gps speed difference

[KING]

Just wondering about a speed difference I am seeing between two gps's. I have a Lowrance lms 350A which will give me 50+ mph, my Garmin 168 says 40+, incedentally the speedo (wheel) says 40+. I tend to beleive the 40+ because that is what it feels like, but how could the Lowrance be 10 mph off. The position and tracking seem good, and slow speed seems good. Any ideas?

[mnrstrider]

Is this one instance, or has this happened multiple times? Sometime my gps just gets off course some how, and plays catch up, says I'm moving 10-12 mph when I'm not, eventually it finds it's spot and returns to normal. First time out with my boat it said I was doing 37-38 mph, then I tried it again, and found out it was "lying" the first time, and I was only doing 29 mph . Other than that I dunno..

[musky hunter]

I too have an LMS350. There is always a difference between the speed wheel reading, the gps, and the boat spedometer. I've always taken the gps as correct, and it is always the lowest of the three. I guess one way to find out which is correct would be to run a straight course of known length at a constant speed and do the math with a stopwatch.

[Surface Tension]

King whats the EPE on the LMS350 and was this a one time occurrence.

[Surface Tension]

Granny thats where I was going with the EPE. I've notice my GPS loosing signal and high EPE since The War.

[KING]

Just got back in from sturgeon fishing on the Rainy. Once again the same old thing, LMS reading 54.3 mph Garmin reading 43 mph speedometer on dash 45. Ran back and forth up the river and it is the same everytime. Tracking seems ok, and the position #'s are very close.

[minnesota mac]

I was wondering if one of your gps's is in knots. Mine has a setting for mph of knots. I have a garmin 176. If not maybe its broken. Good luck mac

[Granny]

I think that you may see a sudden change in speed for National Security reasons. I think I read this in the directions of my old GPS unit.

Granny

[Big-Al]

If one is configured in knots and one in mph that would explain a difference, but the math still doesn't come out right. 54.3 MPH = 47.2 KNOTS. I doubt if it is because of accuracy, being you are on the water and in full view of the sky. Are either if these units WAAS capable? If so and you aren't getting a WAAS signal, try shutting that off. There may be another setting, kilometers per hour, although I don't think so on either of these units.

[Guest]

I have noticed when flying if I have a radio and a gps on, or, two gps's there is some interference. Try comparing both to the boat speedo without the other on. I would trust the Garmin every time, even though I use the lowrance for fishing.

[trollingforeyes]

If that LMS350 is taking the speed reading off of the paddle wheel, I would definately go with the GPS speed. I have the LMS 350 also an the speed off the paddle wheel was so far off the I removed it and went with the GPS speed. I ahve also heard other complaints of the paddle wheel speedos being far off. It has something to do with the flow off water from under the boat to the paddle wheel.