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 ....

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....

sick_em_rex said...

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....

G'day Mr Rex

You should have 3 column on your print out sheet

Speed (the one you want)
Min speed (the slowest point of the run)
Max speed (the fastest point of the run)

If you are still having probs PM with your email add me and I'll email you my "Default" file for the programme

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.

Roo said...

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.

I'd be interested to know how to turn off the filter - I haven't seen this mentioned anywhere previously.

In the real world, Doppler calculations without any filtering, should be erratic - the atmosphere plays a very important part in signal reception, as does any micro-movements of the device - with filtering, we get smoother tracks that we currently see. As we get faster-sampling units, I'd expect the data to become "more jagged" as the unit picks up each micro-movement and signal variation. (assuming infinite precision, zero acquisition time, blah, etc... which differs from the Foretrex's lack of precision).

sailquik said...

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.

Any movement on this???????

Is the advice to still use trackpoints for alpha???

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.

snides8 said...

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.

Thanks Snides, I vaguely remembered this thread a few sessions back, and went back to trackpoints for alphas, just had to reafirm I'm not doing anything different/wrong, to everybody else.

I'll have to check the difference between dopler and trackpoint for an ordinary 500m, versus a 500 alpha.
I have a feeling that doppler and trackpoint aren't that different over 500m, it's more the short times where the differences show up.

decrepit said...

Any movement on this???????

Is the advice to still use trackpoints for alpha???

I have not heard of any changes and Roo's explanation seems to be the best I have heard so far.

My initial suspicions arose because the speed graph from the Doppler did not seem to agree at all with my feeling about how the gybe went. There were some gybes that felt very smooth with no noticeable sudden drop in speed and subsequent acceleration, but that is what the Doppler graph showed. On the other hand the trackpoint graph agreed very closely with how the gybe felt. The more I did the more I felt there was something weird happening with the Doppler in the sharp turn. I have tried to do tests in my car on the beach where I can watch the speed as it happens and compare this with the graphs. I was trying to keep a constant speed in the turn but it was a bit inconclusive because I found it hard to turn that tight at that speed in the car without scrubbing off speed in a huge slide!

I suggest sticking to Trackpoints for the Alpha for now. It seems more consistent and at least it is the same for everyone using different GPS.

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.

frant said...Andrew. Easy to do 50 knots in a straight line along the low water mark though[}:)][}:)][}:)]

Hmmmmmmm [}:)]

Not in the Volvo!!

elmo said...

sailquik said...

frant said...Andrew. Easy to do 50 knots in a straight line along the low water mark though[}:)][}:)][}:)]

Hmmmmmmm [}:)]

Not in the Volvo!!

they can't go that quick[}:)]

Do you remember the year they won a big race, (was it Bathurst???)
Every Volvo you saw on the road was going like a mad thing!
All those years of suppressing the Volvo bashing they had to wear, was finally released.

elmo said...


>>>>>>>>

No Volvo's in the list of Bathurst winners, unless they won a 24hr production car race there (I don't thunk they did).

>>>>>>>>>>>>>>>>

Try this, http://www.worldwideticketing.com/sports/motor-sports/bathurst-1000-supercheap-auto.htm
about 3/4 down the page.

This format continued for 1998, with Jim Richards winning his 7th Bathurst 1000 in a Volvo S40, beating his son Steven in a Nissan Primera.

elmo said...

sailquik said...

frant said...Andrew. Easy to do 50 knots in a straight line along the low water mark though[}:)][}:)][}:)]

Hmmmmmmm [}:)]

Not in the Volvo!!

they can't go that quick[}:)]

Definitely a struggle on the beach........

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