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Fin sanding
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spennie



Joined: 13 Oct 1995
Posts: 809
Location: Thousand Oaks, CA

PostPosted: Wed Apr 17, 2013 1:08 pm    Post subject: Reply with quote

So you guys sand your boards so the water won't stick, then sand your fins so it will? Hello?

Don't sand your fins! You can clean them with Xylene or alcohol or something if you feel the need, but don't sand them unnecessarily! One poster says he "Uses a sander first, then by hand" Arrrggghhhhh! You're changing the foil! Bad idea! I once ruined a fin by spray-painting it, luckily was able to remove the paint with gasoline, at which point it started working again. Serious racers will remove the silk-screened graphics off a new fin to make sure it doesn't set off a spinout.

I had a short how-to article with photos published in Wind Surfing magazine a couple years ago, showing how to fix a fin. It basically boils down to two key elements: Don't change the foil, and get it as smooth as possible. Fill the flaw first with your epoxy of choice, then slowly sand it back to the original shape using progressively finer abrasive, being careful not to sand the surrounding area. Using 600 in the direction of water flow would probably be fine, if you don't do it too much.

I'm sure that there's wave sailors out there who are going to say "I sand my fins all the time, and they work fine!". Maybe, for something as un-critical as wavesailing, but try putting that fin on a slalom board and going fast; You'll be sailing sideways as much as forwards.

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tramontana00



Joined: 15 Feb 2010
Posts: 152

PostPosted: Wed Apr 17, 2013 2:06 pm    Post subject: Reply with quote

Quote:
So you guys sand your boards so the water won't stick, then sand your fins so it will? Hello?


Interesting comment. Who said that?
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KevinDo



Joined: 02 Jul 2012
Posts: 408
Location: Cabrillo Inside

PostPosted: Wed Apr 17, 2013 2:50 pm    Post subject: Reply with quote

spennie wrote:
So you guys sand your boards so the water won't stick, then sand your fins so it will? Hello?

Don't sand your fins! You can clean them with Xylene or alcohol or something if you feel the need, but don't sand them unnecessarily! One poster says he "Uses a sander first, then by hand" Arrrggghhhhh! You're changing the foil! Bad idea! I once ruined a fin by spray-painting it, luckily was able to remove the paint with gasoline, at which point it started working again. Serious racers will remove the silk-screened graphics off a new fin to make sure it doesn't set off a spinout.

I had a short how-to article with photos published in Wind Surfing magazine a couple years ago, showing how to fix a fin. It basically boils down to two key elements: Don't change the foil, and get it as smooth as possible. Fill the flaw first with your epoxy of choice, then slowly sand it back to the original shape using progressively finer abrasive, being careful not to sand the surrounding area. Using 600 in the direction of water flow would probably be fine, if you don't do it too much.

I'm sure that there's wave sailors out there who are going to say "I sand my fins all the time, and they work fine!". Maybe, for something as un-critical as wavesailing, but try putting that fin on a slalom board and going fast; You'll be sailing sideways as much as forwards.


No wonder why all those slalom fins I see are plain and boring! Was curious about that and always thought companies like Tectonics was just lazy lol.
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swchandler



Joined: 08 Nov 1993
Posts: 5746

PostPosted: Wed Apr 17, 2013 3:01 pm    Post subject: Reply with quote

"So you guys sand your boards so the water won't stick, then sand your fins so it will? Hello?"


Seemingly you're a bit mixed up. Sanding the board or the fin yields the same outcome. Sanding a surface allows the water to stick to it rather than resist it. In other words, a water barrier is established on the sanded surface. As mentioned earlier, with water sticking to a sanded surface, the drag or friction is water to water instead of surface to water.
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KevinDo



Joined: 02 Jul 2012
Posts: 408
Location: Cabrillo Inside

PostPosted: Wed Apr 17, 2013 3:31 pm    Post subject: Reply with quote

swchandler wrote:
"So you guys sand your boards so the water won't stick, then sand your fins so it will? Hello?"


Seemingly you're a bit mixed up. Sanding the board or the fin yields the same outcome. Sanding a surface allows the water to stick to it rather than resist it. In other words, a water barrier is established on the sanded surface. As mentioned earlier, with water sticking to a sanded surface, the drag or friction is water to water instead of surface to water.

Going from chemistry, doesn't water have very strong cohesion?
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U2U2U2



Joined: 06 Jul 2001
Posts: 3056
Location: Shipsterns Bluff, Tasmania. Colorado

PostPosted: Wed Apr 17, 2013 3:32 pm    Post subject: Reply with quote

spennie wrote:
So you guys sand your boards so the water won't stick, then sand your fins so it will? Hello?

Don't sand your fins! You can clean them with Xylene or alcohol or something if you feel the need, but don't sand them unnecessarily! One poster says he "Uses a sander first, then by hand" Arrrggghhhhh! You're changing the foil! Bad idea! I once ruined a fin by spray-painting it, luckily was able to remove the paint with gasoline, at which point it started working again. Serious racers will remove the silk-screened graphics off a new fin to make sure it doesn't set off a spinout.

I had a short how-to article with photos published in Wind Surfing magazine a couple years ago, showing how to fix a fin. It basically boils down to two key elements: Don't change the foil, and get it as smooth as possible. Fill the flaw first with your epoxy of choice, then slowly sand it back to the original shape using progressively finer abrasive, being careful not to sand the surrounding area. Using 600 in the direction of water flow would probably be fine, if you don't do it too much.

I'm sure that there's wave sailors out there who are going to say "I sand my fins all the time, and they work fine!". Maybe, for something as un-critical as wavesailing, but try putting that fin on a slalom board and going fast; You'll be sailing sideways as much as forwards.


so it is I who uses a sander, then various grits down to mirror/ultra fine to obtain the surface finish I want. If I epoxy a chip, ding, then I use a sander, to start the process, and finish by hand.

This is just one project that I have have done, and without the sander I would NEVER be done.


some of us do understand foils, and I do change them

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zirtaeb



Joined: 03 Jul 2009
Posts: 2370

PostPosted: Wed Apr 17, 2013 4:16 pm    Post subject: Reply with quote

Changing foils is no biggee, and lots of fins NEED a change for the better....faster.
Flattening the trailing edge is always faster, and slightly less left at lower speeds.
Forcing the draft forwards gives you more angles of attack.
Thinning and moving the draft back gives you more top end.
Softenning any sharp edges not only saves your feet when thrashing around, it can cure humming and allow greater angles of attack.
FEW fins come with good foils, even the 200 dollar variety.
There are over 20 foil shapes that are said to be very low drag and fast.
It's NOT one and done, it's trial and error.
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3-phase



Joined: 26 Jan 2007
Posts: 481

PostPosted: Wed Apr 17, 2013 5:35 pm    Post subject: Reply with quote

The Fin Reality check: Laughing Laughing Laughing

Less then 5 % of people sanding and changing the fin profile gone get the fin perform better then before sanding. Exclusion ZIRTAEB

Imperfection and crushed fin tips or cuts /nicks on the profile will have an influence in lift and laminar water flow on the fin resulting in less performance. So better fill with 2 K epoxy gorilla glue or so and sand a bit.

Sanding in the direction of the water with 500-600 wet sand paper (or scotch bright) to clean some sand, dirt and algae build up is a great advice.

Less then 1 % off fins longer then 40 cm and made out of G10 are perfect. It is based on physics almost impossible to combine a good fin-profile with the correct twist and flex with the G10 material. With a molded fin made out of a Carbon Fiber / Glass Epoxy layup you can create the perfect fin profile and then with adding more or less Carbon fiber on the right place make a defined Flex and Twist.

Jurg
www.windsurfdeal.com
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zirtaeb



Joined: 03 Jul 2009
Posts: 2370

PostPosted: Wed Apr 17, 2013 6:18 pm    Post subject: Reply with quote

Very Happy Actually, a few of us have been sanding and refoiling fins for years, at least since the early '80's.
SteveSylvester, MikePercy, ChendaHerstus, MikeZaijeck, BenBamer, DougTaylor, BobHuberman all have made their fins sail faster with some cleaning up, thinning, and bluntining.
My case is due to my cheapo hand me down fins, made by guys who should know better, who didn't care, so some thinning and reshaping the thick point and especially flattening the trailing edge made them much faster, often less durable, sometimes not so great.....but freebies can be destroyed.
NOT saying I'd refoil a good Tetonics or Kashy, C-3Boogie, even Debs, but some others just aren't nearly as good as can be, some needing just a cleaning up, of course.
Current trend is sailing the slowest, draggiest Rainbow fins ever made, on Freeride boards, and trying to make them competiitve...a lost cause, of course.
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spennie



Joined: 13 Oct 1995
Posts: 809
Location: Thousand Oaks, CA

PostPosted: Wed Apr 17, 2013 7:34 pm    Post subject: Reply with quote

All right now everyone, think hard: HOW did you learn these theories? Seriously, who told you? A very good windsurfer, perhaps a pro? A shop owner? A fin maker? That guy who dulls his fins to protect his feet from cuts? The guy who cuts out his own freestyle fins, who rarely sails over 15 mph?

Sorry to get so snarky, but the endless unsubstatiated claims on this forum get to me after a while. I don't claim to be the all-knowing guru of all things windsurfer, that's ISOBARS, but I've done a lot of personal testing and experimenting over the last 23 years of sailing, and I know what actually works and what is basically wives' tales.

However, since I'm NOT infallible, I sat down with someone who could give me some serious scientific input on this subject, Dr Clint Harper. I have the good fortune to work at Moorpark College here in SoCal, where Dr. Harper is the chair of the Physics dept., and a sailboat owner (that's his latest boat in the picture).

I sat down with Dr. Harper today, and discussed the various aspects of this discussion. The short version is: Sand your hull if you want to, keep your fins smooth. Some of the stuff in this thread is accurate, but mostly it's just stuff somebody heard from someone they consider believable. I sometimes do that, but this is one subject I'm very mental about, as I sail mostly slalom, and love to speed sail (went 40 mph. a couple times). Sanding your hull is scientifically proven to work at sailboat speeds, but my feeling is how much will you gain, 1/2 mph? I'm not on the World Cup tour, so would rather have the extra epoxy on there.

Sanding your fin could cause the laminar flow to detach, which leads to spinout.

If you wish to dispute my assertions, please refer to the photograph, and make sure your source of infomation has a PhD (or better) in physics, and owns their own sailboat.



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