Using the Navi GT-31 Speed Genie GPS for Windsurfing

The Navi GT31 is the best GPS to use for windsurfing, along with their other model the GT32 which includes bluetooth functionality and anything else they subsequently will release to update them. The reason for this is the simplicity of it and the Speed Genie function. Setting the unit up is covered on many other websites, Tom Chalkos being one of the easiest to follow and regularly updated with the correct links. GPS Speedsailing also has a set of instructions. Erik Loots Speedsurfingblog also has some good advice

This post is not intended to duplicate anything on the other sites. I want to help people use it in the easiest possible way so that there is no confusion regarding the different files it produces.

There are two main ways to transfer the data from the GT31 a computer; by either using the SD card, or by connecting the GT31 to a USB port and using the provided software (Navilink). For the first 18months I had the GT31 I connected it to the computer and downloaded all the files it would give me. This meant turning the unit on and putting it into the correct mode in the menu system. The problem with this method is that the 'nmea' file then logs the data at home, so making the track 'distorted' in the analysis software. It is easy enough to delete this part of the file in the software but unnecessary if you follow this method of use.

1. At the start of the session delete all data. This can be done with a simple click on delete-all in the 'MISC' menu. If you also want to reset distance and time then go into the Track menu and do so, but this is not needed unless you are targeting a specific distance or time for the session.
2. Use the device and enjoy your session, hopefully beat your personal bests. Turn the unit off at the end of the session, please remember to do this or your 40knot speeds will probably have been done in the van/car while driving home.
3. At home take out the SD card and put it into your card reader, transfer the files to your computer. If set up correctly you will have two files, a SBN data file with all the data from the session, and a SPD file which is a simple text file that has your best runs on.
4. Use the SBN file in which ever software you choose. I use GPS Results as I like the simple interface and the fact it is not javascript based. Friends of mine prefer GPS Action Replay which I do not find quite as intuitive to use. I know a lot of the sailors from Australia simply upload their file to GPS Speedsailing or GPS Team Challenge on the KA72.com site. Alternatively you can use Sports Track Live to give a basic analysis of the software and a backup of your tracks online, scroll to the bottom of the page to see this software in action.
5. Delete the file from the card if you want and replace it in the GT31 ready for the next session. 
6. Repeat from 1, especially the part about enjoying your session.

If there is a problem with the SBN file or the card then the files contained with the unit itself can be used as a backup and transferred by connecting the unit to the computer and reading them with Navilink.

For the first 18months of use I have hundreds of different files, in several different formats and I never knew which ones to use. Now each session I simply have the SBN file and know that if there is a problem with this then the unit has the backup.

Another small thing to bear in mind is keeping the unit away from salt water. Very occasionally the unit may freeze, the only options when this happens is to either wait for the battery to discharge which can take days, or open it up and disconnect the battery. Mine has frozen once, because the Aquapaks are not 100% waterproof a couple of the screws had become corroded and ended up being 'cracked' out of the plastic case to open it up. Now I always put the unit in a small bag inside the Aquapak. Don't worry about this too much, the GT31 is water resistant so a small amount of water will not damage it, it was the salt that caused the corrosion.

I hope this helps anyone with the small intricacies of using these fantastic bits of kit.