Why ?? What sort of top speed have you recorded, or heard of being recorded (in SUP?)....

I'd be hitting up a search engine like Google for this one....

I googled it. Reams of info on the subject. The op may want to do the same to find an answer to his specific question.

In my opinion, it is a very complex subject. Doppler shift, velocity computed in three dimensions...

As for measuring a quick move of a handheld gps, I suppose you could try it. My guess is that it will not be accurate, because that's not what it's designed for.

I think they use accelerometers for that type of motion.

I'm not a man of science, but I play one on the internet.

teatrea, I looked at your file. We use Gps's on our maliko runs here. My top speeds on an oc-1 are usually in the 13.5mph range. Your 12.8mph is reasonable - if you were flying on a wave.

The fastest gps I've heard of on an SUP is 20, on a 10-6 sufboard, 25mph. Those readings were by a very experienced surfer in very heavy conditions.

Mine where recorded on falt water today , maybee i forgot to tun it off before i got in the car Lol.I have had it on me when surfing runners and the top speed was higher again.
Thats why i posed the question , to see if it is accurate.With the phone in my pockett i thought their would be less movement which would maybee increase the accuracy.

Oh well it was nice to think i got the old 17footer up to 20 clicks for a while.

I haven't done that many runs with GPS but your average speed sounds reasonable whereas the spike of 20km/h is probably just that - a spike. We've managed average speeds of 9km/h where our max never exceeds 11-12km/h on perfectly flat water - no wind or wave assistance. On downwinds we hit max speeds of 25km/h and I've heard of higher in SUP'ing.

GPS Action replay has software you can download to analyze your file which gives more detail.

cheers , thanks for the help i will look those things up.