A question about "One Foot Off" measure

A question about "One Foot Off" measure

Post by expan.. » Tue, 09 Aug 2005 01:54:11


--

A question for technician people; if someone think this post is a
little Off Topic in Neil Pryde Forum, I ask him to help me to put this
question in the right place. Thank you in advance.

You know certainly question of One Foot Off measurement for calculating
fin lenght...

Problem born when you consider a race or formula board with a diamond
stern (called Diamond Tail by AHD), or with characteristic triangular
drainages (used by Fanatic TT or F2 T-Rex); function of these different
devices is to avoid cavitation pheneomena due air suck by fin caused
when it is placed so near the stern as in such type boards.

Now, if you refer to following drawing:

http://dtiozzo.tripod.com/V8/onefootoff.gif

I wonder if One Foot Off has to be measured from extreme stern (point
"a" in both cases), or from edge of fin base (point "b" in both cases).

This because I have a dubt on what to take in consideration:

a) if board surface capable to really generate hydodynamic support
(without appendages, or surface comprised by point "a" and "b" which
function is essentially to avoid fin cavitation);

b) all board parts (with appendages).

In above drawing, Case number 2 shows the extreme limit of this
question due irregular design of board stern and because surface
comprised by points "a" and "b" is really marginal in terms of lift;
but measure the One Foot Off from point "a" instead from point "b" is
NOT quite marginal because may generate measures of fin definitely
different.

Someone has some idea or suggestion?

- Expander.

 
 
 

A question about "One Foot Off" measure

Post by LeeD » Tue, 09 Aug 2005 04:22:56

  I answered on NP I think....
  You are overthinking it waaay too much!  Don't matter, as it's not an
exact sciene anyways.
  And some fins are bigger while being shorter, and vice versa.

 
 
 

A question about "One Foot Off" measure

Post by jeff feeha » Tue, 09 Aug 2005 04:26:40

What is it you are trying to do?

It sounds like you are trying to determine the appropriate fin
length for a particular board. But choosing a fin is not nearly
as exact a thing as you seem to think. I don't think anyone tries
to "calculate" the right fin length. We know what fins work with
which boards by trial and error.

if you want to what fin to use witrh your board, tell us what board
it is, and what size sails you will be using, and we'll give you
a recommendation.

also, have you noticed that your widths, A and B, are basically the
same in each case?

jefff feehan

Quote:

> --

> A question for technician people; if someone think this post is a
> little Off Topic in Neil Pryde Forum, I ask him to help me to put this
> question in the right place. Thank you in advance.

> You know certainly question of One Foot Off measurement for calculating
> fin lenght...

> Problem born when you consider a race or formula board with a diamond
> stern (called Diamond Tail by AHD), or with characteristic triangular
> drainages (used by Fanatic TT or F2 T-Rex); function of these different
> devices is to avoid cavitation pheneomena due air suck by fin caused
> when it is placed so near the stern as in such type boards.

> Now, if you refer to following drawing:

> http://dtiozzo.tripod.com/V8/onefootoff.gif

> I wonder if One Foot Off has to be measured from extreme stern (point
> "a" in both cases), or from edge of fin base (point "b" in both cases).

> This because I have a dubt on what to take in consideration:

> a) if board surface capable to really generate hydodynamic support
> (without appendages, or surface comprised by point "a" and "b" which
> function is essentially to avoid fin cavitation);

> b) all board parts (with appendages).

> In above drawing, Case number 2 shows the extreme limit of this
> question due irregular design of board stern and because surface
> comprised by points "a" and "b" is really marginal in terms of lift;
> but measure the One Foot Off from point "a" instead from point "b" is
> NOT quite marginal because may generate measures of fin definitely
> different.

> Someone has some idea or suggestion?

> - Expander.


 
 
 

A question about "One Foot Off" measure

Post by Glenn Woodel » Tue, 09 Aug 2005 06:03:58

I agree. There are so many variables to fin selection that one can
only make a recommendation and start from there. I typically use fins
much smaller than recommeded but I have learned to sail very
efficiently. Not that great mind you but efficiently.

Glenn

On Sun, 07 Aug 2005 15:26:40 -0400, jeff feehan

Quote:

>What is it you are trying to do?

>It sounds like you are trying to determine the appropriate fin
>length for a particular board. But choosing a fin is not nearly
>as exact a thing as you seem to think. I don't think anyone tries
>to "calculate" the right fin length. We know what fins work with
>which boards by trial and error.

>if you want to what fin to use witrh your board, tell us what board
>it is, and what size sails you will be using, and we'll give you
>a recommendation.

>also, have you noticed that your widths, A and B, are basically the
>same in each case?

>jefff feehan


>> --

>> A question for technician people; if someone think this post is a
>> little Off Topic in Neil Pryde Forum, I ask him to help me to put this
>> question in the right place. Thank you in advance.

>> You know certainly question of One Foot Off measurement for calculating
>> fin lenght...

>> Problem born when you consider a race or formula board with a diamond
>> stern (called Diamond Tail by AHD), or with characteristic triangular
>> drainages (used by Fanatic TT or F2 T-Rex); function of these different
>> devices is to avoid cavitation pheneomena due air suck by fin caused
>> when it is placed so near the stern as in such type boards.

>> Now, if you refer to following drawing:

>> http://dtiozzo.tripod.com/V8/onefootoff.gif

>> I wonder if One Foot Off has to be measured from extreme stern (point
>> "a" in both cases), or from edge of fin base (point "b" in both cases).

>> This because I have a dubt on what to take in consideration:

>> a) if board surface capable to really generate hydodynamic support
>> (without appendages, or surface comprised by point "a" and "b" which
>> function is essentially to avoid fin cavitation);

>> b) all board parts (with appendages).

>> In above drawing, Case number 2 shows the extreme limit of this
>> question due irregular design of board stern and because surface
>> comprised by points "a" and "b" is really marginal in terms of lift;
>> but measure the One Foot Off from point "a" instead from point "b" is
>> NOT quite marginal because may generate measures of fin definitely
>> different.

>> Someone has some idea or suggestion?

>> - Expander.

 
 
 

A question about "One Foot Off" measure

Post by clydepe.. » Tue, 09 Aug 2005 07:18:47

Wouldn't be fun to tank test the question?
 
 
 

A question about "One Foot Off" measure

Post by expan.. » Tue, 09 Aug 2005 17:48:16

--

Yes, message was posted originally on Neil Pryde Forum but I think it

I know that "One Foot Off" (O.F.O.) is NOT an absolute but merely an
indicative mesurement in determining the appropiate fin size but I
think, however, this might be interpreted as a valid and objective
indicator in lack of other objective rules.
If someone knows other indicators, beyond O.F.O. and evidences from
testing in the water, please feel free to suggest.
Anyway, my board is a 145 liters 2003 Fanatic Falcon 90 (270cm lenght x
90cm wide) and my favorite sail is a 10.6 Neil Pryde V8.

Thanks.

- Expander.

 
 
 

A question about "One Foot Off" measure

Post by expan.. » Tue, 09 Aug 2005 17:59:03

--

Quote:

> also, have you noticed that your widths, A and B, are basically the
> same in each case?

No, sorry for some drawing inaccuracy but, due fact board becomes
larger as we approach to front, segment "B" is longer than segment "A"
of about 2-3 cm.

- Exp.

 
 
 

A question about "One Foot Off" measure

Post by Tsunam » Tue, 09 Aug 2005 23:50:23


Quote:
> --

> A question for technician people; if someone think this post is a
> little Off Topic in Neil Pryde Forum, I ask him to help me to put this
> question in the right place. Thank you in advance.

> You know certainly question of One Foot Off measurement for calculating
> fin lenght...

<snip>

Easiest way for waveboards is that one size bigger (about 2cm)  than what
the board came with will be about ideal.
They try to male them too loose and in the process *** it up for everyone
bar pro's at the top and of that board's wind range

 
 
 

A question about "One Foot Off" measure

Post by LeeD » Wed, 10 Aug 2005 00:59:32

  Tsunami, you must be a big strong guy!
  At 147 lbs, I find the stock fin a little too BIG
  If I weighed in the 115 range, for sure I'd consider smaller fins
than stock.
  Hard to appease 100 to 220 lbs riders with ONE fin chosen half a year
ago  by the factory.
 
 
 

A question about "One Foot Off" measure

Post by LeeD » Thu, 11 Aug 2005 13:19:35

  expan....
  Fin surface area including shape and thickness is more likely a
better indicator for fin size than merely width of tail 12" OFO.
  For your board, fin sizing from 35 to 66cm would apply, depending on
shape and surface area.  Thicker fins increase low end planing, so they
can be counted as being bigger in surface area.
  The reason you got so many negative responses was that you left out
one very important catagory.....that of wave boards.  Typically 34cm
tails at 12" from the tip of the tail, they almost exclusively use fins
22cm long for big guys, around 20cm's for guys my size (146lbs.)
  Current fashion on freestyle boards is about a 18cm fin used on a
tail width around 40cms, and it works, for them.
 
 
 

A question about "One Foot Off" measure

Post by expan.. » Thu, 11 Aug 2005 18:35:41

--

Thank you, LeeD, for your detailed reply.
I understand every windsurfer category has its different opinion about
this question.
Anyway, today I'll try a 68 cm Birdi Testa Rossa M + fin, a custom fin
made by a craftsman based in Sardinia, Italy, that has supplied his
fins to some strong European Formula Windsurfing Class guys like Andrea
Cucchi, Alberto Menegatti, Fauster Thomas and Paju Jani.
I have bought this fin as used for its good price and because someone
says to me Birdi has made a products really competetive with Deboichet
fins.
More detailed specifications about this fin is availble at following
link:
http://www.mulliri.it/privato/birdi/TESTAROSSA.htm
I hope 68 cm size (2 cm over your indications) is not too long for my
purposes even if I know performances depend on thickness and surface
too.

- Expander.

 
 
 

A question about "One Foot Off" measure

Post by LeeD » Sat, 13 Aug 2005 02:35:16

  Exp...
  Tail width is a general indicator of fin sizing.  GENERAL!
  On my 34 cm tailed slalom board, fins from 25 to 34cms.
  On my 40cm tailed slalom board, fins from 34 to 48cms.
  On my 35cm tailed freewave board, fins from 22 to 32.
  NOTHING is exact!