Polished or microground ?? - Page 5

27th May 2009, 06:15 PM

from a carbon art press release

"The Pro Model Slalom board is constructed with a higher carbon content and like all CA Pro Models, has a special Teflon™-like polished bottom"

source - http://www.boards.co.uk/news/article.asp?id=3317

Ken · 27th May 2009, 10:19 PM

Quote:

Originally Posted by Unregistered

"

Nex time you board a plane have a look at wing`s surface. Shiny ! Smooth not rough!!!

Suppose they`ve got it wrong too !!!

I wonder why some commercial plane wings have small tabs on top of the wings near the leading edge. Clearly, they are there to create turbulence for some reason - to compensate for the "smooth" surface?

I don't have the answer, but somone out there may.

28th May 2009, 10:04 AM

the little thingamewatsit sticky outy bits on the front of plane wings are: Vortex Generators. The idea behind these is to create a small, but powerful vortex which guides the boundary layer onto the wing surface, which does two things. 1) it delays separation (stall) which is good for takeoff and low speed handling, and 2) it keeps the flow attached to the control surfaces (aelerons etc) keeping them effective.

The cost in terms of drag is minimal since they are so small compared to the rest of the wing, and only affect small parts of the span, effectively creating vortex fences. This also reduces crossflow effects where say separation on one part of the wing would normally spread to the adjacent parts. Its a little like trying to pull a sticker off something. The vortex generators create extra sticky points that keep the boundary layer attached, so the separation is less likely to spread to adjacent spanwise sections.

Cool solution for a plane. Not so useful for a windsurfer.

Ken · 28th May 2009, 09:12 PM

NetWastrel,

Good explanation - Thanks. This may explain why sanded fins have less spinout, with the rough surface generating mini vortexes allowing the water to stay attached to the fin surface.

Erik Loots · 29th May 2009, 05:23 PM

Polished surface faster??? I bet when you can control it a polished fin would have a tiny little bit less drag. I think you will barely notice this difference. My CA speed was polished, but a sanded a few spots now it is sanded and no difference.

A polished fin is easy to ventilate, this means the liftpotential of the fin suddenly decreasing by a huge factor. When going @ low speed 30-35kn, I feel only more drag, and most people will spinout before they notice.

On cavitation speeds 45-50kn ventilation??? That is the rumor about hydroptere and they got up to 60kn, so far I understood they also had a lack of lift& less drag.

On a windsurfer I don't think it is possible to do that all. You don't have a crew... You have trimsail/ keep course/ keep balance/ keep board steady/ keep finpressure all in one time. I use max 600 grid sandpaper.

Cheers,

Erik
www.speedsurfingblog.com

29th May 2009, 06:35 PM

Have you seen the glider in Thomas Crown Affair; glstening in sun, including rudder and tail plane.Super smooth and shiny. !!!

Micro ground is just another case of psuedo science BS.(Which starboard dominate BTW)

Mind you there`s no way any sailor could ever tell difference !!

30th May 2009, 12:00 AM

After checking a new Deboichet, it looks as though it may be sanded with 220 or 320 on the horizontal plane. Not even close to polished or 400 grit.

Since this is a major brand, there must have been some testing?

Also why not vertical sanding?

Anyone with knowledge?

Farlo · 30th May 2009, 02:24 AM

Some twenty years ago Olivier Augé, one of the top speed French windsurfer at the time, advised about how fins should be sanded. He said to sand horizontally near the head and turn vertically near the tip. This was supposed to optimize water flow. Personally I don't think it makes any difference as long as the grit is fine enough.

Come on unregistered #46 (I guess it is a psuedo).
You didn't even told us if you really polish your board, fins (and guitar).

30th May 2009, 04:49 PM

Why is our sport so full of BS and self qualified "experts" quoting stuff from years ago and failing to grasp salient points from studies done by "real" engineers ???

Nasa;air craft manufacturers etc etc (according to some) have got it all wrong !! Cut outs decreasing drag; micro grinding and loads of other BS is playing straight into manufacturers hands. Its unbelievable !! Novelty has replaced development in WS. We read it on here; or in some corrupt magazine so we believe it; buy into it and then promote it !!! Crazy.
Every study (modern) says polished is better for foils/planing surfaces !!

BTW what`s guitars got to do with it ???

Farlo · 31st May 2009, 02:45 AM

Well I guess that if you polish your guitar you will play faster. Exemples and studies you have found are not relevant for windsurf. Also if you look around you will find that much more boards/fins have matte finish than polished. So you may think that most windsurfers and boards manufacturers are idiots, but as you never told us if you really polish your board and fins (and guitar) nobody knows on which side you are. BTW I'm an engineer too but I tend to forget it when windsurfing.

31st May 2009, 02:45 AM	#50
Farlo Member Join Date: Aug 2006 Posts: 513	Well I guess that if you polish your guitar you will play faster. Exemples and studies you have found are not relevant for windsurf. Also if you look around you will find that much more boards/fins have matte finish than polished. So you may think that most windsurfers and boards manufacturers are idiots, but as you never told us if you really polish your board and fins (and guitar) nobody knows on which side you are. BTW I'm an engineer too but I tend to forget it when windsurfing. Last edited by Farlo; 6th November 2009 at 03:21 AM.

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27th May 2009, 06:15 PM	#41
Unregistered Guest Posts: n/a	from a carbon art press release "The Pro Model Slalom board is constructed with a higher carbon content and like all CA Pro Models, has a special Teflon™-like polished bottom" source - http://www.boards.co.uk/news/article.asp?id=3317

28th May 2009, 10:04 AM	#43
NetWastrel Guest Posts: n/a	the little thingamewatsit sticky outy bits on the front of plane wings are: Vortex Generators. The idea behind these is to create a small, but powerful vortex which guides the boundary layer onto the wing surface, which does two things. 1) it delays separation (stall) which is good for takeoff and low speed handling, and 2) it keeps the flow attached to the control surfaces (aelerons etc) keeping them effective. The cost in terms of drag is minimal since they are so small compared to the rest of the wing, and only affect small parts of the span, effectively creating vortex fences. This also reduces crossflow effects where say separation on one part of the wing would normally spread to the adjacent parts. Its a little like trying to pull a sticker off something. The vortex generators create extra sticky points that keep the boundary layer attached, so the separation is less likely to spread to adjacent spanwise sections. Cool solution for a plane. Not so useful for a windsurfer.

28th May 2009, 09:12 PM	#44
Ken Member Join Date: Aug 2006 Location: Dallas, Texas USA Posts: 797	NetWastrel, Good explanation - Thanks. This may explain why sanded fins have less spinout, with the rough surface generating mini vortexes allowing the water to stay attached to the fin surface.

29th May 2009, 05:23 PM	#45
Erik Loots Member Join Date: Aug 2006 Location: The Netherlands, Alkmaar Posts: 109	Polished surface faster??? I bet when you can control it a polished fin would have a tiny little bit less drag. I think you will barely notice this difference. My CA speed was polished, but a sanded a few spots now it is sanded and no difference. A polished fin is easy to ventilate, this means the liftpotential of the fin suddenly decreasing by a huge factor. When going @ low speed 30-35kn, I feel only more drag, and most people will spinout before they notice. On cavitation speeds 45-50kn ventilation??? That is the rumor about hydroptere and they got up to 60kn, so far I understood they also had a lack of lift& less drag. On a windsurfer I don't think it is possible to do that all. You don't have a crew... You have trimsail/ keep course/ keep balance/ keep board steady/ keep finpressure all in one time. I use max 600 grid sandpaper. Cheers, Erik www.speedsurfingblog.com

29th May 2009, 06:35 PM	#46
Unregistered Guest Posts: n/a	Have you seen the glider in Thomas Crown Affair; glstening in sun, including rudder and tail plane.Super smooth and shiny. !!! Micro ground is just another case of psuedo science BS.(Which starboard dominate BTW) Mind you there`s no way any sailor could ever tell difference !!

30th May 2009, 12:00 AM	#47
Unregistered Guest Posts: n/a	After checking a new Deboichet, it looks as though it may be sanded with 220 or 320 on the horizontal plane. Not even close to polished or 400 grit. Since this is a major brand, there must have been some testing? Also why not vertical sanding? Anyone with knowledge?

30th May 2009, 02:24 AM	#48
Farlo Member Join Date: Aug 2006 Posts: 513	Some twenty years ago Olivier Augé, one of the top speed French windsurfer at the time, advised about how fins should be sanded. He said to sand horizontally near the head and turn vertically near the tip. This was supposed to optimize water flow. Personally I don't think it makes any difference as long as the grit is fine enough. Come on unregistered #46 (I guess it is a psuedo). You didn't even told us if you really polish your board, fins (and guitar).

30th May 2009, 04:49 PM	#49
Unregistered Guest Posts: n/a	Why is our sport so full of BS and self qualified "experts" quoting stuff from years ago and failing to grasp salient points from studies done by "real" engineers ??? Nasa;air craft manufacturers etc etc (according to some) have got it all wrong !! Cut outs decreasing drag; micro grinding and loads of other BS is playing straight into manufacturers hands. Its unbelievable !! Novelty has replaced development in WS. We read it on here; or in some corrupt magazine so we believe it; buy into it and then promote it !!! Crazy. Every study (modern) says polished is better for foils/planing surfaces !! BTW what`s guitars got to do with it ???