Precise low speed velocity => help for GPS assisted manned Sailing boat ;-)

Dear all,

I'm considering to build a Arduino/GPS+someting device to have precise feedback about about Velocity and Velocity Made Good on my catamaran. The boat is a small hightech catamaran :

http://dnacat.blogspot.com/2011/01/bundy-pics-by-carolijn-brouwer.html (not me on the pics)

Our speeds are between 0 and 20 knots. I currently use a Locosys GT-31 GPS, but even when GPS doesn't move, the displayed speed varies a lot (oscillating between 0,1 and 0,8 knts). There is a speed 5s average function, but it is the same : too much variations when you try to identify a 0.5 knts difference.

We don't really need "accuracy" but instead "precision" (if I'm not wrong) to see the tuning differences.

I have in mind a Arduino/GPS project, and I'm looking to the ways possible to implement to have a more "precise" velocity information. Let say 0.2 knts error (I'm not sure of the wording) would be good.

Is it possible to achieve this with GPS alone + adequate treatment/algorithm ?

Would the use of accelerometer allow to improve this ? How and in an important way ?

Thanks for your help

JMF

Perfect position information on the cheap. Everyone wants this JMF not just you. Currently there are several DIY dGPS things going on (only one on here as far as I have seen though) which would give you GPS position down to <1m thereby reducing your speed error to less than your 0.2knts but it requires some patience and time to get everything working.

I took a brief look at solutions but they all use a moving GPS receiver (plane/boat/car) and a stationary GPS receiver to give corrections which is not what I had in mind for my own personal use. Take any press released picture of a big UAV (Global Hawk, Reaper etc) and you can see the dGPS antennae dotted all over the body. Being military they probably use something weirder than normal dGPS but still it got me considering using mobile units strung together as an option. After a few days of research it seems that no one else thinks its viable method.

You never know you could create an entirely new version of positioning system if you're lucky :)

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Greg Fletcher January 8, 2011 at 11:54am

I think the problem might be the GPS. I am using a Ublox GPS and I don't see variations in the ground speed when it's not moving. It reads zero with an occasional 1 m/s. That's much better than 8 knts. Averaging would help as your speed is probably pretty steady. If you used a pressure sensor with the right range it would be easy to use a water speed pitot tube. They are cheap enough you could put one on each hull and just ignore the side out of the water. And still have a GPS.
Ritchie January 8, 2011 at 6:13am

Perfect position information on the cheap. Everyone wants this JMF not just you. Currently there are several DIY dGPS things going on (only one on here as far as I have seen though) which would give you GPS position down to <1m thereby reducing your speed error to less than your 0.2knts but it requires some patience and time to get everything working.

I took a brief look at solutions but they all use a moving GPS receiver (plane/boat/car) and a stationary GPS receiver to give corrections which is not what I had in mind for my own personal use. Take any press released picture of a big UAV (Global Hawk, Reaper etc) and you can see the dGPS antennae dotted all over the body. Being military they probably use something weirder than normal dGPS but still it got me considering using mobile units strung together as an option. After a few days of research it seems that no one else thinks its viable method.

You never know you could create an entirely new version of positioning system if you're lucky :)

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Precise low speed velocity => help for GPS assisted manned Sailing boat ;-)

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