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Author Topic: Wing surface finish  (Read 2525 times)

SUPdad

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Wing surface finish
« on: December 09, 2020, 08:15:27 PM »
Anyone notice a change in performance after you’ve accumulated a few scratches on your foil?

surfcowboy

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Re: Wing surface finish
« Reply #1 on: December 10, 2020, 07:44:32 AM »
Haha. Don’t bring this up in LA. 😂

I ride with a crew here in SoCal that have insanely damaged wings (cobblestone reefs are hard.) we recently started a collection of pics showing how bad everyone’s wings are.

Hdip and Pono can comment. I mean, I’m sure there’s a point but at surf speeds it’d be hard to feel.

Nick from Lift talks about sanding wings on the Progression Project and when Erik starts to geek out he slows him down and points out that this is for kite racing at insane speeds and with people who are tuned in at world record levels. I’d guess that if you can feel it you’re either going Mach 5 or ready to design your own wings by feel or have done some crazy hatchet job on a wing.

Isthere damage that you could feel? Sure. But how bad are you talking? 2-3 mm deep and wide? Repairs and refinishing are easy. Search the web there are resources on foil abuse. lol

jondrums

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Re: Wing surface finish
« Reply #2 on: December 10, 2020, 11:31:56 AM »
I didn't notice the difference as I accumulated more and more scratches on my GL210.  HOWEVER, I did notice the difference when I filled and sanded about 100 scratches - refinishing the leading edge and front 2/3rds of the topside to glass smooth 1500grit.  For sure it rode a little bit more stable.  Can't say if it was faster - that's so conditions dependent.  But overnight it got a tiny bit but noticeably more stable in maneuvers, takeoffs, and near breaches.

My theory on this is formed by talking to a hydrodynamicist.  I think the surface finish has a small but real effect on total drag - probably small enough to not be noticeable except under a very tightly controlled experiment.  However, disturbed flow over the top of a wing will separate earlier (closer to the leading edge).  Even with a perfect surface finish by about halfway back it has "separated" anyway due to the shape effects.     My theory is that the surface finish helps hold off a wing stall a little bit longer - which is why it is a little more stable for me in maneuvers.  I'd guess it will also be more stable at top speed - which would matter more for winging I think.

I originally hoped to get a noticeable drag reduction.  I was going to go over the front half of the mast with the same deal.  But since I couldn't feel any effects, I haven't gotten around to messing with the mast yet.

So, the geeks out there should run out and get some of the bondo brand glazing putty and 3M 600,1000,1500 grit wetsanding paper. The glazing putty dries fast and sands pretty easily. Honestly, the whole job took less than an hour.


jondrums

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Re: Wing surface finish
« Reply #3 on: December 10, 2020, 11:34:27 AM »
the way I look at it - if you're the kind of person who spends an hour trolling through online foil content when you're jonesing for a fix but can't get on the water - why not spend an hour messing around with your equipment.  I'd love it if a few more people tried this and reported whether they could actually tell a difference or not.

PonoBill

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Re: Wing surface finish
« Reply #4 on: December 11, 2020, 06:17:25 AM »
I've cleaned up my wings numerous times. All it really accomplishes is that I get a tiny bit less shit about my "hobo" gear from Admin. Even there the effect is too small to measure.
« Last Edit: December 11, 2020, 06:20:24 AM by PonoBill »
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

Admin

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Re: Wing surface finish
« Reply #5 on: December 11, 2020, 06:47:03 AM »
:).  I was out the other day with a friend who is one of the fastest windfoilers here.  Shockingly fast.  I have never seen a winger even come close to these speeds.  He had a look at my 760, ran his hand over a couple of spots, and asked if I wanted him to fix my foil for me.  No visible scratches, dings or visible imperfections to my eyes.  Possibly just some miniscule pitting and yet he was clearly a little uncomfortable being that close to it :).


PonoBill

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Re: Wing surface finish
« Reply #6 on: December 11, 2020, 06:53:48 AM »
That sounds like someone you would immediately befriend. The startling thing is that you are able to be within 50 feet of my truck without apparent discomfort, never mind actually entering my shop.
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

surfcowboy

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Re: Wing surface finish
« Reply #7 on: December 11, 2020, 08:03:39 AM »
The Admin/Pono odd couple threads are some of my favorites.

Jon, I will say as well, no harm, right? But I appreciate you saying your opinion was formed by talking to that scientist. Had you not, and then only smoothed the back of your wing, would it have felt as good? Not saying anything bad about or to you of course, just noting that if you hadn’t said anything I’d probably have only worried about the trailing edge since that makes noise.

We humans have amazing minds. Keep us posted and as I fix up some of these horrible LA wings I’ll ask guys to pay attention. Especially those who have front chunks out.

Hdip

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Re: Wing surface finish
« Reply #8 on: December 11, 2020, 08:55:59 AM »
I have resorted to clear gorilla grip tape for all my board ding repairs, so I'm not the best person to ask about this. For the speed I'm going on the slow waves I prefer to foil. It doesn't bother me one bit to have some tiger stripes on my foils. How many layer's of carbon are these things? They're not fragile surfboards, so I don't treat them as such.

I do try to avoid actively hitting the bottom. My feet get cut up just as much from standing on rocks to avoid drydocking when I'm standing in a shallow takeoff spot and the wave sucks water off the reef. Once you're up and riding you can stay high on the mast and go through some decently shallow water though. That's what happens when you're trying to ride 1 foot waves, it's going to break in shallow water.

Hdip

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Re: Wing surface finish
« Reply #9 on: December 11, 2020, 09:08:06 AM »
the way I look at it - if you're the kind of person who spends an hour trolling through online foil content when you're jonesing for a fix but can't get on the water - why not spend an hour messing around with your equipment. 

Because my foil gear isn't on my laptop and people would know that I'm actively procrastinating instead of typing reports which is what I'm supposed to be doing right now :)

jondrums

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Re: Wing surface finish
« Reply #10 on: December 11, 2020, 11:02:17 AM »
I think this thread pretty much sums up the full spectrum of personality styles we have here.  Its fun to be part of a community and to know you guys well enough to pretty much predict exactly how you'll reply.

I am an engineer with just enough knowledge to be dangerous to myself here - but I have been rolling with some serious heavyweights in the field of fluid flow and aerodynamics.  So, I have learned a lot from them that influences this.  One of the guys I work with recently worked on america's cup boats as an engineer, but talked about the all-hands-on-deck horror sessions of the engineering team having to 1500grit wetsand a giant hull and foils before every practice session.  They wouldn't have done it had it not had an effect.   The old rules of thumb from dingy sailing days that 400grit surfaces being faster than a mirror polish are rubbish.  Beyond form drag, the next influencer of drag is surface finish of the first third to half of the body.  Most of us don't care about this based on the way we approach the sport!

There is a whole world to dive into here, and you don't have to have friends who tell you the answer.  Start in your travels here to get some ideas:
https://en.wikipedia.org/wiki/Flow_separation

I'm still looking for a detailed treatment of the relationship between surface finish and drag.  I was referred to the textbook "Aero-Hyrdodynamics of Sailing" by C.A. Marchaj.  I bought it and am looking through to see what I can find.  I'll scan some pages if I find what I'm looking for.

PonoBill

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Re: Wing surface finish
« Reply #11 on: December 11, 2020, 03:06:02 PM »
I've read as many of the generally published texts on hydrodynamics and hydrofoils as I can get my hands on. I'm sure the pro literature is more authoritative, but it's expensive for a layman to get at that stuff.

My take on the surface finish issue is somewhere between "it depends" and "nobody really knows". You'd think something that mechanical and macro would be well sorted by now with clear indications one way or another, but chaos rules in emergent phenomena and it's just not that easy to sort out. There are no definitive equations for flow through a pipe--only models that work pretty well if you toss enough computing power at them. That is certainly the kind of issue that would be sorted out if it could.

If you subscribe to evolutionary biological models as being more sophisticated than anything we can calculate (yeah, they are) I would point you to fish and sharks with their rough scales and shark denticles as a starter, with swimming mammals screwing up the whole notion with super-smooth skin (dolphins) and slick hair (seals). If nature doesn't know the answer, we aren't likely to either. As far as a bunch of engineers and mechanics sanding down a hull with 1500 grit being clear evidence I point you to the simple fact that 70 percent of Americans believe in angels. 50 percent would be expected since that could be all the dumb folks, but 70 percent suggests a distribution that isn't simply Gaussian. If the guy paying the bills wants the boat sanded smoother than a ten grand pool cue then everyone's gonna sand.

I should make it clear that science has nothing to do with the shabby appearance of my foils and wings--that's pure laziness. I'm not willing to flip my board over and belly crawl half a mile like Admin does to preclude the tiniest scratch on my foil. I just run them in until I think I might not have enough water to flop into or until I hit something. If my foils were pristine, that would hurt a bit. As it is, it's just one more gouge among many.
« Last Edit: December 11, 2020, 03:18:19 PM by PonoBill »
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

PonoBill

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Re: Wing surface finish
« Reply #12 on: December 11, 2020, 03:28:45 PM »
The Admin/Pono odd couple threads are some of my favorites.

You should have been there when I patched a leaker ding on Chan's board with a piece of aluminum tape. I even used scissors to trim it to a perfect rectangle instead of my usual torn edges. You'd have thought I just yanked my boardshorts down and farted loudly. They are both too polite and kind to beat me with a wing pump or rip the patch off in front of me but I'm certain the board was up for sale the same afternoon if they didn't just burn it in the back yard.
« Last Edit: December 11, 2020, 03:33:08 PM by PonoBill »
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

surfcowboy

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Re: Wing surface finish
« Reply #13 on: December 11, 2020, 03:50:54 PM »
Jon, I agree. Some of these relationships have rolled over into the real world and I'm the better for it.

And that's pretty awesome that you get access to those folks. Please keep sharing.

I should also share that on gear I'm 50/50 but trying to lean more "pono/hdip" as time is more valuable and I tend to tweak too much. I'm working to be more about prototyping til I know what's what. But I still do keep my car clean and I have a spare of most parts and foil tools in my car. (I'm the guy who you can always borrow wax off of in my crew, even when I'm running traction on all boards.)

jondrums

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Re: Wing surface finish
« Reply #14 on: December 11, 2020, 05:17:11 PM »
As far as a bunch of engineers and mechanics sanding down a hull with 1500 grit being clear evidence ....  If the guy paying the bills wants the boat sanded smoother than a ten grand pool cue then everyone's gonna sand.

Truth!

 


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