Can anyone help tell me why and help fix why my 31 only records sessions for about three hours, then it starts a new one. so when i sail for about five hours or more, when i go to down load the info i have 2 sometimes 3 sessions on the card. surely the whole day/session can be on file???!! help
Make sure that you have the set up as described here http://www.mtbest.net/setting-up-navi-GT31.htm
Setting up GT31 manually
1. MEMORY CARD
a. LOG SWITCH should be ON-FIX. There is no point to log any data when there is no position fix.
b. NMEA ITEMS should be set to "SBN 1 SEC". Binary logging ensures maximum possible trackpoint accuracy and maximum data reliability. If you want the most complete data set from your sailing session, use SBN (binary) format logging.
c. MIN SPEED should be set somewhere between 2 and 5, unless you are specifically interested to log data when you are stationary.
d. FORMAT CARD. Read readme.txt file to find which cards are compatible with G31. Format the card a few times in a row. If you succeed each time, you can rely on the SD card that you use. Formating is the most drastic writing operation you can perform on your card and hence it is the ultimate test of your SD card compatibility.
e. FILE SIZE should be set to CARD SIZE. This means that you do not put any limit on file size.
Have you set the time zone correctly? If not then it may make a new file as you go past 0:00 GMT.
Also what is the file size of the first file?
Are you really sure about
"e. FILE SIZE should be set to CARD SIZE."
The only other reason I know for more than 1 file, is turning the unit on and off again.
It may be the file size it was set to 1024 which is the max size of the session it used to record, i've tried to set it 2048, hopfully this works?!
wantmore, just in case, and I am sure you have a handle on it now.
When the lads say card size, its "card size" read out on your screen.
Not the actual size of the card you have in the GT31
.
The trick is scroll though til it reads "card size" and select that. Bloody confusing really, and your not the only one to get stuck on this little gem 
Thank you, i relise now, i was thinking they ment the card in the unit, not setting the unit Cheers for the advise.
Not the actual size of the card you have in the GT31. 
