I wonder if our disagreement arises because your theories are based on
ideas originating from the "eliptical wing" and a desire to make the
main adopt an eliptical shape as far as camber is concerned (by making
the top fuller)? Increasing fullness also helps solve the roach support
problem -which is offset in modern sails with full length battens and
stiffer fabrics. Some sudies (e.g. here at Auckland) have shown this is
not correct for high aspect roachy mains where the camber (and lift)
should be reduced at the top of the sail to reduce heeling moment. In
the extreme case, negative (!) camber could improve performance by
reducing the heeling of the vessel.. This is the basis for the flat top
sail whose design is carried to extreme in modern windsurf sails where
the top is completely flat and heavily battened to support a huge roach.

Cheers MC


DSK wrote:

In any event, in light air, a big round section with a relatively
flat entry will keep attached flow and build up much more power
than a draft forward conventional airfoil shape.

The navigator© wrote:
There we disagree, in ligh airs the angle of attack of the leading
section must be close to zero to attach flow.


??? How do you get this out of what I said above?


Hence it should be full.


No. To keep flow attached (actually, to re-attach flow after passing the
mast) the leading section should be flatter further aft. Furthermore, at low
Reynolds numbers, the lift/drag ratio is better for the sort of shape I'm
describing.

This is one case where theory and practice seem to mesh pretty well. I read
a lot about new methods of sail trim and watched some of our competitors,
and found that what looked wrong (a deep round section) was actually quite
fast.




Surely you would agree that aeronautiucs shows that deeper foils
generate more lift at low speeds....


Again, how do you get this out of what I said?


I can see the topping lift, whih is presumably straight, and the
distance from the battens to the topping lift does not appear to
increase towards the middle of the sail.

You are forgetting the roach...



No I'm not, I'm looking at the angle of the battens. When a sail is twisted,
the battens take a series of angles as you look up the sail. Not exactly
rocket science.


Looking closely, I can see what might be leach ribbons flowing.
That's a good sign.


Yes they are, and it is.


Depends on the boat and the conditions. Some boats like the top telltale
flying all the time, some like it curling back some of the time, some more.

Usually boats that like to pinch (as opposed to boats that do better footing
off) want to have the upper leach ribbon curling back at least 25% of the
time, although in light air you have to be careful that the upper section
isn't stalling.


Why do you have a backstay antennae and no wire to it? Is the
wire lead up the mast and to the antennae at the top?

Well spotted. The wire is off.


OK, that's allowed

It's a good idea until you go offshore. Means that the connections don't
'weather' until they are needed.


You need some No-Ox.

Fresh Breezes- Doug King

What do you mean, outhaul?

Cheers MC

Donals Delight. wrote:

On Mon, 24 Nov 2003 08:16:14 -0500, DSK
wrote:



The navigator© wrote:


Here's a well cut main in light airs.

http://community.webshots.com/photo/...56514380nkBEsE

Draft too far forward (unless you're just coming out of some
chop, which doesn't look to be the case)

Not enough draft in upper sections

Leach closed.

Why do you have a backstay antennae and no wire to it? Is the
wire lead up the mast and to the antennae at the top?

Fresh Breezes- Doug King


Yeah that's what I said....He's got the crap dragged out of it.


Oz1...of the 3 twins.

I welcome you to crackerbox palace,We've been expecting you.

C'mon give the guy a break. It looks like too much outhaul and
vang/trveller downhaul on the boom. The leech is too closed... If you
opened the leech you would not have to let the traveller down in those airs.

Cheers MC

Donals Delight. wrote:

On 24 Nov 2003 16:33:22 GMT, (SAIL LOCO) wrote:


You've got the crap dragged out of it!

Well I'm at a loss as to what that means.


Figures!


Oz1...of the 3 twins.

I welcome you to crackerbox palace,We've been expecting you.

Bobsprit wrote:

You are saying that a flat sail
generates more lift in lower winds than a full sail?

The word here is "lift."
And we see that Booby doesn't know what it means!

RB

The navigator© wrote:

Let me try to get this straigt. You are saying that a flat sail
generates more lift in lower winds than a full sail?

No, I am not saying that and never did. I had the (perhaps mistaken) impression
that this discussion was about
1- variation in chord depth from middle to upper sections
2- where the best point of max draft
3- entry shape, which is a partially function of #2 above.

Would it be too much trouble to stick to one of these points?

Fresh Breezes- Doug King

Well there seems to be a communication problem 'cos you said:

In any event, in light air, a big round section with a relatively
flat entry will keep attached flow and build up much more power
than a draft forward conventional airfoil shape.

I saw the "big round section" and "much more power" while you were
saying that flatter at the head was no good.

Cheers MC

DSK wrote:

The navigator© wrote:


Let me try to get this straigt. You are saying that a flat sail
generates more lift in lower winds than a full sail?


No, I am not saying that and never did. I had the (perhaps mistaken) impression
that this discussion was about
1- variation in chord depth from middle to upper sections
2- where the best point of max draft
3- entry shape, which is a partially function of #2 above.

Would it be too much trouble to stick to one of these points?

Fresh Breezes- Doug King

"The_navigator©" wrote in message ...
I saw the "big round section" and "much more power" while you were
saying that flatter at the head was no good.


If a big round section produced horsepower than Bobsprit
can remove his mast and toss his sails. All he has to do is stand
on deck and expose his belly to the elements.

S.Simon

"Simple Simon" wrote in message
...

"The_navigator©" wrote in message
...
I saw the "big round section" and "much more power" while you were
saying that flatter at the head was no good.


If a big round section produced horsepower than Bobsprit
can remove his mast and toss his sails. All he has to do is stand
on deck and expose his belly to the elements.


Bwahahaaa ... errrr .... no, I didn't laugh out loud at that!
[ahem]..[cough]




Regards


Donal
--

The navigator© wrote:

I wonder if our disagreement arises because your theories are based on
ideas originating from the "eliptical wing" and a desire to make the
main adopt an eliptical shape as far as camber is concerned (by making
the top fuller)?

Huh? AFAIK the elliptical wing is usually referred to profile, not section shape.

So, I can definitely say, no that's not it.


Increasing fullness also helps solve the roach support
problem -which is offset in modern sails with full length battens and
stiffer fabrics. Some sudies (e.g. here at Auckland) have shown this is
not correct for high aspect roachy mains where the camber (and lift)
should be reduced at the top of the sail to reduce heeling moment.

Hello? Why are you talking about 'reducing heeling moment' in light air?

In
the extreme case, negative (!) camber could improve performance by
reducing the heeling of the vessel..

Yes it could, but not in light air.

Fresh Breezes- Doug King