GPS accuracy

Discussion in 'Fishing Electronics Review' started by catfishcentral, Dec 19, 2005.

  1. catfishcentral

    catfishcentral New Member

    Messages:
    1,497
    State:
    OK
    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
     
  2. Cyclops01

    Cyclops01 New Member

    Messages:
    578
    State:
    Eden, NC.
    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
     

  3. jim

    jim New Member

    Messages:
    2,579
    State:
    Jacksonville NC
    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
     
  4. bearcat

    bearcat Member

    Messages:
    925
    State:
    Nokomis, Illinois
    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.
     
  5. catfishcentral

    catfishcentral New Member

    Messages:
    1,497
    State:
    OK
    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
     
  6. sal_jr

    sal_jr New Member

    Messages:
    1,390
    State:
    Ithaca, MI
    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.
     
  7. blackwaterkatz

    blackwaterkatz Active Member

    Messages:
    3,659
    State:
    Andrews, SC
    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.
     
  8. gottafish

    gottafish New Member

    Messages:
    308
    State:
    Chesapeake, VA
    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
     
  9. jim

    jim New Member

    Messages:
    2,579
    State:
    Jacksonville NC
    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.
     
  10. Mark J

    Mark J New Member

    Messages:
    9,407
    State:
    Four Oaks, NC
    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.

    http://www.exn.ca/FlightDeck/News/story.cfm?ID=20000502-53
     
  11. jtrew

    jtrew New Member

    Messages:
    4,404
    State:
    Little Rock, AR
    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.
     
  12. jim

    jim New Member

    Messages:
    2,579
    State:
    Jacksonville NC
    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:
     
  13. sal_jr

    sal_jr New Member

    Messages:
    1,390
    State:
    Ithaca, MI
    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
     
  14. bearcat

    bearcat Member

    Messages:
    925
    State:
    Nokomis, Illinois
    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.
     
  15. TDawgNOk

    TDawgNOk Gathering Monitor (Instigator)

    Messages:
    3,365
    State:
    Tulsa, Oklahoma
    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.
     
  16. Mark J

    Mark J New Member

    Messages:
    9,407
    State:
    Four Oaks, NC
    Seen them use GPS on the fertilizer hoppers. It takes about 3 years to build a good data base.
     
  17. blackwaterkatz

    blackwaterkatz Active Member

    Messages:
    3,659
    State:
    Andrews, SC
    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.


     
  18. Mark J

    Mark J New Member

    Messages:
    9,407
    State:
    Four Oaks, NC
    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.
     
  19. blackwaterkatz

    blackwaterkatz Active Member

    Messages:
    3,659
    State:
    Andrews, SC
    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.
     
  20. Mark J

    Mark J New Member

    Messages:
    9,407
    State:
    Four Oaks, NC
    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.