can anyone tell me if we can use trackpoint datqa instead of doppler as i just realised my alpha from the 8th is significantly better than the doppler calc.
if we cant let me know and i will delete it cheers ....
Yes to trackpoints! especially as the navi is about the only one that does doppler, people with garmins have no choice, they have to use trackpoints.
But if your alpha is significantly better with trackpoints, it may be because it's using some invalid data, just check the track, make sure they are the same alpha if they are different runs, the one track points is using probably contains an invalid.
the track should be a continuous "U" with no jumps or funny straight red sections in it, also check the "seconds" column over the alpha range, if they should all show "1sec", having anything bigger is also a sign of invalids.
excuse my ignorance here, but when looking at alphas on Realspeed, do you just take an average of the lowest and highest speeds on that particular run to get the alpha speed? My display just gives those 2 speeds and I'm wondering if I'm missing something somewhere that gives the reading....
thanks Decrep,
just checked the whole of the top 5 alphas and all of them look very kleen and smooth,all of them increased significantly by aprox .4 or .5 of a knot once i selected trackpoint over doppler. the 5th best alpha was 23.54 something knots.
also checked the alphas(dop and track) are the same gybe..
I have done a fair few Alphas now and I am a bit suss about the Doppler in this particular application. There seem to be some things happening in the really sharp turns that produce an unnatural speed graph on some runs. I recommend you use the trackpoint info with the GT-11/Navi rather than the Doppler. Hopefully we will find out what the issue is and a way to fix it.
Biggest problem with the NAVi is the track smoothing filter they use in the firmware. It has a problem adapting to sudden changes in direction and uses a proprietary algorithm to smooth the data. It is possible to turn it off but the resultant data has some interesting spikes that call into question the original data used to validate the accuracy levels for the unit. Suggest you run with trackpoints for all speed measurements.
cheers guys seems i may have raised an interesting issue.... i have had the track checked by 25 and slowy (yeah i know they are team mates
) and they both have found it to be clean.
hi Decrep-
sailquick's comments are as you have stated.
i believe slowboat also believes there may be issues with the way doppler 'interacts' with the alpha measurement,his comments to me last time we spoke was that trackpoints may be a better measurement for this categorie. maybe Chris,Mal or Andrew can comment further.
i know some of you mandurah guys are clearly stating that you are using doppler for all divisions but i feel you could be robbing yourselves of 'faster' alphas in particular.
Up to now I didn't take much notice re Trackpoint V Doppler until tonight and ran some changes over old sessions just to see difference. Trackpoint comes out on top each time. Some hardly worth the effort, others near on a knot.
Its not ever going to impact my scores, as I run at about 60% speed at my very best, of those cracking good alphas, but as Snides said, some may be short changing themselves by only recording Doppler measurements. 
I use doppler on all fields, if Trackpoints can give you an exaggerated speed on a 2 or a 10 sec then it can do the same for a bendy run.
The people most concerned would be the ones who can gybe and had been using TP's then converted over to Doppler, this would have put them behind the 8 ball for a couple of sessions.
Realistically looking at the way people have been improving with their gybing since the Alpha's were introduced it won't cause to much of a problem.
OK done a few quick checks with gpsarpro. on 4 files.
Average difference between doppler and trackpoints for 500m is about .1kt average difference for alpha 500 is about .5kt
So I think the theory that trackpoints are more accurate for alphas is correct, I'll continue to use that method until whatever the problem is, is resolved.
Yep, in the end it is more important that it is the same for everyone than .3kn here and there.
By the way Roo how fast did you go when you were over here? I heard you gave the guys at Melville a hard time.
Had a great time sailing at Melville, first time out there and a great location. Would love to tell you my top speeds but I think Bruce, the Swan River shark, is swimming around recording speeds with my GPS. It dropped off in a jibe and I couldn't find it again. There are certainly some fast guys out at the location and it was a real blast to go flat out through the chop. Look forward to laying some fast runs down on my next visit, say a big g'day to the guys I met on the beach and who made me welcome.
Well at least it is the right colour. Not sure if the through the floor ventilation would help or hinder the aerodynamics but I can't image it would do much for the chassis rigidity in the whoops..
something special about driving right to the waters edge....unless the tide comes in whilst you're out
