Fin-mergency! Help!

[Beasho]

the outside face of the waveside fin is pulling the board into the wave, helping you hold onto the face. . .

Sorry - You are correct.  Flat inside, lift is to the outside.  

Here is a little picture of what is going on.  A foil generates lift by what's called 'circulation.'  Circulation, in simple terms is fluid moving faster over one side of the object than the other.  Circulation can be induced two ways (& more like spinning a cylinder/baseball)

1) By a symmetric foil
2) By Angle of attack  

The problem with a symmetric foil is you can't turn it off.  It is generating lift, 90 degrees to flow, 100% of the time and lift is 100% correlated to drag.
 
Angle of attack can be controlled.  This is why very fast aircraft use symmetric foils otherwise the lift and drag become excessive and somewhat unmanageable because lift & drag are also a function of Velocity^2.  Want to take off, going slow, angle the nose up.  Want to go supersonic juice the throttle and drop angle of attack to 0.000001.  

Then some rocket scientist goes and puts fins on a surfboard with the symmetric foil 'lift' designed to counter the angle of attack, Toe-In 'lift'.  Is this just to induce drag?  This is the type of thing that made NO sense until someone tried it.  It must work, better than not, because nearly every 3 fin board boasts this design (short of some of the recent JP boards).  

Moral of the story you can think all you want but you'll never know until you try it.  And, unless I live in the Bermuda triangle, I tried it and the angle of attack (outside fins) held my turns winning out over symmetric foils (inside fins).  This was NOT what I expected.  Your Asymmetrical has alot of other stuff going on, which adds to the complexity, mystery, intrigue, discovery . . .  I will add that on my biggest wave board (12' PSH gun) I ride it as a single fin to get rid of all these appendages to maximize board speed.    

PS:  What I love is the explanation "which in turn makes the board more responsive to rider input."  Typical surf mantra  
PSS:  That's it!  Now I am going to have to go buy one of those JP boards.
Schematic from here: http://www.tactics.com/info/guide-to-surfboard-fins

[Biggreen]

We're you able to resolve your fin issues, raf?  With all the assym talk going on, myself and I'm sure others would be interested to hear what you've worked out.

And Beasho, that last post was great IMO. Really enjoyed wrapping my pea brain around that explanation.

Let us know, raf.  Love to hear the results!

[Beasho]

PSS: I went out and tested the theory, 3 sessions, more than 45 waves and confirmed with 95% confidence that an object in motion with remain in motion unless acted upon by an outside force:  That outside force is your OUTSIDE fins.

I tested on two different boards, both quads, and found for example that when paddling a quad with just two fins on the left (port side) of the board you could take 12 - 20 strokes on your left and the board paddled as if it had all 4 fins.  Switch to the right hand and the board would yaw nearly 45 degrees in 5 - 8 strokes.

Translated to surfing: ALL the hold and drive in a bottom turn came from the outside fins.  Switch them to the other side, inside near the toes, and the phenomena reversed 100% of the time.  Turning front side with fins on the toe side and the board wanted to slide out as if almost fin-less.  Turning front side with the fins on your heels and the board held fast nearly as well as with all 4 fins.

I tried this with 6 different asymmetric set-ups.  My only hesitation (5%) was when I was asymmetric in 8 - 10 foot surf.  I went for a bottom turn, spun a 180 and found myself sliding backwards down the face, planning on my belly, both me and my board looking up at the careening wave face.  I paddled to shore and put all my fins back in.

I surfed a windsurfer with an asymmetric fin set-up for years and just now realized I had it backward.  Non-intuitive but pretty cool when you try it yourself.  Worth a separate post.  Angle of attack wins:   "Beasho's law"

[Biggreen]

You're the man, Beasho! Now that's taking one for the team.  And you're right, I think you should make this it's own separate post. I'm sure all the responses would be very interesting. Nicely done!

[punasurf]

I do not doubt your conclusion, but I have a hard time wrapping my brain around the thought that the 2 inside fins do not hold onto the face of a wave.  Weird.  Must be my brain...