It has been brought to light recently that the existing system of using trackpoints for alpha calculations on GT-11's, vs doppler for GT-31's is creating a bit of a problem for people who are running both devices.

It seems that the GT-11, which we recommend to use trackpoints for, gives a substantially higher reading compared to the GT-31 (which we recommend to use doppler). This normally gives GT-11 users an advantage of around 0.5 knots -- which can equate to many places in the individual rankings.

In one case, someone was wearing both devices, and got a doppler alpha values within 0.02 of a knot between the GT-11 and GT-31: gpsteamchallenge.com.au/sailor_session/show?date=2009-12-23&team=10 This indicates to me that using doppler on a GT-11 can't be that bad.

As more of us are going towards the GT-31, I'm considering making it a rule that all users (regardless of device) use doppler if available for alphas. This seems to be a fairer system for all. Of course, this depends on the technical committee figuring out if this is viable.

EDIT: Changed text above to make it clearer what the issue is. I think that simpler is better, and if everyone's using doppler then that makes the system fairer, and simpler.


Technical people: What do you think?

Edit 2: Can all people who use a GT-11 and GT-31 at the same time please PM me? We would like to have some more data to compare, this will let us make a sensible decision.