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I have a furuno gp31 and haven't been real pleased with the accuracy of locating artificial reefs, etc. My buddy has the gp36 with differential and he pulls right over the locations every time. I am thinking I got the wrong unit. Please help!
Yes, the 36 is MUCH better accuracy than the 31. The 31 bounces a whole lot, which is very annoying. If you want accuracy, get a WAAS unit, the new GP37.
You can try to increase the position smoothing also, but for accuracy, go with WASS or DGPS.
I've got the GP-35 and it seems to be very accurate. Do miss the near list on the GP-36 that was on the other boat. Gotta tell you though it's like driving blind without a chartplotter. While the trackplotter screen will show nearby waypoints they are not labeled (only the target waypoint is). Can't remember whether the GP-36 corrected that ommission. How bout the 37?
Anyway I'm trying to figure out what $1,000 or less DGPS or WAAS Chartplotter to get now myself.
hblack,
Garmin makes several good ones. As a back up unit I bought the 182 with a blue chart card. I wish I had spent the other $200 for the color unit. The color units are so much easier to read. The 182c comes as waas unit with either external or internal antena- go for the external. This electronics stuff is almost as much fun to play with as the fish. Too many choices, too many hi-tech evolutions.
Joe
Yep, I've been looking at the 182/182C. About the best price I can find for the 182C is $883 from GPS Discount. Also interested in Standard Horizon CP-160 and CP-170C. Boaters World has the 160 for $399 and the 170C for $999. Don't know if that $399 price is for a refurb.
If I had the money I'd get a Furuno GP-1650D or GP-1850D.
Hal
'Albemarlin'
[img]/infopop/emoticons/icon_smile.gif[/img]
the 1650 and the 1850 washout in sunlite more than the 582-Ls do,go garmin 182c,2006c,or 2010c,you dont get the washout in direct sunlite.I own the 582-L good unit but washes out,Im thinking of sending it out to a LCD atm screen business and have the reflective material put behind so i can see it in the derect sunlie like I can my 2006-C Garmin not cheap $300 but worth it.JMO
I have the GP36 and the Garmin 2006C and I have to agree both units have the same lat long #s,One other note,the GP36 rewrityes faster than the Garmin chartplotter,my guess is the graphics of the Garmin slow it down,when trying to setup on hard bottom I find the GP36 a real help.JMO
I was considering the GP31 and would like more of your "lack of accuracy" and "bouncing around" experiences.....in as much detail as you care to provide.
"Lack of accuracy" [img]/infopop/emoticons/icon_eek.gif[/img] maybe someone could explain that to me as well, accuracy compared to what [img]/infopop/emoticons/icon_confused.gif[/img] and if that's WAAS or dGPS then that won't be the correct answer [img]/infopop/emoticons/icon_biggrin.gif[/img]
But I'd still like to hear why there's this "apparent" lack of accuracy and Why.
I have the GP31 connected to my SL72. I keep the SL72 in course up mode when running. While at anchor, in course up mode, the radar displays spins. The heading indicator on the GP31 is constantly moving, and the speed indicator bounces between 0 and .2 mph. Last digit of the position indicator will fluctuate at anchor. The plotter on the screen shows little circles and zig zags. Check out the furuno web page for the GR80 differential beacon. They have a diagram on the brochure showing the accuracy difference between the 31 with and without differential. This is before SA was off, so the distances are greater than what I see.
I have mine set up with no position smoothing, don't want it on.
I have changed my set-up so that I put the radar north up when I anchor.
In addition to the unit bouncing as described, the update on the plotter screen seems slow to me, relative to the Standard cp160 I have used.
That "bouncing around" as you call it is more a characteristic of the system as GPS is not an error free system even with SA set to zero.
Since the Stanadard Positioning Service (SPS) accuracy is spec'd as less than 13m (43 feet) 95% of the time (world average) one will see heading indicators fluctuating, non zero speeds and last digits flicking when at anchor.
That will basically occur with all receievers but it can be noticeable more so on some units than others. Some units don't have the processing power to actually process/output a "true" 1 second position update and transmit the same position over several seconds, which can have the effect of things appearing smooth. There will be constant appearance of change (depending on the mode/settings) in a unit that can actually process and output true 1 second position updates.
Certainly there will be a difference between a receiver using SPS and a SPS receiver with augmentation (such as dGPS). But that difference is not a "lack of accuracy" per say just an improvement in accuracy, which is not entirely what differential/augmentation systems are primarily about anyway.
Seems to me we are discussing two different things here.
I am attributing the lack of accuracy of the GP31 to the way it handles the signals and how fast it processes and displays those signals so that I can make use of them. Not to GPS as a whole.
I think you are saying that two equal machines(two gp31s for instance) will have the same accuracy. I do agree with this.
I have used both the GP31 and the GP36. The GP36 appears to do a better job with getting me the information than the 31. I don't know if the position on the 36 was correct or not, but the darned thing was not moving around like the 31 does.
Casey, still doesn't explain this apparent "lack of accuracy".
Now if this apparent "lack of accuracy" is based on the point that the 31's position moves around more than the 36 then that's not a "lack of accuracy". Got to come to terms with what is a "lack of accuracy" and what is simply a product of the GPS system and augmentation systems.
The 36 is basically identical to a 31 with the inclusion of differential. With a 31 & 36 both running in SPS (that is no differential on the 36) then there basically won't be too much difference.
Now a 36 (with differential on and assuming a signal) and a 31 side by side will/should show different position traits. For sure the 36 will/should show less movement in the position than the 31 but that's not a "lack of accuarcy" attributable to the 31, that's simply Standard Positioning Service Accuracy being compared to dGPS and there will be a difference in accuracy but again that's not a "lack of accuracy" as such.
Actually the 36 has more work to do (receiving and processing differential data) than the 31 but I doubt in processing terms one would visually notice that.
I guess I don't know how to explain it. I do know that the 31 is not a precision instrument and really is not good for finding and returning to waypoints if the location is critical. It is difficult to use that way. The other GPS systems I have mentioned are better at finding and returning to waypoints. I can't tell you why. I really don't know. I do know that when I have tried to use the 31 for that, I/it failed. Luckily I don't really require the 31 to do that, so it is staying on my boat.
You've got the general gist and dGPS units are certainly more accurate then those units relying solely on Standard Positioning Service signals.
That increased/improved accuracy comes at a cost and the more GPS accuracy ones requires the more it will cost. But with this improved accuracy "capability" comes disadvantages as well as third parties are required to provide that service and generally as coverage issues.
As for "why" well it's a thing that used to be termed Repeatable Accuracy but but now it's less than casting distance [img]/infopop/emoticons/icon_razz.gif[/img].
These days with the current accuracy capabilities of standard GPS there's really not a great deal of difference for the normal user. A standard old receiever these days (with SA set to zero) generally has an accuracy in the 7-10 metre range (normally less than 7m), which in some instances is further than the distance from the GPS antenna to the transducer.
No point in having/wanting critical accuracy if the relationship between the antenna/transducer is unknown and more than the accuracy of the system.
I've been primarily using the same receiver for over 10 years [img]/infopop/emoticons/icon_eek.gif[/img] (yeah still, but it has a BIG display and I'm needing those big letters today [img]/infopop/emoticons/icon_wink.gif[/img]) and that still finds the same things as it has done for years.
Accuracy wise, there's bugga all (none really) difference between that 1992 reciever and many available today.
I know I am getting into a "Catfight" here with all of the Garmin guys, but I actually do own 2 chartplotters on my boat. I got a closeout of an electronics store for a Furuno 1850 DF at a price that was a steal, even though I already did own a Standard 170 GPS. And I have looked at accuracy of BOTH of them in terms of repeatability.
In terms of same location repeat the Furuno is a little faster. In terms of usability both are about the same. In terms of "Washout" in sunlight, the Standard is brighter then ANY of the Garmins (and at 1/2 the price). The new C-Map NT chart chips are fully supported on the Standard and give VERY good definition in the area I am in.
I have to use the Navionics on the Furuno and I admit I do like them better for their seamless overlay compared to the C-MAP.
I strongly urge every Daytime Fisherman to look carefully at the CP 170 (and the new color 150) as a comparison to the Garmin units. The daylight visibility of these is unbelieveable.
Don't you miss the number keypad of the 1850 compared to the CP-170C? Of course cost is a consideration and right now I can get a CP 170C for $999 or the CP-160 for $399. Cheapest I've seen for a Furuno 1850 DF is $1349. Where did you get yours?
Also, in my area Navionics charts are supposed to be better than C-Map.
No, I don't miss the Keypad on the Standard, since it has a much easier method of entering route points. Doing a direct entry with the standard is for a masocist, since you have to use the pivot point to indicate a value. The
best and fastest way is to look at a chart, and move the cursor to your locations. Yes, direct entry is faster on the Furuno. But both of them are pretty easy to use. and Setting up a course for the autopilot on the Standard is a Dream.
both of these units are VERY user friendly.
furuno gp31 accuracy 
