Since my BGT-31 GSP failed at second use and waiting for help from manufacturer I was tempted to use GPS in my mobile phone in the meantime.
Since GPS windsurfing is so much fun - once you try hard to stop. GPS Kitesurfing and sailing must be too 
I can now review at home how many km I did, top speed and generally track all sailing on Google Earth.
I tested my mobile phone yesterday ( Nexus 4) , just pack safely into waterproof pack.
I use free Android applet " GPS LOGGER" available from PLAY.
Definitively quality of recording is much inferior in comparison to purpose made GPS logger like GT-31, but for those that could not effort still good alternative ( as oppose to have nothing at all).
So if you got any old mobile phone let it try on the water, but waterproof it first.
Because arm mounted waterproof case is hard to get and bulky I just hang my GPS/phone on the string and kept on the chest behind shirt in plastic watertight pack container.
Here is sample of recording done yesterday.
Maybe not as ideal as GT-31 but readable and without any strange peaks too.
Mobile phone GPS with applet like " GPS LOGGER" could create file .GPX or .KLM and upload it automatically to my email box or gps site.
Settings needs still some fine tuning and chart and recording quality could be further improved.
and here i was thinking that sailing/kiting/surfing was all about getting on the water and enjoying the moment...i really don't understand wanting to dissect every session with gps tracking, go pros, peanut gallery photos etc.
each to their own, but i can't help thinking all this gadgetry detracts from the essence of the sports.
no, no, no
windsurfing is 90% talking, analysis, equipment review and
10% water time
