myiW Current Conditions and Forecasts Community Forums Buy and Sell Services
 
Hi guest · myAccount · Log in
 SearchSearch   ProfileProfile   Log in to check your private messagesLog in to check your private messages   RegisterRegister 
wave fin ques....???
Goto page Previous  1, 2, 3
 
Post new topic   Reply to topic    iWindsurf Community Forum Index -> Windsurfing Discussion
View previous topic :: View next topic  
Author Message
Wind-NC.com



Joined: 30 May 2007
Posts: 980
Location: Formerly Cape Hatteras, now Burlington, VT!

PostPosted: Fri Jan 04, 2013 9:36 am    Post subject: Reply with quote

Oh, wait, bred2shred already said that... Sorry for the repost!
_________________
formerly known as hodad.andy

http://wind-nc.com
Back to top
View user's profile Send private message Visit poster's website
isobars



Joined: 12 Dec 1999
Posts: 20935

PostPosted: Fri Jan 04, 2013 10:23 pm    Post subject: Reply with quote

As did a couple of others. Wink
Back to top
View user's profile Send private message
jingebritsen



Joined: 21 Aug 2002
Posts: 3371

PostPosted: Sat Jan 05, 2013 5:39 am    Post subject: Reply with quote

nature's been designing fins and wings far longer than humans have been trying to manipulate nature. look at the critters and what they do to help you decide what you want to do in windsurfing and choosing fins and sails. fascinating stuff going on all around us.
_________________
www.aerotechsails.com
www.exocet-original.com
www.iwindsurf.com
http://www.epicgearusa.com/
Back to top
View user's profile Send private message
rich1



Joined: 10 Apr 2000
Posts: 156

PostPosted: Sat Jan 05, 2013 3:39 pm    Post subject: Reply with quote

Quote:
nature's been designing fins and wings far longer than humans have been trying to manipulate nature. look at the critters and what they do to help you decide what you want to do in windsurfing and choosing fins and sails. fascinating stuff going on all around us.


I must disagree with this. This has been the attitude driving a lot of design in the surf/windsurf industry and doesn't really make sense. Animals have very different design parameters than we do. Nature has to make it's fins and wings out of living tissue, wings have to fold, and both wings and fins are also sensory and variable in geometry. That's not to say that we can't learn by studying what nature has done, just that we shouldn't blindly copy a dolphin fin and expect it to be the best design for a wave fin.

That being said, I've done quite a bit of reading, and devoted a lot of thought to figuring this out.

So boiling it down, a looser fin has a lower aspect ratio, higher taper ratio and more sweep than a pointer.

The first two (aspect and taper) seem to be pretty straight forward, ie centre of lift is concentrated closer to base of the fin, so we have more leverage over it as mentioned in previous posts. The sweep however is a bit more perplexing. With the addition of sweep, the effective span of the fin changes with the planing angle of the board. What's kind of interesting here, is that the fin becomes effectively longer as we initiate a turn because the angle of attack of the board becomes greater. So, going from rail to rail, the load on the fin transitions from one side to the other. At the initiation of the turn, the lift being generated is actually pushing the tail in the direction that aids the rolling of the board, then as the load moves to the other side of the fin, it begins to resist the continued rolling of the board. Based on this, it would seem a vertical (or very slightly swept like 5 or 6 degrees) fin would be a tiny bit stiffer up to the transition point, but looser as you continue to set the rail. Which, I would think for agressive rail-to-rail riding would be looser overall, so where does that leave us?

The other thing that sweep does is raise the cavitation speed of the fin a bit. This may be important, but I'm not sure. It may allow us to use smaller fins without suffering spin out. So rather than being a design plus for looseness, sweep may be a necessary design compromise to get away with a smaller fin.

How's that for muddying the waters?
Back to top
View user's profile Send private message
U2U2U2



Joined: 06 Jul 2001
Posts: 5467
Location: Shipsterns Bluff, Tasmania. Colorado

PostPosted: Sat Jan 05, 2013 5:49 pm    Post subject: Reply with quote

the water is muddy only if you want to look too far

this interpretation of the concept of probability can be seen as an extension of logic that enables reasoning with propositions whose truth or falsity is uncertain.

seems to me, to be a abstract concept, that we assign theoretically, for the purpose of representing a state of knowledge, or that we calculate from previously assigned probabilities.

referred to as theory

cavitation:
Why do my fins hum?

If your fins make a noise like humming, it is due to cavitation. Cavitation occurs when low pressure bubbles in the water begin to collapse and create tiny shockwaves which are the source of the noise.

To fix humming fins: sand the sides of the trailing edge with a medium grade sand paper. Several passes with sand paper is usually enough.

the other theory is that they hum because they don't know the words.

there are fins that do indeed look like animal this a whale fin.



with many looking like the dorsal fin of the shark.

_________________
K4 fins
4Boards....May the fours be with you

http://www.k4fins.com/fins.html
http://4boards.co.uk/
Back to top
View user's profile Send private message
isobars



Joined: 12 Dec 1999
Posts: 20935

PostPosted: Sat Jan 05, 2013 7:03 pm    Post subject: Reply with quote

U2U2U2 wrote:
If your fins make a noise like humming, it is due to cavitation.

Or it's loose in the box.
Back to top
View user's profile Send private message
westender



Joined: 02 Aug 2007
Posts: 1288
Location: Portland / Gorge

PostPosted: Sat Jan 05, 2013 11:47 pm    Post subject: Reply with quote

I have some Swell fins for the non waves around here but depend on the board for maneuverability more than the fin. For some reason I'm anti technical when it comes to my gear. If it works, I keep it till it breaks and wish I had another.

My go to fin is a old Finworks Pro300 Tuttle design race type fin that turns great.
Back to top
View user's profile Send private message
rich1



Joined: 10 Apr 2000
Posts: 156

PostPosted: Wed Jan 09, 2013 1:41 pm    Post subject: Reply with quote

So after a bit more research I discovered something I had been looking for for a while.

Bottom line, sweep tends to move the centre of pressure more towards the tip.

I think this may explain things. Say you're sailing with a fin with about 20 deg of sweep, and the board is trimmed at about 5deg. The effective sweep now becomes 15 deg just sailing along. As you initiate the turn, there is more lift towards the tip due to the 15 deg of sweep and it aids in the initiation of the turn to the point of the fin beginning to load on the opposite side. As the nose comes up to more like 20 deg, the effective sweep is 0 deg. The centre of pressure migrates toward the base of the fin making it feel a bit easier to continue to roll the board into the turn.

These numbers are "made up" for illustration purposes, I'd like to know the real ones, but I think they're pretty close.

Just a theory, but it all does seem to match observation. Plus I never liked the "higher cavitation speed" explanation anyways.
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    iWindsurf Community Forum Index -> Windsurfing Discussion All times are GMT - 5 Hours
Goto page Previous  1, 2, 3
Page 3 of 3

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You can attach files in this forum
You can download files in this forum

myiW | Weather | Community | Membership | Support | Log in
like us on facebook
© Copyright 1999-2007 WeatherFlow, Inc Contact Us Ad Marketplace

Powered by phpBB © 2001, 2005 phpBB Group