DSK wrote:

This link was posted recently to a racing discussion

http://www.wb-sails.fi/news/470StreamAnim/index.htm#

Not sure how useful this is, but the pictures are cool. One of the
things I found interesting was the vertical difference in air flow,
and the difference in pressure distribution between the main & jib. On
the jib, the max pressure differential is much further forward.

I would have thought you would have known that. Never seen the main luff
rising to windward? It's due to the slot and the mast.

Also if you look at the photos of the sail, they are much flatter than
often said to be ideal (there is no reference to wind speed, it might
be light air) and the drafts are aft.

Yes they are flat, but these sails are trimmed for very very close
sailing -probably much closer than most of the nags sailed here could
achieve. Note the relative narrowness of the slot and the shape of the
battens. Note also that the apparent wind is 22 degrees whereas at 33
degrees we used a slightly fuller set (in even lighter air). The draft
is exaggerated by the camera angle in our shot whose purpose was to
identify the max draft position. Note that this moves forward up the
main as the CFD suggest it should). (Can you see the similar lower
batten wrinkes low down that Booby (and you?) complained about).

http://community.webshots.com/photo/...56514380nkBEsE
http://www.wb-sails.fi/news/470StreamAnim/index.htm#


Also it shows a vortex off the
head of the jib.... now the question is, does a frac rig benefit
because the mainsail supresses the jib's tip vortex, or does the jib
vortex hurt the drive of the mainsail?

Yes, the benefit is from the greater adjustability of the frac. rig.

Cheers