Slalom vs wave fins

Slalom vs wave fins

Post by Petri K Havan » Tue, 20 Jul 1993 05:45:11


Hello net.windsurfers!

This is something that has been bothering me for some time..
What makes a slalom (blade/pointer) fin feel and work so differently
from a strongly curved wave fin? Why does rake have an effect on the feel
of the board? Of course it moves the center of effort (or whatever it is)
back but still, in a 'classic' fin-box I'd move the fin forward to imporove
gybeability...
Open for discussion...

Petri Havanto           !       Perfect when clear,
                        !       perfect when cloudy,

                        !       never changes.

 
 
 

Slalom vs wave fins

Post by Kevin Moo » Thu, 22 Jul 1993 10:54:58


Quote:

> This is something that has been bothering me for some time..
> What makes a slalom (blade/pointer) fin feel and work so differently
> from a strongly curved wave fin?

Here's my guess.

A fin that has a high aspect ratio (long) and very little rake should
act like a sailplane wing, generating more lift than a wave fin with
the opposite characteristics.  However, by being more vertical, some of
the inherent stability of a swept back wave fin is lost.

One day someone will watch the "X Planes" episode of "Wings" and try to
create a fin that mimics the forward swept wing of the X-29 jet plane.
Forward swept is a highly efficient design, but it's also extremely
unstable as the leading edge tries to twist off and flip over the
plane.  This is the extreme case, but it may help you to visiualize why
a near vertical fin isn't as forgiving as a swept back fin that
naturally wants to self correct the board back into the path of least
resistance (straight ahead).   Even when you carve a jibe, the fin is
basically following the front of the board, since both are banked over
a bit and following the same arc.  Thus the sweep of a wave fin doesn't
really hamper turning, but still enhances stability.  (I hate spinning
out in a jibe!)

Ultimately, the leverage on a long straight blade fin may try to lift
and rotate the board along the center line.  Whereas more of the
leverage on a wave fin is trying to straighten out the board along a
vertical axis through the fin.  Basically a wave fin's design gives more
directional stability (like a rudder) while a blade fin gives more lift
(like a wing) at the expense of stability.

Now my question.  Can anyone tell me how it feels to ride and
jibe a big weed fin?

- Kevin

 
 
 

Slalom vs wave fins

Post by David W. Abrah » Fri, 23 Jul 1993 01:24:50


|> >
|>
|> Now my question.  Can anyone tell me how it feels to ride and
|> jibe a big weed fin?
|>
|> - Kevin

I don't like it much- they don't turn as nice, are more prone to spinout than the blades
I prefer (in no weeds that is) and are slower.  BUT I'll still do it if that's the choice.

--


 
 
 

Slalom vs wave fins

Post by Adam Za » Fri, 23 Jul 1993 03:25:15


: >
: > This is something that has been bothering me for some time..
: > What makes a slalom (blade/pointer) fin feel and work so differently
: > from a strongly curved wave fin?
:  
: Here's my guess.

: A fin that has a high aspect ratio (long) and very little rake should
: act like a sailplane wing, generating more lift than a wave fin with
: the opposite characteristics.  However, by being more vertical, some of
: the inherent stability of a swept back wave fin is lost.

[stuff about "X Planes" deleted]

: .... This is the extreme case, but it may help you to visiualize why
: a near vertical fin isn't as forgiving as a swept back fin that
: naturally wants to self correct the board back into the path of least
: resistance (straight ahead).   Even when you carve a jibe, the fin is
: basically following the front of the board, since both are banked over
: a bit and following the same arc.  Thus the sweep of a wave fin doesn't
: really hamper turning, but still enhances stability.  (I hate spinning
: out in a jibe!)

: Ultimately, the leverage on a long straight blade fin may try to lift
: and rotate the board along the center line.  Whereas more of the
: leverage on a wave fin is trying to straighten out the board along a
: vertical axis through the fin.  Basically a wave fin's design gives more
: directional stability (like a rudder) while a blade fin gives more lift
: (like a wing) at the expense of stability.

My thoughts on the subject - The reason the wave fin is considered "a
better turning fin" has to do with the drag created by the curved
trailing edge. This is what causes these fins to be slower in a
straight line than blades, but this is a big help in turning due to
the larger, effectively, area for the sailor to push against; hence
more stable.

Blades can turn really nicely but I think that it has more to do with
jibing ability than the fact that the fin is less stable, by design,
than wave fins. Because blades are faster, you can really rip into a
turn the sudden changes of which can destabilize a fin quite easily. The
sailor that is "smoother" with the transition is going to avoid spinout
better than the "rougher" sailor.

I'd like to know if anyone has done a turning experiment by comparing
a blade and a wave fin of the same area in sq. in.? I wonder if the
wave fins might possibly make the transition from one direction to
another better in this situation or could it be becouse they are
often just smaller in overall area than the blades?

--
  ~o
  ~|\     If you're not planing,                  Adam S. Zais
  ~|-\    then you're complaining.                Atria Software, Inc.

   ,_____                                         ...!gw!adam
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

 
 
 

Slalom vs wave fins

Post by Jaime Corde » Sat, 24 Jul 1993 03:31:31

Quote:
>Now my question.  Can anyone tell me how it feels to ride and
>jibe a big weed fin?

>- Kevin

I tried weed fins for the first time recently on a trip to Corpus Cristi.
You may get different reports from regular users of these contraptions.

Ugh !!! It doesn't point at all, even worse, as expected, than wave fins, and
requires a lot of steering to keep on a straight line. Even when really
powered, I had a hard time getting it fast enough to ride the fin. Maybe
that's an unreasonable expectation for a swept back fin.

I didn't like it at all. Sure does jibe easy, though.

Jaime

P.S. For reference, I usually use a 12" conventional pointer fin on a 9'0"
board.
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