E80/Garmin mileage discrepancy

breausaw · Posted: Tue Jun 18, 2013 2:13 am Post subject: E80/Garmin mileage discrepancy

I bought a Garmin Montana 600 series for backup (an anchor alarm I can take to bed) and supplement the 7 year old Ray Marine E80 on the Triple J 25.

This last weekend I used both the ground trip odometer on the E80 and the Garmin Trip odometer.

On our way back from a 200+ mile run out beyond Montague Island in PWS I noticed a 30 mile discrepancy between the two odometers, the Montana was showing higher mileage.

Not being able to validate the E80 I removed the Montana and put it in my truck. I re-set the truck and Garmin trip odometer and drove the 50+ miles back to the house, the truck and Garmin correlated. I assume the truck is accurate; tire size is OEM.

So, has anyone else seen this type of discrepancy between GPS instruments? I can only assume that the 7 to 8 year old Ray Marine is just lacking the sophisticated technology afforded to the newer Garmin.

In the end this makes me happy, my fuel economy just improved significantly.

Captains Cat · Posted: Tue Jun 18, 2013 7:35 am Post subject:

Jay, just a data point but, was the E80 following a track or just measuring distance traveled? Assume both were measuring the same units too? Is the Garmin measuring statute miles and the E80 measuring NM perhaps?

Charlie

breausaw · Posted: Tue Jun 18, 2013 9:54 am Post subject:

Units the same on both.

Captains Cat · Posted: Tue Jun 18, 2013 10:34 am Post subject:

Sounds as if the E80 dropped the GPS signal for part of your trip and the other one did not.

Hunkydory · Posted: Tue Jun 18, 2013 10:40 am Post subject:

I run three different gps's & there is almost always a discrepancy between them all especially in longer runs or the trip total. These discrepancies in my case come from their differing momentary satellite signal loss causing the boat placement on the chart to move & that non actual movement is recorded as real movement.

When recording daily or trip milage I most often use my little Garmin 276, which very seldom loses its signal.

Jay

starcrafttom · Posted: Tue Jun 18, 2013 12:01 pm Post subject:

you said that you used the garman for a anchor alarm right?? so as you are swinging in a circle all night you are racking up distance right?? was the e80 doing the same??

Aurelia · Posted: Tue Jun 18, 2013 1:45 pm Post subject:

Tom is on the track I was guessing. You would be surpised how much mileage you rack up on the GPS while swinging at anchor. Also the logging interval can be adjusted on some units and not others and this may have an impact on the trip "computed" mileage causing a variance between brands or even on the same model and brand. Configuration is key so check the manual.

breausaw · Posted: Tue Jun 18, 2013 2:54 pm Post subject:

starcrafttom · Posted: Tue Jun 18, 2013 4:37 pm Post subject:

I have a canny resemblance to a blind squirrel.

breausaw · Posted: Tue Jun 18, 2013 4:51 pm Post subject:

I plan on making the same trip Friday so will run the two units side by side. None stop for about 75 miles will be a good test.

8 halibut with one over 100 lbs, 7 large rock fish 4 being yellow eye.. I must return!!

thataway · Posted: Wed Jun 19, 2013 10:14 pm Post subject:

It is very possible that the E 80 measured a straight line, and the Garmin measured the track, which will be longer.