Sail Aerodynamics
 

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.

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. 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?

This is kind of theoretical, I wich I could actually go sailing but
right now everything is covered in snow & ice. Maybe later this
week.....

Fresh Breezes- Doug King

Sail Aerodynamics
 

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

Sail Aerodynamics
 

MC wrote:


....Never seen the main luff
rising to windward? It's due to the slot and the mast.

Why, no, Navvie, I never have!

Are you *sure* that a luff (or 'bubble' as it's often called) along the main
luff is due to the slot & the mast? Who'd a thunk it?



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.

If that's true, then why are the photos of your mainsail, that you're so
proud of, not shaped at all like the ones in the sailmakers web site?

...Note also that the apparent wind is 22 degrees

Gee, Navvie, do you hold a protractor up to your computer screen?




....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.

And the adjustability has *what* to do with the vortex?

I was hoping that somebody might like to discuss rig tuning & sail trim.
Navvie, you are a font of meaningless, self-congratulatory prattle. And
you're not as funny as Boobsie.

DSK

Sail Aerodynamics
 

does a frac rig benefit
because the mainsail supresses the jib's tip vortex,

no.

or does the jib
vortex hurt the drive of the mainsail?

yes.


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

lots of advantages to a frac rig, but suppression of the tip vortex of the jib
is not one of them.

Sail Aerodynamics
 

JAXAshby wrote:
does a frac rig benefit

because the mainsail supresses the jib's tip vortex,


no.


or does the jib
vortex hurt the drive of the mainsail?


yes.


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


lots of advantages to a frac rig, but suppression of the tip vortex of the jib
is not one of them.


Shh, it'll take Doug quite some time to figure this all out.

Cheers

Sail Aerodynamics
 

DSK wrote:

MC wrote:


....Never seen the main luff
rising to windward? It's due to the slot and the mast.


Why, no, Navvie, I never have!

Are you *sure* that a luff (or 'bubble' as it's often called) along the main
luff is due to the slot & the mast? Who'd a thunk it?


Yep a bubble in the luff -if that's what you like to call it. Now do you
realize what it is?



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.


If that's true, then why are the photos of your mainsail, that you're so
proud of, not shaped at all like the ones in the sailmakers web site?


Look at the picture legends. Mine 33 degrees 5k ap. Theirs 22 degrees 16
knots. Are you blind or just so desperate to score one point you drop
the ball (again)?


...Note also that the apparent wind is 22 degrees


Gee, Navvie, do you hold a protractor up to your computer screen?



No but I can read the picture legend and understand what it says.
You are a such clown when it comes to the fine points of sail trim Doug!

Cheers MC

Sail Aerodynamics
 

DSK wrote:



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


And the adjustability has *what* to do with the vortex?


You mean you don't know? Good lord!

I was hoping that somebody might like to discuss rig tuning & sail trim.
Navvie, you are a font of meaningless, self-congratulatory prattle. And
you're not as funny as Boobsie.

Bwhahhahahaha. You are soooooooooooo jealous.

Cheers

Sail Aerodynamics
 

"MC" wrote in message
...


JAXAshby wrote:
does a frac rig benefit

because the mainsail supresses the jib's tip vortex,


no.


or does the jib
vortex hurt the drive of the mainsail?


yes.


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


lots of advantages to a frac rig, but suppression of the tip vortex of
the jib
is not one of them.


Shh, it'll take Doug quite some time to figure this all out.


MC,

I'm usually quite lost (at sea) during your discussions with Doug.
However, I never expected to see you depend on Jax for support. Well,
now I know!




Regards


Donal
--

Sail Aerodynamics
 

Donal wrote:

"MC" wrote in message
...


JAXAshby wrote:

does a frac rig benefit


because the mainsail supresses the jib's tip vortex,


no.



or does the jib
vortex hurt the drive of the mainsail?


yes.



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


lots of advantages to a frac rig, but suppression of the tip vortex of

the jib

is not one of them.


Shh, it'll take Doug quite some time to figure this all out.



MC,

I'm usually quite lost (at sea) during your discussions with Doug.
However, I never expected to see you depend on Jax for support. Well,
now I know!


You miss the point. Jax is correct on this one and I am giving him
credit for that. Just 'cos he's Jax doesn't mean he's always wrong!

Cheers

Sail Aerodynamics
 

Donal wrote:
I'm usually quite lost (at sea) during your discussions with Doug.
However, I never expected to see you depend on Jax for support.


He'll take whatever he can get, first it was Bubbles tremendous
expertise he relied on, now it's Jax.



MC wrote:
You miss the point. Jax is correct on this one and I am giving him
credit for that. Just 'cos he's Jax doesn't mean he's always wrong!


But he did not answer either question meaningfully.

DSK