I guess what you mean is a way of recording the GPS data output from the GPS chip built into the phone.

I looked into this a while back and from memory there were a few apps that could record some of the data, mainly the 'trackpoint' or location data.

AFAIK, there are no apps that can record the equivalent of the Sirf binary data we use to get dopper derived speed and the error correction data.

If the I-phone has a sirf3 GPS chip, it might be possible, but many other brands of GPS chip can not output this data.

Even if you could record this data, you would have a very expensive device that was at very high risk. It would also probably not have the display data that the GT-31 Genie gives you about your previous runs etc.

Better, and less financially risky, to just get a GT-31 and a Paqua bag.

Not an iPhone but I've compared the results from a Navi GT-11 with a cheap Android phone using a GPS tracker application.

The results were very comparable. Not very much variation between the two. However AFAIK no phones are considered to be accurate enough to allowed in GPS speedsailing competitions.

Keep in mind that smashing an IPhone 5 is near $1000 replacement whereas a gps is a few hundred and a lot tougher.

well got a otter case (armour) WATER PROOF 3 METERS DROP PROOF 3 METERS FOR IPHONE 5 . WENT FOR A HOUR LONG SAIL GPS ON AND HAD A FEW STACKS NOTHING BIG. BUT THE CASE DID NOT KEEP WATER OUT SO DONT TRY THIS AT HOME KIDS . ARRRRR WELL I TRYED

taillight said...
well got a otter case (armour) WATER PROOF 3 METERS DROP PROOF 3 METERS FOR IPHONE 5 . WENT FOR A HOUR LONG SAIL GPS ON AND HAD A FEW STACKS NOTHING BIG. BUT THE CASE DID NOT KEEP WATER OUT SO DONT TRY THIS AT HOME KIDS . ARRRRR WELL I TRYED

Yep, sad to hear. Sometimes better to listen to the very experienced ones that posted on the forum. You think you are going "faster" but you're not!

GT-31 is the only way to go. Would not use a sanger bag though.. unless I was taking a sandwich of course..

Aqua pac or Paqua.... best bet