The distance data from my sail this morning doesn't reflect what I really did. KA72 says I only did 2.39 km but my GPS says odometer 6.71nm and trip odometer 5.713 nm (Why do I always get two different readings there?)
and the track is really weird. Apparently I didn't start or finish at the shore, there are no gybes and I have made a 90 degree turn at some point. It's a bit like connect the dots.
The mast did hit me on the arm at one point and paused the GPS for a while but I corrected that.




Any ideas? What has happened and how do I fix it please?

Firstly the difference between the two readings is due to the trip ignoring data below your min speed setting.
With regards to the track, do you have more than one file on the card? Did you wait till it displayed "New File" or did you confirm that it showed the 3D symbol top right of screen before sailing? Lastly try saving the data logger to the card and send me your track and I will have a look.

Lots of files on the card but I did save to card and zero everything at the start of the session.
It did display new file but I did not look for the 3D symbol. You just about need a magnifying glass to see it!
Saved data logger and sent file as requested.

New GPS Challenge: reproduce my track while sailing!

That's nasty!

I ran the track through RealSpeed too, and it reports total Dop distance of 2404m.

I expect the difference comes from min speed settings, and probably from bad data being discarded (there is quite a bit of bad data in the file too.)

(When you remove invalid data in RealSpeed, the distance drops to 2316m.)

As to why the trip odometer reading is different than the odometer reading in your GPS, I'm not sure why this is. Do the different odometers have different min speed settings?

Cheers,

Dylan.

Thanks Dylan.
I sent my files from Wednesday to Lao shi, and saved the data logger to card but there was nothing on the card after the 11th of March! even though I've sailed a few sessions since then, with accurate tracks except for Wednesday.
Maybe when the mast hit me on the arm on Wednesday and reset the GT31 it corrupted it in some way or deleted a whole lot of data.

I hope it works properly next time. I will borrow one from WWA to compare it with.