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Board » General Discussion » MOD70 polar development

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Posted by
76Trombones


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2009-08-03 18:04:56
2012-12-17 00:57:57 - Re: MOD70 polar development
I was playing with the transat data today (will post the grib). The polar that seemed to work well for the European races failed *massively*. Boosted downwind VMG speeds by almost 50% and the tracks snap into place. Insane! Boats go 32 kts average in a pretty wide range of conditions :-)

The Atlantic race gives at least a few good thresholds, as Race For Water was so close, but ended up losing days.
Posted by
76Trombones


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2012-12-18 14:13:55 - Re: MOD70 polar development
Here's the Krys race weather. They sure lucked into a fast window!
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Posted by
Tarco


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2012-12-18 16:19:52 - Re: MOD70 polar development
Yoohoo ! :-D

This new weather will be a relief ! I've been fighting against Leg2 for 2 days.... Either best VMG is around Twa 35/37° (which I had never seen before, I believe...) or there's a bug in the position reports and/or the NOAA's gribs... as this is a multihull, I was waiting for a flat polar, with a best VMG at 45 or more.
So far, she looks more like a fighter jet than a sailboat... =-O

Still not convinced about my results, but I'll let you know when I believe I'm close to something "workable"... :-)

As to the race, their average speed is around 30knts !!! That can't be only luck... ;-)
Posted by
LaoziSailor (Han Tacoma-Emons)


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2011-11-10 00:57:48
2012-12-18 20:21:47 - Re: MOD70 polar development
Tarco, you following me...??
I really don't want to go further S.
We'll see what happens, 2300kn to go, Christmats Morning might have a gift for us :),
Han (aka Laozisailor)
LaoziSailor

Everything gets done by not doing anything!
Posted by
SlashV


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2012-12-18 22:21:52 - Re: MOD70 polar development
I'll have a go at creating the polars as well and maybe we can compare or average later.

Will probably have some time during christmas :)

Data and results will go here


--- Last Edited by Jaap Versteegh at 2012-12-18 23:51:47 ---
Posted by
Tarco


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2012-12-18 23:51:52 - Re: MOD70 polar development
FANTASTIC !!!!

The new ocean grib file you made works on Ugrib, so I can check the wind when and where I need it , without dowloading 8 files per day, providing only the possibility to check exclusively the first minute of each....

Thank you very-very much !!! :-D
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Tarco


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2012-12-19 14:21:52 - Re: MOD70 polar development
Hi,all !
Finishing the Ocean samples... More than 1000 of them...
This time, they are extremely precise ! :-)

It seems Race for Water had a pb, as if they couldn't use their gennaker, or something like that. For every sample, their speed was 5 to 10 knts lower than the others in the same conditions.
Oman probably had problems too : after they drifted south; their speed was never as high as the others'.

Best VMG : around 165 between 16 and 20knts TWS !!!
Max BS : 33 (averaged)

Polar goes up and down, probably depending on the sail they use and if they can sail on one hull or not...
Huge gap around TWA 100-105, below 10knts TWS. And another one at TWA 150, at TWS22 and above...

More news when I'm done with Leg 1... again.
I want to have the polar as complete as possible bafore I "publish" it. ;-)
Posted by
SlashV


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2012-12-21 14:33:03 - Re: MOD70 polar development
The track logs of the races I found contain position data that is already transformed to the addviso maps, it seems.

Does anybody know where to find lat,lon positions for the Krys and European tour races?
Posted by
76Trombones


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2012-12-21 18:12:27 - Re: MOD70 polar development
Hey awesome! Anyone else want to join in as well? Impressively organised - "polar" opposite of my desk :)

They're giving x/y coordinates with origin at upper left. For the Krys race, using a starting lon of 150.312 (map edge) seems to line up the data, though you end up with a funny multiplier (123.55).

You normally expect to end up with nice clean numbers (120 makes sense) so I've probably messed up somewhere.

For the y direction I get ~81N as origin and multiplier of ~167, which not only doesn't match the x scaling but also the bounds of the map.

But it's something like that. The other xml file contains all the x/y values for the race waypoints and features. Which make figuring out the scaling easier as you have clearly defined points.

(here's what I have so far - mostly featureless blob, but "races" pretty fairly against the real boats. Will be interesting to see how the different approaches compare!)



--- Last Edited by 76Trombones at 2012-12-21 18:18:36 ---
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Posted by
SlashV


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2012-12-21 18:32:11 - Re: MOD70 polar development
Ah thanks, was hoping I could avoid having to figure out the transformation from map coords to lat/lon, but since you did it as well I guess that's the way to go. Will do that then :)

Thanks as well for your results so far. "Featureless" would not really surprise me for this kind of boat.
I am not an expert, but the narrow hulls will likely have a boring resistance curve and at the speeds they do, they'll pretty much have just one sail configuration for any true wind angle: close-hauled :D
..as well as high lift/drag ratio's -> low angles of attack -> linear performance

--- Last Edited by Jaap Versteegh at 2012-12-21 19:18:20 ---

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