I'm quite happy with my GT-11 for speed sailing and generally keeping track of my mileage etc...  but when it comes to navigation, it leaves a lot to be desired.
For instance, I'd love to see a 'trackback' function, so I can navigate along an existing track in memory.
Also, once a track has been written to the SD card, I cant find a way to retrieve it back into the unit. (I can download them OK)
Is there any chance of making it a bit more competetive with Garmin when it comes to basic navigation? (Id like to use it for rowing, hiking, etc... as well as windsurfing)

-jim munro
Hi, just got BGT31, went through the 70 pages manual several times
but couldn't figure out some few but important aspects of this device.
Perhaps obvious for others but not for me!

1) Doppler: Is this paramater active by default? I guess yes, but I would
thought that someone may have to scroll across the menu and set it off
or on accordingly. This does not happen, so I guess Doppler adjustment
is always present. Right?

2) Has anyone a 'feeling' of the size of a log file with respect to number of points.
i.e. Does it mean that 1 log point corresponds to 1 byte of data in the
SD card? Manual indicates for instance that the build-in memory can store up to 8192 points, so if points are spaced e.g. 5 secs that's about 11 hours and 18 min, so someone has a feeling of max usable time. Ok, you would say that a 2GB SD is big enough for endless logging, but an actual idea of a simple time calculation? I just want to know how to estimate log file size when time interval is given and vice versa. I will experimentally try to figure
this out if can't find info around. Perhaps I will use the log points 'counter'
provided under 'REMOVE CARD' or 'USAGE' option...

3) Reserved: What does 'RESERVED' mean under MISC Menu Tree? What's its purpose?

4) Any ideas of NMEA Items under 'Memory Card' selection? I read through
original NMEA website about those, but the analysis refer to those who invlolved with code writing...not useful for a windsurfer who wants a simple explanation of those terms...are they useful if activated?

Ok, too many questions, but I hope I bring up some aspects of our lovely toy which might be interesting to know.


Kostas GRE737
Hi Kostas,

Yes, the Doppler information is always written in the binary files. If you use the NMEA mode you will get it too but it does depend on selecting the correct sentences (NMEA items). Use the binary made. It is better.

The data logger can save up to about 7 hours of 1 second logging binary data but I don't know exactly how much and it depends a bit on what logging options you choose (no logging below a certain speed, etc)

I have one 265mb SD card that contains all my sessions for the last 12 months and is still half empty. (Binary format logging with both SBN and SBP files for every session) :)

The reserved items in the menu are for future functions.

Don't use the NMEA mode. The Binary mode is much more efficient and contains all the data we need.

Hope this helps, Andrew

sorry posted first without a text :-)

One of my customers (I own reported detailed size of files all loggerd in 1 sec mode.

In NMEA mode he logged 67 minutes and that produced a file of 1.88 MBytes. He extrapolated that to 1'100 hours or 47 full days with a 2 GB SD-Card.

In SBN Mode he reported for 42 minutes a file of 256 KBytes! Extrapolated this will be 228 full days with the 2 GB SD-Card.

Thank you all for the answers. I now have a better understanding
of how I should start setting my BGT31. I guess I will go through
several experiments and sessions to get a better idea about all
these parameters.

So, in the interface option I have now selected BINARY instead
of NMEA.

Also, since it was stated that for 1 sec log interval a 42min session
corresponds to approximately 256KB then, I will also set file
size to 2048KB to enhance data security too - enough for one
continuous day session on the water.

I let you know my findings when I reach some valid conclusions.