I am curius to know how it was decided historically to set the gates distance to 50m in calculating the alpha. Is it to exclude jibes after bearing away?

A fast gybe seems to just have that radius to come back square to the wind with a little bit of margin. It was just trial and error by Mal Wright (who invented the concept and defined the algorithms) and a few others and we just thought that was about right. Time has confirmed it.

We also experimented with @250 and @1000, but @500m seemed to be about right too!

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sailquik said..
A fast gybe seems to just have that radius to come back square to the wind with a little bit of margin. It was just trial and error by Mal Wright (who invented the concept and defined the algorithms) and a few others and we just thought that was about right. Time has confirmed it.

We also experimented with @250 and @1000, but @500m seemed to be about right too!

That was great work by Mal and you guys, I just love the alpha category, it's a great combo of skill and strategy, of course using alpha markers is cheating a bit, but it all adds to the fun.

The main problem I've become aware of lately is what happens to the data from an arm worn unit. In some cases it can be pristine with very low sdop numbers and trackpoints and doppler traces completely overlapped. In others the data into the gybe entry is very degraded.
Salty nuts has been doing some experimenting, wearing 3 GT31s, in different places. I think I'll start a new thread about his results.

Yes Mike, GPS data degradation has always been the issue with Aphas. It is much better when I wear the GPS's in the helmet. Wearing on the arm makes sudden movements that sometimes tricks the GPS and can lead to loss of sats in the Gybe blocked by the body.

The new 5hz and 10hz GPS's will greatly improve the accuracy if worn on the head.