight and prudence you will get thru that jungle fine.........I assume your talking about that lake we meet at last year??

[catfishcentral]

Yes, you are correct there Charlie. There's some very sweet very untouched spots way back in the jungle of Copan lake and some good hunting also. There is several islands one is about 2 miles via the creeks back in there that's 45 acres in size. It holds deer on it year round and I know where I will be setting up some treestands this fall. That gps unit is very nice and zooms up to .02 miles on mine. I feel a ton more confindate when I'm alone at night way back in the forest. I've been in that forest at night without a gps and gotten totally lost. The first time it took several hours to get out of there, not knowing which way I'm going and getting hung up on tree's just below the surface all the time. I even had my drain plug get pulled out by a tree stump one time at night. Some quick thinking by my friend we cut a noodle jug into a plug for the boat.

[center12]

Oh I have some plans for that "jungle" myself,hehe. I had to chase a jug in there last summer and I can only imagine what that would have been like after dark!! I'm simply amazed at how far a fish can take a jug in there and not be hung up??

Just a thought..........changing water levels could be a nightmare:eek:

The route menu is awesome for running limblines, never miss or forget one that way. You can then add a message to that waypoint.......like.............caught a HUGE one here. Repeat performances are in order!!

[catfishcentral]

I actually don't mind it when the water level is down a foot or two. You end up seeing the thousands of stumps and tree tops that are just lurking under the surface of the water. I don't care too much when it's three feet above normal it's a totally different navagating through there. My lower unit is like a magnet for those stumps.:p I've got some special 3 foot jugs that I run in the forest in the spring that are work very well. I make them only three feet so I can reach the bottom hook with my arm when they get hung up. There's going to be some bank poles set up on the islands that have the creek channel running right next to them and a trotline or three.

[peewee williams]

Trial runs in daylight should tell the tale.1st,go slow and keep to the center of the old channel.Save this track.Then try following the track,going and comming.This will tell the tale.Also,depth finder may or may not be a big help,if the old channel is deep enough.This is what worked for me.peewee-williams