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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.