gps

[57lawney]

how precise is a garmin legand handheld gps for use in trolling?

 

[Silvertip]

Re: gps

About the same as it is for hiking or auto travel. What you mark as a waypoint is of no consequence whether the GPS is a handheld or permanent mount. GPS is GPS. How you use it is up to you. It will take you back to any saved waypoint whenever you wish.

 

[Moody Blue]

Re: gps

Depends on what you are asking.

Pretty much any consumer GPS has an accuracy of about 5 meters (17ft) so if you are trying to retrace a path, you will be within 17ft +/- of your original pass.

Pretty much any GPS, handheld or fixed mount, will give you accurate speed indication if thats what you are looking for.

 

[dingbat]

Re: gps

The Garmin handhelds and car navigation units are not as accurate as their marine counterparts.

Garmin uses different (lower sensitivity) GPS receiver in their marine units than they do in handhelds and car navigation systems. Garmin claims the increased sensitivity is good for low signal areas (i.e. cities,woods,etc.) but the low signal levels actually degrade the overall positioning accuracy of the unit.

In comparing a Garmin fixed mount to the Legend, the handheld is 5 times less accurate than the fixed mount.:

Legend:
Positioning Accuracy: < 15 meters
Velocity Accuracy: 0.05 M/sec steady State

Garmin 4208
Positioning Accuracy: < 3 meters
Velocity Accuracy: 0.01 M/sec steady State

The Legend does not come standard with DGPS or WAAS corrections. You must buy an optional external antenna.

Don?t see how the accuracy would play a part in trolling unless you where using a chartplotter to troll the contour lines. At that point, you also need very accurate maps.

I can?t speak for the Garmin inland maps but their Coastal Bluecharts are about as good as they come. When the chart says I?m in 15 feet from the edge of the shipping channel, I?m 15 feet off the edge.

 

[trendsetter240]

Re: gps

While I agree with dingbats post for the most part, I will add that some handhelds are better than others. I use a Garman 60cx handheld on my boat and find it is excellent for navigation and speed.

Though the accuracy is slightly lower than the 4208 example it is better than the Legend.

I paid about 300 for my 60cx and compared to the price of the 4208 it's a bargain.

60cx stats:

"GPS Performance
Receiver: 12 channel SiRFstar III? high-sensitivity GPS receiver (WAAS-enabled) continously tracks and uses up to 12 satellites to compute and update your position

Acquisition times:

Warm: < 1 sec
Cold: <38 sec
AutoLocate?: <45
Update rate: 1/second, continuous

GPS accuracy:

Position: <10 meters, typical
Velocity: .05 meter/sec steady state
DGPS (WAAS) accuracy:

Position: <5 meters, typical
Velocity: .05 meter/sec steady state
Protocol messages: NMEA 0183 output protocol

Antenna: Built-in quad helix receiving antenna, with external antenna connection (MCX)
"

source : http://www.pocketgpsworld.com/garmin-60cx-review.php

 

[jhebert]

Re: Accuracy of GPS Speed for Trolling

Re: Accuracy of GPS Speed for Trolling

I made the inference from the initial question that the focus was on the speed accuracy of a GPS receiver due to the mention of "trolling," or angling for fish from a moving boat.

The speed accuracy of the GPS receivers cited above is 0.05-meter/sec. To convert to MPH:

0.05-meter/1-sec x 3600-seconds/1-hour x 1-mile/1608.3-meters = 0.1-miles/hour

When trolling for fish, I think a speed accuracy of 0.1-miles/hour is reasonable. It is difficult to adjust the speed of most outboard motors in increments as small as 0.1-MPH

 

[bruceb58]

Re: gps

Garmin uses different (lower sensitivity) GPS receiver in their marine units than they do in handhelds and car navigation systems. Garmin claims the increased sensitivity is good for low signal areas (i.e. cities,woods,etc.) but the low signal levels actually degrade the overall positioning accuracy of the unit.

Has less to do with the sensitivity of the receiver than if WAAS is used.

Since we are quoting Garmin here:

Typical GPS accuracy without WAAS is 15 meters.

Typical GPS accuracy with WAAS < 3 meters.

http://www8.garmin.com/aboutGPS/waas.html

 

[dingbat]

Re: gps

Has less to do with the sensitivity of the receiver than if WAAS is used.

Since we are quoting Garmin here:

Typical GPS accuracy without WAAS is 15 meters.

Typical GPS accuracy with WAAS < 3 meters.

http://www8.garmin.com/aboutGPS/waas.html

I think you'll find it interesting that even with DGPS and WAAS, Garmin still quotes the accuracy of their "newer" handle helds and car navigation systems at 3-5 meters 95% as opposed to the marine units which are rated at < 3 meters 95%. A considerable differnce.

The old handhelds had the same specs as the marine units so it appears that they traded a quick fix and the ability to see in low signal areas for some degradation in the overall accuracy of the unit performance.

2. The Move to High-Sensitivity : SiRFstarIII : This all changed in mid-2005 when Garmin announced they would be using the high sensitivity SiRFstarIII chipset in their upcoming n?vi car system and a bit later in the 60/76 Cx handhelds. The SiRFstarIII chipset was launched by SiRF in early 2005 to take over from the SiRFstarII chipset that was already more powerful than the old Garmin chipset, respective tracking ratings being -159dBm, -148dBm and -143dBm (the lower the better). Acquisition sensitivity remained at about -143dBm as this is the level of signal required to download the live ephemeris data from the satellites needed to calculate a position, but with its massive correlation the power, the SiRFstarIII was able to scan the sky for satellites and TTFF (time to first fix) was much faster, provided that minimum level of signal was available.

This move was applauded by most users as it made acquisition times in the morning much more consistent, never more than a minute in good conditions, a bit more while driving and the GPS systems kept tracking virtually everywhere, including indoors, not that it was really useful...The flip-side was that very weak satellite signals were now being used, resulting in a much less stable position, one of the reasons to stick to low-sensitivity systems for marine GPS systems.

http://www.gpspassion.com/fr/articles.asp?id=259

 

[57lawney]

Re: gps

what i am trying to figure is speed. there are 2 lakes i mainly fish. both have kokanee ,which perfer about 1 mph. the large lake coeur d alene has chinook salmon that like 2.1 mph.seems strange but any thing over a few tenths they wont bite. the hand held garmin legend is what i have now, hope to upgrade some day to gps ff, the problem is they seem to become obsolete in a couple of years.

 

[jhebert]

Re: gps

See my reply above, #6. It was the only reply to address speed accuracy.