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Lüderitz Speed Challenge

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Created by seanhogan > 9 months ago, 1 Nov 2012
Te Hau

Te Hau

479 posts
24 Nov 2012 2:42AM
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Ian K said...
Yes the 58 kph in Dr Speed's diagram is less but not insignificant.

Putting in a few estimates, put in yours if you like, Cd for a person 1.0, cross sectional area presented to wind 0.5 sq metres, density of air 1.2 kg/m^3, 58 kph = 16 m/sec. Put those estimates in the drag equation ie. drag = 1/2 Cd A rho V squared and get drag = 76.8 newtons. (7.8 kg).

Looks like from Dr Speed's diagram only about Sin 45 of that is in direction of travel = 5.46 kg. The other 5.46 kg transverse to the direction of travel adds load to the fin, but the fin has a good lift to drag of say 20:1? 10:1 ?? (I've never been able to wind up a fin designer sufficiently for them to hazard a guess on this ) So maybe add 0.5 kg of extra fin drag to give 6 kg drag opposing the direction of travel. That's a fair bit, how much would streamlining reduce that by?





Cyclists reckon 58kph is real significant dragwise.

seanhogan

seanhogan

QLD, 3424 posts
24 Nov 2012 8:13AM
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quote :
(A² talking about Bjorn's runs)

" I watched his first run, didn't take any risk and I would've done the same, but on the following runs I would've sheated in much more, especially with the wind at the moment".....

stringer

stringer

WA, 703 posts
24 Nov 2012 8:00AM
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Te Hau said...
Ian K said...
Yes the 58 kph in Dr Speed's diagram is less but not insignificant.



Cyclists reckon 58kph is real significant dragwise.


Any excuse to take EPO and wear spandex[}:)]

Te Hau

Te Hau

479 posts
25 Nov 2012 4:38AM
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Te Hau said...
Ian K said...
Yes the 58 kph in Dr Speed's diagram is less but not insignificant.

Putting in a few estimates, put in yours if you like, Cd for a person 1.0, cross sectional area presented to wind 0.5 sq metres, density of air 1.2 kg/m^3, 58 kph = 16 m/sec. Put those estimates in the drag equation ie. drag = 1/2 Cd A rho V squared and get drag = 76.8 newtons. (7.8 kg).

Looks like from Dr Speed's diagram only about Sin 45 of that is in direction of travel = 5.46 kg. The other 5.46 kg transverse to the direction of travel adds load to the fin, but the fin has a good lift to drag of say 20:1? 10:1 ?? (I've never been able to wind up a fin designer sufficiently for them to hazard a guess on this ) So maybe add 0.5 kg of extra fin drag to give 6 kg drag opposing the direction of travel. That's a fair bit, how much would streamlining reduce that by?





Cyclists reckon 58kph is real significant dragwise.


Seems to me.....that human being standing next to the air flow entry area is a problem, 'bout as aero as a barn door.
Sail Rocket........, now that's aero.
Perhaps we need to work on getting the w/surf rider out of the drag story?

seanhogan

seanhogan

QLD, 3424 posts
25 Nov 2012 2:53PM
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A² speed clinic in Namibia :

"ok kids, one at a time !!!"



top bloke, he took the locals kids for a "quick" ride on his board, legend !!

seanhogan

seanhogan

QLD, 3424 posts
25 Nov 2012 3:01PM
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hardie

hardie

WA, 4081 posts
25 Nov 2012 9:32PM
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Bjorn just did 50.9kt 500m in 30 to 35 kts of wind

seanhogan

seanhogan

QLD, 3424 posts
26 Nov 2012 6:25AM
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51.09 for Bjorn

hardie

hardie

WA, 4081 posts
26 Nov 2012 6:39AM
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A2 100km 2sec 54kts www.gps-speedsurfing.com/default.aspx?mnu=user&val=111345&uid=412

stringer

stringer

WA, 703 posts
26 Nov 2012 12:20PM
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DarrylG said...
How about drafting. Cool to see 6 guys on the course at once.


or just one AA

seanhogan

seanhogan

QLD, 3424 posts
26 Nov 2012 4:30PM
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100.26 km/h on 2sec, removing half of the boom seems to work !!

seanhogan

seanhogan

QLD, 3424 posts
26 Nov 2012 4:55PM
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but it's still the tandem board

JonesySail

JonesySail

QLD, 1081 posts
26 Nov 2012 5:38PM
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These speeds are totally unreal!
The length of the harness lines really stands out as being extra long..really using their body weight as apposed to arm strength...
Does anyone have an idea what length lines A2 is using?

LeStef

LeStef

ACT, 514 posts
27 Nov 2012 12:02AM
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JonesySail said...
Does anyone have an idea what length lines A2 is using?

Looks like he has put both on the starboard side !

sailquik

sailquik

VIC, 6089 posts
27 Nov 2012 12:06PM
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New GPS World Record

Antoine Albeau has had his claim for the WGPSSRC record ratified.

WGPSSRC record is now 52.91 Knots (97.98 KMH)

www.gps-speedsurfing.com/default.aspx?mnu=forum&forum=1&val=43772

www.gps-speedsurfing.com/default.aspx?mnu=records

Posted session here:

www.gps-speedsurfing.com/default.aspx?mnu=user&val=111345&uid=412

Te Hau

Te Hau

479 posts
28 Nov 2012 3:52AM
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JonesySail said...
These speeds are totally unreal!
The length of the harness lines really stands out as being extra long..really using their body weight as apposed to arm strength...
Does anyone have an idea what length lines A2 is using?



those long lines also get his body away from the air feed onto the sail, less blockage?

seanhogan

seanhogan

QLD, 3424 posts
2 Dec 2012 6:14AM
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It's over,

Final results :

Antoine Albeau 52,05 noeuds

Anders Bringdal 51,45 noeuds

Jurjen Van Der Noord 51,26 noeuds

Bjorn Dunkerbeck 51,09 noeuds

Nick Vardalachos 50,56 noeuds

Patrik Diethelm 50,49 noeuds

Cedric Bordes 50,23 noeuds


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"Lüderitz Speed Challenge" started by seanhogan



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