GPS reading SOG incorrectly
Submitted by Cruise Control on Mon, 2013-04-29 12:48
Here's one out of the blue.
I have a Raymarine L760 GPS (an oldie but a goodie) and a HDS8 - The Raymarine reads a SOG approx 4 knots slower than the HDS at 25 knots. The differential varies as the speed increases/decreases. I have run up a handheld GPS which aligns with the HDS, so happy that it is reading correctly. Any ideas why the Raymarine would read slow ? GPS aerial is new and Lat/Long readings are close enough to HDS to be the same. Surely it doesn't have to be calibrated ?
cheers
NOHA
Posts: 914
Date Joined: 24/06/07
Right units
Check the ray marine is in Nautical miles not statute miles. The error is 1.15 which 25 knots is 21 miles an hour. something like that
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crasny1
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Just what I thought
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Rob H
Posts: 5812
Date Joined: 18/01/12
ditto
problem looks like your Raymarine is reading knots and HDS in mph, my older Lowrance it was pretty easy to get in and change to knots.
When you going to bring that bad boy up to Gero for a run to the islands?
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Cruise Control
Posts: 973
Date Joined: 03/11/10
OK - when I read the replies
OK - when I read the replies I nearly kicked myself for being so dumb. So raced home to check it out, powered up and lo and behold, both reading in knots . . . . . . . I guess its back to the drawing board.
Rob, will be coming through Gero early morning Friday 17/5 on the way to Coral Bay. Still really keen to get to the islands but that might have to wait a few months. You can bet that I will be looking you up though when its time to go !
cheers
Rob H
Posts: 5812
Date Joined: 18/01/12
Its just seems too much of a
Its just seems too much of a coincidence that it appears exactly the difference between mph/knots.
Maybe a factory reset on one or the other (HDS seems to be the one showing mph when it says its knots)
I get home on the 10th so if ya feel like dropping in for a cuppa on the way thru Im near 440 roadhouse.
We are heading up to CB late July pobably.
Give a man a mask, and he'll show you his true face...
The older you get the more you realize that no one has a f++king clue what they're doing.
Everyone's just winging it.
Brucesta
Posts: 1721
Date Joined: 29/05/09
possibly being an older
possibly being an older model it may not refresh as often as the HDS and thus giving a lower average? external antenna vs internal antenna on either unit, to play devils advocate maybe the handheld and HDS are wrong? does the difference stay the same at different speeds eg 8 knots on the raymarine and 12 on the HDS?
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Cruise Control
Posts: 973
Date Joined: 03/11/10
Yeah . . . . . I dont know
Yeah . . . . . I dont know if that would be it. The Raymarine refreshes quite quickly and the antennae is external mounted on top of the bimini as well as being a relatively new antennae.
You could be right though about being the devils advocate. Next time out I will use yet another handheld to measure speed but this wont be for a couple of weeks.
The speed diffential does not stay the same. It looks to be about 20% so 21 knots on the Raymarine equals 25 on the hds and 10 knotsn on the Raymarine is 12 on the HDS
cheers
Brucesta
Posts: 1721
Date Joined: 29/05/09
i know my Yamaha gauges read
i know my Yamaha gauges read different to my GPS but the GPS is SOG where the motor is a calculation. does either of your units link into the motor via NMEA technology? with the % staying about the same i would still be thinking incorrect speed or distance settings... without being there these are my best guesses
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